350 research outputs found
Calcium signalling pathways in prostate cancer initiation and progression
No full textCancer cells proliferate, differentiate and migrate by repurposing physiological signalling mechanisms. In particular, altered calcium signalling is emerging as one of the most widespread adaptations in cancer cells. Remodelling of calcium signalling promotes the development of several malignancies, including prostate cancer. Gene expression data from in vitro, in vivo and bioinformatics studies using patient samples and xenografts have shown considerable changes in the expression of various components of the calcium signalling toolkit during the development of prostate cancer. Moreover, preclinical and clinical evidence suggests that altered calcium signalling is a crucial component of the molecular re-programming that drives prostate cancer progression. Evidence points to calcium signalling re-modelling, commonly involving crosstalk between calcium and other cellular signalling pathways, underpinning the onset and temporal progression of this disease. Discrete alterations in calcium signalling have been implicated in hormone-sensitive, castration-resistant and aggressive variant forms of prostate cancer. Hence, modulation of calcium signals and downstream effector molecules is a plausible therapeutic strategy for both early and late stages of prostate cancer. Based on this premise, clinical trials have been undertaken to establish the feasibility of targeting calcium signalling specifically for prostate cancer. [Abstract copyright: © 2023. Springer Nature Limited.
The cellular concentration of Bcl-2 determines its pro- or anti-apoptotic effect
No full textBcl-2 is an oncoprotein that is widely known to promote cell survival by inhibiting apoptosis. We explored the consequences of different expression paradigms on the cellular action of Bcl-2. Using either transient or stable transfection combined with doxycycline-inducible expression, we titrated the cellular concentration of Bcl-2. With each expression paradigm Bcl-2 was correctly targeted to the endoplasmic reticulum and mitochondria. However, with protocols that generated the greatest cellular concentrations of Bcl-2 the structure of these organelles was dramatically altered. The endoplasmic reticulum appeared to be substantially fragmented, whilst mitochondria coalesced into dense perinuclear structures. Under these conditions of high Bcl-2 expression, cells were not protected from pro-apoptotic stimuli. Rather Bcl-2 itself caused a significant amount of spontaneous cell death, and sensitised the cells to apoptotic agents such as staurosporine or ceramide. We observed a direct correlation between Bcl-2 concentration and spontaneous apoptosis. Expression of calbindin, a calcium buffering protein, or an enzyme that inhibited inositol 1,4,5-trisphosphate-mediated calcium release, significantly reduced cell death caused by Bcl-2 expression. We further observed that high levels of Bcl-2 expression caused lipid peroxidation and that the deleterious effects of Bcl-2 could be abrogated by the reactive oxygen species (ROS) scavenger Trolox. When stably expressed at low levels, Bcl-2 did not corrupt organelle structure or trigger spontaneous apoptosis. Rather, it protected cells from pro-apoptotic stimuli. These data reveal that high cellular concentrations of Bcl-2 lead to a calcium- and ROS-dependent induction of death. Selection of the appropriate expression paradigm is therefore crucial when investigating the biological role of Bcl-2. (C) 2007 Elsevier Ltd. All rights reserved
Prognostic relevance of a T-type calcium channels gene signature in solid tumours: A correlation ready for clinical validation.
