Dissertations / Theses on the topic 'Potassium channels, pancreatic cancer'

Voltage dependent potassium channels are a group of plasma membrane ion channels with a key role in the immune system as the predominant ion channels controlling the resting membrane potential and tuning intracellular Ca2+ signaling in lymphocytes, monocytes, macrophages, and dendritic cells. Leukocytes present a limited Kv repertoire, including Kv1.3 and Kv1.5 channel isoforms. Kv1.3 is expressed in the immune system, and the blockade of this channel is associated with selective inhibition of T cell activation and proliferation. A functional Kv channel is an oligomeric complex composed of pore-forming and ancillary subunits. The KCNE gene family (KCNE1-5) is a novel group of modulatory Kv channel elements expressed in several tissues including leukocytes. KCNE peptides are small single spanning membrane proteins known to modulate Kv channels trafficking and biophysical properties. The hypothesis of the present PhD thesis entitled “Kv1.3 and Kv1.5 channels in leukocytes” was that changes in the channelosome composition by modulating the heterooligomeric combinations of the Kv1.3 channelosome control physiological and neoplastic cell growth as well as leukocyte responses. Evidence suggests that Kv channels are involved in cell differentiation and cell cycle control (because non-specific drugs, such as 4-AP and TEA, impaire proliferation), and they are also known to be remodeled during carcinogenesis. Thus, we elucidated the role of Kv1.3 and Kv1.5 channels in cell growth and their relationship with cancer, in models such as B lymphocytes and lymphomas (non-Hodgkin lymphomas), pancreatic ductal adenocarcinoma (PDAC) and glioblastomas. In spite of its significance, the mechanisms that regulate Kv1.3 and its role in the T cell activation are not well known. To that end, we analyzed the expression of KCNEs ancillary subunits upon different states of activation and proliferation of leukocytes (macrophages, T and B lymphocytes). In addition, recent data from our laboratory demonstrate that KCNE4, acting as a dominant negative ancillary subunit, physically interacts with Kv1.3 inhibiting K+ currents and retaining the channel intracellularly. Therefore, we studied the Kv1.3 modulation by the auxiliary subunit KCNE4 in leukocytes.

Oscillations in cytoplasmic Ca2+ concentration ([Ca2+]i) is the key signal in glucose-stimulated β-cells governing pulsatile insulin release. The glucose response of mouse β-cells is often manifested as slow oscillations and rapid transients of [Ca2+] i. In the present study, microfluorometric technique was used to evaluate the role of amino acids, glucagon, ryanodine and caffeine on the generation and maintenance of [Ca2+] i oscillations and transients in individual murine β-cells and isolated mouse pancreatic islets. The amino acids glycine, alanine and arginine, at around their physiological concentrations, transformed the glucose-induced slow oscillations of [Ca2+] i in isolated mouse β-cells into sustained elevation. Increased Ca2+ entry promoted the reappearance of the slow [Ca2+] i oscillations. The [Ca2+] i oscillations were more resistant to amino acid transformation in intact islets, supporting the idea that cellular interactions are important for maintaining the oscillatory activity. Individual rat β-cells responded to glucose stimulation with slow [Ca2+] i oscillations due to periodic entry of Ca2+ as well as with transients evoked by mobilization of intracellular stores. The [Ca2+] i oscillations in rat β-cells had a slightly lower frequency than those in mouse β-cells and were more easily transformed into sustained elevation in the presence of glucagon or caffeine. The transients of [Ca2+] i were more common in rat than in mouse β-cells and often appeared in synchrony also in cells lacking physical contact. Depolarization enhanced the generation of [Ca2+] i transients. In accordance with the idea that β-cells have functionally active ryanodine receptors, it was found that ryanodine sometimes restored oscillatory activity abolished by caffeine. However, the IP3 receptors are the major Ca2+ release channels both in β-cells from rats and mice. Single β-cells from ob/ob mice did not differ from those of lean controls with regard to frequency, amplitudes and half-widths of the slow [Ca2+] i oscillations. Nevertheless, there was an excessive firing of [Ca2+] i transients in the β-cells from the ob/ob mice, which was suppressed by leptin at close to physiological concentrations. The enhanced firing of [Ca2+] i transients in ob/ob mouse β-cells may be due to the absence of leptin and mediated by activation of the phospholipase C signaling pathway.

