Antagonism between Retinoic Acid and Fibroblast Growth Factor Signaling during Limb Development

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Modulation of Fibroblast Growth Factor Signaling Is Essential for Mammary Epithelial Morphogenesis

Fibroblast growth factor (FGF) signaling is essential for vertebrate organogenesis, including mammary gland development. The mechanism whereby FGF signaling is regulated in the mammary gland, however, has remained unknown. Using a combination of mouse genetics and 3D ex vivo models, we tested the hypothesis that Spry2 gene, which encodes an inhibitor of signaling via receptor tyrosine kinases (RTKs) in certain contexts, regulates FGF signaling during mammary branching. We found that Spry2 is expressed at various stages of the developing mammary gland. Targeted removal of Spry2 function from mammary epithelium leads to accelerated epithelial invasion. Spry2 is up-regulated by FGF signaling activities and its loss sensitizes mammary epithelium to FGF stimulation, as indicated by increased expression of FGF target genes and epithelia invasion. By contrast, Spry2 gain-of-function in the mammary epithelium results in reduced FGF signaling, epithelial invasion, and stunted branching. Furthermore, reduction of Spry2 expression is correlated with tumor progression in the MMTV-PyMT mouse model. Together, the data show that FGF signaling modulation by Spry2 is essential for epithelial morphogenesis in the mammary gland and it functions to protect the epithelium against tumorigenesis.     

成纤维细胞生长因子与其受体相互作用及其抑制剂的研究进展

成纤维细胞生长因子（FGF）有许多重要的生理功能，并与肿瘤的形成有关.为了弄清FGF与成纤维细胞生长因子受体(FGFR)相互作用的机制，人们对FGF和FGFR的各个结合结构域进行了深入、细致的研究，定位了aFGF、bFGF的肝素结合区、bFGF的受体结合区、FGF受体的肝素结合区、配体结合区和FGF受体相互结合区，提出了两个FGF与FGFR相互作用的模型，在此基础上设计了FGF的核酸类、糖类和多肽类抑制剂，为寻找新一代抗癌药物打下了理论基础.     

Mannose Phosphate Isomerase Regulates Fibroblast Growth Factor Receptor Family Signaling and Glioma Radiosensitivity

Asparagine-linked glycosylation is an endoplasmic reticulum co- and post- translational modification that enables the transit and function of receptor tyrosine kinase (RTK) glycoproteins. To gain insight into the regulatory role of glycosylation enzymes on RTK function, we investigated shRNA and siRNA knockdown of mannose phosphate isomerase (MPI), an enzyme required for mature glycan precursor biosynthesis. Loss of MPI activity reduced phosphorylation of FGFR family receptors in U-251 and SKMG-3 malignant glioma cell lines and also resulted in significant decreases in FRS2, Akt, and MAPK signaling. However, MPI knockdown did not affect ligand-induced activation or signaling of EGFR or MET RTKs, suggesting that FGFRs are more susceptible to MPI inhibition. The reductions in FGFR signaling were not caused by loss of FGF ligands or receptors, but instead were caused by interference with receptor dimerization. Investigations into the cellular consequences of MPI knockdown showed that cellular programs driven by FGFR signaling, and integral to the clinical progression of malignant glioma, were impaired. In addition to a blockade of cellular migration, MPI knockdown also significantly reduced glioma cell clonogenic survival following ionizing radiation. Therefore our results suggest that targeted inhibition of enzymes required for cell surface receptor glycosylation can be manipulated to produce discrete and limited consequences for critical client glycoproteins expressed by tumor cells. Furthermore, this work identifies MPI as a potential enzymatic target for disrupting cell surface receptor-dependent survival signaling and as a novel approach for therapeutic radiosensitization.     

A Mass Action Model of a Fibroblast Growth Factor Signaling Pathway and Its Simplification

We consider a kinetic law of mass action model for Fibroblast Growth Factor (FGF) signaling, focusing on the induction of the RAS-MAP kinase pathway via GRB2 binding. Our biologically simple model suffers a combinatorial explosion in the number of differential equations required to simulate the system. In addition to numerically solving the full model, we show that it can be accurately simplified. This requires combining matched asymptotics, the quasi-steady state hypothesis, and the fact subsets of the equations decouple asymptotically. Both the full and simplified models reproduce the qualitative dynamics observed experimentally and in previous stochastic models. The simplified model also elucidates both the qualitative features of GRB2 binding and the complex relationship between SHP2 levels, the rate SHP2 induces dephosphorylation and levels of bound GRB2. In addition to providing insight into the important and redundant features of FGF signaling, such work further highlights the usefulness of numerous simplification techniques in the study of mass action models of signal transduction, as also illustrated recently by Borisov and co-workers (Borisov et al. in Biophys. J. 89, 951–966, 2005, Biosystems 83, 152–166, 2006; Kiyatkin et al. in J. Biol. Chem. 281, 19925–19938, 2006). These developments will facilitate the construction of tractable models of FGF signaling, incorporating further biological realism, such as spatial effects or realistic binding stoichiometries, despite a more severe combinatorial explosion associated with the latter.     

