Heat shock proteins and p53 play a critical role in K+ channel-mediated tumor cell proliferation and apoptosis

Harnessing the potency of scorpion venom-derived proteins: applications in cancer therapy

Despite breakthroughs in the development of cancer diagnosis and therapy, most current therapeutic approaches lack precise specificity and sensitivity, resulting in damage to healthy cells. Selective delivery of anti-cancer agents is thus an important goal of cancer therapy. Scorpion venom (SV) and/or body parts have been used since early civilizations for medicinal purposes, and in cultures, SV is still applied to the treatment of several diseases including cancer. SV contains numerous active micro and macromolecules with diverse pharmacological effects. These include potent anti-microbial, anti-viral, anti-inflammatory, and anti-cancer properties. This review focuses on the recent advances of SV-derived peptides as promising anti-cancer agents and their diagnostic and therapeutic potential applications in cancers such as glioma, breast cancer, prostate cancer, and colon cancer. Well-characterized SV-derived peptides are thus needed to serve as potent and selective adjuvant therapy for cancer, to significantly enhance the patients' survival and wellbeing.

Proteome landscape and interactome of voltage-gated potassium channel 1.6 (Kv1.6) of the murine ophthalmic artery and neuroretina

The voltage-gated potassium channel 1.6 (Kv1.6) plays a vital role in ocular neurovascular beds and exerts its modulatory functions via interaction with other proteins. However, the interactome and their potential roles remain unknown. Here, the global proteome landscape of the ophthalmic artery (OA) and neuroretina was mapped, followed by the determination of Kv1.6 interactome and validation of its functionality and cellular localization. Microfluorimetric analysis of intracellular [K+] and Western blot validated the native functionality and cellular expression of the recombinant Kv1.6 channel protein. A total of 54, 9 and 28 Kv1.6-interacting proteins were identified in the mouse OA and, retina of mouse and rat, respectively. The Kv1.6-protein partners in the OA, namely actin cytoplasmic 2, alpha-2-macroglobulin and apolipoprotein A-I, were implicated in the maintenance of blood vessel integrity by regulating integrin-mediated adhesion to extracellular matrix and Ca2+ flux. Many retinal protein interactors, particularly the ADP/ATP translocase 2 and cytoskeleton protein tubulin, were involved in endoplasmic reticulum stress response and cell viability. Three common interactors were found in all samples comprising heat shock cognate 71 kDa protein, Ig heavy constant gamma 1 and Kv1.6 channel. This foremost in-depth investigation enriched and identified the elusive Kv1.6 channel and, elucidated its complex interactome.

A potential role of calpains in sulfonylureas (SUs) -mediated death of human pancreatic cancer cells (1.2B4)

Sulfonylureas (SUs) are suggested to accelerate the pancreatic β-cells mass loss via apoptosis. However, little is known whether calpains mediate this process. The aim of the present study is to evaluate the involvement of calpains in SUs-induced death of human pancreatic cancer (PC) cell line 1.2B4. The cells were exposed to: glibenclamide, glimepiride and gliclazide for 72 h. The expression analysis of caspase-3 (CASP-3), TP53, calpain 1 (CAPN-1), calpain 2 (CAPN-2) and calpain 10 (CAPN-10) was detected using RT-PCR method. Intracellular Ca²⁺ concentrations, CASP-3 activity and total calpain activity were also evaluated. Our results have shown that glibenclamide and glimepiride decrease 1.2B4 cells viability with accompanied increase in intracellular Ca²⁺ concentration and increased expression of apoptosis-related CASP-3 and TP53. Gliclazide did not affect 1.2B4 cell viability and Ca²⁺ concentration, however, it downregulated CASP-3 and upregulated TP53. Interestingly, 50 μM glimepiride increased expression of CAPN-1, CAPN-2 and CAPN-10 whereas 50 μM glibenclamide solely upregulated CAPN-2 expression. We have shown that 10 μM and 50 μM glibenclamide and glimepiride increased the activity of CASP-3, but decreased total calpain activity. Our results suggest that calpains may be involved in glibenclamide- and glimepiride-induced death of PC cells. However, further investigation is required to confirm the engagement of calpains in SUs-mediated death of PC cells, especially studies on protein level of particular isoforms of calpains should be conducted.

Emerging Roles for Ion Channels in Ovarian Cancer: Pathomechanisms and Pharmacological Treatment

Ovarian cancer (OC) is the deadliest gynecologic cancer, due to late diagnosis, development of platinum resistance, and inadequate alternative therapy. It has been demonstrated that membrane ion channels play important roles in cancer processes, including cell proliferation, apoptosis, motility, and invasion. Here, we review the contribution of ion channels in the development and progression of OC, evaluating their potential in clinical management. Increased expression of voltage-gated and epithelial sodium channels has been detected in OC cells and tissues and shown to be involved in cancer proliferation and invasion. Potassium and calcium channels have been found to play a critical role in the control of cell cycle and in the resistance to apoptosis, promoting tumor growth and recurrence. Overexpression of chloride and transient receptor potential channels was found both in vitro and in vivo, supporting their contribution to OC. Furthermore, ion channels have been shown to influence the sensitivity of OC cells to neoplastic drugs, suggesting a critical role in chemotherapy resistance. The study of ion channels expression and function in OC can improve our understanding of pathophysiology and pave the way for identifying ion channels as potential targets for tumor diagnosis and treatment.

Myricanol 5-fluorobenzyloxy ether regulation of survivin pathway inhibits human lung adenocarcinoma A549 cells growth in vitro

Background

This study aimed to explore the growth inhibitory effect of myricanol 5-fluorobenzyloxy ether (5FEM) and its underlying mechanisms in human lung adenocarcinoma A549 cells in vitro.

