Mitogenic signal transduction in human breast cancer cells

Biophysical control of plasticity and patterning in regeneration and cancer

Cells and tissues display a remarkable range of plasticity and tissue-patterning activities that are emergent of complex signaling dynamics within their microenvironments. These properties, which when operating normally guide embryogenesis and regeneration, become highly disordered in diseases such as cancer. While morphogens and other molecular factors help determine the shapes of tissues and their patterned cellular organization, the parallel contributions of biophysical control mechanisms must be considered to accurately predict and model important processes such as growth, maturation, injury, repair, and senescence. We now know that mechanical, optical, electric, and electromagnetic signals are integral to cellular plasticity and tissue patterning. Because biophysical modalities underly interactions between cells and their extracellular matrices, including cell cycle, metabolism, migration, and differentiation, their applications as tuning dials for regenerative and anti-cancer therapies are being rapidly exploited. Despite this, the importance of cellular communication through biophysical signaling remains disproportionately underrepresented in the literature. Here, we provide a review of biophysical signaling modalities and known mechanisms that initiate, modulate, or inhibit plasticity and tissue patterning in models of regeneration and cancer. We also discuss current approaches in biomedical engineering that harness biophysical control mechanisms to model, characterize, diagnose, and treat disease states.

Recent Developments on the Roles of Calcium Signals and Potential Therapy Targets in Cervical Cancer

Intracellular calcium (Ca²⁺) concentration ([Ca²⁺]i) is implicated in proliferation, invasion, and metastasis in cancerous tissues. A variety of oncologic therapies and some candidate drugs induce their antitumor effects (in part or in whole) through the modulation of [Ca²⁺]i. Cervical cancer is one of most common cancers among women worldwide. Recently, major research advances relating to the Ca²⁺ signals in cervical cancer are emerging. In this review, we comprehensively describe the current progress concerning the roles of Ca²⁺ signals in the occurrence, development, and prognosis of cervical cancer. It will enhance our understanding of the causative mechanism of Ca²⁺ signals in cervical cancer and thus provide new sights for identifying potential therapeutic targets for drug discovery.

TRP Channels as Molecular Targets to Relieve Endocrine-Related Diseases

Transient receptor potential (TRP) channels are polymodal channels capable of sensing environmental stimuli, which are widely expressed on the plasma membrane of cells and play an essential role in the physiological or pathological processes of cells as sensors. TRPs often form functional homo- or heterotetramers that act as cation channels to flow Na⁺ and Ca²⁺, change membrane potential and [Ca²⁺]_i (cytosolic [Ca²⁺]), and change protein expression levels, channel attributes, and regulatory factors. Under normal circumstances, various TRP channels respond to intracellular and extracellular stimuli such as temperature, pH, osmotic pressure, chemicals, cytokines, and cell damage and depletion of Ca²⁺ reserves. As cation transport channels and physical and chemical stimulation receptors, TRPs play an important role in regulating secretion, interfering with cell proliferation, and affecting neural activity in these glands and their adenocarcinoma cells. Many studies have proved that TRPs are widely distributed in the pancreas, adrenal gland, and other glands. This article reviews the specific regulatory mechanisms of various TRP channels in some common glands (pancreas, salivary gland, lacrimal gland, adrenal gland, mammary gland, gallbladder, and sweat gland).

TRPC6 channel and its implications in breast cancer: an overview

TRPC6 channel is widely expressed in most human tissues and participates in a number of physiological processes. TRPC6 belongs to the DAG-activated subfamily of channels, but has also been postulated as a mediator in the store-operated calcium entry pathway. The recent characterization of TRPC6 crystal structure has granted a wonderful tool to finally dissect and understand TRPC6 physiological and biophysical properties. Growing evidences have demonstrated that the pattern of expression of TRPC6 proteins is upregulated in several pathophysiological conditions, including breast cancer. However, the real role of TRPC6 in breast cancer persists still unknown. Here we present the current state of the art concerning the function and significance of TRPC6 in this disease. Future investigations should be focus in the creation and identification of compounds that specifically target the channel to ameliorate TRPC6-related diseases.

The Sigma-1 Receptor: When Adaptive Regulation of Cell Electrical Activity Contributes to Stimulant Addiction and Cancer

The sigma-1 receptor (σ1R) is an endoplasmic reticulum (ER)-resident chaperone protein that acts like an inter-organelle signaling modulator. Among its several functions such as ER lipid metabolisms/transports and indirect regulation of genes transcription, one of its most intriguing feature is the ability to regulate the function and trafficking of a variety of functional proteins. To date, and directly relevant to the present review, σ1R has been found to regulate both voltage-gated ion channels (VGICs) belonging to distinct superfamilies (i.e., sodium, Na⁺; potassium, K⁺; and calcium, Ca²⁺ channels) and non-voltage-gated ion channels. This regulatory function endows σ1R with a powerful capability to fine tune cells’ electrical activity and calcium homeostasis—a regulatory power that appears to favor cell survival in pathological contexts such as stroke or neurodegenerative diseases. In this review, we present the current state of knowledge on σ1R’s role in the regulation of cellular electrical activity, and how this seemingly adaptive function can shift cell homeostasis and contribute to the development of very distinct chronic pathologies such as psychostimulant abuse and tumor cell growth in cancers.

Cancer-Associated Intermediate Conductance Ca2+-Activated K⁺ Channel KCa3.1

Several tumor entities have been reported to overexpress K_Ca3.1 potassium channels due to epigenetic, transcriptional, or post-translational modifications. By modulating membrane potential, cell volume, or Ca²⁺ signaling, K_Ca3.1 has been proposed to exert pivotal oncogenic functions in tumorigenesis, malignant progression, metastasis, and therapy resistance. Moreover, K_Ca3.1 is expressed by tumor-promoting stroma cells such as fibroblasts and the tumor vasculature suggesting a role of K_Ca3.1 in the adaptation of the tumor microenvironment. Combined, this features K_Ca3.1 as a candidate target for innovative anti-cancer therapy. However, immune cells also express K_Ca3.1 thereby contributing to T cell activation. Thus, any strategy targeting K_Ca3.1 in anti-cancer therapy may also modulate anti-tumor immune activity and/or immunosuppression. The present review article highlights the potential of K_Ca3.1 as an anti-tumor target providing an overview of the current knowledge on its function in tumor pathogenesis with emphasis on vasculo- and angiogenesis as well as anti-cancer immune responses.

