P53对丝氨酸-苏氨酸激酶11-磷酸腺苷激活的蛋白激酶信号传导途径的影响

丝氨酸-苏氨酸激酶11(serine/threonine kinase11,LKB1)的胚系突变可以引起Peutz-Jeghers综合征(PJS)[1].PJS是一种常染色体显性遗传性疾病,其肿瘤的发生率是普通人群的10～18倍[2].研究结果显示,散发性肿瘤中LKB1突变罕见,但在非小细胞肺癌(NSCLC)中,LKB1的突变率可达30%.     

P53对丝氨酸-苏氨酸激酶11-磷酸腺苷激活的蛋白激酶信号传导途径的影响

丝氨酸-苏氨酸激酶11(serine/threonine kinase11,LKB1)的胚系突变可以引起Peutz-Jeghers综合征(PJS)[1].PJS是一种常染色体显性遗传性疾病,其肿瘤的发生率是普通人群的10～18倍[2].研究结果显示,散发性肿瘤中LKB1突变罕见,但在非小细胞肺癌(NSCLC)中,LKB1的突变率可达30%.     

Peutz-Jeghers综合征与信号通路

本文通过介绍Peutz-Jeghers综合征(PJS)的临床特征及其致病基因LKB1,着重阐述了m TOR、Wnt/β-catenin、Hedgehog信号通路与PJS的联系,明确信号通路的改变在PJS致病过程中所起的重要作用;目前已有一些信号通路抑制剂投入临床应用。因此,对信号通路的深入研究对PJS的靶向性治疗具有重要意义。     

Peutz-Jeghers综合征研究进展

Peutz-Jeghers综合征(Peutz-Jeghers syndrome,PJS)是一种以皮肤黏膜色素沉着、胃肠道多发息肉、家族遗传性为主要特征的常染色体显性遗传病,丝氨酸-苏氨酸激酶11/肝激酶B1(STK11/LKB1)基因突变被认为与该病的发生密切相关。PJS患者罹患肿瘤的风险较常人更高。目前针对PJS胃肠道息肉的治疗主要包括内镜及手术治疗。本文就近年来PJS的研究进展作一概述。     

Peutz-Jeghers综合征STK13基因突变分析

目的 研究STK13基因在部分Peutz-Jeghers综合征(PJS)家系中的突变情况，判断它是否为中国人PJS新的致病基因，为基因诊断奠定基础。方法 采用聚合酶链反应-单链构象多态性分析(PCR—SSCP)和DNA测序的方法，选择10个无STK11基因突变的PJS家系，对STK13基因进行突变分析。结果 所有7个外显子均未检测到致病突变。结论 STK13基因不是中国人PJS患者新的致病基因。     

β-catenin基因在Peutz-Jeghers综合征组织中的突变及表达

目的:研究Peutz-Jeghers综合征(PJS)患者体内β-catenin基因突变及其蛋白表达,探讨β-catenin在PJS息肉发生及恶变中的作用.方法:收集PJS息肉、癌旁正常黏膜各12例,结肠腺瘤、结肠癌组织各14例,及相应PJS血液标本,检测β-catenin基因外显子3突变及mRNA表达水平.选取PJS息...     

Peutz-Jeghers综合征:恶性肿瘤高风险人群

目的:评估Peutz-Jeghers综合征(Peutz-Jeghers syndrome,PJS)患者并发恶性肿瘤的风险,提出监测建议.方法:通过Pubmed检索PJS并发恶性肿瘤的群组研究文献,并摘录符合条件的20篇文献中的相关资料进行分析.结果:共纳入3302例PJS患者,其中573人(17.35%)并发619例恶性肿瘤,包括消化系肿瘤368例(60.23%),非消化系肿瘤243例(39.77%).并发的常见恶性肿瘤中,依次为结直肠癌、小肠癌、乳腺癌、胃食管癌、妇科癌、胰腺癌、肺癌,且国内外发病频率具有一致性;PJS患者恶性肿瘤高发年龄段为11-70岁,国内患者有较年轻化的趋势.PJS并发任意癌的相对风险为9.0-18,并发消化系肿瘤的相对风险为13-50.5,并发乳腺癌的相对风险为13.9-20.3,并发妇科癌的相对风险为20.3,各年龄段癌症累积风险明显增高.有无STK11/LKB1基因突变对PJS并发恶性肿瘤风险无明显影响(P>0.05).结论:PJS患者为恶性肿瘤的高风险人群,其并发消化系肿瘤及消化系外癌的风险明显增高,应加强随诊筛查恶性肿瘤.     

