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
. 2007 Dec 14:4:95.
doi: 10.1186/1742-4690-4-95.

Ubiquitination of HTLV-I Tax in response to DNA damage regulates nuclear complex formation and nuclear export

Michael L Gatza  1 , Tajhal Dayaram, Susan J Marriott
Affiliations

Ubiquitination of HTLV-I Tax in response to DNA damage regulates nuclear complex formation and nuclear export

Michael L Gatza et al. Retrovirology. .

Abstract

Background: The HTLV-I oncoprotein, Tax, is a pleiotropic protein whose activity is partially regulated by its ability to interact with, and perturb the functions of, numerous cellular proteins. Tax is predominantly a nuclear protein that localizes to nuclear foci known as Tax Speckled Structures (TSS). We recently reported that the localization of Tax and its interactions with cellular proteins are altered in response to various forms of genotoxic and cellular stress. The level of cytoplasmic Tax increases in response to stress and this relocalization depends upon the interaction of Tax with CRM1. Cellular pathways and signals that regulate the subcellular localization of Tax remain to be determined. However, post-translational modifications including sumoylation and ubiquitination are known to influence the subcellular localization of Tax and its interactions with cellular proteins. The sumoylated form of Tax exists predominantly in the nucleus while ubiquitinated Tax exists predominantly in the cytoplasm. Therefore, we hypothesized that post-translational modifications of Tax that occur in response to DNA damage regulate the localization of Tax and its interactions with cellular proteins.

Results: We found a significant increase in mono-ubiquitination of Tax in response to UV irradiation. Mutation of specific lysine residues (K280 and K284) within Tax inhibited DNA damage-induced ubiquitination. In contrast to wild-type Tax, which undergoes transient nucleocytoplasmic shuttling in response to DNA damage, the K280 and K284 mutants were retained in nuclear foci following UV irradiation and remained co-localized with the cellular TSS protein, sc35.

Conclusion: This study demonstrates that the localization of Tax, and its interactions with cellular proteins, are dynamic following DNA damage and depend on the post-translational modification status of Tax. Specifically, DNA damage induces the ubiquitination of Tax at K280 and K284. Ubiquitination of these residues facilitates the dissociation of Tax from sc35-containing nuclear foci, and stimulates nuclear export of Tax through the CRM1 pathway.

PubMed Disclaimer

Figures

Figure 1
Figure 1
Effect of ubiquitination on subcellular localization of Tax. Tax localization alone (A-F, top row) or together with DAPI to visualize the nucleus (A-F, bottom row) was examined by immunofluorescent microscopy in transfected 293 cells. Tax is expressed in nuclear foci in the absence of DNA damage (A) and is localized in the cytoplasm following UV irradiation (B). The addition of a UB tag at either the N- (C) or C- (E) termini caused Tax to be localized in the cytoplasm but treatment with LMB (D and F) sequestered UB-Tax and Tax-UB to nuclear foci. All images are shown at a magnification of 63×. The percentage of cells expressing nuclear foci (black bar) or cytoplasmic Tax (gray bar) was scored in five hundred transfected cells, in three independent experiments (G). Western blot showing expression of UB-Tax, Tax-UB, and native Tax proteins (H).
Figure 2
Figure 2
UV irradiation increases Tax mono-ubiquitination. Tax was immunoprecipitated from 293 cell lysates that had been transfected with Tax and HA-UB and either mock or UV irradiated (30 J/m2, 30 minute recovery). The immunoprecipitates were analyzed by immunoblot for Tax (left) or HA (right).
Figure 3
Figure 3
Lysine residues 280 and 284 regulate UV-induced Tax localization. (A) Wild-type Tax or Tax mutants were transiently expressed in 293 cells. Localization of Tax mutants in the absence (black bars) or presence of 30 J/m2 UV irradiation (gray bars) is shown. Error bars represent the standard error in three independent experiments. (B) Western blot showing expression of each Tax mutant analyzed.
Figure 4
Figure 4
Lysine residues 280 and 284 are required for UV-induced Tax ubiquitination. Tax was immunoprecipitated from 293 cell lysates that had been transfected with Tax or TaxK7/8R, together with HA-UB. Cells were either mock (-) or UV irradiated (+) and the ubiquitination status of Tax was examined by immunoblot analysis for Tax.
Figure 5
Figure 5
Mutation of lysine residues 280 and 284 prevents UV-induced dissociation of Tax from TSS. Wild-type (A and B), M33 (C and D), K6R (E and F), K7R (G and H), or K8R (I and J) Tax was transiently expressed in 293 cells for 48 hrs and subjected to 30 J/m2 UV irradiation (B, D, F, H, J) or mock irradiated (A, C, E, G, I) and allowed to recover for 30 min. sc35 (left column) and Tax (left center column) were visualized by immunofluorescent microscopy separately, together (Merged, right center column), or together with DAPI (DAPI Merged, right column). All images are shown at a magnification of 63×.
Figure 6
Figure 6
Quantitation of Tax and sc35 nuclear speckles. Nuclear foci (shown in Figure 5) containing sc35 (A), Tax (B), or colocalization (C) were quantitated in the absence (black bars) or presence of 30 J/m2 UV irradiation (gray bars). Error bars represent the standard error in three independent experiments.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Matsuoka M. Human T-cell leukemia virus type I (HTLV-I) infection and the onset of adult T-cell leukemia (ATL) Retrovirology. 2005;2:27. doi: 10.1186/1742-4690-2-27. - DOI - PMC - PubMed
    1. Takatsuki K. Discovery of adult T-cell leukemia. Retrovirology. 2005;2:16. doi: 10.1186/1742-4690-2-16. - DOI - PMC - PubMed
    1. Gatza ML, Watt JC, Marriott SJ. Cellular transformation by the HTLV-I Tax protein, a jack-of-all-trades. Oncogene. 2003;22:5141–5149. doi: 10.1038/sj.onc.1206549. - DOI - PubMed
    1. Yoshida M. Multiple viral strategies of HTLV-1 for dysregulation of cell growth control. Annu Rev Immunol. 2001;19:475-96.:475–496. doi: 10.1146/annurev.immunol.19.1.475. - DOI - PubMed
    1. Azran I, Schavinsky-Khrapunsky Y, Aboud M. Role of Tax protein in human T-cell leukemia virus type-I leukemogenicity. Retrovirology. 2004;1:20. doi: 10.1186/1742-4690-1-20. - DOI - PMC - PubMed

Publication types

MeSH terms

Substances

LinkOut - more resources