正常血钾型周期性麻痹存在SCN4A基因V781I突变

目的研究两例散发正常血钾型周期性麻痹(normokalemicperiodicparalysis,normoKPP)患者的临床特点及其电压门控钠通道型α亚单位(α-subunittypeofvoltage-gatedsodiumchannel,SCN4A)基因的突变。方法应用变性高效液相色谱(denaturinghighperformanceliquidchromatography,DHPLC)技术及测序分析检测患者SCN4A基因第13、19、23、24(部分)外显子是否发生已知导致高钾型周期性麻痹(hyperKPP)的突变(T704M、A1156T、M1360V、I1495F、M1592V);随后应用DHPLC技术筛查SCN4A基因其余外显子,对出现异常洗脱峰者进行测序分析。结果两例患者的SCN4A基因发生点突变2418(G→A)并引起氨基酸序列改变V781I,且为SCN4A基因唯一错义突变。病例1的父亲也发生该突变,但未发病。结论中国人normoKPP患者存在V781I突变,该突变可能是导致normoKPP的突变之一。     

抑癌基因PTEN在肝癌组织中的突变及其对肝癌细胞增殖和凋亡的调控作用

目的 探讨抑癌基因PTEN在人原发性肝癌组织中的突变及其对肝癌细胞增殖和凋亡的调控作用。方法 （1）聚合酶链反应（PCR）-单链构象多态性（SSCP）法和序列分析法检测42例人原发性肝癌组织中抑癌基因PTEN第5、8外显子的突变。（2）脂质体介导的基因转染法将野生型PTEN基因、突变型PTEN基因的真核表达载体pEGFP-wt-PTEN、pEGFP-PTEN;G129R分别转染不表达内源性PTEN蛋白的人肝癌细胞系HHCC,G418筛选稳定表达PTEN蛋白的克隆,MTT比色实验分析测定细胞的增殖能力。以未转染基因的HHCC细胞和转染空载体pEGFP-C1的HHCC细胞为对照。（3）TNF-α诱导上述细胞凋亡,流式细胞仪测定凋亡细胞比例;Western印迹法检测细胞内磷酸化Akt（Ser473）的表达。结果 （1）在4例肝癌组织中检测出PTEN基因第5外显子的异常突变条带（9．5％,4／42）。（2）转染野生型PTEN基因的HHCC细胞生长明显抑制,而转染突变型PTEN基因的HHCC细胞的增殖能力与对照组比较差异无统计学意义。（3）TNF-α诱导分别转染野生型、突变型PTEN基因、空载体的HHCC细胞和未转染基因的HHCC细胞凋亡,细胞凋亡率分别为13．8％、8．1％、4．6％、3．3％,与转染空载体的HHCC细胞比较,转染野生型PTEN基因的HHCC细胞凋亡率增高（P〈0．05）;而转染突变型PTEN基因的HHCC细胞凋亡率差异无统计学意义（P〉0．05）。Western印迹检测显示未经基因转染的HHCC细胞内源性Akt水平较低;HHCC细胞经TNF-α作用,其内源性Akt水平增高;转染野生型PTEN基因,可降低TNF-α诱导的肝癌细胞内信号分子Akt（Ser473）的磷酸化水平。结论 （1）首次发现原发性人肝癌组织中抑癌基因P1EN发生突变;（2）野生型PTEN基因可抑制肝癌细胞增殖,而突变型PTEN基因丧失对肝癌细胞增殖的调控作用;（3）野生型PTEN基因可降低TNF-α诱导的肝癌细胞内重要的信号分子Akt（Ser473）的磷酸化水平,即野生型PTEN基因通过抑制TNF-α诱导的肝癌细胞Akt磷酸化（活化）而抑制细胞增殖,促进细胞凋亡。     