Oscillations in cytoplasmic Ca²⁺ concentration ([Ca²⁺]_i) is the key signal in glucose-stimulated β-cells governing pulsatile insulin release. The glucose response of mouse β-cells is often manifested as slow oscillations and rapid transients of [Ca²⁺] _i. In the present study, microfluorometric technique was used to evaluate the role of amino acids, glucagon, ryanodine and caffeine on the generation and maintenance of [Ca²⁺] _i oscillations and transients in individual murine β-cells and isolated mouse pancreatic islets. The amino acids glycine, alanine and arginine, at around their physiological concentrations, transformed the glucose-induced slow oscillations of [Ca²⁺] _i in isolated mouse β-cells into sustained elevation. Increased Ca²⁺ entry promoted the reappearance of the slow [Ca²⁺] _i oscillations. The [Ca²⁺] _i oscillations were more resistant to amino acid transformation in intact islets, supporting the idea that cellular interactions are important for maintaining the oscillatory activity. Individual rat β-cells responded to glucose stimulation with slow [Ca²⁺] _i oscillations due to periodic entry of Ca²⁺ as well as with transients evoked by mobilization of intracellular stores. The [Ca²⁺] _i oscillations in rat β-cells had a slightly lower frequency than those in mouse β-cells and were more easily transformed into sustained elevation in the presence of glucagon or caffeine. The transients of [Ca²⁺] _i were more common in rat than in mouse β-cells and often appeared in synchrony also in cells lacking physical contact. Depolarization enhanced the generation of [Ca²⁺] _i transients. In accordance with the idea that β-cells have functionally active ryanodine receptors, it was found that ryanodine sometimes restored oscillatory activity abolished by caffeine. However, the IP3 receptors are the major Ca²⁺ release channels both in β-cells from rats and mice. Single β-cells from ob/ob mice did not differ from those of lean controls with regard to frequency, amplitudes and half-widths of the slow [Ca²⁺] _i oscillations. Nevertheless, there was an excessive firing of [Ca²⁺] _i transients in the β-cells from the ob/ob mice, which was suppressed by leptin at close to physiological concentrations. The enhanced firing of [Ca²⁺] _i transients in ob/ob mouse β-cells may be due to the absence of leptin and mediated by activation of the phospholipase C signaling pathway.

