WILD-TYPE ADENOVIRUS TYPE-5 TRANSFORMING GENES FUNCTION AS TRANSDOMINANT SUPPRESSORS OF ONCOGENESIS IN MUTANT ADENOVIRUS TYPE-5 TRANSFORMEDRAT EMBRYO FIBROBLAST CELLS

Transformation of cloned rat embryo fibroblast (CREF) cells with the h ost-range adenovirus type 5 (Ad5) mutant, H5hr1, results in transforma nts with a fibroblastic morphology which display a cold-sensitive tran sformation phenotype and oncogenic potential in both nude mice and syn geneic rats. In contrast, wild-type (wt) Ad5 transformed CREF cells ar e epithelioid in morphology, temperature independent for transformatio n, and nontumorigenic. The present studies were conducted to analyze t he contribution of the mutated E1A and E1B regions of H5hr1 in regulat ing the biological properties of H5hr1-transformed CREF cells. CREF ce lls were constructed which contain the mutated E1A and E1B transformin g regions of H5hr1 and either a wt Ad5 E1A gene, a wt Ad5 E1B gene, or both a wt Ad5 E1A and a wt E1B gene. A wt Ad5 E1A gene was sufficient in reversing the cold-sensitive transformation phenotype. By using a wt Ad5 E1A gene under the transcriptional control of a dexamethasone-i nducible mouse mammary tumor virus promoter, a direct suppressive effe ct of wt Ad5 E1A on colony formation in monolayer culture and agar gro wth of H5br1-transformed cells was demonstrated. Expression of a wt Ad 5 E1A, a wt Ad5 E1B, or both wt transforming genes in H5hr1-transforme d CREF cells also suppressed oncogenicity. The ability or inability to form tumors in animals was found not to correlate with sensitivity to natural killer cell-mediated lysis. These results indicate that both the wt Ad5 E1A and wt Ad5 E1B genes can function as dominant suppresso rs of the oncogenic process when coexpressed in H5hr1-transformed CREF cells. This effect does not require large quantities of wt Ad5 E1A or E1B transforming proteins, nor is it directly related to the acquisit ion of a natural killer cell cytolysis-susceptible phenotype.