SFRP分子对心脏发育的影响

Wnt信号通路对心脏发育起着重要的作用.分泌型卷曲相关蛋白（SFRP）家族作为调控 Wnt信号的重要分子,对心脏发育和心肌分化的作用也越来越被人们所重视.最近,研究人员们对SFRP家族蛋白有了新的认识,认为它们不仅具有拮抗Wnt的作用,还对Wnt信号的转导有着复杂的调节作用.本文就SFRP分子与Wnt信号转导对心脏发育的影响进行综述.     

SFRP4抑表达对HT-29细胞侵袭能力的影响

目的:观察SFRP4对HT29细胞侵袭转移能力的影响。方法:以HT29细胞为研究对象,SFRP4 siRNA通过脂质体转染HT29细胞,western blot检测HT29细胞中Wnt、细胞核β-Catenin蛋白的表达、elisa法检测细胞培养上清MMP-2、MMP-9的含量,Transwell小室观察成的转移侵袭能力。结果:干扰SFRP4后能显著降低HT29细胞中Wnt、细胞核中β-Catenin蛋白的表达、细胞培养上清MMP-2、MMP-9的含量,(P<0.01),降低HT29细胞的转移侵袭能力(P<0.01)。结论:抑制SFRP4表达能抑制HT29细胞的转移侵袭,其机制可能与抑制HT29细胞Wnt信号通路有关。     

Wnt途径—调控细胞增殖和癌变的关键途径

Wnt/Wingless途径是调控细胞生长增殖的关键途径,在胚胎发育和肿瘤发生中起着重要作用。由于肿瘤抑制基因APC失活突变或原癌基因β－catenin激活突变等因素引起的该途径的异常激活可以启动下游靶基因c-myc和cyclin D1,致使细胞恶性转化,发生肿瘤,尤其是结肠癌。本文对Wnt-APC-β-catenin-TCF/LEF-c-myc/cyclin D1信号途径的最新研究进展作一综述。     

猪SFRP4基因的表达规律及sp600125对前体脂肪细胞分化的影响

分泌型卷曲相关蛋白（SFRP4, secreted frizzled-related protein 4）是Wnt信号通路可溶解的调控子.本研究通过高通量测序（Solexa）技术、实时定量PCR（RT-qPCR）对瘦肉型和脂肪型猪不同生长阶段脂肪组织中SFRP4表达规律进行研究;用western免疫印迹及RT-PCR技术对脂肪细胞分化过程中SFRP4蛋白表达和mRNA表达进行检测;用JNK信号通路特异性抑制剂sp600125处理猪原代前体脂肪细胞,研究抑制JNK信号通路对猪前体脂肪分化以及SFRP4 mRNA和蛋白表达的影响.结果显示,SFRP4 在脂肪型猪脂肪组织表达量显著高于瘦肉型猪(P<0.01);不同组织检测结果发现,SFRP4广泛表达于各个组织,并高表达于脂肪组织;前体脂肪细胞向成熟脂肪细胞分化过程中SFRP4表达量逐渐升高;sp600125促进了前体脂肪细胞分化,引起了 PPARγ、FABP4 、ATGL、Perilipin的显著升高(P<0.01),而SFRP4的表达被显著抑制.本研究为调控脂肪细胞分化关键基因的筛选提供新的理论参考.     

X染色体失活——一种特殊方式的基因调控

剂量补偿是使Ｘ连锁基因的表达水平在两性间达到平衡的过程。生物界实现剂量补偿的策略有很多种,真兽亚纲哺乳动物是随机失活雌性的一条Ｘ染色体。Ｘ失活开始于ＸＩＣ,然后传播到整条染色体。ＸＩＳＴ基因定位于ＸＩＣ中,参与Ｘ失活的启动,可能是Ｘ失活决定基因。最近在人和小鼠中发现了逃避Ｘ失活的基因。探讨这些基因逃避Ｘ失活的机制有助于理解Ｘ染色体失活是如何对基因表达进行调控的。人和小鼠中有一些基因的Ｘ失活状态不同,提示了性染色体的持续不断的进化改变 。     

