Ratiometric and nonratiometric Ca2+ indicators for the assessment of intracellular free Ca2+ in a breast cancer cell line using a fluorescence microplate reader

Targeting altered calcium homeostasis and uncoupling protein-2 promotes sensitivity in drug-resistant breast cancer cells

Metastatic breast cancer has the highest mortality rate among women owing to its poor clinical outcomes. Metastatic tumors pose challenges for treatment through conventional surgery or radiotherapy because of their diverse organ localization and resistance to various cytotoxic agents. Chemoresistance is a significant obstacle to effective breast cancer treatment owing to cancer's heterogeneous nature. Abnormalities in intracellular calcium signaling, coupled with altered mitochondrial metabolism, play a significant role in facilitating drug resistance and contribute to therapy resistance. Uncoupling protein-2 (UCP2) is considered as a marker of chemoresistance and is believed to play a major role in promoting metabolic shifts and tumor metastasis. In this context, it is imperative to understand the roles of altered calcium signaling and metabolic switching in the development of chemotherapeutic resistance. This study investigates the roles of UCP2 and intracellular calcium signaling (Ca2+ ) in promoting chemoresistance against cisplatin. Additionally, we explored the effectiveness of combining genipin (GP, a compound that reverses UCP2-mediated chemoresistance) and thapsigargin (TG, a calcium signaling modulator) in treating highly metastatic breast cancers. Our findings indicate that both aberrant Ca2+ signaling and metabolic shifts in cancer cells contribute to developing drug-resistant phenotypes, and the combination treatment of GP and TG significantly enhances drug sensitivity in these cells. Collectively, our study underscores the potential of these drug combinations as an effective approach to overcome drug resistance in chemoresistant cancers.

Cryptotanshinone-Induced p53-Dependent Sensitization of Colon Cancer Cells to Apoptotic Drive by Regulation of Calpain and Calcium Homeostasis

Over-expression of calpains in tumor tissues can be associated with cancer progression. Thus, inhibition of calpain activity using specific inhibitors has become a novel approach to control tumor growth. In this study, the anticancer potential of cryptotanshinone in combination with calpain inhibitor had been investigated in colon cancer cells and tumor xenograft. Cryptotanshinone elicited an initial endoplasmic reticular (ER) stress response, whereas prolonged stress would result in the promotion of apoptosis. It was then discovered that cryptotanshinone could cause rapid and sustained increase in cytosolic calcium in colon cancer cells accompanied by early GRP78 overexpression, which could be attenuated by pre-treatment of the calcium chelator BAPTA-AM. Cryptotanshinone also facilitated an early increase in calpain activity, which could be blocked by BAPTA-AM or the calpain inhibitor PD150606. A dynamic interaction between GRP78 and calpain during the action of cryptotanshinone was unveiled. This together with the altered NF-[Formula: see text]B signaling could be abolished by calpain inhibitor. GRP78 knockdown increased the sensitivity of cancer cells to cryptotanshinone-evoked apoptosis and reduction of cancer cell colony formation. Such sensitization of drug action had been confirmed to be p53-dependent by using p53-mutated (HT-29) and p53-deficient (HCT116 p53^-∕-) cells. The synergistic antitumor effect of cryptotanshinone and calpain inhibitor was further exhibited in vivo. Taken together, findings in this study exemplify a new chemotherapeutic regimen comprising cryptotanshinone and calpain inhibitor by regulation of calpain and calcium homeostasis. This has provided us with new insights in the search of a potential target-specific neoadjuvant therapy against colon cancer.

