CELL-CYCLE PROGRESSION OUT OF G1 SENSITIZES PRIMARY-CULTURED NONTRANSFORMED T-CELLS TO TCR-MEDIATED APOPTOSIS

Shortly after primary activation and IL-2-induced entry into cell cycl e, splenic or lymph node T cells can be induced to undergo apoptosis b y recrosslinking of the TCR complex using anti-TCR antibodies, We demo nstrate here that primary-activated T cells induced to undergo apoptos is by TCR recrosslinking during the G1 phase of the cell cycle did not arrest in the G1 phase of the cell cycle, Instead, the cells continue d to progress through the cell cycle and underwent at least one mitosi s before dying, Rapamycin, an inhibitor of IL-8-induced S phase entry, prevented this apoptotic death, Prevention of cell death correlated w ith delayed entry into S phase from G1 following TCR religation in the rapamycin-treated cultures. Addition of rapamycin after cells had ent ered S phase or had already divided failed to prevent cell death. Trea tment of activated T cells with dibutyryl cAMP or forskolin, which als o block primary-activated T lymphocytes in G1, also inhibited TCR-indu ced cell death, In contrast, treatment of TCR-religated cells with rea gents that blocked cell cycle progression in S phase (aphidicolin, def eroxamine) after TCR religation failed to prevent apoptotic cell death , Activated T cells sorted for S + G2/M DNA content following Hoechst 33342 staining were also found to be more sensitive to TCR-induced apo ptosis than cells sorted for G1 DNA content, Rapamycin inhibited apopt osis in G1-sorted cells, but not in S + G2/M-sorted cells. Together, t hese results suggest that factors regulating cell cycle progression al so control the induction of TCR-mediated apoptosis, Primary-activated T cells may become committed to programmed cell death only after progr essing into S phase of the cell cycle. (C) 1996 Academic Press, Inc.