Expression of cellular oncogenes in teratoma-derived cell lines

The expression of ten proto-oncogenes was studied in cell lines derived from transplantable mouse teratomas. The cell lines represent different forms of early embryonic cell specialization. The analysis included two embryonal carcinoma (EC) lines (PCC3 and F9), and four differentiated cell lines derived from teratocarcinoma, namely trophoblastoma (3-TDM), parietal endoderm (PYS-2), visceral endoderm (PSA5-E) and skeletal myoblasts (Cl10). The expression of c-oncogenes was studied by analysing poly(A)+RNA for complementary sequences by dot blot and Northern blot hybridization. The results were related to the rate of cell multiplication and the state of differentiation by examining [3H]thymidine incorporation, growth curves and tissue-specific differentiation markers. Expression of c-myc and c-Ki-ras was found in all cell lines. In dot blot assays, poly(A)+RNA from all cell lines also hybridized with v-abl and v-sis probes. A marked decrease in c-myc expression was found in teratoma-derived myoblasts differentiating into myotubes. A similar reduction was found when 'nullipotent' F9 cells were induced by retinoic acid (RA) to form primitive endoderm. However, reduction of the growth rates of the parietal and visceral endodermal cell lines were not accompanied by decreased expression of c-myc or c-Ki-ras. Hybridization signals obtained with a v-sis probe was low in all teratoma-derived cell lines tested, except for the myogenic cell line Cl10. Both in exponentially growing and differentiated cultures of this line, two size classes of transcripts hybridized strongly to the v-sis probe. However, these transcripts, 7 and 3 kb, most likely represent endogenous retroviral transcripts and not c-sis transcripts. Expression of c-myb, c-mos, c-fes, c-src and c-erb A and c-erb B could not be detected in any of the cell lines studied.