A potential regulatory linkage between the biosynthesis of colligin, a collagen-binding protein of the ER, and procollagen I was examined under a variety of experimental conditions. Cell lines which did not produce a significant amount of procollagen I mRNA also lacked the capacity to produce colligin mRNA. Anchorage-dependent cell lines like L6 myoblasts and normal rat kidney fibroblasts produced both colligin and procollagen I mRNA, but the level of both was concurrently reduced considerably in their ras-transformed counterparts. Similarly, during the differentiation of L6 myoblasts, levels of both colligin and procollagen declined together. Treatment of myoblasts by dexamethasone or EGF led to a decrease in the steady-state levels of procollagen I mRNA, and this was, again, accompanied by a decrease in colligin mRNA synthesis. On the other hand, when the rate of procollagen I synthesis was stimulated by treatment of myoblasts with TGFbeta, it led to the concurrent augmentation of both the mRNA and protein levels of colligin. A linkage between the regulation of synthesis of procollagen I and colligin thus seems to exist. The only exception to this generalization is provided by the heat induction behavior of the two proteins. Treatment of myoblasts for a very short period leads to an increase in the synthesis of both the mRNA and protein levels of colligin. This, however, is not accompanied by a change in the mRNA levels of procollagen I. These studies establish that colligin and procollagen are generally tightly co-regulated except after heat shock, suggesting an important functional linkage.
