CaAmong ion channels, the transient receptor potential (TRP) melastatin 6 and 7 channel is similarly permeable to both of the dominant divalent cations Ca 2+ and Mg 2+ .(4) TRP channels were first cloned from the Drosophila species (TRP and transient receptor potential-like protein) and constitute a superfamily of proteins that encode a diverse group of Ca 2+ -permeable nonselective cation channels.(5) The TRP family is divided into three subfamilies: classic, vanilloid (TRPV), and melastatin type (TRPM).(5) The eight TRPM family members differ significantly from other TRP channels in terms of domain structure, cation selectivity, and activation mechanisms.(5) By mediating cation entry as well as membrane depolarization, activation of the TRPM subfamily of ion channels has a profound influence on various physiologic and pathologic processes. (6,7) TRPM7 is endogenously expressed in a wide variety of tissues including brain and hematopoietic tissues (8) as well as kidney and heart tissues.(9-11) The TRPM7 cation channel supports multiple cellular and physiological functions, including cellular Mg 2+ homeostasis, (12,13) cell viability and growth, (13)(14)(15)(16) anoxic neuronal cell death, (17) synaptic transmission, (18) cell adhesion, (19,20) and intestinal pacemaking.(21) Recently, Wykes et al. (22) suggested that TRPM7 channels are critical for human mast cell survival, and Jiang et al. (23) suggested that activation of TRPM7 channels is critical for the growth and proliferation of human head and neck carcinoma cells. Also Abed et al. (24) proposed the importance of TRPM7 in human osteoblast-like cell proliferation. However, the presence and potential function of TRPM7 channels in human gastric cancer cells are unknown.In this study, we examined the presence and potential role of TRPM7 channels in the growth and survival of AGS cells, the most common human gastric adenocarcinoma cell line. Our data suggest that TRPM7 channels have an important role in the survival of these tumor cells. Materials and MethodsCells. Five human gastric adenocarcinoma cell lines (AGS, MKN-1, MKN-45, SNU-1, and SNU-484) were used. Among them, we used mainly AGS cell line, the most common human gastric adenocarcinoma cell line. All cell lines were established at

The expression of hypoxia-inducible factor-1 (HIF-1) correlates with poor clinical outcomes and confers resistance to the apoptosis of the tumor cells that are exposed to hypoxia. Presently, the mechanism underlying this phenomenon is poorly understood. In this study we provide evidence that transglutaminase 2 (TG2), an enzyme that catalyses protein crosslinking reactions, is a transcriptional target of HIF-1 to enhance the survival of hypoxic cells. We found that hypoxia induces TG2 expression through an HIF-1 dependent pathway and concurrently activates intracellular TG2. The hypoxic cells overexpressing TG2 showed resistance to apoptosis. Conversely, the hypoxic cells treated with either TG2 inhibitor or small interfering RNA (siRNA) became sensitive to apoptosis. Activation of TG2 in response to hypoxic stress inhibited caspase-3 activity by forming crosslinked multimer, resulting in insoluble aggregates. TG2 also activates nuclear factor (NF)-jB pathway after hypoxic stress, and thereby induces the expression of cellular inhibitor of apoptosis 2. The anti-apoptotic role of TG2 was further confirmed in vivo using xenografts in athymic mice. Our results indicate that TG2 is an antiapoptotic mediator of HIF-1 through modulating both apoptosis and survival pathways and may confer a selective growth advantage to tumor cells. These findings suggest that the inhibition of TG2 may offer a novel strategy for anticancer therapy.

