Extracellular ATP regulates FoxO family of transcription factors and cell cycle progression through PI3K/Akt in MCF-7 cells

Carotenoids Modulate FoxO-Induced Cell Cycle Awrrest in Human Cancer Cell Lines: A Scoping Review

Carotenoids, a class of antioxidants, have shown great potential for cancer management. This scoping review aimed to elucidate the anticancer mechanisms of carotenoids by using a protein interactions and pathways approach. A literature search on five databases (Web of Science, PubMed, Ovid Medline, Ovid Embase and Scopus) was carried out, and studies investigating differential protein expression in cancer cell lines treated with carotenoids published in the last 10 years were included in the analysis. Sixty-three research articles were short-listed, and 17 carotenoids were used in these studies. The most studied carotenoids were fucoxanthin, astaxanthin, and crocin. The key cancer cell lines tested in these studies included breast, gastric, and lung cancers. Analysis of the proteins identified from these studies using the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) revealed the upregulation of proteins belonging to the pro-apoptotic and FoxO signaling pathways. In contrast, several proteins in the PI3k/Akt and TNF signaling pathways and cell cycle regulation were downregulated, which can explain the observed anticancer effects. The findings from this scoping review suggest that the cell cycle arrest observed in carotenoid-treated cancer cells may work through activation of the FoxO signaling pathway in these cells, highlighting their role as potential anticancer agents. Nonetheless, the lack of evidence on the pharmacology, pharmacokinetics, and physiology of carotenoids necessitates more robust and well-designed clinical trials. Similarly, further investigations into the therapeutic effects of targeting the PI3K/Akt/FoxO axis to induce cell cycle arrest and its translational potential are required to ensure the successful development of effective treatments.

ESL attenuates BLM-induced IPF in mice: Dual mediation of the TLR4/NF-κB and TGF-β1/PI3K/Akt/FOXO3a pathways

BACKGROUNDS

Idiopathic pulmonary fibrosis (IPF) is a persistent and advanced pulmonary ailment. The roles of innate immunity and adaptive immunity are pivotal in the evolution of IPF. An ill-adjusted interaction between epithelial cells and immune cells is responsible for initiating the epithelial-mesenchymal transition (EMT) process and sustaining chronic inflammation, thereby fostering fibrosis progression. The intricacy of IPF pathogenesis has hindered the availability of efficacious agents. Elephantopus scaber Linn. (ESL) is a canonical Chinese medicine with significant immunoregulatory effects, and its aqueous extract has been proven to attenuate IPF symptoms in bleomycin (BLM)-induced mice. However, the underlying mechanism through which ESL relieves IPF remains unclear.

AIM

To validate whether ESL reverses IPF by mediating the immune response and EMT.

METHODS

Ultra-performance liquid chromatography with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS/MS) and UPLC were used to identify the components and determine the concentrations of the specific compounds in the ESL. Network pharmacology and molecular docking were applied to predict the potential mechanism underlying the anti-IPF effect of ESL. BLM-induced IPF mice were used to validate the anti-IPF effect of ESL, and lung tissue was collected to test putative pathways involved in inflammation and EMT via immunohistochemistry (ICH), real-time quantitative polymerase chain reaction (RT-qPCR) and Western blotting.

RESULTS

Sixty-one compounds were identified, and thirteen main ingredients were quantified in the ESL. In silico experiments predicted that the IPF-mediated reversal of adverse effects by ESL would be related to interruption of the Toll-like receptor 4 (TLR4)/nuclear factor-k-gene binding (NF-ĸB) inflammatory pathway and the transforming growth factor-beta l (TGF-β1)/phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/forkhead box O3 (FOXO3a) fibrosis pathway. In vivo experiments showed that ESL alleviates BLM-induced lung inflammation and fibrosis by reducing neutrophil aggregation and fibroblast foci, similar to the effects of the positive control drug pirfenidone (PFD). ESL markedly inhibited the transcription of TNF-α, IL-1β, and IL-6, which are downstream genes of the NF-κB signaling pathway. Furthermore, the protein levels of TLR4 and p-NF-κB were correspondingly inhibited in response to ESL treatment. Additionally, ESL reverses BLM-induced changes in the expression of EMT-related biological characteristic indicators (collagen I [COLIA1], E-cadherin, and alpha smooth muscle actin [α-SMA]) at the messenger ribonucleic acid (mRNA) level and markedly inhibits the expression of EMT-related upstream proteins (TGF-β1, p-PI3K, p-Akt, and p-FOXO3a).

