Molecular cloning of human chondromodulin-I, a cartilage-derived growth modulating factor, and its expression in Chinese hamster ovary cells

Bovine chondromodulin-I (ChM-I) purified from fetal cartilage stimulated th e matrix synthesis of chondrocytes, and inhibited the growth of vascular en dothelial cells in vitro. The human counterpart of this bovine growth regul ating factor has not been identified. We report here the cloning of human C hM-I precursor cDNA and its functional expression in Chinese hamster ovary (CHO) cells. We first identified a genomic DNA fragment which encoded the N -terminus of the ChM-I precursor, and then isolated human ChM-I cDNA from c hondrosarcoma tissue by PCR. The deduced amino acid sequence revealed that mature human ChM-I consists of 120 amino acids. In total, 16 amino acid res idues were substituted in the human sequence, compared to the bovine counte rpart. Almost of all the substitutions were found in the N-terminal hydroph ilic domain. In the C-terminal hydrophobic domain (from Phe42 to Val120), t he amino acid sequence was identical except for Tyr90, indicating a functio nal significance of the domain. Northern blotting and in situ hybridization indicated a specific expression of ChM-I mRNA in cartilage. We also succes sfully determined the cartilage-specific localization of ChM-I protein, usi ng a specific antibody against recombinant human ChM-I. Multiple transfecti on of the precursor cDNA into CHO cells enabled us to isolate the mature fo rm of human ChM-I from the culture supernatant. Purified recombinant human ChM-I stimulated proteoglycan synthesis in cultured chondrocytes. In contra st, it inhibited the tube morphogenesis of cultured vascular endothelial ce lls in vitro and angiogenesis in chick chorioallantoic membrane in vivo.