C-Reactive Protein Causes Blood Pressure Drop in Rabbits and Induces Intracellular Calcium Signaling

Systemic diseases characterized by elevated levels of C-reactive protein (CRP), such as sepsis or systemic inflammatory response syndrome, are usually associated with hardly controllable haemodynamic instability. We therefore investigated whether CRP itself influences blood pressure and heart rate. Immediately after intravenous injection of purified human CRP (3.5 mg CRP/kg body weight) into anesthetized rabbits, blood pressure dropped critically in all animals, while control animals injected with bovine serum albumin showed no response. Heart rate did not change in either group. Approaching this impact on a cellular level, we investigated the effect of CRP in cell lines expressing adrenoceptors (CHO-α1A and DU-145). CRP caused a Ca²⁺ signaling being dependent on the CRP dose. After complete activation of the adrenoceptors by agonists, CRP caused additional intracellular Ca²⁺ mobilization. We assume that CRP interacts with hitherto unknown structures on the surface of vital cells and thus interferes with the desensitization of adrenoceptors.

Ca2+ mediates extracellular vesicle biogenesis through alternate pathways in malignancy

Extracellular vesicles (EVs) are small membrane vesicles that serve as important intercellular signalling intermediaries in both malignant and non-malignant cells. For EVs formed by the plasma membrane, their biogenesis is characterized by an increase in intracellular calcium followed by successive membrane and cytoskeletal changes. EV-production is significantly higher in malignant cells relative to non-malignant cells and previous work suggests this is dependent on increased calcium mobilization and activity of calpain. However, calcium-signalling pathways involved in malignant and non-malignant EV biogenesis remain unexplored. Here we demonstrate; malignant cells have high basal production of plasma membrane EVs compared to non-malignant cells and this is driven by a calcium–calpain dependent pathway. Resting vesiculation in malignant cells occurs via mobilization of calcium from endoplasmic reticulum (ER) stores rather than from the activity of plasma membrane calcium channels. In the event of ER store depletion however, the store-operated calcium entry (SOCE) pathway is activated to restore ER calcium stores. Depleting both ER calcium stores and blocking SOCE, inhibits EV biogenesis. In contrast, calcium signalling pathways are not activated in resting non-malignant cells. Consequently, these cells are relatively low vesiculators in the resting state. Following cellular activation however, an increase in cytosolic calcium and activation of calpain increase in EV biogenesis. These findings contribute to furthering our understanding of extracellular vesicle biogenesis. As EVs are key mediators in the intercellular transfer of deleterious cancer traits such as cancer multidrug resistance (MDR), understanding the molecular mechanisms governing their biogenesis in cancer is the crucial first step in finding novel therapeutic targets that circumvent EV-mediated MDR.

Ginsenoside Rg5 induces apoptosis in human esophageal cancer cells through the phosphoinositide‑3 kinase/protein kinase B signaling pathway

The role of ginsenoside in the prevention of cancer has been well established. Ginsenoside Rg5 is one of the main components isolated from red ginseng, which has been demonstrated to have anti-tumor effects by inhibiting cell proliferation and causing DNA damage. However, the role of ginsenoside Rg5 and its molecular mechanisms remain unclear in human esophageal cancer. In the present study, Rg5 was investigated as a novel drug for the chemotherapy of esophageal cancer in in vitro experiments. Esophageal cancer Eca109 cells were exposed to various concentrations of ginsenoside Rg5 (0–32 µΜ) for 24 h. Subsequent cell proliferation assays demonstrated that treatment with ginsenoside Rg5 resulted in the dose-dependent inhibition of proliferation, while a significant increase in apoptotic rate and increased activities of caspase-3, −8 and −9 were observed. In addition, the mitochondrial membrane potential was decreased and the cytoplasmic free calcium level increased following treatment with ginsenoside Rg5. Furthermore, the expression of B-cell lymphoma 2 and phosphorylated-protein kinase B (p-Akt) decreased. The specific phosphoinositide-3 kinase (PI3K) inhibitor LY294002 promoted this effect, while insulin-like growth factor-1, a specific PI3K activator, inhibited this action. Taken together, the results suggested that ginsenoside Rg5 may have a tumor-suppressive effect on esophageal cancer by promoting apoptosis and may be associated with the downregulation of the PI3K/Akt signaling pathway.

