Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2014;13(11):1663-70.
doi: 10.4161/cc.29065. Epub 2014 Apr 30.

Phosphorylation-dephosphorylation cycle of HP1α governs accurate mitotic progression

Arindam Chakraborty  1 , Supriya G Prasanth  1
Affiliations

Phosphorylation-dephosphorylation cycle of HP1α governs accurate mitotic progression

Arindam Chakraborty et al. Cell Cycle. 2014.

Abstract

Heterochromatin protein 1α (HP1α), a bona fide factor of silent chromatin, is required for establishing as well as maintaining the higher-order chromatin structure in eukaryotes. HP1α is decorated with several post-translational modifications, and many of these are critical for its cellular functions. HP1α is heavily phosphorylated; however, its physiological relevance had remained to be completely understood. We have recently demonstrated that human HP1α is a mitotic target for NDR kinase, and the phosphorylation at the hinge region of HP1α at the G 2/M phase of the cell cycle is crucial for mitotic progression and Sgo1 loading at mitotic centromeres (Chakraborty et al., 2014). We now demonstrate that the dephosphorylation of HP1α within its hinge domain occurs during mitosis, specifically soon after prometaphase. In the absence of the hinge-specific HP1α phosphorylation, either as a consequence of depleting NDR1 or in cells expressing a non-phosphorylatable HP1α mutant, the cells arrest in prometaphase with several mitotic defects. In this study we show that NDR1-depleted cells expressing hinge-specific phosphomimetic HP1α mutant rescues the prometaphase arrest but displays defects in mitotic exit, suggesting that the dephosphorylation of HP1α is required for the completion of cytokinesis. Taken together, our results reveal that the phosphorylation-dephosphorylation cycle of HP1α orchestrates accurate progression of cells through mitosis.

Keywords: HP1α; NDR kinases; cell cycle; dephosphorylation; mitosis; phosphorylation.

PubMed Disclaimer

Figures

None
Figure 1. Dephosphorylation of HP1α is required for mitotic exit. (A; a) Phos-tag PAGE analysis of lysates from different sub-stages of mitosis. Immunoblot analysis was performed using HP1α antibody. (b) Quantitation of the relative levels of N-terminal+ hinge and N-terminal phosphorylation of HP1α during different sub-stages of mitosis based on the immunoblot in (Aa). Note the accumulation of slower migrating (*1) form during prometaphase. Only the faster migrating form is evident during G1 (*2). (c) Immunoblot analysis of lysates collected from different mitotic substages. (B). Okadaic acid treatment of nocodazole arrest followed by release. Phos-tag PAGE analysis of these samples and immunoblot analysis with HP1α antibody. Note the retention of the slower migrating form of HP1α. (C). Phos-tag analysis of lysates (that were nocodazole arrested followed by release) treated with DMSO or cycloheximide.
None
Figure 2. Dephosphorylation of HP1α is required for mitotic exit. (A) Depletion of NDR1 kinase using siRNA in YFP-HP1α-WT, YFP-HP1α-S95A, and YFP-HP1α-S95E cells. Note the flow profile shows increased G2/M accumulation in NDR1-si treated cells and a further increase in the YFP-HP1α-S95E background. (B) Distribution of cells at various sub-stages of mitosis following NDR1 siRNA treatment in YFP-HP1α-WT, YFP-HP1α-S95A, and YFP-HP1α-S95E cells. Note a significant increase in the telophase population in YFP-HP1α-S95E cells treated with NDR1 siRNA. Error bars represent s.d. of 3 independent experiments. Statistical significance was determined by Student’s t test. Mean ± s.d., *P < 0.05, **P < 0.01 and ***P < 0.001. (C) Immunoblot analysis of YFP-HP1α-WT, YFP-HP1α-S95A, and YFP-HP1α-S95E stable cells depleted of NDR1. (D). Phenotypic analysis of YFP-HP1α-S95E stable cells depleted of NDR1. Scale bar 10 µm.
None
Figure 3. Model depicting the dynamics of HP1α phosphorylation during G1, G2/early mitosis, and in later parts of mitosis. Phosphorylation of the N terminus of HP1α facilitates its association to the chromatin mark H3trimethylK9. NDR kinase associates with the chromo-shadow domain of HP1α and phosphorylates the hinge domain. Hinge-phosphorylated form of HP1α localizes to centromeres, associates with centromeric proteins (X/Y denote unknown proteins at centromere), and governs chromosome alignment (schematic adapted and modified from Chakraborty et al., 2014). Starting at metaphase, HP1α is dephosphorylated (presumably by PP1/PP2A), and this releases this form of HP1α and associated partners (bound specifically to hinge-phosphorylated HP1α) from the centromere.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. James TC, Elgin SC. Identification of a nonhistone chromosomal protein associated with heterochromatin in Drosophila melanogaster and its gene. Mol Cell Biol. 1986;6:3862–72. - PMC - PubMed
    1. Aasland R, Stewart AF. The chromo shadow domain, a second chromo domain in heterochromatin-binding protein 1, HP1. Nucleic Acids Res. 1995;23:3168–73. doi: 10.1093/nar/23.16.3168. - DOI - PMC - PubMed
    1. Lachner M, O’Carroll D, Rea S, Mechtler K, Jenuwein T. Methylation of histone H3 lysine 9 creates a binding site for HP1 proteins. Nature. 2001;410:116–20. doi: 10.1038/35065132. - DOI - PubMed
    1. Meehan RR, Kao CF, Pennings S. HP1 binding to native chromatin in vitro is determined by the hinge region and not by the chromodomain. EMBO J. 2003;22:3164–74. doi: 10.1093/emboj/cdg306. - DOI - PMC - PubMed
    1. Eissenberg JC, Elgin SC. HP1a: a structural chromosomal protein regulating transcription. Trends Genet. 2014;30:103–10. doi: 10.1016/j.tig.2014.01.002. - DOI - PMC - PubMed

Publication types

MeSH terms

Substances

LinkOut - more resources