A crosstalk between hSiah2 and Pias E3-ligases modulates Pias-dependent activation

Protein inhibitor of activated STAT (Pias) and human homologues of seven in absentia (hSiah) proteins both exhibit properties of ubiquitin-family peptides conjugating enzymes. Pias present E3-ligase activity for small ubiquitin-related modifiers (Sumo) covalent attachment to their targets. This post-translational modification is responsible for the activation of different transcription factors such as AP1. HSiah proteins possess ubiquitin-E3-ligase activity that triggers their partners to proteasomal-dependent degradation. The present study identifies Pias as a new hSiah2-interacting protein. We demonstrate that hSiah2 regulates specifically the proteasome-dependent degradation of Pias proteins. On reverse, Pias does not prevent hSiah2 degradation. We provide evidences for hSiah2-dependent degradation of Pias as being a mechanism in the regulation of c-jun N-terminal kinase-activating pathways. This report describes a new interconnection between sumoylation and ubiquitination pathways by regulating the levels of the E3-ligases available for these processes.