Peutz-Jeghers综合征临床诊断治疗的现状和问题

Peutz-Jeghets综合征(Peutz-Jeghers syndrome,PJS)是一种常染色体显性遗传性疾病,主要突变基因是LKB1/STK11,胃肠道错构瘤,皮肤黏膜色素斑和家族遗传性为其主要特点,主要并发症是肠梗阻和肠道及胃肠道外恶性肿瘤.本病好发于青少年,除有恶变倾向外,由肠道息肉导致的并发症,反复住院,多次手术,高昂的医疗费用,对国内只有一个独生子女的小家庭,危害极大.本文着重论述PJS临床诊断和治疗中的一些问题,如双气囊电子小肠镜的临床应用,内镜配合手术治疗的经验,介绍抑制环氧化酶2(COX-2)抑制剂和雷帕霉素预防PJS的新动向.     

Peutz-Jeghers综合征患者STK11基因突变情况

目的:Peutz-Jeghers综合征(Peutz-Jeghers syndrome,PJS)是一种较为罕见的以胃肠道多发息肉和皮肤黏膜色素沉着为特征的常染色体显性遗传性疾病,具有较高的肿瘤易感性.研究表明,位于19p13.3位点丝/苏氨酸蛋白激酶(serine/threonine kinase 11,STK11)基因的突变是PJS发病的主要原因.我们通过检测36例(16例具有家族史,20例散发患者)PJS患者STK11基因外显子及侧翼序列突变情况,捕获新的突变位点.方法:采用PCR扩增及DNA直接测序的方法检测36例PJS患者STK11基因外显子及侧翼序列突变情况,并与STK11基因的正常序列对比分析.结果:在所有36例P J S患者中22例检测到STK11基因编码区的突变,其中3例患者携带同一个突变位点,余19例患者均携带单一突变位点.其余14例患者STK11基因编码区未见突变位点.22例发生突变的患者中,5例患者发生移码突变(其中2例移码突变位点已被SNP收录);17例患者发生错义突变(其中8例患者错义突变为终止密码子,此8例中4例突变已被SNP收录).所有突变的患者中共15例未被SNP及Clinwar基因库收录,未见相关报道,考虑为新发现的突变位点.家族史组STK11基因突变率62.5%(10/16),散发组STK11基因突变率60.0%(12/20),两组差异无统计学意义(P0.05)结论:STK11基因突变是PJS(无论家族史或散发患者)发病的主要致病原因,新发现的移码突变或错义突变可能是PJS患者发病的遗传基础之一.     

LKB1、VEGFR2在非小细胞肺癌组织中表达及临床意义的研究

目的探究人Liver kinase B1(LKB1)与血管内皮生长因子受体-2(VEGFR2)在非小细胞肺癌组织中的表达情况,并探究其临床意义。方法采用免疫组化方法测定65例非小细胞肺癌组织及40例癌旁组织LKB1、VEGFR2表达情况。分析LKB1、VEGFR2表达情况与临床病理特征的相关性。结果肺癌组织中LKB1阳性率低于癌旁组织,VEGFR2阳性率高于癌旁组织。LKB1在腺癌中的表达阳性率高于鳞癌,VEGFR2在腺癌中的表达阳性率低于鳞癌。在具有吸烟史、淋巴转移、临床低分期以及低分化程度中LKB1阳性率更低,VEGFR2阳性率更高,差异均有统计学意义(均P0.05)。结论腺癌组织中LKB1表达水平高于鳞癌组织;非小细胞肺癌组织中LKB1、VEGFR2呈现相反的表达趋势。LKB1低表达与VEGFR2高表达提示肺癌患者具有吸烟史、出现淋巴转移、高临床分期以及低分化程度。     

LKB1调节细胞周期的主要分子机制

LKB1基因编码丝氨酸/苏氨酸蛋白激酶,该基因突变导致黑斑息肉综合征。在非小细胞肺癌中LKB1基因突变率可高达30％。作为抑癌基因,LKB1可以引起细胞周期阻滞在G1期,抑制细胞生长。LKB1主要以p53依赖的机制上调p21表达来对细胞周期进行调控。定位在细胞质中的LKB1可以引起细胞生长负调控的信号传递,而定位在细胞...     