Loss of Dlg-1 in the Mouse Lens Impairs Fibroblast Growth Factor Receptor Signaling

Coordination of cell proliferation, differentiation and survival is essential for normal development and maintenance of tissues in the adult organism. Growth factor receptor tyrosine kinase signaling pathways and planar cell polarity pathways are two regulators of many developmental processes. We have previously shown through analysis of mice conditionally null in the lens for the planar cell polarity gene (PCP), Dlg-1, that Dlg-1 is required for fiber differentiation. Herein, we asked if Dlg-1 is a regulator of the Fibroblast growth factor receptor (Fgfr) signaling pathway, which is known to be required for fiber cell differentiation. Western blot analysis of whole fiber cell extracts from control and Dlg-1 deficient lenses showed that levels of the Fgfr signaling intermediates pErk, pAkt, and pFrs2α, the Fgfr target, Erm, and the fiber cell specific protein, Mip26, were reduced in the Dlg-1 deficient fiber cells. The levels of Fgfr2 were decreased in Dlg-1 deficient lenses compared to controls. Conversely, levels of Fgfr1 in Dlg-1 deficient lenses were increased compared to controls. The changes in Fgfr levels were found to be specifically in the triton insoluble, cytoskeletal associated fraction of Dlg-1 deficient lenses. Immunofluorescent staining of lenses from E13.5 embryos showed that expression levels of pErk were reduced in the transition zone, a region of the lens that exhibits PCP, in the Dlg-1 deficient lenses as compared to controls. In control lenses, immunofluorescent staining for Fgfr2 was observed in the epithelium, transition zone and fibers. By E13.5, the intensity of staining for Fgfr2 was reduced in these regions of the Dlg-1 deficient lenses. Thus, loss of Dlg-1 in the lens impairs Fgfr signaling and leads to altered levels of Fgfrs, suggesting that Dlg-1 is a modulator of Fgfr signaling pathway at the level of the receptors and that Dlg-1 regulates fiber cell differentiation through its role in PCP.     

Fibroblast Growth Factor Signaling Is Essential for Self-renewal of Dental Epithelial Stem Cells

A constant supply of epithelial cells from dental epithelial stem cell (DESC) niches in the cervical loop (CL) enables mouse incisors to grow continuously throughout life. Elucidation of the cellular and molecular mechanisms underlying this unlimited growth potential is of broad interest for tooth regenerative therapies. Fibroblast growth factor (FGF) signaling is essential for the development of mouse incisors and for maintenance of the CL during prenatal development. However, how FGF signaling in DESCs controls the self-renewal and differentiation of the cells is not well understood. Herein, we report that FGF signaling is essential for self-renewal and the prevention of cell differentiation of DESCs in the CL as well as in DESC spheres. Inhibiting the FGF signaling pathway decreased proliferation and increased apoptosis of the cells in DESC spheres. Suppressing FGFR or its downstream signal transduction pathways diminished Lgr5-expressing cells in the CL and promoted cell differentiation both in DESC spheres and the CL. Furthermore, disruption of the FGF pathway abrogated Wnt signaling to promote Lgr5 expression in DESCs both in vitro and in vivo. This study sheds new light on understanding the mechanism by which the homeostasis, expansion, and differentiation of DESCs are regulated.     

Fibroblast Growth Factor 10-Fibroblast Growth Factor Receptor 2b Mediated Signaling Is Not Required for Adult Glandular Stomach Homeostasis

The signaling pathways that are essential for gastric organogenesis have been studied in some detail; however, those that regulate the maintenance of the gastric epithelium during adult homeostasis remain unclear. In this study, we investigated the role of Fibroblast growth factor 10 (FGF10) and its main receptor, Fibroblast growth factor receptor 2b (FGFR2b), in adult glandular stomach homeostasis. We first showed that mouse adult glandular stomach expressed Fgf10, its receptors, Fgfr1b and Fgfr2b, and most of the other FGFR2b ligands (Fgf1, Fgf7, Fgf22) except for Fgf3 and Fgf20. Fgf10 expression was mesenchymal whereas FGFR1 and FGFR2 expression were mostly epithelial. Studying double transgenic mice that allow inducible overexpression of Fgf10 in adult mice, we showed that Fgf10 overexpression in normal adult glandular stomach increased epithelial proliferation, drove mucous neck cell differentiation, and reduced parietal and chief cell differentiation. Although a similar phenotype can be associated with the development of metaplasia, we found that Fgf10 overexpression for a short duration does not cause metaplasia. Finally, investigating double transgenic mice that allow the expression of a soluble form of Fgfr2b, FGF10''s main receptor, which acts as a dominant negative, we found no significant changes in gastric epithelial proliferation or differentiation in the mutants. Our work provides evidence, for the first time, that the FGF10-FGFR2b signaling pathway is not required for epithelial proliferation and differentiation during adult glandular stomach homeostasis.     