敲低IK1钾通道抑制ClC-3氯通道的表达和功能

 目的: 探讨ClC-3氯通道是否为IK1钾通道的调节靶点,重点研究鼻咽癌细胞IK1钾通道对ClC-3氯通道功能及蛋白表达的影响。方法: 采用siRNA转染技术抑制低分化鼻咽癌上皮细胞(CNE-2Z) IK1 基因的表达;real-time PCR技术检测ClC-3 mRNA的表达;Western blot检测ClC-3的蛋白表达;细胞免疫荧光结合激光共聚焦显微镜技术检测ClC-3和IK1蛋白在细胞内分布;全细胞膜片钳记录细胞氯电流。结果: IK1 siRNA可以成功转染CNE-2Z细胞,有效抑制鼻咽癌细胞IK1钾离子通道的表达;用IK1 siRNA抑制鼻咽癌细胞IK1钾离子通道的表达后, ClC-3的mRNA表达上调而ClC-3蛋白却表达减少:在低分化鼻咽癌上皮细胞,低渗刺激可激活氯通道,产生一个较大的氯电流,在成功转染IK1 siRNA的细胞,此氯电流明显减弱。结论: 敲低IK1钾离子通道可抑制ClC-3氯离子通道的表达和功能。     

CACNA1H基因G773D突变对钙通道功能的影响

目的研究儿童失神癫痫（childhood absence epilepsy，CAE）患儿CACNA1H基因G773D突变对钙通道功能的影响。方法用定点突变重叠延伸聚合酶链反应（polymerase chain reaction，PCR）方法构建G773D突变体，脂质体法将突变体和野生型人Cav3．2a cDNA分别转染HEK-293细胞，获得稳定表达细胞株，全细胞膜片钳法研究其电生理变化。结果突变体和野生型细胞钙通道激活和失活动力学差异无统计学意义，但突变体G773D钙电流密度明显高于野生型。结论CACNA1H基因G773D突变可使其编码通道电流增加，并可能引起神经元兴奋性增加。     

野生型和突变型GDF5蛋白表达及亚细胞定位的研究

目的研究人生长分化因子5基因(GDF5)c.1118T>G(p.L373R)突变对GDF5蛋白在HEK-293细胞系表达及其亚细胞定位的影响。方法构建pDsRed1-N1-GDF5-WT和pDsRed1-N1-GDF5-L373R载体,分别转染HEK-293细胞,细胞培养72h后通过荧光显微镜观察比较野生型和突变型GDF5蛋白荧光分布情况。结果 GDF5蛋白在HEK-293细胞中成功表达,在荧光显微镜下观察到转染野生型和突变型GDF5的细胞胞浆均匀发出红色荧光,而空载体组的红色荧光则弥散于全细胞,荧光强度均匀一致。结论野生型和突变型GDF5蛋白均定位于HEK-293细胞质。     

小泛素样修饰蛋白对α-突触核蛋白线粒体亚细胞定位及α-突触核蛋白经泛素系统降解的影响

目的 探讨α-突触核蛋白(α-synuclein)的小泛素样修饰蛋白1(small ubiquitin-like modifier1,SUMO-1)化修饰对α-synuclein蛋白亚细胞线粒体定位及α-synuelein蛋白经泛素系统降解的影响.方法 构建野生型、A53T突变型和缺失SUMO-1互作氨基酸的K96R突变型α-synuclein真核表达质粒.将野生型、A53T突变型和K96R突变型α-synuclein真核表达质粒分别转染HEK293细胞;在转染后48 h通过应用线粒体染色剂和激光共聚焦技术,观察野生型、A53T突变型及缺失SUMO-1修饰的α-synuclein蛋白的亚细胞线粒体定位和蛋白聚集情况.在转染后48 h应用anti-ubiquitin抗体进行Western印迹分析,明确野生型、A53T突变型及缺失SUMO-1修饰的α-synuclein蛋白泛素化程度有无差别.结果 将构建所得EGFP-α-synuclein-WT、EGFP-α-synuclein-A53T、EGFP-α-synuclein-K96R真核表达质粒经双酶切鉴定及DNA测序证实;激光共聚焦结果显示野生型、A53T突变型、K96R突变型α-synuclein蛋白均广泛分布于细胞质和细胞核中,以细胞质为主,野生型、A53T型细胞可见绿色荧光物质在胞质积聚,形成强荧光斑块,K96R型胞质内绿色荧光物质聚集少;野生型、A53T突变型、K96R突变型α-synuclein均与线粒体存在共定位,A53T突变型、K96R突变型α-synuclein在SUMO-1修饰或缺失的情况下对α-synuclein蛋白的线粒体亚细胞定位无明显影响.Western印迹结果显示转染缺失SUMO-1互作氨基酸的K96R突变型α-synuclein真核表达质粒组的细胞泛素蛋白的含量与转染空质粒组相比无明显变化,转染野生型、A53T突变型α-synuclein真核表达质粒组HEK293细胞中泛素蛋白的含量减少.结论 α-synuclein基因过度表达及致病突变A53T对α-synuclein蛋白的线粒体亚细胞定位无明显影响;SUMO-1修饰对α-synuclein蛋白的线粒体亚细胞定位也无明显影响;SUMO-1对a-αsynuclein基因过度表达及A53T突变型α-synuclein细胞内泛素化蛋白数量产生影响.     