A novel de novo mutation in LKB1 gene in a Chinese Peutz Jeghers syndrome patient significantly diminished p53 activity

Peutz Jeghers syndrome (PJS) is an autosomal dominant disease caused by mutations in the LKB1 gene. We screened for the LKB1 gene mutation in a Chinese PJS patient. Sequence analysis of LKB1 exons showed that there was a novel de novo mis-sense mutation of codon?16 (GAG to GGG) in exon?1 in LKB1 gene in the Chinese PJS patient. Furthermore, we observed that wild type LKB1 expression increased p53 activity, while LKB1 A47G mutation had no such effect on p53 activity, indicating that the mis-sense variant of LKB1 influenced the p53 activation function of LKB1 protein. In addition, real-time RT-PCR analysis revealed that the expression levels of p53 downstream targets were significantly diminished in affected PJS patient compared with those in unaffected parents, further confirming the roles of LKB1 and p53 in PJS pathogenesis. Therefore, a novel PJS associated LKB1 gene mutation is provided, and the roles of LKB1 and p53 in PJS pathogenesis is validated in this research.     

Cancer risks in LKB1 germline mutation carriers

BACKGROUND AND AIMS: Germline mutations in the LKB1 gene are known to cause Peutz-Jeghers syndrome, which is an autosomal dominant disorder characterised by hamartomatous polyposis and mucocutaneous pigmentation. This syndrome is associated with an increased risk of malignancies in different organs but there is a lack of data on cancer range and risk in LKB1 germline mutation carriers. PATIENTS AND METHODS: The cumulative incidence of cancer in 149 Peutz-Jeghers syndrome patients with germline mutation(s) in LKB1 was estimated using Kaplan-Meier time to cancer onset analyses and compared between relevant subgroups with log rank tests. RESULTS: Thirty two cancers were found in LKB1 mutation carriers. Overall cancer risks at ages 30, 40, 50, 60, and 70 years were 6%, 18%, 31%, 41%, and 67%, respectively. There were similar overall cancer risks between male and female carriers. However, there were overall cancer risk differences for exon 6 mutation carriers versus non-exon 6 mutation carriers (log rank p=0.022 overall, 0.56 in males, 0.0000084 in females). Most (22/32) of the cancers occurred in the gastrointestinal tract, and the overall gastrointestinal cancer risks at ages 40, 50, 60, and 70 years were 12%, 24%, 34%, and 63%, respectively. In females, the risks for developing gynaecologic cancer at ages 40 and 50 years were 13% and 18%, respectively. CONCLUSIONS: Mutations in exon 6 of LKB1 are associated with a higher cancer risk than mutations within other regions of the gene. Moreover, this study provides age related cumulative risks of developing cancer in LKB1 mutation carriers that should be useful for developing a tailor made cancer surveillance protocol for Peutz-Jeghers syndrome patients.     

The tumor suppressor LKB1 kinase directly activates AMP-activated kinase and regulates apoptosis in response to energy stress

AMP-activated protein kinase (AMPK) is a highly conserved sensor of cellular energy status found in all eukaryotic cells. AMPK is activated by stimuli that increase the cellular AMP/ATP ratio. Essential to activation of AMPK is its phosphorylation at Thr-172 by an upstream kinase, AMPKK, whose identity in mammalian cells has remained elusive. Here we present biochemical and genetic evidence indicating that the LKB1 serine/threonine kinase, the gene inactivated in the Peutz-Jeghers familial cancer syndrome, is the dominant regulator of AMPK activation in several mammalian cell types. We show that LKB1 directly phosphorylates Thr-172 of AMPKalpha in vitro and activates its kinase activity. LKB1-deficient murine embryonic fibroblasts show nearly complete loss of Thr-172 phosphorylation and downstream AMPK signaling in response to a variety of stimuli that activate AMPK. Reintroduction of WT, but not kinase-dead, LKB1 into these cells restores AMPK activity. Furthermore, we show that LKB1 plays a biologically significant role in this pathway, because LKB1-deficient cells are hypersensitive to apoptosis induced by energy stress. On the basis of these results, we propose a model to explain the apparent paradox that LKB1 is a tumor suppressor, yet cells lacking LKB1 are resistant to cell transformation by conventional oncogenes and are sensitive to killing in response to agents that elevate AMP. The role of LKB1/AMPK in the survival of a subset of genetically defined tumor cells may provide opportunities for cancer therapeutics.     