Intermediate-Conductance-Ca2-Activated K Channel IKCa1 Is Upregulated and Promotes Cell Proliferation in Cervical Cancer

BACKGROUND Accumulating data point to intermediate-conductance calcium-activated potassium channel (IKCa1) as a key player in controlling cell cycle progression and proliferation of human cancer cells. However, the role that IKCa1 plays in the growth of human cervical cancer cells is largely unexplored. MATERIAL AND METHODS In this study, Western blot analysis, immunohistochemical staining, and RT-PCR were first used for IKCa1protein and gene expression assays in cervical cancer tissues and HeLa cells. Then, IKCa1 channel blocker and siRNA were employed to inhibit the functionality of IKCa1 and downregulate gene expression in HeLa cells, respectively. After these treatments, we examined the level of cell proliferation by MTT method and measured IKCa1 currents by conventional whole-cell patch clamp technique. Cell apoptosis was assessed using the Annexin V-FITC/Propidium Iodide (PI) double-staining apoptosis detection kit. RESULTS We demonstrated that IKCa1 mRNA and protein are preferentially expressed in cervical cancer tissues and HeLa cells. We also showed that the IKCa1 channel blocker, clotrimazole, and IKCa1 channel siRNA can be used to suppress cervical cancer cell proliferation and decrease IKCa1 channel current. IKCa1 downregulation by specific siRNAs induced a significant increase in the proportion of apoptotic cells in HeLa cells. CONCLUSIONS IKCa1 is overexpressed in cervical cancer tissues, and IKCa1 upregulation in cervical cancer cell linea enhances cell proliferation, partly by reducing the proportion of apoptotic cells.

High expression of KCa3.1 in patients with clear cell renal carcinoma predicts high metastatic risk and poor survival

Background

Ca²⁺-activated K⁺ channels have been implicated in cancer cell growth, metastasis, and tumor angiogenesis. Here we hypothesized that high mRNA and protein expression of the intermediate-conductance Ca²⁺-activated K⁺ channel, KCa3.1, is a molecular marker of clear cell Renal Cell Carcinoma (ccRCC) and metastatic potential and survival.

Methodology/Principal Findings

We analyzed channel expression by qRT-PCR, immunohistochemistry, and patch-clamp in ccRCC and benign oncocytoma specimens, in primary ccRCC and oncocytoma cell lines, as well as in two ccRCC cell lines (Caki-1 and Caki-2). CcRCC specimens contained 12-fold higher mRNA levels of KCa3.1 than oncocytoma specimens. The large-conductance channel, KCa1.1, was 3-fold more highly expressed in ccRCC than in oncocytoma. KCa3.1 mRNA expression in ccRCC was 2-fold higher than in the healthy cortex of the same kidney. Disease specific survival trended towards reduction in the subgroup of high-KCa3.1-expressing tumors (p<0.08 vs. low-KCa3.1-expressing tumors). Progression-free survival (time to metastasis/recurrence) was reduced significantly in the subgroup of high-KCa3.1-expressing tumors (p<0.02, vs. low-KCa3.1-expressing tumors). Immunohistochemistry revealed high protein expression of KCa3.1 in tumor vessels of ccRCC and oncocytoma and in a subset of ccRCC cells. Oncocytoma cells were devoid of KCa3.1 protein. In a primary ccRCC cell line and Caki-1/2-ccRCC cells, we found KCa3.1-protein as well as TRAM-34-sensitive KCa3.1-currents in a subset of cells. Furthermore, Caki-1/2-ccRCC cells displayed functional Paxilline-sensitive KCa1.1 currents. Neither KCa3.1 nor KCa1.1 were found in a primary oncocytoma cell line. Yet KCa-blockers, like TRAM-34 (KCa3.1) and Paxilline (KCa1.1), had no appreciable effects on Caki-1 proliferation in-vitro.

Conclusions/Significance

Our study demonstrated expression of KCa3.1 in ccRCC but not in benign oncocytoma. Moreover, high KCa3.1-mRNA expression levels were indicative of low disease specific survival of ccRCC patients, short progression-free survival, and a high metastatic potential. Therefore, KCa3.1 is of prognostic value in ccRCC.

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.

L-Type Ca(2+) Channels and SK Channels in Mouse Embryonic Stem Cells and Their Contribution to Cell Proliferation

Mouse embryonic stem cells (mESCs) are capable of both self-renewal and multilineage differentiation; thus, they can be expanded in vivo or in vitro and differentiated to produce different cell types. Despite their biological and medical interest, many physiological properties of undifferentiated mESCs, such as ion channel function, are not fully understood. Ion channels are thought to be involved in cell proliferation and differentiation. The aim of this study was to characterize functional ion channels in cultured undifferentiated mESCs and their role in cell proliferation. L-type voltage-activated Ca(2+) channels sensitive to nifedipine and small-conductance Ca(2+)-activated K(+) (SK) channels sensitive to apamin were identified. Ca(2+)-activated K(+) currents were blocked by millimolar concentrations of tetraethylammonium. The effects of Ca(2+) channel and Ca(2+)-activated K(+) channel blockers on the proliferation of undifferentiated mESCs were investigated by bromodeoxyuridine (BrdU) incorporation. Dihydropyridine derivatives, such as nifedipine, inhibited cell growth and BrdU incorporation into the cells, whereas apamin, which selectively blocks SK channels, had no effect on cell growth. These results demonstrate that functional voltage-operated Ca(2+) channels and Ca(2+)-activated K(+) channels are present in undifferentiated mESCs. Moreover, voltage-gated L-type Ca(2+) channels, but not SK channels, might be necessary for proliferation of undifferentiated mESCs.

Involvement of potassium channels in the progression of cancer to a more malignant phenotype

Potassium channels are a diverse group of pore-forming transmembrane proteins that selectively facilitate potassium flow through an electrochemical gradient. They participate in the control of the membrane potential and cell excitability in addition to different cell functions such as cell volume regulation, proliferation, cell migration, angiogenesis as well as apoptosis. Because these physiological processes are essential for the correct cell function, K+ channels have been associated with a growing number of diseases including cancer. In fact, different K+ channel families such as the voltage-gated K+ channels, the ether à-go-go K+ channels, the two pore domain K+ channels and the Ca2+-activated K+ channels have been associated to tumor biology. Potassium channels have a role in neoplastic cell-cycle progression and their expression has been found abnormal in many types of tumors and cancer cells. In addition, the expression and activity of specific K+ channels have shown a significant correlation with the tumor malignancy grade. The aim of this overview is to summarize published data on K+ channels that exhibit oncogenic properties and have been linked to a more malignant cancer phenotype. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Two-layer modular analysis of gene and protein networks in breast cancer

Background

Genomic, proteomic and high-throughput gene expression data, when integrated, can be used to map the interaction networks between genes and proteins. Different approaches have been used to analyze these networks, especially in cancer, where mutations in biologically related genes that encode mutually interacting proteins are believed to be involved. This system of integrated networks as a whole exhibits emergent biological properties that are not obvious at the individual network level. We analyze the system in terms of modules, namely a set of densely interconnected nodes that can be further divided into submodules that are expected to participate in multiple biological activities in coordinated manner.

