Thrombospondin gene expression is associated with mitogenesis in 3T3 cells: Induction by basic fibroblast growth factor

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Abstract
Growth factor-depleted Swiss 3T3 cells responded to basic fibroblast growth factor (bFGF) with a burst of mitogenesis and with a rapid and marked increase in thrombospondin (TS) mRNA levels. mRNA levels for the α1 chain of type I collagen and for fibronectin were unaffected. At early times following stimulation (0–2 h), “superinduction” of TS mRNA by inhibition of protein synthesis with cycloheximide was not observed and the increase in TS mRNA could be attributed primarily to an increase in transcription rate of the TS gene. However, at later times (4–8 h) the combination of cycloheximide and bFGF superinduced TS mRNA levels, suggesting the existence of a labile inhibitor of transcription or a short-lived RNase that might be produced in response to prolonged treatment with bFGF. In contrast to its stimulatory effect on 3T3 cells, bFGF did not stimulate the proliferation of mouse muscle BC3H1 cells nor did it cause an increase in TS mRNA levels, but BC3H1 cells do respond to bFGF by inhibition of myogenic differentiation. We propose, on the basis of these and other findings, that TS facilitates the progression of some anchorage-dependent cells through the cell cycle.