Wnt基因/Wnt信号通路与乳腺癌

Wnt蛋白是一组调控胚胎形成期间细胞间信号传导的高度保守的分泌信号分子.在过去的几年里,由Wnt蛋白触发的不同信号通路已经得到了详尽的研究.Wnt基因与Wnt信号通路组成分子的突变可引起发育缺陷,异常的Wnt信号传导可导致人类疾病包括肿瘤的发生.许多证据都表明,Wnt信号通路的失调与乳腺癌的发生发展密切相关.micro...     

经典Wnt信号通路与人类肿瘤

近年来,随着对肿瘤的深入研究,Wnt信号的研究也受到了高度的关注．Wnt信号通路是一条在进化上保守的信号途径,在控制胚胎发育,调节细胞生长、迁移、分化,调控正常组织重建等生命活动中发挥重要的作用,其异常活化与众多人类肿瘤的发生、发展密切相关．Wnt信号途径异常的核心是β-catenin在细胞内累积,并通过其下游途径引起特异靶基因的转录．本文着重介绍Wnt/β-catenin信号转导通路的研究进展及其与肿瘤的关系,了解该通路在肿瘤发生过程中的具体分子机制有助于为临床诊断提供依据,为早期干预治疗提供方法．     

Wnt Signaling Drives Prostate Cancer Bone Metastatic Tropism and Invasion

Wnt signaling has been implicated as a driver of prostate cancer-related osteoblast differentiation, and previous studies have linked modifications in Wnt function with the induction of tumor metastasis. A unique aspect of prostate cancer bone metastases in mouse models is their relative predilection to the hindlimb (femur) compared to the forelimb (humerus). Comparative gene expression profiling was performed within the humerus and femur from non–tumor-bearing mice to evaluate differences in the microenvironments of these locations. This revealed the relative overexpression of the Wnt signaling inhibitors WIF1 and SOST in the humerus compared to the femur, with increased WNT5A expression in femur bone marrow, suggesting a coordinated upregulation of Wnt signals within the femur compared to the humerus. Conditioned medium (CM) from bone marrow stromal cells (HS-5 cells) was used to mimic the bone marrow microenvironment, which strongly promoted prostate cancer cell invasion (3.3-fold increase in PC3 cells, P < .05; 7-fold increase in LNCaP cells, P < .05). WNT5A shRNA knockdown within the CM-producing HS-5 cells significantly decreased PC3 (56%, P < .05) and LNCaP (60%, P < .05) cell invasion. Similarly, preincubation of CM with WIF1 significantly blocked LNCaP cell invasion (40%, P < .05). shRNA-mediated knockdown of the Wnt receptors FZD4 and FZD8 also strongly inhibited tumor cell invasion (60% inhibition shFZD4, P < .05; 63% shFZD8, P < .05). Furthermore, small molecule inhibition of JNK, which is an important component of the noncanonical Wnt signaling pathway, significantly inhibited CM-mediated tumor invasion. Overall, this study reveals a role for Wnt signaling as a driver of prostate cancer bone metastatic tropism and invasion.     

Wnt Signaling in Neuromuscular Junction Development

Wnt proteins are best known for their profound roles in cell patterning, because they are required for the embryonic development of all animal species studied to date. Besides regulating cell fate, Wnt proteins are gaining increasing recognition for their roles in nervous system development and function. New studies indicate that multiple positive and negative Wnt signaling pathways take place simultaneously during the formation of vertebrate and invertebrate neuromuscular junctions. Although some Wnts are essential for the formation of NMJs, others appear to play a more modulatory role as part of multiple signaling pathways. Here we review the most recent findings regarding the function of Wnts at the NMJ from both vertebrate and invertebrate model systems.Wnt proteins are evolutionarily conserved, secreted lipo-glycoproteins involved in a wide range of developmental processes in all metazoan organisms examined to date. In addition to governing many embryonic developmental processes, Wnt signaling is also involved in nervous system maintenance and function, and deregulation of Wnt signaling pathways occurs in many neurodegenerative and psychiatric diseases (De Ferrari and Inestrosa 2000; Caricasole et al. 2005; Okerlund and Cheyette 2011). The first link between Wnt signaling and synapse development was established by Salinas and colleagues in the vertebrate nervous system (Lucas and Salinas 1997; Hall et al. 2000) and by Budnik and colleagues at the invertebrate neuromuscular junction (NMJ) (Packard et al. 2002). Since then, Wnt signaling has emerged as an essential regulator of synaptic development and function in both central and peripheral synapses. Although important roles for Wnt signaling have become known from studies in both the central and peripheral nervous system, this article is concerned with the role of Wnts at the NMJ.     