Effects of non-euphoric plant cannabinoids on muscle quality and performance of dystrophic mdx mice

BACKGROUND AND PURPOSE

Duchenne muscular dystrophy (DMD), caused by dystrophin deficiency, results in chronic inflammation and irreversible skeletal muscle degeneration. Moreover, the associated impairment of autophagy greatly contributes to the aggravation of muscle damage. We explored the possibility of using non-euphoric compounds present in Cannabis sativa, cannabidiol (CBD), cannabidivarin (CBDV) and tetrahydrocannabidivarin (THCV), to reduce inflammation, restore functional autophagy and positively enhance muscle function in vivo.

EXPERIMENTAL APPROACH

Using quantitative PCR, western blots and [Ca²⁺ ]_i measurements, we explored the effects of CBD and CBDV on the differentiation of both murine and human skeletal muscle cells as well as their potential interaction with TRP channels. Male dystrophic mdx mice were injected i.p. with CBD or CBDV at different stages of the disease. After treatment, locomotor tests and biochemical analyses were used to evaluate their effects on inflammation and autophagy.

KEY RESULTS

CBD and CBDV promoted the differentiation of murine C2C12 myoblast cells into myotubes by increasing [Ca²⁺ ]_i mostly via TRPV1 activation, an effect that undergoes rapid desensitization. In primary satellite cells and myoblasts isolated from healthy and/or DMD donors, not only CBD and CBDV but also THCV promoted myotube formation, in this case, mostly via TRPA1 activation. In mdx mice, CBD (60 mg·kg^-1 ) and CBDV (60 mg·kg^-1 ) prevented the loss of locomotor activity, reduced inflammation and restored autophagy.

CONCLUSION AND IMPLICATIONS

We provide new insights into plant cannabinoid interactions with TRP channels in skeletal muscle, highlighting a potential opportunity for novel co-adjuvant therapies to prevent muscle degeneration in DMD patients.

LINKED ARTICLES

This article is part of a themed section on 8^th European Workshop on Cannabinoid Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.10/issuetoc.

Glucotoxicity results in apoptosis in H9c2 cells via alteration in redox homeostasis linked mitochondrial dynamics and polyol pathway and possible reversal with cinnamic acid

Several mechanisms have been proposed for the heart dysfunction during hyperglycemia. The aim of the present in vitro study is to elucidate the role of alterations in redox homeostasis in the induction of apoptosis during hyperglycemia in H9c2 cells via dysfunction in mitochondria and polyol pathway and evaluation of the beneficial effect of cinnamic acid against the same. The H9c2 cells were incubated with 33 mM glucose for 48 h to simulate the diabetic condition. Cell injury was confirmed with a significant increase of atrial natriuretic peptide and lactate dehydrogenase release. Alterations in the innate antioxidant system, polyol pathway, mitochondrial integrity, dynamics and apoptosis were investigated. Hyperglycemic insult has significantly affected redox homeostasis via depletion of superoxide dismutase, glutathione and enhanced reactive oxygen species generation. It also caused dysregulation in mitochondrial dynamics (fusion, fission proteins), dissipation of mitochondrial transmembrane potential and increased sorbitol accumulation. Finally, apoptosis was observed with upregulation of Bax, activation of caspase-3 and downregulation of Bcl-2. Cinnamic acid cotreatment increased the innate antioxidant status, improved mitochondrial function and prevented apoptosis in H9c2 cardiomyoblasts. Moreover, this in vitro model is found to be ideal for the elucidation of mechanisms at the cellular and molecular level of any physiological, pharmacological and toxicological incidents in H9c2 cells.

