修回日期: 2005-02-28
接受日期: 2005-03-03
在线出版日期: 2005-05-01
目的: 克隆与肿瘤恶性演进相关但未知功能的新基因MGC39325, 构建其真核表达载体, 并应用生物信息学初步探讨其功能.
方法: 应用RT-PCR技术从LoVo细胞中扩增MGC39325基因全长ORF, 选用pGEM-T载体进行TA克隆, 再将其亚克隆到真核表达载体pcDNA3.1(+)的启动子和终止子之间, 通过PCR、限制性酶切分析及测序进行鉴定. 应用生物信息学初步分析其染色体定位、蛋白序列、结构域及功能.
结果: 从LoVo细胞中扩增出1 158 bp的cDNA, 成功进行TA克隆并进一步亚克隆至pcDNA3.1(+)真核表达载体, 测序证实为人MGC39325基因. 生物信息学分析显示此基因定位于8q12.1, 含有2个外显子(1 113 bp), DNA序列含有表皮样生长因子位点标记(3-14, 12-23)、整合素beta链半胱氨酸富集区位点标记(183-196)、铁氧化还原蛋白铁硫结合区位点标记(389-397, 1027-1038)、第Ⅷ因子结构域位点标记(105-157, 548-591)、羧基端胱氨酸结位点标记(744-782)等, 编码由370个氨基酸组成蛋白质, Mr 40 727.9, pI值为9.45, 疏水性平均值为-0.668, 含3个低复杂性区域结构, 氨基酸序列含有豆蔻酰化位点(19-24, 130-135)、cAMP和cGMP依赖性蛋白激酶(38-41, 46-49, 204-207)、酪蛋白激酶(49-52, 158-161)、酪氨酸激酶(53-61)、蛋白激酶C磷酸化位点(97-99, 140-142, 208-210)、N-糖基化位点(97-99)等结构域, 提示这一新的蛋白质可能在细胞生长、黏附及细胞信号转导方面具有重要功能.
结论: 成功地克隆了人MGC39325基因全长ORF, 构建了其pcDNA3.1(+)真核表达载体, 为进一步研究其功能及其肿瘤中的作用创造了条件.
引文著录: 李学农, 李亚玲, 刘国炳, 丁彦青. 肿瘤相关未知功能基因MGC39325的克隆及生物信息学分析. 世界华人消化杂志 2005; 13(9): 1059-1064
Revised: February 28, 2005
Accepted: March 3, 2005
Published online: May 1, 2005
AIM: To clone human MGC39325, a novel gene possibly involved in tumor progression identified in our laboratory by cDNA microarray analysis of colonic carcinoma and choriocarcinoma, and to construct its recombinant eukaryotic expression vector so as to explore its function and roles in neoplasms.
METHODS: Human MGC39325 full length ORF was amplified by RT-PCR from colonic carcinoma LoVo cells and inserted into the vector pGEM-T by TA cloning. Recombinant eukaryotic expression vector (pcDNA3.1-MGC) was then constructed by subcloning technique and confirmed by restriction enzyme digestion analysis and sequencing. Bioinformatic methods were used to analyze its possible structure and function.
RESULTS: MGC39325, with 1158bp, was amplified by RT-PCR from human LoVo cells. The eukaryotic expression vector corresponding to MGC39325 (pcDNA3.1-MGC) was successfully constructed, which was confirmed by RT-PCR and sequencing. Bioinformatic analyses indicated that this gene was mapped on chromosome 8q12.1 with an open reading frame of 1 113 bp. It contained EGF-like domain signature 1 (3-14, 12-23), integrin beta chain cysteine-rich domain signature (183-196), iron-sulfur binding region signature (389-397, 1027-1038), Von Willebrand factor domain signature (105-157, 548-591), and C-terminal cystine knot signature (744-782) in DNA sequence. It encoded a 370 aa protein as expected. The putative protein, with molecular weight 40 727.9, pI 9.45, and grand average of hydropathicity -0.668, included N-myristoylation site (19-24, 130-135), cAMP- and cGMP-dependent protein kinase phosphorylation site (38-41, 46-49, 204-207), casein kinase II phosphorylation site (49-52, 158-161), tyrosine kinase phosphorylation site (53-61), protein kinase C phosphorylation site (97-99, 140-142, 208-210), and N-glycosylation site (97-99). These structural characteristics suggested that it might play a role on cell growth, adhesion and cell signal transduction that may be related to tumor progression and metastasis.
CONCLUSION: Human MGC39325 gene has been successfully cloned, which will benefit further research on its function as well as its implications in cancer and other diseases.
