COLON-CARCINOMA CELLS SWITCH THEIR RESPONSE TO TRANSFORMING GROWTH-FACTOR BETA(1) WITH TUMOR PROGRESSION

Transforming growth factor beta(1) (TGF-beta(1)) switches from an inhi bitor of tumor cell growth to a stimulator of growth and invasion duri ng human colon carcinoma progression. We originally observed that meta static colon carcinoma cells in primary culture responded to TGF-beta( 1) by proliferation, whereas moderate to well-differentiated primary s ite colon carcinomas were growth inhibited by TCF-beta(1) (P. Schroy e t al., Cancer Res., 50: 261-265, 1990). We then cloned several colon c arcinoma cell lines which modeled these responses to TCF-beta(1), and expressed TCF-beta(1) (M. M. Hafez et al., Cell Growth and Differ., 1: 617-626, 1990; 3: 753-762, 1992). Two of these colon carcinoma cell l ines, U9 and HD3, which activate approximately equal amounts of TCF-be ta(1), and express equal amounts of TGF-beta receptors, are now used t o compare the effects of TGF-beta(1) in modulating invasive behavior. The U9 cell line exhibits autocrine-positive growth regulation in vitr o by TCF-beta(1), whereas the HD3 cell line shows the opposite respons e, autocrine-negative regulation. Blocking endogenous TGF-beta(1) with isotype-specific antibody inhibited U9 cell growth because autocrine TGF-beta(1) acts as a mitogen for U9 cells. In contrast, antibody to T GF-beta(1) stimulated HD3 cell proliferation because autocrine TGF-bet a(1) inhibits growth of these cells. U9 cells were 13-fold more invasi ve in vitro through a collagen I layer than HD3 cells. In vitro invasi on by U9 cells but not by HD3 cells was stimulated 2-fold by TCF-beta( 1), and U9 invasion was inhibited by antibody to TCF-beta(1). When inj ected into athymic mice, U9 cells induced tumors 6-fold the size of th ose induced by HD3 cells. Tumors induced by each cell line retained ex pression of TCF-beta(1), in vivo, as shown by immunohistochemistry usi ng isotype-specific antibody. Antibody to TCF-beta(1) inhibited the gr owth of U9 cells in athymic mice 4-fold compared to control antibody, demonstrating that autocrine TCF-beta(1) stimulated U9 cell growth in vivo. Thus, the U9 cells with autocrine-positive growth regulation by TGF-beta(1) were more tumorigenic in vivo and more invasive in vitro t han HD3 cells with autocrine-negative regulation by TCF-beta(1). Diffe rences in the induction of three immediate early genes were observed b etween TGF-beta(1) growth-stimulated U9 cells and TGF-beta(1) growth-i nhibited HD3 cells. Thirty min of TCF-beta(1) treatment stimulated exp ression of c-fos approximately 50-fold in TGF-beta(1) growth-inhibited HD3 cells, whereas only a 2-fold induction was observed in U9 cells. A small increase (50%) in expression of c-jun was seen with TGF-beta(1 ) treatment in HD3 cells, whereas expression of c-jun was inhibited in U9. In contrast, c-myc was inhibited 3-5-fold by exogenous TCF-beta(1 ) in both HD3 and U9 cells, suggesting a common role for c-myc in both responses to TCF-beta(1).