Methods

5FEM was obtained by the chemical modification of myricanol with fluorobenzyloxy ether at the OH(5) position. The cytotoxicity, cell apoptosis, cell cycle, mitochondrial membrane potential (ΔΨm), scratch test, colony formation, and the expression levels of the key survivin pathway-related genes in A549 were evaluated.

Results

5FEM could significantly inhibit A549 cell growth; induce cell apoptosis; increase G0/G1 population; reduce ΔΨm; inhibit cell migration and colony formation; upregulate caspase-9, P21, and Bax expression levels; and downregulate PARP, survivin, and Bcl-2 expression level.

Conclusion

These results enhanced our understanding of 5FEM and aid the discovery of novel myricanol derivatives as potential antitumor agents.

Targeting Ion Channels for Cancer Treatment: Current Progress and Future Challenges

Ion channels are key regulators of cancer cell pathophysiology. They contribute to a variety of processes such as maintenance of cellular osmolarity and membrane potential, motility (via interactions with the cytoskeleton), invasion, signal transduction, transcriptional activity and cell cycle progression, leading to tumour progression and metastasis. Ion channels thus represent promising targets for cancer therapy. Ion channels are attractive targets because many of them are expressed at the plasma membrane and a broad range of existing inhibitors are already in clinical use for other indications. However, many of the ion channels identified in cancer cells are also active in healthy normal cells, so there is a risk that certain blockers may have off-target effects on normal physiological function. This review describes recent research advances into ion channel inhibitors as anticancer therapeutics. A growing body of evidence suggests that a range of existing and novel Na⁺, K⁺, Ca²⁺ and Cl^- channel inhibitors may be effective for suppressing cancer cell proliferation, migration and invasion, as well as enhancing apoptosis, leading to suppression of tumour growth and metastasis, either alone or in combination with standard-of-care therapies. The majority of evidence to date is based on preclinical in vitro and in vivo studies, although there are several examples of ion channel-targeting strategies now reaching early phase clinical trials. Given the strong links between ion channel function and regulation of tumour growth, metastasis and chemotherapy resistance, it is likely that further work in this area will facilitate the development of new therapeutic approaches which will reach the clinic in the future.

Subunits of BK channels promote breast cancer development and modulate responses to endocrine treatment in preclinical models

BACKGROUND AND PURPOSE

Pore-forming α subunits of the voltage- and Ca²⁺ -activated K⁺ channel with large conductance (BKα) promote malignant phenotypes of breast tumour cells. Auxiliary subunits such as the leucine-rich repeat containing 26 (LRRC26) protein, also termed BKγ1, may be required to permit activation of BK currents at a depolarized resting membrane potential that frequently occur in non-excitable tumour cells.

EXPERIMENTAL APPROACH

Anti-tumour effects of BKα loss were investigated in breast tumour-bearing MMTV-PyMT transgenic BKα knockout (KO) mice, primary MMTV-PyMT cell cultures, and in a syngeneic transplantation model of breast cancer derived from these cells. The therapeutic relevance of BK channels in the context of endocrine treatment was assessed in human breast cancer cell lines expressing either low (MCF-7) or high (MDA-MB-453) levels of BKα and BKγ1, as well as in BKα-negative MDA-MB-157.

KEY RESULTS

BKα promoted breast cancer onset and overall survival in preclinical models. Conversely, lack of BKα and/or knockdown of BKγ1 attenuated proliferation of murine and human breast cancer cells in vitro. At low concentrations, tamoxifen and its major active metabolites stimulated proliferation of BKα/γ1-positive breast cancer cells, independent of the genomic signalling controlled by the oestrogen receptor. Finally, tamoxifen increased the relative survival time of BKα KO but not of wild-type tumour cell recipient mice.

CONCLUSION AND IMPLICATIONS

Breast cancer initiation, progression, and tamoxifen sensitivity depend on functional BK channels thereby providing a rationale for the future exploration of the oncogenic actions of BK channels in clinical outcomes with anti-oestrogen therapy.

Pleiotropic Anticancer Properties of Scorpion Venom Peptides: Rhopalurus princeps Venom as an Anticancer Agent

To date, the success of conventional chemotherapy, radiotherapy, and targeted biological therapies in cancer treatment is not satisfactory. The main reasons for such outcomes rely on low target selectivity, primarily in chemo- and radiotherapy, ineffectiveness to metastatic disease, drug resistance, and severe side effects. Although immune checkpoint inhibitors may offer better clinical promise, success is still limited. Since cancer is a complex systemic disease, the need for new therapeutic modalities that can target or block several steps of cancer cell characteristics, modulate or repolarize immune cells, and are less toxic to healthy tissues is essential. Of these promising therapeutic modalities are pleiotropic natural products in which scorpion venom (SV) is an excellent example. SV consists of complex bioactive peptides that are disulfide-rich of different peptides’ length, potent, stable, and exerts various multi-pharmacological actions. SV peptides also contain ion channel inhibitors. These ion channels are dysregulated and overexpressed in cancer cells, and play essential roles in cancer development and invasion, as well as depolarizing immune cells. Furthermore, SV has been found to induce cancer cell apoptosis, and inhibit cancer cells proliferation, invasion, metastasis, and angiogenesis. In the current review, we are presenting data that show the pleiotropic effect of SV against different types of human cancer as well as revealing one potential anticancer agent, Rhopalurus princeps venom. Furthermore, we are addressing what is needed to be done to translate these potential cancer therapeutics to the clinic.

