Alternative titles; symbols
HGNC Approved Gene Symbol: STUB1
SNOMEDCT: 782719004;
Cytogenetic location: 16p13.3 Genomic coordinates (GRCh38) : 16:680,410-682,801 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 16p13.3 | Spinocerebellar ataxia 48 | 618093 | Autosomal dominant | 3 |
| Spinocerebellar ataxia, autosomal recessive 16 | 615768 | Autosomal recessive | 3 |
STUB1, or CHIP, is an E3 ubiquitin ligase/cochaperone that participates in protein quality control by targeting a broad range of misfolded chaperone protein substrates for proteasomal degradation (Min et al., 2008, summary by Cocozza et al., 2020).
In a search for tetratricopeptide repeat (TPR)-containing proteins, Ballinger et al. (1999) isolated a cDNA encoding STUB1, which they termed CHIP, from a heart cDNA library. The deduced 303-amino acid protein has a molecular mass of 35 kD and contains three 34-amino acid TPR domains at its N terminus, a central domain rich in charged residues, and 2 potential nuclear localization signals. The N terminus shares similarity with several TPR-containing proteins, particularly those that interact with members of the heat-shock protein family. Human CHIP shares 97% and 53% amino acid identity with its mouse and Drosophila homologs, respectively, with the highest conservation in the 94 residues of the C terminus. Northern blot analysis detected a 1.3-kb transcript at highest levels in striated muscle (heart and skeletal muscle), with lower expression in pancreas and brain, and relatively little expression in lung, liver, placenta, and kidney. Expression of CHIP was readily detected in most cell lines and primary culture cells tested, the exceptions being cells of hematopoietic origin and undifferentiated neuronal cells. Transient transfection experiments in COS-7 cells localized CHIP expression to the cytoplasm.
In mouse brain, Shi et al. (2013) found expression of the Stub1 gene in the cerebellum, pons, medulla oblongata, hippocampus, and cerebral cortex. The protein was present in Purkinje cells and colocalized with the glutamate receptor subunit Grin2a (138253) in the cerebellum, pons, and medulla oblongata. Coexpression of Stub1 and Fbx2 (607112) increased the degradation of Grin2a.
Shi et al. (2014) found expression of STUB1 in human brain, including within Purkinje cells in the molecular and granular regions of the cerebellum.
Using a yeast 2-hybrid screen, Ballinger et al. (1999) identified HSC70 (600816) and HSP70 (140550) as potential interaction partners for CHIP. In vitro binding assays demonstrated direct interactions between CHIP and both HSC70 and HSP70, and complexes containing CHIP and HSC70 were identified in immunoprecipitates of human skeletal muscle cells in vivo. CHIP interacted with the C-terminal residues 540 to 650 of HSC70, whereas HSC70 interacted with the N-terminal residues 1 to 197 of CHIP, which contain the TPR domain and the adjacent charged domain. Recombinant CHIP inhibited HSP40 (see 604572)-stimulated ATPase activity of HSC70 and HSP70, suggesting that CHIP blocks the forward reaction of the HSC70-HSP70 substrate-binding cycle. Both luciferase refolding and substrate binding in the presence of HSP40 and HSP70 were inhibited by CHIP. These results indicated that CHIP decreases net ATPase activity and reduces chaperone efficiency, and they implicated CHIP in the negative regulation of the forward reaction of the HSC70-HSP70 substrate-binding cycle.
Using an in vitro ubiquitylation assay with recombinant proteins, Jiang et al. (2001) demonstrated that CHIP possesses intrinsic E3 ubiquitin ligase activity and promotes ubiquitylation. This activity was dependent on the C-terminal U box, a domain that shares similarity with yeast UFD2 (603753). CHIP interacted functionally and physically with the stress-responsive ubiquitin-conjugating enzyme family UBCH5 (602961). A major target of the ubiquitin ligase activity of CHIP was HSC70 itself. CHIP ubiquitylated HSC70, primarily with short, noncanonical multiubiquitin chains, but had no appreciable effect on steady-state levels or half-life of this protein. The authors concluded that CHIP is a bona fide ubiquitin ligase and suggested that U box-containing proteins may constitute a novel family of E3s.
Unfolded PAELR (602583) is a substrate of the E3 ubiquitin ligase parkin (602544). Accumulation of PAELR in the endoplasmic reticulum (ER) of dopaminergic neurons induces ER stress leading to neurodegeneration. Imai et al. (2002) showed that CHIP, HSP70, parkin, and PAELR formed a complex in vitro and in vivo. The amount of CHIP in the complex increased during ER stress. CHIP promoted the dissociation of HSP70 from parkin and PAELR, thus facilitating parkin-mediated PAELR ubiquitination. Moreover, CHIP enhanced parkin-mediated in vitro ubiquitination of PAELR in the absence of HSP70. CHIP also enhanced the ability of parkin to inhibit cell death induced by PAELR. The authors concluded that CHIP is therefore a mammalian E4-like molecule that positively regulates parkin E3 activity.
Kampinga et al. (2003) found that overexpression of Chip in hamster fibroblasts increased the refolding of proteins after thermal denaturation. Inhibition of Hsp70 abolished the effect of Chip on protein folding. Hsp40 competitively inhibited Chip-dependent refolding, suggesting that Chip and Hsp40 have opposing effects on Hsp70 ATPase activity. Consistent with this, Chip overexpression did not alter protein folding following ATP depletion, when Hsp70 is in the ADP-bound state. Kampinga et al. (2003) concluded that CHIP attenuates the HSP70 ATPase cycle.
Alberti et al. (2004) found that epitope-tagged HSPBP1 (612939) immunoprecipitated HSC70 and CHIP from HeLa cell lysates. In the absence of HSC70, HSPBP1 and CHIP bound each other with low affinity. In the presence of ubiquitin-activating and -conjugating enzymes, CHIP mediated ubiquitination of test proteins when bound to HSC70. Addition of HSPBP1 inhibited CHIP-mediated ubiquitination of test proteins as well as CHIP-mediated ubiquitination of HSC70. Complex formation between HSPBP1, HSC70, and CHIP was necessary for HSPBP1 to inhibit CHIP. Alberti et al. (2004) concluded that HSPBP1 regulates CHIP ubiquitin ligase activity.