一个遗传性低钾周期性麻痹家系的CACNA1S基因突变研究

目的在中国人低钾周期性麻痹（hypokalemic periodic paralysis，HOKPP）家系中寻找HOKPP新的突变。方法分析了一个具有4代共46名家族成员的中国HOKPP家系。应用聚合酶链反应、连锁分析、DNA测序和限制性片段长度多态性分析技术研究了第1和第2代成员，以发现该家系可能的致病基因突变；然后用上述研究的结果检测第3和第4代成员，进一步验证结果并对正常成员作出患病的预测。结果对第1和第2代的连锁分析显示该家系的致病基因为CACNAIS基因，其LOD值为3．71；DNA测序显示1582位的核苷酸C被G所替代，为一种新的突变R528G；所有患病个体均带有此突变，而200名对照中没有此突变。检测第3和第4代成员R528G突变，发现所有患者和两名正常年轻女性携带此突变基因。结论发现了CACNAIS基因的一个R528G新突变，能导致中国人低钾周期性麻痹，其外显率可能存在性别差异，此突变将有助于低钾周期性麻痹的诊断和预测。     

分子伴侣Rer1参与人胚胎肾上皮细胞系HEK293T中hERG钾通道蛋白转运

目的探讨分子伴侣Rer1在hERG钾通道蛋白转运中的作用机制,并进行可能恢复hERG转运异常的药物Baf A1研究。方法将A561V突变体及野生型hERG载体瞬时转染人胚胎肾上皮细胞系(HEK293T),建立野生、突变及混合转染细胞模型;运用免疫荧光、蛋白免疫印迹检测hERG及Rer1的表达;采用小干扰RNA技术敲低Rer1表达后检测hERG蛋白的表达;V-ATP酶抑制剂Bafilomycin A1(Baf A1)以1 mmol/L孵育各组细胞6 h后Western blot检测hERG蛋白表达;用膜片钳对有潜在功能的混转细胞给予Baf A1孵育后测定膜电流。结果与野生组相比,A561V突变可致hERG蛋白转运缺陷并表现不同条带水平,突变组hERG蛋白的膜表达明显减少(P0.01);Rer1在突变、混转组中表达明显下降(P0.01),进一步敲低Rer1后可促进部分相对成熟hERG蛋白的顺向转运;此外,与对照组相比,Baf A1孵育可使野生、突变组中成熟hERG蛋白明显增加(P0.05),混转组中未成熟hERG蛋白则显著上调(P0.05);而在混转细胞中,Baf A1孵育可使尾电流相对密度明显增强(P0.05)。结论 Rer1参与hERG钾通道蛋白的转运,并能抑制部分异常hERG蛋白在细胞中的顺向转运,Baf A1能明显增强混转细胞的尾电流密度。     

转录因子Sox2 SUMO修饰位点突变体的构建及真核表达

目的:构建Sox2及突变体Sox2 K247R的真核表达载体, 并在293FT细胞中表达.方法:以含有Sox2基因全长的馈赠质粒为模板, 用循环延伸PCR法得到该基因的突变体Sox2 K247R, 并将野生型及突变型基因定向亚克隆到真核表达载体pCMV-HA上.得到的重组质粒经限制性内切酶消化和DNA测序鉴定.其后用脂质体包埋法将pCMV-HA-Sox2及pCMV-HA-Sox2 K247R分别单独转染或与pCMV-Myc-SUMO1共转染293FT细胞.采用Western blot分析蛋白表达情况及SUMO修饰情况.结果:经酶切和DNA序列测定, 重组子序列正确, 突变体第247位密码子由AAG转变为CGG.Western blot结果显示野生型及突变型的Sox2都在细胞内得到了很好的表达, SUMO修饰位点突变后, Sox2不能与SUMO蛋白结合.结论:Sox2野生型及突变型真核表达载体构建成功, 在蛋白水平体现了SUMO修饰的差异性.     

