Ion channels as physiological effectors for growth factor receptor and Ras/ERK signaling pathways

Cervical carcinoma high expressed 1 (CCHE1): An oncogenic lncRNA in diverse neoplasms

Recent studies have shown prominent role of long non-coding RNAs (lncRNAs) in the carcinogenesis process. These transcripts are flexible in the term of three dimensional conformations. This property endowed them the potential to have interaction with several biomolecules such as proteins, DNA or other RNAs. They control gene expression, cell differentiation, invasiveness of cancer cells and their metastatic ability. Dysregulation of these transcripts accounts for several disorders. They have particular application in cancer diagnosis and prediction of cancer course. Cervical Cancer High-Expressed lncRNA 1 (CCHE1) is an lncRNA which has been primarily identified during screening of differently expressed lncRNAs in cervical cancer. Being located in an intergenic area on chromosome 10, CCHE1 has been found to upregulate expression of proliferating cell nuclear antigen (PCNA) via binding with its mRNA, thus enhancing proliferation rate of cervical cancer cells. In addition to cervical cancer, CCHE1 contributes in the pathology of other types of cancers. In this paper, we discuss the role of CCHE1 the carcinogenic process in different tissues.

The Role of PI3K/Akt and ERK in Neurodegenerative Disorders

Disruption of Akt and Erk-mediated signal transduction significantly contributes in the pathogenesis of various neurodegenerative diseases (NDs), such as Parkinson's disease, Alzheimer's diseases, Huntington's disease, and many others. These regulatory proteins serve as the regulator of cell survival, motility, transcription, metabolism, and progression of the cell cycle. Therefore, targeting Akt and Erk pathway has been proposed as a reasonable approach to suppress ND progression. This review has emphasized on involvement of Akt/Erk cascade in the neurodegeneration. Akt has been reported to regulate neuronal toxicity through its various substrates like FOXos, GSK3β, and caspase-9 etc. Akt is also involved with PI3K in signaling pathway to mediate neuronal survival. ERK is another kinase which also regulates proliferation, differentiation, and survival of the neural cell. There has also been much progress in developing a therapeutic molecule targeting Akt and Erk signaling. Therefore, improved understanding of the molecular mechanism behind the regulatory aspect of Akt and Erk networks can make strong impact on exploration of the neurodegenerative disease pathogenesis.

Store-Operated Ca2+ Channel in Renal Microcirculation and Glomeruli

Store-operated Ca2+ channel (SOC) is defined as a channel that opens in response to depletion of the internal Ca2+ stores. During the last decade, many investigators have made a great effort to identify and characterize SOC, and to evaluate its physiologic function and pathophysiologic relevance in a variety of cell lines, primary cultures, and native tissues. To date, accumulating evidence has demonstrated that SOC is an essential Ca2+ entry mechanism in vascular smooth-muscle cells of renal microvasculature and glomerular mesangial cells, both of which tightly control glomerular hemodynamics and filtration. Store-operated Ca2+, combined with other types of Ca2+ entry channels, constitutes a profile of Ca2+ changes in response to physiologic vasoconstrictors and, thereby, regulates renal microcirculation and mesangial function. In addition, SOC is associated with altered Ca2+ signaling occurring in diseased kidneys, such as diabetic nephropathy. Although the gating mechanism and molecular identity of SOC are still enigmatic and may be cell-type and tissue specific, data from several independent groups suggest that protein kinase C plays an important role in SOC activation and that certain isoforms of canonical transient receptor potential (TRPC) proteins are candidates of SOC in renal mlcrovessels and mesangial cells.

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.

Protective induction of Hsp70 in heat-stressed primary myoblasts: Involvement of MAPKs

The involvement of extracellular signal-regulated kinases 1 and 2 (ERK1,2), stress kinase p38 and c-Jun NH2 -terminal kinases 1 and 2 (JNK1,2) on Hsp70-upregulation following mild heat shock, and resulting cell protection, was studied on rabbit primary myoblasts. Cells subjected to heat stress (42°C; 60 min) showed a significantly enhanced amount of heat-shock-induced protein 70 (Hsp70), correlating with sustained phosphorylation of MAP kinases ERK1,2, inhibition of p38 and JNK1,2 activation. Induced Hsp70 did not autocrinally suppress activation of transcription factor c-Jun, suggesting involvement of the latter in the protection of myoblasts following heat shock. The inhibition of stress kinases p38, JNK1,2, and MEK1,2 by SP600125, SB203580, and UO126, respectively, established the involvement of JNK1,2 and p38 as upstream, and ERK1,2 as downstream targets of Hsp70 induction. Moreover, the effect of the MEK1,2 inhibitor UO126 revealed a new pathway of c-Jun activation by ERK1,2 in myogenic heat-stressed stem cells. The presented data show that transient activation of JNK1, JNK2, and p38 is necessary for Hsp70 induction and ensuing cell protection. In conclusion, affecting myogenic stem cell protective mechanisms might be a useful strategy in improving stem cell survival and their expanded application in therapy.

