REGULATION OF SCATTER FACTOR PRODUCTION VIA A SOLUBLE INDUCING FACTOR

Scatter factor (SF) (also known as hepatocyte growth factor [HGF]) is a fibroblast-derived cytokine that stimulates motility, proliferation, and morphogenesis of epithelia. SF may play major roles in developmen t, repair, and carcinogenesis. However, the physiologic signals that r egulate its production are not well delineated. We found that various human tumor cell lines that do not produce SF secrete factors that sti mulate SF production by fibroblasts, suggesting a paracrine mechanism for regulation of SF production. Conditioned medium from these cell li nes contained two distinct scatter factor-inducing factor SF-IF activi ties: a high molecular weight (>30 kD), heat sensitive activity and a low molecular weight (<30 kD) heat stable activity. Further studies re vealed that SF-producing fibroblasts also secrete factors that stimula te their own SF production. We characterized the <30-kD SF-IF activity from ras-3T3 (clone D4), a mouse cell line that overproduces both SF and SF-IE The <30-kD filtrate from ras-3T3 conditioned medium induced four- to sixfold increases in expression of SF biologic activity, immu noreactive protein, and mRNA by multiple SF-producing fibroblast lines . Ras-3T3 SF-IF activity was stable to boiling, extremes of pH, and re ductive alkylation, but was destroyed by proteases. We purified ras-3T 3 SF-IF about 10,000-fold from serum-free conditioned medium by a comb ination of ultrafiltration, cation exchange chromatography, and revers e phase chromatography. The purified protein exhibited electrophoretic mobility of about 12 kD (reduced) and 14 kD (nonreduced) by SDS-PAGE. The identity of the protein was verified by elution of biologic activ ity from gel slices. Purified SEIF stimulated SF production in a physi ologic concentration range (about 20-400 pM). Its properties and activ ities were distinct from those of IL-1 and TNF, two known inducers of SF production. We suggest that SF-IF is a physiologic regulator of SF production.