Extracellular matrix 22-kDa protein interacts with decorin core protein and is expressed in cutaneous fibrosis

A protein with an Mr of 22,000 was purified from bovine dermis. The amino acid sequence of the protein was identical to 22-kDa protein [Neame, P.J. et al. (1989) J. Biol. Chem. 264, 5474-5479] and showed highly homologous sequences to TRAMP (tyrosine rich acidic matrix protein) [Cronshaw, A.D. et al. (1993) Matrix 13, 255-266] and dermatopontin [Superti-Furga, A. et al. (1993) Genomics 17, 463-467]. The protein was proved to associate with decorin and a modified decorin with carboxymethylated cysteinyl residues, but not to assemble to hyaluronate or dermatan sulfate chains. The pyridylethylation of cysteinyl residues in the 22-kDa protein did not affect its binding activity to decorin or modified decorin. Immunohistochemical analyses revealed positive stains in endothelial cells and the periphery of collagen fibers in normal dermis but not in the fibroblasts in tissue. Collagen fibers in sclerotic regions of progressive systemic sclerosis were stained diffusely, suggesting that the 22-kDa protein increases in parallel to the accumulation of collagen in the disease. Western blotting analyses of extracts of cultured endothelial cells revealed a lower Mr protein than that from cultured fibroblasts, suggesting the presence of a molecule related to the 22-kDa protein.