K+ channels regulate ENaC expression via changes in promoter activity and control fluid clearance in alveolar epithelial cells

Active Na+ absorption by alveolar ENaC is the main driving force of liquid clearance at birth and lung edema resorption in adulthood. We have demonstrated previously that long-term modulation of KvLQT1 and KATP K+ channel activities exerts sustained control in Na+ transport through the regulation of ENaC expression in primary alveolar type II (ATII) cells. The goal of the present study was: 1) to investigate the role of the alpha-ENaC promoter, transfected in the A549 alveolar cell line, in the regulation of ENaC expression by K+ channels, and 2) to determine the physiological impact of K+ channels and ENaC modulation on fluid clearance in ATII cells. KvLQT1 and KATP channels were first identified in A549 cells by PCR and Western blotting. We showed, for the first time, that KvLQT1 activation by R-L3 (applied for 24 h) increased alpha-ENaC expression, similarly to KATP activation by pinacidil. Conversely, pharmacological KvLQT1 and KATP inhibition or silencing with siRNAs down-regulated alpha-ENaC expression. Furthermore, K+ channel blockers significantly decreased alpha-ENaC promoter activity. Our results indicated that this decrease in promoter activity could be mediated, at least in part, by the repressor activity of ERK1/2. Conversely, KvLQT1 and KATP activation dose-dependently enhanced alpha-ENaC promoter activity. Finally, we noted a physiological impact of changes in K+ channel functions on ERK activity, alpha-, beta-, gamma-ENaC subunit expression and fluid absorption through polarized ATII cells. In summary, our results disclose that K+ channels regulate alpha-ENaC expression by controlling its promoter activity and thus affect the alveolar function of fluid clearance.

ERK activation is required for hydrostatic pressure-induced tensile changes in engineered articular cartilage

The objective of this study was to identify ERK 1/2 involvement in the changes in compressive and tensile mechanical properties associated with hydrostatic pressure treatment of self-assembled cartilage constructs. In study 1, ERK 1/2 phosphorylation was detected by immunoblot, following application of hydrostatic pressure (1 h of static 10 MPa) applied at days 10-14 of self-assembly culture. In study 2, ERK 1/2 activation was blocked during hydrostatic pressure application on days 10-14. With pharmacological inhibition of the ERK pathway by the MEK1/ERK inhibitor U0126 during hydrostatic pressure application on days 10-14, the increase in Young's modulus induced by hydrostatic pressure was blocked. Furthermore, this reduction in Young's modulus with U0126 treatment during hydrostatic pressure application corresponded to a decrease in total collagen expression. However, U0126 did not inhibit the increase in aggregate modulus or GAG induced by hydrostatic pressure. These findings demonstrate a link between hydrostatic pressure application, ERK signalling and changes in the biomechanical properties of a tissue-engineered construct.

The ERK Cascade: Distinct Functions within Various Subcellular Organelles

The extracellular signal-regulated kinase 1/2 (ERK1/2) cascade is a central signaling pathway that regulates a wide variety of stimulated cellular processes, including mainly proliferation, differentiation, and survival, but apoptosis and stress response as well. The ability of this linear cascade to induce so many distinct and even opposing effects after various stimulations raises the question as to how the signaling specificity of the cascade is regulated. Over the past years, several specificity-mediating mechanisms have been elucidated, including temporal regulation, scaffolding interactions, crosstalks with other signaling components, substrate competition, and multiple components in each tier of the cascade. In addition, spatial regulation of various components of the cascade is probably one of the main ways by which signals can be directed to some downstream targets and not to others. In this review, we describe first the components of the ERK1/2 cascade and their mode of regulation by kinases, phosphatases, and scaffold proteins. In the second part, we focus on the role of MEK1/2 and ERK1/2 compartmentalization in the nucleus, mitochondria, endosomes, plasma membrane, cytoskeleton, and Golgi apparatus. We explain that this spatial distribution may direct ERK1/2 signals to regulate the organelles' activities. However, it can also direct the activity of the cascade's components to the outer surface of the organelles in order to bring them to close proximity to specific cytoplasmic targets. We conclude that the dynamic localization of the ERK1/2 cascade components is an important regulatory mechanism in determining the signaling specificity of the cascade, and its understanding should shed a new light on the understanding of many stimulus-dependent processes.

