Phorbol ester-induced inhibition of collagen accumulation by human lung fibroblasts.

The effect of phorbol 12-myristate 13-acetate (PMA) on collagen accumulation by human embryonic lung fibroblasts was determined. PMA (10 nM) dramatically inhibited collagen formation in cultures that were unstimulated or stimulated with transforming growth factor-beta (TGF-beta). Collagen accumulation was decreased by 50% in unstimulated cultures and by 80% in TGF-beta-treated cultures. This inhibition was associated with a marked decrease in steady-state levels for alpha 1(I) collagen mRNA and decreases in alpha 1(I) gene transcription as determined by nuclear run-off assays. The PMA-mediated decrease in alpha 1(I) collagen mRNA was not affected by the addition of cycloheximide or indomethacin. Prolonged treatment with PMA (100 nM) resulted in down-regulation of protein kinase C (PKC) activity to less than 3% of untreated cultures. When PKC activity was down-regulated, treatment with PMA did not block TGF-beta-stimulated collagen formation, and prostaglandin E2-induced inhibition of protein formation was still evident. These results suggests that PKC activity modulates the level of transcription of collagen genes and collagen accumulation in lung fibroblast cultures.