Cell Lines from grc Congenic Strains of Rats Having Different Susceptibilities to Chemical Carcinogens¹

The growth and reproduction complex (grc^-) strains of rats have a 70-kilobase deletion in the major histocompatibility complex (MHC)-linked grc-G/C region that is associated with embryonic death, developmental defects, and an increased susceptibility to chemical carcinogens. To study further the effects associated with the deletion, fibroblastic cell lines from grc^-, grc⁺, and grc^+/- rat embryos were developed: BIL-derived cell lines are congenic for the MHC and grc, whereas R16-derived cell lines are congenic for the grc alone. In early passages, all cell lines expressed the MHC class I antigen RT1.A, had a diploid chromosome number, and did not display anchorage-independent growth or in vivo tumorigenicity. The grc^- cells [median population doubling time (PDT), 47 h] grew more slowly than the grc⁺ (PDT, 30.5 h) and grc^+/- (PDT, 33 h) cells. All cells underwent crisis, but the crisis stage began earlier and lasted longer in the grc^- cells. The established grc^- cell lines (PDT, 32.5 h) grew faster than the grc⁺ (PDT, 48.5 h) and grc^+/- (PDT, 54 h) cell lines. Two of the three BIL-derived grc^- lines that survived crisis became anchorage independent in tissue culture and tumorigenic in histocompatible F1 rats (highly malignant fibrosarcomas) at passages 33 and 48, respectively; by contrast, none of the R16-derived grc^- cell lines transformed. None of 8 grc⁺ or 8 grc^+/- cell lines that survived crisis displayed anchorage-independent growth or tumorigenicity under the same conditions up to passage 50. All of the established cell lines, including the two tumorigenic ones, expressed MHC class I antigens. Southern and Northern blot analyses of BIL-derived cell lines before and after crisis showed that they all constitutively expressed H-ras and Rb and that no cell line showed rearrangement, amplification, or overexpression of c-myc, H-ras, K-ras, Rb, and p53 either before or after crisis. These observations indicate that: (a) the homozygous grc^- deletion is necessary but not sufficient for in vitro transformation; (b) another genetic factor(s) required for transformation is linked to, or possibly in, the MHC; and (c) passage through crisis, spontaneous transformation, or carcinogen treatment does not alter the cellular expression of MHC class I antigens or of several oncogenes and tumor suppressor genes.