小鼠Klf4基因的克隆及原核表达分析

目的克隆Klf4基因并对其重组蛋白进行原核表达及分析。方法提取胎鼠皮肤mRNA后反转录为cDNA序列,用一对两端引入特定酶切位点引物,从该cDNA中扩增出Klf4基因编码区序列,将其克隆到pEasy-T3载体上。对质粒双酶切并回收其中Klf4基因片段后,克隆入pET-52b（＋）载体后转化Origmai B（DE3）型大肠杆菌,用IPTG诱导表达,最后采用SDS-PAGE对重组蛋白进行鉴定及分析。结果对所克隆的Klf4mRNA蛋白编码区的DNA序列分析表明,klf4CDS区包括终止密码子在内为1452 bp,与参照序列对比仅有四处存在差异,不仅其同源性达到99.72%,且其氨基酸序列同源性为100%;在IPTG诱导下pET-52b（＋）-Klf4重组质粒可表达与预期相符的约为57×103的蛋白质;经IPTG刺激后重组蛋白表达明显上调,其中IPTG为0.4 mol/L时效果最佳。结论从胎鼠皮肤中克隆的Klf4基因可在原核中表达。     

白鹅催乳素基因的克隆及诱导表达条件的优化

摘要: 运用RT-PCR方法, 从白鹅脑垂体总RNA中扩增得到了催乳素(Prolactin, PRL)基因编码区序列cDNA, 并将其克隆到pMD18-T载体上。DNA序列分析表明, PRL cDNA包括终止密码子在内的长度为690 bp,编码230个氨基酸残基的蛋白质, 与皖西白鹅的有所差异, 二者碱基同源性在99.57%, 氨基酸同源性达99.56%。将PRL基因编码区序列cDNA定向克隆到表达载体pET-32a (+)中, 构建表达质粒pET-32a(+)-PRL。该质粒的BL21 (DE3)转化菌在IPTG的诱导下可表达PRL基因融合蛋白, IPTG终浓度1 mmol/L, 37℃, 诱导4 h表达量最高, 表达量约占菌体总蛋白的28.96%。     

小鼠canstatin C端片段基因的克隆及其在大肠杆菌中的表达

为了构建小鼠canstatinC端片段的原核表达载体并在大肠杆菌中表达。以小鼠肝脏组织总RNA为模板,通过RT-PCR扩增小鼠canstatinC端片段(mCan-C)基因,克隆到pMD18-T载体中并进行序列分析。将mCan-C基因定向克隆于原核表达载体pET30a(+)中,构建表达载体pET／mCan-C,转化大肠杆菌BL21(DE3),IPTG诱导表达。结果表明,小鼠canstatinC端片段的cDNA长度为399bp,含有1个终止密码,编码132个氨基酸,与已知的人canstatinC端片段氨基酸的同源性为61％。IPTG诱导mCan-C在大肠杆菌E．coliBL21中表达,表达量约占菌体总蛋白量的28％,重组蛋白主要以包涵体形式存在。首次克隆了小鼠canstatinC端片段的cDNA,IPTG诱导mCan-C在大肠杆菌E．coliBL21中高效表达。小鼠canstatinC端片段的cDNA序列已收入GenBank,接受号为:AY502947。     

家蝇伴侣蛋白TCP-1基因的序列分析、克隆及诱导表达

旨在对EST筛选得到的家蝇伴侣蛋白TCP-1(MD-TCPⅠ)基因进行序列分析,克隆其cDNA序列并在大肠杆菌中诱导表达。采用EST测序技术从已构建的家蝇幼虫cDNA质粒文库中筛选到MD-TCPⅠ基因,对其进行序列测定和分析。以该基因的cDNA文库质粒为模板,通过PCR的方法进行扩增,以pET-28a(+)为载体构建重组质粒,再转化到表达宿主大肠杆菌BL21(DE3)中,IPTG诱导表达。表达产物通过SDS-PAGE进行鉴定。结果显示,MD-TCPⅠ基因ORF全长753 bp,编码250个氨基酸,理论分子量27.07 kD;等电点5.92,该序列编码的蛋白属于热休克蛋白60家族的TCP。构建了正确基因序列MD-TCPⅠ重组表达质粒,重组蛋白在大肠杆菌BL21(DE3)中诱导表达。     