Shin et al. (2005) identified CHIP as a component of Lewy bodies in human brain, where it colocalized with alpha-synuclein (SNCA; 163890) and HSP70. In a human neuroglioma cell line, endogenous CHIP colocalized with alpha-synuclein and HSP70 in intracellular inclusions, and CHIP immunoprecipitated with alpha-synuclein, synphilin-1 (SNCAIP; 603779), and HSP70. Overexpression of CHIP reduced alpha-synuclein protein levels and inclusion formation. CHIP mediated alpha-synuclein degradation by both the proteasome and lysosome pathways. Mutation analysis revealed that the TRP domain of CHIP directed alpha-synuclein toward the proteasome, whereas the U-box domain of CHIP directed alpha-synuclein toward the lysosome. Shin et al. (2005) concluded that CHIP acts as a molecular switch for the degradation of misfolded proteins via the proteasome and lysosome pathways.
Qian et al. (2006) demonstrated that CHIP not only enhances HSP70 induction during acute stress, but also mediates its turnover during the stress recovery process. Central to this dual phase regulation is its substrate dependence: CHIP preferentially ubiquitinates chaperone-bound substrates, whereas degradation of HSP70 by CHIP-dependent targeting to the ubiquitin-proteasome system occurs when misfolded substrates have been depleted. Qian et al. (2006) concluded that the sequential analysis of the CHIP-associated chaperone adaptor and its bound substrate provides an elegant mechanism for maintaining homeostasis by tuning chaperone levels appropriately to reflect the status of protein building within the cytoplasm.
Cystic fibrosis (219700) arises from misfolding and premature degradation of CFTR (602421) containing a deletion of phe508 (delF508; 602421.0001). Younger et al. (2006) identified an endoplasmic reticulum (ER) membrane-associated ubiquitin ligase complex containing the E3 RMA1 (RNF5; 602677), the E2 UBC6E (UBE2J1; 616175), and derlin-1 (DERL1; 608813) that cooperated with the cytosolic HSC70/CHIP E3 complex to triage CFTR and delFl508. Derlin-1 retained CFTR in the ER membrane and interacted with RMA1 and UBC6E to promote proteasomal degradation of CFTR. RMA1 could recognize folding defects in delF508 coincident with translation, whereas CHIP appeared to act posttranslationally. A folding defect in delF508 detected by RMA1 involved the inability of the second membrane-spanning domain of CFTR to productively interact with N-terminal domains. Younger et al. (2006) concluded that the RMA1 and CHIP E3 ubiquitin ligases act sequentially in ER membrane and cytosol to monitor the folding status of CFTR and delF508.
Base excision repair (BER) is the major pathway for processing simple lesions in DNA and involves a stable complex of the scaffold protein XRCC1 (194360), DNA polymerase-beta (POLB; 174760), and DNA ligase III-alpha (LIG3; 600940). Cellular levels of these enzymes must be tightly regulated, because increased amounts of BER enzymes lead to elevated mutagenesis and genetic instability. Parsons et al. (2008) showed that BER proteins not involved in a repair complex were ubiquitinated by CHIP and subsequently degraded by the proteasome in HeLa cells. Overexpression of CHIP reduced the levels of both endogenous and transfected POLB and XRCC1 by about 3-fold compared with control cells. Conversely, reduction in CHIP protein levels by RNA interference increased the levels of POLB, XRCC1, and LIG3. CHIP-mediated control of BER proteins did not require interaction of CHIP with heat-shock proteins. Parsons et al. (2008) concluded that CHIP controls the cellular level of BER enzymes and, correspondingly, the efficiency and capacity of BER.
Okiyoneda et al. (2010) identified the components of the peripheral protein quality control network that removes unfolded CFTR containing the F508del mutation (602421.0001) from the plasma membrane. Based on their results and proteostatic mechanisms at different subcellular locations, Okiyoneda et al. (2010) proposed a model in which the recognition of unfolded cytoplasmic regions of CFTR is mediated by HSC70 (600816) in concert with DNAJA1 (602837) and possibly by the HSP90 machinery (140571). Prolonged interaction with the chaperone-cochaperone complex recruits CHIP-UBCH5C (602963) and leads to ubiquitination of conformationally damaged CFTR. This ubiquitination is probably influenced by other E3 ligases and deubiquitinating enzyme activities, culminating in accelerated endocytosis and lysosomal delivery mediated by Ub-binding clathrin adaptors and the endosomal sorting complex required for transport (ESCRT) machinery, respectively. In an accompanying perspective, Hutt and Balch (2010) commented that the 'yin-yang' balance maintained by the proteostasis network is critical for normal cellular, tissue, and organismal physiology.
Gross (2015) mapped the STUB1 gene to chromosome 16p13.3 based on an alignment of the STUB1 sequence (GenBank AF039689) with the genomic sequence (GRCh38).
Spinocerebellar Ataxia 16, Autosomal Recessive
In affected members of 3 unrelated Chinese families with autosomal recessive spinocerebellar ataxia-16 (SCAR16; 615768), Shi et al. (2013) identified homozygous or compound heterozygous mutations in the STUB1 gene (see, e.g., 607207.0001-607207.0003). The mutation in the first family was found by linkage analysis and whole-exome sequencing. The 2 additional families were ascertained by direct sequencing of the STUB1 gene in a larger cohort of 36 families with spinocerebellar ataxia and 196 patients with sporadic disease in whom mutations in common ataxia genes had been excluded. In vitro functional expression studies in HEK293 cells showed that none of the mutations identified by Shi et al. (2014) effectively promoted the degradation of GRIN2A (138253), indicating a loss of ubiquitinase activity. Shi et al. (2014) hypothesized that the inability to degrade NMDA receptors in neurons may contribute to the pathogenesis of ataxia.
