Virus proliferation mechanism by the monoubiquitin-dependent vesicular transport complex

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Although significance of the vesicular transport system in virus proliferation is suspected, precise mechanisms underlying it remains unknown. In this study, we investigated transport proteins STAM1, STAM2 and Hrs, all of which sort cell surface receptors, in virus life cycle. Mouse cytomegalovirus (MCMV) proliferation was decreased by the Hrs-depletion. Since MCMV attachment and entry left unaffected by Hrs, we next examined immediate early gene, ie1 mRNAs for ie1 showed no significant difference irrespective of Hrs. Unexpectedly, however, IE1 protein showed significant suppression by Hrs-depletion. I found that some portion of IE1 protein travels out of the nucleus into the cytoplasm, where it locates on the endosomes. Because Hrs is an endosomal protein, we suspect that Hrs binds and sorts Iel, leading to the lysosome dependent degradation. In conclusion, we found a novel role of a vesicular sorting protein Hrs in the regulation of a virus transcription factor, which is required for a normal virus replication.