Involvement of TRPM2 and L-type Ca²⁺ channels in Ca²⁺ entry and cell death induced by hydrogen peroxide in rat β-cell line RIN-5F

Molecular mechanisms of cell death by parthanatos: More questions than answers

Regulated cell death by a non-apoptotic pathway known as parthanatos is increasingly recognised as a central player in pathological processes, including ischaemic tissue damage and neurodegenerative diseases. Parthanatos is activated under conditions that induce high levels of DNA damage, leading to hyperactivation of the DNA damage sensor PARP1. While this strict dependence on PARP1 activation is a defining feature of parthanatos that distinguishes it from other forms of cell death, the molecular events downstream of PARP1 activation remain poorly understood. In this mini-review, we highlight a number of important questions that remain to be answered about this enigmatic form of cell death.

Bidirectional regulation mechanism of TRPM2 channel: role in oxidative stress, inflammation and ischemia-reperfusion injury

Transient receptor potential melastatin 2 (TRPM2) is a non-selective cation channel that exhibits Ca2+ permeability. The TRPM2 channel is expressed in various tissues and cells and can be activated by multiple factors, including endogenous ligands, Ca2+, reactive oxygen species (ROS) and temperature. This article reviews the multiple roles of the TRPM2 channel in physiological and pathological processes, particularly on oxidative stress, inflammation and ischemia-reperfusion (I/R) injury. In oxidative stress, the excessive influx of Ca2+ caused by the activation of the TRPM2 channel may exacerbate cellular damage. However, under specific conditions, activating the TRPM2 channel can have a protective effect on cells. In inflammation, the activation of the TRPM2 channel may not only promote inflammatory response but also inhibit inflammation by regulating ROS production and bactericidal ability of macrophages and neutrophils. In I/R, the activation of the TRPM2 channel may worsen I/R injury to various organs, including the brain, heart, kidney and liver. However, activating the TRPM2 channel may protect the myocardium from I/R injury by regulating calcium influx and phosphorylating proline-rich tyrosine kinase 2 (Pyk2). A thorough investigation of the bidirectional role and regulatory mechanism of the TRPM2 channel in these physiological and pathological processes will aid in identifying new targets and strategies for treatment of related diseases.

Beta-Cell Ion Channels and Their Role in Regulating Insulin Secretion

Beta cells of the pancreatic islet express many different types of ion channels. These channels reside in the β-cell plasma membrane as well as subcellular organelles and their coordinated activity and sensitivity to metabolism regulate glucose-dependent insulin secretion. Here, we review the molecular nature, expression patterns, and functional roles of many β-cell channels, with an eye toward explaining the ionic basis of glucose-induced insulin secretion. Our primary focus is on KATP and voltage-gated Ca2+ channels as these primarily regulate insulin secretion; other channels in our view primarily help to sculpt the electrical patterns generated by activated β-cells or indirectly regulate metabolism. Lastly, we discuss why understanding the physiological roles played by ion channels is important for understanding the secretory defects that occur in type 2 diabetes. © 2021 American Physiological Society. Compr Physiol 11:1-21, 2021.

Possible involvement of TRPM2 activation in 5-fluorouracil-induced myelosuppression in mice

Transient receptor potential melastatin 2 (TRPM2) is an oxidative stress-sensitive Ca2+-permeable channel. The activation of TRPM2 by H2O2 causes cell death in various types of cells. 5-Fluorouracil (5-FU) is an important anticancer drug, but myelosuppression is one of the most frequent adverse effects. The involvement of oxidative stress in 5-FU-induced myelosuppression has been reported, and bone marrow cells are known to express TRPM2. The aim of this study was to investigate whether TRPM2 is involved in 5-FU-induced myelosuppression. Enhancement of H2O2-induced intracellular Ca2+ concentration ([Ca2+]i) increase by 5-FU treatment was observed in human embryonic kidney 293 (HEK) cells stably expressing TRPM2 but not in HEK cells, indicating that 5-FU stimulates TRPM2 activation. In CD117 positive cells from wild type (WT) mouse bone marrow, 5-FU also enhanced the H2O2-induced [Ca2+]i increases, but not in cells from Trpm2 knockout (KO) mice. In the CFU-GM colony assay, the 5-FU-induced reduction of colony number was alleviated by Trpm2 deficiency. Moreover, the reduction of leukocytes in blood by administration with 5-FU in WT mice was also alleviated in Trpm2 KO mice. The activation of TRPM2 in bone marrow cells seems to be involved in 5-FU-induced myelosuppression.