Potassium and Sodium Channels and the Warburg Effect: Biophysical Regulation of Cancer Metabolism

Ion channels are progressively emerging as a novel class of membrane proteins expressed in several types of human cancers and regulating the different aspects of cancer cell behavior. The metabolism of cancer cells, usually composed by a variable proportion of respiration, glycolysis, and glutaminolysis, leads to the excessive production of acidic metabolic products. The presence of these acidic metabolites inside the cells results in intracellular acidosis, and hinders survival and proliferation. For this reason, tumor cells activate mechanisms of pH control that produce a constitutive increase in intracellular pH (pHi) that is more acidic than the extracellular pH (pHe). This condition forms a perfect microenvironment for metastatic progression and may be permissive for some of the acquired characteristics of tumors. Recent analyses have revealed complex interconnections between oncogenic activation, ion channels, hypoxia signaling and metabolic pathways that are dysregulated in cancer. Here, we summarize the molecular mechanisms of the Warburg effect and hypoxia and their association. Moreover, we discuss the recent findings concerning the involvement of ion channels in various aspects of the Warburg effect and hypoxia, focusing on the role of Na+ and K+ channels in hypoxic and metabolic reprogramming in cancer.

Sulfonylurea derivatives and cancer, friend or foe?

Type 2 diabetes mellitus (T2DM) is associated with a higher risk of cancer and cancer-related mortality. Increased blood glucose and insulin levels in T2DM patients may be, at least in part, responsible for this effect. Indeed, lowering glucose and/or insulin levels pharmacologically appears to reduce cancer risk and progression, as has been demonstrated for the biguanide metformin in observational studies. Studies investigating the influence of sulfonylurea derivatives (SUs) on cancer risk have provided conflicting results, partly due to comparisons with metformin. Furthermore, little attention has been paid to within-class differences in systemic and off-target effects of the SUs. The aim of this systematic review is to discuss the available preclinical and clinical evidence on how the different SUs influence cancer development and risk. Databases including PubMed, Cochrane, Database of Abstracts on Reviews and Effectiveness, and trial registries were systematically searched for available clinical and preclinical evidence on within-class differences of SUs and cancer risk. The overall preclinical and clinical evidence suggest that the influence of SUs on cancer risk in T2DM patients differs between the various SUs. Potential mechanisms include differing affinities for the sulfonylurea receptors and thus differential systemic insulin exposure and off-target anti-cancer effects mediated for example through potassium transporters and drug export pumps. Preclinical evidence supports potential anti-cancer effects of SUs, which are of interest for further studies and potentially repurposing of SUs. At this time, the evidence on differences in cancer risk between SUs is not strong enough to guide clinical decision making.

Tetrandrine, a novel inhibitor of ether-à-go-go-1 (Eag1), targeted to cervical cancer development

Mortality-to-incidence ratios in patients with cancer are extremely high, positioning cancer as a major cause of death worldwide. Ether-à-go-go-1 (Eag1) is an ion channel that plays important roles in tumour proliferation, malignant transformation, invasion, metastasis, recurrence, and prognosis. Therefore, identifying potent and specific Eag1 channel inhibitors is crucial. In this study, we identified the first natural inhibitor of Eag1, the traditional Chinese medicine agent tetrandrine, and explored the underlying mechanism. Tetrandrine directly interacted with Eag1 and inhibited the currents in a concentration-dependent manner (IC50 of 69.97 ± 5.2 μM), and the amino acids Ile 550 , Thr 552 , and Gln 557 in the Eag1 C-linker domain were critical for tetrandrine's inhibitory effect. Moreover, tetrandrine reduced the proliferation of HeLa cells and Chinese hamster ovary (CHO) cells stably expressing Eag1 in a concentration-dependent manner. Finally, tetrandrine (30 mg/kg/day) inhibited tumor growth in mice, demonstrating a 64.21% inhibitory rate of HeLa cell-transplanted tumors. These results suggest that tetrandrine is a potent and selective Eag1 channel inhibitor, and could act as a leading compound in the development of therapies for Eag1 ion channel dysfunction-induced diseases.

Calcium-activated potassium channels as potential early markers of human cervical cancer

Cervical cancer is a major cause of cancer-associated mortality in women in developing countries. Thus, novel early markers are required. Ion channels have gained great interest as tumor markers, including cervical cancer. The calcium-activated potassium channel KCNMA1 (subunit α-1 from subfamily M) has been associated with different malignancies, including tumors such as breast and ovarian cancer that are influenced by hormones. The KCNMA1 channel blocker iberiotoxin decreases the proliferation of HeLa cervical cancer cells. Nevertheless, KCNMA1 channel expression during cervical carcinogenesis remains elusive. Therefore, KCNMA1 expression was studied in cervical cancer development. FVB transgenic mice expressing the E7-oncogene of high-risk human papilloma virus, and non-transgenic mice were treated with estradiol-releasing pellets during 3 or 6 months to induce cervical lesions. Twenty-four human cervical biopsies from non-cancerous, low- or high-grade intraepithelial lesions, or cervical cancer were also studied. mRNA and protein expression was assessed by reverse transcription-quantitative polymerase chain reaction and immunohistochemistry, respectively. Cervical dysplasia and carcinoma were observed only in the transgenic mice treated with estradiol for 3 and 6 months, respectively. Estradiol treatment increased KCNMA1 mRNA and protein expression in all groups; however, the highest levels were observed in the transgenic mice with carcinoma. KCNMA1 protein expression in the squamous cells of the transformation zone was observed only in the transgenic mice with cervical dysplasia or cancer. Human biopsies from non-cancerous cervix did not display KCNMA1 protein expression; in contrast, the majority of the tissues with cervical lesions (16/18) displayed KCNMA1 protein expression. The lowest channel immunostaining intensity was observed in biopsies from low-grade dysplasia and the strongest in the carcinoma tissues. These results suggest KCNMA1 channels as potential early cervical cancer markers.

