Calcium-activated Potassium Channel Gene Research Articles

Study on mechanism of down-regulating ikca1 molecule affecting the increment of oral squamous cell carcinoma

This research aimed to explore the mechanism of mediating the down-regulation of the calcium-activated potassium channel (IKCa1) gene expression in human oral squamous cell carcinoma Tca-8113 cells, thereby affecting cell proliferation and apoptosis. The expression level of IKCa1 in Tca-8113 cell line (oral squamous cell carcinoma) and HOEC cell line (human normal oral epithelial cell) was detected by RT-PCR. Then, after IKCa1 was knocked down in Tca-8113 cell line and HOEC cell line by RNA interference, and then cell proliferation levels were detected by cell counting kit 8 (CCK-8) method. Cell cycle distribution was detected by flow cytometry. Apoptosis was detected by membrane linked protein V-FITC/propidium iodide (PI) double-staining apoptosis detection kit. The protein expression level of IKCa1 was detected by Western Blot method. According to RT-PRC results, IKCa1 was significantly more expressed in Tca-8113 cell line than in HOEC cell line (P< 0.01). In addition, the mRNA expression levels in the normal oral epithelium and oral squamous cell carcinoma showed the same trend. After knocking down IKCa1 in Tca-8113 cell line, the IKCa1siRNA group significantly inhibited cell proliferation compared with the siNC control group. The results of flow cytometry showed that the proportion of apoptotic Tca-8113 cells transfected with IKCa1siRNA was significantly increased. The ratio of early apoptosis and late apoptosis of Tca-8113 cells increased (P< 0.05). To investigate the effect of IKCa1 on apoptosis, we tested the expression levels of apoptosis-related proteins. The results showed that the mRNA level of IKCa1siRNA group was significantly decreased by 44.41% compared with the control group (p< 0.01). Meanwhile, the mRNA level of Bax was significantly increased by 36.0% (p< 0.05). Our results showed that knocking down IKCa1 in Tca-8113 cells could induce cell cycle arrest and apoptosis to produce an anti-proliferation effect, thus inhibiting the expression of IKCa1 has an anti-cancer effect in oral squamous cell carcinoma.

EP News: Basic and Translational

Ellinor et al (Nat Med 2010;42:240, PMID 20173747) sought to identify common genetic variants underlying lone atrial fibrillation (AF). This condition affects a subset of individuals without overt heart disease and with an increased heritability of AF. The authors report a meta-analysis of genome-wide association studies conducted using 1,335 individuals with lone AF (cases) and 12,844 unaffected individuals (referents). They identified an association on chromosome 1q21 to lone AF (rs13376333; adjusted odds ratio = 1.56, P = 6.3 × 10–12) and replicated this association in two independent cohorts with lone AF (overall combined odds ratio = 1.52, 95% confidence interval 1.40–1.64, P = 1.83 × 10–21). rs13376333 is intronic to KCNN3. The authors identified a new locus for lone AF at the calcium-activated potassium channel gene KCNN3. Future studies will seek to determine the mechanistic links between genetic variation at this locus and AF.

Molecular cloning and tissue expression patterns of a small conductance calcium-activated potassium channel gene in turbot ( Scophthalmus maximus L.)

Calcium-activated potassium channels on plasma membrane enable potassium influx into the cell with ensuing changes in plasma membrane potential and consequent effects on cellular metabolic functions. Recently, this potassium channel was reported to regulate the cellular responses of mammalian immune cells. We have postulated the presence of such a channel in fish immune cells and its potential role in immunoregulation in fish. Employing specific primers and RNA template, we cloned a segment of a novel gene from turbot blood sample and subsequently obtained a full cDNA sequence using RACE approaches. Bioinformatic analysis revealed structural and phylogenetic characteristics of a novel small conductance calcium-activated potassium channel gene, we called TSKCa, which exhibits homologous domains to other species particularly in the transmembrane regions. Full-length TSKCa cDNA is 1698 bp with a 1632 bp open reading frame encoding a protein of 544 amino acids. TSKCa gene is expressed in majority of the tested organs and tissues of turbot. To assess the postulated immune function of TSKCa, we infected turbot with the pathogen Vibrio anguillarum. Here, semi-quantitative RT-PCR analysis demonstrated increased mRNA expression of TSKCa in head kidney, spleen and blood, indicating an important role of TSKCa in these organ tissues that mediate the immune defense response of turbot. In contrast, there was less change in expression in the turbot intestines and liver which were less implicated in the immune response in present study.

