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Lok G.T.-M.,University of Hong Kong | Sy S.M.-H.,University of Hong Kong | Dong S.-S.,University of Hong Kong | Ching Y.-P.,University of Hong Kong | And 3 more authors.
Nucleic Acids Research | Year: 2012

Pairing of a given E3 ubiquitin ligase with different E2s allows synthesis of ubiquitin conjugates of different topologies. While this phenomenon contributes to functional diversity, it remains largely unknown how a single E3 ubiquitin ligase recognizes multiple E2s, and whether identical structural requirements determine their respective interactions. The E3 ubiquitin ligase RNF8 that plays a critically important role in transducing DNA damage signals, interacts with E2s UBCH8 and UBC13, and catalyzes both K48-and K63-linked ubiquitin chains. Interestingly, we report here that a single-point mutation (I405A) on the RNF8 polypeptide uncouples its ability in catalyzing K48-and K63-linked ubiquitin chain formation. Accordingly, while RNF8 interacted with E2s UBCH8 and UBC13, its I405A mutation selectively disrupted its functional interaction with UBCH8, and impaired K48-based poly-ubiquitylation reactions. In contrast, RNF8 I405A preserved its interaction with UBC13, synthesized K63-linked ubiquitin chains, and assembled BRCA1 and 53BP1 at sites of DNA breaks. Together, our data suggest that RNF8 regulates K48-and K63-linked poly-ubiquitylation via differential RING-dependent interactions with its E2s UBCH8 and UBC13, respectively. © 2011 The Author(s). Source

Scheper J.,Institute for Molecular Biology IBMB CSIC | Guerra-Rebollo M.,Institute for Molecular Biology IBMB CSIC | Sanclimens G.,CSIC - Institute of Advanced Chemistry of Catalonia | Moure A.,CSIC - Institute of Advanced Chemistry of Catalonia | And 12 more authors.
PLoS ONE | Year: 2010

Background: Several pathways that control cell survival under stress, namely RNF8-dependent DNA damage recognition and repair, PCNA-dependent DNA damage tolerance and activation of NF-κB by extrinsic signals, are regulated by the tagging of key proteins with lysine 63-based polyubiquitylated chains, catalyzed by the conserved ubiquitin conjugating heterodimeric enzyme Ubc13-Uev. Methodology/Principal Findings: By applying a selection based on in vivo protein-protein interaction assays of compounds from a combinatorial chemical library followed by virtual screening, we have developed small molecules that efficiently antagonize the Ubc13-Uev1 protein-protein interaction, inhibiting the enzymatic activity of the heterodimer. In mammalian cells, they inhibit lysine 63-type polyubiquitylation of PCNA, inhibit activation of NF-κB by TNF-α and sensitize tumor cells to chemotherapeutic agents. One of these compounds significantly inhibited invasiveness, clonogenicity and tumor growth of prostate cancer cells. Conclusions/Significance: This is the first development of pharmacological inhibitors of non-canonical polyubiquitylation that show that these compounds produce selective biological effects with potential therapeutic applications. © 2010 Scheper et al. Source

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