Mephebrindole, a synthetic indole analog coordinates the crosstalk between p38MAPK and eIF2α/ATF4/CHOP signalling pathways for induction of apoptosis in human breast carcinoma cells

The efficacy of cancer chemotherapeutics is limited by side effects resulting from narrow therapeutic windows between the anticancer activity of a drug and its cytotoxicity. Thus identification of small molecules that can selectively target cancer cells has gained major interest. Cancer cells under stress utilize the Unfolded protein response (UPR) as an effective cell adaptation mechanism. The purpose of the UPR is to balance the ER folding environment and calcium homeostasis under stress. If ER stress is prolonged, tumor cells undergo apoptosis. In the present study we demonstrated an 3,3'-(Arylmethylene)-bis-1H-indole (AMBI) derivative 3,3'-[(4-Methoxyphenyl) methylene]-bis-(5-bromo-1H-indole), named as Mephebrindole (MPB) as an effective anti-cancer agent in breast cancer cells. MPB disrupted calcium homeostasis in MCF7 cells which triggered ER stress development. Detailed evaluations revealed that mephebrindole by activating p38MAPK also regulated GRP78 and eIF2α/ATF4 downstream to promote apoptosis. Studies extended to in vivo allograft mice models revalidated its anti-carcinogenic property thus highlighting the role of MPB as an improved chemotherapeutic option.

SERCA1 attenuates diaphragm relaxation and uptake rate of SERCA in rats with acute sepsis

The present study aimed to investigate the effects of acute sepsis on diaphragm contractility and relaxation, via examining the Ca2+‑uptake function of sarco/endoplasmic reticulum Ca2+ adenosine triphosphatase (SERCA), and the protein levels of SERCA1, SERCA2 and the ryanodine receptor (RyR) of the sarcoplasmic reticulum (SR). A sepsis rat model was established through cecal ligation and puncture (CLP). A total of 6 and 12 h following CLP, the isometric contractile and relaxation parameters of the diaphragm were measured. In addition, Ca2+ uptake and release from the SR, and the protein expression levels of SERCA1, SERCA2 and RyR in diaphragm muscle tissue were investigated. At 6 and 12 h post‑CLP, the diaphragm half‑relaxation time was prolonged and the maximum rate of tension decline was decreased and the Ca2+‑uptake function of SERCA was markedly reduced. The maximum rate of twitch force development, the maximal twitch and tetanic tension, and the release function of SR were decreased at 12 h post‑CLP. A total of 12 h following CLP, the protein expression levels of SERCA1 were significantly downregulated, and its activity was significantly reduced; conversely, the protein levels of SERCA2 remained unaltered. The present findings indicated that at the acute stage of sepsis induced by CLP the contractile and relaxation functions of the diaphragm were significantly compromised. The impairments in relaxation may be a result of the impaired uptake function of the SR and the downregulation in SERCA1 protein expression. Conversely, the compromised contractility may be a result of the impaired release function of the SR and the downregulation in RyR protein levels. This could provide some new insights into the treatment of sepsis. In acute stages of sepsis, the improvement of SERCA function could reduce the disequilibrium of calcium homeostasis to improve the critical illness myopathy and respiratory failure.

Effect of acute peritonitis on rocuronium-induced intraperitoneal pressure reduction and the uptake function of the sarcoplasmic reticulum

Previous studies have reported the incomplete relaxation effect of neuromuscular blockers on skeletal muscles in acute peritonitis (AP) and other inflammatory processes; however, the underlying mechanisms responsible for this effect have not yet been satisfactorily identified. The impaired removal of cytosolic Ca²⁺ through sarcoendoplasmic Ca²⁺-ATPase (SERCA) and defects in sarcoplasmic reticulum (SR) Ca²⁺ uptake are the major contributing factors to diastolic dysfunction. Previous studies on the effects of neuromuscular blockers have primarily focused on neuromuscular transmission. Because of the reduced calcium uptake in the SR itself, even when neuromuscular transmission is fully blocked, the muscle is not able to relax effectively. In the present study, the impact of AP on rocuronium-induced intraperitoneal pressure reduction and rectus abdominal muscle relaxation, and SERCA uptake function was investigated. AP was induced via gastric perforation and changes in the intraperitoneal pressure before and after the administration of rocuronium were recorded. Muscle contractile properties, uptake and release functions and SERCA activity in the rectus abdominal muscles of AP model rats were measured. The half-relaxation time in the AP group was significantly prolonged compared with that in the control group (P<0.01). The peak rate of SR Ca²⁺ uptake for whole muscle homogenates was significantly reduced (P<0.05) in AP model rats without reduction of the rate of Ca²⁺ release evoked through AgNO₃. In conclusion, gastric perforation-induced AP attenuates the intraperitoneal pressure-reducing effect of rocuronium, and AP induces diastolic dysfunction of the rectus abdominal muscle. The SR Ca²⁺-ATPase uptake rate was also reduced by AP.