In 2 Chinese sisters with SCAR16, Shi et al. (2014) identified a homozygous missense mutation in the STUB1 gene (T246M; 607207.0004). The mutation was found by whole-exome sequencing and homozygosity mapping. In vitro functional expression studies showed that the mutation caused a loss of ubiquitin ligase activity, but chaperone function was not disturbed. The patients presented with ataxia in their late teenage years, and also showed hypogonadotrophic hypogonadism with lack of secondary sexual development. Loss of Stub1 function in mice resulted in behavioral and reproductive impairments that resembled the human ataxia and hypogonadism. Shi et al. (2014) concluded that the disorder resulted from loss of STUB1 function.
In 3 (1.8%) of 167 patients with autosomal recessive cerebellar ataxia, Synofzik et al. (2014) identified 4 novel homozygous or compound heterozygous missense mutations in the STUB1 gene (607207.0005-607207.0008). One of the mutations affected the ubiquitin ligase domain, whereas the others affected the TPR domain. No STUB1 mutations were found in 133 patients with spastic paraplegia.
In 3 sibs, born of consanguineous parents of Arab descent, with SCAR16, Heimdal et al. (2014) identified a homozygous missense mutation in the STUB1 gene (N65S; 607207.0009). In vitro functional expression studies showed that N65S-mutant STUB1 had significantly impaired ability to ubiquitinate HSC70 (600816) compared to wildtype, most likely due to low substrate affinity. The findings were consistent with a loss of function.
In 2 Belgian sibs with SCAR16, Depondt et al. (2014) identified compound heterozygous mutations in the STUB1 gene (607207.0013 and 607207.0015). Functional studies of the variants and studies of patient cells were not performed.
In 4 patients from 2 unrelated French families (families 1 and 2) with SCAR16, Ravel et al. (2021) identified compound heterozygous mutations in the STUB1 gene. There were 3 missense variants and an in-frame deletion. The mutations were found by targeted next-generation sequencing. The mutations occurred throughout the gene and often affected functional domains; functional studies of the variants and studies of patient cells were not performed.
Spinocerebellar Ataxia 48, Autosomal Dominant
In 9 affected members of a multigenerational family from Catalonia, Spain, with autosomal dominant spinocerebellar ataxia-48 (SCA48; 618093), Genis et al. (2018) identified a heterozygous 2-bp deletion (c.823_824delCT) in exon 7 of the STUB1 gene (607207.0010), resulting in a frameshift and premature termination (Leu275AspfsTer16). The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing and linkage analysis, segregated with the disorder in the family. It was found at a low frequency (0.0000081) in the ExAC database. Functional studies of the variant and studies of patient cells were not performed.
In affected members of 2 large multigenerational families from southern Italy with SCA48, De Michele et al. (2019) identified heterozygous missense mutations in the STUB1 gene (G33S, 607207.0011 and P228S, 607207.0012). The mutations, which were found by whole-exome sequencing or targeted multigene sequencing and confirmed by Sanger sequencing, segregated with the disorder in the families. Neither was present in the gnomAD database. Functional studies of the variants and studies of patient cells were not performed.
In 11 Italian patients from 8 unrelated families with SCA48, Lieto et al. (2020) identified 8 different heterozygous mutations in the STUB1 gene (see, e.g., 607207.0010; 607207.0015-607207.0016). There were 3 missense, 1 nonsense, and 4 frameshift mutations. The mutations, which were found by next-generation sequencing, including both whole-exome sequencing and targeted sequencing using a gene panel, segregated with the disorder in the 3 families (families A, B, and C) in whom affected family members were available for study. The probands in families D, F, G, and H had sporadic disease. The proband in family E had an affected mother who was deceased and for whom no genetic material was available for analysis. Functional studies of the mutations were not performed, but all affected highly conserved residues or functional domains of the protein, particularly the TRP and U-box domains. These patients were ascertained from a cohort of 235 Italian patients with adult-onset autosomal dominant familial cerebellar ataxia (17 families) or sporadic disease (218 patients). STUB1 mutations were identified in 8 (3.4%) of 235 patients, rising to 23.5% when considering familial cases (4 of 17).
In affected members of a large Dutch kindred with SCA48, Mol et al. (2020) identified a heterozygous frameshift mutation (c.731_732delGC) in the STUB1 gene that segregated with the disorder in the family and was absent from public databases. However, 1 mutation carrier and 1 obligate carrier were unaffected at ages 75 and 64 years, suggesting either incomplete penetrance or variable expressivity. Functional studies of the variant were not performed, but it was predicted to result in premature truncation in the highly conserved U-box (Cys244TyrfsTer24). Whether this mutation resulted in nonsense-mediated mRNA decay and a loss of function or production of a truncated protein with a possible dominant-negative effect could not be established. Mol et al. (2020) hypothesized that the mutation impairs the intracellular ubiquitin-mediated degradation of protein aggregates, thus leading to neurodegeneration.
In 9 affected members of 5 French families (families 3-7) with SCA48, Ravel et al. (2021) identified heterozygous missense mutations in the STUB1 gene. The mutations, which were found by targeted next-generation sequencing and confirmed by Sanger sequencing, segregated with the disorder in the families. The mutations affected functional domains, including the TPR and U-box domains; functional studies of the variants and studies of patient cells were not performed.
In 28 probands with either familial or sporadic SCA48, Roux et al. (2020) identified heterozygous mutations in the STUB1 gene. The mutations were found by direct examination of the STUB1 gene in a cohort of 440 families with cerebellar ataxia. Polyglutamine expansions in several ataxia-related genes, including TBP (600075), were excluded in all but 2 families. Most of the STUB1 mutations were missense, although there were also a few nonsense, splice site, or frameshift mutations. The mutations occurred throughout the gene with no evidence of a genotype/phenotype correlation; a few had previously been identified in patients with biallelic mutations (SCAR16). Functional studies were not performed, but the authors postulated haploinsufficiency as the pathogenic mechanism. Five patients from 3 unrelated families (AAD-262, AAD-452, and AAD-575) all carried the same heterozygous missense variant (N65S; 607207.0009); homozygosity for the N65S variant has been reported in a family with SCAR16 who had onset of the disorder in the first decade. The heterozygous N65S variant segregated with SCA48 in the 3 patients from family AAD-262. However, only 1 of the 3 patients in this family had cognitive impairment. Four of the patients had onset of symptoms between 30 and 55 years of age. The fifth patient (AAD-452) had earlier onset at age 27 years; she also carried a heterozygous missense (H347R) variant in the PRKCG gene (176980), which is associated with SCA14 (605361). The authors suggested that the early onset in this patient may have been due to synergistic effects of the STUB1 and PRKCG variants. Two additional patients (from families AAD-075 and AAD-391) with heterozygous STUB1 missense variants (A113D and R154C) also carried heterozygous repeat expansions in the TBP gene (41 and 46 CAG/CAA repeats, respectively; 600075.0001), which cause SCA17 (607136). The authors suggested that the TBP expansion may have contributed to the phenotype. Two families with autosomal recessive SCAR16 and biallelic STUB1 mutations were also identified in the cohort. In general, patients with heterozygous mutations had later age at onset and an overall less severe disorder compared to those with biallelic mutations.