果蝇心脏发育标记基因Kruppel的多克隆抗体制备

Kruppel在果蝇发育过程中起着重要的调控作用。为了进一步研究Kruppel的功能,需要制备Kruppel蛋白及其抗体.对已有的Kruppel序列进行分析,选取适当区域进行引物设计,从果蝇心脏cDNA文库中PCR扩增得到Kruppel部分编码区序列,并其连接到pET-28a载体上。将重组质粒（pET-28a-Kruppel）转化rosetta受体菌,通过IPTG（Isopropylβ-D-thiogalactoside）诱导表达融合蛋白,用镍柱进行亲和纯化。将纯化得到的融合蛋白免疫新西兰大白兔制备多克隆抗体,并用Western blot检测抗体的效价。     

棉花GhDHAR2基因克隆、功能序列分析及原核表达

通过RT-PCR方法从棉花纤维组织中克隆得到脱氢抗坏血酸还原酶基因GhDHAR2的cDNA,该基因开放阅读框为639 bp,编码212个氨基酸的蛋白质。同源性序列对比分析显示,GhDHAR2蛋白具有较高的保守性,具有典型的功能结构域,包括GST-N家族和GST-C-DHAR家族的功能结构域;进化树分析显示GhDHAR2和拟南芥AtDHAR2在进化关系上较近。将GhDHAR2基因连接到原核表达载体pET-28a中,将重组载体pET28a-GhDHAR2转入到表达菌株BL21(DE3)中,通过IPTG诱导表达出重组GhDHAR2蛋白,SDS-PAGE凝胶电泳分析显示重组蛋白大小约为28 kD,诱导表达的重组蛋白具有较高的DHAR活性。首次克隆了棉花GhDHAR2基因,通过结构域分析其可能的作用,并成功进行蛋白体外表达及酶活性分析。     

球毛壳菌（Chaetomium globosum）过氧化物膜蛋白过敏原基因克隆、序列分析及原核表达

以球毛壳菌cDNA文库中获得过氧化物膜蛋白（pero）基因片段（GenBank Accn:BP099709）为基础,用RACE 技术获得该基因的全长cDNA序列。序列长747bp,由412bp的3′RACE产物和508bp的5′RACE产物拼接而成。开放阅读框501bp,编码166个氨基酸,蛋白分子量为17.5kD,理论等电点为5.75。利用cDNA两侧非编码区序列作引物克隆出该基因的DNA序列,序列分析表明该基因由2个内含子和3个外显子组成。ClustalX多序列比对表明：该基因与粗糙脉孢菌（Neurospora crassa）的过氧化物膜蛋白过敏原同源性最高（83%）。将pero基因编码区克隆到原核表达载体pET28a中,构建成表达质粒pET28a-pero并转化大肠杆菌BL21,IPTG诱导后SDS-PAGE检测表达情况,结果发现在21kD处有一特异性融合蛋白带,大小与预期相符,说明该基因已经在大肠杆菌中表达。克隆的cDNA序列、DNA序列及推测的氨基酸序列在GenBank登录(登录号分别为AY555771,AY584753,AAS66898)。     

小鼠Nanog基因的克隆及其在大肠杆菌中的表达

按照nanog基因编码序列设计合成引物,利用RT-PCB从小鼠的囊胚期胚胎中扩增得到该 基因,并将该基因克隆到pET-28b(+)载体上,获得pET-28b(+)-nanog原核表达重组质粒,限制 性酶分析和DNA序列测定均证实该克隆插入片段为nanog基因编码序列。重组质粒转化大肠杆 菌BL21(DE3),经IPTG诱导表达,在大肠杆菌表达系统中获得了高效表达,western杂交证实该 蛋白具有6-His抗原活性,从而证实目的蛋白为Nanog蛋白。     

CTX-M-14型超广谱β-内酰胺酶的序列分析与原核表达

目的对大肠埃希菌所产CTX-M-14型超广谱β-内酰胺酶（ESBLs）进行基因克隆和重组表达,探讨其特性。方法以产CTX-M-14型超广谱β-内酰胺酶大肠埃希菌12号菌总基因组DNA为模板,PCR扩增CTX-M-14,将其克隆入pUCm-T Vector载体后测定该核苷酸序列;再将基因编码区克隆到原核表达载体pET-28α,构建含CTX-M-14基因的重组表达质粒,转化到大肠埃希菌BL21中进行IPTG诱导表达。SDS-PAGE电泳鉴定表达的酶蛋白后再过Ni-NTA柱纯化。结果PCR扩增出大小为876bp的基因片段,与GenBank上同类酶的基因序列同源性为100％。大肠埃希菌BL21转化pET-28a／CTX-M-14重组质粒后,ESBLs试验为阳性。此基因能在大肠埃希菌中大量表达,SDS-PAGE电泳显示蛋白分子质量大约为30KD。结论成功表达重组的CTX-M-14型酶,为进一步做酶动力学及酶的其他分子生物学特性研究奠定基础。     

