Sumoylation at the Host-Pathogen Interface

Wilson, Van G.

There have been reports of two viral proteins that exhibit SUMO ligase activity, the Kaposi's sarcoma-associated herpes virus (KSHV) K-bZIP protein [73] and the adenovirus E1B-55K protein [74, 75] . K-bZIP is a nuclear transcription factor that is a strong repressor when sumoylated at lysine 158 [76] . Phosphorylation at threonine 111 prevents sumoylation and converts K-bZIP to a strong transcriptional activator [77] . Chang et al. showed that K-bZIP has a SIM motif at residues 73-77 that binds SUMO2/3 but not SUMO1 [73] . They also showed that K-bZIP acts as a SUMO2/3-specific SUMO ligase that enhances sumoylation of its binding partners, including p53 and pRB, and that the ligase activity required the intact SIM motif. Additionally, expression of K-bZIP in an inducible cell line resulted in a global increase in SUMO2/3 conjugates with no effect on SUMO1 conjugates, illustrating that K-zBIP could have wide-spread effects on cellular events through changing the sumoylation status of numerous proteins. Exactly how this benefits viral reproduction is not yet determined, but clearly K-bZIP is both regulated by sumoylation and is able in turn to regulate sumoylation of host proteins.