TRANSREPRESSION OF TYPE-II COLLAGEN BY TGF-BETA AND FGF IS PROTEIN-KINASE-C DEPENDENT AND IS MEDIATED THROUGH REGULATORY SEQUENCES IN THE PROMOTER AND 1ST INTRON

Transforming growth factor beta and basic fibroblast growth factor are multipotential factors found in bone and cartilage that may be involv ed in both the proliferation and differentiation of chondrocytes. It w as previously reported that TGF-beta plus FGF caused a modulation of c hondrocyte phenotype that included the down-regulation of steady-state level of the collagen II transcript. In this report, the results of n uclear run-off data indicate that repression of transcript initiation from the collagen II gene is the primary mechanism involved in the gro wth factor induced inhibition. Transient transfection assays with CAT expression vectors containing portions of the collagen II gene show th at the TGF-beta/FGF induced transrepression requires a region in the f irst intron previously reported to have transcriptional enhancer activ ity and to bind chondrocyte nuclear proteins. In addition, silencer el ements in the promoter also appear to play a role. Protein data as wel l as transient transfection experiments indicate that the activation o f protein kinase C is necessary for the growth factor-induced down-reg ulation of collagen II expression. These studies suggest that a cascad e initiating with PKC activation is responsible for modifying transcri ption factors that interact with regulatory sequences in the collagen II gene. A detailed understanding of the factors involved in cartilage -specific gene regulation in chondrocytes would facilitate development of therapeutic protocols for the repair of degenerated cartilage in d iseases such as osteoarthritis. (C) 1994 Wiley-Liss, Inc.