Serum response factor orchestrates nascent sarcomerogenesis and silences the biomineralization gene program in the heart

Our conditional serum response factor (SRF) knockout, Srf (Cko), in the heart-forming region blocked the appearance of rhythmic beating myocytes, one of the earliest cardiac defects caused by the ablation of a cardiac-enriched transcription factor. The appearance of Hand1 and Smyd1, transcription and chromatin remodeling factors; Acta1, Acta2, Myl3, and Myom1, myofibril proteins; and calcium-activated potassium-channel gene activity (KCNMB1), the channel protein, were powerfully attenuated in the Srf(CKO) mutant hearts. A requisite role for combinatorial cofactor interactions with SRF, as a major determinant for regulating the appearance of organized sarcomeres, was shown by viral rescue of SRF-null ES cells with SRF point mutants that block cofactor interactions. In the absence of SRF genes associated with biomineralization, GATA-6, bone morphogenetic protein 4 (BMP4), and periostin were strongly up-regulated, coinciding with the down regulation of many SRF dependent microRNA, including miR1, which exerted robust silencer activity over the induction of GATA-6 leading to the down regulation of BMP4 and periostin.

The slowpoke Gene Is Necessary for Rapid Ethanol Tolerance in Drosophila

Ethanol is one of the most commonly used drugs in the world. We are interested in the compensatory mechanisms used by the nervous system to counter the effects of ethanol intoxication. Recently, the slowpoke BK-type calcium-activated potassium channel gene has been shown to be involved in ethanol sensitivity in Caenorhabditis elegans and in rapid tolerance to the anesthetic benzyl alcohol in Drosophila. We used Drosophila mutants to investigate the role of slowpoke in rapid tolerance to sedation with ethanol vapor. Rapid tolerance was defined as a reduction in the sedative phase caused by a single previous sedation. The ethanol and water contents of flies were measured to determine if pharmacodynamic changes could account for tolerance. A saturated ethanol air stream caused sedation in <20 min and resulted in rapid tolerance that was apparent 4 hr after sedation. Two independently isolated null mutations in the slowpoke gene eliminated the capacity for tolerance. In addition, a third mutation that blocked expression specifically in the nervous system also blocked rapid tolerance. Water measurements showed that both ethanol and mock sedation caused equivalent dehydration. Furthermore, a single prior exposure to ethanol did not cause a change in the ethanol clearance rate. Rapid tolerance, measured as a reduction in the duration of sedation, is a pharmacokinetic response to ethanol that does not occur without slowpoke expression in the nervous system in Drosophila. The slowpoke channel must be involved in triggering or producing a homeostatic mechanism that opposes the sedative effects of ethanol.

Association analysis of a highly polymorphic CAG Repeat in the human potassium channel gene KCNN3 and migraine susceptibility

BackgroundMigraine is a polygenic multifactorial disease, possessing environmental and genetic causative factors with multiple involved genes. Mutations in various ion channel genes are responsible for a number of neurological disorders. KCNN3 is a neuronal small conductance calcium-activated potassium channel gene that contains two polyglutamine tracts, encoded by polymorphic CAG repeats in the gene. This gene plays a critical role in determining the firing pattern of neurons and acts to regulate intracellular calcium channels.MethodsThe present association study tested whether length variations in the second (more 3') polymorphic CAG repeat in exon 1 of the KCNN3 gene, are involved in susceptibility to migraine with and without aura (MA and MO). In total 423 DNA samples from unrelated individuals, of which 202 consisted of migraine patients and 221 non-migraine controls, were genotyped and analysed using a fluorescence labelled primer set on an ABI310 Genetic Analyzer. Allele frequencies were calculated from observed genotype counts for the KCNN3 polymorphism. Analysis was performed using standard contingency table analysis, incorporating the chi-squared test of independence and CLUMP analysis.ResultsOverall, there was no convincing evidence that KCNN3 CAG lengths differ between Caucasian migraineurs and controls, with no significant difference in the allelic length distribution of CAG repeats between the population groups (P = 0.090). Also the MA and MO subtypes did not differ significantly between control allelic distributions (P > 0.05). The prevalence of the long CAG repeat (>19 repeats) did not reach statistical significance in migraineurs (P = 0.15), nor was there a significant difference between the MA and MO subgroups observed compared to controls (P = 0.46 and P = 0.09, respectively), or between MA vs MO (P = 0.40).ConclusionThis association study provides no evidence that length variations of the second polyglutamine array in the N-terminus of the KCNN3 channel exert an effect in the pathogenesis of migraine.