Voltage gated K+ channels (Kv) are transmembrane proteins that allow the pass-thorugh of potassium ions, regulating the electrochemical gradient of the cell membrane. This way, they modulate several physiological processes, such as proliferation, migration or cell volume. Of particular interest in this dissertation is their role in excitable cells, were they control several key functions. The relevance of this ion channels is evidenced when mutations or alterations in the proper functioning of Kv channels causes severe pathologies, including cardiovascular or neuronal diseases, autoimmune affectations or cancer. Kv channels are tetramers of 4 α subunits with 6 transmembrane segments each one, that associate to form the pore and generate a functional channel. The wide functional diversity of currents is due to a vast number of modulations: heterotetramerization of α subunits, splicing variants, post-translational modifications or the association with regulatory subunits. The last ones include KCNE family, which co-assemble with the channel and modulate its electrophysiological, pharmacological or physiological properties. Kv7.1 associates with KCNE1 in cardiomyocytes to generate IKs cardiac repolarizing currents, in charge of finishing the cardiac action potential. Their assembly and traffic to the plasma membrane have been subject of discussion over the last years, with two opposite schools claiming an association early in the biogenesis versus a independent traffic to the plasma membrane, were both proteins would diffuse to assemble. We aimed in the present work to shed a light to this controversial topic. Kv channels have also been described in vascular smooth muscle, were they set the resting membrane potential and, therefore, control vascular tone. Kv7.1, Kv7.4 and Kv7.5 have been detected in different veins and arteries, were aberrations in their expression promote physiological alterations, but the specific role of each subunit remains unknown. In this scenario, the proposed objectives for the current PhD dissertation included the study of Kv7.1-KCNE1 complex, its assembly and traffic mechanisms. We hypothesized an unconventional secretion for the complex and suggest ER-PM junctions as the potential trafficking system. Therefore, we aim to characterize this structures and their implication in Kv7.1 membrane targeting. Finally, due to its implication in proliferation, their importance in cardiovascular system and their known role in some cancers, we studied the changes in the expression of Kv channels in endothelial-derived vascular tumors. We have been able to solve the traffic controversy of Kv7.1-KCNE1 complexes as they are not assembled early in their biogenesis. While KCNE1 is using the conventional secretion pathway, Kv7.1 takes an unconventional route that skips Golgi. Upon co-assembly, Kv7.1 redirects KCNE1 to this unconventional pathway. Moreover, we have proved that this non-conventional route are indeed ER-PM junctions, which also host the assembly of the complex. The molecular interactors of the channel during its ER-PM junction targeting have also been analysed during this PhD thesis, unravelling a complex and dynamic proteomic context. In addition, we have described for the first time the expression of Kv1.3, Kv1.5, Kv7.1 and Kv7.5 in endothelial cells of human veins and arteries. A remodelling of this composition is observed in different vascular cancers, related with the malignancy of the tumor in some of the cases.
Els canals de potassi dependents (Kv) regulen processos fisiològics molt importants, com la proliferació, la migració o el volum cel·lular. La seva rellevància es posa de manifest amb les diferents patologies associades a alteracions en la expressió dels canals, incloent malalties cardiovasculars, cerebrals, autoimmunes o càncer. Es tracta de proteïnes transmembrana formades per l’associació de 4 subunitats α que s’uneixen per formar el por. La gran varietat de diversitat funcional és deguda a la capacitat de heterotetramerització dels canals, variants d’splicing, modificacions post-traduccionals o la associació a subunitats reguladores KCNE, entre d’altres. En cardiomiòcits, Kv7.1 s’associa a KCNE1 per generar les corrents IKs, encarregades de la repolarització del potencial cardíac. La seva associació i tràfic són tema de debat des de fa anys, amb dues escoles defensant idees oposades. La primera, que les dues proteïnes s’associen en les fases inicials de la biogènesi; la segona, que trafiquen independent cap a la membrana, on difondran per trobar-se. Els Kv també s’han detectat a musculatura vascular llisa, on mantenen el potencial de repòs i controlen així el to vascular. Kv7.1, Kv7.4 i Kv7.5 es troben en diferents venes i arteries, on una expressió aberrant provoca alteracions fisiològiques. Tot i així, el seu paper concret encara es desconeix. En la present tesi doctoral hem comprovat que Kv7.1 i KCNE1 utilitzen vies diferents per arribar a la membrana plasmàtica. KCNE1 viatja per la via convencional, mentre que Kv7.1 utilitza una ruta no convencional que escapa del Golgi. Quan co-expressats, Kv7.1 redirigeix KCNE1 cap aquesta via alternativa. Hem demostrat que aquesta via són les ER-PM junctions, que també són el compartiment on la seva associació té lloc. Els interactors moleculars del canal durant el seu tràfic cap a ER-PM junctions també s’ha estudiat durant aquest treball. A més a més, hem descrit per primer cop l’expressió de Kv1.3, Kv1.5, Kv7.1 i Kv7.5 en l’endoteli de venes i artèries humanes. Hem vist un remodelatge en aquesta expressió en diferents càncers vasculars, en alguns casos relacionat amb la malignitat del tumor.

Most of the cancer cells and primary cancers show increased expression of various membrane proteins including ion channels, receptors like EGFR, integrin receptors etc. In this work we characterized the expression of potassium ion channels Kv11.1 (hERG1), EGFR and integrins in pancreatic ductal adenocarcinoma (PDAC). Firstly, our study shows that hERG1 specific blocking decreases the PDAC cell proliferation and anchorage independent colony formation. The study further demonstrates that blocking of hERG1 channels modulates the MAPK signaling pathway most likely mediated by EGFR receptors. In deed hERG1 makes complex formation with EGFR in both PDAC cell lines and primary samples. We then investigated the interactions between hERG1 and integrins. HERG1 and β1 integrins complex formation requires both functional hERG1 channels and activated β1 integrins. In other words, functional blocking of hERG1channels or nonstimulated β1 integrin or both would impair the complex formation between hERG1 and β1. We further demonstrate, using model cell lines, that the interactions between hERG1 and β1 could occur through transmembrane domains. We further investigated the role of hERG1 channels in PDAC cell adhesion, migration and actin cytoskeleton organization. HERG1 specific blocking did not affect the integrin-mediated cell adhesion and focal adhesion formation on ECM proteins. However, when hERG1 was blocked we observed the alterations in filamentous actin organization mediated by β1 integrins. HERG1 blocking specifically induced longer and finely organized f-actin in the cytoplasm, whereas over expression of hERG1 channels induced scattered shorter filaments. Next, we studied the role of hERG1 channels in cell migration and actin dynamics. For this purpose we challenged the role of hERG1 channels in multifactorial dynamic system that is similar to tumor microenvironment. PDAC cells were stimulated with conditioned media of hypoxia activated pancreatic stellate cells and, migration and actin dynamics were quantified. HERG1 blocking decreased the migration rate and interestingly, increased the actin flow (velocity). The increase in velocity was found to be due to increase in diffusion co-efficient of actin flow. Finally, we hypothesize that the hERG1 could mediate the actin dynamics and migration by altering the intracellular calcium concentration ([Ca2+]i). In fact hERG1 blocking decreased the [Ca2+]i by more than two-fold.

