External calcium ion concentration is a major regulator of epidermal keratinocyte differentiation in vitro and probably also in vivo. Regulation of calcium-induced differentiation changes is proposed to occur via an external calcium-sensing, signaling pathway that utilizes increases in intracellular calcium ion concentration to activate differentiation-related gene expression. Calcium ion release from intracellular stores and calcium ion influx via store-operated calcium-permeable channels are key elements in this proposed signaling pathway; however, the channels involved have not yet been identified. The present report shows that human gingival keratinocytes (HGKs) also undergo calcium-induced differentiation in vitro as indicated by involucrin expression and morphological changes. Moreover, TRPC1, which functions as a store-operated calcium channel in a number of cell types, including epidermal keratinocytes, is expressed in both proliferating and differentiating HGKs. Transfection of HGKs with TRPC1 siRNA disrupted expression of TRPC1 mRNA and protein compared with transfection with scrambled TRPC1 siRNA. Cells with disrupted TRPC1 expression showed decreased calcium-induced differentiation as measured by involucrin expression or morphological changes, as well as decreased thapsigargin-induced calcium ion influx, and a decreased rate of store calcium release. These results indicate that TRPC1 is involved in calcium-induced differentiation of HGKs likely by supporting a store-operated calcium ion influx.
"A major Ca 2+ entry route into cells is the store-operated route, whereby an increase in the concentration of extracellular Ca 2+ is detected and leads to the release of Ca 2+ from internal stores, such as the ER and Golgi, within the cell, which in turn activates store-operated calcium (SOC) channels in the plasma membrane, allowing an influx of extracellular Ca 2+ and increasing the intracellular Ca 2+ concentration to a level required to induce differentiation. TRPC1 and TRPC4 have been demonstrated to act as SOC channels in Ca 2+ -induced differentiation of human keratinocytes in vitro (Tu et al., 2005; Cai et al., 2006; Beck et al., 2008). Moreover, the importance of TRPC channels in keratinocyte differentiation is highlighted by the finding that activation of TRPC6 is sufficient to induce in vitro keratinocyte differentiation to levels similar to those seen when the cells are stimulated with high concentrations of extracellular Ca 2+ (Müller et al., 2008). "
[Show abstract][Hide abstract] ABSTRACT: Channels are integral membrane proteins that form a pore, allowing the passive movement of ions or molecules across a membrane (along a gradient), either between compartments within a cell, between intracellular and extracellular environments or between adjacent cells. The ability of cells to communicate with one another and with their environment is a crucial part of the normal physiology of a tissue that allows it to carry out its function. Cell communication is particularly important during keratinocyte differentiation and formation of the skin barrier. Keratinocytes in the skin epidermis undergo a programme of apoptosis-driven terminal differentiation, whereby proliferating keratinocytes in the basal (deepest) layer of the epidermis stop proliferating, exit the basal layer and move up through the spinous and granular layers of the epidermis to form the stratum corneum, the external barrier. Genes encoding different families of channel proteins have been found to harbour mutations linked to a variety of rare inherited monogenic skin diseases. In this Commentary, we discuss how human genetic findings in aquaporin (AQP) and transient receptor potential (TRP) channels reveal different mechanisms by which these channel proteins function to ensure the proper formation and maintenance of the skin barrier.
"SOCs and, in many cases ROCs, have been identified as canonical transient receptor potential (TRPC) channels. Furthermore, several studies indicated that TRPC channels are involved in the CaSR stimulation-induced calcium influx in some cell types, such as salivary ductal cells , MCF-7 breast cancer cells , aortic smooth muscle cells , keratinocytes , pulmonary neuroendocrine cells  and osteoclasts . "
[Show abstract][Hide abstract] ABSTRACT: Calcium-sensing receptor (CaSR) has been demonstrated to be present in several tissues and cells unrelated to systemic calcium homeostasis, where it regulates a series of diverse cellular functions. A previous study indicated that CaSR is expressed in mouse glomerular mesangial cells (MCs), and stimulation of CaSR induces cell proliferation. However, the signaling cascades initiated by CaSR activation in MCs are currently unknown. In this study, our data demonstrate that CaSR mRNA and protein are expressed in a human mesangial cell line. Activating CaSR with high extracellular Ca2+ concentration ([Ca2+]o) or spermine induces a phospholipase C (PLC)-dependent increase in intracellular Ca2+ concentration ([Ca2+]i). Interestingly, the CaSR activation-induced increase in [Ca2+]i results not only from intracellular Ca2+ release from internal stores but also from canonical transient receptor potential (TRPC)-dependent Ca2+ influx. This increase in Ca2+ was attenuated by treatment with a nonselective TRPC channel blocker but not by treatment with a voltage-gated calcium blocker or Na+/Ca2+ exchanger inhibitor. Furthermore, stimulation of CaSR by high [Ca2+]o enhanced the expression of TRPC3 and TRPC6 but not TRPC1 and TRPC4, and siRNA targeting TRPC3 and TRPC6 attenuated the CaSR activation-induced [Ca2+]i increase. Further experiments indicate that 1-oleoyl-2-acetyl-sn-glycerol (OAG), a known activator of receptor-operated calcium channels, significantly enhances the CaSR activation-induced [Ca2+]i increase. Moreover, under conditions in which intracellular stores were already depleted with thapsigargin (TG), CaSR agonists also induced an increase in [Ca2+]i, suggesting that calcium influx stimulated by CaSR agonists does not require the release of calcium stores. Finally, our data indicate that pharmacological inhibition and knock down of TRPC3 and TRPC6 attenuates the CaSR activation-induced cell proliferation in human MCs. With these data, we conclude that CaSR activation mediates Ca2+ influx and cell proliferation via TRPC3 and TRPC6 in human MCs.
