Syndecan 4 (SDC4)

Syndecan-4 is a transmembrane (type I) heparan sulfate proteoglycan that functions as a receptor in intracellular signaling. The protein is found as a homodimer and is a member of the syndecan proteoglycan family. Syndecan4 is upregulated in osteoarthritis and inhibition of syndecan 4 reduces cartilage destruction in mouse models of OA.

Syndecans, including SDC4, can function as in trans HIV receptors via binding of HIV-1 gp120 to the syndecan heparan sulfate chains. Flow cytometric analysis demonstrated SDC expression on endothelial cells. HIV bound to SDC on endothelial cell lines maintained its infectivity for at least 1 week, compared with less than 1 day for unbound virus.