CONCLUSION

Our research suggested that ESL attenuates BLM-induced IPF through mediating the EMT process via the TGF-β1/PI3K/Akt/FOXO3a signaling pathway and inhibiting inflammation through the TLR4/NF-κB signaling pathway, highlighting that ESL can serve as an immunoregulator for relieving the abnormal immune response and reversing the EMT in IPF.

ATP Promotes Oral Squamous Cell Carcinoma Cell Invasion and Migration by Activating the PI3K/AKT Pathway via the P2Y2-Src-EGFR Axis

Oral cancer is one of the most common malignancies of the head and neck, and approximately 90% of oral cancers are oral squamous cell carcinomas (OSCCs). The purinergic P2Y2 receptor is upregulated in breast cancer, pancreatic cancer, colorectal cancer, and liver cancer, but its role in OSCC is still unclear. Here, we examined the effects of P2Y2 on the invasion and migration of oral cancer cells (SCC15 and CAL27). The BALB/c mouse model was used to observe the involvement of P2Y2 with tumors in vivo. P2Y2, Src, and EGFR are highly expressed in OSCC tissues and cell lines. Stimulation with ATP significantly enhanced cell invasion and migration in oral cancer cells, and enhanced the activity of Src and EGFR protein kinases, which is mediated by the PI3K/AKT signaling pathway. P2Y2 knockdown attenuated the above ATP-driven events in vitro and in vivo. The PI3K/AKT signaling pathway was blocked by Src or EGFR inhibitor. Extracellular ATP activates the PI3K/AKT pathway through the P2Y2-Src-EGFR axis to promote OSCC invasion and migration, and thus, P2Y2 may be a potential novel target for antimetastasis therapy.

Synthesis and Antitumor Activities of Novel Mitochondria-Targeted Dihydroartemisinin Ether Derivatives

Ten novel mitochondria-targeted dihydroartemisinin ether derivatives were designed, synthesized, and evaluated for antitumor activity against five cancer cell lines in vitro. Profoundly, compound D8-T (IC₅₀ = 56.9 nM) showed the most potent antiproliferative activity against the T24 cells with low cytotoxicity in normal human umbilical vein endothelial cells. High-performance liquid chromatography analysis confirmed that D8-T targeted mitochondria 6.3-fold higher than DHA. ATP content assay demonstrated that D8-T decreased the ATP level of bladder cancer cells. The effect of D8-T on cell apoptosis was determined by flow cytometry and western blot of Bax and Bcl-2. Surprisingly, the results indicated that D8-T did not induce bladder cancer cell apoptosis. In contrast, the cell cycle analysis and western blot of CDK4, CDK6, cyclin D1, and p21 demonstrated that the cancer cell cycle was arrested at the G1 phase after D8-T treatment. Furthermore, the consistent results were received by RNA-seq assay. These promising findings implied that D8-T could serve as a great candidate against bladder cancer for further investigation.

Unraveling the Molecular Mechanism of Xuebijing Injection in the Treatment of Chronic Obstructive Pulmonary Disease by Combining Network Pharmacology and Affymetrix Array

