The Regulation and Role of c-FLIP in Human Th Cell Differentiation

Abstract

The early differentiation of T helper (Th) cells is a tightly controlled and finely balanced process, which involves several factors including cytokines, transcription factors and co-stimulatory molecules. Recent studies have shown that in addition to the regulation of apoptosis, caspase activity is also needed for Th cell proliferation and activation and it might play a role in Th cell differentiation. The isoforms of the cellular FLICE inhibitory protein (c-FLIP) are regulators of CASPASE-8 activity and the short isoform, c-FLIPS, has been shown to be up-regulated by IL-4, the Th2 driving cytokine. In this work, we have studied the expression and functional role of three c-FLIP isoforms during the early Th cell differentiation. Only two of the isoforms, c-FLIPS and c-FLIPL, were detected at the protein level although c-FLIPR was expressed at the mRNA level. The knockdown of c-FLIPL led to enhanced Th1 differentiation and elevated IL-4 production by Th2 cells, whereas the knockdown of c-FLIPS diminished GATA3 expression and IL-4 production by Th2 cells. In summary, our results provide new insight into the role of c-FLIP proteins in the early differentiation of human Th cells.

FAS-ligand regulates differential activation-induced cell death of human T-helper 1 and 17 cells in healthy donors and multiple sclerosis patients

“…The discrepancies between human and mouse studies might also be due to the different modality of Th cell generation: we performed all the experiments on clones of memory cells amplified in vitro in the absence of polarising cytokines, whereas previous studies used memory cells cultured in the presence of IL-12 (Th1 cells), IL-6 and TGF- β (Th17 cells). FLIP expression can be modulated by cytokines in Th cells; 40 the addition of polarising cytokines in T-cell culture could potentially modulate FLIP expression and explain the discrepancies between our results and previous mouse studies.…”

Interferon-gamma regulates inflammatory cell death by targeting necroptosis in experimental autoimmune arthritis

“…2C ). Because cFLIP L has antiapoptotic activity and is related to Th1 cell differentiation and the IFN-γ level 19 , 20 , we analysed the expression of cFLIP L and MLKL. IFN-γ deficiency increased the expression of cFLIP L and MLKL (Fig.…”

“…cFLIP L is required for T cell proliferation 36 and inhibits apoptosis and necroptosis 19 , 37 . Additionally, loss of cFLIP L makes T cells susceptible to apoptosis, and cFLIP L expression negatively regulates Th1 cell differentiation and IFN-γ level 20 . Although the function of cFLIP L in necroptosis is unclear, its overexpression leads to upregulation of MLKL and necroptosis mediated by TNF-α 9 .…”

The three as: Alternative splicing, alternative polyadenylation and their impact on apoptosis in immune function

“…191,192 The cFLIP isoforms also appear to differ in their effects on T cell differentiation, in that siRNA knockdown of cFLIPL increased IFNgamma secretion in Th1 cells and IL4 production in Th2 cells, while siRNA knockdown of cFLIPS decreased IL4 production and GATA3 expression of Th2 cells. 193 cFLIP is yet another example where isoform levels are differentially regulated upon T cell activation. Specifically, cFLIPS, but not cFLIPL, is upregulated in primary T cells activated with either PHA or anti-CD3 antibody and upon restimulation of effector T cells with anti-CD3 and anti-CD28 antibodies.…”

“…[194][195][196] cFLIPS is also selectively upregulated by activated T cells polarized to the Th2 subset compared to Th1 and Th0 (unpolarized) cells, in a manner which is dependent on STAT6 signaling. 193 NFAT, p38alpha, and DHX32 have all been implicated to be specific inducers of cFLIPS expression and activity in T cells, although it is not clear if this is due to splicing or to selective stabilization of the cFLIPS protein. 191,194,197,198 Although the mechanisms by which RBP activity may regulate AS changes in cFLIP are not well characterized in T cells, a few studies have begun to characterize the role of RBP activity mediating cFLIP AS in other cell types.…”