Wilson, Van G.

Human papillomaviruses (HPVs) replicate in the nucleus and modulate several host cell pathways to create a favorable environment for viral reproduction. The HPV E6 proteins utilize the host ubiquitin‐proteosome pathway to target several cellular proteins for degradation. Several HPV proteins are substrates for sumoylation, so the objective of this study was to determine if HPV E6 proteins interacted with or influenced the parallel host sumoylation system. Transient expression of E6 caused an apparent general reduction in the overall level of host sumoylation. To explore the mechanistic basis, we examined the effect of E6 proteins on Ubc9, the sole sumoylation conjugation enzyme. HPV E6 proteins reduced intracellular levels of Ubc9, without affecting transcript levels, so a direct effect on Ubc9 protein stability is likely. Consistent with typical E6‐mediated proteasomal degradation, E6 bound to Ubc9 in vitro, and required E6AP for reduction of Ubc9 levels. To examine the effect of E6 on sumoylated proteins in more detail, a fluorescent 2‐dimensional gel system was used to visualize sumoylated proteins. Stable expression of E6 resulted in the loss of 32 sumoylated proteins out of a matched set of over 200 protein spots. Thus, E6 exerts a significant, though selective, effect on host protein sumoylation through its action on Ubc9, which likely helps to create a cellular environment conducive to viral replication. Grant Funding Source : Supported by NIH grant CA089298 to V.G.W.