细胞外钾对HERG基因无义突变L539fs/47表达的调控

 目的: 研究持续细胞外钾对野生型HERG与其突变体L539fs/47蛋白表达的影响。方法: 用脂质体转染法将野生型HERG(WT)及其突变体HERG-L539fs/47(MT)分别转染HEK293细胞36 h后,0.8、4.3及10 mmol/L的钾干预6 h,流式细胞术检测HERG蛋白表达量;干预12 h用激光共聚焦成像和免疫印迹法进行HERG蛋白定位及表达量检测。结果: 用激光共聚焦成像检测发现野生型HERG蛋白主要分布在细胞膜上;而HERG突变体L539fs/47蛋白大部分滞留胞浆;并且HERG蛋白的表达均随细胞外钾浓度升高而增多。流式细胞术结果显示细胞外高钾组荧光增多(P < 0.01),WT组荧光阳性细胞百分比和荧光强度均高于MT组(P < 0.05)。免疫印迹显示,不同于野生型 HERG 135 kD及155 kD 2个条带,突变体仅60 kD 1个条带,3个条带均受细胞外钾影响(P < 0.05)。结论: 细胞外高钾增强细胞膜上野生型和突变型HERG通道蛋白的稳定性,持续低钾干预时间依赖性地减少HERG通道蛋白的表达。     

Mutation screening in Chinese hypokalemic periodic paralysis patients

Thyrotoxic periodic paralysis (TPP), familial periodic paralysis (FPP), and sporadic periodic paralysis (SPP) are the most common causes of hypokalemic periodic paralysis (hypoKPP). The patients present with similar clinical features characterized by episodic attacks of muscle weakness and a decrease in blood potassium. Mutations in the gene encoding the voltage-sensor coding regions of the skeletal muscle sodium channel gene (SCN4A) and the alpha-1 subunit of the skeletal muscle calcium channel gene were analyzed in 23 Chinese hypoKPP patients, including 1 FPP pedigree, 14 TPP patients, and 8 SPP patients. In addition, R83H mutation of the potassium channel subunit gene which was originally published as periodic paralysis mutation was also analyzed. A heterozygous CGT-TGT mutation at codon 672 in SCN4A gene was identified to segregate with the disease in the FPP family. Mutations in these regions were excluded in those patients with SPP and TPP. The results suggest that a likely genetic basis for FPP does not contribute to TPP and SPP, despite close similarities among FPP, TPP, and SPP.     

A de novo missense mutation (R1623Q) of the SCN5A gene in a Japanese girl with sporadic long QT sydrome. Mutations in brief no. 140. Online

Two missense mutations and a nine-nucleotide deletion of the cardiac sodium channel (SCN5A) gene have been shown to cause long QT syndrome (LQTS) in several familial cases. We identified a novel missense mutation (R1623Q) of the SCN5A gene in a Japanese girl with sporadic LQTS. We used polymerase chain reaction, single-strand conformation polymorphism analysis and DNA sequence analysis to identify a mutation of the SCN5A gene in the patient. A single nucleotide substitution of guanine to adenine, in codon 1612, changed the coding sense of the SCN5A from arginine to glutamine (R1623Q) in the S4 segment of domain IV which is a highly conserved region of the SCN5A. This mutation was not identified in the unaffected biological parents and brother of the patient, and 100 normal, unrelated individuals. This finding is the first evidence of a de nova mutation in SCN5A associated with LQTS.     