A novel germline mutation of the LKB1 gene in a patient with Peutz-Jeghers syndrome with early-onset gastric cancer

The gene responsible for Peutz-Jeghers syndrome (PJS), LKB1 (also called STK11) was mapped to chromosome 19p13.3 and was found to encode a putative serine/threonine protein kinase, LKB1. As only a limited number (100) of germline mutations of the gene have been reported, and because the protein function is still unclear, information about LKB1 mutations and their expression should be accumulated to understand the phenotype-genotype correlation of this disease. Here we report a patient with sporadic PJS with early-onset gastric cancer. We found a novel germline frameshift mutation (757-758insT) in the LKB1 gene and a marked reduction in LKB1 protein expression in the carcinoma cells, suggesting that the loss of LKB1 function may have led to the carcinogenesis of the gastric cancer.     

AMP-activated protein kinase and human cancer: cancer metabolism revisited

AMP-activated protein kinase (AMPK) and its upstream kinase, LKB1, act to both monitor and restore cellular energy in response to energy depletion. Studied extensively in liver and skeletal muscle, AMPK is phosphorylated and activated by LKB1 in response to increasing AMP/ATP ratios, which occur in a variety of settings including hypoxia, nutrient starvation and redox imbalance. Interest in the roles of both AMPK and LKB1 in cancer has grown substantially, following the identification of LKB1 as the tumor suppressor gene mutated in the Peutz-Jegher familial cancer syndrome. Patients with the Peutz-Jegher syndrome harbor a single inactive LKB1 gene, and acquisition of a second inactivating lesion (loss of heterozygosity) leads to the development of the cancer in a variety of organs. Thus, the loss of AMPK activation is hypothesized to promote the development of malignancy. Conversely, pharmacological AMPK activation has recently been shown to be cytotoxic to many established human cancer cell lines in vitro and in human cancer xenograft and mouse cancer allografts. Previously, changes in cell metabolism that accompanied the malignant phenotype have largely been considered a consequence of cellular transformation. Now, AMPK and energy metabolism are linked to the development and maintenance of the malignant phenotype. These findings have led to renewed interest in AMPK and cancer cell metabolism in general as potential targets for cancer therapy.     

Growth suppression by Lkb1 is mediated by a G1 cell cycle arrest

Germ-line mutations of LKB1 (STK11) lead to Peutz-Jeghers syndrome characterized by gastrointestinal polyps and cancer of different organ systems. The mutations lead to loss or severe impairment of Lkb1 serine/threonine kinase activity. Therefore LKB1 has been implicated as a tumor suppressor gene, but only a few mutations in the coding exons of LKB1 have been detected in sporadic tumors. Here, we have identified tumor cell lines with severely reduced mRNA levels and impaired Lkb1 kinase activity. Reintroducing Lkb1 into these cells suppressed cell growth. The Lkb1-mediated growth inhibition was caused by a G(1) cell cycle block and was not detected with several naturally occurring Lkb1 mutants. These results indicate that LKB1 has functional and specific growth-suppressing activity.     

Molecular insights into Peutz-Jeghers syndrome: two probands with a germline mutation of <Emphasis Type="Italic">LKB1</Emphasis>