In Vitro Safety/Protection Assessment of Resveratrol and Pterostilbene in a Human Hepatoma Cell Line (HepG2)

The aim of this work was to evaluate in vitro the genotoxic and/or antigenotoxic effects of resveratrol (RESV) and pterostilbene (PTER) on HepG2 cells. Moreover, additional tests were performed to evaluate early and late apoptosis events induced by the tested stilbenes. RESV and PTER did not show any genotoxic activity. As regards antigenotoxicity testing, RESV and PTER showed a typical, U-shaped hormetic dose-response relationship characterized by a biphasic trend with small quantities having opposite effects to large ones. HepG2 cells treated with PTER exhibited a marked increase in early apoptosis (40.1 %) at 250 μM; whereas, the highest concentration tested for both RESV and PTER significantly increased the proportion of HepG2 cells undergoing late apoptosis (32.5 and 51.2 %, respectively). The observed pro-apoptotic activity could, at least in part, explain the hormetic response observed when the compounds were tested for antigenotoxicity ( i.e., in the presence of induced DNA damage).

Targeting ion channels for cancer therapy by repurposing the approved drugs

Ion channels have been shown to be involved in oncogenesis and efforts are being poured in to target the ion channels. There are many clinically approved drugs with ion channels as "off" targets. The question is, can these drugs be repurposed to inhibit ion channels for cancer treatment? Repurposing of drugs will not only save investors' money but also result in safer drugs for cancer patients. Advanced bioinformatics techniques and availability of a plethora of open access data on FDA approved drugs for various indications and omics data of large number of cancer types give a ray of hope to look for possibility of repurposing those drugs for cancer treatment. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Calcium homeostasis in cancer: A focus on senescence

Senescence is one of the primary responses to the activation of oncoproteins or down-regulation of tumor suppressors in normal cells and is therefore considered as being anti-tumorigenic but the mechanisms controlling this process are still much unknown. Calcium (Ca²⁺) plays a major role in many cellular processes and calcium channels control many of the "hallmarks of cancer" but their involvement in tumor initiation is poorly understood and remains unclear. Therefore, in this article we review some striking senescence-associated characteristics and their potential regulation by Ca²⁺. The main aim is to produce plausible hypothesis on how calcium homeostasis may participate in cancer-related senescence. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.

Myricanol induces apoptotic cell death and anti-tumor activity in non-small cell lung carcinoma in vivo

This study explored the inhibiting effect and mechanism of myricanol on lung adenocarcinoma A549 xenografts in nude mice. Forty nude mice with subcutaneous A549 xenografts were randomly divided into five groups: high-dose myricanol (40 mg/kg body weight) group; middle-dose myricanol (20 mg/kg body weight) group; low-dose myricanol (10 mg/kg body weight) group; polyethylene glycol 400 vehicle group (1 mL/kg); and tumor model group. Nude mice were sacrificed after 14 days of treatment and the tumor inhibition rate (TIR, %) was then calculated. The relative mRNA expression levels of Bax, Bcl-2, VEGF, HIF-1α, and survivin in the tumor tissues were determined by real-time PCR. TUNEL assay was applied to determine cellular apoptosis, while IHC test was performed to detect the protein expression levels of Bax, Bcl-2, VEGF, HIF-1α, and survivin. The TIR of the three myricanol-treated groups ranged from 14.9% to 38.5%. The IHC results showed that the protein expression of Bcl-2, VEGF, HIF-1α, and survivin were consistently downregulated, whereas that of Bax was upregulated after myricanol treatment. Myricanol also significantly upregulated the mRNA expression of Bax and downregulated that of Bcl-2, VEGF, HIF-1α, and survivin in a dose-dependent manner (p < 0.05 to 0.001). These results are consistent with those of IHC. The TUNEL assay results indicated that apoptotic-positive cells significantly increased in the myricanol-treated tumor tissues compared with the cells of the vehicle control group (p < 0.01 to 0.001). These data suggest that myricanol could significantly decelerate tumor growth in vivo by inducing apoptosis.

Big Potassium (BK) ion channels in biology, disease and possible targets for cancer immunotherapy

The Big Potassium (BK) ion channel is commonly known by a variety of names (Maxi-K, KCNMA1, slo, stretch-activated potassium channel, KCa1.1). Each name reflects a different physical property displayed by this single ion channel. This transmembrane channel is found on nearly every cell type of the body and has its own distinctive roles for that tissue type. The BKα channel contains the pore that releases potassium ions from intracellular stores. This ion channel is found on the cell membrane, endoplasmic reticulum, Golgi and mitochondria. Complex splicing pathways produce different isoforms. The BKα channels can be phosphorylated, palmitoylated and myristylated. BK is composed of a homo-tetramer that interacts with β and γ chains. These accessory proteins provide a further modulating effect on the functions of BKα channels. BK channels play important roles in cell division and migration. In this review, we will focus on the biology of the BK channel, especially its role, and its immune response towards cancer. Recent proteomic studies have linked BK channels with various proteins. Some of these interactions offer further insight into the role that BK channels have with cancers, especially with brain tumors. This review shows that BK channels have a complex interplay with intracellular components of cancer cells and still have plenty of secrets to be discovered.