Xuebijing injection (XBJ), one of the classical prescriptions for treating inflammation-related diseases, has been used to chronic obstructive pulmonary disease (COPD) in clinical practice. However, its molecular mechanism is still unclear. Network pharmacology combined with Affymetrix arrays and molecular docking techniques were applied to explore the molecular mechanism of XBJ for COPD. Predictive analysis of 728 active compounds in XBJ and 6 sets of Affymetrix arrays expression data resulted in 106 potential therapeutic targets. Next, based on the active compound-co-target network topology analysis, most of these targets were found to be modulated by quercetin, myricetin, and ellagic acid. Furthermore, protein–protein interaction (PPI) analysis revealed that the key targets may be EGFR, STAT3, AKT1, CCND1, MMP9, AR, ESR1, and PTGS2. Then, by constructing a component-target-pathway network, we found that XBJ was a multi-pathway, multi-target, multi-compound synergistic therapy for COPD, and four key targets were involved in the FoxO signaling pathway. Luteolin and salvianolic acid b had the optimal binding ability to several key proteins. Therefore, we hypothesize that quercetin, myricetin, ellagic acid, luteolin, and salvianolic acid b mainly contribute to the therapeutic effect of XBJ on COPD by modulating the FoxO signaling pathway by regulating EGFR, STAT3, AKT1, and CCND1. XBJ exerts anti-inflammatory and antioxidative stress effects through the PI3K/Akt/FoxO axis combined with MMP9, AR, ESR1, and PTGS2 to regulate other signaling pathways.

Nicotinamide as a Foundation for Treating Neurodegenerative Disease and Metabolic Disorders

Neurodegenerative disorders impact more than one billion individuals worldwide and are intimately tied to metabolic disease that can affect another nine hundred individuals throughout the globe. Nicotinamide is a critical agent that may offer fruitful prospects for neurodegenerative diseases and metabolic disorders, such as diabetes mellitus. Nicotinamide protects against multiple toxic environments that include reactive oxygen species exposure, anoxia, excitotoxicity, ethanolinduced neuronal injury, amyloid (Aß) toxicity, age-related vascular disease, mitochondrial dysfunction, insulin resistance, excess lactate production, and loss of glucose homeostasis with pancreatic β-cell dysfunction. However, nicotinamide offers cellular protection in a specific concentration range, with dosing outside of this range leading to detrimental effects. The underlying biological pathways of nicotinamide that involve the silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1), the mechanistic target of rapamycin (mTOR), AMP activated protein kinase (AMPK), and mammalian forkhead transcription factors (FoxOs) may offer insight for the clinical translation of nicotinamide into a safe and efficacious therapy through the modulation of oxidative stress, apoptosis, and autophagy. Nicotinamide is a highly promising target for the development of innovative strategies for neurodegenerative disorders and metabolic disease, but the benefits of this foundation depend greatly on gaining a further understanding of nicotinamide's complex biology.

Targeting the core of neurodegeneration: FoxO, mTOR, and SIRT1

The global increase in lifespan noted not only in developed nations, but also in large developing countries parallels an observed increase in a significant number of non-communicable diseases, most notable neurodegenerative disorders. Neurodegenerative disorders present a number of challenges for treatment options that do not resolve disease progression. Furthermore, it is believed by the year 2030, the services required to treat cognitive disorders in the United States alone will exceed $2 trillion annually. Mammalian forkhead transcription factors, silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae), the mechanistic target of rapamycin, and the pathways of autophagy and apoptosis offer exciting avenues to address these challenges by focusing upon core cellular mechanisms that may significantly impact nervous system disease. These pathways are intimately linked such as through cell signaling pathways involving protein kinase B and can foster, sometimes in conjunction with trophic factors, enhanced neuronal survival, reduction in toxic intracellular accumulations, and mitochondrial stability. Feedback mechanisms among these pathways also exist that can oversee reparative processes in the nervous system. However, mammalian forkhead transcription factors, silent mating type information regulation 2 homolog 1, mechanistic target of rapamycin, and autophagy can lead to cellular demise under some scenarios that may be dependent upon the precise cellular environment, warranting future studies to effectively translate these core pathways into successful clinical treatment strategies for neurodegenerative disorders.