Breast cancer is the most prevalent cancer type among Canadian women. Breast cancers originate from the malignant transformation of mammary epithelial cells, which causes them to adopt an uncontrolled cell proliferation phenotype. My research suggests that the activity of specific ion channels (KV10.1, KCa3.1 and TRPM8) contribute to the proliferation of MCF-7 cells, a cell line commonly used to study breast cancer in vitro. Pharmacologically inhibiting the activities of KV10.1 or KCa3.1 channels decreased basal, but not estrogen-stimulated [3H]-thymidine incorporation, demonstrating that these channels contribute to MCF-7 cell proliferation. One way K+ channel activity is hypothesized to control cell proliferation is via regulation of membrane potential-dependent Ca2+ influx. Inhibition of KCa3.1 but not KV10.1 channel activity resulted in a membrane potential-dependent decrease in basal Ca2+ influx, suggesting that the way in which KCa3.1 channels contribute to cell proliferation is via regulating Ca2+ influx. In addition, my research also demonstrated that TRAM-34 increased or decreased cell proliferation depending on the concentration used and mitogenesis by TRAM-34 was blocked by estrogen receptor antagonists. TRAM-34 increased progesterone receptor mRNA expression, decreased estrogen receptor-alpha mRNA expression and reduced the binding of radiolabelled estrogen to estrogen receptor protein, in each case mimicking the effects of estrogen. Our finding that TRAM-34 is able to activate the estrogen receptor suggests a novel action of this supposedly specific K+ channel inhibitor and raises concerns of interpretation in its use. TRPM8 channels were also identified in MCF-7 cells, where they appeared to be important Ca2+ entry pathways. Inhibiting the activity of TRPM8 pharmacologically, as well as knocking down TRPM8 mRNA expression decreased cell proliferation, indicating that TRPM8 also contributed to MCF-7 cell proliferation. In conclusion, my research demonstrates that the activities of KV10.1, KCa3.1 and TRPM8 channels contribute to basal breast cancer cell proliferation. These findings suggest that the activity of specific ion channels may be potential targets for future therapeutic agents to treat breast cancer.

Breast cancer is a leading cause of cancer death and in 2009, the American Cancer Society estimates that over 192,000 new cases of breast cancer will be diagnosed, and over 40,000 women will die from breast cancer. Estrogen (E2) is required for normal female development and reproduction, but long-term exposure is carcinogenic and considered a risk factor for breast cancer. Membrane ion channels are essential for cell proliferation and are suggested to have a role in cancer, especially potassium channels. In the present study, we investigate the effects of estrogen and the estrogen antagonist ICI182780 on G-protein inwardly rectifying potassium channels (GIRK) in estrogen responsive MCF-7 breast cancer cells. GIRK1 and GIRK2 specific channels are thought to play a major role in rapid channel activation. We found increases in GIRK1 and GIRK2 membrane protein levels in response to estrogen treatment, as well as increases in intracellular potassium concentrations and cellular proliferation. ICI182780 treatment increased GIRK1, GIRK2 and GIRK4 membrane protein levels but resulted in an initial decrease in intracellular potassium concentration and decreased cell proliferation. GIRK1 RNAi knockdown decreased estrogen receptor alpha protein levels and activation. In addition, estrogen treatment resulted in increased phosphorylation of specific members of GPCR and MAPK signaling pathways that have been shown to be responsive to GIRK1 knockdown. Using microarray analysis of nontreated and E2 treated MCF7 cells, we observed 489 differentially expressed genes (283 upregulated and 206 downregulated) that were comprised largely of transcription and cell cycle associated genes. This study identified several human cell cycle associated genes that are both responsive to E2 treatment and are functionally correlated with GIRKs. Five genes were selected for further analysis by real time PCR. Our data suggests that specific GIRK channel composition at the cell membrane may be stimulated by estrogen exposure or downstream targets of estrogen signaling and may contribute to increased cell proliferation in MCF-7 breast cancer cells. Taken together, these data add further support of GIRK involvement in cancer progression and identify some potential biological roles of GIRKs in cancer biology beyond the initilal findings of GIRK1 assciation in metastatic breast cancer.