Genetic and biophysical basis of sudden unexplained nocturnal death syndrome (SUNDS), a disease allelic to Brugada syndrome

Sudden unexplained nocturnal death syndrome (SUNDS), a disorder found in southeast Asia, is characterized by an abnormal electrocardiogram with ST-segment elevation in leads V1-V3 and sudden death due to ventricular fibrillation, identical to that seen in Brugada syndrome. We screened patients with SUNDS for mutations in SCN5A, the gene known to cause Brugada syndrome, as well as genes encoding ion channels associated with the long-QT syndrome. Ten families were enrolled, and screened for mutations using single-strand DNA conformation polymorphism analysis, denaturing high-performance liquid chromatography and DNA sequencing. Mutations were identified in SCN5A in three families. One mutation, R367H, lies in the first P segment of the pore-lining region between the DIS5 and DIS6 transmembrane segments of SCN5A. A second mutation, A735V, lies in the first transmembrane segment of domain II (DIIS1) close to the first extracellular loop between DIIS1 and DIIS2, whereas the third mutation, R1192Q, lies in domain III. Analysis of these mutations in Xenopus oocytes showed that the R367H mutant channel did not express any current and the likely effect of this mutation is to depress peak current due to the loss of one functional allele. The A735V mutant expressed currents with steady state activation voltage shifted to more positive potentials. The R1192Q mutation accelerated the inactivation of the sodium channel current. Both mutations resulted in reduced sodium channel current (I(Na)) at a time corresponding to the end of phase 1 of the action potential, as described previously in the Brugada syndrome. Based upon these observations we suggest that SUNDS and Brugada syndrome are phenotypically, genetically and functionally the same disorder.     

Genetic variation in LINGO-1 (rs9652490) and risk of Parkinson's disease: twelve studies and a meta-analysis

Mutations of the voltage gated sodium channel gene (SCN4A) are responsible for non-dystrophic myotonia including hyperkalemic periodic paralysis, paramyotonia congenita, and sodium channel myotonia, as well as congenital myasthenic syndrome. In vitro functional analyses have demonstrated the non-dystrophic mutants to show a gain-of-function defect of the channel; a disruption of fast inactivation, an enhancement of activation, or both, while the myasthenic mutation presents a loss-of function defect. This report presents a case of non-dystrophic myotonia that is incidentally accompanied with acquired myasthenia. The patient presented a marked warm-up phenomenon of myotonia but the repeated short exercise test suggested mutations of the sodium channel. The genetic analysis identified a novel mutation, G1292D, of SCN4A. A functional study of the mutant channel revealed marked enhancement of activation and slight impairment of fast inactivation, which should induce muscle hyperexcitability. The effects of the alteration of channel function to the myasthenic symptoms were explored by using stimulation of repetitive depolarization pulses. A use-dependent channel inactivation was reduced in the mutant in comparison to normal channel, thus suggesting an opposing effect to myasthenia.     

Mutation of sodium channel SCN3A in a patient with cryptogenic pediatric partial epilepsy

Mutations in the sodium channel genes SCN1A and SCN2A have been identified in monogenic childhood epilepsies, but SCN3A has not previously been investigated as a candidate gene for epilepsy. We screened a consecutive cohort of 18 children with cryptogenic partial epilepsy that was classified as pharmacoresistant because of nonresponse to carbamazepine or oxcarbazepine, antiepileptic drugs that bind sodium channels. The novel coding variant SCN3A-K354Q was identified in one patient and was not present in 295 neurological normal controls. Twelve novel SNPs were also detected. K354Q substitutes glutamine for an evolutionarily conserved lysine residue in the pore domain of SCN3A. Functional analysis of this mutation in the backbone of the closely related gene SCN5A demonstrated an increase in persistent current that is similar in magnitude to epileptogenic mutations of SCN1A and SCN2A. This observation of a potentially pathogenic mutation of SCN3A (Nav1.3) indicates that this gene should be further evaluated for its contribution to childhood epilepsy.     

