[Molecular mechanism of androgen-dependent transformation--analysis using serum-free culture system]

SC-3 cells, derived from androgen-dependent mouse breast cancer Shionogi carcinoma 115, have shown not only androgen-dependent growth stimulation but also morphological changes in serum-free culture. We have demonstrated that this androgen-dependent growth is mediated through an induction of heparin-binding growth factor (termed as androgen-induced growth factor: AIGF). We studied the molecular mechanism of androgen-dependent growth. NIH3T3 cells transfected to express AIGF showed focus-forming activity, anchorage-independent growth and tumor formation in nude mice indicating AIGF is an oncogene. The findings that AIGF inhibited binding of [125I]basic fibroblast growth factor (bFGF) and only FGF receptor (FGFR)-1 mRNA expressed in SC-3 cells suggested that AIGF acts through FGFR-1. Therefore, we cloned FGFR-1 from cDNA library of SC-3 cells, which was found to have three mutations. When this variant FGFR-1 was expressed in FGFR-negative myoblast L6 cells, AIGF-dependent inhibition of the differentiation to myocytes was observed suggesting that variant FGFR-1 is receptor of AIGF. Since expressions of c-myc mRNA as well as AIGF mRNA were induced by testosterone treatment, we studied the role of c-myc in androgen-dependent growth in SC-3 cells using phosphorothioate derived antisense oligonucleotides (antisense) of c-myc or AIGF. Not only AIGF antisense but also c-myc antisense inhibited androgen-dependent growth. c-myc antisense did not affect androgen-induced AIGF mRNA expression. c-myc antisense inhibited AIGF-, but not bFGF-induced DNA synthesis. These results suggest that c-myc has a critical role of AIGF-, but not bFGF-induced growth.