An association of CAG repeats at the KCNN3 locus with symptom dimensions of schizophrenia

Background: In 1999 Cardno et al reported that long CAG repeats in the calcium-activated potassium channel gene hSKCa3/KCNN3 are associated with higher negative symptom dimension scores in schizophrenia patients. There has been no attempt to replicate the results. In this study, we investigated whether a symptom polymorphism of schizophrenia is associated with both the CAG repeat numbers and the difference in allele sizes. Methods: We tested the association of CAG repeats with symptom models of schizophrenia in 117 unrelated Jewish patients. A multivariate analysis (MANOVA) of two models of schizophrenia with the repeat distribution and the difference in allele sizes was performed. Results: We found a significant positive association of the number of CAG repeats with negative syndrome, anergia, activation, and paranoid symptoms. In addition, nonparanoid schizophrenia patients who had differences in allele sizes were characterized by earlier onset of illness. Conclusions: The study supports the hypothesis that the combined effect of long CAG repeats and the differences in allele sizes contribute to symptom expression of schizophrenia, particularly on the anergia-activation-paranoid axis.

HKCNN3 which maps to chromosome 1q21 is not the causative gene in periodic catatonia, a familial subtype of schizophrenia.

The human calcium-activated potassium channel gene (hKCNN3, hSKCa3) contains two tandemly arranged, multiallelic CAG repeats located in exon 1 which result in short to moderate polyglutamine stretches of unknown functional significance. Case-control and family-based association studies suggested an association of hKCNN3 repeats with susceptibility for schizophrenia. Twelve multiplex pedigrees with periodic catatonia, a schizophrenia subtype with major gene effect and patterns of anticipation, were genotyped using the multiallelic hKCNN3 repeat polymorphism. Using a dominant model of inheritance with sex- and age-dependent penetrance classes, cumulative results showed exclusion of linkage of hKCNN3 to periodic catatonia under the assumption of genetic homogeneity with lod score of -48.01 at zero recombination fraction. Our results provide evidence that hKCNN3 is not the causative gene in the familial schizophrenia subtype of periodic catatonia. By fluorescent in situ hybridization we confirmed the assignment of hKCNN3 to chromosome 1q21 near the heterochromatin region. Linkage mapping showed segregation with marker D1S498 (theta = 0.05) and placed hKCNN3 in the genetic linkage map in a cluster of genes near the centromeric region of chromosome 1.

Muscle-specific Transcriptional Regulation of theslowpoke Ca2+-activated K+Channel Gene

Transcriptional regulation of the Drosophila slowpoke calcium-activated potassium channel gene is complex. To date, five transcriptional promoters have been identified, which are responsible for slowpoke expression in neurons, midgut cells, tracheal cells, and muscle fibers. The slowpoke promoter called Promoter C2 is active in muscles and tracheal cells. To identify sequences that activate Promoter C2 in specific cell types, we introduced small deletions into the slowpoke transcriptional control region. Using transformed flies, we asked how these deletions affected the in situ tissue-specific pattern of expression. Sequence comparisons between evolutionarily divergent species helped guide the placement of these deletions. A section of DNA important for expression in all cell types was subdivided and reintroduced into the mutated control region, a piece at a time, to identify which portion was required for promoter activity. We identified 55-, 214-, and 20-nucleotide sequences that control promoter activity. Different combinations of these elements activate the promoter in adult muscle, larval muscle, and tracheal cells.

Genetic association study of a polymorphic CAG repeats array of calcium-activated potassium channel (KCNN3) gene and schizophrenia among the Chinese population from Taiwan.