Wnt Signaling in Vertebrate Axis Specification

The Wnt pathway is a major embryonic signaling pathway that controls cell proliferation, cell fate, and body-axis determination in vertebrate embryos. Soon after egg fertilization, Wnt pathway components play a role in microtubule-dependent dorsoventral axis specification. Later in embryogenesis, another conserved function of the pathway is to specify the anteroposterior axis. The dual role of Wnt signaling in Xenopus and zebrafish embryos is regulated at different developmental stages by distinct sets of Wnt target genes. This review highlights recent progress in the discrimination of different signaling branches and the identification of specific pathway targets during vertebrate axial development.Wnt pathways play major roles in cell-fate specification, proliferation and differentiation, cell polarity, and morphogenesis (Clevers 2006; van Amerongen and Nusse 2009). Signaling is initiated in the responding cell by the interaction of Wnt ligands with different receptors and coreceptors, including Frizzled, LRP5/6, ROR1/2, RYK, PTK7, and proteoglycans (Angers and Moon 2009; Kikuchi et al. 2009; MacDonald et al. 2009). Receptor activation is accompanied by the phosphorylation of Dishev-elled (Yanagawa et al. 1995), which appears to transduce the signal to both the cell membrane and the nucleus (Cliffe et al. 2003; Itoh et al. 2005; Bilic et al. 2007). Another common pathway component is β-catenin, an abundant component of adherens junctions (Nelson and Nusse 2004; Grigoryan et al. 2008). In response to signaling, β-catenin associates with T-cell factors (TCFs) and translocates to the nucleus to stimulate Wnt target gene expression (Behrens et al. 1996; Huber et al. 1996; Molenaar et al. 1996).This β-catenin-dependent activation of specific genes is often referred to as the “canonical” pathway. In the absence of Wnt signaling, β-catenin is destroyed by the protein complex that includes Axin, GSK3, and the tumor suppressor APC (Clevers 2006; MacDonald et al. 2009). Wnt proteins, such as Wnt1, Wnt3, and Wnt8, stimulate Frizzled and LRP5/6 receptors to inactivate this β-catenin destruction complex, and, at the same time, trigger the phosphorylation of TCF proteins by homeodomain-interacting protein kinase 2 (HIPK2) (Hikasa et al. 2010; Hikasa and Sokol 2011). Both β-catenin stabilization and the regulation of TCF protein function by phosphorylation appear to represent general strategies that are conserved in multiple systems (Sokol 2011). Thus, the signaling pathway consists of two branches that together regulate target gene expression (Fig. 1).Open in a separate windowFigure 1.Conserved Wnt pathway branches and components. In the absence of Wnt signals, glycogen synthase kinase 3 (GSK3) binds Axin and APC to form the β-catenin destruction complex. Some Wnt proteins, such as Wnt8 and Wnt3a, stimulate Frizzled and LRP5/6 receptors to inhibit GSK3 activity and stabilize β-catenin (β-cat). Stabilized β-cat forms a complex with T-cell factors (e.g., TCF1/LEF1) to activate target genes. Moreover, GSK3 inhibition leads to target gene derepression by promoting TCF3 phosphorylation by homeodomain-interacting protein kinase 2 (HIPK2) through an unknown mechanism, for which β-catenin is required as a scaffold. This phosphorylation results in TCF3 removal from target promoters and gene activation. Other Wnt proteins, such as Wnt5a and Wnt11, use distinct receptors such as ROR2 and RYK, in addition to Frizzled, to control the the cytoskeletal organization through core planar cell polarity (PCP) proteins, small GTPases (Rho/Rac/Cdc42), and c-Jun amino-terminal kinase (JNK).Other Wnt proteins, such as Wnt5a or Wnt11, strongly affect the cytoskeletal organization and morphogenesis without stabilizing β-catenin (Torres et al. 1996; Angers and Moon 2009; Wu and Mlodzik 2009). These “noncanonical” ligands do not influence TCF3 phosphorylation (Hikasa and Sokol 2011), but may use distinct receptors such as ROR1/2 and RYK instead of or in addition to Frizzled (Hikasa et al. 2002; Lu et al. 2004; Mikels and Nusse 2006; Nishita et al. 2006, 2010; Schambony and Wedlich 2007; Grumolato et al. 2010; Lin et al. 2010; Gao et al. 2011). In such cases, signaling mechanisms are likely to include planar cell polarity (PCP) components, such as Vangl2, Flamingo, Prickle, Diversin, Rho GTPases, and c-Jun amino-terminal kinases (JNKs), which do not directly affect β-catenin stability (Fig. 1) (Sokol 2000; Schwarz-Romond et al. 2002; Schambony and Wedlich 2007; Komiya and Habas 2008; Axelrod 2009; Itoh et al. 2009; Tada and Kai 2009; Sato et al. 2010; Gao et al. 2011). This simplistic dichotomy of the Wnt pathway does not preclude some Wnt ligands from using both β-catenin-dependent and -independent routes in a context-specific manner.Despite the existence of many pathway branches, only the β-catenin-dependent branch has been implicated in body-axis specification. Recent experiments in lower vertebrates have identified additional pathway components and targets and provided new insights into the underlying mechanisms.     