果蝇心脏发育标记基因lbe的多克隆抗体制备

lbe是已经证明的心脏标记基因。为了深入研究lbe在心脏发育中的功能,需要获得lbe蛋白并制备其抗体。首先提取野生型成体果蝇的总RNA,反转录获得其cDNA文库,通过PCR克隆出lbe编码区序列,将其连接到pET-28a原核表达载体上。经酶切及测序鉴定后,质粒构建成功。将重组质粒（pET-28a-lbe）转化大肠杆菌菌株Rosseta,用IPTG诱导表达出融合蛋白,经Ni-IDA凝胶柱纯化后,最后将纯化的融合蛋白免疫新西兰大白兔制备lbe多克隆抗体,并用Western blotting检测抗体的效价和特异性。结果显示获得了lbe原核表达重组融合蛋白及高效价的特异性兔抗lbe多克隆抗体,为lbe功能的进一步研究奠定了基础。     

Lin28a enhances in vitro osteoblastic differentiation of human periosteum‐derived cells

Despite a capacity for proliferation and an ability to differentiate into multiple cell types, in long‐term culture and with ageing, stem cells show a reduction in growth, display a decrease in differentiation potential, and enter senescence without evidence of transformation. The Lin28a gene encodes an RNA‐binding protein that plays a role in regulating stem cell activity, including self‐renewal and differentiation propensity. However, the effect of the Lin28a gene on cultured human osteoprecursor cells is poorly understood. In the present study, alkaline phosphatase activity, alizarin red‐positive mineralization, and calcium content, positive indicators of osteogenic differentiation, were significantly higher in cultured human periosteum‐derived cells (hPDCs) with Lin28a overexpression compared with cells without Lin28a overexpression. Lin28a overexpression by hPDCs also increased mitochondrial activity, which is essential for cellular proliferation, as suggested by a reduced presence of reactive oxygen species and significantly enhanced lactate levels and ATP production. Our results suggest that, in hPDCs, the Lin28a gene enhances osteoblastic differentiation and increases mitochondrial activity. Although Lin28a is known as a marker of undifferentiated human embryogenic stem cell, there is limited evidence regarding the influence of Lin28a on osteoblastic differentiation of cultured osteoprecursor cells. This study was to examine the impact of Lin28a on osteogenic phenotypes of human periosteum‐derived cells. Their phenotypes can be similar to those of mesenchymal stem cells. Our results suggest that the Lin28a gene enhances the osteoblastic differentiation of human periosteum‐derived cells. In addition, the Lin28a gene increases mitochondrial activity in human periosteum‐derived cells.     

Lin28B Is an Oncofetal Circulating Cancer Stem Cell-Like Marker Associated with Recurrence of Hepatocellular Carcinoma

By using an expressed sequence tag bioinformatic algorithm, we identified that Lin28 homolog B (Lin28B) may have an oncofetal expression pattern which may facilitate detecting cancer cells in adults. It is also reported to be a potential marker for cancer stem cells. Therefore, we sought to verify oncofetal-stemness characters of Lin28B and test its potential as a circulating cancer stem cell-like marker in adult HCC patients. Lin28B mRNA was examined in a panel of fetal tissue, adult tissue and tumors. Lin28B was over-expressed or knocked down in HepG2 cells to evaluate its potential as a stem cell-like marker. RT-qPCR for Lin28B was performed in the peripheral blood mononuclear cells from patients with HCC receiving surgery (n=96) and non-HCC controls (n=60) and analyzed its clinical significance. Lin28B showed an oncofetal expression pattern. Its overexpression could upregulate stemness markers (OCT4, Nanog and SOX2) and enhance tumorsphere formation in vitro. Lin28B knockdown had opposite effects. Circulating Lin28B was detected in peripheral blood mononuclear cells in 3 cases (5%) of non-HCC controls and 32 cases (33.3%) of HCC patients. In HCC patients, circulating Lin28B was associated with high tumor grade (P=0.046), large size (P=0.005), high AJCC stage (P=0.044) and BCLC stage (P=0.017). Circulating Lin28B was significantly associated with decreased recurrence-free survival (P<0.001). Circulating Lin28B separated early stage HCC into 2 recurrence-free survival curves (P=0.003). In multivariate analysis, circulating Lin28B was an independent variable associated with early recurrence (P=0.045) and recurrence in early stage HCC (P=0.006). In conclusion, the oncofetal gene Lin28B is a potential oncofetal cancer-stem-cell-like circulating tumor cell marker that correlates with HCC recurrence after hepatectomy. Circulating Lin28B could refine early AJCC stages. Our finding supports the possible use of a TNMC (C for circulating tumor cells) staging system in HCC.     