Chandy et al suggested that a novel human neuronal small conductance, calcium-activated potassium channel gene, KCNN3, might be a candidate for schizophrenia. The KCNN3 cDNA sequences contain two stretches of CAG trinucleotide repeats encoding two separate polyglutamine segments near the N-terminus of this channel protein. The second CAG repeat was found to be highly polymorphic in the Caucasian population from both Europe and USA. Upon comparing the allelic frequency distribution between schizophrenic patients and ethnically matched controls, a significant excess of longer CAG repeats in schizophrenic patients was observed. A similar result was obtained in a recent replication study by Bowen et al, performed in Caucasians from UK or Eire. These results suggest an association between the longer CAG repeat allele of the KCNN3 gene and schizophrenia susceptibility. To verify if similar results can be observed in the Chinese population, we carried out a case-control study to compare the allelic frequency distribution of the CAG repeat of the KCNN3 gene between 92 Chinese schizophrenic patients and 100 normal controls from Taiwan. No significant difference of the allelic frequency distribution of the second CAG repeats was detected between the two groups (Wilcoxon Rank Sum test, P = 0.664). In addition, no over-representation of CAG repeats longer than the mode (19 repeats) was found in the patients' group (Fisher's exact test, P = 0.739). Thus, our data do not support that the second polymorphic CAG repeat of the KCNN3 gene may have an association with schizophrenia in our population.

HKCa3/KCNN3 potassium channel gene: association of longer CAG repeats with schizophrenia in Israeli Ashkenazi Jews, expression in human tissues and localization to chromosome 1q21.

We demonstrate a significant association between longer CAG repeats in the hKCa3/KCNN3 calcium-activated potassium channel gene and schizophrenia in Israeli Ashkenazi Jews. We genotyped alleles from 84 Israeli Jewish patients with schizophrenia and from 102 matched controls. The overall allele frequency distribution is significantly different in patients vs controls (P = 0.00017, Wilcoxon Rank Sum test), with patients showing greater lengths of the CAG repeat. Northern blots reveal substantial levels of approximately 9 kb and approximately 13 kb hKCa3/KCNN3transcripts in brain, striated muscle, spleen and lymph nodes. Within the brain, hKCa3/KCNN3transcripts are most abundantly expressed in the substantia nigra, lesser amounts are detected in the basal ganglia, amygdala, hippocampus and subthalamic nuclei, while little is seen in the cerebral cortex, cerebellum and thalamus. In situ hybridization reveals abundant hKCa3/KCNN3 message localized within the substantia nigra and ventral tegmental area, and along the distributions of dopaminergic neurons from these regions into the nigrostriatal and mesolimbic pathways. FISH analysis shows that hKCa3/KCNN3 is located on chromosome 1q21.

Mapping of hKCa3 to chromosome 1q21 and investigation of linkage of CAG repeat polymorphism to schizophrenia.

CAG trinucleotide polymorphisms in the neuronal small conductance calcium-activated potassium channel gene hKCa3 have been reported to be associated with schizophrenia. Attempts to confirm this finding have met with mixed results. We investigated hKCa3 CAG allele lengths in families from the National Institute of Mental Health (NIMH) Schizophrenia Genetics Initiative, by comparing transmission to discordant siblings and parental transmission to affected offspring. Overall, there was no convincing evidence that hKCa3 CAG lengths differ between schizophrenics and controls. We did, however, observe a trend (P = 0.063) toward over-representation of long (> or = 19) CAG repeats in the shorter of the two hKCa3 alleles in schizophrenics. There was no evidence of excessive parental transmission of long CAG repeat alleles to affected offspring. In addition, we re-mapped hKCa3 and found that it resides on chromosome 1q21, in a region which has been linked to familial hemiplegic migraine, but not to schizophrenia. These data provide no significant support for the association of hKCa3 with schizophrenia.