Results

In the present work we construct two layers of the breast cancer network: the gene layer, where the correlation network of breast cancer genes is analyzed to identify gene modules, and the protein layer, where each gene module is extended to map out the network of expressed proteins and their interactions in order to identify submodules. Each module and its associated submodules are analyzed to test the robustness of their topological distribution. The constituent biological phenomena are explored through the use of the Gene Ontology. We thus construct a “network of networks”, and demonstrate that both the gene and protein interaction networks are modular in nature. By focusing on the ontological classification, we are able to determine the entire GO profiles that are distributed at different levels of hierarchy. Within each submodule most of the proteins are biologically correlated, and participate in groups of distinct biological activities.

Conclusions

The present approach is an effective method for discovering coherent gene modules and protein submodules. We show that this also provides a means of determining biological pathways (both novel and as well those that have been reported previously) that are related, in the present instance, to breast cancer. Similar strategies are likely to be useful in the analysis of other diseases as well.

DNA microarray-based gene expression profiling of estrogenic chemicals

We summarize updated information about DNA microarray-based gene expression profiling by focusing on its application to estrogenic chemicals. First, estrogenic chemicals, including natural/industrial estrogens and phytoestrogens, and the methods for detection and evaluation of estrogenic chemicals were overviewed along with a comprehensive list of estrogenic chemicals of natural or industrial origin. Second, gene expression profiling of chemicals using a focused microarray containing estrogen-responsive genes is summarized. Third, silent estrogens, a new type of estrogenic chemicals characterized by their estrogenic gene expression profiles without growth stimulative or inhibitory effects, have been identified so far exclusively by DNA microarray assay. Lastly, the prospect of a microarray assay is discussed, including issues such as commercialization, future directions of applications and quality control methods.

A model for the regulation of T-type Ca(2+) channels in proliferation: roles in stem cells and cancer

Ca(2+) influx at critical points in the cell cycle is required for proliferation. This requirement is so ubiquitous that its occurrence is often treated as background noise. Yet without it, cells stop dividing, suggesting an obvious and potentially effective way to treat cancer. To control proliferation by controlling Ca(2+) influx requires that the mechanism be elucidated, but this field of study has been filled with controversy and devoid of therapeutic utility. In this study, the authors present a model for the regulation of Ca(2+) influx at the G1/S restriction point in cancer and stem cells that is simple, cohesive and, we believe, reasonably complete. The model illustrates the essential role of T-type Ca(2+) channels in mediating influx and points clearly to the therapeutic strategies that have recently entered clinical trials.

The voltage-dependent K(+) channels Kv1.3 and Kv1.5 in human cancer

Voltage-dependent K⁺ channels (Kv) are involved in a number of physiological processes, including immunomodulation, cell volume regulation, apoptosis as well as differentiation. Some Kv channels participate in the proliferation and migration of normal and tumor cells, contributing to metastasis. Altered expression of Kv1.3 and Kv1.5 channels has been found in several types of tumors and cancer cells. In general, while the expression of Kv1.3 apparently exhibits no clear pattern, Kv1.5 is induced in many of the analyzed metastatic tissues. Interestingly, evidence indicates that Kv1.5 channel shows inversed correlation with malignancy in some gliomas and non-Hodgkin's lymphomas. However, Kv1.3 and Kv1.5 are similarly remodeled in some cancers. For instance, expression of Kv1.3 and Kv1.5 correlates with a certain grade of tumorigenicity in muscle sarcomas. Differential remodeling of Kv1.3 and Kv1.5 expression in human cancers may indicate their role in tumor growth and their importance as potential tumor markers. However, despite of this increasing body of information, which considers Kv1.3 and Kv1.5 as emerging tumoral markers, further research must be performed to reach any conclusion. In this review, we summarize what it has been lately documented about Kv1.3 and Kv1.5 channels in human cancer.

Up-regulation of Kv7.1 channels in thromboxane A2-induced colonic cancer cell proliferation

Thromboxane A2 (TXA2) is known to stimulate colonic cancer cell proliferation, although the mechanism has not been clarified. In this study, we compared the expression levels of Kv7.1 K(+) channels between human colorectal cancer tissue and the accompanying non-tumor mucosa. Kv7.1 proteins were found to be consistently up-regulated in the cancer tissues from different patients. Kv7.1 was also expressed in human colonic cancer cell lines. Treatment of colonic cancer cells with 9,11-epithio-11,12-methano-thromboxane A2 (STA2), a stable analogue of TXA2, significantly increased whole-cell K(+) currents sensitive to chromanol 293B, an inhibitor of Kv7.1 channels, in parallel with an increased expression of Kv7.1 proteins. In contrast, TXB2, an inactive metabolite of TXA2, had no effects on expression level and function of Kv7.1. A TXA2 receptor antagonist (SQ29548) and an inhibitor of cAMP-dependent protein kinase (Rp-8-Br-MB-cAMPS) inhibited STA2-induced increases in both Kv7.1 expression and chromanol 293B-sensitive K(+) currents. Interestingly, STA2-stimulated proliferation of colonic cancer cells was inhibited by chromanol 293B. These results suggest that Kv7.1 channels are involved in the TXA2-induced cancer cell proliferation and that they are up-regulated by the TXA2 receptor-mediated cAMP pathway.

Membrane potential and cancer progression

Membrane potential (V_m), the voltage across the plasma membrane, arises because of the presence of different ion channels/transporters with specific ion selectivity and permeability. V_m is a key biophysical signal in non-excitable cells, modulating important cellular activities, such as proliferation and differentiation. Therefore, the multiplicities of various ion channels/transporters expressed on different cells are finely tuned in order to regulate the V_m. It is well-established that cancer cells possess distinct bioelectrical properties. Notably, electrophysiological analyses in many cancer cell types have revealed a depolarized V_m that favors cell proliferation. Ion channels/transporters control cell volume and migration, and emerging data also suggest that the level of V_m has functional roles in cancer cell migration. In addition, hyperpolarization is necessary for stem cell differentiation. For example, both osteogenesis and adipogenesis are hindered in human mesenchymal stem cells (hMSCs) under depolarizing conditions. Therefore, in the context of cancer, membrane depolarization might be important for the emergence and maintenance of cancer stem cells (CSCs), giving rise to sustained tumor growth. This review aims to provide a broad understanding of the V_m as a bioelectrical signal in cancer cells by examining several key types of ion channels that contribute to its regulation. The mechanisms by which V_m regulates cancer cell proliferation, migration, and differentiation will be discussed. In the long term, V_m might be a valuable clinical marker for tumor detection with prognostic value, and could even be artificially modified in order to inhibit tumor growth and metastasis.

