BOTH TNF RECEPTORS ARE REQUIRED FOR TNF-MEDIATED INDUCTION OF APOPTOSIS IN PC60 CELLS

A rat/mouse T cell hybridoma (PC60) was transfected either with human (h) TNF-R p55 (TNF-R55), p75 (TNF-R75) or both cDNAs. hTNF-R55 express ion was below 50 molecules/cell, whereas the number of hTNF-R75 reache d about 4000 molecules/cell. Only cells co-expressing the two types of receptor showed TNF-dependent apoptosis, in contrast to cells express ing similar levels of only one receptor type, indicating that both TNF -R55 and TNF-R75 are required. Stable co-transfection of the bcl-2 pro to-oncogene largely prevented this TNF-mediated induction of apoptosis . We found that a high level of hTNF-R75 expression was essential for obtaining TNF-dependent apoptosis in PC60 cells in addition to a low n umber of hTNF-R55. Both receptors are signal transducing because simul taneous triggering of hTNF-R55 and hTNF-R75 by agonistic mAbs or by TN F-R-specific TNF muteins induced similar levels of apoptosis as wild-t ype hTNF. Apoptotic killing of only those lymphocytes expressing a hig h, induced level of TNF-R75, in addition to TNF-R55, may play a physio logically important role.