Growth-inhibiting and apoptosis-inducing activities of Myricanol from the bark of Myrica rubra in human lung adenocarcinoma A549 cells

Myrica rubra (Lour.) Sieb. Et Zucc. is a myricaceae Myrica plant. It is a subtropical fruit tree in China and other Asian countries. The bark of M. rubra is used in Chinese folk medicine because of its antibacterial, antioxidant, anti-inflammatory, and anticancer activities. However, the mechanisms underlying such activities remain unclear. This study investigated whether or not Myricanol extracted from M. rubra bark elicits anti-cancer effects on human lung adenocarcinoma A549 cells by inducing apoptosis in vivo. Myricanol was extracted from M. rubra bark through system solvent extraction and silica gel layer column separation. The results of tritiated thymidine assay, colony formation assay, and flow cytometry indicated that Myricanol inhibited the growth of A549 cells. The effects of Myricanol on the expression of key apoptosis-related genes in A549 cells were evaluated by quantitative PCR and Western blot analyses. Myricanol significantly inhibited the growth of A549 cells in a dose-dependent manner, with a half maximal inhibitory concentration of 4.85 μg/ml. Myricanol significantly decreased colony formation and induced A549 cell apoptosis. Myricanol upregulated the expression of Caspase-3, Caspase-9, Bax, and p21 and downregulated the expression of Bcl-2 at the mRNA and protein levels. These changes were associated with apoptosis. Based on these results, we propose that Myricanol elicits growth inhibitory and cytotoxic effects on lung cancer cells. Therefore, Myricanol may be a clinical candidate for the prevention and treatment of lung cancer.

Ion channels and apoptosis in cancer

Humans maintain a constant cell number throughout their lifespan. This equilibrium of cell number is accomplished when cell proliferation and cell death are kept balanced, achieving a steady-state cell number. Abnormalities in cell growth or cell death can lead to an overabundance of cells known as neoplasm or tumours. While the perception of cancer is often that of an uncontrollable rate of cell growth or increased proliferation, a decrease in cell death can also lead to tumour formation. Most cells when detached from their normal tissue die. However, cancer cells evade cell death, tipping the balance to an overabundance of cell number. Therefore, overcoming this resistance to cell death is a decisive factor in the treatment of cancer. Ion channels play a critical role in cancer in regards to cell proliferation, malignant angiogenesis, migration and metastasis. Additionally, ion channels are also known to be critical components of apoptosis. In this review, we discuss the modes of cell death focusing on the ability of cancer cells to evade apoptosis. Specifically, we focus on the role ion channels play in controlling and regulating life/death decisions and how they can be used to overcome resistance to apoptosis in the treatment of cancer.

The evidence of HeLa cell apoptosis induced with tetraethylammonium using proteomics and various analytical methods

Tetraethylammonium (TEA) is a potassium channel (KCh) blocker applied in the functional and pharmacological studies of the KChs. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, a colorimetric assay to quantitatively measure living cells, demonstrated that TEA reduced the HeLa cell viability dose-dependently. Flow cytometry analysis indicated an increased apoptosis rate of the HeLa cell after exposing to TEA. The patch clamp technique revealed that the K(+) current of the HeLa cell was inhibited up to 80% when exposed to TEA. In addition, quantitative real-time PCR approach set up cross-talk among the cytotoxicity of TEA, 4-aminopyridine, and anti-cancer drug such as cisplatin. Using comparative proteomics combined with MALDI-TOF MS/MS, 33 significantly changed proteins were found from TEA treatment group; among these proteins, 12 were up-regulated, and 21 were down-regulated. Here we indicated that these proteins were closely connected with many biological functions such as oxidative stress response, signal transduction, metabolism, protein synthesis, and degradation. Both Western blotting and quantitative real-time PCR approaches further verified these differential proteins. Ingenuity Pathways Analysis software, a tool to analyze "omics" data and model biological system, was applied to analyze the interaction pathways of these proteins. The subcellular locations of the differential proteins are also predicted from Uniprot. All results above can help in our understanding of the mechanism of TEA-induced cytotoxicity and provide potential cancer biomarkers. Various experimental results in this study (like those for cisplatin) indicated that TEA is not only a KCh blocker but also a potential anti-cancer drug.

Gene expression of Hsp70, Hsp90 and Hsp110 families in normal palate and cleft palate during mouse embryogenesis

Most previous studies focused on a small number of heat shock proteins (Hsps) and their relationships with embryogenesis, and the actual roles of these Hsps in normal and abnormal embryonic development remain unclear. It was found in the present systemic study that except for Grp170, whose expression was not detectable at GD18, all 19 Hsps of Hsp70, Hsp90 and Hsp110 families were expressed in the normal development of embryonic palate tissue in mice, but their expression patterns varied with different Hsps, presenting as a correlation with the developmental phases. In the treatment group by all-trans retinoic acid (atRA), the messenger RNA (mRNA) abundance of HspA1A, HspA1L, HspA8, HspA9, HspA12A, HspA12B, HspA13, HspA14, Hsp90AA1, Hsp90AB1, Grp94, Trap1, Hsp105, Hsp110 and Grp170 was higher in the palates at GD11 (the beginning of palate development), the mRNA abundance of HspA1A, HspA12A and HspA12B was higher at GD18 (before birth) and an mRNA expression peak of HspA1L, HspA8, HspA9, Hsp90AA1, Grp94, Hsp110 and Grp170 was observed at GD17. The mRNA abundance of most genes in atRA-induced cleft palates of the treatment group was different from that of the control group. Grp78, HspA14 and Hsp105 were closely associated with the normal palate development and cleft palate in mouse embryo, possibly as palate development-related genes. Except Grp170, the other genes may be closely associated with the development of mouse palates through participating in the stress response process and/or the antiapoptosis process.

