Characterisation of the human cytomegalovirus immunomodulatory gene UL141

Human cytomegalovirus (HCMV) UL141 is a potent modulator of natural killer (NK) cell function that acts by suppressing cell surface expression of CD155, a recognised ligand for the ubiquitous NK. cell activating receptors DNAM-1 and CD96. CD155, also known as nectin-like molecule 5 (necl-5) or poliovirus receptor (PVR), is an important adhesion molecule that impacts on cell motility, proliferation and cellular signalling complexes. The focus of this study is to characterise UL141 expression, interactions and biological properties. Consistent with the role of CD 155 as a cell adhesion molecule, UL141 expression was associated with reduced cellular adhesion whether expressed in continuous cell lines or by adenovirus vector. UL14 and UL141 exhibit significant amino acid sequence homology and are members of the same HCMV gene family. Interestingly, UL14 also impaired cell adhesion. Consistent with HCMV downregulating multiple adhesion molecules, productive infection was associated with greatly reduced cell adhesion. Against this background, deletion of UL141 from the virus had no overt effect in adhesion assays. When co-expressed with C-terminal fluorescent tags, gpUL141 and CD 155 co-localise with each other and endoplasmic reticulum marker. When over-expressed CD 155 and gpUL141 co-localised in inclusion bodies along with calnexin implying gpUL141 may hold CD 155 in a partially destabilised form. gpUL141 was identified as a component of the envelope of mature HCMV virus particles, whilst CD 155 and gpUL14 were excluded. gpUL141 is predominantly an endoglycosidaseH (Endo-H)-sensitive, ER-resident glycoprotein in HCMV infected cell that is subject to post-translational modification, consistent with proteolytic cleavage, during the later stages of infection. However, the protein incorporated into virions is full length and had acquired Endo-H resistance, consistent with transit through the Golgi apparatus. As CD 155 is recognised to be a cellular receptor for poliovirus and other herpesviruses, the identification of UL141 as a virion protein may have implications for virus entry