A mutation in a rare type of intron in a sodium-channel gene results in aberrant splicing and causes myotonia

Many mutations in the skeletal-muscle sodium-channel gene SCN4A have been associated with myotonia and/or periodic paralysis, but so far all of these mutations are located in exons. We found a patient with myotonia caused by a deletion/insertion located in intron 21 of SCN4A, which is an AT-AC type II intron. This is a rare class of introns that, despite having AT-AC boundaries, are spliced by the major or U2-type spliceosome. The patient's skeletal muscle expressed aberrantly spliced SCN4A mRNA isoforms generated by activation of cryptic splice sites. In addition, genetic suppression experiments using an SCN4A minigene showed that the mutant 5' splice site has impaired binding to the U1 and U6 snRNPs, which are the cognate factors for recognition of U2-type 5' splice sites. One of the aberrantly spliced isoforms encodes a channel with a 35-amino acid insertion in the cytoplasmic loop between domains III and IV of Nav1.4. The mutant channel exhibited a marked disruption of fast inactivation, and a simulation in silico showed that the channel defect is consistent with the patient's myotonic symptoms. This is the first report of a disease-associated mutation in an AT-AC type II intron, and also the first intronic mutation in a voltage-gated ion channel gene showing a gain-of-function defect.     

The genotype and clinical phenotype of Korean patients with familial hypokalemic periodic paralysis

Familial hypokalemic periodic paralysis (HOPP) is a rare autosomal-dominant disease characterized by reversible attacks of muscle weakness occurring with episodic hypokalemia. Mutations in the skeletal muscle calcium (CACNA1S) and sodium channel (SCN4A) genes have been reported to be responsible for familial HOPP. Fifty-one HOPP patients from 20 Korean families were studied to determine the relative frequency of the known mutations and to specify the clinical features associated with the identified mutations. DNA analysis identified known mutations in 12 families: 9 (75%) were linked to the CACNA1S gene and 3 (25%) to the SCN4A gene. The Arg528His mutation in the CACNA1S gene was found to be predominant in these 12 families. Additionally, we have detected one novel silent exonic mutation (1950C>T) in the SCN4A gene. As for a SCN4A Arg669His mutation, incomplete penetrance in a woman was observed. Characteristic clinical features were observed both in patients with and without mutations. This study presents comprehensive data on the genotype and phenotype of Korean families with HOPP.     

A gain-of-function mutation in the sodium channel gene Scn2a results in seizures and behavioral abnormalities

The GAL879-881QQQ mutation in the cytoplasmic S4-S5 linker of domain 2 of the rat brain IIA sodium channel (Na(v)1.2) results in slowed inactivation and increased persistent current when expressed in Xenopus oocytes. The neuron-specific enolase promoter was used to direct in vivo expression of the mutated channel in transgenic mice. Three transgenic lines exhibited seizures, and line Q54 was characterized in detail. The seizures in these mice began at two months of age and were accompanied by behavioral arrest and stereotyped repetitive behaviors. Continuous electroencephalogram monitoring detected focal seizure activity in the hippocampus, which in some instances generalized to involve the cortex. Hippocampal CA1 neurons isolated from presymptomatic Q54 mice exhibited increased persistent sodium current which may underlie hyperexcitability in the hippocampus. During the progression of the disorder there was extensive cell loss and gliosis within the hippocampus in areas CA1, CA2, CA3 and the hilus. The lifespan of Q54 mice was shortened and only 25% of the mice survived beyond six months of age. Four independent transgenic lines expressing the wild-type sodium channel were examined and did not exhibit any abnormalities.The transgenic Q54 mice provide a genetic model that will be useful for testing the effect of pharmacological intervention on progression of seizures caused by sodium channel dysfunction. The human ortholog, SCN2A, is a candidate gene for seizure disorders mapped to chromosome 2q22-24.     

The genomic structure of the human skeletal muscle sodium channel gene.

Electrical excitability of neurons and muscle cells reflects the actions of a family of structurally related sodium channels. Mutations in the adult skeletal muscle sodium channel have been associated with the inherited neuromuscular disorders paramyotonia congenita (PMC) and hyperkalemic periodic paralysis (HPP). We have deciphered the entire genomic structure of the human skeletal muscle sodium channel gene and developed a restriction map of the locus. SCN4A consists of 24 exons spanning 35 kb of distance on chromosome 17q. We describe the sequence of all intron/exon boundaries, the presence of several polymorphisms in the coding sequence, and the locations within introns of two dinucleotide repeat polymorphisms. This is the first sodium channel for which the entire genomic structure has been resolved. The organization of the SCN4A exons relative to the proposed protein structure is presented and represents a foundation for functional and evolutionary comparisons of sodium channels. Knowledge of the exon structure and flanking intron sequences for SCN4A will permit a systematic search for mutations in PMC and HPP.