Monitoring ER/SR Calcium Release with the Targeted Ca2+ Sensor CatchER

Establishment and evaluation of targeted molecular screening model for the ryanodine receptor or sarco/endoplasmic reticulum calcium ATPase

BACKGROUD

Endoplasmic reticulum/sarcoplasmic reticulum (ER/SR) is crucial for maintaining intracellular calcium homeostasis due to the calcium-signaling-related proteins on its membrane. While ryanodine receptors (RyR) on insect ER/SR membranes are well-known as targets for diamide insecticides, little is known about other calcium channels. Given the resistance of diamide insecticides, the establishment of molecular screening models targeting RyR or sarco/endoplasmic reticulum calcium ATPase (SERCA) is conducive to the discovery of new insecticidal molecules.

RESULTS

The morphological features of Mythimna separata SR have closed vesicles with integrity and high density. The 282 proteins in the SR component contained RyR and SERCA. A measurement model for the release and uptake of calcium was successfully established by detecting calcium ions outside the SR membrane using a fluorescence spectrophotometer. In vitro testing systems using SR vesicles found that diamide insecticides could activate dose-dependently RyR, with EC50 values of 0.14 μM (Chlorantraniliprole), 0.21 μM (Flubendiamide), and 0.57 μM (Cyantraniliprole), respectively. However, dantrolene inhibited RyR-mediated calcium release with an IC50 value of 353.9 μM, suggesting that dantrolene can weakly antagonize RyR. Moreover, cyclopiazonic acid significantly reduced the enzyme activity and calcium uptake capacity of SERCA. On the contrary, CDN1163 markedly activated the enzyme activity and improved the calcium transport capacity of SERCA.

CONCLUSIONS

SR vesicles can be used to study the function of unknown proteins on the SR membranes, as well as for high-throughput screening of highly active compounds targeting RyR or SERCA. © 2024 Society of Chemical Industry.

Ca2+ Signalling Differentially Regulates Germ-Tube Formation and Cell Fusion in Fusarium oxysporum

Fusarium oxysporum is an important plant pathogen and an emerging opportunistic human pathogen. Germination of conidial spores and their fusion via conidial anastomosis tubes (CATs) are significant events during colony establishment in culture and on host plants and, hence, very likely on human epithelia. CAT fusion exhibited by conidial germlings of Fusarium species has been postulated to facilitate mitotic recombination, leading to heterokaryon formation and strains with varied genotypes and potentially increased virulence. Ca²⁺ signalling is key to many of the important physiological processes in filamentous fungi. Here, we tested pharmacological agents with defined modes of action in modulation of the mammalian Ca²⁺ signalling machinery for their effect on germination and CAT-mediated cell fusion in F. oxysporum. We found various drug-specific and dose-dependent effects. Inhibition of calcineurin by FK506 or cyclosporin A, as well as chelation of extracellular Ca²⁺ by BAPTA, exclusively inhibit CAT induction but not germ-tube formation. On the other hand, inhibition of Ca2+ channels by verapamil, calmodulin inhibition by calmidazolium, and inhibition of mitochondrial calcium uniporters by RU360 inhibited both CAT induction and germ-tube formation. Thapsigargin, an inhibitor of mammalian sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA), partially inhibited CAT induction but had no effect on germ-tube formation. These results provide initial evidence for morphologically defining roles of Ca²⁺-signalling components in the early developmental stages of F. oxysporum colony establishment—most notably, the indication that calcium ions act as self-signalling molecules in this process. Our findings contribute an important first step towards the identification of Ca²⁺ inhibitors with fungas-specific effects that could be exploited for the treatment of infected plants and humans.

Extracellular calcium alters calcium-sensing receptor network integrating intracellular calcium-signaling and related key pathway

G-protein-coupled receptors (GPCRs) are a target for over 34% of current drugs. The calcium-sensing receptor (CaSR), a family C GPCR, regulates systemic calcium (Ca²⁺) homeostasis that is critical for many physiological, calciotropical, and noncalciotropical outcomes in multiple organs. However, the mechanisms by which extracellular Ca²⁺ (Ca²⁺_ex) and the CaSR mediate networks of intracellular Ca²⁺-signaling and players involved throughout the life cycle of CaSR are largely unknown. Here we report the first CaSR protein–protein interactome with 94 novel putative and 8 previously published interactors using proteomics. Ca²⁺_ex promotes enrichment of 66% of the identified CaSR interactors, pertaining to Ca²⁺ dynamics, endocytosis, degradation, trafficking, and primarily to protein processing in the endoplasmic reticulum (ER). These enhanced ER-related processes are governed by Ca²⁺_ex-activated CaSR which directly modulates ER-Ca²⁺ (Ca²⁺_ER), as monitored by a novel ER targeted Ca²⁺-sensor. Moreover, we validated the Ca²⁺_ex dependent colocalizations and interactions of CaSR with ER-protein processing chaperone, 78-kDa glucose regulated protein (GRP78), and with trafficking-related protein. Live cell imaging results indicated that CaSR and vesicle-associated membrane protein-associated A (VAPA) are inter-dependent during Ca²⁺_ex induced enhancement of near-cell membrane expression. This study significantly extends the repertoire of the CaSR interactome and reveals likely novel players and pathways of CaSR participating in Ca²⁺_ER dynamics, agonist mediated ER-protein processing and surface expression.