The MAP kinase signaling cascades: a system of hundreds of components regulates a diverse array of physiological functions

Sequential activation of kinases within the mitogen-activated protein (MAP) kinase (MAPK) cascades is a common, and evolutionary-conserved mechanism of signal transduction. Four MAPK cascades have been identified in the last 20 years and those are usually named according to the MAPK components that are the central building blocks of each of the cascades. These are the extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-Terminal kinase (JNK), p38, and ERK5 cascades. Each of these cascades consists of a core module of three tiers of protein kinases termed MAPK, MAPKK, and MAP3K, and often two additional tiers, the upstream MAP4K and the downstream MAPKAPK, which can complete five tiers of each cascade in certain cell lines or stimulations. The transmission of the signal via each cascade is mediated by sequential phosphorylation and activation of the components in the sequential tiers. These cascades cooperate in transmitting various extracellular signals and thus control a large number of distinct and even opposing cellular processes such as proliferation, differentiation, survival, development, stress response, and apoptosis. One way by which the specificity of each cascade is regulated is through the existence of several distinct components in each tier of the different cascades. About 70 genes, which are each translated to several alternatively spliced isoforms, encode the entire MAPK system, and allow the wide array of cascade's functions. These components, their regulation, as well as their involvement together with other mechanisms in the determination of signaling specificity by the MAPK cascade is described in this review. Mis-regulation of the MAPKs signals usually leads to diseases such as cancer and diabetes; therefore, studying the mechanisms of specificity-determination may lead to better understanding of these signaling-related diseases.

Knockdown of inwardly rectifying potassium channel Kir2.2 suppresses tumorigenesis by inducing reactive oxygen species-mediated cellular senescence

Senescence is an important determinant of treatment outcome in cancer therapy. In the present study, we show that knockdown of the inwardly rectifying K(+) channel Kir2.2 induced growth arrest without additional cellular stress in cancer cells lacking functional p53, p16, and/or Rb. Kir2.2 knockdown also induced senescence-associated β-galactosidase activity and upregulated senescence marker proteins in multiple cancer cell lines derived from different tissues, including prostate, stomach, and breast. Interestingly, knockdown of Kir2.2 induced a significant increase in reactive oxygen species (ROS) that was accompanied by cell cycle arrest, characterized by significant upregulation of p27, with concomitant downregulation of cyclinA, cdc2, and E2F1. Kir2.2 knockdown cells displayed increased levels of PML bodies, DNA damage (γH2AX) foci, senescence-associated heterochromatin foci, mitochondrial dysfunction, secretory phenotype, and phosphatase inactivation. Conversely, overexpression of Kir2.2 decreased doxorubicin-induced ROS accumulation and cell growth inhibition. Kir2.2 knockdown-induced cellular senescence was blocked by N-acetylcysteine, indicating that ROS is a critical mediator of this pathway. In vivo tumorigenesis analyses revealed that tumors derived from Kir2.2 knockdown cells were significantly smaller than those derived from control cells (P < 0.0001) and showed a remarkable increase in senescence-associated proteins, including senescence-associated β-galactosidase, p27, and plasminogen activator inhibitor-1. Moreover, the preestablished tumors are reduced in size after the injection of siKir2.2 (P = 0.0095). Therefore, we propose for the first time that Kir2.2 knockdown induces senescence of cancer cells by a mechanism involving ROS accumulation that requires p27, but not Rb, p53, or p16.

ATP-sensitive potassium channels control glioma cells proliferation by regulating ERK activity

Ion channels are found in a variety of cancer cells and necessary for cell cycle and cell proliferation. The roles of K(+) channels in the process are, however, poorly understood. In the present study, we report that adenosine triphosphate (ATP)-sensitive potassium channel activity plays a critical role in the proliferation of glioma cells. The expression of K(ATP) channels in glioma tissues was greatly increased than that in normal tissues. Treatment of glioma cells with tolbutamide, K(ATP) channels inhibitor, suppressed the proliferation of glioma cells and blocked glioma cell cycle in G(0)/G(1) phase. Similarly, downregulation of K(ATP) channels by small interfering RNA (siRNA) inhibited glioma cell proliferation. On the other hand, K(ATP) channels agonist diazoxide and overexpression of K(ATP) channels promoted the proliferation of glioma cells. Moreover, inhibiting K(ATP) channels slowed the formation of tumor in nude mice generated by injection of glioma cells. Whereas activating K(ATP) channels promoted development of tumor in vivo. The effect of K(ATP) channels activity on glioma cells proliferation is mediated by extracellular signal-regulated kinase (ERK) activation. We found that activating K(ATP) channel triggered ERK activation and inhibiting K(ATP) channel depressed ERK activation. U-0126, the mitogen-activated protein kinase kinase (MAPK kinase) inhibitors blocked ERK activation and cell proliferation induced by diazoxide. Furthermore, constitutively activated MEK plasmids transfection reversed the inhibitory effects of tolbutamide on glioma proliferation, lending further support for a role of ERK in mediating this process. Our results suggest that K(ATP) channels control glioma cell proliferation via regulating ERK pathway. We concluded that K(ATP) channels are important in pathological cell proliferation and open a promising pathway for novel targeted therapies.