Wnt信号转导途径及其与结肠癌的关联

Wnt信号转导途径参与细胞多种复杂的生化反应过程。目前认为Wnt通路的组成主要包括：细胞外因子(Wnt)、跨膜受体Frizzled(Frz)、β-连环蛋白(β-catenin)及T细胞趋化因子(Tcell factor,TCF)等一系列蛋白。细胞外因子Wnt激活的信号通过胞质蛋白的相互作用,能够使胞浆内β-连环蛋白保持稳定并累积,β-连环蛋白进而入核与T细胞趋化因子联合作用激活靶基因(多数是参与细胞增殖与凋亡的基因,如：Cyclin D1、c—myc等)的转录,而且在Wnt信号途径的不同阶段有各种蛋白因子进行调控;另外,Wnt胞内信号途径的异常激活与人类各种癌症的产生有联系,尤其是结肠癌变。大多数结肠癌患的转化细胞存在APC(adenomatous polyposis coli)基因缺失突变或失活,导致β-连环蛋白在核内的累积,并能影响相关基因转录,被认为是结肠癌发生的关键因素之一。由于该信号转导途径具有如此重要的作用,因此受到研究越来越多的重视。     

外源基因在转基因植物中的失活

进行植物基因工程研究首先需要获得外源基因稳定表达的转基因植株。近年来,有大量文献报道,转基因植株中外源基因的失活是一种普遍发生的现象。引起外源基因失活的原因是多方面的,外源基因失活在ＤＮＡ修饰水平,基因转录水平和转录后调节水平均可能发生。深入地了解外源基因失活的原因以及寻找出有效的防范对策,对顺利开展植物基因工程育种是非常必要的。     

抑癌基因D L C-1 的研究进展

DLC-1（frequently deletedin liver cancer）基因是新发现的一个肿瘤抑制基因。它的失活有可能参与肿瘤的发生和发展。本文拟就DLC-1基因的结构功能及其在遗传和表遗传方面的失活机制作一综述。     

GUS基因拷贝数对转基因在受体植物烟草中表达的影响

对农杆菌介导法获得的转 β_葡糖醛酸酶 (β_glucuronidase ,GUS)基因 (uidA)烟草 (NicotianatabacumL .)进行GUS表达分析 ,发现部分转基因植株无GUS活性。进一步Southern杂交结果发现 ,GUS基因失活植株的基因组中整合了多个uidA拷贝 ,而GUS活性高的转基因植株多为uidA单拷贝整合 ,表明uidA基因失活与基因多拷贝整合有关。Northern杂交结果显示 ,失活植株无特异uidARNA杂交带 ,而GUS活性高的植株可检测到明显的杂交信号 ,说明多拷贝引起的基因失活发生在RNA水平。     

Secreted frizzled related proteins: Implications in cancers

The Wnt (wingless-type) signaling pathway plays an important role in embryonic development, tissue homeostasis, and tumor progression becaluse of its effect on cell proliferation, migration, and differentiation. Secreted frizzled-related proteins (SFRPs) are extracellular inhibitors of Wnt signaling that act by binding directly to Wnt ligands or to Frizzled receptors. In recent years, aberrant expression of SFRPs has been reported to be associated with numerous cancers. As gene expression of SFRP members is often lost through promoter hypermethylation, inhibition of methylation through the use of epigenetic modifying agents could renew the expression of SFRP members and further antagonize deleterious Wnt signaling. Several reports have described epigenetic silencing of these Wnt signaling antagonists in various human cancers, suggesting their possible role as tumor suppressors. SFRP family members thus come across as potential tools in combating Wnt-driven tumorigenesis. However, little is known about SFRP family members and their role in different cancers. This review comprehensively covers all the available information on the role of SFRP molecules in various human cancers.     

Loss of sfrp1 promotes ductal branching in the murine mammary gland

ABSTRACT: BACKGROUND: Secreted frizzled-related proteins (SFRPs) are a family of proteins that block the Wnt signaling pathway and loss of SFRP1 expression is found in breast cancer along with a multitude of other human cancers. Activated Wnt signaling leads to inappropriate mammary gland development and mammary tumorigenesis in mice. When SFRP1 is knocked down in immortalized non-malignant mammary epithelial cells, the cells exhibit a malignant phenotype which resembles the characteristics observed in metastatic breast cancer stem-like cells. However, the effects of SFRP1 loss on mammary gland development in vivo are yet to be elucidated. The work described here was initiated to investigate the role of SFRP1 in mammary gland development and whether SFRP1/ mice exhibit changes in mammary gland morphology and cell signaling pathways shown to be associated with SFRP1 loss in vitro. RESULTS: 10 week old nulliparous SFRP1/ mammary glands exhibited branching with clear lobulo-alveolar development, which normally only occurs in hormonally stimulated mid-pregnant wt mammary glands. Explant cultures of SFRP1/ mammary glands display increased levels of a well known Wnt signaling target gene, Axin2. Histomorphologic evaluation of virgin glands revealed that by 10 weeks of age, the duct profile is markedly altered in SFRP1/ mice showing a significantly higher density of ducts with distinct alveoli present throughout the mammary gland, and with focal ductal epithelial hyperplasia. These findings persist as the mice age and are evident at 23 weeks of age. Changes in gene expression, including c-Myc, TGFbeta-2, Wnt4, RANKL, and Rspo2 early in mammary gland development are consistent with the excessive hyper branching phenotype. Finally, we found that loss of SFRP1 significantly increases the number of mammary epithelial cells capable of mammosphere formation. CONCLUSIONS: Our study indicates that SFRP1 gene is critical for maintaining proper mammary gland development, and that reduced levels of SFRP1 results in hyperplastic lesions and its loss may be a critical event in cancer initiation.     