Overexpression of Lin28 Decreases the Chemosensitivity of Gastric Cancer Cells to Oxaliplatin,Paclitaxel, Doxorubicin,and Fluorouracil in Part via microRNA-107

Higher Lin28 expression is associated with worse pathologic tumor responses in locally advanced gastric cancer patients undergoing neoadjuvant chemotherapy. However, the characteristics of Lin28 and its mechanism of action in chemotherapy resistance is still unclear. In this study, we found that transfection of Lin28 into gastric cancer cells (MKN45 and MKN28) increased their resistance to the chemo-drugs oxaliplatin (OXA), paclitaxel (PTX), doxorubicin (ADM), and fluorouracil (5-Fu) compared with gastric cancer cells transfected with a control vector. When knockdown Lin28 expression by Lin28 small interfering RNA (siRNA) was evaluated in vitro, we found that the resistance to chemo-drugs was reduced. Furthermore, we found that Lin28 up-regulates C-myc and P-gp and down-regulates Cylin D1. Finally, we found that miR-107 is a target microRNA of Lin28 and that it participates in the mechanism of chemotherapy resistance. Our results suggest that the Lin28/miR-107 pathway could be one of many signaling pathways regulated by Lin28 and associated with gastric cancer chemo-resistance.     

Increased Expression of Lin28B Associates with Poor Prognosis in Patients with Oral Squamous Cell Carcinoma

Recent studies showed that incomplete cell reprogramming can transform cells into tumour-like cells. Lin28A is associated with fibroblast and sarcoma cell reprogramming, whereas its homologue Lin28B is associated with hematopoietic cell reprogramming. This study aimed to investigate the expression and prognostic difference between Lin28A and Lin28B in oral squamous cell carcinoma (OSCC). Expression level was assessed by immunohistochemistry and staining location was confirmed by immunofluorescence. Prognostic values were analysed and compared by the Kaplan–Meier analysis and uni and multivariate Cox regression models. Besides, in vitro cell assays and in vivo nude mice xenograft were used to demonstrate the influence of increased Lin28B expression in OSCC. Lin28A and Lin28B expression increased in OSCC, and co-expression of Lin28A and Lin28B showed no significant association with patient prognosis. Kaplan–Meier analysis showed that patients with high Lin28B but not Lin28A expression had lower overall survival (OS) rates than those with low Lin28B expression. Further Univariate analysis showed that patients with increased Lin28B expression had shorter disease-free survival (DFS) and shorter OS, while multivariate analysis showed Lin28B overexpression with TNM stage predicted poor prognosis in patients with OSCC. Besides, stable expressing Lin28B in oral cancer cells promoted cell migration, invasion, colony formation, in vivo proliferation and increased the expression of cancer suppressor miRNA let-7 targeted genes IL-6, HMGA2, the EMT markers Snail and Twist, the angiogenesis inducer VEGF, and the apoptosis inhibitor Survivin. These combined results indicate that Lin28B is a novel marker for predicting prognosis in patients with OSCC and may be a therapeutic target.     

Ectopic over-expression of tristetraprolin in human cancer cells promotes biogenesis of let-7 by down-regulation of Lin28

Tristetraprolin (TTP) is a AU-rich element (ARE) binding protein and exhibits suppressive effects on cell growth through down-regulation of ARE-containing oncogenes. The let-7 microRNA has emerged as a significant factor in tumor suppression. Both TTP and let-7 are often repressed in human cancers, thereby promoting oncogenesis by derepressing their target genes. In this work, an unexpected link between TTP and let-7 has been found in human cancer cells. TTP promotes an increase in expression of mature let-7, which leads to the inhibition of let-7 target gene CDC34 expression and suppresses cell growth. This event is associated with TTP-mediated inhibition of Lin28, which has emerged as a negative modulator of let-7. Lin28 mRNA contains ARE within its 3'-UTR and TTP enhances the decay of Lin28 mRNA through binding to its 3'-UTR. This suggests that the TTP-mediated down-regulation of Lin28 plays a key role in let-7 miRNA biogenesis in cancer cells.     

