The H-ras oncogene regulates expression of 70- and 45-kDa cell-surface molecules whose expression correlates with tumor-cell immunogenicity

The effects of the H-ras oncogene on fibroblast cell tumorigenicity and immunogenicity was studied in transfectants of the BALB/c 3T3 clone A31 fibroblastoid cell-line. Cells that were transfected with MC29-LTR-H-ras (98/6) or MC29-LTR-v-myc + H-ras (98/4v) and were inoculated into syngeneic BALB/c mice were tumorigenic in 100% and 60% of animals respectively. By contrast, transfectants containing the pSV2neo plasmid alone (98/1) displayed normal characteristics both in vitro and in vivo. Inoculation of mice with mitomycin-C-treated 98/1 or 98/4v cells induced an effective protective immunity to a challenge of live 98/4v cells, and a partial immunity against 98/6 cells. Mitomycin-C-treated 98/6 cells failed to render immunity against a challenge of either 98/6 or 98/4v cells. To correlate immunogenicity and tumorigenicity of the different cell types with cell-surface-antigen expression, we prepared MAbs against 98/4v cells in syngeneic mice. Immunohistochemical and immunoblot analysis revealed that MAbs 102 and 104 recognized 2 protein band of 70 and 45 kDa respectively, which were expressed predominantly in 98/1 and 98/4v cells. A third immunoreactive protein band of 44 kDa that reacted with MAb 6 was expressed at a similar cell-surface density on all cell types. Cell-differentiation-inducing agents, such as DMSO, retinoic acid or sodium butyrate, were all found to induce 98/6 cell flattening and morphological changes toward a normal phenotype that were followed by up-regulation of the 70- and 45-kDa antigens. The results suggest that regulation of expression of the 70- and 45-kDa molecules is affected by H-ras, and that expression of these cell-surface molecules may be relevant to tumor cell immunogenicity.