The Important Role of Ion Transport System in Cervical Cancer

Cervical cancer is a significant gynecological cancer and causes cancer-related deaths worldwide. Human papillomavirus (HPV) is implicated in the etiology of cervical malignancy. However, much evidence indicates that HPV infection is a necessary but not sufficient cause in cervical carcinogenesis. Therefore, the cellular pathophysiology of cervical cancer is worthy of study. This review summarizes the recent findings concerning the ion transport processes involved in cell volume regulation and intracellular Ca2+ homeostasis of epithelial cells and how these transport systems are themselves regulated by the tumor microenvironment. For cell volume regulation, we focused on the volume-sensitive Cl− channels and K+-Cl− cotransporter (KCC) family, important regulators for ionic and osmotic homeostasis of epithelial cells. Regarding intracellular Ca2+ homeostasis, the Ca2+ store sensor STIM molecules and plasma membrane Ca2+ channel Orai proteins, the predominant Ca2+ entry mechanism in epithelial cells, are discussed. Furthermore, we evaluate the potential of these membrane ion transport systems as diagnostic biomarkers and pharmacological interventions and highlight the challenges.

Properties, Structures, and Physiological Roles of Three Types of Anion Channels Molecularly Identified in the 2010’s

Molecular identification was, at last, successfully accomplished for three types of anion channels that are all implicated in cell volume regulation/dysregulation. LRRC8A plus LRRC8C/D/E, SLCO2A1, and TMEM206 were shown to be the core or pore-forming molecules of the volume-sensitive outwardly rectifying anion channel (VSOR) also called the volume-regulated anion channel (VRAC), the large-conductance maxi-anion channel (Maxi-Cl), and the acid-sensitive outwardly rectifying anion channel (ASOR) also called the proton-activated anion channel (PAC) in 2014, 2017, and 2019, respectively. More recently in 2020 and 2021, we have identified the S100A10-annexin A2 complex and TRPM7 as the regulatory proteins for Maxi-Cl and VSOR/VRAC, respectively. In this review article, we summarize their biophysical and structural properties as well as their physiological roles by comparing with each other on the basis of their molecular insights. We also point out unsolved important issues to be elucidated soon in the future.

Homeostasis Regulation by Potassium Channel Subfamily K Member 3 (KCNK3) in Various Fishes

Potassium channels are important for K+ transport and cell volume regulation, which play important roles in many biological processes such as hormone secretion, ion homeostasis, excitability, and cell development. In mammals, a total of 15 potassium channels were identified and they were divided into six subfamilies, including TALK (TALK1, TALK2, TASK2), TASK (TASK1, TASK3, TASK5), TREK (TREK1, TREK2, TRAAK), TWIK (TWIK1, TWIK2, KCNK7), THIK (THIK1, THIK2) and TRESK. TASK1, also known as potassium channel subfamily k member 3 (KCNK3), is the first member identified in the TASK subfamily. This K2P channel has potential applications in fish breeding and aquaculture industry due to its important roles in various physiological processes. Despite its functional role has been well studied in mammals; however, it is less known in fishes. In this review, we systematically summarize recent research advances of this critical potassium channel in representative fishes, such as gene number variation, tissue distribution, phylogeny, and potential homeostasis regulation role. This paper provides novel insights into the functional properties of these fish kcnk3 genes (including osmoregulation, energy homeostasis maintenance and fatty acids metabolism regulation), and also expands our knowledge about their variations among diverse fishes.

Transcriptomic and proteomic analysis of marine nematode Litoditis marina acclimated to different salinities

Salinity is a critical abiotic factor for all living organisms. The ability to adapt to different salinity environments determines an organism′s survival and ecological niches. Litoditis marina is a euryhaline marine nematode widely distributed in coastal ecosystems all over the world, although numerous genes involved in its salinity response have been reported, the adaptive mechanisms underlying its euryhalinity remain unexplored. Here, we utilized worms which have been acclimated to either low salinity or high salinity conditions and evaluated their basal gene expression at both transcriptomic and proteomic levels. We found that several conserved regulators, including osmolytes biosynthesis genes, transthyretin-like family genes, V-type H+-transporting ATPase and potassium channel genes, were involved in both short-term salinity stress response and long-term acclimation processes. In addition, we identified genes related to cell volume regulation, such as actin regulatory genes, Rho family small GTPases and diverse ion transporters, might contribute to hyposaline acclimation, while the glycerol biosynthesis genes gpdh-1 and gpdh-2 accompanied hypersaline acclimation in L. marina. Furthermore, gpdh-2 might play an essential role in transgenerational inheritance of osmotic stress protection in L. marina as in its relative nematode Caenorhabditis elegans. Hereby, this study paves the way for further in-depth exploration on adaptive mechanisms underlying euryhalinity, and may also contribute to the studies of healthy ecosystems in the context of global climate change.