Regulation of cartilage formation and maturation by mitogen-activated protein kinase signaling

The majority of bones comprising the adult vertebrate skeleton are generated from hyaline cartilage templates that form during embryonic development. A process known as endochondral ossification is responsible for the conversion of these transient cartilage anlagen into mature, calcified bone. Endochondral ossification is a highly regulated, multistep cell specification program involving the initial differentiation of prechondrogenic mesenchymal cells into hyaline chondrocytes, terminal differentiation of hyaline chondrocytes into hypertrophic chondrocytes, and finally, apoptosis of hypertrophic chondrocytes followed by bone matrix deposition. Recently, extensive research has been carried out describing roles for the three major mitogen-activated protein kinase (MAPK) signaling pathways, the extracellular signal-regulated kinase 1/2 (ERK1/2), p38, and c-jun N-terminal kinase (JNK) pathways, in the successive stages of chondrogenic differentiation. In this review, we survey this research examining the involvement of ERK1/2, p38, and JNK pathway signaling in all aspects of the chondrogenic differentiation program from embryonic through postnatal stages of development. In addition, we summarize evidence from in vitro studies examining MAPK function in immortalized chondrogenic cell lines and adult mesenchymal stem cells. We also provide suggestions for future studies that may help ameliorate existing confusion concerning the specific roles of MAPK signaling at different stages of chondrogenesis.

Association of VASP with TRPC4 in PKG-mediated inhibition of the store-operated calcium response in mesangial cells

We tested the hypotheses that the NO-cGMP-PKG pathway mediates inhibition of the store-operated cation channel (SOC) in human glomerular mesangial cells (HMC) and that TRPC4, a molecular component of SOC in HMC, is associated with PKG-phosphorylated vasodilator-stimulated phosphoprotein (VASP). Using fura 2 ratiometry, we measured intracellular Ca(2+) concentration [Ca(2+)](i) to determine whether sodium nitroprusside (SNP), an NO donor, and 8-Br-cGMP affected SOC-TRPC4 via PKG. We found that the SOC response in HMC was attenuated in the presence of 100 microM SNP, an NO donor, or 100 microM 8-Br-cGMP. Addition of DT-3 (2.5 microM), a specific PKG-1alpha inhibitor, reversed the effects of 8-Br-cGMP on the SOC response. Application of 100 microM cAMP did not significantly inhibit the SOC response. RT-PCR and Western blotting revealed PKG-1alpha transcript and protein in HMC. Immunocytochemical analysis localized PKG-1alpha to the cytoplasm and plasma membrane of HMC. Previous studies have shown that PKG-mediated phosphorylation of VASP attenuates cellular Ca(2+) entry, resulting in altered growth and proliferation. Therefore, we used Western blotting and immunocytochemistry to determine whether PKG-phosphorylated VASP associates with TRPC4. Western blot analysis revealed that 8-Br-cGMP enhanced the phosphorylation of VASP at serine 239 (Ser239), a known PKG phosphorylation site, in HMC within 5 min. Coimmunoprecipitation and coimmunostaining showed that P-Ser239-VASP associated with TRPC4. However, VASP that was unphosphorylated at Ser239 was not associated with TRPC4. These results indicate that VASP has a role in the NO/PKG-1alpha-mediated inhibition of the TRPC4-SOC response in HMC.

Blockage of intermediate-conductance-Ca(2+) -activated K(+) channels inhibits progression of human endometrial cancer

Potassium (K(+)) channels have been implicated in proliferation of some tumor cells. However, whether K(+) channels are important to the pathogenesis of endometrial cancer (EC) remains unknown. In the present study, we report that intermediate-conductance Ca(2+)-activated K(+) (IKCa1) channels play a critical role in the development of EC. The expression of IKCa1 at both mRNA and protein levels in EC tissues was greatly increased than that in atypical hyperplasia and normal tissues. Treatment of EC cells with clotrimazole and TRAM-34, two agents known to inhibit IKCa1 channels, suppressed the proliferation of EC cells and blocked EC cell cycle at G(0)/G(1) phase. Similarly, downregulation of IKCa1 by siRNA against IKCa1 inhibited EC cell proliferation and arrested its cell cycle at G(0)/G(1) phase. A clotrimazole-sensitive K(+) current was induced in EC cells in response to the increased Ca(2+). The current density induced by Ca(2+) was greatly reduced by clotrimazole, TRAM-34, charybdotoxin or downregulation of IKCa1 by the siRNA against IKCa1. Furthermore, TRAM-34 and clotrimazole slowed the formation in nude mice of tumor generated by injection of EC cells. Our results suggest that increased activity of IKCa1 channel is necessary for the development of EC.

