Induction of sensitivity to the cytotoxic action of tumor necrosis factor alpha by adenovirus E1A is independent of transformation and transcriptional activation

We have previously shown that expression of the adenovirus E1A 12S or 13S products in NIH 3T3 fibroblasts induces susceptibility to the cytotoxic actions of tumor necrosis factor alpha (TNF alpha). A large number of studies have mapped the multiple biological functions of the 12S and 13S products to three highly conserved regions (CR) within the E1A sequence. Here we used plasmids coding for E1A deletion and point mutants in these regions to generate target cell lines for TNF alpha cytotoxicity assays to determine which regions and functions are necessary for the induction of TNF alpha sensitivity. Expression of CR1 was required for the induction of TNF alpha sensitivity. This finding did not reflect a requirement for transforming or transcriptional repression activity, since some mutants that were defective in both of these properties were able to induce TNF alpha sensitivity. CR2 transformation-defective point mutants, but not a CR2/3 region deletion mutant, were also able to induce sensitivity. In addition, NIH 3T3 cells expressing the retroviral transcription activators tat from human immunodeficiency virus type 1 and tax from human T-lymphotropic virus type I were not sensitive to TNF alpha. However, the possibility that E1A-mediated transcriptional activation can augment the induction of TNF alpha sensitivity is not excluded. Comparison of data from previous biological studies with the TNF alpha cytotoxicity assays presented here suggested that the mechanism by which E1A induces sensitivity to TNF alpha in NIH 3T3 cells is independent of many of the known E1A biological functions, including transformation in cooperation with ras, immortalization, induction of DNA synthesis in quiescent cells, and transcriptional repression. A novel E1A-mediated effect may be involved, although our data do not exclude the possibility that sensitization to TNF alpha is mediated through E1A binding to cellular proteins.

Role of tumor necrosis factor-alpha in E1A oncogene-induced susceptibility of neoplastic cells to lysis by natural killer cells and activated macrophages

NIH-3T3 cells transfected with adenovirus E1A oncogene cDNA were found to exhibit cytolytic susceptibility to murine NK cells and activated macrophages associated with a threshold level of oncogene product expression exceeding that required for morphological transformation. A similar correlation was observed between threshold levels of E1A gene product expression and target cell susceptibility to direct cytotoxicity by rTNF. Inhibition of splenic NK cell and peritoneal macrophage cytolysis by antisera specific for murine rTNF confirmed the importance of E1A-induced TNF susceptibility as one determinant of target cell cytolytic susceptibility. Anti-TNF antibody was, however, unable to block killing of E1A-expressing targets by the NK cell line, NKB61A2. These results suggest a direct link between the functions of E1A oncogene products and cellular mechanisms of action of TNF elaborated by host effector cells and indicate that E1A expression also affects target cell susceptibility to TNF-independent cytolytic mechanisms.

Role of tumor necrosis factor-alpha in E1A oncogene-induced susceptibility of neoplastic cells to lysis by natural killer cells and activated macrophages

NIH-3T3 cells transfected with adenovirus E1A oncogene cDNA were found to exhibit cytolytic susceptibility to murine NK cells and activated macrophages associated with a threshold level of oncogene product expression exceeding that required for morphological transformation. A similar correlation was observed between threshold levels of E1A gene product expression and target cell susceptibility to direct cytotoxicity by rTNF. Inhibition of splenic NK cell and peritoneal macrophage cytolysis by antisera specific for murine rTNF confirmed the importance of E1A-induced TNF susceptibility as one determinant of target cell cytolytic susceptibility. Anti-TNF antibody was, however, unable to block killing of E1A-expressing targets by the NK cell line, NKB61A2. These results suggest a direct link between the functions of E1A oncogene products and cellular mechanisms of action of TNF elaborated by host effector cells and indicate that E1A expression also affects target cell susceptibility to TNF-independent cytolytic mechanisms.

Induction by E1A oncogene expression of cellular susceptibility to lysis by TNF

Tumour necrosis factor alpha (ref. 1), synthesized primarily by monocytes in response to various invasive agents, induces a wide variety of biological effects relevant to regulating cell growth and differentiation, including the selective killing of some tumour cells and the growth stimulation of some normal fibroblasts. As tumour necrosis factor (TNF) appears to kill tumour cells preferentially, we asked whether TNF sensitivity correlates with the expression of specific oncogene(s). If so, by examining the cellular target(s) of the oncogene product, it might be possible to identify specific factor(s) which mediate TNF action. By using an in vitro cytotoxicity assay with NIH 3T3 and Fisher BRK-derived cells expressing exogenously introduced oncogenes, we found that adenovirus E1A proteins induce susceptibility to TNF killing.