|beta IG‑H3 in Mouse Embryo. beta IG‑H3 was detected in immersion fixed frozen sections of mouse embryo (13 d.p.c.) using Sheep Anti-Mouse beta IG‑H3 Antigen Affinity-purified Polyclonal Antibody (Catalog # AF2559) at 5 µg/mL overnight at 4 °C. Tissue was stained using the Anti-Goat HRP-DAB Cell & Tissue Staining Kit (brown; Catalog # CTS008) and counterstained with hematoxylin (blue). Specific staining was localized to developing duodenum. View our protocol for Chromogenic IHC Staining of Frozen Tissue Sections.|
Beta IG-H3, also known as TGFBI and RGD-CAP, is a matricellular adaptor protein that is induced in most cell types in response to TGF-beta stimulation (1‑4). The mouse beta IG-H3 cDNA encodes a 683 amino acid (aa) precursor that includes a 23 aa signal sequence, one EMI domain, four FAS1 domains, and one RGD motif (2). Mouse beta IG-H3 shares 91% aa sequence identity with human and porcine beta IG-H3. beta IG-H3 is expressed as a 75 kDa protein with no post-translational additions (5). Following secretion, cleavages at multiple positions near the C-terminal end liberate peptides with pro-apoptotic activity (5, 6). Peptides that encompass the RGD motif contribute to the pro-apoptotic effects of TGF-beta (6). FAS1 domains contain YH motifs that are characterized by conserved Tyr and His residues (7). The YH motifs in each of the FAS1 domains enable beta IG-H3 to bind to matrix fibronectin, collagen I, collagen VI, biglycan, and decorin (3, 8‑11), in addition to cell expressed integrins alpha V/ beta 3, alpha V beta 5, and alpha 3 beta 1 (7, 8, 12, 13). The expression of beta IG-H3 is modulated at particular developmental stages in some cell types. It is upregulated in keratinocytes and immature dendritic cells but downregulated in osteoblasts (8, 12, 14). It promotes keratinocyte differentiation but blocks osteoblast differentiation (8, 12). beta IG-H3 stimulates macrophage endocytosis and vascular endothelial cell proliferation and migration (13, 14). High glucose levels induce beta IG-H3 in renal proximal tubule cells which is predictive of diabetic nephropathy (3). Several point mutations (clustered in the fourth FAS1 domain) of beta IG-H3 are linked to different corneal dystrophies (15). beta IG-H3 is downregulated in many cancers (4, 16) and functions as a suppressor of tumorigenicity when overexpressed (2, 4, 16).