Platelet-derived growth factor-α receptor activation is required for human cytomegalovirus infection

Human cytomegalovirus ( HCMV) is a ubiquitous human herpesvirus that can cause life- threatening disease in the fetus and the immunocompromised host(1). Upon attachment to the cell, the virus induces robust inflammatory, interferon- and growth- factor-like signalling(2-9). The mechanisms facilitating viral entry and gene expression are not clearly understood(4). Here we show that platelet- derived growth factor-alpha receptor (PDGFR-alpha) is specifically phosphorylated by both laboratory and clinical isolates of HCMV in various human cell types, resulting in activation of the phosphoinositide-3-kinase (PI(3)K) signalling pathway. Upon stimulation by HCMV, tyrosine- phosphorylated PDGFR-alpha associated with the p85 regulatory subunit of PI( 3) K and induced protein kinase B ( also known as Akt) phosphorylation, similar to the genuine ligand, PDGF-AA. Cells in which PDGFR-alpha was genetically deleted(10) or functionally blocked were non- permissive to HCMV entry, viral gene expression or infectious virus production. Re- introducing human PDGFRA gene into knockout cells restored susceptibility to viral entry and essential viral gene expression. Blockade of receptor function with a humanized PDGFR-alpha blocking antibody (IMC-3G3)(11) or targeted inhibition of its kinase activity with a small molecule (Gleevec)(12) completely inhibited HCMV viral internalization and gene expression in human epithelial, endothelial and fibroblast cells. Viral entry in cells harbouring endogenous PDGFR-alpha was competitively inhibited by pretreatment with PDGF-AA. We further demonstrate that HCMV glycoprotein B directly interacts with PDGFR-alpha, resulting in receptor tyrosine phosphorylation, and that glycoprotein B neutralizing antibodies(13) inhibit HCMV- induced PDGFR-alpha phosphorylation. Taken together, these data indicate that PDGFR-alpha is a critical receptor required for HCMV infection, and thus a target for novel anti- viral therapies.