In 7 patients from 3 unrelated families with SCA48, Pakdaman et al. (2021) identified heterozygous mutations in the STUB1 gene (see, e.g., 607207.0017 and 607207.0018). The mutations, which were found by exome sequencing and confirmed by Sanger sequencing, segregated with the disorder in families A and B; genetic material was available only from the proband of family C, precluding segregation studies, although she did have a family history of a similar disorder. There were 2 in-frame ins/del mutations and 1 missense variant (G249V). In vitro functional expression studies showed that the STUB1 mutations caused impaired ubiquitination activity toward the Hsc70 (600816) substrate compared to controls; G249V also showed impaired self-ubiquitination. Further studies showed that the variants adversely impacted the structure and conformation of the CHIP protein with a propensity to form aggregates. The authors suggested that the pathogenicity of heterozygous STUB1 mutations could reflect a dominant-negative effect. Pathogenic repeat expansions in several ataxia-associated genes, including TBP, were excluded in family A, whereas the 2 affected patients in family B both carried a heterozygous 41-repeat expansion in the TBP gene (600025.0001) that may have contributed to the phenotype. The patient from family C was not tested for TBP repeat expansions.
Magri et al. (2022) questioned the existence of SCA48 as a monogenic disease, noting that relatives of SCAR16 patients who are heterozygous for a STUB1 variant are unaffected, even though some STUB1 mutations have been reported in both SCAR16 and SCA48. In their study of 30 families diagnosed with SCA17 (607136) associated with intermediate-sized (41 to 46 repeats) expanded TBP (600075) alleles, only individuals who also carried a STUB1 variant were affected. Eight family members who carried only a STUB1 variant were clinically unaffected. No STUB1 variants were identified in individuals carrying TBP alleles with 47 or more repeats, which were fully penetrant. These findings led the authors to conclude that heterozygous STUB1 variants alone are insufficient for disease manifestation and that SCA17 with intermediate expanded TBP alleles is a digenic disorder that manifests only when a concurrent STUB1 mutation is present. Since the phenotype of SCA48 and SCA17 is similar, SCA48 and digenic SCA17 may represent the same disorder. Magri et al. (2022) noted that the range of the size of TBP alleles considered pathogenic differs between laboratories. Individuals previously diagnosed with SCA48 due to a heterozygous STUB1 variant may have also carried small-sized TBP repeat alleles that were either not detected or not considered pathogenic.
Min et al. (2008) found that Chip -/- mice exhibited increased perinatal lethality compared with wildtype mice, likely due to impaired adaptation to the stress of parturition. Both male and female Chip -/- mice were smaller than controls, and the difference became more obvious as the mice aged. Chip -/- mice, particularly males, showed significantly reduced longevity. The median survival time for both male and female wildtype mice was 25 months, whereas it was only 7.8 and 11.2 months for Chip -/- males and females, respectively. Chip deficiency led to accelerated age-related pathophysiologic changes that were accompanied by accelerated cellular senescence, increased oxidative stress, deregulation of protein quality control, and reduced proteasome activity. Min et al. (2008) concluded that impaired protein quality control contributes to cellular senescence and that CHIP-dependent quality control influences longevity.
By testing Chip heterozygous mice for neurobehavioral and physiologic activities, McLaughlin et al. (2012) found a significant elevation in baseline heart rate and specific motor disturbances, whereas most other functions appeared normal. McLaughlin et al. (2012) concluded that moderate CHIP underexpression results in functional impairments in brain circuits, but normal survival and growth rates.
Shi et al. (2014) found that Chip-null mice had severe motor impairment due to cerebellar dysfunction. They also showed mild defects in learning and memory, suggesting hippocampal compromise. Neuropathologic examination showed loss of Purkinje cells in the cerebellum of mutant mice. In addition, mutant mice showed evidence of gonadal dysfunction, with decreased testicular weight and decreased levels of follicle-stimulating hormone (FSH; see 136530).
In 4 Chinese sibs with autosomal recessive spinocerebellar ataxia-16 (SCAR16; 615768), Shi et al. (2013) identified a homozygous c.493C-T transition in exon 3 of the STUB1 gene, resulting in a leu165-to-phe (L165F) substitution at a highly conserved residue adjacent to the third TPR domain. The mutation, which was found using a combination of linkage analysis and whole-exome sequencing, segregated with the disorder in the family. It was not present in the dbSNP (build 129) or 1000 Genomes Project databases, in 800 normal controls, or in 500 ethnically matched controls. The patients had onset of progressive gait and truncal ataxia in their teenage years.
In a 23-year-old man of Han Chinese descent with autosomal recessive spinocerebellar ataxia-16 (SCAR16; 615768), Shi et al. (2013) identified compound heterozygous mutations in the STUB1 gene: a c.389A-T transversion, resulting in an asn130-to-ile (N130I) substitution, and a c.441G-T transversion, resulting in a trp147-to-cys substitution (W147C; 607207.0003). The mutations, which segregated with the disorder in the family, were not found in 500 controls.
For discussion of the trp147-to-cys (W147C) mutation in the STUB1 gene that was found in compound heterozygous state in a patient with autosomal recessive spinocerebellar ataxia-16 (SCAR16; 615768) by Shi et al. (2013), see 607207.0002.