Targeted polymersome delivery of siRNA induces cell death of breast cancer cells dependent upon Orai3 protein expression

Polymersomes, polymeric vesicles that self-assemble in aqueous solutions from block copolymers, have been avidly investigated in recent years as potential drug delivery agents. Past work has highlighted peptide-functionalized polymersomes as a highly promising targeted delivery system. However, few reports have investigated the ability of polymersomes to operate as gene delivery agents. In this study, we report on the encapsulation and delivery of siRNA inside of peptide-functionalized polymersomes composed of poly(1,2-butadiene)-b-poly(ethylene oxide). In particular, PR_b peptide-functionalized polymer vesicles are shown to be a promising system for siRNA delivery. PR_b is a fibronectin mimetic peptide targeting specifically the α(5)β(1) integrin. The Orai3 gene was targeted for siRNA knockdown, and PR_b-functionalized polymer vesicles encapsulating siRNA were found to specifically decrease cell viability of T47D breast cancer cells to a certain extent, while preserving viability of noncancerous MCF10A breast cells. siRNA delivery by PR_b-functionalized polymer vesicles was compared to that of a current commercial siRNA transfection agent, and produced less dramatic decreases in cancer cell viability, but compared favorably in regards to the relative toxicity of the delivery systems. Finally, delivery and vesicle release of a fluorescent encapsulate by PR_b-functionalized polymer vesicles was visualized by confocal microscopy, and colocalization with cellular endosomes and lysosomes was assessed by organelle staining. Polymersomes were observed to primarily release their encapsulate in the early endosomal intracellular compartments, and data may suggest some escape to the cytosol. These results represent a promising first generation model system for targeted delivery of siRNA.

Effects on human transcriptome of mutated BRCA1 BRCT domain: a microarray study

BACKGROUND

BRCA1 (breast cancer 1, early onset) missense mutations have been detected in familial breast and ovarian cancers, but the role of these variants in cancer predisposition is often difficult to ascertain. In this work, the molecular mechanisms affected in human cells by two BRCA1 missense variants, M1775R and A1789T, both located in the second BRCT (BRCA1 C Terminus) domain, have been investigated. Both these variants were isolated from familial breast cancer patients and the study of their effect on yeast cell transcriptome has previously provided interesting clues to their possible role in the pathogenesis of breast cancer.

METHODS

We compared by Human Whole Genome Microarrays the expression profiles of HeLa cells transfected with one or the other variant and HeLa cells transfected with BRCA1 wild-type. Microarray data analysis was performed by three comparisons: M1775R versus wild-type (M1775RvsWT-contrast), A1789T versus wild-type (A1789TvsWT-contrast) and the mutated BRCT domain versus wild-type (MutvsWT-contrast), considering the two variants as a single mutation of BRCT domain.

RESULTS

201 differentially expressed genes were found in M1775RvsWT-contrast, 313 in A1789TvsWT-contrast and 173 in MutvsWT-contrast. Most of these genes mapped in pathways deregulated in cancer, such as cell cycle progression and DNA damage response and repair.

CONCLUSIONS

Our results represent the first molecular evidence of the pathogenetic role of M1775R, already proposed by functional studies, and give support to a similar role for A1789T that we first hypothesized based on the yeast cell experiments. This is in line with the very recently suggested role of BRCT domain as the main effector of BRCA1 tumor suppressor activity.

Biopotential signals of breast cancer versus tumor types and proliferation stages

Clinical studies have shown compelling data of elevated biopotential signals recorded noninvasively from the breasts of women with breast cancer. While these data are compelling and show a strong potential for use in the noninvasive early detection of breast cancer, there remains significant knowledge gaps which must be addressed before this technology can be routinely used for breast cancer detection. A diffusion-drift model is developed to study the spatial and temporal characteristics of the biopotential signals of breast tumors taking into account the morphology and cell division stages. The electric signals of the most common tumor types-papillary, compact, and comedo-are also considered. The largest biopotential signal is observed from the compact tumor, while the smallest signal is observed from the papillary type. The results also show an increase in the time duration of the generated biopotential signals when cancer cells start their transitions at different time instants. The spatial and temporal variations of the biopotential signals are correlated with the tumor pattern which can have important implications for breast cancer detection.

The life and death of breast cancer cells: proposing a role for the effects of phytoestrogens on potassium channels

Changes in the regulation of potassium channels are increasingly implicated in the altered activity of breast cancer cells. Increased or reduced expression of a number of K(+) channels have been identified in numerous breast cancer cell lines and cancerous tissue biopsy samples, compared to normal tissue, and are associated with tumor formation and spread, enhanced levels of proliferation, and resistance to apoptotic stimuli. Through knockout or silencing of K(+) channel genes, and use of specific or more broad pharmacologic K(+) channel blockers, the growth of numerous cell lines, including breast cancer cells, has been modified. In this manner it has been proposed that in MCF7 breast cancer cells proliferation appears to be regulated by the activity of a number of K(+) channels, including the Ca(2+) activated K(+) channels, and the voltage-gated K(+) channels hEAG and K(v)1.1. The effect of phytoestrogens on K(+) channels has not been extensively studied but yields some interesting results. In a number of cell lines the phytoestrogen genistein inhibits K(+) current through several channels including K(v)1.3 and hERG. Where it has been used, structurally similar daidzein has little or no effect on K(+) channel activity. Since many K(+) channels have roles in proliferation and apoptosis in breast cancer cells, the impact of K(+) channel regulation by phytoestrogens is of potentially great relevance.

Mechanism of Cancer Growth Suppression of Alpha-Fetoprotein Derived Growth Inhibitory Peptides (GIP): Comparison of GIP-34 versus GIP-8 (AFPep). Updates and Prospects

The Alpha-fetoprotein (AFP) derived Growth Inhibitory Peptide (GIP) is a 34-amino acid segment of the full-length human AFP molecule that inhibits tumor growth and metastasis. The GIP-34 and its carboxy-terminal 8-mer segment, termed GIP-8, were found to be effective as anti-cancer therapeutic peptides against nine different human cancer types. Following the uptake of GIP-34 and GIP-8 into the cell cytoplasm, each follows slightly different signal transduction cascades en route to inhibitory pathways of tumor cell growth and proliferation. The parallel mechanisms of action of GIP-34 versus GIP-8 are demonstrated to involve interference of signaling transduction cascades that ultimately result in: (1) cell cycle S-phase/G2-phase arrest; (2) prevention of cyclin inhibitor degradation; (3) protection of p53 from inactivation by phosphorylation; and (4) blockage of K+ ion channels opened by estradiol and epidermal growth factor (EGF). The overall mechanisms of action of both peptides are discussed in light of their differing modes of cell attachment and uptake fortified by RNA microarray analysis and electrophysiologic measurements of cell membrane conductance and resistance. As a chemotherapeutic adjunct, the GIPs could potentially aid in alleviating the negative side effects of: (1) tamoxifen resistance, uterine hyperplasia/cancer, and blood clotting; (2) Herceptin antibody resistance and cardiac (arrest) arrhythmias; and (3) doxorubicin's bystander cell toxicity.