No full textT-type calcium channels (TTCCs) mediate calcium influx across the cell membrane. TTCCs regulate numerous physiological processes including cardiac pacemaking and neuronal activity. In addition, they have been implicated in the proliferation, migration and differentiation of tumour tissues. Although the signalling events downstream of TTCC-mediated calcium influx are not fully elucidated, it is clear that variations in the expression of TTCCs promote tumour formation and hinder response to treatment.We examined the expression of TTCC genes (all three subtypes; CACNA-1G, CACNA-1H and CACNA-1I) and their prognostic value in three major solid tumours (i.e. gastric, lung and ovarian cancers) via a publicly accessible database.In gastric cancer, expression of all the CACNA genes was associated with overall survival (OS) among stage I-IV patients (all p<0.05). By combining the three potential biomarkers, a TTCC signature was developed, which retained a significant association with OS both in stage IV and stage I-III patients. In lung and ovarian cancer, association with OS was also significant when all tumour stages were considered, but was partly lost or inconclusive after splitting cases into localized and metastatic subsets.Alterations in CACNA gene expression are linked to tumour prognosis. Gastric cancer represents the most promising setting for further evaluation
Calcium signalling: Ringing changes to the ‘bell-shaped curve’
No full textAbstractThe ‘bell-shaped’ curve relating cytosolic Ca2+ concentration to IP3 receptor activation is considered important in the generation of the complex Ca2+ signals seen inside many cells. But recent findings suggest this bimodal relationship is not always evident and may not apply to some IP3 receptor isoforms
Tissue Specificity: Store-Operated Ca<sup>2+</sup> Entry in Cardiac Myocytes
No full textCalcium (Ca2+) is a key regulator of cardiomyocyte contraction. The Ca2+ channels, pumps, and exchangers responsible for the cyclical cytosolic Ca2+ signals that underlie contraction are well known. In addition to those Ca2+ signaling components responsible for contraction, it has been proposed that cardiomyocytes express channels that promote the influx of Ca2+ from the extracellular milieu to the cytosol in response to depletion of intracellular Ca2+ stores. With non-excitable cells, this store-operated Ca2+ entry (SOCE) is usually easily demonstrated and is essential for prolonging cellular Ca2+ signaling and for refilling depleted Ca2+ stores. The role of SOCE in cardiomyocytes, however, is rather more elusive. While there is published evidence for increased Ca2+ influx into cardiomyocytes following Ca2+ store depletion, it has not been universally observed. Moreover, SOCE appears to be prominent in embryonic cardiomyocytes but declines with postnatal development. In contrast, there is overwhelming evidence that the molecular components of SOCE (e.g., STIM, Orai, and TRPC proteins) are expressed in cardiomyocytes from embryo to adult. Moreover, these proteins have been shown to contribute to disease conditions such as pathological hypertrophy, and reducing their expression can attenuate hypertrophic growth. It is plausible that SOCE might underlie Ca2+ influx into cardiomyocytes and may have important signaling functions perhaps by activating local Ca2+-sensitive processes. However, the STIM, Orai, and TRPC proteins appear to cooperate with multiple protein partners in signaling complexes. It is therefore possible that some of their signaling activities are not mediated by Ca2+ influx signals, but by protein-protein interactions
Calmidazolium and arachidonate activate a calcium entry pathway that is distinct from store-operated calcium influx in HeLa cells
No full textAgonists that deplete intracellular Ca2+ stores also activate Ca2+ entry, although the mechanism by which store release and Ca2+ influx are linked is unclear. A potential mechanism involves ‘store-operated channels’ that respond to depletion of the intracellular Ca2+ pool. Although SOCE (store-operated Ca2+ entry) has been considered to be the principal route for Ca2+ entry during hormonal stimulation of non-electrically excitable cells, recent evidence has suggested that alternative pathways activated by metabolites such as arachidonic acid are responsible for physiological Ca2+ influx. It is not clear whether such messenger-activated pathways exist in all cells, whether they are truly distinct from SOCE and which metabolites are involved. In the present study, we demonstrate that HeLa cells express two pharmacologically and mechanistically