ERK/MAPK pathway regulates GABAA receptors

The GABAA receptor is a ligand-gated ion channel whose function and activity can be regulated by ligand binding or alternatively may be influenced indirectly through the phosphorylation of specific subunits that comprise the GABAA receptor pentamer. With respect to phosphorylation, most studies have focused on either beta or gamma subunits, whereas the role of the alpha subunit as a relevant target of signaling kinases is largely unknown. Interestingly, we found a putative phosphorylation site for extracellular-signal regulated kinase (ERK), a key effector of the MAPK pathway, in almost all known alpha subunits of the GABAA receptor, including the ubiquitously expressed alpha1 subunit. To determine whether this putative ERK phosphorylation site was functionally relevant, we evaluated if ERK inhibition (through pharmacological inhibition of its upstream kinase, MEK) altered GABA-gated currents. Using HEK293 cells stably transfected with the alpha1beta2gamma2 form of the GABAA receptor, we found that UO126 reduced basal ERK phosphorylation and resulted in an enhancement of GABA-induced peak current amplitudes. Further, the enhancement of GABA-gated currents required an intact intracellular environment as it was robust in perforated patch recordings (which preserves the intracellular milieu), but absent in conventional whole-cell recordings (which dialyzes the cytosolic contents), supporting the involvement of an intracellular signaling pathway. Finally, mutation of the ERK phosphorylation site (T375-->A) prevented the UO126-induced enhancement of GABA-gated currents. Collectively, our results implicate the MAPK pathway as a negative modulator of GABAA receptor function, whose influence on GABA-gated currents may be mediated by phosphorylation of the alpha subunit.

The ERK cascade: a prototype of MAPK signaling

Sequential activation of protein kinases within the mitogen-activated protein kinase (MAPK) cascades is a common mechanism of signal transduction in many cellular processes. Four such cascades have been elucidated thus far, and named according to their MAPK tier component as the ERK1/2, JNK, p38MAPK, and ERK5 cascades. These cascades cooperate in transmitting various extracellular signals, and thus control cellular processes such as proliferation, differentiation, development, stress response, and apoptosis. Here we describe the classic ERK1/2 cascade, and concentrate mainly on the properties of MEK1/2 and ERK1/2, including their mode of regulation and their role in various cellular processes and in oncogenesis. This cascade may serve as a prototype of the other MAPK cascades, and the study of this cascade is likely to contribute to the understanding of mitogenic and other processes in many cell lines and tissues.

MEK-ERK signaling plays diverse roles in the regulation of facial chondrogenesis

The extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase pathway, also known as the MEK-ERK cascade, has been shown to regulate cartilage differentiation in embryonic limb mesoderm and several chondrogenic cell lines. In the present study, we employed the micromass culture system to define the roles of MEK-ERK signaling in the chondrogenic differentiation of neural crest-derived ectomesenchyme cells of the embryonic chick facial primordia. In cultures of frontonasal mesenchyme isolated from stage 24/25 embryos, treatment with the MEK inhibitor U0126 increased type II collagen and glycosaminoglycan deposition into cartilage matrix, elevated mRNA levels for three chondrogenic marker genes (col2a1, aggrecan, and sox9), and increased expression of a Sox9-responsive collagen II enhancer-luciferase reporter gene. Transfection of frontonasal mesenchyme cells with dominant negative ERK increased collagen II enhancer activation, whereas transfection of constitutively active MEK decreased its activity. Thus, MEK-ERK signaling inhibits chondrogenesis in stage 24/25 frontonasal mesenchyme. Conversely, MEK-ERK signaling enhanced chondrogenic differentiation in mesenchyme of the stage 24/25 mandibular arch. In mandibular mesenchyme cultures, pharmacological MEK inhibition decreased cartilage matrix deposition, cartilage-specific RNA levels, and collagen II enhancer activity. Expression of constitutively active MEK increased collagen II enhancer activation in mandibular mesenchyme, while dominant negative ERK had the opposite effect. Interestingly, MEK-ERK modulation had no significant effects on cultures of maxillary or hyoid process mesenchyme cells. Moreover, we observed a striking shift in the response of frontonasal mesenchyme to MEK-ERK modulation by stage 28/29 of development.

Minoxidil, a K(ATP) channel opener, accelerates DNA synthesis following partial hepatectomy in rats

A large number of studies have reported the action of K(ATP) channel openers in accelerating the proliferation of hepatocytes and many other cell types in vitro. Few studies, however, have examined the proliferative effect of K(ATP) channel openers in vivo. The aim of this study was to determine whether the K(ATP) channel opener minoxidil accelerates liver regeneration after partial hepatectomy (PH) in vivo. Male Wistar rats underwent a 70% partial hepatectomy (PH) after receiving a subcutaneous injection of minoxidil (0.01 mg/kg or 0.03 mg/kg). Some of the rats were intravenously treated with 5-hydroxydecanoic acid (5-HD, 10 mg/kg) just before the minoxidil injection. Seventy-two hours after PH, DNA synthesis was immunohistochemically assessed by bromodeoxyuridine (BrdU) incorporation into the nuclei. Minoxidil induced significant and dose-dependent increase in the BrdU labeling index after PH, and 5-HD reversed this minoxidil-induced change. Minoxidil did not significantly affect the changes in liver weight and liver function after PH. The hepatic levels of prealbumin decreased by about 60% after PH and minoxidil inhibited the decrease. In conclusion, the K(ATP) channel opener minoxidil enhanced DNA synthesis after PH without affecting the liver function.

