Human Thrombospondin-4 Antibody

Thrombospondin-4 (THSP4) is a 140 kDa calcium-binding protein that interacts with other extracellular matrix molecules and modulates the activity of various cell types. THSP1 and THSP2 constitute subgroup A and form disulfide-linked homotrimers, whereas THSP3, THSP4, and THSP5/COMP constitute subgroup B and form pentamers (1, 2). The human THSP4 cDNA encodes a 961 amino acid (aa) precursor that includes a 26 aa signal sequence followed by an N-terminal heparin-binding domain, a coiled-coil motif, four EGF-like repeats, seven THSP type-3 repeats (one with an RGD motif), and a THSP C‑terminal domain (3). Human THSP4 shares 93% aa sequence identity with mouse and rat THSP4. Within the THSP type-3 repeats and the THSP C‑terminal domain, human THSP4 shares 79% aa sequence identity with THSP3 and COMP, and 58% aa sequence identity with THSP1 and THSP2. The coiled-coil motif mediates pentamer formation with COMP, either homotypically or heterotypically (3-6). THSP4 binds a variety of matrix proteins including collagens I, II, III, V, laminin-1, fibronectin, and matrilin-2 (4). Interactions of THSP4 with non-collagenous proteins are independent of divalent cations, while interactions with collagenous proteins are enhanced in the presence of zinc (4). THSP4 is expressed in heart, skeletal muscle, vascular smooth muscle, and vascular endothelial cells (7-9). It accumulates at neuromuscular junctions and synapse-rich regions and is upregulated in muscle by experimental denervation (8). THSP4 mediates the adhesion of motor and sensory neurons and promotes neurite outgrowth (8). A polymorphism of THSP4 (A387P) is associated with early coronary artery disease (10-12). Unlike wild type THSP4, the A387P variant does not support HUVEC attachment and spreading (9). Integrin alphaM/ beta2 enables activated neutrophil adhesion to both the variant A387P and wild type THSP4, although the A387P variant induces a greater release of pro-inflammatory molecules (13).