In 2 Chinese sisters with autosomal recessive spinocerebellar ataxia-16 (SCAR16; 615768), Shi et al. (2014) identified a homozygous c.737C-T transition in the STUB1 gene, resulting in a thr246-to-met (T246M) substitution at a highly conserved residue in the U box domain, which is responsible for ubiquitin ligase activity. The mutation, which was found by whole-exome sequencing and homozygosity mapping and confirmed by Sanger sequencing, segregated with the disorder in the family. It was not present in the dbSNP (build 132), 1000 Genomes Project, or Exome Sequencing Project databases, or in 500 Chinese control individuals. In vitro functional expression studies showed that the mutation caused a loss of ubiquitin ligase activity, but chaperone function was not disturbed.
In a 16-year-old boy, born of consanguineous parents, with autosomal recessive spinocerebellar ataxia-16 (SCAR16; 615768), Synofzik et al. (2014) identified a homozygous c.367C-G transversion in the STUB1 gene, resulting in a leu123-to-val (L123V) substitution at a highly conserved residue in the TPR domain. The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family and was not present in the Exome Variant Server or another large database of over 2,500 exomes. The patient had onset of ataxia at age 2 years. Functional studies of the variant were not performed.
In a 21-year-old woman, born of consanguineous parents, with autosomal recessive spinocerebellar ataxia-16 (SCAR16; 615768), Synofzik et al. (2014) identified a homozygous c.719T-C transition in the STUB1 gene, resulting in a met240-to-thr (M240T) substitution at a highly conserved residue in the U box domain. The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family and was not present in the Exome Variant Server or another large database of over 2,500 exomes. The patient had onset of ataxia at age 16 years. Functional studies of the variant were not performed.
In 2 brothers with autosomal recessive spinocerebellar ataxia-16 (SCAR16; 615768), Synofzik et al. (2014) identified compound heterozygous mutations in the STUB1 gene: a c.235G-A transition, resulting in an ala79-to-thr (A79T) substitution, and a c.236C-A transversion, resulting in an ala79-to-asp (A79D; 607207.0008) substitution. Both mutations occurred at a highly conserved residue in the TPR domain. The mutations, which were found by whole-exome sequencing and confirmed by Sanger sequencing, were not present in the Exome Variant Server or another large database of over 2,500 exomes. The patients had relatively late onset of ataxia, at age 29 and 49, respectively. Both also had clinical evidence of lower limb spasticity. Functional studies of the variants were not performed.
For discussion of the ala79-to-asp (A79D) mutation in the STUB1 gene that was found in compound heterozygous state in 2 brothers with autosomal recessive spinocerebellar ataxia-16 (SCAR16; 615768) by Synofzik et al. (2014), see 607207.0007.
Autosomal Recessive Spinocerebellar Ataxia 16
In 3 sibs, born of consanguineous parents of Arab origin, with autosomal recessive spinocerebellar ataxia-16 (SCAR16; 615768), Heimdal et al. (2014) identified a homozygous c.194A-G transition (c.194A-G, NM_005861.2) in exon 2 of the STUB1 gene, resulting in an asn65-to-ser (N65S) substitution at a highly conserved residue in the TPR domain important for chaperone interactions. The mutation, which was found using a combination of homozygosity mapping and whole-exome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family. It was not present in the dbSNP or 1000 Genomes Project databases or in 100 Norwegian control exomes. Patient fibroblasts had lower STUB1 protein levels, and the migration pattern was different from wildtype, suggesting a conformational change. In vitro functional expression studies showed that N65S-mutant STUB1 had significantly impaired ability to ubiquitinate HSC70 (HSPA8; 600816) compared to wildtype, most likely due to low substrate affinity. The findings were consistent with a loss of function. The patients had onset of symptoms in the first decade.
Autosomal Dominant Spinocerebellar Ataxia 48
In 5 patients from 3 unrelated families (AAD-262, AAD-452, and AAD-575) with autosomal dominant spinocerebellar ataxia-48 (SCA48; 618093), Roux et al. (2020) identified a heterozygous N65S mutation in the STUB1 gene. The variant, which was found by direct examination of the STUB1 gene and confirmed by Sanger sequencing, was not present in the gnomAD database. The variant segregated with the disorder in the 3 patients from family AAD-262. However, only 1 of the 3 patients in this family had cognitive impairment. Functional studies of the variant were not performed. Four of the patients had onset of symptoms between 30 and 55 years of age. The fifth patient (AAD-452) had earlier onset at age 27 years; he also carried a heterozygous missense (H347R) variant in the PRKCG gene (176980), which is associated with SCA14 (605361). The authors suggested that the early onset in this patient may have been due to synergistic effects of the STUB1 and PRKCG variants. Functional studies were not performed.
In 9 affected members of a multigenerational family from Catalonia, Spain, with autosomal dominant spinocerebellar ataxia-48 (SCA48; 618093), Genis et al. (2018) identified a heterozygous 2-bp deletion (c.823_824delCT) in exon 7 of the STUB1 gene, resulting in a frameshift and premature termination (Leu275AspfsTer16). The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing and linkage analysis, segregated with the disorder in the family. It was found at a low frequency (0.0000081) in the ExAC database. Functional studies of the variant and studies of patient cells were not performed.
In a 60-year-old Italian woman (patient 10, family G) with sporadic occurrence of SCA48, Lieto et al. (2020) identified a heterozygous c.823_824delCT mutation in the STUB1 gene, predicted to result in a frameshift and premature termination in the U-box domain. The mutation was found by targeted multigene sequencing; functional studies of the variant and studies of patient cells were not performed.
Palvadeau et al. (2020) identified a heterozygous c.823_824delCT mutation (c.823_824delCT, ENST00000219548) in the STUB1 gene in a 65-year-old Turkish woman with SCA48. The mutation was found by whole-exome sequencing and confirmed by Sanger sequencing; functional studies of the variant and studies of patient cells were not performed.
In 5 affected members of a large multigenerational family from southern Italy (family 1) with autosomal dominant spinocerebellar ataxia-48 (SCA48; 618093), De Michele et al. (2019) identified a heterozygous c.97G-A transition in the STUB1 gene, resulting in a gly33-to-ser (G33S) substitution at a conserved residue in the N-terminal TRP domain. The mutation, which was found by whole-exome sequencing or targeted multigene sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family. It was not present in the gnomAD database. Functional studies of the variant and studies of patient cells were not performed.