Blockage of intermediate-conductance Ca2+-activated K+ channels inhibit human pancreatic cancer cell growth in vitro

Ion channels are important in controlling cell cycle progression and proliferation in a variety of cell types. Using the whole-cell recording mode of the patch-clamp technique, functional ion channels were electrophysiologically characterized in PANC-1 (K-ras G12D (+/-), p53 R273C, Deltap16), BxPC-3 (smad4-, p53 Y220C, Deltap16), and MiaPaCa-2 [transforming growth factor-beta receptor type II defect, K-ras G12C(-/-), p53 R248W, Deltap16] human pancreatic cancer cell lines. In BxPC-3 and the MiaPaCa-2 cells, we could identify approximately 600 or approximately 1200 functional Ca2+-activated K+ channels (IK) per cell, respectively, whereas PANC-1 cells expressed approximately 200 functional IK channels per cell. These channels were observed by using pipette solutions buffering [Ca2+]i to 1 microM. The channels were voltage-independent, blocked by charybdotoxin, clotrimazole, 1-[(2-chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34), and blocked by Ba2+ in a voltage-dependent manner. In the presence of 10 microM clotrimazole or TRAM-34, proliferation of the BxPC-3 as well as the MiaPaCa-2 cells was completely stopped. In contrast, proliferation of PANC-1 cells was hardly affected by clotrimazole or TRAM-34. Proliferation in all three cell lines could be inhibited in the presence of the Ca2+ channel antagonists verapamil, diltiazem, and nifedipine. By quantitative RT-PCR, we could show that MiaPaCa-2 cells exhibit a 2.8-fold and BxPC3 cells a more than 8-fold elevated level of IK mRNA level compared with PANC-1 cells. Interestingly, in primary pancreatic tumors we found a tremendous up-regulation of IK mRNA. In eight of nine (or 89%) primary pancreatic tumor tissues, we found a 6- to 66-fold increase in IK mRNA. Our findings suggest that a certain amount of functional IK channels is crucial for the proliferation of some pancreatic cancer types. The blockade of IK channels may ultimately prove useful as a therapeutic option for some patients with ductal adenocarcinoma of the pancreas with an up-regulated IK channel expression.

Epidermal growth factor activates store-operated Ca2+ channels through an inositol 1,4,5-trisphosphate-independent pathway in human glomerular mesangial cells

One of the fastest cellular responses following activation of epidermal growth factor receptor is an increase in intracellular Ca2+ concentration. This event is attributed to a transient Ca2+ release from internal stores and Ca2+ entry from extracellular compartment. Store-operated Ca2+ channels are defined the channels activated in response to store depletion. In the present study, we determined whether epidermal growth factor activated store-operated Ca2+ channels and further, whether depletion of internal Ca2+ stores was required for the epidermal growth factor-induced Ca2+ entry in human glomerular mesangial cells. We found that 100 nm epidermal growth factor activated a Ca2+-permeable channel that had identical biophysical and pharmacological properties to channels activated by 1 microm thapsigargin in human glomerular mesangial cells or A431 cells. The epidermal growth factor-induced Ca2+ currents were completely abolished by a selective phospho-lipase C inhibitor, U73122. However, xestospongin C, a specific inositol 1,4,5-trisphosphate receptor inhibitor, did not affect the membrane currents elicited by epidermal growth factor despite a slight reduction in background currents. Following emptying of internal Ca2+ stores by thapsigargin, epidermal growth factor still potentiated the Ca2+ currents as determined by the whole-cell patch configuration. Furthermore, epidermal growth factor failed to trigger measurable Ca2+ release from endoplasmic reticulum. However, another physiological agent linked to phospholipase C and inositol 1,4,5-trisphosphate cascade, angiotensin II, produced a striking Ca2+ transient. These results indicate that epidermal growth factor activates store-operated Ca2+ channels through an inositol 1,4,5-trisphosphate-independent, but phospholipase C-dependent, pathway in human glomerular mesangial cells.

