E3 ubiquitin ligase E6AP-mediated TSC2 turnover in the presence and absence of HPV16 E6.

We previously found that HPV16 E6 causes the degradation of the tumor suppressor protein TSC2, resulting in the phosphorylation of S6 kinase and S6 even in the absence of insulin. In the present study, we investigated the role of E6-associated protein (E6AP) in HPV16 E6-induced TSC2 degradation. Our results demonstrated that TSC2 was targeted for degradation in the presence or absence of HPV16 E6. Over-expression of E6AP enhanced the degradation of TSC2 by HPV16 E6, while expression of a dominant negative E6AP (C833A) inhibited the E6-induced degradation. Additionally, by using shRNAs to block E6AP expression in HPV16 positive and negative cells, we found a significantly prolonged TSC2 half-life. An in vivo ubiquitination assay was done to reveal that E6AP promoted the ubiquitination of TSC2 independent of HPV16 E6. We further found that TSC2 bound E6AP in the presence as well as in the absence of HPV16 E6. The binding regions on E6AP and TSC2 have been identified as amino acid (aa) 260-316, aa 428-500 and aa 1-175, aa 1251-1807, respectively. Taken together, degradation of TSC2 is mediated by E6AP ubiquitin ligase.