In 2 affected members of a large multigenerational family from southern Italy (family 2) with autosomal dominant spinocerebellar ataxia-48 (SCA48; 618093), De Michele et al. (2019) identified a heterozygous c.682C-T transition in the STUB1 gene, resulting in a pro228-to-ser (P228S) substitution at a conserved residue in the ubiquitin ligase. The mutation, which was found by whole-exome sequencing or targeted multigene sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family. It was not present in the gnomAD database. Functional studies of the variant and studies of patient cells were not performed.
In 2 Belgian brothers with autosomal recessive spinocerebellar ataxia-16 (SCAR16; 615768), Depondt et al. (2014) identified compound heterozygous mutations in the STUB1 gene: a c.433A-C transversion in exon 3, resulting in a lys145-to-gln (K145Q) substitution at a highly conserved residue, and a 4-bp deletion in exon 6 (c.687_690delCTAC; 607207.0015), predicted to result in a frameshift and premature termination (Tyr230CysfsTer8) before the U-box domain. This deletion was also predicted to lead to nonsense-mediated mRNA decay and complete loss of the STUB1 protein. The mutations were found by whole-exome sequencing: K145Q was present in the heterozygous state at a low frequency (0.00054) in the Exome Variant Server database (7 of 12,979 chromosomes), whereas the 4-bp deletion was not listed in the database. Functional expression studies of the variants and studies of patient cells were not performed. It was not clear from the report whether or not the parents carried the mutations, but they were noted to be unaffected.
Ravel et al. (2021) found the K145Q mutation in compound heterozygosity with another missense mutation in 2 sisters (family 2) with SCAR16.
Spinocerebellar Ataxia, Autosomal Recessive 16
For discussion of the 4-bp deletion in exon 6 of the STUB1 gene (c.687_690delCTAC), predicted to result in a frameshift and premature termination (Tyr230CysfsTer8), that was found in compound heterozygous state in 2 brothers with autosomal recessive spinocerebellar ataxia-16 (SCAR16; 615768) by Depondt et al. (2014), see 607207.0013.
Spinocerebellar Ataxia 48
In an Italian mother and son (family A) with autosomal dominant spinocerebellar ataxia-48 (SCA48; 618093), Lieto et al. (2020) identified a heterozygous 4-bp deletion in the STUB1 gene (c.689_692delACCT), predicted to result in a frameshift and premature termination (Tyr230CysfsTer9). The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family. Lieto et al. (2020) noted that this frameshift was predicted to result in the same protein consequence as that reported by Depondt et al. (2014) in the 2 brothers with autosomal recessive SCAR16. Functional studies of the variant and studies of patient cells were not performed.
In an Italian mother and daughter (family B) with autosomal dominant spinocerebellar ataxia-48 (SCA48; 618093), Lieto et al. (2020) identified a heterozygous 2-bp duplication in the STUB1 gene (c.818_819dupGC), predicted to result in a frameshift and premature termination (Pro274AlafsTer3) in the U-box domain. The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family. Functional studies of the variant and studies of patient cells were not performed.
In 4 members of a 2-generation family (family A) with autosomal dominant spinocerebellar ataxia-48 (SCA48; 618093), Pakdaman et al. (2021) identified a heterozygous deletion/insertion mutation in the STUB1 gene (c.152_158delinsCAGC, NM_005861.3) resulting in an Arg51_Ile53delinsProAla substitution. The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, was not present in the gnomAD database. Pathogenic repeat expansions in several ataxia-associated genes, including TBP (600075), were excluded in this family. In vitro functional expression studies showed that the STUB1 mutation caused impaired ubiquitination activity toward the Hsc70 (600816) substrate compared to controls. Further studies showed that the variant adversely impacted the structure and conformation of the CHIP protein with a propensity to form aggregates. The authors suggested that the pathogenicity of heterozygous STUB1 mutations could reflect a dominant-negative effect. The patients presented between 40 and 50 years of age with gait ataxia, dysphagia, dysarthria, and cerebellar atrophy. Cognitive decline was variable.
In a father and daughter (family B) with autosomal dominant spinocerebellar ataxia-48 (SCA48; 618093), Pakdaman et al. (2021) identified a heterozygous deletion/insertion mutation in the STUB1 gene (c.426_441delinsT, NM_005861.3) predicted to result in Lys143_Trp147del. The mutation, which was found by exome sequencing and confirmed by Sanger sequencing, was not present in the gnomAD database. Both patients were also heterozygous for a 41-repeat expansion in the TBP gene (600025.0001) that may have contributed to the phenotype. In vitro functional expression studies showed that the STUB1 mutation caused impaired ubiquitination activity toward the Hsc70 (600816) substrate compared to controls. Further studies showed that the variant adversely impacted the structure and conformation of the CHIP protein with a propensity to form aggregates. The authors suggested that the pathogenicity of heterozygous STUB1 mutations could reflect a dominant-negative effect. The proband developed dysarthria and cerebellar ataxia at age 30. The disorder progressed, necessitating wheelchair use, and she developed encephalopathy and nystagmus. Her father presented with cerebellar ataxia in his seventies. Both had cerebellar atrophy on brain imaging.