LKB1 encodes a serine/threonine protein kinase that is defective in patients with Peutz-Jeghers syndrome (PJS), a hereditary disorder characterized by gastrointestinal hamartomatous polyposis and an increased risk of cancer development. Although a tentative molecular classification of PJS patients was recently made according to their LKB1 mutation status, it is difficult to clarify the genotype-phenotype relationship because of the rarity and genetic heterogeneity of this disease. Here we report on two probands with PJS whose intestinal hamartomatous polyposis was treated by laparoscopyassisted polypectomy. Direct sequencing analyses revealed a nonsense mutation at codon 240 in exon 5 in one patient, and a mutation at a splicing donor site in intron 5 in the other patient. No additional somatic mutations were detected in the resected hamartomas in either case. Immunohistochemical analysis revealed an elevated expression of cyclooxygenase-2, and almost complete loss of LKB1 expression in the polyps, suggesting that a biallelic inactivation of the LKB1 gene was responsible for the hamartoma formation. Methylation-specific polymerase chain reaction analysis revealed no hypermethylation of the LKB1 promoter. Mutation analysis is useful in making a precise diagnosis of PJS in candidate probands, and may in the near future provide valuable information for predicting cancer risk based on genotype-phenotype correlations.     

5'-CpG island methylation of the LKB1/STK11 promoter and allelic loss at chromosome 19p13.3 in sporadic colorectal cancer

BACKGROUND: In patients with Peutz-Jeghers syndrome (PJS), causative germline mutations in the LKB1/STK11 gene on chromosome 19p13.3 have been identified. Because of the loss of heterozygosity (LOH) at 19p13.3 in hamartomas and the cancer susceptibility of patients with PJS, LKB1/STK11 is suggested to act as a tumour suppressor. However, the frequency of genetic and epigenetic inactivation of LKB1/STK11 in sporadic tumours is unclear. AIMS: To investigate the LKB1/STK11 gene for promoter hypermethylation and allelic loss in tumour specimens of patients with sporadic colorectal cancer. METHODS: DNA from 50 consecutive paraffin embedded sporadic colorectal adenocarcinomas and corresponding normal epithelium was extracted. After bisulphite treatment, specimens were analysed for methylation of the LKB1/STK11 promoter 5'-CpG island by methylation specific polymerase chain reaction (MSP). In addition, tumours were analysed for LOH of chromosome 19p13.3. In tumours exhibiting LOH, LKB1/STK11 was sequenced. RESULTS: MSP was successful in 48 of 50 tumour specimens. Of those, four (8%) demonstrated hypermethylation of the LKB1/STK11 promoter 5'-CpG island. Moreover, LOH at either D19S886 or D19S878 was observed in five of 38 (13%) informative tumours. All five tumours showing LOH at 19p13.3 were advanced and four of five were located in the left sided colon. There was no correlation between LOH and LKB1/STK11 promoter hypermethylation or somatic mutation. CONCLUSIONS: In sporadic colorectal cancer, hypermethylation of the LKB1/STK11 promoter and allelic loss at the STK 11 gene locus are rare events. LOH at 19p13.3 was associated with advanced tumour stage and left sided location but not with LKB1/STK11 promoter hypermethylation or somatic mutation.     

The serine-threonine kinase LKB1 is essential for survival under energetic stress in zebrafish

Mutations in the serine-threonine kinase (LKB1) lead to a gastrointestinal hamartomatous polyposis disorder with increased predisposition to cancer (Peutz-Jeghers syndrome). LKB1 has many targets, including the AMP-activated protein kinase (AMPK) that is phosphorylated under low-energy conditions. AMPK phosphorylation in turn, affects several processes, including inhibition of the target of rapamycin (TOR) pathway, and leads to proliferation inhibition. To gain insight into how LKB1 mediates its effects during development, we generated zebrafish mutants in the single LKB1 ortholog. We show that in zebrafish lkb1 is dispensable for embryonic survival but becomes essential under conditions of energetic stress. After yolk absorption, lkb1 mutants rapidly exhaust their energy resources and die prematurely from starvation. Notably, intestinal epithelial cells were polarized properly in the lkb1 mutants. We show that attenuation of metabolic rate in lkb1 mutants, either by application of the TOR inhibitor rapamycin or by crossing with von Hippel-Lindau (vhl) mutant fish (in which constitutive hypoxia signaling results in reduced metabolic rate), suppresses key aspects of the lkb1 phenotype. Thus, we demonstrate a critical role for LKB1 in regulating energy homeostasis at the whole-organism level in a vertebrate. Zebrafish models of Lkb1 inactivation could provide a platform for chemical genetic screens to identify compounds that target accelerated metabolism, a key feature of tumor cells.