Mechanism of apoptosis induced by diazoxide, a K+ channel opener, in HepG2 Human hepatoma cells

How Dysregulated Ion Channels and Transporters Take a Hand in Esophageal, Liver, and Colorectal Cancer

Over the last two decades, the understanding of how dysregulated ion channels and transporters are involved in carcinogenesis and tumor growth and progression, including invasiveness and metastasis, has been increasing exponentially. The present review specifies virtually all ion channels and transporters whose faulty expression or regulation contributes to esophageal, hepatocellular, and colorectal cancer. The variety reaches from Ca²⁺, K⁺, Na⁺, and Cl^- channels over divalent metal transporters, Na⁺ or Cl^- coupled Ca²⁺, HCO₃^- and H⁺ exchangers to monocarboxylate carriers and organic anion and cation transporters. In several cases, the underlying mechanisms by which these ion channels/transporters are interwoven with malignancies have been fully or at least partially unveiled. Ca²⁺, Akt/NF-κB, and Ca²⁺- or pH-dependent Wnt/β-catenin signaling emerge as cross points through which ion channels/transporters interfere with gene expression, modulate cell proliferation, trigger epithelial-to-mesenchymal transition, and promote cell motility and metastasis. Also miRs, lncRNAs, and DNA methylation represent potential links between the misexpression of genes encoding for ion channels/transporters, their malfunctioning, and cancer. The knowledge of all these molecular interactions has provided the basis for therapeutic strategies and approaches, some of which will be broached in this review.

FAM3 gene family: A promising therapeutical target for NAFLD and type 2 diabetes

Non-alcoholic fatty liver disease (NAFLD) and diabetes are severe public health issues worldwide. The Family with sequence similarity 3 (FAM3) gene family consists of four members designated as FAM3A, FAM3B, FAM3C and FAM3D, respectively. Recently, there had been increasing evidence that FAM3A, FAM3B and FAM3C are important regulators of glucose and lipid metabolism. FAM3A expression is reduced in the livers of diabetic rodents and NAFLD patients. Hepatic FAM3A restoration activates ATP-P2 receptor-Akt and AMPK pathways to attenuate steatosis and hyperglycemia in obese diabetic mice. FAM3C expression is also reduced in the liver under diabetic condition. FAM3C is a new hepatokine that activates HSF1-CaM-Akt pathway and represses mTOR-SREBP1-FAS pathway to suppress hepatic gluconeogenesis and lipogenesis. In contrast, hepatic expression of FAM3B, also called PANDER, is increased under obese state. FAM3B promotes hepatic lipogenesis and gluconeogenesis by repressing Akt and AMPK activities, and activating lipogenic pathway. Under obese state, the imbalance among hepatic FAM3A, FAM3B and FAM3C signaling networks plays important roles in the pathogenesis of NAFLD and type 2 diabetes. This review briefly discussed the latest research progress on the roles and mechanisms of FAM3A, FAM3B and FAM3C in the regulation of hepatic glucose and lipid metabolism.

Highly pathogenic H5N1 avian influenza virus induces extracellular Ca2+ influx, leading to apoptosis in avian cells

In this study, we show that the highly pathogenic H5N1 avian influenza virus (AIV) (A/crow/Kyoto/53/04 and A/chicken/Egypt/CL6/07) induced apoptosis in duck embryonic fibroblasts (DEF). In contrast, apoptosis was reduced among cells infected with low-pathogenic AIVs (A/duck/HK/342/78 [H5N2], A/duck/HK/820/80 [H5N3], A/wigeon/Osaka/1/01 [H7N7], and A/turkey/Wisconsin/1/66 [H9N2]). Thus, we investigated the molecular mechanisms of apoptosis induced by H5N1-AIV infection. Caspase-dependent and -independent pathways contributed to the cytopathic effects. We further showed that, in the induction of apoptosis, the hemagglutinin of H5N1-AIV played a major role and its cleavage sequence was not critical. We also observed outer membrane permeabilization and loss of the transmembrane potential of the mitochondria of infected DEF, indicating that mitochondrial dysfunction was caused by the H5N1-AIV infection. We then analyzed Ca(2+) dynamics in the infected cells and demonstrated an increase in the concentration of Ca(2+) in the cytosol ([Ca(2+)](i)) and mitochondria ([Ca(2+)](m)) after H5N1-AIV infection. Regardless, gene expression important for regulating Ca(2+) efflux from the endoplasmic reticulum did not significantly change after H5N1-AIV infection. These results suggest that extracellular Ca(2+) may enter H5N1-AIV-infected cells. Indeed, EGTA, which chelates extracellular free Ca(2+), significantly reduced the [Ca(2+)](i), [Ca(2+)](m), and apoptosis induced by H5N1-AIV infection. In conclusion, we identified a novel mechanism for influenza A virus-mediated cell death, which involved the acceleration of extracellular Ca(2+) influx, leading to mitochondrial dysfunction and apoptosis. These findings may be useful for understanding the pathogenesis of H5N1-AIV in avian species as well as the impact of Ca(2+) homeostasis on influenza A virus infection.

Diazoxide-mediated growth inhibition in human lung cancer cells via downregulation of beta-catenin-mediated cyclin D1 transcription

Treatment of various types of cells with the mitochondrial ATP-sensitive K(+) channel opener, diazoxide, preconditions cells to subsequent injuries and inhibits apoptosis. However, the role and mechanism(s) of diazoxide in solid tumor cell growth are largely unknown. Here we demonstrate that diazoxide inhibited the proliferation of lung cancer cells as well as the transcription of cell cycle-related protein Cyclin D1. Cyclin D1 overexpression inhibited the negative role of diazoxide in cell cycle progression. We further explored the mechanisms by which diazoxide affected Cyclin D1 transcription and found that the beta-catenin transcription factor was downregulated by diazoxide, with a corresponding decrease in Cyclin D1 promoter activity. Taken together, these results suggest that diazoxide inhibits lung cancer cell proliferation via downregulation of Cyclin D1 transcription, which may have important therapeutic implications in lung cancer patients.

Potential Roles of Electrogenic Ion Transport and Plasma Membrane Depolarization in Apoptosis

Apoptosis is characterized by the programmed activation of specific biochemical pathways leading to the organized demise of cells. To date, aspects of the intracellular signaling machinery involved in this phenomenon have been extensively dissected and characterized. However, recent studies have elucidated a novel role for changes in the intracellular milieu of the cells as important modulators of the cell death program. Specially, intracellular ionic homeostasis has been reported to be a determinant in both the activation and progression of the apoptotic cascade. Several apoptotic insults trigger specific changes in ionic gradients across the plasma membrane leading to depolarization of the plasma membrane potential (PMP). These changes lead to ionic imbalance early during apoptosis. Several studies have also suggested the activation and/or modulation of specific ionic transport mechanisms including ion channels, transporters and ATPases, as mediators of altered intracellular ionic homeostasis leading to PMP depolarization during apoptosis. However, the role of PMP depolarization and of the changes in ionic homeostasis during the progression of apoptosis are still unclear. This review summarizes the current knowledge regarding the causes and consequences of PMP depolarization during apoptosis. We also review the potential electrogenic ion transport mechanisms associated with this event, including the net influx/efflux of cations and anions. An understanding of these mechamisms could lead to the generation of new therapeutic approaches for a variety of diseases involving apoptosis.