Alberti, S., Bohse, K., Arndt, V., Schmitz, A., Hohfeld, J. The cochaperone HspBP1 inhibits the CHIP ubiquitin ligase and stimulates the maturation of the cystic fibrosis transmembrane conductance regulator. Molec. Biol. Cell 15: 4003-4010, 2004. [PubMed: 15215316] [Full Text: https://doi.org/10.1091/mbc.e04-04-0293]
Ballinger, C. A., Connell, P., Wu, Y., Hu, Z., Thompson, L. J., Yin, L.-Y., Patterson, C. Identification of CHIP, a novel tetratricopeptide repeat-containing protein that interacts with heat shock proteins and negatively regulates chaperone functions. Molec. Cell. Biol. 19: 4535-4545, 1999. [PubMed: 10330192] [Full Text: https://doi.org/10.1128/MCB.19.6.4535]
Cocozza, S., Pontillo, G., De Michele, G., Perillo, T., Guerriero, E., Ugga, L., Salvatore, E., Galatolo, D., Riso, V., Sacca, F., Quarantelli, M., Brunetti, A. The 'crab sign': an imaging feature of spinocerebellar ataxia type 48. Neuroradiology 62: 1095-1103, 2020. [PubMed: 32285148] [Full Text: https://doi.org/10.1007/s00234-020-02427-7]
De Michele, G., Lieto, M., Galatolo, D., Salvatore, E., Cocozza, S., Barghigiani, M., Tessa, A., Baldacci, J., Pappata, S., Filla, A., De Michele, G., Santorelli, F. M. Spinocerebellar ataxia 48 presenting with ataxia associated with cognitive, psychiatric, and extrapyramidal features: a report of two Italian families. Parkinsonism Relat. Disord. 65: 91-96, 2019. [PubMed: 31126790] [Full Text: https://doi.org/10.1016/j.parkreldis.2019.05.001]
Depondt, C., Donatello, S., Simonis, N., Rai, M., van Heurck, R., Abramowicz, M., D'Hooghe, M., Pandolfo, M. Autosomal recessive cerebellar ataxia of adult onset due to STUB1 mutations. Neurology 82: 1749-1750, 2014. [PubMed: 24719489] [Full Text: https://doi.org/10.1212/WNL.0000000000000416]
Genis, D., Ortega-Cubero, S., San Nicolas, H., Corral, J., Gardenyes, J., de Jorge, L., Lopez, E., Campos, B., Lorenzo, E., Tonda, R., Beltran, S., Negre, M., and 9 others. Heterozygous STUB1 mutation causes familial ataxia with cognitive affective syndrome (SCA48). Neurology 91: e1988-e1998, 2018. Note: Electronic Article. [PubMed: 30381368] [Full Text: https://doi.org/10.1212/WNL.0000000000006550]
Gross, M. B. Personal Communication. Baltimore, Md. 12/28/2015.
Heimdal, K., Sanchez-Guixe, M., Aukrust, I., Bollerslev, J., Bruland, O., Jablonski, G. E., Erichsen, A. K., Gude, E., Koht, J. A., Erdal, S., Fiskerstrand, T., Haukanes, B. I., Boman, H., Bjorkhaug, L., Tallaksen, C. M. E., Knappskog, P. M., Johansson, S. STUB1 mutations in autosomal recessive ataxias--evidence for mutation-specific clinical heterogeneity. Orphanet J. Rare Dis. 9: 146, 2014. Note: Electronic Article. [PubMed: 25258038] [Full Text: https://doi.org/10.1186/s13023-014-0146-0]
Hutt, D., Balch, W. E. The proteome in balance. Science 329: 766-767, 2010. [PubMed: 20705837] [Full Text: https://doi.org/10.1126/science.1194160]
Imai, Y., Soda, M., Hatakeyama, S., Akagi, T., Hashikawa, T., Nakayama, K., Takahashi, R. CHIP is associated with Parkin, a gene responsible for familial Parkinson's disease, and enhances its ubiquitin ligase activity. Molec. Cell 10: 55-67, 2002. [PubMed: 12150907] [Full Text: https://doi.org/10.1016/s1097-2765(02)00583-x]
Jiang, J., Ballinger, C. A., Wu, Y., Dai, Q., Cyr, D. M., Hohfeld, J., Patterson, C. CHIP is a U-box-dependent E3 ubiquitin ligase: identification of Hsc70 as a target for ubiquitylation. J. Biol. Chem. 276: 42938-42944, 2001. [PubMed: 11557750] [Full Text: https://doi.org/10.1074/jbc.M101968200]
Kampinga, H. H., Kanon, B., Salomons, F. A., Kabakov, A. E., Patterson, C. Overexpression of the cochaperone CHIP enhances Hsp70-dependent folding activity in mammalian cells. Molec. Cell. Biol. 23: 4948-4958, 2003. [PubMed: 12832480] [Full Text: https://doi.org/10.1128/MCB.23.14.4948-4958.2003]
Lieto, M., Riso, V., Galatolo, D., De Michele, G., Rossi, S., Barghigiani, M., Cocozza, S., Pontillo, G., Trovato, R., Sacca, F., Salvatore, E., Tessa, A., Filla, A., Santorelli, F. M., De Michele, G., Silvestri, G. The complex phenotype of spinocerebellar ataxia type 48 in eight unrelated Italian families. Europ. J. Neurol. 27: 498-505, 2020. [PubMed: 31571321] [Full Text: https://doi.org/10.1111/ene.14094]
Magri, S., Nanetti, L., Gellera, C., Sarto, E., Rizzo, E., Mongelli, A., Ricci, B., Fancellu, R., Sambati, L., Cortelli, P., Brusco, A., Bruzzone, M. G., Mariotti, C., Di Bella, D., Taroni, F. Digenic inheritance of STUB1 variants and TBP polyglutamine expansions explains the incomplete penetrance of SCA17 and SCA48. Genet. Med. 24: 29-40, 2022. [PubMed: 34906452] [Full Text: https://doi.org/10.1016/j.gim.2021.08.003]
McLaughlin, B., Buendia, M. A., Saborido, T. P., Palubinsky, A. M., Stankowski, J. N., Stanwood, G. D. Haploinsufficiency of the E3 ubiquitin ligase C-terminus of heat shock cognate 70 interacting protein (CHIP) produces specific behavioral impairments. PLoS One 7: e36340, 2012. Note: Electronic Article. [PubMed: 22606257] [Full Text: https://doi.org/10.1371/journal.pone.0036340]