Ion channnels and transporters in cancer. 5. Ion channels in control of cancer and cell apoptosis

Ion channels contribute to virtually all basic cellular processes, including such crucial ones for maintaining tissue homeostasis as proliferation, differentiation, and apoptosis. The involvement of ion channels in regulation of programmed cell death, or apoptosis, has been known for at least three decades based on observation that classical blockers of ion channels can influence cell death rates, prolonging or shortening cell survival. Identification of the central role of these channels in regulation of cell cycle and apoptosis as well as the recent discovery that the expression of ion channels is not limited solely to the plasma membrane, but may also include membranes of internal compartments, has led researchers to appreciate the pivotal role of ion channels plays in development of cancer. This review focuses on the aspects of programmed cell death influenced by various ion channels and how dysfunctions and misregulations of these channels may affect the development and progression of different cancers.

The potential of tetrandrine as a protective agent for ischemic stroke

Stroke is one of the leading causes of mortality, with a high incidence of severe morbidity in survivors. The treatment to minimize tissue injury after stroke is still unsatisfactory and it is mandatory to develop effective treatment strategies for stroke. The pathophysiology of ischemic stroke is complex and involves many processes including energy failure, loss of ion homeostasis, increased intracellular calcium level, platelet aggregation, production of reactive oxygen species, disruption of blood brain barrier, and inflammation and leukocyte infiltration, etc. Tetrandrine, a bisbenzylisoquinoline alkaloid, has many pharmacologic effects including anti-inflammatory and cytoprotective effects. In addition, tetrandrine has been found to protect the liver, heart, small bowel and brain from ischemia/reperfusion injury. It is a calcium channel blocker, and can inhibit lipid peroxidation, reduce generation of reactive oxygen species, suppress the production of cytokines and inflammatory mediators, inhibit neutrophil recruitment and platelet aggregation, which are all devastating factors during ischemia/reperfusion injury of the brain. Because tetrandrine can counteract these important pathophysiological processes of ischemic stroke, it has the potential to be a protective agent for ischemic stroke.

Activity of BK(Ca) channel is modulated by membrane cholesterol content and association with Na+/K+-ATPase in human melanoma IGR39 cells

Interaction of large conductance Ca(2+)- and voltage-activated K(+) (BK(Ca)) channels with Na(+)/K(+)-ATPase, caveolin-1, and cholesterol was studied in human melanoma IGR39 cells. Functional BK(Ca) channels were enriched in caveolin-rich and detergent-resistant membranes, i.e. rafts, and blocking of the channels by a specific BK(Ca) blocker paxilline reduced proliferation of the cells. Disruption of rafts by selective depletion of cholesterol released BK(Ca) channels from these domains with a consequent increase in their activity. Consistently, cholesterol enrichment of the cells increased the proportion of BK(Ca) channels in rafts and decreased their activity. Immunocytochemical analysis showed that BK(Ca) channels co-localize with Na(+)/K(+)-ATPase in a cholesterol-dependent manner, thus suggesting their co-presence in rafts. Supporting this, ouabain, a specific blocker of Na(+)/K(+)-ATPase, inhibited BK(Ca) whole-cell current markedly in control cells but not in cholesterol-depleted ones. This inhibition required the presence of external Na(+). Collectively, these data indicate that the presence of Na(+)/K(+)-ATPase in rafts is essential for efficient functioning of BK(Ca) channels, presumably because the pump maintains a low intracellular Na(+) proximal to the BK(Ca) channel. In conclusion, cholesterol could play an important role in cellular ion homeostasis and thus modulate many cellular functions and cell proliferation.

Biophysical properties of human medulloblastoma cells

Medulloblastoma is a pediatric high-grade cerebellar malignancy derived from neuronal precursors. Although electrophysiologic characteristics of cerebellar granule neurons at all stages of cell development have been well described, such characterization has not been reported for medulloblastoma. In this study we attempt to characterize important electrophysiologic features of medulloblastoma that may distinguish it from the surrounding cerebellum. Using patient-derived cell lines and tumor tissues, we show that medulloblastoma cells have no inward Na+ current or transient K+ current involved in action potential generation and propagation, typically seen in granule neurons. Expression and function of calcium-activated, large-conductance K+ channels are diminished in medulloblastoma, judged by electrophysiology and Western analysis. The resting membrane potential of medulloblastoma cells in culture is quite depolarized compared to granule neurons. Interestingly, medulloblastoma cells express small, fast-inactivating calcium currents consistent with T-type calcium channels, but these channels are activated only from hyperpolarized potentials, which are unlikely to occur. Additionally, a background acid-sensitive K+ current is present with features characteristic of TASK1 or TASK3 channels, such as inhibition by ruthenium red. Western analysis confirms expression of TASK1 and TASK3. In describing the electrophysiologic characteristics of medulloblastoma, one can see features that resemble other high-grade malignancies as opposed to normal cerebellar granule neurons. This supports the notion that the malignant phenotype of medulloblastoma is characterized by unique changes in ion channel expression.