- Citation: Li XN, Li YL, Liu GB, Ding YQ. Molecular cloning and bioinformatic analysis of a novel tumor-associated gene MGC39325. Shijie Huaren Xiaohua Zazhi 2005; 13(9): 1059-1064
- URL: https://www.wjgnet.com/1009-3079/full/v13/i9/1059.htm
- DOI: https://dx.doi.org/10.11569/wcjd.v13.i9.1059
我们在研究大肠癌及绒毛膜癌基因表达谱过程中新发现一个可能与肿瘤恶性演进相关的ESTs序列U79298 cDNA[1-2], 他在大肠癌及绒毛膜癌中均显著高表达, 而在相应正常大肠黏膜及正常胎盘绒毛中低表达, 通过NCBI Entrz搜索发现U79298 cDNA所代表的基因为未知功能基因MGC39325. 有关MGC39325基因的生物学功能及其在肿瘤中的作用尚未见国内外文献报道(中国生物医学文献数据库、中国期刊网及Medline检索), 为探讨其生物学功能及其作用, 我们首次构建了其真核表达载体, 并进行生物信息学初步分析.
Taq酶, AMV反转录酶, Oligo(dT), dNTP, 琼脂糖, pGEM-T vector System I(内含pGEM-T vecter, T4 DNA ligation, 10X buffer, JM109 competent cells), PCR产物纯化试剂盒及质粒抽提试剂盒均为Promega产品, EcoRI, HindIII, DL2000 DNA ladder为Takara公司产品, pCDNA3.1(+), SNAP MiniPrep kit购自Invitrogen公司. RPMI 1640, Trizol购自Gibco公司. SDS, DEPC, G418, 溴化乙锭(EB, Ethidium Bromide)购自Sigma公司. 小牛血清购自杭州四季青公司; 氯仿, 异丙醇等均为国产分析纯.
人大肠癌LoVo细胞系(本室细胞库保存)在含100 mL/L小牛血清的RPMI1640培养液于5% CO2湿化孵箱常规培养, 收获细胞(1.0×107), 用Trizol试剂抽提总RNA, 并进行RT-PCR. RT反应以oligodT为引物, 反应条件为: 70℃ 5 min, 42℃ 90 min, 94℃灭活AMV反转录酶6 min. PCR扩增反应条件为: 94℃预变性5 min, 94℃变性30 s, 56℃退火30 s, 72℃延伸90 s, 35个循环, 72℃延伸10 min. 根据GenBank人MGC39325基因全长ORF序列设计PCR引物, 上游引物: 5'ATAAGCTTAGAAGAGCATCCAACACG 3', 引入Hind Ⅲ酶切位点及A突出端; 下游引物: 5'ATGAATTCTTTACACATGGGAGACC 3'引入EcoRⅠ酶切位点及A突出端[3], 并由上海生工公司合成. PCR产物用15 g/L低溶点琼脂糖凝胶电泳鉴定及回收, PCR产物纯化试剂盒抽提及纯化, -20℃保存备用. 利用pGEM-T vector system I将纯化PCR产物进行连接反应(30 min及 4℃过夜), 常规转化JM109感受态细菌, X-gal/LB平板(含氨苄青霉素和IPTG)筛选, 37℃培养过夜得到抗性白色菌落, 碱裂解法抽提质粒DNA, 并进行EcoR I、Hind Ⅲ双酶切鉴定, 阳性克隆命名为pGEM-MGC.
1.2.1 pcDNA3.1(+)真核表达载体的定向克隆: 挑取上述白色菌落扩大培养, 碱裂解法提取质粒, 选择酶切鉴定阳性克隆, 并回收纯化目的MGC39325基因片断; 同时将pcDNA3.1(+)真核表达载体进行EcoR I, Hind Ⅲ双酶切反应, 回收纯化线性化pcDNA3.1(+)载体, 以T4连接酶构建pcDNA3.1(+)-MGC重组载体. 按上述方法常规转化感受态细菌, X-gal/LB平板筛选, 提取质粒, 作EcoR I, Hind Ⅲ双酶切鉴定, 并在ABI377自动测序仪上进行序列测定.
