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Molecular and Cellular Biology, August 2000, p. 5503-5515, Vol. 20, No. 15
CRC Institute for Cancer Studies, The
University of Birmingham Medical School, Birmingham B15
2TT,1 and Liver Research
Laboratories, The University of Birmingham Institute of Clinical
Science, Birmingham B15 2TH,2 United Kingdom
Received 15 December 1999/Returned for modification 8 February
2000/Accepted 8 May 2000
CD40, a tumor necrosis factor (TNF) receptor (TNFR) family member,
conveys signals regulating diverse cellular responses, ranging from
proliferation and differentiation to growth suppression and cell death.
The ability of CD40 to mediate apoptosis in carcinoma cells is
intriguing given the fact that the CD40 cytoplasmic C terminus lacks a
death domain homology with the cytotoxic members of the TNFR
superfamily, such as Fas, TNFR1, and TNF-related apoptosis-inducing ligand (TRAIL) receptors. In this study, we have probed the mechanism by which CD40 transduces death signals. Using a trimeric recombinant soluble CD40 ligand to activate CD40, we have found that this phenomenon critically depends on the membrane proximal domain (amino
acids 216 to 239) but not the TNFR-associated factor-interacting PXQXT
motif in the CD40 cytoplasmic tail. CD40-mediated cytotoxicity is
blocked by caspase inhibitors, such as zVAD-fmk and crmA, and involves
activation of caspase 8 and caspase 3. Interestingly, CD40 ligation was
found to induce functional Fas ligand, TRAIL (Apo-2L) and TNF in
apoptosis-susceptible carcinoma cells and to up-regulate expression of
Fas. These findings identify a novel proapoptotic mechanism which is
induced by CD40 in carcinoma cells and depends on the endogenous
production of cytotoxic cytokines and autocrine or paracrine induction
of cell death.
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
CD40 Induces Apoptosis in Carcinoma Cells through
Activation of Cytotoxic Ligands of the Tumor Necrosis Factor
Superfamily
*
Corresponding author. Mailing address: CRC Institute
for Cancer Studies, The University of Birmingham Medical School,
Birmingham B15 2TA, England, United Kingdom. Phone: (44) 121 414 2801. Fax: (44) 121 414 4486. E-mail:
A.G.Eliopoulos{at}bham.ac.uk.
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