[Lowered sarcoendoplasmic reticulum calcium uptake and diaphragmatic SERCA1 expression contribute to diaphragmatic contractile and relaxation dysfunction in septic rats]

OBJECTIVE

The explore the mechanism responsible for diaphragmatic contractile and relaxation dysfunction in a rat model of sepsis.

METHODS

Thirty-six adult male Sprague-Dawley rats were randomized equally into a sham-operated group and two model groups of sepsis induced by cecal ligation and puncture (CLP) for examination at 6 and 12 h following CLP (CLP-6 h and CLP-12 h groups). The parameters of diaphragm contractile and relaxation were measured, and the calcium uptake and release rates of the diaphragmatic sarcoendoplasmic reticulum (SR) and the protein expressions of SERCA1, SERCA2 and RyR in the diaphragmatic muscles were determined.

RESULTS

The half-relaxation time of the diaphragm was extended in both the CLP-6 h and CLP-12 h groups with significantly reduced maximum tension declinerate and the peek uptake rate of SERCA (P<0.01). Diaphragmatic maximum twitch force development rate, the maximal twitch, tetanus tensions and the peek release rate of SR decreased only at 12h after CLP (P<0.01). The expression levels of SERCA1 protein decreased significantly in the diaphragmatic muscles at 12h following CLP (P<0.01) while SERCA2 expression level and SERCA activity showed no significant changes.

CONCLUSION

In the acute stage of sepsis, both the contractile and relaxation functions of the diaphragm are impaired. Diaphragmatic relaxation dysfunction may result from reduced calcium uptake in the SR and a decreased level of SERCA1 in the diaphragmatic muscles.

[Application of the Ca2+ indicator fluo-3 and fluo-4 in the process of H2O2 induced apoptosis of A549 cell]

BACKGROUND AND OBJECTIVE

Lung cancer is a common malignant tumor all over the world, and Ca(2+) is a critical regulator for apoptosis of cancer cells. The monitoring of cytoplastic Ca(2+) level in real-time will contribute to further investigate the molecular mechanisms of apoptosis mediated by Ca2+ in lung cancer cells. To evaluate the Ca(2+) indicator fluo-3 and fluo-4 in the process of H2O2 induced the apoptosis of lung adenocarcinoma A549 cells. The cytoplastic Ca(2+) concentration ([Ca(2+)]i) was determined in real-time, and the correlations between [Ca(2+)]i and cell apoptosis were investigated. The differences in fluorescence intensity and measured value were compared between the two Ca(2+) indicators.

METHODS

Cells were loaded with the Ca(2+) indicator fluo-3 or fluo-4 for 1 h, and then stimulated with 50 mM H2O2. Laser scanning confocal microscope was applied to perform real-time monitoring on the variation of [Ca(2+)]i in selected cells. DAPI staining was used to observe apoptosis in H2O2 treated cells.

RESULTS

Our results showed that the fluorescence intensity of fluo-4 was stronger than that of fluo-3 in the same condition of dye concentration, loading time and image acquisition parameters before or after H2O2 stimulation. The cytoplastic [Ca(2+)]i was rapidly elevated in H2O2 stimulated A549 cells. The range of [Ca(2+)]i in selected cells loaded with fluo-3 was 112.2 nM-1,069.6 nM, and that in selected cells loaded with fluo-4 was 7.6 nM-505.4 nM. Moreover, the apoptotic rate was significantly increased in H2O2 treated cells, compared with untreated ones (P<0.01).

