CD138Syndecan1

CD138, also known as Syndecan-1, is a transmembrane heparan sulfate proteoglycan that participates in cell–matrix adhesion and growth factor signaling. It carries covalently attached heparan sulfate chains that bind a variety of ligands, enabling its role as a co-receptor for several growth factors and extracellular matrix components. The protein is encoded by the SDC1 gene and is a member of the Syndecan family.

Expression of CD138 is prominent on epithelial cells and on plasma cells. It is widely used as a marker to identify plasma cells in diagnostic laboratories. The extracellular portion of CD138 can be shed from the cell surface, generating soluble CD138 (sCD138) detectable in serum. The balance between membrane-bound and soluble forms can influence cell–environment interactions and may reflect physiological or pathological states.

Functionally, CD138 mediates cell adhesion and migration by presenting heparan sulfate–bound growth factors such as FGFs, VEGFs, and HGF to their receptors, thereby modulating signaling pathways. It also interacts with components of the extracellular matrix, including laminin and fibronectin, and can influence integrin-mediated signaling. In plasma cell biology and certain cancers, CD138 expression supports cell survival and localization within tissue microenvironments.

Clinical significance of CD138 centers on its use as a diagnostic marker for plasma cell disorders, notably multiple myeloma, where CD138 expression helps identify malignant plasma cells. Elevated levels of soluble CD138 in serum have been investigated as a marker of disease activity and prognosis in myeloma and other conditions. CD138 is also pursued as a therapeutic target, with antibody-based therapies and antibody–drug conjugates evaluated in clinical trials.