Leptin is a pivotal regulator of energy and glucose homeostasis, and defects in leptin signaling result in obesity and diabetes. The ATP-sensitive potassium (K ATP ) channels couple glucose metabolism to insulin secretion in pancreatic β-cells. In this study, we provide evidence that leptin modulates pancreatic β-cell functions by promoting K ATP channel translocation to the plasma membrane via AMP-activated protein kinase (AMPK) signaling. K ATP channels were localized mostly to intracellular compartments of pancreatic β-cells in the fed state and translocated to the plasma membrane in the fasted state. This process was defective in leptin-deficient ob/ob mice, but restored by leptin treatment. We discovered that the molecular mechanism of leptin-induced AMPK activation involves canonical transient receptor potential 4 and calcium/calmodulindependent protein kinase kinase β. AMPK activation was dependent on both leptin and glucose concentrations, so at optimal concentrations of leptin, AMPK was activated sufficiently to induce K ATP channel trafficking and hyperpolarization of pancreatic β-cells in a physiological range of fasting glucose levels. There was a close correlation between phospho-AMPK levels and β-cell membrane potentials, suggesting that AMPK-dependent K ATP channel trafficking is a key mechanism for regulating β-cell membrane potentials. Our results present a signaling pathway whereby leptin regulates glucose homeostasis by modulating β-cell excitability.T he K ATP channel, an inwardly rectifying K + channel that consists of pore-forming Kir6.2 and regulatory sulfonylurea receptor 1 (SUR1) subunits (1), functions as an energy sensor: its gating is regulated mainly by the intracellular concentrations of ATP and ADP. In pancreatic β-cells, K ATP channels are inhibited or activated in response to the rise or fall in blood glucose levels, leading to changes in membrane excitability and insulin secretion (2, 3). Thus, K ATP channel gating has been considered an important mechanism in coupling blood glucose levels to insulin secretion. Recently, trafficking of K ATP channels to the plasma membrane was highlighted as another important mechanism for regulating K ATP channel activity (4-6).AMP-activated protein kinase (AMPK) is a key enzyme regulating energy homeostasis (7). We recently demonstrated that K ATP channels are recruited to the plasma membrane in glucosedeprived conditions via AMPK signaling in pancreatic β-cells (6). Inhibition of AMPK signaling significantly reduces K ATP currents, even after complete wash-out of intracellular ATP (6). Given these results, we proposed a model that recruitment of K ATP channels to the plasma membrane via AMPK signaling is crucial for K ATP channel activation in low-glucose conditions. However, the physiological relevance of this model remains unclear because pancreatic β-cells had to be incubated in media containing less than 3 mM glucose to recruit a sufficient number of K ATP channels to the plasma membrane (6). We thus hypothesized that there should be an e...

Transglutaminase (TGase) 2 is a ubiquitously expressed enzyme that modifies proteins by cross-linking or polyamination. An aberrant activity of TGase 2 has implicated its possible roles in a variety of diseases including age-related cataracts. However, the molecular mechanism by which TGase 2 is activated has not been elucidated. In this report, we showed that oxidative stress or UV irradiation elevates in situ TGase 2 activity. Neither the expression level nor the in vitro activity of TGase 2 appeared to correlate with the observed elevation of in situ TGase 2 activity. Screening a number of cell lines revealed that the level of TGase 2 activation depends on the cell type and also the environmental stress, suggesting that unrecognized cellular factor(s) may specifically regulate in situ TGase 2 activity. Concomitantly, we observed that human lens epithelial cells (HLE-B3) exhibited about 3-fold increase in in situ TGase 2 activity in response to the stresses. The activated TGase 2 catalyzed the formation of water-insoluble dimers or polymers of ␣B-crystallin, ␤B 2 -crystallin, and vimentin in HLE-B3 cells, providing evidence that TGase 2 may play a role in cataractogenesis. Thus, our findings indicate that in situ TGase 2 activity must be evaluated instead of in vitro activity to study the regulation mechanism and function of TGase 2 in biological and pathological processes.

Background: Activation of TRPC4/5 channels is mediated by GPCR activation. Results: TRPC4/5 was activated by the G␣ i/o -coupled receptor and the G␣ i protein, which interacted directly with each other. Conclusion: G␣ i proteins play an essential role as novel activators of TRPC4/5. Significance: Our findings provide new insights into the activation mechanism of inhibitory G␣ proteins.