Wnt信号通路与哺乳动物生殖

Wnt蛋白及其受体、调节蛋白等一起组成了复杂的信号通路,调控细胞的分化,参与发育的多个重要过程.近来的研究表明：Wnt信号通路也是调节哺乳动物生殖系统正常发育所必需.它主要参与了缪勒氏管及其派生器官的形成,调控卵泡的发育、排卵及黄体化,另外与正常妊娠的建立以及妊娠过程中乳腺的变化也有关.     

Wnt信号通路与前体脂肪细胞

Wnt蛋白是一类分泌型蛋白生长因子,通过自分泌和旁分泌作用调节多种细胞的发生和发育.新近研究表明,Wnt信号通路在前体脂肪细胞的增殖分化中发挥着重要作用.Wnt蛋白的配基通过与细胞膜上的特异性受体Frizzled1/2/5及辅助受体LRP5/6结合,激活经典或非经典的Wnt信号通路,影响下游靶基因产物的磷酸化作用,进而抑制C/EBPα、PPARγ等脂肪细胞关键转录因子,使细胞保持未分化状态,从而抑制脂肪的形成.本文就Wnt信号通路的研究史和主要分支、作用方式及其抑制脂肪细胞的机制方面进行了综述,并对今后的研究方向和应用作了展望.     

Methylation of DACT2 Promotes Papillary Thyroid Cancer Metastasis by Activating Wnt Signaling

Thyroid cancer is the most common endocrine malignant disease and the incidence is increasing. DACT2 was found frequently methylated in human lung cancer and hepatocellular carcinoma. To explore the epigenetic change and the role of DACT2 in thyroid cancer, 7 thyroid cancer cell lines, 10 cases of non-cancerous thyroid tissue samples and 99 cases of primary thyroid cancer samples were involved in this study. DACT2 was expressed and unmethylated in K1, SW579, FTC-133, TT, W3 and 8505C cell lines. Loss of expression and complete methylation was found in TPC-1 cells. Restoration of DACT2 expression was induced by 5-aza-2′deoxycytidine treatment. It demonstrates that the expression of DACT2 was regulated by promoter region methylation. In human primary papillary thyroid cancer, 64.6% (64/99) was methylated and methylation of DACT2 was related to lymph node metastasis (p<0.01). Re-expression of DACT2 suppresses cell proliferation, invasion and migration in TPC-1 cells. The activity of TCF/LEF was inhibited by DACT2 in wild-type or mutant β-catenin cells. The activity of TCF/LEF was increased by co-transfecting DACT2 and Dvl2 in wild-type or mutant β-catenin cells. Overexpression of wild-type β-catenin promotes cell migration and invasion in DACT2 stably expressed cells. The expression of β-catenin, c-myc, cyclinD1 and MMP-9 were decreased and the level of phosphorylated β-catenin (p-β-catenin) was increased after restoration of DACT2 expression in TPC-1 cells. The expression of β-catenin, c-myc, cyclinD1 and MMP-9 were increased and the level of p-β-catenin was reduced after knockdown of DACT2 in W3 and SW579 cells. These results suggest that DACT2 suppresses human papillary thyroid cancer growth and metastasis by inhibiting Wnt signaling. In conclusion, DACT2 is frequently methylated in papillary thyroid cancer. DACT2 expression was regulated by promoter region methylation. DACT2 suppresses papillary thyroid cancer proliferation and metastasis by inhibiting Wnt signaling.     

Common Genetic Variants in Wnt Signaling Pathway Genes as Potential Prognostic Biomarkers for Colorectal Cancer