Persistent and non-persistent changes in gene expression result from long-term estrogen exposure of MCF-7 breast cancer cells

Life-long estrogen exposure is recognized as a major risk factor for the development of breast cancer. While the initial events in the regulation of gene expression by estrogen have been described in detail, far less is known of the role of estrogen in the long-term regulation of gene expression. In this study, we investigated the effects of long-term exposure of MCF-7 breast cancer cells to 1nM 17β-estradiol on gene expression with the goal of distinguishing between gene expression that is continually reliant on estrogen receptor (ER) function as opposed to secondary and persistent effects that are downstream of ER. To assess the direct involvement of ER in the differential gene expression of long-term estrogen exposed (LTEE) cells in comparison with that of control cells, we exposed cultures to the selective estrogen receptor modulator raloxifene (RAL). cDNA microarray analysis showed that exposure to RAL inhibited expression of numerous characterized estrogen-regulated genes, including PGR, GREB1, and PDZK1. Genes that were increased in expression in LTEE cells yet were unaffected by RAL exposure included the aryl hydrocarbon receptor (AHR) and numerous other genes that were not previously reported to be regulated by estrogen. Epigenetic regulation was evident for the AHR gene; AhR transcript levels remained elevated for several cell passages after the removal of estrogen. Signal transducer and activator of transcription 1 (STAT1); STAT1-regulated genes including ISG15, IFI27, and IFIT1; and MHC class I genes were also up-regulated in LTEE cells and were unaffected by RAL exposure. STAT1 is commonly overexpressed in breast and other cancers, and is associated with increased resistance to radiation and chemotherapy. This is the first study to relate estrogen exposure to increased STAT1 expression in breast cancer cells, an effect that may represent an additional role of estrogen in the pathogenesis of breast cancer.

Down-regulation of Orai3 arrests cell-cycle progression and induces apoptosis in breast cancer cells but not in normal breast epithelial cells

Breast cancer (BC) is the leading cancer in the world in terms of incidence and mortality in women. However, the mechanism by which BC develops remains largely unknown. The increase in cytosolic free Ca(2+) can result in different physiological changes including cell growth and death. Orai isoforms are highly Ca(2+) selective channels. In the present study, we analyzed Orai3 expression in normal and cancerous breast tissue samples, and its role in MCF-7 BC and normal MCF-10A mammary epithelial cell lines. We found that the expression of Orai3 mRNAs was higher in BC tissues and MCF-7 cells than in normal tissues and MCF-10A cells. Down-regulation of Orai3 by siRNA inhibited MCF-7 cell proliferation and arrested cell cycle at G1 phase. This phenomenon is associated with a reduction in CDKs 4/2 (cyclin-dependent kinases) and cyclins E and D1 expression and an accumulation of p21(Waf1/Cip1) (a cyclin-dependent kinase inhibitor) and p53 (a tumor-suppressing protein). Orai3 was also involved in MCF-7 cell survival. Furthermore, Orai3 mediated Ca(2+) entry and contributed to intracellular calcium concentration ([Ca(2+)](i)). In MCF-10A cells, silencing Orai3 failed to modify [Ca(2+)](i), cell proliferation, cell-cycle progression, cyclins (D1, E), CDKs (4, 2), and p21(Waf1/Cip1) expression. Our results provide strong evidence for a significant effect of Orai3 on BC cell growth in vitro and show that this effect is associated with the induction of cell cycle and apoptosis resistance. Our study highlights a possible role of Orai3 as therapeutic target in BC therapy.

Reviewing once more the c-myc and Ras collaboration: converging at the cyclin D1-CDK4 complex and challenging basic concepts of cancer biology

The c-myc is a proto-oncogene that manifests aberrant expression at high frequencies in most types of human cancer. C-myc gene amplifications are often observed in various cancers as well. Ample studies have also proved that c-myc has a potent oncogenicity, which can be further enhanced by collaborations with other oncogenes such as Bcl-2 and activated Ras. Studies on the collaborations of c-myc with Ras or other genes in oncogenicity have established several basic concepts and have disclosed their underlying mechanisms of tumor biology, including "immortalization" and "transformation". In many cases, these collaborations may converge at the cyclin D1-CDK4 complex. In the meantime, however, many results from studies on the c-myc, Ras and cyclin D1-CDK4 also challenge these basic concepts of tumor biology and suggest to us that the immortalized status of cells should be emphasized. Stricter criteria and definitions for a malignantly transformed status and a benign status of cells in culture also need to be established to facilitate our study of the mechanisms for tumor formation and to better link up in vitro data with animal results and eventually with human cancer pathology.

Estrogen prevents sustained COLO-205 human colon cancer cell growth by inducing apoptosis, decreasing c-myb protein, and decreasing transcription of the anti-apoptotic protein bcl-2

The proto-oncogene c-myb is overexpressed in human colon cancer cells. c-myb is known to be affected by estrogen in some breast cancers and leukemias. However, the mechanism of c-myb regulation via estrogen in colon cancer requires further investigation. Human COLO-205 colon cancer cells were cultured and treated with beta-estradiol for 24 h. Apoptosis was quantified using acridine orange/propidium iodide labeling and confirmed with DNA fragmentation gel electrophoresis. Expression of c-myb protein was assessed via SDS-PAGE and immunoblotting and RT-PCR was used to quantify bcl-2 RNA. Protein and RNA expression levels were also assayed after c-myb siRNA treatment for 24 h. We demonstrate an increase in apoptosis after 24 h of beta-estradiol treatment of human COLO-205 colon cancer cells. Estrogen treatment also decreases c-myb protein levels as well as expression of its transcriptional target bcl-2. Suppression of c-myb protein also results in increased apoptosis and decreases bcl-2 expression. These results indicate that estrogen has a protective effect from sustained colon cancer cell growth at least partly through suppression of c-myb and bcl-2.

Modeling electrical activities of a growing breast cancerous cell based on a semiconductor approach

A two dimensional diffusion-drift model is developed to simulate the electrical activities of a breast cancerous cell during the hyperpolarization which occurs at the G1/S transition. The model focuses on calculating the temporal and the spatial patterns of the electric current densities and biopotentials generated at the cell boundary and its surroundings. Different durations for the hyperpolarization phase were studied. The results show that the electric signals generated in the tumor cell's surroundings increase as the duration of the hyperpolarization phase decreases or when the transition becomes faster.

Evidence that TRPM7 is required for breast cancer cell proliferation

Because transient receptor potential (TRP) channels have been implicated in tumor progression, we have investigated the potential role of TRPM7 channel in breast cancer cell proliferation. Under whole cell patch clamp, a Mg2+-inhibited cationic (MIC) current was observed in MCF-7 cells. This current was characterized by an inward current and a strong outward rectifying current that were both inhibited in a concentration-dependent manner by the presence of intracellular Mg2+ or Mg2+-ATP. The inward current was reduced by La3+, and the outward current was sensitive to 2-aminoethoxydiphenyl borate (2-APB), spermine, La3+, and flufenamic acid. Importantly, a similar MIC current was also recorded in the primary culture of human breast cancerous epithelial cells (hBCE). Moreover, TRPM7 transcripts were found in both hBCE and MCF-7 cells. In MCF-7 cells, the MIC current was inhibited by TRPM7 small interfering RNA. Interestingly, we found that cell proliferation and intracellular Ca2+ concentration were also reduced by TRPM7 silencing in MCF-7 cells. TRPM7 channels were also found in both human breast cancer and healthy tissues. Importantly, TRPM7 channel was overexpressed in grade III breast cancer samples associated with important Ki67 or tumor size. Our findings strongly suggest that TRPM7 is involved in the proliferative potentiality of breast cancer cells, probably by regulating Ca2+ influx.