Cytotoxicity of eupatorin in MCF-7 and MDA-MB-231 human breast cancer cells via cell cycle arrest, anti-angiogenesis and induction of apoptosis

Eupatorin has been reported with in vitro cytotoxic effect on several human cancer cells. However, reports on the mode of action and detail mechanism of eupatorin in vitro in breast cancer disease are limited. Hence, eupatorin's effect on the human breast carcinoma cell line MCF-7 and MDA-MB-231 was investigated. MTT assay showed that eupatorin had cytotoxic effects on MCF-7 and MDA-MB-231 cells but was non-toxic to the normal cells of MCF-10a in a time-dose dependent manner. At 24 h, the eupatorin showed mild cytotoxicity on both MCF-7 and MDA-MB-231 cells with IC50 values higher than 20 μg/mL. After 48 h, eupatorin at 5 μg/mL inhibited the proliferation of MCF-7 and MDA-MB-231 cells by 50% while the IC50 of MCF-10a was significantly (p < 0.05) high with 30 μg/mL. The concentration of eupatorin at 5 μg/mL induced apoptosis mainly through intrinsic pathway by facilitating higher fold of caspase 9 compared to caspase 8 at 48 h. The cell cycle profile also showed that eupatorin (5 μg/mL) exerted anti-proliferation activity with the cell cycle arrest of MCF-7 and MDA-MB-231 cells at sub Gθ/G1 in a time-dependent manner. In addition, wound healing assay showed an incomplete wound closure of scratched MDA-MB-231 cells, and more than 60% of the MDA-MB-231 cells were prevented to migrate and invade the membrane in the Boyden chamber after 24 h. Eupatorin also inhibited angiogenic sprouting of new blood vessels in ex vivo mouse aorta ring assay. In gene expression assay, eupatorin up-regulated pro-apoptotic genes such as Bak1, HIF1A, Bax, Bad, cytochrome c and SMAC/Diablo and blocked the Phospho-Akt pathway. In conclusion, eupatorin is a potent candidate to induce apoptosis and concurrently inhibit the invasion, migration and angiogenesis of MDA-MB-231 and MCF-7 cells through inhibition of Phospho-Akt pathway and cell cycle blockade.

Forkhead Transcription Factors: Formulating a FOXO Target for Cognitive Loss

BACKGROUND

With almost 47 million individuals worldwide suffering from some aspect of dementia, it is clear that cognitive loss impacts a significant proportion of the global population. Unfortunately, definitive treatments to resolve or prevent the onset of cognitive loss are limited. In most cases such care is currently non-existent prompting the need for novel treatment strategies.

METHODS

Mammalian forkhead transcription factors of the O class (FoxO) are one such avenue of investigation that offer an exciting potential to bring new treatments forward for disorders that involve cognitive loss. Here we examine the background, structure, expression, and function of FoxO transcription factors and their role in cognitive loss, programmed cell death in the nervous system with apoptosis and autophagy, and areas to target FoxOs for dementia and specific disorders such as Alzheimer's disease.

RESULTS

FoxO proteins work in concert with a number of other cell survival pathways that involve growth factors, such as erythropoietin and neurotrophins, silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1), Wnt1 inducible signaling pathway protein 1 (WISP1), Wnt signaling, and cancer-related pathways. FoxO transcription factors oversee proinflammatory pathways, affect nervous system amyloid (Aβ) production and toxicity, lead to mitochondrial dysfunction, foster neuronal apoptotic cell death, and accelerate the progression of degenerative disease. However, under some scenarios such as those involving autophagy, FoxOs also can offer protection in the nervous system and reduce toxic intracellular protein accumulations and potentially limit Aβ toxicity.

CONCLUSION

Given the ability of FoxOs to not only promote apoptotic cell death in the nervous system, but also through the induction of autophagy offer protection against degenerative disease that can lead to dementia, a fine balance in the activity of FoxOs may be required to target cognitive loss in individuals. Future work should yield exciting new prospects for FoxO proteins as new targets to treat the onset and progression of cognitive loss and dementia.

