Coordinate regulation of type IX and type II collagen synthesis during growth of chick chondrocytes in retinoic acid or 5-bromo-2'-deoxyuridine.

Chondrocytes isolated from 15-day-old embryonic chick sterna were cultured as monolayers for 7 days in control medium or in medium supplemented with retinoic acid or 5-bromo-2'-deoxyuridine. Control cells exhibited characteristic polygonal morphology and maintained the synthesis of cartilage-specific collagens, i.e. type II, type IX, 1 alpha, 2 alpha, and 3 alpha chains, and 45 K (presumptive type X). Type IX was the second most prevalent collagen and represented 12-15% of the phenotype. When exposed to retinoic acid, chrondrocytes displayed a fibroblast-like morphology and decreased collagen synthesis by day 2. The synthesis of collagen types II and IX declined in parallel along with that of the other cartilage collagens and ceased by day 7. During the same period, the synthesis of collagen types I, III, and V and two unidentified collagen chains was initiated and stimulated. Similar changes in collagen expression were caused by 5-bromo-2'-deoxyuridine but were delayed, beginning after day 4. Type III collagen, however, was never detected in 5-bromo-2'-deoxyuridine or control cultures. Because two different agents and two rates of modulation produced parallel changes in the synthesis of collagen types II and IX, these collagens appear to be coordinately regulated.