An analysis of human cytomegalovirus gene family function

Abstract

Human cytomegalovirus (HCMV) is a β-herpesvirus that causes complications in immuno-compromised individuals and is the leading infectious cause of birth defects. The HCMV genome contains 15 gene families, which contain between 2 to 14 members. One of these, the US12 gene family, consists of a sequential cluster of 10 genes (US12 to US21) that are highly conserved in clinical isolates. This family has roles in tropism and immune evasion and was recently found to regulate the cell surface expression of a wide array of immune ligands. This included the regulation of ligands for the natural killer (NK) cell activating receptors NKG2D and NKp30 (MICA and B7-H6 respectively), which were targeted by US18 and US20. To complement these mechanistic studies, a C-terminal V5 epitope tag was added to each US12 family gene within the HCMV Merlin genome. A large proportion of the US12 family were shown to be degraded within the cell, possibly within lysosomes, which suggests that they may interact with their targets proteins in order to redirect them for degradation. Expression of US12 family members was detectable by immunoblotting during an infection time-course, with many US12 family members expressed during the Tp3 temporal class of HCMV gene expression. Three members of the family were also demonstrated to be N-glycosylated during HCMV infection. The US12 family appear to have associations with the virion assembly compartment, and correspondingly, 7 US12 family members are found within the virion. Furthermore, the majority of the US12 family also show co-localisation with endoplasmic reticulum-derived membranes. These data build on our previous functional characterisation to give insights into the workings of this important HCMV gene family