Evidence of Coordinated and Adjustable Osmolytes Movements Following Hyposmotic Swelling in Rainbow Trout Red Blood Cells

BACKGROUND/AIMS: The osmolytes involved in the volume regulation of hyposmotically-swollen fish cells are well identified. However, if a coordination and adjustments of their fluxes are obvious, few studies have clearly illustrated these aspects. METHODS: Trout red blood cells volume variations were estimated from water contents obtained by a gravimetric method. Intracellular K+ and Na+ contents, and Cl- content of haemolysed cells were determined by photometry and colorimetry, respectively. The taurine contribution to cell volume regulation was calculated from the net changes of water, K+, Cl- and Na+ contents. The intracellular pH was calculated from the chloride distribution across the cells membranes according to the Donnan equilibrium. RESULTS: Cells responses to a rapid change (from 296 to 176 mOsm.kg-1) of the saline osmolality were examined in three conditions designed to not impact (Hypo. I) or to reduce the K+ (Hypo. II) and Cl- (Hypo. III) contributions to the volume regulation. Hypo. I condition caused an immediate increase in water content, followed by a 90 min. full regulation, concomitant with gradual lowering of K+ and Cl- contents and a surprising increase in Na+ content. Hypo. II and III conditions showed a partial and complete volume regulation, respectively. This was made possible by an increase in the taurine involvement. These experiments allowed to confirm that K+ and Cl- were released via KCl cotransport and by separate channels. The comparison of Hypo. I and III conditions led to the observation that the partially amiloride-sensitive Na+ influx is proportional to the taurine efflux; the latter being sustained mainly by a Na+/taurine cotransport. The Hypo. II condition was suitable for the (Na+/K+)ATPase activity inhibition. This effect could explain the observed lack of Na+ uptake, the consecutive depletion of intracellular taurine stock and the incomplete volume regulation. Finally, the results support the importance of taurine in pH control under Hypo. I (physiologic) condition. The alkalosis observed in Hypo. II and III conditions were the consequences of changes in the salines compositions, not of physiologic adjustments. CONCLUSION: The regulatory volume decrease process of trout RBCs is complex and adjustable through coordinated osmolytes movements. The obliged decrease in K+ and/or Cl- contributions stimulates taurine and Na+ pathways. This study highlights the importance of taurine as a compensatory variable in cell volume regulation and explains for the first time the significance of the Na+ uptake during this process

Comparison of Isotonic Activation of Cell Volume Regulation in Rat Peritoneal Mesothelial Cells and in Kidney Outer Medullary Collecting Duct Principal Cells

In disease states, mesothelial cells are exposed to variable osmotic conditions, with high osmotic stress exerted by peritoneal dialysis (PD) fluids. They contain unphysiologically high concentrations of glucose and result in major peritoneal membrane transformation and PD function loss. The effects of isotonic entry of urea and myo-inositol in hypertonic (380 mOsm/kg) medium on the cell volume of primary cultures of rat peritoneal mesothelial cells and rat kidney outer medullary collecting duct (OMCD) principal cells were studied. In hypertonic medium, rat peritoneal mesothelial cells activated a different mechanism of cell volume regulation in the presence of isotonic urea (100 mM) in comparison to rat kidney OMCD principal cells. In kidney OMCD cells inflow of urea into the shrunken cell results in restoration of cell volume. In the shrunken peritoneal mesothelial cells, isotonic urea inflow caused a small volume increase and activated regulatory volume decrease (RVD). Isotonic myo-inositol activated RVD in hypertonic medium in both cell types. Isotonic application of both osmolytes caused a sharp increase of intracellular calcium both in peritoneal mesothelial cells and in kidney OMCD principal cells. In conclusion, peritoneal mesothelial cells exhibit RVD mechanisms when challenged with myo-inositol and urea under hyperosmolar isotonic switch from mannitol through involvement of calcium-dependent control. Myo-inositol effects were identical with the ones in OMCD principal cells whereas urea effects in OMCD principal cells led to no RVD induction.

Abstract P368: Caveolin-3 Prevents Swelling-induced Cell Lysis Via Regulation Of I Cl,swell Expression And Activity

Background: Caveolae membrane structures harbor mechanosensitive chloride channels (MCCs) which form a swelling-activated chloride current ( I Cl,swell ) and play an important role in cell volume regulation and mechano-electrical signal transduction. However, the role of muscle-specific caveolar scaffolding protein caveolin-3 (Cav3) in regulation of MCCs expression, activity, and contribution to cell viability in response to mechanical stress remains unclear. We hypothesized that Cav3-based mechano-protection is enabled by complimentary expression of MCCs. Methods and Results: Experiments were performed on native (Cav3-) and Cav3-transfected (Cav3+) HEK-293 cells. Cell stretch was mimicked by light (220 mOsM) or extreme hypoosmotic swelling (<20mOsM). Cav3+ HEK-293 cells were significantly resistant to extreme hypotonic solutions (15 minute incubation) compared to Cav3- HEK-293 cells, and this mechano-protection was significantly reduced when exposed to I Cl,swell selective inhibitor DCPIB (1 μM). We found that three MCCs (ClC-2, ClC-3, and SWELL1, also known as LRRC8A) contain caveolin-binding motifs in their structure, indicating their possible localization in caveolae structures. Co-IP analysis confirmed association of SWELL1 with Cav3. Interestingly, Cav3+ HEK-293 cells showed a significant (by 2-fold) increase of SWELL1 protein level, while ClC-2/3 protein levels remained unchanged. This was accompanied by a 2-fold increase of I Cl,swell , but no change in mRNA expression levels. FRET analysis showed a <10 nm membrane and intracellular association between Cav3 and tested MCCs. Furthermore, Cav3/SWELL1 membrane FRET efficiency was halved in light hypoosmotic solution, as well as after disruption of caveolae structures via cholesterol depletion by 1-hour treatment with 10 μM methyl-β-cyclodextrin. Cav3/ClC-2/3 average membrane FRET efficiency remained unchanged in hypotonic solution. Conclusions: We concluded that of MCCs tested, SWELL1 abundance and activity is regulated by Cav3 and that their association relies on membrane tension and caveolae integrity. The present study highlights the mechano-protective properties of Cav3 which are partially facilitated by complimentary SWELL1 expression and activity.