DELETION MUTANTS IN HUMAN CYTOMEGALOVIRUS GLYCOPROTEIN US9 ARE IMPAIRED IN CELL-CELL TRANSMISSION AND IN ALTERING TIGHT JUNCTIONS OF POLARIZED HUMAN RETINAL-PIGMENT EPITHELIAL-CELLS

Retinal cytomegalovirus (CMV) disease is one of the major manifestatio ns of viral pathogenesis in immunosuppressed patients with the acquire d immunodeficiency syndrome (AIDS). CMV infection of the retina causes directional destruction which begins at the optic nerve head adjacent to the retinal capillaries and progresses, if untreated, to retinal d etachment and blindness. Infection does not occur across the basal mem brane of the retinal pigment epithelium (RPE), adjacent to the highly vascularized choroid. CMV replicates in polarized RPE cells, and proge ny virions cross apical and lateral membranes of RPE cells grown on pe rmeable filter supports, but not basal membranes. Cell-cell junctions of CMV-infected RPE cells are permeabilized, and the tight junction pr otein zonula occludens (ZO-1) is disassembled; progeny virions then sp read to neighboring cells through the lateral cell membranes, which in polarized cells differ significantly in lipid and protein composition from the apical cell membranes. We found that CMV mutants with deleti ons in US9 and US8/US9 failed to spread from cell to cell, exhibiting a small-plaque phenotype in polarized RPE cells. Immunofluorescence co nfocal microscopy staining of ZO-1 protein revealed that RPE cells inf ected with CMV deletion mutants RV35, RV80, and RV61 did not exhibit a ltered tight junctions, in contrast to RPE cells infected with wild-ty pe strain AD169 virus. Our findings indicate that US9, which is an acc essory glycoprotein in infected foreskin fibroblasts, is required for transmission of virus across cell-cell junctions of polarized RPE cell s. The relationship between US9 expression and virus transmission acro ss cell-cell boundaries suggests that US9 may directly or indirectly p ermeabilize tight junction complexes of polarized RPE cells.