FoxO1 regulates apoptosis induced by asbestos in the MT-2 human T-cell line

Abstract

Asbestos is known to cause malignant mesothelioma and lung cancer. Recent studies implicate tumor immunity in the development of various tumors, including malignant mesothelioma. In order to establish an in vitro T-cell model to clarify the effects of long-term exposure of asbestos on tumor immunity, in this study, human T-cell line MT-2 cells were cultured with asbestos for longer than 8 months and the resultant cells (MT-2Rst) were assessed for the expression of forkhead transcription factor FoxO1. Gene expression analysis revealed that the amount of FoxO1 mRNA decreased after long-term exposure of the MT-2 cells to asbestos. In accordance with this reduction in FoxO1, pro-apoptotic Foxo1 target genes Puma, Fas ligand and Bim were also seen to be downregulated in MT-2Rst cells. Furthermore, shRNA-mediated knock-down of FoxO1 reduced the number of apoptotic parental MT-2 cells after treatment with asbestos. On the other hand, overexpression of FoxO1 did not affect asbestos-induced apoptosis in MT-2Rst cells. These results suggested that FoxO1 played an important role in regulating asbestos-induced apoptosis and confirmed the presence of multiple pathways regulating resistance to asbestos in MT-2Rst cells.ARTICLE HISTORY

Accelerated cell cycle progression of human regulatory T cell-like cell line caused by continuous exposure to asbestos fibers

“…These sublines showed resistance against the asbestos-induced apoptosis via upregulation of IL-10, increased phosphorylation of STAT3 by autocrine usage of IL-10, and subsequent upregulation of Bcl-2 located downstream of STAT3 (22). Moreover, our recent study revealed that reduced FoxO1 caused reduction of other apoptosis-related molecules such as Bim, Puma, and Fas ligand, which are known to be regulated by FoxO1 (31). …”

“…The procedures for western blotting were performed according to the previously reported methods (31). Briefly, MT-2Org cells and cells from asbestos continuously exposed sublines were lysed in 20 mM Tris-HCl (pH 7.5) containing 1 mM EDTA, 1 mM EGTA, 10 mM 2-mercaptoethanol, 1% Triton X-100, 1% sodium deoxycholate, 0.1% sodium lauryl sulfate, 150 mM NaCl and 1% protease inhibitor cocktail (Sigma) and briefly sonicated.…”

“…Procedures regarding knock-down of FoxO1 in MT-2Org with lentivirus have been described (31). Lentivirus plasmid vectors pLKO.1-puro-Control having scramble shRNA sequence and pLKO.1-puro containing shRNA sequence targeting human FoxO1 (TRCN0000039579 and TRCN0000039580), and the packaging plasmids kit of pLP1, pLP2 and pLP/VSVG, were obtained from Sigma and Invitrogen (Carlsbad, CA, USA), respectively.…”

“…It was also found that sublines continuously exposed to asbestos showed remarkably reduced expression of forkhead transcriptional factor 1 (FoxO1) (31). We reported that this reduced FoxO1 caused reduction of pro-apoptotic molecules such as Puma, Bim and Fas ligand in exposed sublines (CB1-3, CA1-3 and CR1), in addition to Bcl-2 overexpression induced by phosphorylation of signal tranducer and activator of transcription 3 (STAT3) caused by autocrine usage of overproduced IL-10 (31).…”

“…We reported that this reduced FoxO1 caused reduction of pro-apoptotic molecules such as Puma, Bim and Fas ligand in exposed sublines (CB1-3, CA1-3 and CR1), in addition to Bcl-2 overexpression induced by phosphorylation of signal tranducer and activator of transcription 3 (STAT3) caused by autocrine usage of overproduced IL-10 (31). FoxO1 is known to regulate various cell cycle regulators such as cyclins and cyclin-dependent kinase-inhibitors (CDK-Is) (32–36).…”