Saturday, July 10, 2010

Fas-associated death domain (FADD) is a negative regulator of T-cell receptor-mediated necroptosis

Proc Natl Acad Sci U S A. 2010 Jul 6. [Epub ahead of print]

Fas-associated death domain (FADD) is a negative regulator of T-cell receptor-mediated necroptosis

Osborn SL, Diehl G, Han SJ, Xue L, Kurd N, Hsieh K, Cado D, Robey EA, Winoto A.

Cancer Research Laboratory and Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720.

Cell death is an important mechanism to limit uncontrolled T-cell expansion during immune responses. Given the role of death-receptor adapter protein Fas-associated death domain (FADD) in apoptosis, it is intriguing that T-cell receptor (TCR)-induced proliferation is blocked in FADD-defective T cells. Necroptosis is an alternate form of death that can be induced by death receptors and is linked to autophagy. It requires the death domain-containing kinase RIP1 and, in certain instances, RIP3. FADD and its apoptotic partner, Caspase-8, have also been implicated in necroptosis. To accurately assess the role of FADD in mature T-cell proliferation and death, we generated a conditional T-cell-specific FADD knockout mouse strain. The T cells of these mice develop normally, but lack FADD at the mature stage. FADD-deficient T cells respond poorly to TCR triggering, exhibit slow cell cycle entry, and fail to expand over time. We find that programmed necrosis occurs during the late stage of normal T-cell proliferation and that this process is greatly amplified in FADD-deficient T cells. Inhibition of necroptosis using an inhibitor of RIP1 kinase activity rescues the FADD knockout proliferative defect. However, TCR-induced necroptosis did not appear to require autophagy or involve RIP3. Consistent with their defective CD8 T-cell response, these mice succumb to Toxoplasma gondii infection more readily than wild-type mice. We conclude that FADD constitutes a mechanism to keep TCR-induced programmed necrotic signaling in check during early phases of T-cell clonal expansion.

PMID: 20615958 [PubMed - as supplied by publisher]

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