Lin28 mediates paclitaxel resistance by modulating p21, Rb and Let-7a miRNA in breast cancer cells

Resistance to chemotherapy is a major obstacle for the effective treatment of cancers. Lin28 has been shown to contribute to tumor relapse after chemotherapy; however, the relationship between Lin28 and chemoresistance remained unknown. In this study, we investigated the association of Lin28 with paclitaxel resistance and identified the underlying mechanisms of action of Lin28 in human breast cancer cell lines and tumor tissues. We found that the expression level of Lin28 was closely associated with the resistance to paclitaxel treatment. The T47D cancer cell line, which highly expresses Lin28, is more resistant to paclitaxel than the MCF7, Bcap-37 or SK-BR-3 cancer cell lines, which had low-level expression of Lin28. Knocking down of Lin28 in Lin28 high expression T47D cells increased the sensitivity to paclitaxel treatment, while stable expression of Lin28 in breast cancer cells effectively attenuated the sensitivity to paclitaxel treatment, resulting in a significant increase of IC50 values of paclitaxel. Transfection with Lin28 also significantly inhibited paclitaxel-induced apoptosis. We also found that Lin28 expression was dramatically increased in tumor tissues after neoadjuvant chemotherapy or in local relapse or metastatic breast cancer tissues. Moreover, further studies showed that p21, Rb and Let-7 miRNA were the molecular targets of Lin28. Overexpression of Lin28 in breast cancer cells considerably induced p21 and Rb expression and inhibited Let-7 miRNA levels. Our results indicate that Lin28 expression might be one mechanism underlying paclitaxel resistance in breast cancer, and Lin28 could be a potential target for overcoming paclitaxel resistance in breast cancer.     

Lin28 promoting the protective effect of PMSCs on hepatic ischaemia–reperfusion injury by regulating glucose metabolism

Human placental mesenchymal stem cells (PMSCs) can prevent liver ischaemia–reperfusion injury (LIRI). However, their therapeutic effects are limited. Therefore, additional research is required to elucidate the mechanisms of PMSC-mediated LIRI prevention and enhance the related therapeutic effects. This study aimed to examine the role of the Lin28 protein in the regulation of glucose metabolism in PMSCs. Further, it explored whether Lin28 could enhance the protective effects of PMSCs against LIRI and investigated the underlying mechanisms. Western blotting was performed to examine Lin28 expression in PMSCs under hypoxic conditions. A Lin28 overexpression construct was introduced into PMSCs, and the effect on glucose metabolism was examined using a glucose metabolism kit. Further, the expression of some proteins involved in glucose metabolism and the PI3K-AKT pathway and the levels of microRNA Let-7a–g were examined using western blots and real-time quantitative PCR, respectively. To examine the relationship between Lin28 and the PI3K-Akt pathway, the effects of AKT inhibitor treatment on the changes induced by Lin28 overexpression were examined. Subsequently, AML12 cells were co-cultured with PMSCs to elucidate the mechanisms via which PMSCs prevent hypoxic injury in liver cells in vitro. Finally, C57BL/6J mice were used to establish a partial warm ischaemia–reperfusion model. The mice received intravenous injections containing PMSCs (control and Lin28-overexpressing PMSCs). Finally, their serum transaminase levels and degree of liver injury were assessed using biochemical and histopathological methods, respectively. Lin28 was upregulated under hypoxic conditions in PMSCs. Lin28 exerted protective effects against hypoxia-induced cell proliferation. Moreover, it increased the glycolytic capacity of PMSCs, allowing PMSCs to produce more energy under hypoxic conditions. Lin28 also activated the PI3K-Akt signalling pathway under hypoxic conditions, and its effects were attenuated by AKT inhibition. Lin28 overexpression could protect cells against LIRI-induced liver damage, inflammation and apoptosis and could also attenuate hypoxia-induced hepatocyte injury. Lin28 enhances glucose metabolism under hypoxic conditions in PMSCs, thereby exerting protective effects against LIRI by activating the PI3K-Akt signalling pathway. Our study is the first to report the potential of genetically modified PMSCs for LIRI treatment.