distinct Ca2+ entry pathways. One is the ubiquitous SOCE route and the other is an arachidonate-sensitive non-SOCE. We show that both these Ca2+ entry pathways can provide long-lasting Ca2+ elevations, but that the channels are not the same, based on their differential sensitivity to 2-aminoethoxydiphenyl borate, LOE-908 {(R,S)-(3,4-dihydro-6,7-dimethoxy-isochinolin-1-yl)-2-phenyl-N,N-di[2-(2,3,4-trimethoxyphenyl)ethyl]acetamid mesylate} and gadolinium. In addition, non-SOCE and not SOCE was permeable to strontium. Furthermore, unlike SOCE, the non-SOCE pathway did not require store depletion and was not sensitive to displacement of the endoplasmic reticulum from the plasma membrane using jasplakinolide or ionomycin pretreatment. These pathways did not conduct Ca2+ simultaneously due to the dominant effect of arachidonate, which rapidly curtails SOCE and promotes Ca2+ influx via non-SOCE. Although non-SOCE could be activated by exogenous application of arachidonate, the most robust method for stimulation of this pathway was application of the widely used calmodulin antagonist calmidazolium, due to its ability to activate phospholipase A2
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Quantal Ca<sup>2+</sup> release from InsP<sub>3</sub>-sensitive intracellular Ca<sup>2+</sup> stores
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Bcl-2 suppresses Ca<sup>2+</sup> release through inositol 1,4,5-trisphosphate receptors and inhibits Ca<sup>2+</sup> uptake by mitochondria without affecting ER calcium store content
No full textCell survival is promoted by the oncoprotein Bcl-2. Previous studies have established that one of the pro-survival actions of Bcl-2 is to reduce cellular fluxes of Ca2+ within cells. In particular, Bcl-2 has been demonstrated to inhibit the release of Ca2+ from the endoplasmic reticulum. However, the mechanism by which Bcl-2 causes reduced Ca2+ release is unclear. In the accompanying paper [C.J. Hanson, M.D. Bootman, C.W. Distelhorst, T. Maraldi, H.L. Roderick, The cellular concentration of Bcl-2 determines its pro- or anti-apoptotic effect, Cell Calcium (2008)], we described that only stable expression of Bcl-2 allowed it to work in a pro-survival manner whereas transient expression did not. In this study, we have employed HEK-293 cells that stably express Bcl-2, and which are, therefore, protected from pro-apoptotic stimuli, to examine the effect of Bcl-2 on Ca2+ homeostasis and signalling. We observed that Bcl-2 expression decreased the Ca2+ responses of cells induced by application of submaximal agonist concentrations. Whereas, decreasing endogenous Bcl-2 concentration using siRNA potentiated Ca2+ responses. Furthermore, we found that Bcl-2 expression reduced mitochondrial Ca2+ uptake by raising the threshold cytosolic Ca2+ concentration required to activate sequestration. Using a number of different assays, we did not find any evidence for reduction of endoplasmic reticulum luminal Ca2+ in our Bcl-2-expressing cells. Indeed, we observed that Bcl-2 served to preserve the content of the agonist-sensitive Ca2+ pool. Endogenous Bcl-2 was found to interact with inositol 1,4,5-trisphosphate receptors (InsP3Rs) in our cells, and to modify the profile of InsP3R expression. Our data suggest that the presence of Bcl-2 in the proteome of cells has multiple effects on agonist-mediated Ca2+ signals, and can abrogate responses to submaximal levels of stimulation through direct control of InsP3Rs
Calcium signalling and regulation of cell function
No full textThe calcium ion (Ca2+) is a versatile intracellular messenger. It provides dynamic regulation of vast array of cellular processes such as gene transcription, differentiation and contraction. Ca2+ signals range from microsecond, nanoscopic events to intercellular waves lasting for many seconds. This diversity of Ca2+ signals arises from the wide assortment of Ca2+ transport and Ca2+ buffering processes employed by cells. Additional diversity in Ca2+ signalling stems from the ability of cells to utilise different sources of Ca2+. The cytosol is the principal Ca2+ signalling compartment. When Ca2+ ions enter the cytosol they interact with numerous Ca2+-binding proteins, thereby leading to activation, or inhibition, of cellular processes. Specificity is achieved by regulating the spatial and kinetic properties of Ca2+ signal. In this way, many concurrent Ca2+-sensitive cellular processes can be discretely regulated. A number of pathologies have been related to the breakdown of cellular Ca2+ homoeostasis or to aberrant Ca2+ signalling
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