Transrepression of type II collagen by TGF‐β and FGF is protein kinase C dependent and is mediated through regulatory sequences in the promoter and first intron

Abstract

Transforming growth factor beta and basic fibroblast growth factor are multipotential factors found in bone and cartilage that may be involved in both the proliferation and differentiation of chondrocytes. It was previously reported that TGF-β plus FGF caused a modulation of chondrocyte phenotype that included the downregulation of steady-state level of the collagen II transcript. In this report, the results of nuclear run-off data indicate that repression of transcript initiation from the collagen II gene is the primary mechanism involved in the growth factor induced inhibition. Transient transfection assays with CAT expression vectors containing portions of the collagen II gene show that the TGF-β/FGF induced transrepression requires a region in the first intron previously reported to have transcriptional enhancer activity and to bind chondrocyte nuclear proteins. In addition, silencer elements in the promoter also appear to play a role. Protein data as well as transient transfection experiments indicate that the activation of protein kinase C is necessary for the growth factor–induced down-regulation of collagen II expression. These studies suggest that a cascade initiating with PKC activation is responsible for modifying transcription 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 diseases such as osteoarthritis.