Interleukin-1-induced suppression of type II collagen gene transcription involves DNA regulatory elements

Interleukin-1 is a proinflammatory polypeptide that influences cartilage macromolecular degradation and synthesis. Since previous studies have suggested that interleukin-1 may inhibit type II collagen synthesis, we have studied the mechanism of inhibition of type II collagen synthesis by interleukin-1. When rabbit articular chondrocytes were treated with purified recombinant interleukin-1 beta or macrophage-conditioned medium, the synthesis and assembly of type II collagen into the extracellular matrix were greatly reduced. The inhibition was concentration-dependent and occurred within 10 h of treatment with interleukin-1, with greater inhibition occurring at 30 h. The reduced level of collagen synthesis correlated with a reduction in the steady-state mRNA levels coding for type II collagen, as measured by a Northern blot analysis. This further correlated with a reduction in the transcription of type II collagen gene, as determined by nuclear run-on experiments. Finally, transfection studies using plasmid constructs containing DNA regulatory sequences from the type II gene, coupled to a reporter gene (CAT), revealed that in comparison to control chondrocytes, interleukin-1 treated cells showed a reduced level of CAT activity. These studies demonstrate that the inhibition of collagen type II synthesis by interleukin-1 is due to a reduction in the transcription of the type II collagen gene and that the reduction in gene transcription involves DNA regulatory sequences that determine type II collagen gene expression.