Forkhead transcription factors: new considerations for alzheimer's disease and dementia

Life expectancy of individuals in both developed and undeveloped nations continues to rise at an unprecedented rate. Coupled to this increase in longevity for individuals is the rise in the incidence of chronic neurodegenerative disorders that includes Alzheimer's disease (AD). Currently, almost ten percent of the population over the age of 65 suffers from AD, a disorder that is presently without definitive therapy to prevent the onset or progression of cognitive loss. Yet, it is estimated that AD will continue to significantly increase throughout the world to impact millions of individuals and foster the escalation of healthcare costs. One potential target for the development of novel strategies against AD and other cognitive disorders involves the mammalian forkhead transcription factors of the O class (FoxOs). FoxOs are present in "cognitive centers" of the brain to include the hippocampus, the amygdala, and the nucleus accumbens and may be required for memory formation and consolidation. FoxOs play a critical role in determining survival of multiple cell types in the nervous system, drive pathways of apoptosis and autophagy, and control stem cell proliferation and differentiation. FoxOs also interface with multiple cellular pathways that include growth factors, Wnt signaling, Wnt1 inducible signaling pathway protein 1 (WISP1), and silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1) that ultimately may control FoxOs and determine the fate and function of cells in the nervous system that control memory and cognition. Future work that can further elucidate the complex relationship FoxOs hold over cell fate and cognitive function could yield exciting prospects for the treatment of a number of neurodegenerative disorders including AD.

CRM1 inhibitor S109 suppresses cell proliferation and induces cell cycle arrest in renal cancer cells

Abnormal localization of tumor suppressor proteins is a common feature of renal cancer. Nuclear export of these tumor suppressor proteins is mediated by chromosome region maintenance-1 (CRM1). Here, we investigated the antitumor eff ects of a novel reversible inhibitor of CRM1 on renal cancer cells. We found that S109 inhibits the CRM1-mediated nuclear export of RanBP1 and reduces protein levels of CRM1. Furthermore, the inhibitory eff ect of S109 on CRM1 is reversible. Our data demonstrated that S109 signifi cantly inhibits proliferation and colony formation of renal cancer cells. Cell cycle assay showed that S109 induced G1-phase arrest, followed by the reduction of Cyclin D1 and increased expression of p53 and p21. We also found that S109 induces nuclear accumulation of tumor suppressor proteins, Foxo1 and p27. Most importantly, mutation of CRM1 at Cys528 position abolished the eff ects of S109. Taken together, our results indicate that CRM1 is a therapeutic target in renal cancer and the novel reversible CRM1 inhibitor S109 can act as a promising candidate for renal cancer therapy.

Regeneration in the nervous system with erythropoietin

Globally, greater than 30 million individuals are afflicted with disorders of the nervous system accompanied by tens of thousands of new cases annually with limited, if any, treatment options. Erythropoietin (EPO) offers an exciting and novel therapeutic strategy to address both acute and chronic neurodegenerative disorders. EPO governs a number of critical protective and regenerative mechanisms that can impact apoptotic and autophagic programmed cell death pathways through protein kinase B (Akt), sirtuins, mammalian forkhead transcription factors, and wingless signaling. Translation of the cytoprotective pathways of EPO into clinically effective treatments for some neurodegenerative disorders has been promising, but additional work is necessary. In particular, development of new treatments with erythropoiesis-stimulating agents such as EPO brings several important challenges that involve detrimental vascular outcomes and tumorigenesis. Future work that can effectively and safely harness the complexity of the signaling pathways of EPO will be vital for the fruitful treatment of disorders of the nervous system.

Foxo3 activity promoted by non-coding effects of circular RNA and Foxo3 pseudogene in the inhibition of tumor growth and angiogenesis

It has recently been shown that the upregulation of a pseudogene specific to a protein-coding gene could function as a sponge to bind multiple potential targeting microRNAs (miRNAs), resulting in increased gene expression. Similarly, it was recently demonstrated that circular RNAs can function as sponges for miRNAs, and could upregulate expression of mRNAs containing an identical sequence. Furthermore, some mRNAs are now known to not only translate protein, but also function to sponge miRNA binding, facilitating gene expression. Collectively, these appear to be effective mechanisms to ensure gene expression and protein activity. Here we show that expression of a member of the forkhead family of transcription factors, Foxo3, is regulated by the Foxo3 pseudogene (Foxo3P), and Foxo3 circular RNA, both of which bind to eight miRNAs. We found that the ectopic expression of the Foxo3P, Foxo3 circular RNA and Foxo3 mRNA could all suppress tumor growth and cancer cell proliferation and survival. Our results showed that at least three mechanisms are used to ensure protein translation of Foxo3, which reflects an essential role of Foxo3 and its corresponding non-coding RNAs.

