Interaction of HPV E6 oncoproteins with specific proteasomal subunits

Abstract

The Human Papillomavirus E6 oncoproteins have the capacity to target several of their cellular interacting partners for proteasome mediated degradation, and recent proteomic analyses suggest a close involvement of E6 with the cellular proteasome machinery. In this study we have performed an extensive analysis of the capacity of different E6 oncoproteins to interact with specific proteasome components. We demonstrate that multiple subunits of the proteasome can be bound by different HPV E6 oncoproteins. Furthermore, whilst most of these interactions appear independent of the E6AP ubiquitin ligase, the association of E6 with the major ubiquitin-accepting proteasome subunit, S5a, does require the presence of E6AP. One consequence of the interaction between E6/E6AP and S5a is enhanced ubiquitination of this proteasome subunit. These results suggest a complex interplay between E6 and the proteasome, only some aspects of which are dependent upon the E6AP ubiquitin ligase.

Angelman syndrome–associated point mutations in the Zn2+-binding N-terminal (AZUL) domain of UBE3A ubiquitin ligase inhibit binding to the proteasome

“…The 26S proteasome is one of the major cellular complexes interacting with UBE3A (21)(22)(23)(24)(25)(26)(27)(28)(29). Although immunoprecipitation and MS cannot distinguish which specific protein subunit within the 26S proteasome directly binds UBE3A, PSMD4 was the only proteasomal subunit identified as a direct UBE3Abinding partner in a yeast two-hybrid screen we recently reported, suggesting that PSMD4 likely bridges the interaction of UBE3A with the 26S proteasome (24).…”

“…PSMD4 functions as a ubiquitin receptor in the 19S lid of the 26S proteasome to help recruit polyubiquitylated proteins to the proteasome for their subsequent proteolytic degradation. However, PSMD4 also exists in a proteasome-unbound manner in the cytosol (23,29). As other proteasomal subunits are copurified with PSMD4 in UBE3A immunoprecipitation experiments, we can assume that UBE3A binds to the proteasomeassociated PSMD4.…”

“…Although the proteins of the lid complex are responsible for the recruitment of ubiquitylated proteins, the barrel and its intrinsic proteolytic activities mediate the breakdown of proteins (20). UBE3A associates with the proteasome (21)(22)(23)(24)(25)(26)(27)(28)(29). In that context, the UBE3A-interacting protein PMSD4 (also known as Rpn10/S5a) is part of the regulatory lid complex and known to bind to polyubiquitin chains of ubiquitylated proteins via its ubiquitin-interacting motif (UIM), resulting in their recruitment to the proteasome (30 -32).…”

“…In that context, the UBE3A-interacting protein PMSD4 (also known as Rpn10/S5a) is part of the regulatory lid complex and known to bind to polyubiquitin chains of ubiquitylated proteins via its ubiquitin-interacting motif (UIM), resulting in their recruitment to the proteasome (30 -32). PSMD4, however, also exists unbound to the proteasome in the cytosol, and its proteasome-independent functions are still unclear (23,29).…”

Functional Roles of E6 and E7 Oncoproteins in HPV-Induced Malignancies at Diverse Anatomical Sites

“…In addition, HR α-HPV E6s interact directly with the S5a proteasome subunit, one of the two major ubiquitin acceptor molecules of the proteasome. The interaction is E6AP-dependent and results in the upregulated ubiquitination of S5a, indicating the complexity of E6 association with the proteasome [68]. …”