EFFECT OF GENE-TRANSFER OF TUMOR-NECROSIS-FACTOR RECEPTORS INTO HUMANLUNG-CARCINOMA CELL-LINE

human lung adenocarcinoma cell line A549 is known to be resistant to t umor necrosis factor alpha (TNF-alpha)-mediated tumor cell lysis in sp ite of the expression of 55 kDa TNF receptor (TNF-R55) mRNA and its ce ll surface protein, In this study, we investigated the mechanism of TN F-alpha 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 trans fected into A549 cells. In addition, a C-terminal deletion mutant of T NF-R75 which lacks the intracellular domain of TNF-R75 was also transf ected into A549 cells, We assessed the TNF-alpha-mediated tumor cell l ysis 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-alp ha was observed in TNF-R75-transfected clones even when expression was low Furthermore, the cytotoxic effect was also observed in clones tra nsfected 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-alpha-mediated tumor cell lysis in the absence of TNF-R75. On the other hand, the expression of TNF-R 75 strongly induces TNF-alpha-mediated cytotoxicity through TNF-R55 in the absence of an intracellular signal via TNF-R75.