Lack of association between the hSKCa3 channel gene CAG polymorphism and schizophrenia

Genetic anticipation, a phenomenon characterized by increased severity of symptoms and earlier age at onset of a disease in successive generations, is believed to be present in schizophrenia. In several neurodegenerative diseases showing anticipation, the mutation causing the disease is an expanded trinucleotide repeat. Therefore, genes containing trinucleotide repeats prone to expansion have become a suitable family of candidate genes in schizophrenia. A human calcium-activated potassium channel gene (hSKCa3), possibly mapping to chromosome 22q11-13, a region previously linked to schizophrenia, was recently described. This gene contains two contiguous expressed CAG repeat stretches. Recently, long allelic variants of one of these CAG repeats were found to be overrepresented in schizophrenic patients compared to normal controls. In this study we attempted to replicate this result and to study the relationship between the length of this CAG repeat on the one hand and the severity and age at onset of the disease on the other hand. No association with the disease or correlation with the severity of schizophrenia was identified. In addition, hSKCa3 was mapped to chromosome 1. Our results do not support the involvement of this particular CAG repeat-containing gene in schizophrenia.

Calcium-Activated Potassium Channel Gene Expression in the Midgut of Drosophila

The slowpoke gene of Drosophila encodes a pore-forming subunit of a BK-type Ca2+-activated K+ channel. The gene is expressed in neurons, muscles, tracheal cells and in the midgut. The P1 transgene gene contains the entire slowpoke transcriptional control region and drives the expression of a reporter protein comprised of slowpoke amino terminal sequences fused to β-galactosidase. Here we show that midgut expression is limited to the copper cell and iron cell regions. The copper cell region is composed of two cell types, the copper cells and the interstitial cells. The P1 transgene is expressed in the interstitial cells but not the copper cells. Furthermore, we show that the reporter protein is apically localized in the interstitial cells. In these cells, the slowpoke Ca2+-activated K+ channel is thought to participate in the transport of ions between the hemolymph and the lumen of the gut. Subcellularly localized BK channels may be involved in the secretion of acid into the gut lumen. An analogous role for basolaterally localized BK channels has been proposed in the acid-secreting intercalating cells of the human kidney.

A human calcium-activated potassium channel gene expressed in vascular smooth muscle

Large-conductance Ca(2+)-activated K+ (BK) channels are widespread and functionally heterogeneous. In other classes of K+ channels, functional heterogeneity derives from large gene families, alternative splicing, heterologous subunit composition, and functional modulation. The molecular basis of mammalian BK channel heterogeneity is unknown, since only a single gene (mSlo) has been identified. BK channels in native vascular smooth muscle have an apparent Ca2+ sensitivity approximately 10-fold greater than native brain or skeletal muscle channels, or cloned mSlo channels. Using mSlo as a low-stringency probe, we screened human arterial smooth muscle and genomic libraries extensively in search of genes or splice variants with novel properties. We isolated the human homologue of mSlo, including two novel splice variant forms, but found no other related genes. Electrophysiological characterization of the hSlo clones in Xenopus oocytes and Chinese hamster ovary cells gave BK currents that were not measurably different from mSlo currents. However, coexpression of hSlo with a recently cloned beta-subunit derived from smooth muscle dramatically increased apparent Ca2+ sensitivity. Thus alpha-subunits alone may not determine Ca2+ sensitivity of vascular smooth muscle BK channels. hSlo was mapped to human chromosome 10q23.1, and the genomic structure was analyzed. Immediately after the amino terminal, two unusual regions of trinucleotide repeating sequences are present. The first of these regions encodes polyglycine, and the second encodes polyserine. Both regions of repeated sequence are conserved between the mouse and human genome.

Cloning and characterization of human and mouse homologs of the Drosophila calcium-activated potassium channel gene, slowpoke.

Potassium channels play important roles in a wide variety of physiological processes. Although several genes encoding voltage-activated potassium channels have been analyzed at the molecular level, no calcium-activated potassium channel gene has yet been characterized in humans. In an effort to provide the foundation for functional analysis of such polypeptides we report the cloning of mouse and human homologs of the Drosophila melanogaster calcium-activated potassium channel gene, slowpoke. Both the human and mouse genes encode polypeptides that have more than 50% amino acid identifies with their Drosophila counterpart. In addition, like the Drosophila slowpoke gene, both the mouse and human genes generate multiple transcripts by alternative splicing. The human gene maps to chromosome 10 based on the results of polymerase chain reaction analysis of genomic DNA from human-hamster hybrid cell lines. Because calcium-activated potassium channels participate in wide variety of cellular functions including neuromuscular communication, secretion and cellular immunity, their continued analysis promises to have broad biological and medical significance.