Alteration of T cell function in tumor environment: non-apoptotic pathway of Fas signal favors Th-17 phenotype

Autor: Chung-Chen Su, 蘇重禎
Rok vydání: 2009
Druh dokumentu: 學位論文 ; thesis
Popis: 97
Fas is a member of tumor necrosis factor (TNF) receptor family and mediates apoptosis when engagement with Fas ligand (FasL). It has been demonstrated that FasL expressed on tumor cells would crosslink with Fas protein of tumor-infiltrating lymphocytes (TILs), causing them to undergo programmed cell death. However, the hypothesis of why FasL expression of tumor cells could not trigger TILs cell death even with the fact that numerous TILs accumulated in the proximity of tumor nodule is yet not clear. In this study, we have analyzed Fas-triggered apoptosis in T cells in contact with tumor cells, which resembles cell-to-cell interactions found in tumor cells. When human Fas-sensitivity Jurkat cells were co-cultured with glioma, the sensitivity of Fas-mediated apoptosis by CH-11 (agonistic anti-Fas monoclonal Ab) is diminished. Meanwhile, Fas expression of Jurkat cells is not reduced and the apoptotic body does not decreased by way of phagocytosis of glioma cells. In contrast, the tumor cell lines MCF-7 and HepG2 produced no such protective effect. Caspase activation and death-inducing signaling complex (DISC) were reduced when co-cultured with glioma. Recently it has become apparent that the microenvironment made up of the extracellular matrix (ECM) may affect cell signaling. While interrupting the β integrins-matrix interaction, it diminished the co-culture effect. Cell matrix contact enhanced the phosphorylation of ERK1/2, p38 MAPK and Akt in Jurkat cells. PI3K inhibitor completely abolished contact-associated protection on these tumor cells and in parallel restored Fas-induced Bcl-xL cleavage as well as decreasing the phosphorylation of Bad at serine 136. We further studied the possible effect on these so called “been protected” T cells. Recently, IL-17-secreting cells have been found to be abundant in several murine FasL-expressing tumors and associated with intensive neutrophils infiltration. CD4+ T helper cells are the major producers of IL-17 and involved in the pathogenesis of many autoimmune diseases and inflammatory conditions. At the moment how FasL triggers the production of IL-17 is not well understood. We suspected that Fas signaling stimulated IL-17 production in those TILs. Upon Fas ligation by CH-11 under non-apoptotic conditions, the expression of transcription factor RORγt (a thymus-specific isoform of the retinoic acid receptor-related orphan receptor) was stimulated in PHA/IL-2-activated CD4+ and CD8+ T cells, but not those of T-bet, GATA3 and FOXP3. Fas signaling stimulated transcriptions of Th-17-related cytokines, including IL-17A, IL-17F, IL-22 and IL-26 in CD4+ T cells. CD8+ T cells expressed only IL-17A, IL-17F but not IL-22 and IL-26. Caspase-8 inhibitor Z-IETD-FMK diminished the effects of Fas-associated induction on the ERK1/2 phosphorylation and transcriptions of IL-22 and IL-26 in CD4+ T cells. In addition, the Fas signal-enhanced RORγt, IL-17A, and IL-17F, as well as the phosphorylated signal transducer and activator of transcription 3 (Stat3) were reduced by treatment with caspase-1 inhibitor Z-YVAD-FMK. On top of it, our studies identified two Fas signaling pathways favoring the Th-17 phenotype. One activates ERK1/2 via caspase-8 to stimulate the IL-22 and IL-26 transcription. The other enhances Stat3 via caspase-1, leading to elevate RORγt and subsequently IL-17A and IL-17F expression in T cells. In overall, the results of this study demonstrated that stimulation of the β integrin signal of T cells by contact with tumor cells may triggers a novel protective signaling through the PI3K/Akt pathway of T cells against Fas-mediated apoptosis. Delayed apoptosis in those infiltrating T cells contributes to express IL-17 through Fas signaling to attract more neutrophils infiltration in inflammatory response. These findings provides a new inspiration of assessment regarding the effects of Fas signaling of which not only triggers cell death but also induces TILs toward Th-17 phenotype through MAPK- and Stat3-dependent signaling pathway relevant to the pathogenesis of many autoimmune diseases and inflammatory reactions.
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