Regulation of tumor necrosis factor cytotoxicity by calcineurin

Abstract

Cyclosporin (CsA) inhibits mitochondrial death signaling and opposes tumor necrosis factor (TNF)-induced apoptosis in vitro. However, CsA is also a potent inhibitor of calcineurin, a phosphatase that may participate in cell death. Therefore, we tested the hypothesis that calcineurin regulates TNF cytotoxicity in rat hepatoma cells (FTO2B). TNF-treated FTO2B cells appeared apoptotic by DNA fragmentation, nuclear condensation, annexin V binding, and caspase activation. We studied two calcineurin inhibitors, CsA and FK506, and found that each potently inhibited TNF cytotoxicity. Western blot demonstrated calcineurin in FTO2B homogenates. In a model of mitochondrial permeability transition (MPT), we found that CsA prevented MPT and cytochrome c release, while FK506 inhibited neither. In summary, we present evidence that calcineurin participates in an apoptotic death pathway activated by TNF. CsA may oppose programmed cell death by inhibiting calcineurin activity and/or inhibiting mitochondrial signaling. ß

TNFα mediates susceptibility to heat-induced apoptosis by protein phosphatase-mediated inhibition of the HSF1/hsp70 stress response

“…Thus, PPs appear as key linker molecules between the cellular effects of TNFa, the activation of HSF1/hsp70 stress responses and cellular susceptibility to apoptosis. Several points of evidence support this concept: (i) PPs PP1/PP2a and PP2b can be activated by TNFa, 29,39 (ii) activation of these PPs increases susceptibility to apoptotic cell death, 28,29 (iii) activation of PP1/PP2a and PP2b (calcineurin) as well as elevated intracellular calcium levels inhibit phosphorylation of HSF1 and thus activation of the HSF1/hsp70 stress response, [40][41][42] (iv) hsp70, which acts in a negative-feedback loop on HSF1 activation, 18 induces PP1/PP2a as well as PP2b and thus blocks continuing activation of HSF1 43,44 and (v) ERK and NF-kB signaling, which maintained a certain responsiveness of HSF1/hsp70 and also protected cells from apoptotic death, is a concurring mechanism to PPs, since their mutual inhibition has been repeatedly demonstrated. 45,46 In summary, the data presented provide insights into the interplay of signals essential for cell survival, stress resistance and apoptosis.…”

“…27 Some of these may involve the activation of protein phosphatases. 28,29 Signals involved in inflammatory responses of TNFa, such as NF-kB, suppress TNFa-mediated apoptosis (Figure 9b; arrow c) and thereby prevent a conflicting cellular response. 2,30 This concept of suppression of conflicting cellular responses is also applicable for the HSF1/hsp70 system.…”

Response to steroids inde novoautoimmune hepatitis after liver transplantation

“…We studied HLA class I and II polymorphism by standard complement-dependent microcytotoxicity assays and/or by PCR with sequence-specific primers for the following antigens/alleles: A (1,2,3,11,23,24,25,26,29,30,31,32,33,34,66,68,69,80), B (7,8,13,18,27,35,37,38,39,41,42,44,45,47,48,49,50,51,52,53,55,56,57,58,60,61,62,63,64,65,67,70,73), Cw (1,2,3,4,…”

Protein Phosphatase 4 Is Involved in Tumor Necrosis Factor-α-induced Activation of c-Jun N-terminal Kinase

“…It has been known that the catalytic subunit of PP2A is subject to phosphorylation of a conserved tyrosine and an as yet unidentified threonine (46 -48), and that phosphorylation of either the tyrosine or the threonine site inhibits phosphatase activity of PP2A in vitro. However, in human hepatoma Hep3B cells, interleukin-6 induced an increase in both the phosphorylation and phosphatase activity of PP2A (39). The nature of PP4 serine and threonine phosphorylation in response to TNF-␣ remains unknown at this point.…”

“…A variety of protein phosphatases have been implicated in TNF-␣ signaling. For example, calcineurin, a calcium-dependent serine/threonine phosphatase, participates in TNF-␣-mediated apoptosis in rat hepatoma cells (39) and SHP-2, a Src homology 2-containing phosphotyrosine phosphatase, mediates the induction of interleukin-6 by TNF-␣ through modulation of the NF-B pathway (40). Another phosphotyrosine phosphatase, SHP-1, has been shown to mediate TNF-␣'s inhibitory effect on vascular endothelial cell growth factorinduced endothelial cell proliferation (41).…”