Silencing of Kv4.1 potassium channels inhibits cell proliferation of tumorigenic human mammary epithelial cells

Potassium channel activity has been shown to facilitate cell proliferation in cancer cells. In the present study, the role of Kv4.1 channels in immortal and tumorigenic human mammary epithelial cells was investigated. Kv4.1 protein expression was positively correlated with tumorigenicity. Moreover, transfection with siRNAs targeting Kv4.1 mRNA suppressed proliferation of tumorigenic mammary epithelial cells. Experiments using mRNA isolated from human breast cancer tissues revealed that the level of Kv4.1 mRNA expression varied depending on the stage of the tumor. Kv4.1 protein expression increased during stages T2 and T3 compared to normal tissue. These results demonstrated that Kv4.1 plays a role in proliferation of tumorigenic human mammary epithelial cells. In addition, elevated Kv4.1 expression may be useful as a diagnostic marker for staging mammary tumors and selective blockers of Kv4.1 may serve to suppress tumor cell proliferation.

Ion channel regulation of intracellular calcium and airway smooth muscle function

Airway hyper-responsiveness associated with asthma is mediated by airway smooth muscle cells (SMCs) and has a complicated etiology involving increases in cell contraction and proliferation and the secretion of inflammatory mediators. Although these pathological changes are diverse, a common feature associated with their regulation is a change in intracellular Ca(2+) concentration ([Ca(2+)](i)). Because the [Ca(2+)](i) itself is a function of the activity and expression of a variety of ion channels, in both the plasma membrane and sarcoplasmic reticulum of the SMC, the modification of this ion channel activity may predispose airway SMCs to hyper-responsiveness. Our objective is to review how ion channels determine the [Ca(2+)](i) and influence the function of airway SMCs and emphasize the potential of ion channels as sites for therapeutic approaches to asthma.

Expression of TRPC6 channels in human epithelial breast cancer cells

Background

TRP channels have been shown to be involved in tumour generation and malignant growth. However, the expression of these channels in breast cancer remains unclear. Here we studied the expression and function of endogenous TRPC6 channels in a breast cancer cell line (MCF-7), a human breast cancer epithelial primary culture (hBCE) and in normal and tumour breast tissues.

Methods

Molecular (Western blot and RT-PCR), and immunohistochemical techniques were used to investigate TRPC6 expression. To investigate the channel activity in both MCF-7 cells and hBCE we used electrophysiological technique (whole cell patch clamp configuration).

Results

A non selective cationic current was activated by the oleoyl-2-acetyl-sn-glycerol (OAG) in both hBCE and MCF-7 cells. OAG-inward current was inhibited by 2-APB, SK&F 96365 and La³⁺. TRPC6, but not TRPM7, was expressed both in hBCE and in MCF-7 cells. TRPC3 was only expressed in hBCE. Clinically, TRPC6 mRNA and protein were elevated in breast carcinoma specimens in comparison to normal breast tissue. Furthermore, we found that the overexpression of TRPC6 protein levels were not correlated with tumour grades, estrogen receptor expression or lymph node positive tumours.

Conclusion

Our results indicate that TRPC6 channels are strongly expressed and functional in breast cancer epithelial cells. Moreover, the overexpression of these channels appears without any correlation with tumour grade, ER expression and lymph node metastasis. Our findings support the idea that TRPC6 may have a role in breast carcinogenesis.

Upregulation of ATP-sensitive potassium channels for estrogen-mediated cell proliferation in human uterine leiomyoma cells

OBJECTIVES

The objectives of the present study were to evaluate the expression level of ATP-sensitive potassium (K(ATP)) channels in smooth muscle cells in human uterine leiomyoma and the involvement of the channel in potentiating effect of estrogen on leiomyoma growth.

METHODS

Reverse transcription-polymerase chain reaction (RT-PCR), real-time PCR and Western blot were used for the identification and quantification of K(ATP)-channel subunits in the control myometrial and leiomyoma cells. Furthermore, we measured the K(ATP)-channel activity in enzymatically isolated single uterine smooth muscle cells by whole-cell patch-clamp recordings. The estrogen-induced cell proliferation in leiomyoma was measured by the MTT assay.

RESULTS

The subunits of K(ATP) channels (Kir6.1, Kir6.2, SUR2B) were more highly expressed in leiomyoma cells than in control cells. The whole-cell currents mainly through K(ATP) channels were also greater in the leiomyoma cells. Estrogen applied in the bath solution could acutely enhance the channel activity. Estrogen-induced proliferation of the leiomyoma cells was inhibited by pretreatment with glibenclamide, a K(ATP)-channel inhibitor.

CONCLUSION

Estrogen may induce the proliferation of leiomyoma cells, at least in part, by activating the K(ATP) channel. Increased expression of the K(ATP) channel may be a causal factor for the high growth rate of uterine leiomyoma.

Can cancer be reversed by engineering the tumor microenvironment?

To advance cancer research in a transformative way, we must redefine the problem. Although epithelial cancers, such as breast cancer, may be caused by random somatic gene mutations, the reality is that this is only one of many ways to induce tumor formation. Cancers also can be produced in experimental systems in vitro and in vivo, for example, by inducing sustained alterations of extracellular matrix (ECM) structure. Moreover, certain epithelial cancers can be induced to 'reboot' and regenerate normal tissue morphology when combined with embryonic mesenchyme or exogenous ECM scaffolds that are produced through epithelial-stromal interactions. At the same time, work in the field of Mechanical Biology has revealed that many cell behaviors critical for cancer formation (e.g., growth, differentiation, motility, apoptosis) can be controlled by physical interactions between cells and their ECM adhesions that alter the mechanical force balance in the ECM, cell and cytoskeleton. Epithelial tumor progression also can be induced in vitro by changing ECM mechanics or altering cytoskeletal tension generation through manipulation of the Rho GTPase signaling pathway. Mechanical interactions between capillary cells and ECM that are mediated by Rho signaling similarly mediate control of capillary cell growth and angiogenesis, which are equally critical for cancer progression and metastasis. These findings question basic assumptions in the cancer field, and raise the intriguing possibility that cancer may be a reversible disease that results from progressive deregulation of tissue architecture, which leads to physical changes in cells and altered mechanical signaling. This perspective raises the possibility of developing a tissue engineering approach to cancer therapy in which biologically inspired materials that mimic the embryonic microenvironment are used to induce cancers to revert into normal tissues.