Compelling evidence has implicated the Wnt signaling pathway in the pathogenesis of colorectal cancer. We assessed the use of tag single nucleotide polymorphisms (tSNPs) in adenomatous polyposis coli (APC)/β-catenin (CTNNB1) genes to predict outcomes in patients with colorectal cancer. We selected and genotyped 10 tSNP to predict common variants across entire APC and CTNNB1 genes in 282 colorectal cancer patients. The associations of these tSNPs with distant metastasis-free survival and overall survival were evaluated by Kaplan-Meier analysis, Cox regression model, and survival tree analysis. The 5-year overall survival rate was 68.3%. Survival tree analysis identified a higher-order genetic interaction profile consisting of the APC rs565453, CTNNB1 2293303, and APC rs1816769 that was significantly associated with overall survival. The 5-year survival overall rates were 89.2%, 66.1%, and 58.8% for the low-, medium-, and high-risk genetic profiles, respectively (log-rank P = 0.001). After adjusting for possible confounders, including age, gender, carcinoembryonic antigen levels, tumor differentiation, stage, lymphovascular invasion, perineural invasion, and lymph node involvement, the genetic interaction profile remained significant. None of the studied SNPs were individually associated with distant metastasis-free survival and overall survival. Our results suggest that the genetic interaction profile among Wnt pathway SNPs might potentially increase the prognostic value in outcome prediction for colorectal cancer.     

Wnt/beta-catenin 信号通路相关蛋白在胃癌组织中的表达和 肿瘤转移的关系

目的：探讨了Wnt信号通路相关蛋白在胃癌组织中的表达及与肿瘤转移的关系。方法：选取2011 年6 月到2012 年6 月我 院胃癌术后47 例肿瘤标本作为研究对象,并选取同一患者的正常胃组织作为对照研究。采用实时荧光定量PCR 和Western blot 对胃癌组织和正常胃组织Wnt 信号通路相关蛋白进行分析,并分析了肿瘤转移和非转移患者Wnt信号通路相关蛋白的变化。结 果：与正常胃组织比较,胃癌组织中Wnt1、Wnt3、Wnt3a、beta-catenin、CyclinD1 和c-Myc 等分子的mRNA 水平明显上调,差异有显 著统计学意义（P<0.05）。胃癌组织中总beta-catenin 和核内beta-catenin蛋白较正常胃组织明显增加,而磷酸化beta-catenin 较正常组明显 下降、差异有显著统计学意义（P<0.05）。与非转移组比较,转移组患者胃癌组织中Wnt1、Wnt3、Wnt3a 等分子mRNA水平显著上 调,差异有统计学意义（P<0.05）。结论：Wnt信号通路异常激活在胃癌发生和癌细胞转移中发挥着重要的作用,为临床治疗提供了 一定靶点。     

Association of Single Nucleotide Polymorphisms in Wnt Signaling Pathway Genes with Breast Cancer in Saudi Patients

Breast cancer is a complex heterogeneous disease involving genetic and epigenetic alterations in genes encoding proteins that are components of various signaling pathways. Candidate gene approach have identified association of genetic variants in the Wnt signaling pathway genes and increased susceptibility to several diseases including breast cancer. Due to the rarity of somatic mutations in key genes of Wnt pathway, we investigated the association of genetic variants in these genes with predisposition to breast cancers. We performed a case-control study to identify risk variants by examining 15 SNPs located in 8 genes associated with Wnt signaling. Genotypic analysis of individual locus showed statistically significant association of five SNPs located in β-catenin, AXIN2, DKK3, SFRP3 and TCF7L2 with breast cancers. Increased risk was observed only with the SNP in β-catenin while the other four SNPs conferred protection against breast cancers. Majority of these associations persisted after stratification of the cases based on estrogen receptor status and age of on-set of breast cancer. The rs7775 SNP in exon 6 of SFRP3 gene that codes for either arginine or glycine exhibited very strong association with breast cancer, even after Bonferroni''s correction. Apart from these five variants, rs3923086 in AXIN2 and rs3763511 in DKK4 that did not show any association in the overall population were significantly associated with early on-set and estrogen receptor negative breast cancers, respectively. This is the first study to utilize pathway based approach to identify association of risk variants in the Wnt signaling pathway genes with breast cancers. Confirmation of our findings in larger populations of different ethnicities would provide evidence for the role of Wnt pathway as well as screening markers for early detection of breast carcinomas.     

Wnt信号途径及其作用机制

Ｗｎｔ信号途径的重要性近年来逐渐为人们所认识。在胚胎发育过程中 ,Ｗｎｔ途径不但参与了胚胎背腹轴的形成 ,而且与细胞极性建立、细胞命运决定等多个发育事件有关。一旦阻断Ｗｎｔ信号途径 ,动物胚胎会因为形态建成过程遭到破坏而产生非常明显的突变表型 ,例如果蝇的异常表皮、小鼠腹侧化肢体、线虫ＥＭＳ细胞丧失不对称分裂[1] 等等。此外 ,科学家也发现 ,许多肿瘤的发生与Ｗｎｔ途径成员的突变相关[2 ] 。本文通过对近年来所发表的结果综合整理 ,从Ｗｎｔ信号在细胞内外作用位点的决定、关键信号途径成员Ａｒｍ/β 连环蛋白 ( β ｃａ…