TRPM2 channel-mediated cell death: An important mechanism linking oxidative stress-inducing pathological factors to associated pathological conditions

Oxidative stress resulting from the accumulation of high levels of reactive oxygen species is a salient feature of, and a well-recognised pathological factor for, diverse pathologies. One common mechanism for oxidative stress damage is via the disruption of intracellular ion homeostasis to induce cell death. TRPM2 is a non-selective Ca2+-permeable cation channel with a wide distribution throughout the body and is highly sensitive to activation by oxidative stress. Recent studies have collected abundant evidence to show its important role in mediating cell death induced by miscellaneous oxidative stress-inducing pathological factors, both endogenous and exogenous, including ischemia/reperfusion and the neurotoxicants amyloid-β peptides and MPTP/MPP+ that cause neuronal demise in the brain, myocardial ischemia/reperfusion, proinflammatory mediators that disrupt endothelial function, diabetogenic agent streptozotocin and diabetes risk factor free fatty acids that induce loss of pancreatic β-cells, bile acids that damage pancreatic acinar cells, renal ischemia/reperfusion and albuminuria that are detrimental to kidney cells, acetaminophen that triggers hepatocyte death, and nanoparticles that injure pericytes. Studies have also shed light on the signalling mechanisms by which these pathological factors activate the TRPM2 channel to alter intracellular ion homeostasis leading to aberrant initiation of various cell death pathways. TRPM2-mediated cell death thus emerges as an important mechanism in the pathogenesis of conditions including ischemic stroke, neurodegenerative diseases, cardiovascular diseases, diabetes, pancreatitis, chronic kidney disease, liver damage and neurovascular injury. These findings raise the exciting perspective of targeting the TRPM2 channel as a novel therapeutic strategy to treat such oxidative stress-associated diseases.

Molecular Regulations and Functions of the Transient Receptor Potential Channels of the Islets of Langerhans and Insulinoma Cells

Insulin secretion from the β-cells of the islets of Langerhans is triggered mainly by nutrients such as glucose, and incretin hormones such as glucagon-like peptide-1 (GLP-1). The mechanisms of the stimulus-secretion coupling involve the participation of the key enzymes that metabolize the nutrients, and numerous ion channels that mediate the electrical activity. Several members of the transient receptor potential (TRP) channels participate in the processes that mediate the electrical activities and Ca²⁺ oscillations in these cells. Human β-cells express TRPC1, TRPM2, TRPM3, TRPM4, TRPM7, TRPP1, TRPML1, and TRPML3 channels. Some of these channels have been reported to mediate background depolarizing currents, store-operated Ca²⁺ entry (SOCE), electrical activity, Ca²⁺ oscillations, gene transcription, cell-death, and insulin secretion in response to stimulation by glucose and GLP1. Different channels of the TRP family are regulated by one or more of the following mechanisms: activation of G protein-coupled receptors, the filling state of the endoplasmic reticulum Ca²⁺ store, heat, oxidative stress, or some second messengers. This review briefly compiles our current knowledge about the molecular mechanisms of regulations, and functions of the TRP channels in the β-cells, the α-cells, and some insulinoma cell lines.

Calcium Homeostasis: A Potential Vicious Cycle of Bone Metastasis in Breast Cancers