Functional role of CCCTC binding factor in insulin-stimulated cell proliferation

OBJECTIVES

CCCTC binding factor (CTCF) is a nuclear protein containing an 11-zinc-finger DNA-binding domain. CTCF plays important roles in the regulation of epigenetics and gene transcription. As a multifunctional protein, CTCF is also involved in the regulation of cell proliferation and of apoptosis. However, mechanisms underlining the regulatory function of CTCF in mediating growth factor- and cytokine-stimulated cell fate are largely unknown.

MATERIALS AND METHODS

The effect of CTCF on insulin-induced ML-1 cell proliferation was investigated by studying insulin-stimulated extracellular signal-regulated kinase (Erk) and Akt signalling pathways, and the alterations of CTCF activity in these cells.

RESULTS

The present study demonstrates that insulin-induced human haematopoietic myeloblastic ML-1 cell proliferation requires increased CTCF expression. Inhibition of Erk and Akt pathways with specific blockers or by dominantly negative expression of Erk and Akt mutants markedly suppressed expression of CTCF and resulted in retardation of cell proliferation. Furthermore, insulin-induced ML-1 cell proliferation was significantly enhanced by overexpression of cDNA encoding full-length CTCF. In contrast, ML-1 cell proliferation was inhibited by knocking down CTCF mRNA using specific small interference RNA.

CONCLUSIONS

Our results indicate that CTCF is indeed a protein with multifunctional activity that plays a significant role in modulating signalling pathways to mediate insulin-induced ML-1 cell proliferation.

K+ channel expression in human breast cancer cells: involvement in cell cycle regulation and carcinogenesis

K+ channels are a most diverse class of ion channels in the plasma membrane and are distributed widely throughout a variety of cells including cancer cells. Evidence has been accumulating from fundamental studies indicating that tumour cells possess various types of K+ channels and that these K+ channels play important roles in regulating tumor cell proliferation, cell cycle progression and apoptosis. Moreover, a significant increase in K+ channel expression has been correlated with tumorigenesis, suggesting the possibility of using these proteins as transformation markers and perhaps reducing the tumor growth rate by selectively inhibiting their functional activity. Significant progress has been made in defining the properties of breast K+ channels, including their biophysical and pharmacological properties and distribution throughout different phases of the cell cycle in breast cell line MCF-7. This review aims to provide a comprehensive overview of the current state of research into K+ channels/currents in breast cancer cells. The possible mechanisms by which K+ channels affect tumor cell proliferation and cell cycle progression are discussed.

Injury-induced neurogenesis in Bax-deficient mice: evidence for regulation by voltage-gated potassium channels

Adult neural stem and progenitor cells may help remodel the brain in response to injury. The pro-apoptotic molecule Bax has recently been identified as a key player in adult neural stem cell survival. In Bax-deficient mice that have undergone traumatic brain injury, we find increased numbers of neural progenitor cells in the dentate gyrus and improved remodeling of the hippocampus. Exogenous potassium chloride mimics spreading depression (SD)-like events in vitro, and Bax-deficient neural stem cells proliferate in response to these events more robustly than wild-type neural stem cells. Selective potassium channel blockers interrupt SD-mediated stimulation of stem cells. In addition, the potassium channel Kv4.1 is expressed within neural stem and progenitor cells in the dentate gyrus and is increased in Bax-deficiency. These data suggest that the neuroprotection observed after injury in Bax-deficiency may be due to increased neurogenesis via activation of the Kv4 family of potassium channels.

KCa3.1 Ca2+ activated K+ channels regulate human airway smooth muscle proliferation

Airway smooth muscle cell hyperplasia contributes to airway remodeling and hyperreactivity characteristic of asthma. Changes to potassium channel activity in proliferating human airway smooth muscle (HASM) cells have been described, but no regulatory role in proliferation has been attributed to them. We sought to investigate the expression of the intermediate conductance calcium-activated potassium channel K(Ca)3.1 in HASM cells and investigate its role in proliferation. Smooth muscle cells derived from human airways were grown in vitro and K(Ca)3.1 channel expression was measured using Western blot, RT-PCR, and patch clamp electrophysiology. Pharmacologic inhibitors of the channel were used in assays of cellular proliferation, and flow cytometry was used to identify cell cycle regulation. HASM cells expressed K(Ca)3.1 channel mRNA, protein, and activity with up-regulation evident after transforming growth factor-beta stimulation. Pharmacologic inhibition of K(Ca)3.1 led to growth arrest in cells stimulated to proliferate with mitogens. These inhibitors did not cause cellular toxicity or induce apoptosis. We have demonstrated, for the first time, the expression of K(Ca)3.1 channels in HASM cells. In addition, we have shown that K(Ca)3.1 channels are important in HASM cell proliferation, making these channels a potential therapeutic target in airway remodeling.

Voltage-gated K+ channels are associated with cell proliferation and cell cycle of ovarian cancer cell

OBJECTIVES

To study the role of Voltage-gated potassium ion channels (Kv) in cell proliferation and cell cycle of ovarian cancer cell.

METHODS

The effects of voltage-gate K+ channels on human ovarian cancer cell line (A2780 cell) proliferation and cell cycle were observed by means of MTT and flow cytometry. A variety of K+ channel blockers were used in order to differentiate the critical subtype of K+ channels involved. Mechanism of K+ channel in cell proliferation was explored by studying the relationship between the K+ channel and Ca2+ entry. Kv and L-type Ca2+ channel gene expressions were determined by RT-PCR.

RESULTS

4-Aminopyridine, an inhibitor of voltage-gated K+ channels, significantly inhibited the proliferation of A2780 cells as measured by MTT. 4-Aminopyridine also significantly affected the cell cycle, which increased the percentage of cells in G0/G1, and reduced the percentage of cells in S phase and G2/M phase. Non-selective K+ channel blockers tetrapentylammonium (TPeA) and verapamil had similar inhibitory effects on A2780 cell proliferation and cell cycle. In contrast, iberiotoxin, a selective inhibitor of KCa channels, and glibenclamide, a potent inhibitor of KATP channels, had no effect on the cell proliferation and cell cycle of A2780. Moreover K+ channels inhibitor, TPeA and verapamil, can blocked Ca2+ influx in these cells.

CONCLUSION

Voltage-gated K+ channels play an important role in the proliferation and cell cycle of ovarian cancer cell. It is likely that the influence of Kv channels on A2780 cell proliferation and cell cycle is mediated by a Ca2+-dependent mechanism.

