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      Polycystins and cellular Ca 2+ signaling

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          Abstract

          The cystic phenotype in autosomal dominant polycystic kidney disease is characterized by a profound dysfunction of many cellular signaling patterns, ultimately leading to an increase in both cell proliferation and apoptotic cell death. Disturbance of normal cellular Ca 2+ signaling seems to be a primary event and is clearly involved in many pathways that may lead to both types of cellular responses. In this review, we summarize the current knowledge about the molecular and functional interactions between polycystins and multiple components of the cellular Ca 2+-signaling machinery. In addition, we discuss the relevant downstream responses of the changed Ca 2+ signaling that ultimately lead to increased proliferation and increased apoptosis as observed in many cystic cell types.

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          Most cited references163

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          TSC2 integrates Wnt and energy signals via a coordinated phosphorylation by AMPK and GSK3 to regulate cell growth.

          Mutation in the TSC2 tumor suppressor causes tuberous sclerosis complex, a disease characterized by hamartoma formation in multiple tissues. TSC2 inhibits cell growth by acting as a GTPase-activating protein toward Rheb, thereby inhibiting mTOR, a central controller of cell growth. Here, we show that Wnt activates mTOR via inhibiting GSK3 without involving beta-catenin-dependent transcription. GSK3 inhibits the mTOR pathway by phosphorylating TSC2 in a manner dependent on AMPK-priming phosphorylation. Inhibition of mTOR by rapamycin blocks Wnt-induced cell growth and tumor development, suggesting a potential therapeutic value of rapamycin for cancers with activated Wnt signaling. Our results show that, in addition to transcriptional activation, Wnt stimulates translation and cell growth by activating the TSC-mTOR pathway. Furthermore, the sequential phosphorylation of TSC2 by AMPK and GSK3 reveals a molecular mechanism of signal integration in cell growth regulation.
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            Control of macroautophagy by calcium, calmodulin-dependent kinase kinase-beta, and Bcl-2.

            Macroautophagy is an evolutionary conserved lysosomal pathway involved in the turnover of cellular macromolecules and organelles. In spite of its essential role in tissue homeostasis, the molecular mechanisms regulating mammalian macroautophagy are poorly understood. Here, we demonstrate that a rise in the free cytosolic calcium ([Ca(2+)](c)) is a potent inducer of macroautophagy. Various Ca(2+) mobilizing agents (vitamin D(3) compounds, ionomycin, ATP, and thapsigargin) inhibit the activity of mammalian target of rapamycin, a negative regulator of macroautophagy, and induce massive accumulation of autophagosomes in a Beclin 1- and Atg7-dependent manner. This process is mediated by Ca(2+)/calmodulin-dependent kinase kinase-beta and AMP-activated protein kinase and inhibited by ectopic Bcl-2 located in the endoplasmatic reticulum (ER), where it lowers the [Ca(2+)](ER) and attenuates agonist-induced Ca(2+) fluxes. Thus, an increase in the [Ca(2+)](c) serves as a potent inducer of macroautophagy and as a target for the antiautophagy action of ER-located Bcl-2.
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              PKD2, a gene for polycystic kidney disease that encodes an integral membrane protein.

              A second gene for autosomal dominant polycystic kidney disease was identified by positional cloning. Nonsense mutations in this gene (PKD2) segregated with the disease in three PKD2 families. The predicted 968-amino acid sequence of the PKD2 gene product has six transmembrane spans with intracellular amino- and carboxyl-termini. The PKD2 protein has amino acid similarity with PKD1, the Caenorhabditis elegans homolog of PKD1, and the family of voltage-activated calcium (and sodium) channels, and it contains a potential calcium-binding domain.
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                Author and article information

                Contributors
                humbert.desmedt@med.kuleuven.be
                Journal
                Cell Mol Life Sci
                Cell. Mol. Life Sci
                Cellular and Molecular Life Sciences
                Springer Basel (Basel )
                1420-682X
                1420-9071
                18 October 2012
                18 October 2012
                August 2013
                : 70
                : 15
                : 2697-2712
                Affiliations
                Laboratory of Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine, KU Leuven, Campus Gasthuisberg O/N-I, B-802, Herestraat 49, 3000 Leuven, Belgium
                Article
                1188
                10.1007/s00018-012-1188-x
                3708286
                23076254
                70bb2271-b9f3-4ba9-98ea-033356f94560
                © The Author(s) 2012
                History
                : 22 August 2012
                : 1 October 2012
                : 2 October 2012
                Categories
                Review
                Custom metadata
                © Springer Basel 2013

                Molecular biology
                calcium signaling,polycystin,adpkd,renal pathology
                Molecular biology
                calcium signaling, polycystin, adpkd, renal pathology

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