Augmentation by IL-1 alpha of tumor necrosis factor-alpha cytotoxicity in cells transfected with adenovirus E1A.

The introduction of adenovirus E1A into NIH3T3 mouse fibroblasts renders them susceptible to the cytotoxic action of TNF-alpha. We found that cells transfected with 13S E1A cDNA were not similarly rendered sensitive to IL-1 alpha; however, in cells transfected with 13S E1A cDNA, TNF cytotoxicity was augmented by treatment with IL-1. To understand the role of E1A in the cytotoxic action of these cytokines, several 13S E1A cDNA deletion mutants were constructed, transfected into NIH3T3 cells, and tested for their ability to induce TNF sensitivity in the presence and absence of IL-1. Cells transfected with mutants of 13S E1A with deletions of carboxyl-terminal amino acids 223 to 289 or 151 to 289 (conserved region 3) exhibited a minimal ability to reverse E1A-induced TNF cytotoxicity but a significant ability to reverse IL-1-mediated augmentation of TNF cytotoxicity. Cells transfected with other deletion mutants of 13S E1A, including those with an internal deletion encompassing conserved region 1 (amino acid positions 23 to 107) or a deletion including conserved regions 2 and 3 (amino acid positions 108 to 289), although initially TNF resistant, became TNF sensitive on prolonged exposure to TNF. Cells transfected with these mutants also showed a reduction in IL-1-augmented TNF cytotoxicity. The larger internal deletion of E1A at amino acid positions 23 to 150 (conserved regions 1 and 2), which includes regions important for transformation, transcriptional repression, and association with cellular proteins, resulted in the complete loss of the ability of E1A to induce TNF sensitivity even in the presence of IL-1. Immunoprecipitation experiments showed that E1A proteins in NIH3T3 cells associated with a cellular 115-kDa protein, which did not co-migrate with the RB gene product; the possible involvement of this protein in E1A-mediated TNF cytotoxicity is discussed. Taken together, these results indicate that conserved regions 1 and 2 are required for E1A-mediated TNF cytotoxicity. In contrast, maximal IL-1-augmented TNF cytotoxicity requires conserved region 3 as well as the nonconserved carboxyl-terminal region of the 13S E1A product.