A chemical biology approach identifies a beta-2 adrenergic receptor agonist that causes human tumor regression by blocking the Raf-1/Mek-1/Erk1/2 pathway

A chemical biology approach identifies a beta 2 adrenergic receptor (beta2AR) agonist ARA-211 (Pirbuterol), which causes apoptosis and human tumor regression in animal models. beta2AR stimulation of cAMP formation and protein kinase A (PKA) activation leads to Raf-1 (but not B-Raf) kinase inactivation, inhibition of Mek-1 kinase and decreased phospho-extracellular signal-regulated kinase (Erk)1/2 levels. ARA-211 inhibition of the Raf/Mek/Erk1/2 pathway is mediated by PKA and not exchange protein activated by cAMP (EPAC). ARA-211 is selective and suppresses P-Erk1/2 but not P-JNK, P-p38, P-Akt or P-STAT3 levels. beta2AR stimulation results in inhibition of anchorage-dependent and -independent growth, induction of apoptosis in vitro and tumor regression in vivo. beta2AR antagonists and constitutively active Mek-1 rescue from the effects of ARA-211, demonstrating that beta2AR stimulation and Mek kinase inhibition are required for ARA-211 antitumor activity. Furthermore, suppression of growth occurs only in human tumors where ARA-211 induces cAMP formation and decreases P-Erk1/2 levels. Thus, beta2AR stimulation results in significant suppression of malignant transformation in cancers where it blocks the Raf-1/Mek-1/Erk1/2 pathway by a cAMP-dependent activation of PKA but not EPAC.

Cell volume regulatory ion channels in cell proliferation and cell death

Alterations of cell volume are key events during both cell proliferation and apoptotic cell death. Cell proliferation eventually requires an increase of cell volume, and apoptosis is typically paralleled by cell shrinkage. Alterations of cell volume require the participation of ion transport across the cell membrane, including appropriate activity of Cl(-) and K(+) channels. Cl(-) channels modify cytosolic Cl(-) activity and mediate osmolyte flux, and thus influence cell volume. Most Cl(-) channels allow exit of HCO(3)(-), leading to cytosolic acidification, which in turn inhibits cell proliferation and favors apoptosis. K(+) exit through K(+) channels decreases cytosolic K(+) concentration, which may sensitize the cell for apoptotic cell death. K(+) channel activity further maintains the cell membrane potential, a critical determinant of Ca(2+) entry through Ca(2+) channels. Ca(2+) may, in addition, enter through Ca(2+)-permeable cation channels, which, in some cells, are activated by hyperosmotic shock. Increases of cytosolic Ca(2+) activity may trigger both mechanisms required for cell proliferation and mechanisms, leading to apoptosis. Thereby cell proliferation and apoptosis depend on magnitude and temporal organization of Ca(2+) entry, as well as activity of other signaling pathways. Accordingly, the same ion channels may participate in the stimulation of both cell proliferation and apoptosis. Specific ion channel blockers may thus abrogate both cellular mechanisms, depending on cell type and condition.

Insulin-like growth factor 1 differentially regulates estrogen receptor-dependent transcription at estrogen response element and AP-1 sites in breast cancer cells

Cross-talk between insulin-like growth factor 1 (IGF-1) and estrogen receptor alpha (ER) regulates gene expression in breast cancer cells, but the underlying mechanisms remain unclear. Here, we studied how 17-beta-estradiol (E2) and IGF-1 affect ER transcriptional machinery in MCF-7 cells. E2 treatment stimulated ER loading on the estrogen response element (ERE) in the pS2 promoter and on the AP-1 motif in the cyclin D1 promoter. On ERE, similar amounts of liganded ER were found at 1-24-h time points, whereas on AP-1, ER binding fluctuated over time. At 1 h, liganded ER was recruited to ERE together with histone acetyltransferases SRC-1 and p300, ubiquitin ligase E6-AP, histone methyltransferase Carm1 (Carm), and polymerase (pol) II. This coincided with increased histone H3 acetylation and up-regulation of pS2 mRNA levels. At the same time, E2 moderately increased cyclin D1 expression, which was associated with the recruitment of liganded ER, SRC-1, p300, ubiquitin ligase E6-AP (E6L), Mdm2, and pol II, but not other regulatory proteins, to AP-1. In contrast, at 1 h, IGF-1 increased the recruitment of the ER.SRC-1.p300.E6L.Mdm2.Carm.pol II complex on AP-1, but not on ERE, and induced cyclin D1, but not pS2, mRNA expression. Notably, ER knockdown reduced the association of ER, E6L, Mdm2, Carm, and pol II with AP-1 and resulted in down-regulation of cyclin D1 expression. IGF-1 potentiated the effects of E2 on ERE but not to AP-1 and increased E2-dependent pS2, but not cyclin D1, mRNA expression. In conclusion, E2 and IGF-1 differentially regulate ER transcription at ERE and AP-1 sites.

HRPAP20: a novel calmodulin-binding protein that increases breast cancer cell invasion

We previously reported the identification of HRPAP20 (hormone-regulated proliferation-associated protein 20), a novel hormone-regulated, proliferation-associated protein. In tumor cell lines, constitutive HRPAP20 expression enhanced proliferation and suppressed apoptosis, characteristics frequently associated with malignant progression. Here, we report that highly invasive breast cancer cell lines and human breast tumor specimens express elevated HRPAP20, which in transfection experiments in MCF-7 and MDA-MB-231 cells, increased invasion. Results from mechanistic studies revealed that HRPAP20 bound to calmodulin (CaM) via a conserved CaM-binding motif. Transfection of MCF-7 breast cancer cells with HRPAP20 harboring a mutated CaM-binding motif (HRPAP20K73A) inhibited its interaction with CaM and failed to increase invasion. Other experiments revealed that transfection with HRPAP20, but not HRPAP20K73A, increased secretion of matrix metalloproteinase-9 (MMP-9). Moreover, knockdown of HRPAP20 with small interfering RNA in MCF-7/HRPAP20 transfectants and wild-type MDA-MB-231 cells reduced invasion and inhibited secretion of MMP-9. Together these observations suggest that HRPAP20 may be an important regulator of breast tumor cell invasion by a CaM-mediated mechanism that leads to increased MMP-9 secretion. We conclude that dysregulation of HRPAP20 expression in tumor cells may contribute to the observed phenotypic changes associated with breast cancer progression.

Involvement of Kv1.1 and Nav1.5 in proliferation of gastric epithelial cells

In the present study, patch clamp experiments demonstrated the expression of multiple ionic currents, including a Ba2+-sensitive inward rectifier K+ current (IKir), a 4-aminopyridine- (4-AP) sensitive delayed rectifier K+ current (IKDR), and a nifedipine-sensitive, tetrodotoxin-resistant inward Na+ current (INa.TTXR) in the non-transformed rat gastric epithelial cell line RGM-1. RT-PCR revealed molecular identities of mRNAs for the functional ionic currents, including Kir1.2 for IKir, Kv1.1, Kv1.6, and Kv2.1 for IKDR, and Nav1.5 for INa.TTXR. Pharmacologic blockade of Kv and Nav, but not Kir, suppressed RGM-1 cell proliferation. To further elucidate which subtypes of the ion channels were involved in cell proliferation, RNA interference was employed to knockdown specific gene expression. Downregulation of Kv1.1 or Nav1.5 by RNA interference suppressed RGM-1 cell proliferation. To conclude, our study is the first to delineate the expression of ion channels and their functions as growth modulators in gastric epithelial cells.