Min, J.-N., Whaley, R. A., Sharpless, N. E., Lockyer, P., Portbury, A. L., Patterson, C. CHIP deficiency decreases longevity, with accelerated aging phenotypes accompanied by altered protein quality control. Molec. Cell. Biol. 28: 4018-4025, 2008. [PubMed: 18411298] [Full Text: https://doi.org/10.1128/MCB.00296-08]
Mol, M. O., van Rooij, J. G. J., Brusse, E., Verkerk, A. J. M. H., Melhem, S., den Dunnen, W. F. A., Rizzu, P., Cupidi, C., van Swieten, J. C., Donker Kaat, L. Clinical and pathologic phenotype of a large family with heterozygous STUB1 mutation. Neurol. Genet. 6: e417, 2020. Note: Electronic Article. [PubMed: 32337344] [Full Text: https://doi.org/10.1212/NXG.0000000000000417]
Okiyoneda, T., Barriere, H., Bagdany, M., Rabeh, W. M., Du, K., Hohfeld, J., Young, J. C., Lukacs, G. L. Peripheral protein quality control removes unfolded CFTR from the plasma membrane. Science 329: 805-810, 2010. [PubMed: 20595578] [Full Text: https://doi.org/10.1126/science.1191542]
Pakdaman, Y., Berland, S., Bustad, H. J., Erdal, S., Thompson, B. A., James, P. A., Power, K. N., Ellingsen, S., Krooni, M., Berge, L. I., Sexton, A., Bindoff, L. A., Knappskog, P. M., Johansson, S., Aukrust, I. Genetic dominant variants in STUB1, segregating in families with SCA48, display in vitro functional impairments indistinctive from recessive variants associated with SCAR16. Int. J. Molec. Sci. 22: 5870, 2021. [PubMed: 34070858] [Full Text: https://doi.org/10.3390/ijms22115870]
Palvadeau, R., Kaya-Gulec, Z. E., Simsir, G., Vural, A., Oztop-Cakmak, O., Genc, G., Aygun, M. S., Falay, O., Basak, A. N., Ertan, S. Cerebellar cognitive-affective syndrome preceding ataxia associated with complex extrapyramidal features in a Turkish SCA48 family. Neurogenetics 21: 51-58, 2020. [PubMed: 31741143] [Full Text: https://doi.org/10.1007/s10048-019-00595-0]
Parsons, J. L., Tait, P. S., Finch, D., Dianova, I. I., Allinson, S. L., Dianov, G. L. CHIP-mediated degradation and DNA damage-dependent stabilization regulate base excision repair proteins. Molec. Cell 29: 477-487, 2008. [PubMed: 18313385] [Full Text: https://doi.org/10.1016/j.molcel.2007.12.027]
Qian, S.-B., McDonough, H., Boellmann, F., Cyr, D. M., Patterson, C. CHIP-mediated stress recovery by sequential ubiquitination of substrates and Hsp70. Nature 440: 551-555, 2006. [PubMed: 16554822] [Full Text: https://doi.org/10.1038/nature04600]
Ravel, J. M., Benkirane, M., Calmels, N., Marelli, C., Ory-Magne, F., Ewenczyk, C., Halleb, Y., Tison, F., Lecocq, C., Pische, G., Casenave, P., Chaussenot, A., and 16 others. Expanding the clinical spectrum of STIP1 homology and U-box containing protein 1-associated ataxia. J. Neurol. 268: 1927-1937, 2021. [PubMed: 33417001] [Full Text: https://doi.org/10.1007/s00415-020-10348-x]
Roux, T., Barbier, M., Papin, M., Davoine, C.-S., Sayah, S., Coarelli, G., Charles, P., Marelli, C., Parodi, L., Tranchant, C., Goizet, C., Klebe, S., and 10 others. Clinical, neuropathological, and genetic characterization of STUB1 variants in cerebellar ataxias: a frequent cause of predominant cognitive impairment. Genet. Med. 22: 1851-1862, 2020. Note: Erratum: Genet. Med. 23: 2021 only, 2021. [PubMed: 32713943] [Full Text: https://doi.org/10.1038/s41436-020-0899-x]
Shi, C.-H., Schisler, J. C., Rubel, C. E., Tan, S., Song, B., McDonough, H., Xu, L., Portbury, A. L., Mao, C.-Y., True, C., Wang, R.-H., Wang, Q.-Z., Sun, S.-L., Seminara, S. B., Patterson, C., Xu, Y.-M. Ataxia and hypogonadism caused by the loss of ubiquitin ligase activity of the U box protein CHIP. Hum. Molec. Genet. 23: 1013-1024, 2014. [PubMed: 24113144] [Full Text: https://doi.org/10.1093/hmg/ddt497]
Shi, Y., Wang, J., Li, J.-D., Ren, H., Guan, W., He, M., Yan, W., Zhou, Y., Hu, Z., Zhang, J., Xiao, J., Su, Z., and 16 others. Identification of CHIP as a novel causative gene for autosomal recessive cerebellar ataxia. PLoS One 8: e81884, 2013. Note: Electronic Article. [PubMed: 24312598] [Full Text: https://doi.org/10.1371/journal.pone.0081884]
Shin, Y., Klucken, J., Patterson, C., Hyman, B. T., McLean, P. J. The co-chaperone carboxyl terminus of Hsp70-interacting protein (CHIP) mediates alpha-synuclein degradation decisions between proteasomal and lysosomal pathways. J. Biol. Chem. 280: 23727-23734, 2005. [PubMed: 15845543] [Full Text: https://doi.org/10.1074/jbc.M503326200]
Synofzik, M., Schule, R., Schulze, M., Gburek-Augustat, J., Schweizer, R., Schirmacher, A., Krageloh-Mann, I., Gonzalez, M., Young, P., Zuchner, S., Schols, L., Bauer, P. Phenotype and frequency of STUB1 mutations: next-generation screenings in Caucasian ataxia and spastic paraplegia cohorts. Orphanet J. Rare Dis. 9: 57, 2014. Note: Electronic Article. [PubMed: 24742043] [Full Text: https://doi.org/10.1186/1750-1172-9-57]
Younger, J. M., Chen, L., Ren, H.-Y., Rosser, M. F. N., Turnbull, E. L., Fan, C.-Y., Patterson, C., Cyr, D. M. Sequential quality-control checkpoints triage misfolded cystic fibrosis transmembrane conductance regulator. Cell 126: 571-582, 2006. [PubMed: 16901789] [Full Text: https://doi.org/10.1016/j.cell.2006.06.041]