Complex Regulation of Transforming Growth Factor β1, β2, and β3 mRNA Expression in Mouse Fibroblasts and Keratinocytes by Transforming Growth Factors β1 and β2

Abstract

Regulation of transforming growth factor β1 (TGFβ1), TGFP2, and TGFβ3 mRNAs in murine fibroblasts and keratinocytes by ΤGΕβ1 and ΤGΕβ2 was studied. In quiescent AKR-2B fibroblasts, in which ΤGΕβ induces delayed stimulation of DNA synthesis, TGFβ1 autoregulation of TGFβ1 expression was observed as early as 1 h, with maximal induction (25-fold) after 6 to 12 h. Increased expression of ΤGΕβ1 mRNA was accompanied by increased TGFβ protein production into conditioned medium of AKR-2B cells. Neither TGFβ2 nor TGFβ3 mRNA, however, was significantly induced, but both were apparently down regulated at later times by TGFβ1. Protein synthesis was not required for autoinduction of TGFβ1 mRNA in AKR-2B cells. Nuclear run-on analyses and dactinomycin experiments indicated that autoregulation of TGFβ1 expression is complex, involving both increased transcription and message stabilization. In contrast to ΊGΡβ1, TGFβ2 treatment of quiescent AKR-2B cells increased expression of ΤGFβ1, ΤGFβ2, and ΤGFβ3 mRNAs, but with different kinetics. Autoinduction of TGFβ2 mRNA occurred rapidly with maximal induction at 1 to 3 h, enhanced ΤGFβ3 mRNA levels were observed after 3 h, and increased expression of ΤGΡβ1 occurred later, with maximal mRNA levels obtained after 12 to 24 h. Nuclear run-on analyses indicated that ΤGFβ2 regulation of ΤGFβ2 and TGFβ3 mRNA levels is transcriptional, while TGFβ2 induction of TGFβ1 expression most likely involves both transcriptional and posttranscriptional controls. In BALB/MK mouse keratinocytes, minimal autoinduction of TGFβ1 occurred at only the 12- and 24-h time points and protein synthesis was required for this autoinduction. The results of this study provide an example in which ΤGFβ1 and ΤGFβ2 elicit different responses and demonstrate that expressions of ΤGFβ1, TGFβ2, and TGFβ3 are regulated differently. The physiological relevance of TGFβ1 autoinduction in the context of wound healing is discussed.