Optimizing Calcium Detection Methods in Animal Systems: A Sandbox for Synthetic Biology

Since the 1970s, the emergence and expansion of novel methods for calcium ion (Ca2+) detection have found diverse applications in vitro and in vivo across a series of model animal systems. Matched with advances in fluorescence imaging techniques, the improvements in the functional range and stability of various calcium indicators have significantly enhanced more accurate study of intracellular Ca2+ dynamics and its effects on cell signaling, growth, differentiation, and regulation. Nonetheless, the current limitations broadly presented by organic calcium dyes, genetically encoded calcium indicators, and calcium-responsive nanoparticles suggest a potential path toward more rapid optimization by taking advantage of a synthetic biology approach. This engineering-oriented discipline applies principles of modularity and standardization to redesign and interrogate endogenous biological systems. This review will elucidate how novel synthetic biology technologies constructed for eukaryotic systems can offer a promising toolkit for interfacing with calcium signaling and overcoming barriers in order to accelerate the process of Ca2+ detection optimization.

Channels that Cooperate with TRPV4 in the Brain

Transient receptor potential vanilloid 4 (TRPV4) is a nonselective Ca²⁺-permeable cation channel that is a member of the TRP channel family. It is clear that TRPV4 channels are broadly expressed in the brain. As they are expressed on the plasma membrane, they interact with other channels and play a crucial role in nervous system activity. Under some pathological conditions, TRPV4 channels are upregulated and sensitized via cellular signaling pathways, and this can cause nervous system diseases. In this review, we focus on receptors that cooperate with TRPV4, including large-conductance Ca²⁺-activated K⁺(BKca) channels, N-methyl-D-aspartate receptors (NMDARs), α-amino-3-hydroxy-5-methyl-4-isoxazole-propionate receptors (AMPARs), inositol 1,4,5-trisphosphate receptors (IP3Rs), ryanodine receptors (RyRs), aquaporin 4 (AQP4), and other potential cooperative receptors in the brain. The data demonstrate how these channels work together to cause nervous system diseases under pathological conditions. The aim of this review was to discuss the receptors and signaling pathways related to TRPV4 based on recent data on the important physiological functions of TRPV4 channels to provide new clues for future studies and prospective therapeutic targets for related brain diseases.

Design of Calcium-Binding Proteins to Sense Calcium

Calcium controls numerous biological processes by interacting with different classes of calcium binding proteins (CaBP’s), with different affinities, metal selectivities, kinetics, and calcium dependent conformational changes. Due to the diverse coordination chemistry of calcium, and complexity associated with protein folding and binding cooperativity, the rational design of CaBP’s was anticipated to present multiple challenges. In this paper we will first discuss applications of statistical analysis of calcium binding sites in proteins and subsequent development of algorithms to predict and identify calcium binding proteins. Next, we report efforts to identify key determinants for calcium binding affinity, cooperativity and calcium dependent conformational changes using grafting and protein design. Finally, we report recent advances in designing protein calcium sensors to capture calcium dynamics in various cellular environments.

IP3R and RyR channels are involved in traffic-related PM2.5-induced disorders of calcium homeostasis

Traffic-related PM_2.5 can result in immune system damage and diseases; however, the possible mechanism of its effect remains unclear. Calcium (Ca²⁺) is a critical signaling molecule in a variety of cells. Indeed, Ca²⁺ is involved in numerous basic functions, including cell growth and death. In this study, Jurkat T cells were used to explore the possible mechanisms of PM_2.5-elicited intracellular Ca²⁺signal responses. The results indicate that PM_2.5 could raise the level of intracellular Ca²⁺ concentration ([Ca²⁺]i). The [Ca²⁺]i in Jurkat T cells significantly decreased after treatment with heparin as an inhibitor of inositol trisphosphate receptors (IP3 R), or procaine as an inhibitor of ryanodine receptors (RyR). The expression of calmodulin (CAM) protein decreased in a time-dependent manner after exposure to PM_2.5, whereas the activity of Ca²⁺-Mg²⁺-ATPase seemed to show a slight drop trend after exposure to PM_2.5. Our findings demonstrate that PM_2.5 stimulation to Jurkat T cells would result in an increase in [Ca²⁺]i, which is modulated by IP3 R and RyR, as well as CAM.