SUPPRESSION OF AUTOCRINE CELL-PROLIFERATION AND TUMORIGENESIS OF HUMAN-MELANOMA CELLS AND FIBROBLAST GROWTH-FACTOR TRANSFORMED FIBROBLASTS BY A KINASE-DEFICIENT FGF RECEPTOR-1 - EVIDENCE FOR THE INVOLVEMENT OFSRC-FAMILY KINASES

Basic Fibroblast Growth Factor (bFGF/FGF2) is thought to play a decisi ve role in malignant progression. Aberrant expression of bFGF causes c onstitutive autocrine activation of its cognate receptor and autonomou s growth of human melanoma cells or bFGF transformed fibroblasts in cu lture, It remains to be determined, however, whether the endogenous bF GF confers growth advantage to tumors and what are the downstream targ ets of the activated FGF receptor critical for its transforming capaci ty, We therefore transfected metastatic melanoma cells and bFGF transf ormed mouse fibroblasts with a dominant-negative mutant of the murine FGF receptor 1 (fgfr1/flg), comprising the extracellular and transmemb rane domains but lacking the intracellular kinase domain (dnflg), Reve rse transcriptase-PCR, I-125-bFGF binding and affinity labeling analys es show that the truncated receptor is targeted to the membrane and is expressed at much higher levels than the endogenous receptor in all o f the selected clones, Expression of the dnflg dramatically reduces th e basal as well as bFGF induced growth of these cells in vitro and als o suppresses their tumorigenic potential in nude mice, The expression of the dnflg does not significantly alter the general level of tyrosyl -phosphorylated proteins in the transduced melanoma cells. Rather, a m ajor downstream affected target is a Src-family kinase, whose activity , determined by an in vitro immune kinase assay, is stimulated in norm al melanocytes by exogenous bFGF, and is markedly reduced in the dnflg -expressing melanoma cells, The present study demonstrates that direct interference with the activity of FGF receptors has a deleterious eff ect on cell proliferation and survival in vitro and in vivo leading to the suppression of melanoma tumor progression possibly through the in activation of a Src-family kinase.