CONCLUSION

In summary, H2O2 promoted Ca(2+) release in A549 cells, and induced cell apoptosis. Ca(2+) indicator fluo-4 was probably more applicable to measure [Ca(2+)]i in cells with less content of Ca(2+).

Progastrin stimulates colonic cell proliferation via CCK2R- and β-arrestin-dependent suppression of BMP2

BACKGROUND & AIMS

Progastrin stimulates colonic mucosal proliferation and carcinogenesis through the cholecystokinin 2 receptor (CCK2R)-partly by increasing the number of colonic progenitor cells. However, little is known about the mechanisms by which progastrin stimulates colonic cell proliferation. We investigated the role of bone morphogenetic proteins (BMPs) in progastrin induction of colonic cell proliferation via CCK2R.

METHODS

We performed microarray analysis to compare changes in gene expression in the colonic mucosa of mice that express a human progastrin transgene, gastrin knockout mice, and C57BL/6 mice (controls); the effects of progastrin were also determined on in vitro colonic crypt cultures from cholecystokinin 2 receptor knockout and wild-type mice. Human colorectal and gastric cancer cells that expressed CCK2R were incubated with progastrin or Bmp2; levels of β-arrestin 1 and 2 were knocked down using small interfering RNAs. Cells were analyzed for progastrin binding, proliferation, changes in gene expression, and symmetric cell division.

RESULTS

The BMP pathway was down-regulated in the colons of human progastrin mice compared with controls. Progastrin suppressed transcription of Bmp2 through a pathway that required CCK2R and was mediated by β-arrestin 1 and 2. In mouse colonic epithelial cells, down-regulation of Bmp2 led to decreased phosphorylation of Smads1/5/8 and suppression of inhibitor of DNA binding 4. In human gastric and colorectal cancer cell lines, CCK2R was necessary and sufficient for progastrin binding and induction of proliferation; these effects were blocked when cells were incubated with recombinant Bmp2. Incubation with progastrin increased the number of CD44(+), bromodeoxyuridine+, and NUMB(+) cells, indicating an increase in symmetric divisions of putative cancer stem cells.

CONCLUSIONS

Progastrin stimulates proliferation in colons of mice and cultured human cells via CCK2R- and β-arrestin 1 and 2-dependent suppression of Bmp2 signaling. This process promotes symmetric cell division.

Molecular interaction and functional coupling between type 3 inositol 1,4,5-trisphosphate receptor and BKCa channel stimulate breast cancer cell proliferation

BACKGROUND

The implication of ion channels and inositol 1,4,5-trisphosphate (IP3)-induced Ca(2+) signalling (IICS) in the carcinogenesis processes, including deregulation of cell proliferation, migration and invasion, is increasingly studied. Studies from our laboratory have shown that type 3 IP3 receptor (IP3R3) and voltage- and Ca(2+)-dependent K(+) channels BKCa channels are involved in human breast cancer cell proliferation. In this context, we investigated the probable interaction between these two proteins (IP3R3 and BKCa channel) in normal and in breast cancer cells.

METHODS

MCF-7 and MCF-10A cell viability was measured by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)-assay in the presence or absence of adenosine triphosphate (ATP). Furthermore, cell-cycle analysis was carried out and cell cycle protein expression was examined by Western blotting. Immunocytochemistry and co-immunoprecipitation assays were used to check co-localisation of BKCa and IP3R3 and their molecular interaction. Finally, whole cell patch-clamp and Ca(2+) imaging were performed to assess the functional interaction.

