Inhibition of NF-kappa B activity in human T lymphocytes induces caspase-dependent apoptosis without detectable activation of caspase-1 and-3

NF-KB is involved in the transcriptional control of various genes that act as extrinsic and intrinsic survival factors for T cells. Our findings show that suppression of NF-kappa B activity with cell-permeable SN50 peptide, w hich masks the nuclear localization sequence of NF-kappa B1 dimers and prev ents their nuclear localization, induces apoptosis in resting normal human PBL. Inhibition of NF-kappa B resulted in the externalization of phosphatid ylserine, induction of DNA breaks, and morphological changes consistent wit h apoptosis, DNA fragmentation was efficiently blocked by the caspase inhib itor Z-VAD-fmk and partially blocked by Ac-DEVD-fmk, suggesting that SN50-m ediated apoptosis is caspase-dependent, Interestingly, apoptosis induced by NF-kappa B suppression, in contrast to that induced by TPEN (N,N,N',N'-tet rakis [2-pyridylmethyl]ethylenediamine) or soluble Fas ligand (CD95), was o bserved in the absence of active death effector proteases caspase-1-like (I L-1 converting enzyme), caspase-like (CPP32/Yama/apopain) and caspase-6-lik e and without cleavage of caspase-3 substrates poly(ADP-ribose) polymerase and DNA fragmentation factor-45. These findings suggest either low level of activation is required or that different caspases are involved. Preactivat ion of T cells resulting in NF-kappa B nuclear translocation protected cell s from SN50-induced apoptosis, Our findings demonstrate an essential role o f NF-KB in survival of naive PBL.