Transforming growth factor beta increases mRNA for matrix proteins both in the presence and in the absence of changes in mRNA stability.

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Abstract
Transforming growth factor-.beta. (TGF-.beta.) has been shown to stimulate synthesis of extracellular matrix proteins, both in animals and in cell culture. We found that mRNAs for .alpha.1(I) collagen, fibronectin, and thrombospondin were markedly increased in TGF-.beta.-treated 3T3 (mouse) cells. For collagen and fibronectin this increase was 10- to 20-fold, as measured by quantitative blot hybridization analysis. A maximal value was reached at 16-24 hr, with a subsequent gradual decline. Concomitant treatment with cycloheximide prevented the stimulation observed with TGF-.beta.. Under conditions of confluent growth a clear increase in .alpha.1(I) collagen mRNA stability was observed, whereas in subconfluent cells no change in mRNA half-life was found, despite an equally large increase in mRNA levels. We suggest that the mode of action of TGF-.beta. varies with the target cell and depends on the interplay of a number of complex cellular factors.