RESULTS

Our results are in favour of a functional and a molecular coupling between IP3R3 and BKCa channel that is involved in MCF-7 proliferation. Indeed, ATP increased MCF-7 cell proliferation and this effect was impaired when the expression of BKCa and/or IP3R3 has been reduced by specific small interfering RNAs (siRNAs). Flow cytometry experiments showed that both siRNAs led to cell cycle arrest in the G0/G1 phase and these results were confirmed by the analysis of cell cycle protein expression. Specifically, BKCa and IP3R3 silencing decreased both cyclin-D1 and cyclin-dependent kinase 4 (CDK4) expression levels. Furthermore, ATP elicited a phospholipase C (PLC)-dependent elevation of internal Ca(2+) that triggered in turn an iberiotoxin (IbTx)- and a tetra-ethyl-ammonium (TEA)-sensitive membrane hyperpolarisation that was strongly reduced in the cells with silenced IP3R3 or BKCa. In the same way, intracellular application of Ins(2,4,5)P3 triggered an IbTx-sensitive membrane hyperpolarisation. Moreover, intracellular Ca(2+) chelation with 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) prevented ATP-induced BKCa activation. BKCa and IP3R3 also co-immunoprecipitated and this interaction seemed to occur in cholesterol-enriched microdomains. Conversely, in the normal breast cell line MCF-10A, neither ATP application nor BKCa silencing affected cell proliferation. Furthermore, IP3R3 and BKCa did not co-immunoprecipitate, suggesting the absence of a molecular coupling between BKCa and IP3R3 in the MCF-10A normal cell line.

CONCLUSION

Altogether, our results suggest a molecular and functional link between BKCa channel and IP3R3 in cancer cells. Our findings led us to propose this coupling between BKCa and IP3R3 as an important mechanism for tumour cell proliferation.

A method to measure myocardial calcium handling in adult Drosophila

RATIONALE

Normal cardiac physiology requires highly regulated cytosolic Ca(2+) concentrations and abnormalities in Ca(2+) handling are associated with heart failure. The majority of approaches to identifying the components that regulate intracellular Ca(2+) dynamics rely on cells in culture, mouse models, and human samples. However, a genetically robust system for unbiased screens of mutations that affect Ca(2+) handling remains a challenge.

OBJECTIVE

We sought to develop a new method to measure myocardial Ca(2+) cycling in adult Drosophila and determine whether cardiomyopathic fly hearts recapitulate aspects of diseased mammalian myocardium.

METHODS AND RESULTS

Using engineered transgenic Drosophila that have cardiac-specific expression of Ca(2+)-sensing fluorescent protein, GCaMP2, we developed methods to measure parameters associated with myocardial Ca(2+) handling. The following key observations were identified: (1) Control w(1118) Drosophila hearts have readily measureable Ca(2+)-dependent fluorescent signals that are dependent on L-type Ca(2+) channels and SR Ca(2+) stores and originate from rostral and caudal pacemakers. (2) A fly mutant, held-up(2) (hdp(2)), that has a point mutation in troponin I and has a dilated cardiomyopathic phenotype demonstrates abnormalities in myocardial Ca(2+) handling that include increases in the duration of the 50% rise in intensity to peak intensity, the half-time of fluorescence decline from peak, the full duration at half-maximal intensity, and decreases in the linear slope of decay from 80% to 20% intensity decay. (3) Hearts from hdp(2) mutants had reductions in caffeine-induced Ca(2+) increases and reductions in ryanodine receptor (RyR) without changes in L-type Ca(2+) channel transcripts in comparison with w(1118).

CONCLUSIONS

Our results show that the cardiac-specific expression of GCaMP2 provides a means of characterizing propagating Ca(2+) transients in adult fly hearts. Moreover, the adult fruit fly heart recapitulates several aspects of Ca(2+) regulation observed in mammalian myocardium. A mutation in Drosophila that causes an enlarged cardiac chamber and impaired contractile function is associated with abnormalities in the cytosolic Ca(2+) transient as well as changes in transcript levels of proteins associated with Ca(2+) handling. This new methodology has the potential to permit an examination of evolutionarily conserved myocardial Ca(2+)-handing mechanisms by applying the vast resources available in the fly genomics community to conduct genetic screens to identify new genes involved in generated Ca(2+) transients and arrhythmias.

