HIV-1 Nef-mediated acceleration of HPV-associated cancer through differential ubiquitination of cellular proteins

While the emergence of combination anti-retroviral therapy (cART) has reduced AIDS-defining cancer in individuals with HIV-1, the morbidity and mortality of non-AIDS defining cancers such as those caused by HPV remain high. However, the molecular mechanism by which coinfection of HIV-1 and HPV accelerates HPV-mediated cancer in coinfected individuals is unknown, as they infect distinct target cells using disparate receptor molecules. Our transduction experiment using pseudotyped HIV-1 indicates that HIV-1 cannot enter HeLa cells, human cervical cells, suggesting that viral protein generated by infected cells, not HIV-1 infection, may be responsible for accelerating HPV-associated cancer in coinfected individuals. Specifically, our study shows that HIV-1 Nef could be the major culprit. Proteomic analysis in the presence or absence of Nef indicated that ubiquitination was up-regulated in 93 cellular proteins and down-regulated in 232, highlighting that Nef plays a key role in regulating cellular protein stability through ubiquitination and the UPS-mediated proteasomal degradation pathway. Western blot analysis demonstrated that differential ubiquitination was not caused by differential protein expression, validating our analyses. Computational analysis classified the majority of identified proteins as metabolite interconversion enzymes or nucleic acid metabolism proteins, with most being responsible for binding or catalytic activity, functioning in cellular and metabolic processes, and localizing to cellular anatomical entities and intracellular regions. Additionally, several proteins directly interact with Nef (23), the UPS (15), P53 (28), and E6, E6-BP, and E6-AP (1 each). Taken together, our data show that HIV-1 Nef plays a pivotal role in acceleration of HPV-mediated cancer progression in coinfectees.