FoxO proteins in the nervous system

Acute as well as chronic disorders of the nervous system lead to significant morbidity and mortality for millions of individuals globally. Given the ability to govern stem cell proliferation and differentiated cell survival, mammalian forkhead transcription factors of the forkhead box class O (FoxO) are increasingly being identified as potential targets for disorders of the nervous system, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and auditory neuronal disease. FoxO proteins are present throughout the body, but they are selectively expressed in the nervous system and have diverse biological functions. The forkhead O class transcription factors interface with an array of signal transduction pathways that include protein kinase B (Akt), serum- and glucocorticoid-inducible protein kinase (SgK), IκB kinase (IKK), silent mating type information regulation 2 homolog 1 (S. cerevisiae) (SIRT1), growth factors, and Wnt signaling that can determine the activity and integrity of FoxO proteins. Ultimately, there exists a complex interplay between FoxO proteins and their signal transduction pathways that can significantly impact programmed cell death pathways of apoptosis and autophagy as well as the development of clinical strategies for the treatment of neurodegenerative disorders.

Long‑term exposure to leptin enhances the growth of prostate cancer cells

Obesity correlates with an increased risk of developing prostate cancer (PCa) and leptin plays an important role in PCa progression. Since leptin is produced by adipocytes, the serum leptin level is higher in obese than in non-obese individuals. However, the effects of leptin remain controversial and unclear. The aim of the present study was to investigate the effect of leptin on PCa cell aggressiveness. Three human PCa cell lines (LNCaP, DU145 and PC-3) were treated with recombinant leptin for 28 days. Cell proliferation, migration, and invasion were estimated using the WST assay, a wound-healing assay, and a BD Matrigel invasion assay, respectively. The mechanism underlying the proliferative effect of leptin was investigated by cell transfections with small interfering RNA (siRNA) against the leptin receptor (ObR) or forkhead box O1 (FOXO1), and by immunocytochemistry. Long-term exposure of PCa cells to leptin enhanced their proliferation, migration and invasion. Leptin increased ObR expression and enhanced Akt phosphorylation constitutively. Leptin also increased the phosphorylation of FOXO1 via PI3K signaling and FOXO1 gene silencing enhanced PCa cell proliferation. Leptin induced the translocation of FOXO1 from the nucleus to the cytoplasm. Furthermore, the PI3K inhibitor, LY294002 suppressed this translocation. These results suggested that leptin regulated the subcellular localization of FOXO1 and induced Akt phosphorylation. Additionally, we revealed that leptin increased the expression of cyclin D1 and decreased the expression of p21 protein. In conclusion, long-term exposure to leptin increased the cell proliferation, migration, and invasion of PCa cells through inactivation of FOXO1. This inactivation resulted from exclusion of FOXO1 from the nucleus and its restriction to the cytoplasm through PI3K/Akt signaling. Our findings contribute to an understanding of the association between obesity and PCa aggressiveness.

FoxO Transcription Factors and Regenerative Pathways in Diabetes Mellitus

Mammalian forkhead transcription factors of the O class (FoxO) are exciting targets under consideration for the development of new clinical entities to treat metabolic disorders and diabetes mellitus (DM). DM, a disorder that currently affects greater than 350 million individuals globally, can become a devastating disease that leads to cellular injury through oxidative stress pathways and affects multiple systems of the body. FoxO proteins can regulate insulin signaling, gluconeogenesis, insulin resistance, immune cell migration, and cell senescence. FoxO proteins also control cell fate through oxidative stress and pathways of autophagy and apoptosis that either lead to tissue regeneration or cell demise. Furthermore, FoxO signaling can be dependent upon signal transduction pathways that include silent mating type information regulation 2 homolog 1 (S. cerevisiae) (SIRT1), Wnt, and Wnt1 inducible signaling pathway protein 1 (WISP1). Cellular metabolic pathways driven by FoxO proteins are complex, can lead to variable clinical outcomes, and require in-depth analysis of the epigenetic and post-translation protein modifications that drive FoxO protein activation and degradation.

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.