Endoplasmic reticulum calcium release potentiates the ER stress and cell death caused by an oxidative stress in MCF-7 cells

Increase in cytosolic calcium concentration ([Ca2+](c)), release of endoplasmic reticulum (ER) calcium ([Ca2+](er)) and ER stress have been proposed to be involved in oxidative toxicity. Nevertheless, their relative involvements in the processes leading to cell death are not well defined. In this study, we investigated whether oxidative stress generated during ascorbate-driven menadione redox cycling (Asc/Men) could trigger these three events, and, if so, whether they contributed to Asc/Men cytoxicity in MCF-7 cells. Using microspectrofluorimetry, we demonstrated that Asc/Men-generated oxidative stress was associated with a slow and moderate increase in [Ca2+](c), largely preceding permeation of propidium iodide, and thus cell death. Asc/Men treatment was shown to partially deplete ER calcium stores after 90 min (decrease by 45% compared to control). This event was associated with ER stress activation, as shown by analysis of eIF2 phosphorylation and expression of the molecular chaperone GRP94. Thapsigargin (TG) was then used to study the effect of complete [Ca2+](er) emptying during the oxidative stress generated by Asc/Men. Surprisingly, the combination of TG and Asc/Men increased ER stress to a level considerably higher than that observed for either treatment alone, suggesting that [Ca2+](er) release alone is not sufficient to explain ER stress activation during oxidative stress. Finally, TG-mediated [Ca2+](er) release largely potentiated ER stress, DNA fragmentation and cell death caused by Asc/Men, supporting a role of ER stress in the process of Asc/Men cytotoxicity. Taken together, our results highlight the involvement of ER stress and [Ca2+](er) decrease in the process of oxidative stress-induced cell death in MCF-7 cells.

Mitochondria, Calcium, and Calpain are Key Mediators of Resveratrol-Induced Apoptosis in Breast Cancer

Resveratrol (RES), a natural plant polyphenol, has gained interest as a nontoxic chemopreventive agent capable of inducing tumor cell death in a variety of cancer types. However, the early molecular mechanisms of RES-induced apoptosis are not well defined. Using the human breast cancer cell lines MDA-MB-231 and MCF-7, we demonstrate that RES is antiproliferative and induces apoptosis in a concentration- and time-dependent manner. Preceding apoptosis, RES instigates a rapid dissipation of mitochondrial membrane potential by directly targeting mitochondria. This is followed by release of cytochrome c and second mitochondria-derived activator of caspase/direct inhibitor of apoptosis-binding protein with low pI (Smac/DIABLO) into the cytoplasm and substantial increase in the activities of caspases-9 and -3 in MDA-MB-231 cells. In addition, live cell microscopy demonstrates that RES causes an early biphasic increase in the concentration of free intracellular calcium ([Ca2+]i), probably resulting from depletion of the endoplasmic reticulum stores in breast cancer cells. In caspase-3-deficient MCF-7 cells, apoptosis is mediated by the Ca2+-activated protease, calpain, leading to the degradation of plasma membrane Ca2+-ATPase isoform 1 and fodrin; the degradation is attenuated by buffering [Ca2+]i and blocked by calpain inhibitors. Mitochondrial permeability transition pore antagonists also blocked calpain activation. In vivo mouse xenograft studies demonstrate that RES treatment inhibits breast cancer growth with no systemic toxicities. Together, these results suggest a critical role for mitochondria not only in the intrinsic apoptotic pathway but also in the Ca2+ and calpain-dependent cell death initiated by RES. Thus, RES may prove useful as a nontoxic alternative for breast cancer treatment.

Calcium transport and signaling in the mammary gland: targets for breast cancer

The mammary gland is subjected to extensive calcium loads during lactation to support the requirements of milk calcium enrichment. Despite the indispensable nature of calcium homeostasis and signaling in regulating numerous biological functions, the mechanisms by which systemic calcium is transported into milk by the mammary gland are far from completely understood. Furthermore, the implications of calcium signaling in terms of regulating proliferation, differentiation and apoptosis in the breast are currently uncertain. Deregulation of calcium homeostasis and signaling is associated with mammary gland pathophysiology and as such, calcium transporters, channels and binding proteins represent potential drug targets for the treatment of breast cancer.