Fibroblast Growth Factor Receptor 2c Signaling Is Required for Intestinal Cell Differentiation in Zebrafish

Background

There are four cell lineages derived from intestinal stem cells that are located at the crypt and villus in the mammalian intestine the non-secretory absorptive enterocytes, and the secretory cells, which include mucous-secreting goblet cells, regulatory peptide-secreting enteroendocrine cells and antimicrobial peptide-secreting Paneth cells. Although fibroblast growth factor (Fgf) signaling is important for cell proliferation and differentiation in various tissues, its role in intestinal differentiation is less well understood.

Methodology/Principal Findings

We used a loss of function approach to investigate the importance of Fgf signaling in intestinal cell differentiation in zebrafish; abnormal differentiation of goblet cells was observed when Fgf signaling was inhibited using SU5402 or in the Tg(hsp70ldnfgfr1-EGFP) transgenic line. We identified Fgfr2c as an important receptor for cell differentiation. The number of goblet cells and enteroendocrine cells was reduced in fgfr2c morphants. In addition to secretory cells, enterocyte differentiation was also disrupted in fgfr2c morphants. Furthermore, proliferating cells were increased in the morphants. Interestingly, the loss of fgfr2c expression repressed secretory cell differentiation and increased cell proliferation in the mib^ta52b mutant that had defective Notch signaling.

Conclusions/Significance

In conclusion, we found that Fgfr2c signaling derived from mesenchymal cells is important for regulating the differentiation of zebrafish intestine epithelial cells by promoting cell cycle exit. The results of Fgfr2c knockdown in mib^ta52b mutants indicated that Fgfr2c signaling is required for intestinal cell differentiation. These findings provide new evidences that Fgf signaling is required for the differentiation of intestinal cells in the zebrafish developing gut.     

Fibroblast Growth Factor Receptor 1 Signaling in Adult Cardiomyocytes Increases Contractility and Results in a Hypertrophic Cardiomyopathy

Fibroblast growth factors (FGFs) and their receptors are highly conserved signaling molecules that have been implicated in postnatal cardiac remodeling. However, it is not known whether cardiomyocyte-expressed FGF receptors are necessary or sufficient for ventricular remodeling in the adult heart. To determine whether cardiomyocytes were competent to respond to an activated FGF receptor, and to determine if this signal would result in the development of hypertrophy, we engineered a doxycycline (DOX)-inducible, cardiomyocyte-specific, constitutively active FGF receptor mouse model (αMHC-rtTA, TRE-caFgfr1-myc). Echocardiographic and hemodynamic analysis indicated that acute expression of caFGFR1 rapidly and directly increased cardiac contractility, while chronic expression resulted in significant hypertrophy with preservation of systolic function. Subsequent histologic analysis showed increased cardiomyocyte cross-sectional area and regions of myocyte disarray and fibrosis, classic features of hypertrophic cardiomyopathy (HCM). Analysis of downstream pathways revealed a lack of clear activation of classical FGF-mediated signaling pathways, but did demonstrate a reduction in Serca2 expression and troponin I phosphorylation. Isolated ventricular myocytes showed enhanced contractility and reduced relaxation, an effect that was partially reversed by inhibition of actin-myosin interactions. We conclude that adult cardiomyocytes are competent to transduce FGF signaling and that FGF signaling is sufficient to promote increased cardiomyocyte contractility in vitro and in vivo through enhanced intrinsic actin-myosin interactions. Long-term, FGFR overexpression results in HCM with a dynamic outflow tract obstruction, and may serve as a unique model of HCM.     

