Human Cytomegalovirus Tropism Modulator UL148 Interacts with SEL1L, a Cellular Factor That Governs Endoplasmic Reticulum-Associated Degradation of the Viral Envelope Glycoprotein gO

Viral glycoproteins in large part determine the cell types that an enveloped virus can infect and hence play crucial roles in transmission and pathogenesis. The glycoprotein H/L heterodimer (gH/gL) is part of the conserved membrane fusion machinery that all herpesviruses use to enter cells. In human cytomegalovirus (HCMV), gH/gL participates in alternative complexes in virions, one of which is a trimer of gH/gL with glycoprotein O (gO). Here, we show that gO is constitutively degraded during infection by the endoplasmic reticulum-associated degradation (ERAD) pathway and that UL148, a viral factor that regulates HCMV cell tropism, interacts with the ERAD machinery and slows gO decay. Since gO is required for cell-free virus to enter new host cells but dispensable for cell-associated spread that resists antibody neutralization, our findings imply that the posttranslational instability of a viral glycoprotein provides a basis for viral mechanisms to modulate tropism and spread.