Role of PACS-1 in trafficking of human cytomegalovirus glycoprotein B and virus production

The final envelopment of herpesviruses during assembly of new virions is thought to occur by the budding of core viral particles into a late secretory pathway organelle, the trans-Golgi network (TGN), or an associated endosomal compartment. Several herpesvirus envelope glycoproteins have been previously shown to localize to the TGN when expressed independently from other viral proteins. In at least some cases this TGN localization has been shown to be dependent on clusters of acidic residues within their cytoplasmic domains. Similar acidic cluster motifs are found in endogenous membrane proteins that also localize to the TGN. These acidic cluster motifs interact with PACS-1, a connector protein that is required for the trafficking of proteins containing such motifs from endosomes to the TGN. We show here that PACS-1 interacts with the cytoplasmic domain of the HCMV envelope glycoprotein B (gB) and that PACS-1 function is required for normal TGN localization of HCMV gB. Furthermore, inhibition of PACS-1 activity in infected cells leads to a decrease in HCMV titer, whereas an increase in expression of functional PACS-1 leads to an increase in HCMV titer, suggesting that PACS-1 is required for efficient production of HCMV.