1.2.2 生物信息学分析: 通过Internet查询美国国家生物信息中心(NCBI, http://www.ncbi.nlm.nih.gov/)EST, Unigene和CGAP(cancer genome anatomy project)数据库, 核酸数据库为GenBank, 数据库搜索采用BLAST. MGC39325基因染色体定位依据Genecard (http://bioinfo. weizmann. ac. il/cards /index. html)和Ensembl (http://www.ensembl.org/)获得. 数字化组织分布表达分析在Genecard及Unigene服务器 (http://genecards. weizmann. ac. il/)上进行, 以待检基因的全长cDNA序列为"探针", 采用BLAST程序对人类EST数据库进行匹配分析, 得到一致性大于95%, P值小于e-10的代表该基因的EST, 通过计算各类组织的cDNA文库中代表该基因的EST数量, 代表该基因在不同组织中的表达丰度[4]. MGC39325基因的氨基酸序列由蛋白质专家分析系统(ExPASy, http://au. expasy. org)推算产生. 蛋白质二级结构模拟、结构域及氨基酸序列比对分析则在Prosite(http://au. expasy. org/Prosite)及EMBL-EBI蛋白预测服务器(http://www.ebi.ac.uk/services/)上运算获得[5], 蛋白质二级结构预测采用APSSP2服务器(http://www.imtech.res.in/raghava/apssp2/)进行.
LoVo细胞总RNA变性琼脂糖凝胶电泳可见28 s, 18 s条带, 分光光度计测定A260/A280值为2.01. 将PCR产物进行琼脂糖凝胶电泳, 可见1 200 bp左右的1条带(图1). 利用pGEM-T vector System I将纯化PCR产物进行TA克隆(图2). EcoR I, Hind Ⅲ双酶切得2条带, 1 200 bp左右为MGC3932基因片断. 该质粒即为阳性克隆, 命名为pGEM-MGC. 进一步地将pcDNA3.1和pGEM-MGC作EcoR I, Hind Ⅲ双酶切, 回收目的片段, 构建了重组pcDNA3.1(+)真核表达载体pcDNA3.1-MGC, 经酶切鉴定重组载体在1 200 bp左右见1条带, 证明pcDNA3.1-MGC构建成功(图3). DNA测序结果(图4)如下: DNA测序结果与GenBank进行比对分析示, 与MGC39325基因cDNA序列同源性为99.35%, 含人MGC39325基因的全长ORF.
通过Ensembl和Genecard数据库搜寻, MGC39325基因定位于人染色体8q12.1, 转录本(NM_147189)为2 971 bp, 包含2个外显子(图5). DNA序列含有表皮样生长因子位点标记(3-14, 12-23)、整合素beta链半胱氨酸富集区位点标记(183-196)、铁氧化还原蛋白铁硫结合区位点标记(389-397, 1027-1038)、第Ⅷ因子结构域位点标记(105-157, 548-591)、羧基端胱氨酸结位点标记(744-782)等标记, Unigene数字化组织分布表达分析发现MGC39325基因主要表达于乳腺、脾、肝、骨骼肌、肾、肺、前列腺等(图6). EMBL-EBI蛋白质预测显示, MGC39325基因编码由370个氨基酸组成蛋白质, 分子质量为40727.9 u, pI值为9.45, MGC39325蛋白分子式为C1768H2850N532O553S10, 不稳定指数为64.12. 应用Hphob./Kyte & Doolittle算法预测蛋白质的疏水性(图7), 其疏水性平均值为-0.668(-2.83-1.34), 脂溶指数(Aliphatic index)为71.73, MGC39325半寿期为30 h, 为疏水性脂溶性蛋白. 应用神经网络算法, 蛋白质位于细胞浆(可能性61.5%). ScanProsite蛋白结构域分析氨基酸序列含有豆蔻酰化位点(19-24, 130-135)、cAMP和cGMP依赖性蛋白激酶(38-41, 46-49, 204-207)、酪蛋白激酶(49-52, 158-161)、酪氨酸激酶(53-61)、蛋白激酶C磷酸化位点(97-99, 140-142, 208-210)、N-糖基化位点(97-99)等结构域, 与整合素beta家族的特有结构域同源性达100%, 含3个低复杂性区域结构(图8), 提示这一新的蛋白质可能在细胞生长、黏附及细胞信号转导方面具有重要功能. 蛋白质二级结构预测显示蛋白主体结构为螺管结构(coil), 并含有5个螺旋结构(helix)及8个绞链区(strand).