TGF-beta1 induces the expression of fast inactivating K+ (I(A)) channels in rat vascular myofibroblasts

It is well established that transforming growth factor-beta1 (TGF-beta1) can induce the transformation of fibroblasts to myofibroblasts. The molecular mechanisms of the phenotypic change remain unknown. The effect of TGF-beta1 on the expression of K(+) channels in cultured rat vascular fibroblasts was investigated by using the patch-clamp technique and quantitative RT-PCR. In fibroblasts, the only voltage-dependent outward K(+) current that can be electrophysiologically detected is non-inactivating. In myofibroblasts, induced by the treatment of fibroblasts with TGF-beta1, we report the emergence of an additional transient outward K(+) current The TGF-beta1-induced outward current is inhibited by 4-aminopyridine. K(V2.1), the transcript for a non-inactivating potassium channel gene, was detected by quantitative RT-PCT in both cultured fibroblasts and myofibroblasts. In contrast, the transcript of the transient I(A) gene, K(V4.1), can be detected only in myofibroblasts. The results suggest that TGF-beta1-induced phenotypic transformation of vascular fibroblasts to myofibroblasts is accompanied by the induction of I(A) channels.

Molecular basis of voltage-dependent potassium currents in porcine granulosa cells

The major objective of this study was to elucidate the molecular bases for K(+) current diversity in porcine granulosa cells (GC). Two delayed rectifier K(+) currents with distinct electrophysiological and pharmacological properties were recorded from porcine GC by using whole-cell patch clamp: 1) a slowly activating, noninactivating current (I(Ks)) antagonized by clofilium, 293B, L-735,821, and L-768,673; and 2) an ultrarapidly activating, slowly inactivating current (I(Kur)) antagonized completely by clofilium and 4-aminopyridine and partially by tetraethylammonium, charybdotoxin, dendrotoxin, and kaliotoxin. The molecular identity of the K(+) channel genes underlying I(Ks) and I(Kur) was examined using reverse transcription-polymerase chain reaction and immunoblotting to detect K(+) channel transcripts and proteins. We found that GC could express multiple voltage-dependent K(+) (Kv) channel subunits, including KCNQ1, KCNE1, Kv1.1, Kv1.2, Kv1.3, Kv1.4, Kv1.5, Kv1.6, Kvbeta1.3, and Kvbeta2. Coimmunoprecipitation was used to establish the hetero-oligomeric nature of granulosa cell Kv channels. KCNE1 and KCNQ1 were coassociated in GC, and their expression coincided with the expression of I(Ks). Extensive coassociation of the various Kv alpha- and beta-subunits was also documented, suggesting that the diverse electrophysiological and pharmacological properties of I(Kur) currents may reflect variation in the composition and stoichiometry of the channel assemblies, as well as differences in post-translational modification of contributing Kv channel subunits. Our findings provide an essential background for experimental definition of granulosa K(+) channel function(s). It will be critical to define the functional roles of specific GC K(+) channels, because these proteins may represent either novel targets for assisted reproduction or potential sites of drug toxicity.

Characterization of a novel, broad-based fungicidal activity for the antiarrhythmic drug amiodarone

Fungal infections are common in patients with acquired immunodeficiency syndrome and pose a major health management problem. There is a need for identification of new antifungals to complement the limited current repertoire and to combat newly arising resistant fungal strains. We have identified a novel antifungal activity for the antiarrhythmic drug amiodarone. Extensive characterization of this activity shows that amiodarone exhibits a growth inhibition for several diverse fungi, including species of Cryptococcus, Saccharomyces, Aspergillus, Candida, and Fusarium. The antifungal activity was shown to be fungicidal; Cryptococcus neoformans treated with amiodarone lost viability within hours of drug exposure. Growth inhibition could be suppressed by addition of very high concentrations (10 mM) of calcium to the medium, suggesting that disruption of calcium homeostasis was involved in the antifungal activity. Direct measurement of radiolabeled calcium efflux showed that addition of amiodarone resulted in an immediate efflux of cellular calcium. In conclusion, amiodarone displays broad-based fungicidal activity and may be acting in part by perturbing the calcium balance.

Epidermal growth factor activates store-operated calcium channels in human glomerular mesangial cells

Acellular influx of Ca2+ is critical for initiating and maintaining growth in a variety of cell types. Experiments were performed to determine whether epidermal growth factor (EGF), which is known to initiate a proliferative response in mesangial cells, could regulate by intracellular signal transduction the store-operated Ca2+ channels (SOC) of human mesangial cells (HMC) in culture. The cell-attached patch configuration was used to monitor the activity of SOC, with 90 mM Ba2+ in the pipette and physiologic saline solution in the bath. Under control conditions, the mean NP(o) value was 1.06 at a holding potential of -80 mV. When 100 nM EGF was added to the bath, SOC were activated by 53%. The EGF-evoked response was dose-dependent, with a half-maximal activation concentration of 4.8 nM. An inhibitor of tyrosine kinase, i.e., tyrphostin A23 (100 microM), completely abolished EGF-evoked channel activation. EGF combined with the inactive control compound tyrphostin A1 (100 microM) elicited significant (85%) activation of SOC. Calphostin C, an inhibitor of protein kinase C (PKC), did not affect the baseline activity of SOC but abolished the EGF-evoked enhancement of SOC activity. The PKC activator phorbol-12-myristate-13-acetate (PMA) significantly activated SOC. However, the effects of PMA were duplicative rather than additive or potentiating with maximal concentrations (100 nM) of EGF, suggesting that PMA and EGF activate SOC through a common PKC pathway. In addition, downregulation of PKC via incubation of HMC with PMA for 1 to 20 h depressed both basal activity and EGF-induced activation of SOC. It is concluded that EGF stimulates SOC in HMC through an intracellular signaling mechanism involving tyrosine kinase and PKC.

