INTERLEUKIN-1-ALPHA AND PHORBOL ESTER INHIBIT COLLAGEN-SYNTHESIS IN OSTEOBLASTIC MC3T3-E1 CELLS BY A TRANSCRIPTIONAL MECHANISM

The effects of recombinant human interleukin-1α(IL-1) on procollagen gene expression were examined in the clonal mouse osteoblastic cell line MC3T3-E1. Cells were grown in Dulbecco’s Modified Eagle’s Medium containing 10% fetal calf serum and 50 µg ml ascorbic acid. Collagen synthesis was assessed as [3H]proline incorporation into collagenase-digestible protein (CDP). Procollagen mRNA levels were determined by Northern blot analysis using a 32P-labeled α1(I) cDNA. Transcription rates were determined by nuclear run-off assay. IL-1 at 1-1000 pg/ml caused a concentration-dependent inhibition of CDP, which was maximally reduced by 75-80%, and a parallel reduction of procollagen α1(I)mRNA levels. The effects of IL-1 were mimicked by the tumor promoter phorbol 12-myristate 13-acetate (PMA) at 1-100 nM, which inhibited CDP and reduced procollagen α1(I) mRNA levels to a similar extent. The effects of IL-1 and PMA were independent of prostaglandin production, since indomethacin did not alter the inhibitory effect of either agent on CDP. Neither IL-1 (up to 10 ng/ml) nor PMA (100 nM) affected adenylate cyclase activity, while forskolin (10 µm), PTH (10 nM) and prostaglandin E2(1 µm) stimulated adenylate cyclase activity 3- to 5-fold. However, forskolin (10 µm) and (Bu)2cAMP (100 μm) failed to alter CDP or procollagen α1(I) mRNA levels. IL-1 (1 ng/ml) and PMA (100 nM) reduced transcription of the α1(l) procollagen gene by 70% and 80%, respectively, while α2(I) transcription was decreased by 59% and 53%. Neither IL-1 nor PMA affected transcription of the β-actin or β-tubulin genes. In conclusion, IL-1 inhibits collagen synthesis in MC3T3-E1 cells by a transcriptional mechanism which appears to be independent of cAMP. Since PMA mimics the effects of IL-1 on collagen gene expression, protein kinase-C may mediate these actions of IL-1. © 1990 by The Endocrine Society.