TARGET CELL-DIRECTED RAPID DEGRADATION OF TNF-ALPHA MESSENGER-RNA IN HUMAN CYTOTOXIC T-CELLS

Previously we have shown that upon exposure to sensitive target cells (TC), human cytotoxic T cells (CTL) and natural killer cells (NK) undergo functional inactivation and specifically degrade mRNA-encoding lytic proteins stored in cytoplasmic granules. These lytic proteins include perforin (PFP) and the serine proteases (granzymes). In this study we show that tumor necrosis factor-alpha (TNF-alpha) mRNA undergoes rapid down-regulation after interaction with TC, in a manner identical to PFP and serine protease mRNA. Both PFP and TNF-alpha messages are down-regulated and maintained at low baseline levels while effector cells (EC) are in contact with TC. Moreover, treatment of CTL with antibodies against CD2, CD3, CD8, and class I could not reproduce TC-directed mRNA down-regulation of TNF-alpha and PFP even though lytic ability was inhibited. Anti-CD2 and anti-CD3, however, markedly induced the expression of TNF-alpha mRNA within 15 min. The increase of TNF-alpha mRNA by anti-CD2 and anti-CD3 was offset by the presence of TC, suggesting that TC supply a negative signal to the CTL resulting in degradation_of the TNF-alpha mRNA. Furthermore, treatment of CTL with cycloheximide (CHX) did not prevent PFP message loss and did not allow its recovery, suggesting that de novo protein synthesis is not required for mRNA degradation. In contrast, whereas CHX did not prevent TNF-alpha message loss, CHX allowed recovery of TNF-alpha mRNA within 120 min after TC-directed degradation. Taken as a whole, these data suggest that TC provides a negative regulatory signal that triggers the degradation of TNF-alpha message.