EXPRESSION OF THE 75 KDA TNF RECEPTOR AND ITS ROLE IN CONTACT-MEDIATED NEURONAL CELL-DEATH

We previously demonstrated TNF toxicity, at high TNF doses or in the p resence of actinomycin D, in the N1E-115 neuronal cell line (N1Es), wh ich expresses only the 55 kDa TNF receptor (TNFR). To determine whethe r presence of the 75 kDa TNFR increases N1E sensitivity to TNF toxicit y, cells were transfected with a 75 kDa TNFR expression construct. How ever, 75 kDa TNFR protein expression was undetectable in stably transf ected N1Es. Further investigation revealed endogenous membrane-associa ted TNF in this neuronal line. Co-transfection with beta-galactosidase and the 75 kDa TNFR or empty vector (pcDNA3) indicated cell loss in t he 75 kDa TNFR-transfected population relative to vector-transfected p opulations, while inhibition of membrane-associated TNF with a neutral izing antibody led to increased 75 kDa TNFR expression in transiently transfected N1Es. We conclude that neutralization of membrane-associat ed TNF inhibits its interaction with the introduced 75 kDa TNFR, incre asing neuronal survival and promoting 75 kDa TNFR expression. Induced 75 kDa TNFR expression in the presence of membrane-associated TNF and the 55 kDa TNFR results in lymphocyte cell death [J.K. Lazdins, M. Gre ll, M.R. Walker, K. Woods-Cook, P. Scheurich, K. Pfizenmaier, Membrane tumor necrosis factor (TNF) induced cooperative signaling of the TNFR 60 and TNFR80 favors induction of cell death rather than virus product ion in HIV-infected T cells, J. Exp. Med. 185 (1997) 81-90]. This repo rt demonstrates that membrane-associated TNF and the 75 kDa TNFR simil arly contribute to neuronal cell death. (C) 1998 Elsevier Science B.V. All rights reserved.