Transformation of human breast epithelial cells by 7, 12, dimethylbenz(a)anthracene, but not by N-methyl-N-nitrosourea, is accompanied by up-regulation of basic fibroblast growth factor

Normal human breast epithelial cells (HBL100) are immortalized by endogenous SV40 genome and are not tumorigenic in nude mice if injected in the first 50 passages in culture. This cell line also depends on the expression of basic fibroblast growth factor (bFGF) for its viability in culture. The present study was designed to transform these cells with chemical carcinogens to establish malignant HBL100 cell lines in order to evaluate the eventual modulation in the expression of bFGF. In the first experiment, HBL100 cells were treated with 2 mu g/ml of 7, 12, dimethylbenz(a)anthracene (DMBA) for two 24 h periods. In a second experiment, HBL100 cells were transformed by exposing them to 20 mu g/ml of N-methyl-N-nitrosourea (MNU) twice a day for two days. Unlike the HBL100 parental cell line, the two newly derived cell lines (named respectively HBLTDMBA and HBLTMNU) were tumorigenic when injected in nude mice. The expression of bFGF, as measured by immunocytochemistry and Western blot analysis, was higher in the DMBA-transformed cell line than in the parental HBL100 and MNU-transformed lines. These results differentiate between transformation selectivity by two different carcinogens. The direct-acting carcinogen MNU, which induces point mutation, does not require enhanced expression of bFGF, whereas bFGF may be necessary for early events leading towards transformation by carcinogens requiring metabolism for their action, such as DMBA.