Calcium-activated potassium channels BK and IK1 are functionally expressed in human gliomas but do not regulate cell proliferation

Gliomas are morbid brain tumors that are extremely resistant to available chemotherapy and radiology treatments. Some studies have suggested that calcium-activated potassium channels contribute to the high proliferative potential of tumor cells, including gliomas. However, other publications demonstrated no role for these channels or even assigned them antitumorogenic properties. In this work we characterized the expression and functional contribution to proliferation of Ca²⁺-activated K⁺ channels in human glioblastoma cells. Quantitative RT-PCR detected transcripts for the big conductance (BK), intermediate conductance (IK1), and small conductance (SK2) K⁺ channels in two glioblastoma-derived cell lines and a surgical sample of glioblastoma multiforme. Functional expression of BK and IK1 in U251 and U87 glioma cell lines and primary glioma cultures was verified using whole-cell electrophysiological recordings. Inhibitors of BK (paxilline and penitrem A) and IK1 channels (clotrimazole and TRAM-34) reduced U251 and U87 proliferation in an additive fashion, while the selective blocker of SK channels UCL1848 had no effect. However, the antiproliferative properties of BK and IK1 inhibitors were seen at concentrations that were higher than those necessary to inhibit channel activity. To verify specificity of pharmacological agents, we downregulated BK and IK1 channels in U251 cells using gene-specific siRNAs. Although siRNA knockdowns caused strong reductions in the BK and IK1 current densities, neither single nor double gene silencing significantly affected rates of proliferation. Taken together, these results suggest that Ca²⁺-activated K⁺ channels do not play a critical role in proliferation of glioma cells and that the effects of pharmacological inhibitors occur through their off-target actions.

Ion channels and the hallmarks of cancer

Plasma membrane (PM) ion channels contribute to virtually all basic cellular processes and are also involved in the malignant phenotype of cancer cells. Here, we review the role of ion channels in cancer in the context of their involvement in the defined hallmarks of cancer: 1) self-sufficiency in growth signals, 2) insensitivity to antigrowth signals, 3) evasion of programmed cell death (apoptosis), 4) limitless replicative potential, 5) sustained angiogenesis and 6) tissue invasion and metastasis. Recent studies have indicated that the contribution of specific ion channels to these hallmarks varies for different types of cancer. Therefore, to determine the importance of ion channels as targets for cancer diagnosis and treatment their expression, function and regulation must be assessed for each cancer.

Anticancer properties of Ganoderma lucidum methanol extracts in vitro and in vivo

Anticancer activities of various extracts of the medicinal mushroom, Ganoderma lucidum, have been widely demonstrated and are mainly associated with the presence of different bioactive polysaccharides and triterpenoids. We have evaluated and compared in vitro and in vivo the antitumor effects of two preparations from Ganoderma lucidum: a methanol extract containing total terpenoids (GLme) and a purified methanol extract containing mainly acidic terpenoids (GLpme). Both extracts inhibited tumor growth of B16 mouse melanoma cells inoculated subcutaneously into syngeneic C57BL/6 mice and reduced viability of B16 cells in vitro, whereby GLme exhibited stronger effect. Furthermore, anticancer activity of GLme was demonstrated for the first time against two other rodent tumor cell lines, L929-mouse fibrosarcoma and C6-rat astrocytoma. The mechanism of antitumor activity of GLme comprised inhibition of cell proliferation and induction of caspase-dependent apoptotic cell death mediated by upregulated p53 and inhibited Bcl-2 expression. Moreover, the antitumor effect of the GLme was associated with intensified production of reactive oxygen species, whereas their neutralization by the antioxidant, N-acetyl cysteine, resulted in partial recovery of cell viability. Thus, our results suggest that GLme might be a good candidate for treatment of diverse forms of cancers.

A protein interaction network for the large conductance Ca(2+)-activated K(+) channel in the mouse cochlea

The large conductance Ca(2+)-activated K(+) or BK channel has a role in sensory/neuronal excitation, intracellular signaling, and metabolism. In the non-mammalian cochlea, the onset of BK during development correlates with increased hearing sensitivity and underlies frequency tuning in non-mammals, whereas its role is less clear in mammalian hearing. To gain insights into BK function in mammals, coimmunoprecipitation and two-dimensional PAGE, combined with mass spectrometry, were used to reveal 174 putative BKAPs from cytoplasmic and membrane/cytoskeletal fractions of mouse cochlea. Eleven BKAPs were verified using reciprocal coimmunoprecipitation, including annexin, apolipoprotein, calmodulin, hippocalcin, and myelin P0, among others. These proteins were immunocolocalized with BK in sensory and neuronal cells. A bioinformatics approach was used to mine databases to reveal binary partners and the resultant protein network, as well as to determine previous ion channel affiliations, subcellular localization, and cellular processes. The search for binary partners using the IntAct molecular interaction database produced a putative global network of 160 nodes connected with 188 edges that contained 12 major hubs. Additional mining of databases revealed that more than 50% of primary BKAPs had prior affiliations with K(+) and Ca(2+) channels. Although a majority of BKAPs are found in either the cytoplasm or membrane and contribute to cellular processes that primarily involve metabolism (30.5%) and trafficking/scaffolding (23.6%), at least 20% are mitochondrial-related. Among the BKAPs are chaperonins such as calreticulin, GRP78, and HSP60 that, when reduced with siRNAs, alter BKalpha expression in CHO cells. Studies of BKalpha in mitochondria revealed compartmentalization in sensory cells, whereas heterologous expression of a BK-DEC splice variant cloned from cochlea revealed a BK mitochondrial candidate. The studies described herein provide insights into BK-related functions that include not only cell excitation, but also cell signaling and apoptosis, and involve proteins concerned with Ca(2+) regulation, structure, and hearing loss.