Methylation and loss of Secreted Frizzled-Related Protein 3 enhances melanoma cell migration and invasion

Background

Wnt signaling is important in development and can also contribute to the initiation and progression of cancer. The Secreted Frizzled Related Proteins (SFRPs) constitute a family of Wnt modulators, crucial for controlling Wnt signaling. Here we investigate the expression and role of SFRP3 in melanoma.

Methodology/Principal Findings

We show that SFRP3 mRNA is down-regulated in malignant melanoma tumors as compared to normal/benign tissue. Furthermore, we found that SFRP3 expression was lost in the malignant melanoma cell lines, A2058, HTB63 and A375, but not in the non-transformed melanocyte cell line, Hermes 3A. Methylated CpG rich areas were detected in the SFRP3 gene in melanoma cell lines and their SFRP3 expression could be restored using the demethylating agent, 5′aza-deoxycytidine. Addition of recombinant SFRP3 to melanoma cells had no effect on viable cell numbers, but decreased cell migration and invasion. Wnt5a signaling has been shown to increase the migration and invasion of malignant melanoma cells, and high expression of Wnt5a in melanoma tumors has been connected to a poor prognosis. We found that recombinant SFRP3 could inhibit Wnt5a signaling, and that it inhibited melanoma cell migration and invasion in a Wnt5a-dependent manner.

Conclusion/Significance

We conclude that SFRP3 functions as a melanoma migration and invasion suppressor by interfering with Wnt5a signaling.     

Turning the Tables: Myc Activates Wnt in Breast Cancer

Previous molecular and genetic data implicate the c-myc gene as a critical downstream effector of the Wnt/TCF pathway in colon cancer. However, the involvement of c-myc in mammary epithelial cell transformation had not been explored. We recently showed that c-Myc induces a profound morphological transformation in human mammary epithelial cells accompanied by anchorage-independent growth. The mechanism of c-Myc transformation was revealed in part through the finding that, in contrast to colon cancer, c-Myc activates the Wnt pathway and endogenous TCF activity by suppressing the Wnt inhibitors DKK1 and SFRP1. Notably, DKK1 and SFRP1 were found to be strongly suppressed in human breast cancer cell lines and their re-expression inhibited the transformed phenotype. We demonstrated that breast cancer cells become dependent on repression of the Wnt inhibitors for cell proliferation, i.e. they have acquired an “oncogene addiction”, suggesting that the Myc-Wnt pathway is an attractive therapeutic target. We propose that a positive feedback loop of c-myc and Wnt signaling operates in breast cancer.     

Secreted frizzled-related protein 4 regulates two Wnt7a signaling pathways and inhibits proliferation in endometrial cancer cells

In the endometrium, hormonal effects on epithelial cells are often elicited through stromal hormone receptors via unknown paracrine mechanisms. Several lines of evidence support the hypothesis that Wnts participate in stromal-epithelial cell communication. Wnt7a is expressed in the luminal epithelium, whereas the extracellular modulator of Wnt signaling, secreted frizzled-related protein 4 (SFRP4), is localized to the stroma. Studies have reported that SFRP4 expression is significantly decreased in endometrial carcinoma and that both SFRP4 and Wnt7a genes are differentially regulated in response to estrogenic stimuli. Aberrant Wnt7a signaling irrevocably causes organ defects and infertility and contributes to the onset of disease. However, specific frizzled receptors (Fzd) that bind Wnt7a and the particular signal transduction pathway each Wnt7a-Fzd pair activates have not been identified. Additionally, the function of SFRP4 in the endometrium has not been addressed. We show here that Wnt7a coimmunoprecipitates with Fzd5, Fzd10, and SFRP4 in Ishikawa cells. Wnt7a binding to Fzd5 was shown to activate beta-catenin/canonical Wnt signaling and increase cellular proliferation. Conversely, Wnt7a signaling mediated by Fzd10 induced a noncanonical c-Jun NH2-terminal kinase-responsive pathway. SFRP4 suppresses activation of Wnt7a signaling in both an autocrine and paracrine manner. Stable overexpression of SFRP4 and treatment with recombinant SFRP4 protein inhibited endometrial cancer cell growth in vitro. These findings support a mechanism by which the nature of the Wnt7a signal in the endometrium is dependent on the Fzd repertoire of the cell and can be regulated by SFRP4.     

