Basal and inducible expression of metallothionein and heat shock protein 70 genes in bovine articular chondrocytes

Abstract

Human metallothionein (MT) and heat shock protein 70 (hsp70) cRNA probes cross-hybridized with the respective bovine mRNAs under high-stringency conditions, suggesting DNA sequence conservation of the two genes. Released primary bovine articular chondrocytes expressed MT and hsp70 mRNAs constitutively at variable levels, suggesting a possible physiological role of these proteins in cartilage. In first-passage chondrocytes both CdCl2 and ZnCl2 induced MT and hsp70 mRNAs. However, CdCl2 and ZnCl2 were better inducers of hsp70 and MT mRNAs relative to CuCl2. Serum, interleukin-1, and dexamethasone also induced MT but not hsp70 mRNAs. Actinomycin D severely reduced the basal and metal-induced expression of MT and hsp70 mRNAs, suggesting transcriptional control. Inclusion of cycloheximide, an inhibitor of protein synthesis, along with the metal inducers did not influence hsp70 induction but resulted in superinduction of MT mRNA, possibly due to the post-transcriptional stabilization of polysomes. MT and hsp70 induction by metals is therefore independent of de novo protein synthesis. These results demonstrate the potential of articular chondrocytes to express mRNAs for the two stress proteins in response to various physiologically relevant agents by transcriptional and post-transcriptional mechanisms. MTs and hsp70 are likely to have important functions in cartilage metabolism under normal and pathological conditions.