我们首次构建了MGC39325真核表达载体, 并应用生物信息学预测其结构及功能, 为进一步研究其功能及其肿瘤中的作用创造了条件. 本实验采用分子克隆技术构建了其真核表达载体, 以期采用基因转染及表达方法探讨其在人类疾病中的作用. 分子克隆的困难之一在于重组子的筛选, 克隆设计的瑕疵, 将导致筛选工作巨大甚至无法筛选, 有时还无法解释实验结果[6-9]. 我们设计的特异定向克隆策略使筛选工作量降至最低, 从而提高了克隆效率. 其中引入合适的酶切位点极为关键. 合适的酶切位点由所用的两种载体序列、目的基因片断序列等决定, 最佳设计是所引入的位点在T载体、pcDNA3.1(+)载体及所克隆的目的基因片断中均只有唯一的识别点, 且扩增片断的酶切位点与载体相互匹配, 以便于相互唯一性地识别和连接, 从而保证正确的插入位置及方向. 我们在MGC39325片断上游、下游分别引入EcoR I, Hind III酶切位点, 并且均加入A突出端, 利用pGEM-T载体对RT-PCR产物进行TA克隆, 将TA克隆双酶切产物鉴定后的片断纯化回收, 再克隆至pcDNA3.1(+)真核表达载体. 分子克隆实验的成败关键在于最优化的克隆设计策略和方法, 如RNA的完整性、设计最合适的引物、最优化PCR扩增条件、RT-PCR产物回收纯化质量、合适的连接反应及酶切反应体系等. RT-PCR产物的直接酶切克隆, 虽然简便但效率很低[10-13], 我们选用高效率的TA克隆, 他利用Taq DNA聚合酶可以在双链DNA的3'端独立地加上一个脱氧腺苷酸(A), 产生一个带有3'-A的尾巴的特征, 制备在外源片断切口处有一突出的T的载体(称为T载体), 使PCR产物直接与T载体以粘端方式连接. 这样既不需要对PCR产物进行酶切处理, 又提高了连接效率. 由此将目的基因片断先进行高质量的生物法扩增, 提取重组质粒, 进行较高效的酶切反应, 再进行二次克隆, 将目的基因片断正确插入到真核表达载体, 二步克隆策略设计较好地解决了RT-PCR等较低质量的DNA 的分子克隆问题.
我们选用pcDNA3.1(+)真核表达载体, 他具有合适的多克隆位点, 有高效能稳定和瞬时转染哺乳动物及人类细胞的能力, 具有高效率hCMV立即早期启动子和增强子、T7启动子、BGH多腺苷酸信号、SV40早期启动子、SV40复制起点(origin)和pUC复制起点(ori), 特别是具有在转染细胞中以载体附加体(episome)这一染色体外形式复制的能力, 能在广泛的宿主细胞中稳定复制, 载体在细胞中拷贝数可高达103, 且该载体己去掉编码病毒结构蛋白的反式作用序列, 无转座作用的长未端重复序列(LTR), 一般认为无再次形成病毒之虞, 因而是一种高效的、相对安全的真核表达载体[14-17], 较适宜于进一步实验研究. 生物信息学分析发现 MGC39325基因定位于人染色体8q12.1, 主要表达于乳腺、脾、肝、骨骼肌、肾、肺、前列腺等, DNA序列含有表皮样生长因子位点标记(3-14, 12-23)、整合素β链半胱氨酸富集区位点标记(183-196)、铁氧化还原蛋白铁硫结合区位点标记(389-397, 1027-1038)、第Ⅷ因子结构域位点标记(105-157, 548-591)、羧基端胱氨酸结位点标记(744-782)等, 基因编码由370个氨基酸组成蛋白质, 为小分子量、疏水性脂溶性蛋白, 可能定位于细胞浆. ScanProsite蛋白结构域分析显示MGC39325氨基酸序列含有豆蔻酰化位点(19-24, 130-135)、cAMP和cGMP依赖性蛋白激酶(38-41, 46-49, 204-207)、酪蛋白激酶(49-52, 158-161)、酪氨酸激酶(53-61)、蛋白激酶C磷酸化位点(97-99, 140-142, 208-210)、N-糖基化位点(97-99)等结构域, 含3个低复杂性区域结构, 与整合素β家族的特有结构域同源性达100%, 其中整合素[18]、豆蔻酰化位点[19-21]、cAMP和cGMP依赖性蛋白激酶[22-24]、酪蛋白激酶[25-27]、酪氨酸激酶[28-29]、蛋白激酶C[30-31]、N-糖基化位点[32]等均与肿瘤失调生长、黏附性及细胞信号转导有关, 有的已列为肿瘤转移促进基因. MGC39325半寿期较短, 我们推测他可能是细胞浆内与细胞运动相关某个功能复合体的亚单位或调节分子, 其疏水性结构可能有助于他通过细胞膜相结构, 提示这一新的蛋白质可能在细胞生长、黏附方面具有重要功能. 这些生物信息学分析为下一步的研究提供了线索, 对MGC39325基因功能的进一步分析及实验尚在进行中.
编辑: 张海宁 电编: 潘伯荣
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