Protein phosphorylation cascades associated with methamphetamine-induced glial activation

Reactive gliosis is the most prominent response to diverse forms of central nervous system (CNS) injury. The signaling events that mediate this characteristic response to neural injury are under intense investigation. Several studies have demonstrated the activation of phosphoproteins within the mitogen-activated protein kinase (MAPK) and Janus kinase (JAK) pathways following neural insult. These signaling pathways may be involved or responsible for the glial response following injury, by virtue of their ability to phosphorylate and dynamically regulate the activity of various transcription factors. This study sought to delineate, in vivo, the relative contribution of MAPK- and JAK-signaling components to reactive gliosis as measured by induction of glial-fibrillary acidic protein (GFAP), following chemical-induced neural damage. At time points (6, 24, and 48 h) following methamphetamine (METH, 10 mg/kg x 4, s.c.) administration, female C57BL/6J mice were sacrificed by focused microwave irradiation, a technique that preserves steady-state phosphorylation. Striatal (target) and nontarget (hippocampus) homogenates were assayed for METH-induced changes in markers of dopamine (DA) neuron integrity as well as differences in the levels of activated phosphoproteins. GFAP upregulation occurred as early as 6 h, reaching a threefold induction 48 h following METH exposure. Neurotoxicant-induced reductions in striatal levels of DA and tyrosine hydroxylase (TH) paralleled the temporal profile of GFAP induction. Blots of striatal homogenates, probed with phosphorylation-state specific antibodies, demonstrated significant changes in activated forms of extracellular-regulated kinase 1/2 (ERK 1/2), c-jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK), MAPK/ERK kinase (MEK1/2), 70-kDa ribosomal S6 kinase (p70 S6), cAMP responsive element binding protein (CREB), and signal transducer and activator of transcription 3 (STAT3). MAPK-related phosphoproteins exhibited an activation profile that peaked at 6 h, remained significantly increased at 24, and fell to baseline levels 48 h following neurotoxicant treatment. The ribosomal S6 kinase was enhanced over 60% for all time points examined. Immunoreactivity profiles for the transcription factors CREB and STAT3 indicated maximal increases in phosphorylation occurring at 24 h, and measuring greater than 2- or 17-fold, respectively. Specific signaling events were found to occur with a time course suggestive of their involvement in the gliotic response. The toxicant-induced activation of these growth-associated signaling cascades suggests that these pathways could be obligatory for the triggering and/or persistence of reactive gliosis and may therefore serve as potential targets for modulation of glial response to neural damage.

KATP channels regulate mitogenically induced proliferation in primary rat hepatocytes and human liver cell lines. Implications for liver growth control and potential therapeutic targeting

To determine whether K(ATP) channels control liver growth, we used primary rat hepatocytes and several human cancer cell lines for assays. K(ATP) channel openers (minoxidil, cromakalim, and pinacidil) increased cellular DNA synthesis, whereas K(ATP) channel blockers (quinidine and glibenclamide) attenuated DNA synthesis. The channel inhibitor glibenclamide decreased the clonogenicity of HepG2 cells without inducing cytotoxicity or apoptosis. To demonstrate the specificity of drugs for K(+) channels, whole-cell patch-clamp recordings were made. Hepatocytes revealed K(+) currents with K(ATP) channel properties. These K(+) currents were augmented by minoxidil and pinacidil and attenuated by glibenclamide as well as tetraethylammonium, in agreement with established responses of K(ATP) channels. Reverse transcription of total cellular RNA followed by polymerase chain reaction showed expression of K(ATP) channel-specific subunits in rat hepatocytes and human liver cell lines. Calcium fluxes were unperturbed in glibenclamide-treated HepG2 cells and primary rat hepatocytes following induction with ATP and hepatocyte growth factor, respectively, suggesting that the effect of K(ATP) channel activity upon hepatocyte proliferation was not simply due to indirect modulation of intracellular calcium. The regulation of mitogen-related hepatocyte proliferation by K(ATP) channels advances our insights into liver growth control. The findings have implications in mechanisms concerning liver development, regeneration, and oncogenesis.