Gsdma3 is required for hair follicle differentiation in mice

Apoptosis can result from activation of three major pathways: the extrinsic, the intrinsic, and the most recently identified endoplasmic reticulum (ER) stress-mediated pathway. While the two former pathways are known to be operational in human polymorphonuclear neutrophils (PMNs), the existence of the ER stress-mediated pathway, generally involving caspase-4, has never been reported in these cells. Recently, we have documented that arsenic trioxide (ATO) induced apoptosis in human PMNs by a mechanism that needs to be further investigated. In this study, using immunofluorescence and electron microscopy, we present evidence of ER alterations in PMNs activated by the ER stress inducer arsenic trioxide (ATO). Several key players of the unfolded protein response, including GRP78, GADD153, ATF6, XBP1 and eIF2α are expressed and activated in PMNs treated with ATO or other ER stress inducers. Although caspase-4 is expressed and activated in neutrophils, treatment with a caspase-4 inhibitor did not attenuate the pro-apoptotic effect of ATO at a concentration that reverses caspase-4 processing and activation. Our results demonstrate for the first time that the ER stress-mediated apoptotic pathway operates in human neutrophils.     

三氧化二砷联合氨氯地平对肝癌HepG2细胞体外作用的实验研究

目的:探讨三氧化二砷与氨氯地平单独用药及联合用药对肝癌Hep G2细胞增殖和凋亡的作用。方法:用不同浓度的三氧化二砷(4.0、2.0、1.0μmol/L)和氨氯地平(27×103、18×103、12×103 mg/m L)处理体外培养的人肝癌Hep G-2细胞,观察细胞形态的变化,采用CCK-8法检测两种药物单独及联合应用对Hep G-2细胞生长增殖的影响,并通过流式细胞术观察其对细胞凋亡及细胞周期的影响。结果:三氧化二砷和氨氯地平均可以浓度依赖性方式显著增加Hep G2细胞的生长抑制率及其凋亡率,以联合用药的作用较单独用药更显著(P0.05)。与三氧化二砷和氨氯地平单独用药相比,联合用药可显著阻滞Hep G2细胞于G2期及S期。结论:三氧化二砷和氨氯地平均可显著抑制人肝癌Hep G2细胞的生长和增殖,并促进其凋亡,且二者联合应用时具有协同作用。     

Fluoride induces endoplasmic reticulum stress in ameloblasts responsible for dental enamel formation

The mechanism of how fluoride causes fluorosis remains unknown. Exposure to fluoride can inhibit protein synthesis, and this may also occur by agents that cause endoplasmic reticulum (ER) stress. When translated proteins fail to fold properly or become misfolded, ER stress response genes are induced that together comprise the unfolded protein response. Because ameloblasts are responsible for dental enamel formation, we used an ameloblast-derived cell line (LS8) to characterize specific responses to fluoride treatment. LS8 cells were growth-inhibited by as little as 1.9-3.8 ppm fluoride, whereas higher doses induced ER stress and caspase-mediated DNA fragmentation. Growth arrest and DNA damage-inducible proteins (GADD153/CHOP, GADD45alpha), binding protein (BiP/glucose-responsive protein 78 (GRP78), the non-secreted form of carbonic anhydrase VI (CA-VI), and active X-box-binding protein-1 (Xbp-1) were all induced significantly after exposure to 38 ppm fluoride. Unexpectedly, DNA fragmentation increased when GADD153 expression was inhibited by short interfering RNA treatment but remained unaffected by transient GADD153 overexpression. Analysis of control and GADD153(-/-) embryonic fibroblasts demonstrated that caspase-3 mediated the increased DNA fragmentation observed in the GADD153 null cells. We also demonstrate that mouse incisor ameloblasts are sensitive to the toxic effects of high dose fluoride in drinking water. Activated Ire1 initiates an ER stress response pathway, and mouse ameloblasts were shown to express activated Ire1. Ire1 levels appeared induced by fluoride treatment, indicating that ER stress may play a role in dental fluorosis. Low dose fluoride, such as that present in fluoridated drinking water, did not induce ER stress.     

Hydrogen peroxide induces GADD153 in Jurkat cells through the protein kinase C-dependent pathway

Growth arrest and DNA damage-inducible gene 153 (GADD153) is a CCAAT/enhancer binding protein (C/EBP) related gene and is induced in response to various stimuli including DNA damaging agents, UV irradiation, and serum starvation. In this study, we investigated which intracellular signals contribute to the expression of GADD153 mRNA in Jurkat cells in response to oxidative stress using several kinds of kinase inhibitors. GADD153 mRNA expression was immediately enhanced following hydrogen peroxide exposure and was significantly inhibited by treatment with H-7, staurosporin, and Ro-31-8220. In particular, rottlerin, a PKCdelta specific inhibitor, markedly attenuated hydrogen peroxide-induced GADD153 mRNA expression even at 1 microM. Treatment with a potent PKC activator, phorbol-12-myristate-13-acetate (PMA), augmented GADD153 mRNA in Jurkat cells in the presence of hydrogen peroxide, although PMA alone induced GADD153 mRNA marginally. Hydrogen peroxide significantly enhanced the AP-1 binding activity of the nuclear extract from Jurkat cells to the GADD153 AP-1 binding site. AP-1 binding activity was suppressed by rottlerin treatment. These findings indicate that PKC, especially PKCdelta, plays an important role in the induction of GADD153 mRNA following oxidative stress.