Modulation of cell growth and transformation by doxycycline-regulated FGF-2 expression in NIH-3T3 cells

The single-copy fibroblast growth factor 2 (FCF-2) gene encodes four coexpr essed isoforms of different molecular masses. The 18-kDa FGF-2 is primarily localized in the cytoplasm, whereas the higher molecular mass isoforms (HM W FGF-2) localize to the nucleus and nucleolus. The overexpression of eithe r 18-kDa FGF-2 or HMW FGF-2 promotes cell transformation in a dose-dependen t manner. In NIH 3T3 cells, the selective overexpression of HMW FCF-2 but n ot of 18-kDa FGF-2 confers upon the cells the unique phenotype of growth in low serum-containing medium. Thus, the distinct intracellular localization and the revel of expression of FCF-2 are pivotal requirements for the diff erential effects of FCF-2 isoforms on the cellular phenotype. On this basis , we established a doxycycline-regulatable FCF-2 expression system that per mitted us to regulate the expression of each isoform in a time- and dose-de pendent manner. We analyzed the growth properties of cells in the presence and absence of doxycycline in both normal and low serum-containing medium a nd in soft agar. The doxycycline-activated expression of 18-kDa FGF-2 did n ot allow growth in low serum medium. The growth of cells expressing HMW FGF -2 was increased by doxycycline under all three conditions, and a relations hip between the revel of HMW FGF-2 expression and cell growth was observed for all three conditions. This doxycycline-regulatable FGF-2 expression sys tem provides a mechanism to analyze changes in FCF-2 targeted pathways and genes and to characterize pathways specifically activated by either the 18- kDa FCF-2 or the HMW FGF-2 isoforms. (C) 1999 Wiley-Liss, inc.