Monoubiquitination Is Critical for Otub1 to Suppress UbcH5 and Stabilize p53 [Signal Transduction]

January 8th, 2014 by Li, Y., Sun, X.-X., Elferich, J., Shinde, U., David, L. L., Dai, M.-S.

Otub1 regulates p53 stability and activity via non-canonical inhibition of the MDM2 cognate ubiquitin (Ub)-conjugating enzyme (E2) UbcH5. However, it is not clear how this activity of Otub1 is regulated in cells. Here we report that Otub1 is monoubiquitinated by UbcH5 in cells and in vitro, primarily at lysine 59 and 109 residues. This monoubiquitination in turn contributes to the activity of Otub1 to suppress UbcH5. The lysine-free Otub1 mutant (Otub1K0) fails to be monoubiquitinated and is unable to suppress the Ub-conjugating activity of UbcH5 in vitro and the MDM2-mediated p53 ubiquitination in cells. Consistently, this mutant is unable to stabilize p53, induce apoptosis, and suppress cell growth. Overexpression of Otub1K0 inhibits DNA-damage induced apoptosis. Adding either Lys 59 or Lys 109 back to the Otub1K0 mutant restored the monoubiquitination of Otub1 and its function to stabilize and activate p53. We further show that UbcH5 preferentially binds to the monoubiquitinated Otub1 via Ub interaction with its backside donor Ub-interacting surface, suggesting that this binding interferes with the self-assembly of Ub-charged UbcH5 (UbcH5~Ub) conjugates, which is critical for the Ub transfer. Thus, our data reveal novel insights into the Otub1 inhibition of E2 wherein monoubiquitination promotes the interaction of Otub1 with and its function to suppress UbcH5.