Syndecan 1

Syndecan 1 is a is_associated_with::protein which in humans is encoded by the SDC1 is_associated_with::gene.

Function
The protein encoded by this gene is a transmembrane (type I) is_associated_with::heparan sulfate is_associated_with::proteoglycan and is a member of the is_associated_with::syndecan proteoglycan family. The syndecans mediate cell binding, is_associated_with::cell signaling, and cytoskeletal organization and syndecan receptors are required for internalization of the HIV-1 tat protein. The syndecan-1 protein functions as an is_associated_with::integral membrane protein and participates in cell proliferation, is_associated_with::cell migration and cell-matrix interactions via its receptor for extracellular matrix proteins. Syndecan-1 is a sponge for growth factors, with binding largely via heparan sulfate chains.

An exception is the prosecretory mitogen is_associated_with::lacritin that binds syndecan-1 only after heparanase modification. Binding utilizes an enzyme-regulated 'off-on' switch in which active epithelial is_associated_with::heparanase (HPSE) cleaves off heparan sulfate to expose a binding site in the N-terminal region of syndecan-1's core protein. Three SDC1 elements are required. (1) The heparanase-exposed hydrophobic sequence GAGAL that promotes the alpha helicity of lacritin's C-terminal amphipathic alpha helix form and likely binds to the hydrophobic face. (2) Heparanase-cleaved heparan sulfate that is 3-O sulfated. This likely interacts with the cationic face of lacritin's C-terminal amphipathic alpha helix. (3) An N-terminal is_associated_with::chondroitin sulfate chain that also likely binds to the cationic face. Point mutagenesis of lacritin has narrowed the ligation site. Altered syndecan-1 expression has been detected in several different tumor types. While several transcript variants may exist for this gene, the full-length natures of only two have been described to date. These two represent the major variants of this gene and encode the same protein.

Application
It is a useful marker for is_associated_with::plasma cells, but only if the cells tested are already known to be derived from blood.