成纤维细胞生长因子与骨相关疾病的研究进展

骨相关疾病是目前临床常见慢性疾病之一,特别对中老年人的健康带来严重损害。研究发现,成纤维细胞生长因子（FGFs）家族成员对骨相关疾病有治疗作用,主要为骨质疏松和骨关节炎及这两种疾病引起的其他综合症,但其作用机制尚不清楚。针对不同FGFs对不同骨相关疾病的相关作用进行总结,并对其潜在治疗作用进行了综述。     

碱性成纤维细胞生长因子在苜蓿中的表达

为了降低bFGF(basic fibroblast growth factor)的生产成本,结合植物生物反应器的优点,就bFGF在转基因苜蓿中的表达进行了探索.将bFGF插入植物表达载体pBⅡ21中,获得了含有bFGF基因的植物表达pBIcbFGF,再将pBIcbFGF利用冻融法转到农杆菌中.利用农杆菌介导法将基因转化保定苜蓿,转基因苜蓿在TM-1培养基+20 mg/L卡那霉素(Kan)+200 mg/L特美汀(Tim)中诱导分化,在生根培养基中生根,获得再生植株.再生植株通过PCR检测、RT-PCR及Western blot证实外源基因已经在苜蓿中成功表达.获得含有目的蛋白的阳性植株.为苜蓿作为植物生物反应器生产bFGF奠定了理论及技术基础.     

牛脑成纤维细胞生长因子的分离纯化与鉴定

新鲜牛脑组织匀浆液经两步硫酸铵沉淀、CM-Sephadex C50 离子交换层析以及肝素-Sepharose 亲和层析,可得到纯化的酸性和碱性成纤维细胞生长因子(aFGF 和bFGF),分子量分别为13.2kD 和15.2—15.8kD.两种因子均可有效促进3T3细胞的 DNA 合成,ED₅₀分别为15.8ng/ml 和 0.32ng/ml.进一步对 aFGF 的等电点及氨基酸组成做了分析.     

成纤维细胞生长因子8(FGF8)研究进展

成纤维细胞生长因子8(fibroblast growth factor 8,FGF8)是成纤维细胞生长因子(FGFs)家族的成员之一。其在人胚胎时期多种组织内进行表达,对各种器官的形成中起着重要的作用。在正常成人体内,FGF8的表达水平受到严格的限制,然而在某些癌细胞或炎症部位中大量表达,特别是在激素类癌症的发生和发展中起着重要的作用。因此应用FGF8抗体治疗激素类癌症,为临床提供了新的治疗途径。     

成纤维细胞生长因子6(FGF6)的研究进展

成纤维细胞生长因子6(fibroblast growth factor 6,FGF6)是成纤维细胞生长因子家族(FGFs)的成员之一,主要通过与酪氨酸激酶受体(fibroblast growth factor receptor,FGFR)1和4结合发挥其生物学活性。研究发现,人FGF6几乎都积聚在肌源性细胞系中,参与肌源性细胞系的增殖及分化,在肌肉修复和再生过程中起重要作用,同时它还是一个重要的调节骨生成和骨重建的因子;FGF6在心脏中也有表达,进一步试验结果表明其具有促进心肌细胞增殖及保护心肌细胞凋亡的作用;在成体睾丸和乳腺癌中也检测到有FGF6的转录物,表明其在肿瘤发生发展中的作用。目前,FGF6在多种疾病中的功能和相关机制仍有待进一步研究和确认,但其所具备的生物学活性尤其是在肌肉再生方面具有重要的意义和巨大的应用潜力。     

成纤维细胞生长因子5的研究进展 *

成纤维细胞生长因子5(fibroblast growth factor 5,FGF5)是成纤维细胞生长因子家族(FGFs)的成员之一,在哺乳动物毛囊,神经系统,睾丸等多个部位及胚胎发育过程中均有表达.研究发现,FGF5具有广泛的生物学活性,如作为毛发生长重要的调节因子其编码基因突变将导致毛发异常生长,作为丝裂原在干细胞增殖,血管生成和肢体肌发育等方面发挥重要作用,以及在高血压,肿瘤等方面具有重要的生物学功能.目前,FGF5在多种疾病中的功能和作用机制尚需进一步深入研究,但其在毛发生长,干细胞增殖及在心血管疾病等方面的生物学作用具有重大的意义和临床应用价值.总结了近些年FGF5的研究进展,系统阐述了FGF5在毛发生长,干细胞增殖分化,心血管疾病及癌症等方面的相关作用机制,为进一步深入研究FGF5在疾病治疗中的作用和开发利用提供参考.     

成纤维细胞生长因子17研究进展

成纤维细胞生长因子17(FGF17)是成纤维细胞生长因子(FGF)家族的成员之一,并与FGF8、FGF18组成FGF8亚家族。在胚胎时期FGF17扮演重要角色,对多种组织器官起着重要作用。研究发现,FGF17不仅参与了脑部发育和神经形成,而且参与骨骼、动脉的发育和肿瘤等生物过程。现针对FGF17的特点,及其在胚胎发育、神经系统、癌症等方面的作用进行综述。