FIBROBLAST GROWTH-FACTOR-I INDUCTION OF DELAYED-EARLY MESSENGER-RNA EXPRESSION IN NIH 3T3 CELLS IS PROLONGED BY HEPARIN ADDITION

Fibroblast growth factor (FGF)-1, also known as acidic FGF, is a multi functional heparin-binding protein that is mitogenic for a wide variet y of cell types cultured in vitro and a potent angiogenic agent in viv o. These cellular responses are mediated via high-affinity binding to a family of four membrane-spanning tyrosine kinase receptors. FGF-1-st imulated mitogenesis is potentiated by heparin, a sulfated glycosamino glycan. In this study, we examined the effect of exogenous heparin on FGF-l-inducible gene expression in murine NIH 3T3 cells using both wil d-type FGF-I and FGF-1/glu132, an FC;F-I mutant with a reduced apparen t affinity for heparin. The induction levels and temporal expression k inetics of two immediate-early response mRNAs (early growth response g ene-1, thrombospondin-l) as well as two delayed-early response mRNAs ( proliferin, ornithine decarboxylase) were monitored by Northern blot h ybridization analysis. We found that although FGF-1 alone can promote the initial induction of these four mRNAs, heparin coaddition is neces sary for prolonged delayed-early mRNA expression. This heparin effect occurs when cells are stimulated with wild-type FGF-1 but not with FGF -1/glu132. Furthermore, FGF-1 and heparin must be added together at th e initial time of mitogen stimulation and they must remain present in the cell culture medium for a minimum period of 8 h to promote sustain ed delayed early mRNA expression. These findings are consistent with t he proposal that heparin promotes a long-term FGF-1:FGFR interaction w hich is required for sustained delayed-early gene expression and a ful l mitogenic response. (C) 1997 Academic Press.