Trafficking to the plasma membrane of the seven-transmembrane protein encoded by human herpesvirus 6 U51 gene involves a cell-specific function present in T lymphocytes

The sequence of human herpesvirus 6 (HHV-6) U51 open reading frame predicts a protein of 301 amino acid residues,vith seven transmembrane domains. To identify and characterize U51, we derived antipeptide polyclonal antibodies and developed a transient expression assay. We ascertained that U51 was sy nthesized in cord blood mononuclear cells infected with either variant A- o r variant B-HHV-6 and was transported to the surface of productively infect ed cells. When synthesized in transient expression systems, U51 intracellul ar trafficking was regulated in a cell-type-dependent fashion. In human mon olayer HEK-293 and 143tk- cells, U51 accumulated predominantly in the endop lasmic reticulum and failed to be transported to the cell surface. In contr ast, in T-lymphocytic cell lines J-Jhan, Molt-3, and Jurkat, U51 was succes sfully transported to the plasma membrane. We infer that transport of U51 t o the cell surface requires a cell-specific function present in activated T lymphocytes and T-cell lines.