c-Myc transforms human mammary epithelial cells through repression of the Wnt inhibitors DKK1 and SFRP1

c-myc is frequently amplified in breast cancer; however, the mechanism of myc-induced mammary epithelial cell transformation has not been defined. We show that c-Myc induces a profound morphological transformation in human mammary epithelial cells and anchorage-independent growth. c-Myc suppresses the Wnt inhibitors DKK1 and SFRP1, and derepression of DKK1 or SFRP1 reduces Myc-dependent transforming activity. Myc-dependent repression of DKK1 and SFRP1 is accompanied by Wnt target gene activation and endogenous T-cell factor activity. Myc-induced mouse mammary tumors have repressed SFRP1 and increased expression of Wnt target genes. DKK1 and SFRP1 inhibit the transformed phenotype of breast cancer cell lines, and DKK1 inhibits tumor formation. We propose a positive feedback loop for activation of the c-myc and Wnt pathways in breast cancer.     

Methylation of secreted frizzled-related protein 1 (SFRP1) promoter downregulates Wnt/β-catenin activity in keloids

Keloid, a benign skin disorder, forms during wound healing in genetically susceptible individuals. To better control keloid and understand the molecular mechanisms, this study screened gene hypermethylations of GEO database microarray data on keloids and identified the hypermethylation of the secreted frizzled related protein-1 (SFRP1) promoter. Subsequently, hypermethylation and mRNA and protein levels were assessed in 57 cases of keloid vs. normal skin tissues. Fibroblasts from tissues were isolated for the assessment of gene regulation in vitro. The methods used were bioinformatic analysis, lentiviral infection carrying SFRP1 cDNA, qRT-PCR, western blot, immunohistochemistry, luciferase reporter assay, methylation-specific PCR and methylated DNA immunoprecipitation-qPCR, ELISA, and/or 5-Aza-2′-deoxycytidine treatment. The data revealed that the SFRP1 promoter was hypermethylated in keloid tissues, compared with that in normal skin tissues. The SFRP1 promoter methylation contributed to the downregulation of SFRP1 mRNA and protein in keloid tissues and keloid fibroblasts. The 5-Aza treatment significantly upregulated SFRP1 mRNA and protein level in keloid fibroblasts. Furthermore, the knockdown of DNMT1 expression, and not the expression of DNMT3a or DMNT3b, was responsible for the hypermethylation of the SFRP1 promoter and upregulation of SFRP1 mRNA and protein in keloid fibroblasts. In addition, the infection of lentivirus carrying SFRP1 cDNA significantly inhibited the signaling activity of Wnt/β-catenin and the mRNA and protein expression of β-catenin and α-SMA in keloid fibroblasts. In summary, the lost SFRP1 expression-induced Wnt/β-catenin signaling due to the hypermethylation of the SFRP1 promoter could associate with keloid development, suggesting that SFRP1 might be a therapeutic target for keloid treatment.     

Down-regulation of sfrp1 in a mammary epithelial cell line promotes the development of a cd44high/cd24low population which is invasive and resistant to anoikis

Background  

The Wnt family of secreted proteins is implicated in the regulation of cell fate during development, as well as in cell proliferation, morphology, and migration. Aberrant activation of the Wnt/β-catenin signaling pathway leads to the development of several human cancers, including breast cancer. Secreted frizzled-related protein 1 (SFRP1) antagonizes this pathway by competing with the Frizzled receptor for Wnt ligands resulting in an attenuation of the signal transduction cascade. Loss of SFRP1 expression is observed in breast cancer, along with several other cancers, and is associated with poor patient prognosis. However, it is not clear whether the loss of SFRP1 expression predisposes the mammary gland to tumorigenesis.     

Wnt Antagonist SFRP1 Functions as a Secreted Mediator of Senescence

Cellular senescence has emerged as a critical tumor suppressive mechanism in recent years, but relatively little is known about how senescence occurs. Here, we report that secreted Frizzled-related protein 1 (SFRP1), a secreted antagonist of Wnt signaling, is oversecreted upon cellular senescence caused by DNA damage or oxidative stress. SFRP1 is necessary for stress-induced senescence caused by these factors and is sufficient for the induction of senescence phenotypes. We present evidence suggesting that SFRP1 functions as a secreted mediator of senescence through inhibition of Wnt signaling and activation of the retinoblastoma (Rb) pathway and that cancer-associated SFRP1 mutants are defective for senescence induction.