Effect of gene transfer of tumor necrosis factor receptors into human lung carcinoma cell line

The human lung adenocarcinoma cell line A549 is known to be resistant to tumor necrosis factor alpha (TNF-α)-mediated tumor cell lysis in spite of the expression of 55 kDa TNF receptor (TNF-R55) mRNA and its cell surface protein. In this study, we investigated the mechanism of TNF-α resistance and the role of two types of TNF receptors (TNF-R55 and TNF-R75 (75 kDa TNF receptor)). TNF-R55 or TNF-R75 cDNA was transfected into A549 cells. In addition, a C-terminal deletion mutant of TNF-R75 which lacks the intracellular domain of TNF-R75 was also transfected into A549 cells. We assessed the TNF-α-mediated tumor cell lysis of these transfected clones, and found that the cytotoxic effect increased in transfected clones highly expressing TNF-R55, but not in low-expression clones. As for TNF-R75, the cytotoxic effect of TNF-α was observed in TNF-R75-transfected clones even when expression was low. Furthermore, the cytotoxic effect was also observed in clones transfected with the deletion mutant of TNF-R75, as well as the complete TNF-R75. These results indicate that a certain level of expression of TNF-R55 is necessary for obtaining TNF-α-mediated tumor cell lysis in the absence of TNF-R75. On the other hand, the expression of TNF-R75 strongly induces TNF-α-mediated cytotoxicity through TNF-R55 in the absence of an intracellular signal via TNF-R75.