Water extract of Rheum officinale Baill. induces apoptosis in human lung adenocarcinoma A549 and human breast cancer MCF-7 cell lines

ETHNOPHARMACOLOGICAL RELEVANCE

Rheum officinale Baill. (Da Huang) is one of the herbs commonly used in traditional Chinese medicine formulae against cancer. The traditional decoction is similar to the water extract used in the present study.

AIM OF THE STUDY

The water extract of Da Huang was investigated to see if it possesses anticancer effects through apoptotic pathways.

MATERIALS AND METHODS

Human lung adenocarcinoma A549 and human breast cancer MCF-7 cell lines were treated with different concentrations of Da Huang water extract at different time intervals. Growth inhibition was detected by MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] and colony formation assays; apoptosis was detected by cell morphologic analysis, DNA fragmentation analysis and COMET assay.

RESULTS

Da Huang water extract was found to have significant growth inhibitory effects on both A549 and MCF-7 cell lines with IC(50) values 620+/-12.7 and 515+/-10.1 microg/ml, respectively. Growth inhibitory effects were dose- and time-dependent. A significant decrease in cell number, DNA fragmentation and single DNA strand breakages were observed in the Da Huang water extract treated A549 and MCF-7 cells.

CONCLUSIONS

This suggests that the water extract of Da Huang exerts potential anticancer activity through growth inhibition and apoptosis on MCF-7 and A549 cells lines.

MaxiK potassium channels in the function of chemoreceptor cells of the rat carotid body

Hypoxia activates chemoreceptor cells of the carotid body (CB) promoting an increase in their normoxic release of neurotransmitters. Catecholamine (CA) release rate parallels the intensity of hypoxia. Coupling of hypoxia to CA release requires cell depolarization, produced by inhibition of O(2)-regulated K(+) channels, and Ca(2+) entering the cells via voltage-operated channels. In rat chemoreceptor cells hypoxia inhibits large-conductance, calcium-sensitive K channels (maxiK) and a two-pore domain weakly inward rectifying K(+) channel (TWIK)-like acid-sensitive K(+) channel (TASK)-like channel, but the significance of maxiK is controversial. A proposal envisions maxiK contributing to set the membrane potential (E(m)) and the hypoxic response, but the proposal is denied by authors finding that maxiK inhibition does not depolarize chemoreceptor cells or alters intracellular Ca(2+) concentration or CA release in normoxia or hypoxia. We found that maxiK channel blockers (tetraethylammonium and iberiotoxin) did not modify CA release in rat chemoreceptor cells, in either normoxia or hypoxia, and iberiotoxin did not alter the Ca(2+) transients elicited by hypoxia. On the contrary, both maxiK blockers increased the responses elicited by dinitrophenol, a stimulus we demonstrate does not affect maxiK channels in isolated patches of rat chemoreceptor cells. We conclude that in rat chemoreceptor cells maxiK channels do not contribute to the genesis of the E(m), and that their full inhibition by hypoxia, preclude further inhibition by maxiK channel blockers. We suggest that full inhibition of this channel is required to generate the spiking behavior of the cells in acute hypoxia.

Ethanol modulates BKCa channels by acting as an adjuvant of calcium

Ethanol modulation of calcium- and voltage-gated potassium (slo1) channels alters neuronal excitability, cerebrovascular tone, brain function, and behavior, yet the mechanism of this modulation remains unknown. Using patch-clamp electrophysiology on recombinant BK(Ca) channels cloned from mouse brain and expressed in Xenopus laevis oocytes, we demonstrate that ethanol, even at concentrations maximally effective to modulate BK(Ca) channel function (100 mM), fails to gate the channel in absence of activating calcium. Moreover, ethanol does not modify intrinsic, voltage- or physiological magnesium-driven gating. The alcohol works as an adjuvant of calcium by selectively facilitating calcium-driven gating. This facilitation, however, renders differential ethanol effects on channel activity: potentiation at low (<10 microM) and inhibition at high (>10 microM) calcium, this dual pattern remaining largely unmodified by coexpression of brain slo1 channels with the neuronally abundant BK(Ca) channel beta(4) subunit. Calcium recognition by either of the slo1 high-affinity sensors (calcium bowl and RCK1 Asp362/Asp367) is required for ethanol to amplify channel activation by calcium. The Asp362/Asp367 site, however, is necessary and sufficient to sustain ethanol inhibition. This inhibition also results from ethanol facilitation of calcium action; in this case, ethanol favors channel dwelling in a calcium-driven, low-activity mode. The agonist-adjuvant mechanism that we advance from the calcium-ethanol interaction on slo1 might be applicable to data of ethanol action on a wide variety of ligand-gated channels.

A mutually exclusive alternative exon of slo1 codes for a neuronal BK channel with altered function

Large-conductance Ca(2+)- and voltage-activated K(+) (BK) channels are comprised of four pore-forming -subunits (Slo1), whose mRNA is alternatively spliced in a cell-specific manner. Here we report the first case of a correctly spliced mutually exclusive exon in a mammalian (human and mouse) BK channel; an exon coding for the region from S6 to the RCK1 domain is exchanged for an alternative exon of the same length. The slo1 transcript with this novel exon is present in native brain tissues and inclusion of the alternative exon profoundly alters the channel's gating characteristics: faster activation at low Ca(2+) concentrations and greater open probability at resting membrane potential at high Ca(2+) concentrations. The novel gating features conferred by the alternative exon are dominant over those of the commonly described Slo1 variant when coexpressed. The evolutionarily preserved splicing of the Slo1 S6-RCK1 linker segment possess great potential to fine-tune neuronal excitability.