PLoS ONE 06/2014; 9(6):e98777. DOI:10.1371/journal.pone.0098777 · 3.23 Impact Factor
"On the right (in red) is a list of cell or whole tissue/body effects that have been suggested to be driven or potentiated by TRPC activity; in other words, if TRPC channels were to be inhibited, the opposite of the effect is predicted to occur (e.g. less pancreatitis). Example references for cell expression items: acinar gland cells (Liu et al., 2007); adipocytes (Sukumar et al., 2012); astrocytes (Shirakawa et al., 2010); cardiac myocytes (Eder and Molkentin, 2011); cochlea hair cells (Quick et al., 2012); endothelial cells (Ahmmed et al., 2004); epithelial cells (Kim et al., 2011); fibroblasts (Xu et al., 2008); hepatocytes (Rychkov and Barritt, 2011); keratinocytes (Cai et al., 2006); leukocytes (Yildirim et al., 2012); mast cells (Freichel et al., 2012); mesangial cells (Sours et al., 2006); neurones (Bollimuntha et al., 2011); osteoclasts/blasts (Abed et al., 2009); platelets (Ramanathan et al., 2012); podocytes (Dryer and Reiser, 2010); skeletal muscle (Gervasio et al., 2008); smooth muscle cells (Beech et al., 2004); and tumour cells (Thebault et al., 2006). Example references for effect items: angiogenesis (Yu et al., 2010); cancer cell drug resistance (Ma et al., 2012); cell adhesion (Smedlund et al., 2010); cell migration (Xu et al., 2006); cell proliferation (Sweeney et al., 2002); cell survival (Selvaraj et al., 2012); cell turning (Wang and Poo, 2005); efferocytosis (Tano et al., 2011); gastrointestinal motility (Tsvilovskyy et al., 2009); glomerular filtration (Dryer and Reiser, 2010); hypoadiponectinaemia (Sukumar et al., 2012); hypo-matrix metalloproteinase (Xu et al., 2008); hypertrophy (cardiac) (Eder and Molkentin, 2011); innate fear (Riccio et al., 2009); lung hyper-responsiveness (Yildirim et al., 2012); mast cell degranulation (Ma et al., 2008); motor coordination (Trebak, 2010); muscle endurance (Zanou et al., 2010); neointimal hyperplasia (Kumar et al., 2006); oedema (Weissmann et al., 2012); permeability (Tiruppathi et al., 2002); pancreatitis (Kim et al., 2011); saliva secretion (Liu et al., 2007); seizure (Phelan et al., 2013); survival after MI (myocardial infarction) (Jung et al., 2011); thrombosis (Ramanathan et al., 2012); vaso-modulation (e.g. "
[Show abstract][Hide abstract] ABSTRACT: The primary purpose of this review is to address the progress towards small molecule modulators of human Transient Receptor Potential Canonical proteins (TRPC1, TRPC3, TRPC4, TRPC5, TRPC6 and TRPC7). These proteins generate channels for calcium and sodium ion entry. They are relevant to many mammalian cell types including acinar gland cells, adipocytes, astrocytes, cardiac myocytes, cochlea hair cells, endothelial cells, epithelial cells, fibroblasts, hepatocytes, keratinocytes, leukocytes, mast cells, mesangial cells, neurones, osteoblasts, osteoclasts, platelets, podocytes, smooth muscle cells, skeletal muscle, and tumour cells. There are broad-ranging positive roles of the channels in cell adhesion, migration, proliferation, survival and turning, vascular permeability, hypertrophy, wound-healing, hypo-adiponectinaemia, angiogenesis, neointimal hyperplasia, oedema, thrombosis, muscle endurance, lung hyper-responsiveness, glomerular filtration, gastrointestinal motility, pancreatitis, seizure, innate fear, motor coordination, saliva secretion, mast cell degranulation, cancer cell drug resistance, survival after myocardial infarction, efferocytosis, hypo-matrix metalloproteinase, vasoconstriction and vasodilatation. Known small molecule stimulators of the channels include hyperforin, genistein and rosiglitazone, but there is more progress with inhibitors, some of which have promising potency and selectivity. The inhibitors include 2-aminoethoxydiphenyl borate, 2-aminoquinolines, 2-aminothiazoles, fatty acids, isothiourea derivatives, naphthalene sulphonamides, N-phenylanthranilic acids, phenylethylimidazoles, piperazine/piperidine analogues, polyphenols, pyrazoles, and steroids. A few of these agents are starting to be useful as tools for determining the physiological and pathophysiological functions of TRPC channels. We suggest that the pursuit of small molecule modulators for TRPC channels is important but that it requires substantial additional effort and investment before we can reap the rewards of highly potent and selective pharmacological modulators.
British Journal of Pharmacology 06/2013; 170(3). DOI:10.1111/bph.12274 · 4.84 Impact Factor
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