Exploring the biophysical evidence that mammalian two‐pore channels are NAADP‐activated calcium‐permeable channels

Abstract

Nicotinic acid adenine dinucleotide phosphate (NAADP) potently releases Ca 2+ from acidic intracellular endolysosomal Ca 2+ stores. It is widely accepted that two types of two-pore channels, termed TPC1 and TPC2, are responsible for the NAADP-mediated Ca 2+ release but the Samantha Pitt gained her PhD degree from the University of Cambridge. Following two postdoctoral positions studying mechanisms of ion-channel regulation, one at University College London (Department of Pharmacology) and one at the University of Bristol (Department of Pharmacology) she moved to her current position as a Royal Society of Edinburgh Biomedical Fellow in the School of Medicine, University of St Andrews. Her research group investigates intracellular calcium dynamics and the molecular function of intracellular ion channels. At present, she has a particular interest in understanding the molecular mechanisms of NAADP-regulated signalling via two-pore channels. Benedict Reilly-O'Donnell is a second year PhD student at the University of St Andrews. He is interested in the single channel properties of two-pore channels and other intracellular calcium-release channels. Using a combination of electrophysiological, molecular and biochemical methods, he is currently investigating the role of zinc in intracellular calcium release. Benedict completed his undergraduate studies in pharmacology at University College London in 2013. Rebecca Sitsapesan obtained her PhD at the University of Strathclyde and following appointment as British Heart Foundation Basic Science Lecturer at Imperial College London moved to Bristol University and then to the University of Oxford where she is currently Professor of Pharmacology. Her group investigates the biophysical properties of RyR and other ion channels that are present on intracellular organelles and are involved in the process of intracellular Ca 2+ release, particularly in regard to cardiac physiology and pathophysiology.This review was presented at the symposium "Non-selective cationic channels in chemical and physical stress", which took place at Physiology 2015 in Cardiff, UK, 6-8 July 2015.C 2016 The Authors. Abstract figure legend TPC1 and TPC2: NAADP-activated Ca 2+ -release pathways. TPC1 and TPC2 both play a role in the release of Ca 2+ from lysosomes and endolysosomes. Evidence suggests that TPC1 and TPC2 exhibit subtle but significant differences in ion conduction and selectivity, and although both channels appear to be activated by NAADP, regulation of gating by various additional modulators (such as cytosolic and luminal Ca 2+ , PI(3,5)P 2 , luminal pH, voltage) is also different. Thus, TPC1 and TPC2 may play complementary physiological roles. AbbreviationsNAADP, nicotinic acid adenine dinucleotide phosphate; TPC, two-pore channel; PI(3,5)P 2 , phosphatidylinositol 3,5-bisphosphate.

Differential effects of two-pore channel protein 1 and 2 silencing in MDA-MB-468 breast cancer cells

“…TPC1 and TPC2 silencing also had different effects on CPA-mediated changes in [Ca 2+ ] CYT . The gating and permeability of TPC1 and TPC2 vary [4] and examples of differential roles are also reflected in the effects of TPC isoform silencing on endomembrane dynamics [5], effects of overexpression on multinucleation [6], and roles on local and global Ca 2+ signals [25]. In light of previous studies indicating a role for TPC2 in store-operated calcium entry [26], future studies assessing the mechanism by which TPC2 remodels CPA-induced changes in [Ca 2+ ] CYT in this model are required, particularly in the context of calcium induced Ca 2+ release [27].…”

“…Studies of calcium channels in breast cancer cells have mostly focused on transient receptor potential (TRP), Orai, ligand-gated, and voltage-gated Ca 2+ channels. Two-pore channel (TPC) proteins, TPC1 and TPC2, are recently identified ion channels that contribute to nicotinic acid adenine dinucleotide phosphate (NAADP)-mediated Ca 2+ release from acidic intracellular endolysosomal stores [4]. TPC1 and TPC2 appear to have distinct gating mechanisms and have been reported to play differential roles in a variety of cell types and signaling pathways [4,5].…”

“…Two-pore channel (TPC) proteins, TPC1 and TPC2, are recently identified ion channels that contribute to nicotinic acid adenine dinucleotide phosphate (NAADP)-mediated Ca 2+ release from acidic intracellular endolysosomal stores [4]. TPC1 and TPC2 appear to have distinct gating mechanisms and have been reported to play differential roles in a variety of cell types and signaling pathways [4,5]. Despite the reported role of TPC1 in cell cycle regulation in a HEK293 overexpression model [6], and the role of TPC2, but not TPC1, in angiogenesis-associated signaling pathways [7], these channels have not been assessed in detail in breast cancer cell lines.…”

“…We also assessed the consequences of TPC1 and TPC2 silencing on the proliferation of MDA-MB-468 breast cancer cells, EGF-induced changes in the expression of vimentin and E-cadherin, and phosphorylation of STAT3. Finally, in light of recent evidence suggesting differential selectivity of TPC1 and TPC2 for Ca 2+ ions [4,13,14], we assessed the consequences of channel silencing on calcium influx in the MDA-MB-468 cell line.…”

Analysis of Single Nucleotide Polymorphisms in human Voltage-Gated Ion Channels

“…Apart from these distinguished members of the superfamily of VGICs, other families have been described more recently. However, members of these families either do not follow the "topological profile" described above [21][22][23][24][25] or are non-selective, voltage-insensitive and their activation is affected by neurotransmitters and biochemical mediators [24,[26][27][28][29].…”