Update on BK virus entry and intracellular trafficking.

BK virus (BKV) is a small, non-enveloped, double-stranded DNA virus and a member of the Polyomaviridae family. As the recently recognized etiologic agent of polyomavirus-associated nephropathy, the events involved in BKV invasion of host cells are an important area of study. Using cell culture models, the mechanism by which BKV infects permissive hosts to gain access to the replication machinery within these cells is beginning to unfold. BKV uses an N-linked glycoprotein containing an alpha(2,3)-linked sialic acid as a receptor. After this initial attachment, BKV enters cells through caveolae-mediated endocytosis. Intracellular trafficking via cellular cytoskeletal components follows this relatively slow and cholesterol-dependent internalization. BKV must reach the nucleus for viral transcription and replication to occur. Elucidating the steps of the early viral lifecycle would provide clues to help explain the infectious spread and pathology of this human pathogen.