Identification of annexin A1 as a novel substrate for E6AP-mediated ubiquitylation.

E6-associated protein (E6AP) is a cellular ubiquitin protein ligase that mediates ubiquitylation and degradation of p53 in conjunction with the high-risk human papillomavirus E6 proteins. However, the physiological functions of E6AP are poorly understood. To identify a novel biological function of E6AP, we screened for binding partners of E6AP using GST pull-down and mass spectrometry. Here we identified annexin A1, a member of the annexin superfamily, as an E6AP-binding protein. Ectopic expression of E6AP enhanced the degradation of annexin A1 in vivo. RNAi-mediated downregulation of endogenous E6AP increased the levels of endogenous annexin A1 protein. E6AP interacted with annexin A1 and induced its ubiquitylation in a Ca(2+)-dependent manner. GST pull-down assay revealed that the annexin repeat domain III of annexin A1 is important for the E6AP binding. Taken together, our data suggest that annexin A1 is a novel substrate for E6AP-mediated ubiquitylation. Our findings raise the possibility that E6AP may play a role in controlling the diverse functions of annexin A1 through the ubiquitin-proteasome pathway. Copyright 2009 Wiley-Liss, Inc.