DIFFERENTIAL MODULATION OF CELL PHENOTYPE BY DIFFERENT MOLECULAR-WEIGHT FORMS OF BASIC FIBROBLAST GROWTH-FACTOR - POSSIBLE INTRACELLULAR SIGNALING BY THE HIGH-MOLECULAR-WEIGHT FORMS

To study possible functional differences of the 18-kD and high molecul ar weight forms of basic fibroblast growth factor (bFGF), we have exam ined the effect of endogenous production of different bFGF forms on th e phenotype of NIH 3T3 cells. Cells transfected with cDNAs coding for either 18-kD bFGF (18-kD bFGF) or all four molecular forms (18, 22, 22 .5, 24 kD; wild type [WT] bFGF) exhibit increased migration and decrea sed FGF receptor number compared to parental cells. However, migration and FGF receptor number of cells transfected with a cDNA coding only for high molecular weight bFGF (22, 22.5, and 24 kD; HMW bFGF) were si milar to that of parental cells transfected with vector alone. Cells e xpressing HMW, 18 kD, or WT bFGF grew to high saturation densities in 10% serum. However, only cells expressing HMW or WT bFGF grew in low s erum. Cell surface or metabolic labeling of the different cell types f ollowed by immunoprecipitation with anti-bFGF antibody showed primaril y cell surface-associated 18-kD bFGE In addition, when cells expressin g exclusively HMW bFGF were transfected with a cDNA coding for 18-kD b FGF, migration was increased, bFGF receptors were down-regulated, and 18-kD bFGF was found on the cell surface. Cells expressing 18-kD bFGF transfected with a cDNA encoding FGF receptor-2 lacking the COOH-termi nal domain (dominant negative bFGF receptor) exhibited a flat morpholo gy and decreases in migration and saturation density. Cells expressing HMW bFGF transfected with the dominant negative bFGF receptor continu ed to grow to a high saturation density, proliferated in low serum, an d exhibited no morphological changes. These results indicate that incr eased cell migration and FGF receptor down-regulation are mediated by the extracellular interaction of 18-kD bFGF with its cell surface rece ptor. Growth in low serum may be stimulated by the intracellular actio n of HMW bFGF through mechanisms independent of the presence of a cell surface receptor. Thus, the different molecular forms of bFGF may act through distinct but convergent pathways.