REGULATION OF MULTIPLE BASIC FIBROBLAST GROWTH-FACTOR MESSENGER RIBONUCLEIC-ACID TRANSCRIPTS BY PROTEIN KINASE-C ACTIVATORS

The human astrocytoma cell line U87-MG expressed two major basic fibroblast growth factor (FGF) mRNA transcripts of 7.0 and 3.7 kilobase (kb), as well as several low abundance transcripts of lower mol wt (1.0-1.8 kb). The phorbol ester phorbol-12, 13-dibutyrate caused a time- and dose-dependent increase in the abundance of basic FGF mRNA transcripts. At a concentration of 1 .mu.M, phorbol ester increased the level of both the 7.0 and 3.7 kb transcripts within 4 h, reached a plateau at 1.5- to 2.5-fold above control levels by 6 h and remained elevated for at least 12 h. When measured at 6 h after drug addition, the abundance of both 7.0 and 3.7 kb transcripts was maximally stimulated by 100 nM phorbol ester (EC50 = 10-20 nM). FGF mRNA levels were also stimulated to a similar extent by platelet-derived growth factor (0.15-5 U/ml) or the synthetic diacycglycerol analog 1-oleoyl-2-acetyl-rac glycerol (1-300 nM) at doses which stimulated DNA synthesis in these cells. Neither (Bu)2 cAMP (0.03-2 mM) nor A23187 (0.3-1000 nM) had any effect on FGF expression. When U87-MG cells were exposed to phorbol ester for 24 h several differences were observed: the dose response curve was shifted to the left (EC50 = 3-5 nM; maximum response at 10 nM phorbol ester) and the response of the 7.0 and 3.7 kb transcripts was attenuated at higher doses (100-1000 nM), perhaps reflecting down-regulation of protein kinase C by the phorbol ester. In addition, prolonged exposure to phorbol ester stimulated (2.8- to 3-fold) the expression of two low mol wt transcripts of approximately 1.5 and 1.8 kb in size. These data demonstrate that FGF mRNA expression is regulated by protein kinase C and provide evidence that multiple FGF mRNAs (perhaps resulting from alternative splicing) are capable of being transcribed under different conditions.