Transforming growth factor-beta up-regulates elastin gene expression in human skin fibroblasts. Evidence for post-transcriptional modulation.

Transforming growth factor-beta s (TGF-beta) are potent enhancers of the expression of several connective tissue genes. In this study we examined the effects of TGF-beta 1 and TGF-beta 2 on human elastin mRNA abundance, promoter activity, and mRNA stability in cultured human skin fibroblasts. Treatment of cell cultures with varying concentrations of TGF-beta 1 or TGF-beta 2 for 24 hours resulted in a dose-dependent increase in the elastin mRNA steady-state levels, with a maximum enhancement of approximately 30-fold being noted with 1 ng/ml. Addition of cycloheximide (10 micrograms/ml) failed to block up-regulation of elastin gene expression by TGF-beta, indicating that this effect can occur in the absence of active protein synthesis. Furthermore, TGF-beta elicited enhancement of elastin mRNA levels could be abrogated by tumor necrosis factor-alpha and partially counteracted by interferon-gamma. Transient transfections of human skin fibroblasts with elastin promoter/chloramphenicol acetyl-transferase reporter gene constructs, which contained up to approximately 5 kb of the 5' flanking DNA, revealed no change in the promoter activity in the presence of TGF-beta. However, TGF-beta appeared to stabilize the elastin mRNA transcripts as determined by Northern hybridizations after inhibition of initiation of the transcription. As a result of this stabilization, the elastin mRNA levels were clearly detectable in TGF-beta 1-treated cultures even up to 48 hours after inhibition of transcription while they were undetectable in the control cells after 24 hours of incubation. These results demonstrate that TGF-beta 1 and TGF-beta 2 are potent enhancers of elastin gene expression and that this effect is mediated, at least in part, post-transcriptionally. These results suggest that TGF-beta s are involved in regulation of elastin deposition during fetal development and tissue repair, as well as in pathological conditions.