Ovarian Cancer

DNA repare

Proc Natl Acad Sci U S A. 2006 Nov 28;103(48):18107-12. Epub 2006 Nov 15. Links

Human SHPRH is a ubiquitin ligase for Mms2-Ubc13-dependent polyubiquitylation of proliferating cell nuclear antigen.

· Unk I, Hajdu I, Fatyol K, Szakal B, Blastyak A, Bermudez V, Hurwitz J,Prakash L,Prakash S

, Haracska L.

Institute of Genetics, Biological Research Center, Hungarian Academy of Sciences, H-6726 Szeged, Hungary.

Human SHPRH gene is located at the 6q24 chromosomal region, and loss of heterozygosity in this region is seen in a wide variety of cancers. SHPRH is a member of the SWI/SNF family of ATPases/helicases, and it possesses a C(3)HC(4) RING motif characteristic of ubiquitin ligase proteins. In both of these features, SHPRH resembles the yeast Rad5 protein, which, together with Mms2-Ubc13, promotes replication through DNA lesions via an error-free postreplicational repair pathway. Genetic evidence in yeast has indicated a role for Rad5 as a ubiquitin ligase in mediating the Mms2-Ubc13-dependent polyubiquitylation of proliferating cell nuclear antigen. Here we show that SHPRH is a functional homolog of Rad5. Similar to Rad5, SHPRH physically interacts with the Rad6-Rad18 and Mms2-Ubc13 complexes, and we show that SHPRH protein is a ubiquitin ligase indispensable for Mms2-Ubc13-dependent polyubiquitylation of proliferating cell nuclear antigen. Based on these observations, we predict a role for SHPRH in promoting error-free replication through DNA lesions. Such a role for SHPRH is consistent with the observation that this gene is mutated in a number of cancer cell lines, including those from melanomas and ovarian cancers, which raises the strong possibility that SHPRH function is an important deterrent to mutagenesis and carcinogenesis in humans.

PMID: 17108083 [PubMed - in process]

Mol Cell Biol. 2006 Dec;26(23):8901-13. Epub 2006 Sep 25. Links

Regulation of p53 localization and activity by Ubc13.

· Laine A, Topisirovic I, Zhai D, Reed JC, Borden KL, Ronai Z.

Signal Transduction Program, Burnham Institute for Medical Research, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA.

The abundance and activity of p53 are regulated largely by ubiquitin ligases. Here we demonstrate a previously undisclosed regulation of p53 localization and activity by Ubc13, an E2 ubiquitin-conjugating enzyme. While increasing p53 stability, Ubc13 decreases p53 transcriptional activity and increases its localization to the cytoplasm, changes that require its ubiquitin-conjugating activity. Ubc13 elicits K63-dependent ubiquitination of p53, which attenuates Hdm2-induced polyubiquitination of p53. Ubc13 association with p53 requires an intact C-terminal domain of p53 and is markedly stronger with a p53 mutant that cannot tetramerize. Expression of Ubc13 in vivo increases the pool of monomeric p53, indicating that Ubc13 affects tetramerization of p53. Significantly, wild-type but not mutant Ubc13 is associated with polysomes and enriches p53 within this fraction. In response to DNA damage, Ubc13 is no longer capable of facilitating p53 monomerization, in part due to a decrease in its own levels which is p53 dependent. Our findings point to a newly discerned mechanism important in the regulation of p53 organization, localization, and activity by Ubc13.

PMID: 17000756 [PubMed - indexed for MEDLINE

FEBS Lett. 2004 May 21;566(1-3):229-33. Links

The TRAF6 RING finger domain mediates physical interaction with Ubc13.

· Wooff J, Pastushok L, Hanna M, Fu Y, Xiao W.

Department of Microbiology and Immunology, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E5.

Tumor necrosis factor receptor associated factor 6 (TRAF6) is an important signaling molecule involved in a diverse array of physiological processes. It has been proposed that TRAF6, a RING finger-containing protein, acts as a ubiquitin ligase (E3) and a target for Lys-63 linked polyubiquitination mediated by Ubc13-Uev, a ubiquitin conjugating (E2) complex. However, the physical interaction between TRAF6 and this E2 complex has not been reported. We used the yeast two-hybrid assay to demonstrate that TRAF6 indeed interacts with the E2 complex through its direct binding to Ubc13. Either a single Cys-to-Ser substitution within the TRAF6 RING finger domain or an amino acid substitution on the Ubc13 surface, that is predicted to interact with RING finger proteins, is able to abolish the interaction. In addition, we found that TRAF6 can interact with itself and this self-interaction domain is mapped to the N-terminus containing the RING finger motif. Based on this study and our previous Ubc13-Uev structural analysis, the interface of Ubc13-TRAF6 RING finger can be predicted.

PMID: 15147900 [PubMed - indexed for MEDLINE]