Syndecan 1 (SDC1, CD138) is a cell surface heparin sulfate proteoglycan that links the cytoskeleton to the interstitial matrix. It mediates cell binding, cell signaling, cytoskeletal organization, and participates in cell proliferation and cell migration. It is also involved in internalization of the HIV-1 tat protein. Altered SDC1 expression has been detected in several cancers, including multiple myeloma. It is expressed in plasma cells, squamous epithelia of the esophagus and skin, placental trophoblasts, and a variety of epithelial cells including those of the prostate, GI tract and breast. References: Ref: Am J Clin Path 2004, 121(2):254; Adv Exp Med Biol 1992, 313:69