Cancers have been considered as one of the most severe health problems in the world. Efforts to elucidate the cancer progression reveal the importance of bone metastasis for tumor malignancy, one of the leading causes for high mortality rate. Multiple cancers develop bone metastasis, from which breast cancers exhibit the highest rate and have been well-recognized. Numerous cells and environmental factors have been believed to synergistically facilitate bone metastasis in breast cancers, from which breast cancer cells, osteoclasts, osteoblasts, and their produced cytokines have been well-recognized to form a vicious cycle that aggravates tumor malignancy. Except the cytokines or chemokines, calcium ions are another element largely released from bones during bone metastasis that leads to hypercalcemia, however, have not been well-characterized yet in modulation of bone metastasis. Calcium ions act as a type of unique second messenger that exhibits omnipotent functions in numerous cells, including tumor cells, osteoclasts, and osteoblasts. Calcium ions cannot be produced in the cells and are dynamically fluxed among extracellular calcium pools, intracellular calcium storages and cytosolic calcium signals, namely calcium homeostasis, raising a possibility that calcium ions released from bone during bone metastasis would further enhance bone metastasis and aggravate tumor progression via the vicious cycle due to abnormal calcium homeostasis in breast cancer cells, osteoclasts and osteoblasts. TRPs, VGCCs, SOCE, and P2Xs are four major calcium channels/routes mediating extracellular calcium entry and affect calcium homeostasis. Here we will summarize the overall functions of these four calcium channels in breast cancer cells, osteoclasts and osteoblasts, providing evidence of calcium homeostasis as a vicious cycle in modulation of bone metastasis in breast cancers.

TRPM2 promotes the proliferation and invasion of pancreatic ductal adenocarcinoma

The aim of the present study was to investigate transient receptor potential cation channel subfamily M member 2 (TRPM2), a promising therapeutic target and biomarker for pancreatic ductal adenocarcinoma (PDAC) prognosis, in addition to determining its effects regarding tumor progression and invasion. PDAC is a fatal disease with a poor prognosis, and its associated pathogenic molecular mechanisms remain to be determined. In the present study, combined analysis using genomic and transcriptomic data from two PDAC studies was performed to discover a survival‑associated biomarker of PDAC. Survival analysis for genes mutated in ≥10 patients was performed using a Kaplan‑Meier curve and tested for significance using a log‑rank test. Furthermore, gene‑expression correlation analysis was performed to determine the genes with the strongest correlations to TRPM2. In addition, a Cell Counting Kit‑8 assay, a scratch wound‑healing assay and a Transwell assay were performed in the present study to investigate the proliferative, invasive and metastatic ability of PANC‑1 cells in TRPM2‑overexpressing and downregulated groups. The mutated TRPM2 gene had a strong negative correlation with patient survival probability compared with the normal control group (P=1.06x10‑4). Expression of TRPM2 was strongly correlated with expression of probable phospholipid‑transporting ATPase IM, γ‑parvin, tudor domain containing 9, Toll‑like receptor 7 and Scm‑like with four MBT domains protein 2 according to the criterion of a correlation coefficient >0.5. Furthermore, the results of the present study demonstrated that the TRPM2 overexpression in a PDAC cell line (PANC‑1) promoted cell proliferation, invasion and metastatic ability. TRPM2 represents a potential therapeutic target and prognostic marker for patients with PDAC. TRPM2 regulates cell proliferation, invasion and migration; however, the underlying mechanism requires further investigation in future studies.

Inhibition of the transient receptor potential melastatin-2 channel causes increased DNA damage and decreased proliferation in breast adenocarcinoma cells

Transient receptor potential, melastatin-2 (TRPM2) is a plasma membrane cation channel with important roles in sensory functions and promoting cell death. However, we demonstrated here that TRPM2 was present in the nuclei of MCF-7 and MDA-MB-231 human breast adenocarcinoma cells, and its pharmacologic inhibition or RNAi silencing caused decreased cell proliferation. Neither an effect on proliferation nor a localization of TRPM2 in the nucleus was observed in noncancerous HMEC and MCF-10A human mammary epithelial cells. Investigation of possible effects of TRPM2 function in the nucleus demonstrated that pharmacologic inhibition or RNAi silencing of TRPM2 in MCF-7 and MDA-MB-231 human breast adenocarcinoma cells caused up to 4-fold increases in DNA damage levels, as compared to noncancerous breast cells after equivalent treatments. These results indicate that TRPM2 has a novel nuclear function in human breast adenocarcinoma cells that facilitates the integrity of genomic DNA, a finding that is distinct from its previously reported role as a plasma membrane cation channel in noncancerous cells. In summary, we report here a novel effect promoted by TRPM2, where it functions to minimize DNA damage and thus may have a role in the protection of genomic DNA in breast cancer cells. Our study therefore provides compelling evidence that TRPM2 has a unique role in breast adenocarcinoma cells. Accordingly, these studies suggest that TRPM2 is a potential therapeutic target, where its pharmacologic inhibition may provide an innovative strategy to selectively increase DNA damage levels in breast cancer cells.