Aberrant glutathione or Ca(2+) homeostasis due to oxidative stress is associated with the pathogenesis of neurodegenerative disorders. The Ca(2+)-permeable transient receptor potential cation (TRPC) channel is predominantly expressed in the brain, which is sensitive to oxidative stress. However, the role of the TRPC channel in neurodegeneration is not known. Here, we report a mechanism of TRPC5 activation by oxidants and the effect of glutathionylated TRPC5 on striatal neurons in Huntington's disease. Intracellular oxidized glutathione leads to TRPC5 activation via TRPC5 S-glutathionylation at Cys176/Cys178 residues. The oxidized glutathione-activated TRPC5-like current results in a sustained increase in cytosolic Ca(2+), activated calmodulin-dependent protein kinase and the calpain-caspase pathway, ultimately inducing striatal neuronal cell death. We observed an abnormal glutathione pool indicative of an oxidized state in the striatum of Huntington's disease transgenic (YAC128) mice. Increased levels of endogenous TRPC5 S-glutathionylation were observed in the striatum in both transgenic mice and patients with Huntington's disease. Both knockdown and inhibition of TRPC5 significantly attenuated oxidation-induced striatal neuronal cell death. Moreover, a TRPC5 blocker improved rearing behaviour in Huntington's disease transgenic mice and motor behavioural symptoms in littermate control mice by increasing striatal neuron survival. Notably, low levels of TRPC1 increased the formation of TRPC5 homotetramer, a highly Ca(2+)-permeable channel, and stimulated Ca(2+)-dependent apoptosis in Huntington's disease cells (STHdh(Q111/111)). Taken together, these novel findings indicate that increased TRPC5 S-glutathionylation by oxidative stress and decreased TRPC1 expression contribute to neuronal damage in the striatum and may underlie neurodegeneration in Huntington's disease.

Due to the exquisite specificity and potency of the immune system, vaccination is in theory the most precise and powerful approach for controlling cancer. However, current data from clinical trials indicate that vaccination rarely yields significant benefits for cancer patients in terms of tumor progression and long-term survival. The poor clinical outcomes of vaccination are primarily caused by mechanisms of immune tolerance, especially within the tumor microenvironment. Here we report that vaccination drives the evolution of tumor cells towards an immune-resistant and stem-like phenotype that promotes tumor growth and nullifies the cytotoxic T lymphocyte (CTL) response. The emergence of this phenotype required the transcription factor Nanog, which is induced as a consequence of immune selection. Nanog expression enhanced the stem-like features of tumor cells and protected them from killing by tumor-reactive CTLs. Delivery of siNanog into tumor-bearing mice rendered the tumor vulnerable to immune surveillance and strongly suppressed its growth. Together, our findings demonstrate tumor adaptation to vaccination through gain of an immune-resistant, stem-like phenotype and identify Nanog as a central molecular target in this process. Future vaccination technology should consider Nanog an important target to enhance the immunotherapeutic response.

Geraniol is a dietary monoterpene alcohol that is found in the essential oils of aromatic plants. To date, experimental evidence supports the therapeutic or preventive effects of geraniol on different types of cancer, such as breast, lung, colon, prostate, pancreatic, and hepatic cancer, and has revealed the mechanistic basis for its pharmacological actions. In addition, geraniol sensitizes tumor cells to commonly used chemotherapy agents. Geraniol controls a variety of signaling molecules and pathways that represent tumor hallmarks; these actions of geraniol constrain the ability of tumor cells to acquire adaptive resistance against anticancer drugs. In the present review, we emphasize that geraniol is a promising compound or chemical moiety for the development of a safe and effective multi-targeted anticancer agent. We summarize the current knowledge of the effects of geraniol on target molecules and pathways in cancer cells. Our review provides novel insight into the challenges and perspectives with regard to geraniol research and to its application in future clinical investigation.