Ifat Sher

Bnai Zion Medical Center, Haifa, H̱efa, Haifa District, Israel

Are you Ifat Sher?

Claim your profile

Publications (8)44.09 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: FGF10, a heparan sulfate (HS)-binding growth factor, is required for branching morphogenesis of mouse submandibular glands (SMGs). HS increases the affinity of FGF10 for FGFR2b, which forms an FGF10.FGFR2b.HS ternary signaling complex, and results in diverse biological outcomes, including proliferation and epithelial morphogenesis. Defining the HS structures involved in specific FGF10-mediated events is critical to understand how HS modulates growth factor signaling in specific developmental contexts. We used HS-deficient BaF3/FGFR2b cells, which require exogenous HS to proliferate, to investigate the HS requirements for FGF10-mediated proliferation and primary SMG epithelia to investigate the structural requirements of HS for FGF10-mediated epithelial morphogenesis. In BaF3/FGFR2b cells, heparin with at least 10 saccharides and 6-O-, 2-O-, and N-sulfates were required for maximal proliferation. During FGF10-mediated SMG epithelial morphogenesis, HS increased proliferation and end bud expansion. Defined heparin decasaccharide libraries showed that 2-O-sulfation with either an N-or 6-O-sulfate induced end bud expansion, whereas decasaccharides with 6-O-sulfation alone induced duct elongation. End bud expansion resulted from increased FGFR1b signaling, with increased FGFR1b, Fgf1, and Spry1 as well as increased Aqp5 expression, a marker of end bud differentiation. Duct elongation was associated with expression of Cp2L1, a marker of developing ducts. Collectively, these findings show that the size and sulfate patterns of HS modulate specific FGF10-mediated events, such as proliferation, duct elongation, end bud expansion, and differentiation, and provide mechanistic insight as to how the developmental localization of specific HS structures in tissues influences FGF10-mediated morphogenesis and differentiation.
    Journal of Biological Chemistry 05/2008; 283(14):9308-17. · 4.65 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Growth alterations within the gastric mucosa during chronic gastric inflammation are key steps in gastric cancer development. FGF7, a specific mitogen for epithelial cells, is implicated in epithelial tissue repair and cancer. We investigated FGF7 expression in normal human stomach, and in 35 cases from various gastric pathologies including 23 gastritis and 8 adenocarcinoma cases. Modest FGF7 protein levels were detected in the normal mucosal gland epithelium and in stromal fibroblasts. FGF7 protein levels, however, were markedly increased in the mucosal epithelium of all gastric inflammation cases. A similar elevated expression was also observed in gastric adenocarcinoma. Upregulation of FGF7 protein was associated with a modest increase in FGF7 mRNA expression. Interestingly, high levels of FGF7 anti-sense (AS) RNA were observed in the gastric pathologies, at the same sites where FGF7 protein was upregulated. Altogether, these findings suggest a role for FGF7 in maintaining gastric mucosa integrity, and that FGF7 protein levels are regulated mainly by posttranscriptional mechanisms. The elevated FGF7 protein levels in gastric inflammation and gastric cancer, together with the known oncogenic potential of FGF7, implicate excessive FGF7 signaling in gastric tumorigenesis, and point to FGF7 as an attractive target for gastric cancer prevention and treatment.
    Biochemical and Biophysical Research Communications 01/2007; 350(4):825-33. · 2.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Heparin-binding growth factors are crucial for the formation of human epidermis, but little is known about the role of heparan sulfate proteoglycans in this process. Here we investigated the role of the heparan sulfate proteoglycan, perlecan, in the formation of human epidermis, by utilizing in vitro engineered human skin. By disrupting perlecan expression either in the dermis or the epidermis, we found that epidermally derived perlecan is essential for epidermal formation. Perlecan-deficient keratinocytes formed a strikingly thin and poorly organized epidermis because of premature apoptosis and failure to complete their stratification program. Exogenous perlecan fully restored epidermal formation. Perlecan deposition in the basement membrane zone correlated with formation of multilayered epidermis. Perlecan deficiency, however, had no effect on the lining and deposition of major basement membrane components as was evident by a continuous linear staining of laminin and collagen IV. Similarly, perlecan deficiency did not affect the distribution of beta1 integrin. Addition of the perlecan ligand, fibroblast growth factor 7, protected perlecan-deficient keratinocytes from cell death and improved the thickness of the epidermis. Taken together, our results revealed novel roles for perlecan in epidermal formation. Perlecan regulates both the survival and terminal differentiation steps of keratinocytes. Our results suggested a model whereby perlecan regulates these processes via controlling the bioavailability of perlecan-binding soluble factors involved in epidermal morphogenesis.
    Journal of Biological Chemistry 03/2006; 281(8):5178-87. · 4.65 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Receptor tyrosine kinases (RTKs) control a multitude of biological processes and are therefore subjected to multiple levels of regulation. Negative feedback is one of the mechanisms that provide an effective means to control RTK-mediated signaling. Sef has recently been identified as a specific antagonist of fibroblast growth factor (FGF) signaling in zebrafish and subsequently in mouse and human. Sef encodes a putative type I transmembrane protein that antagonizes the Ras/mitogen-activated protein kinase pathway in all three species. Mouse Sef was also shown to inhibit the phosphatidylinositol 3-kinase pathway. We show here that an alternative splicing mechanism generates an isoform of human Sef, hSef-b, which unlike the previously reported Sef (hSef-a) is a cytosolic protein. Contrary to hSef-a, which is ubiquitously expressed, hSef-b transcripts display a restricted pattern of expression in human tissues. hSef-b inhibits FGF-induced cell proliferation and prevents the activation of mitogen-activated protein kinase without affecting the upstream component MAPK kinase. Furthermore, hSef-b does not antagonize FGF induction of the phosphatidylinositol 3-kinase pathway. In addition to the effects on FGF signaling, hSef-b inhibited cellular response to platelet-derived growth factor but not other RTK ligands. Therefore, alternative splicing of the hSef gene expands the Sef feedback inhibition repertoire of RTK signaling.
    Proceedings of the National Academy of Sciences 03/2004; 101(5):1229-34. · 9.81 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Receptor binding specificity is an essential element in regulating the diverse activities of fibroblast growth factors (FGFs). FGF7 is ideal to study how this specificity is conferred at the structural level, as it interacts exclusively with one isoform of the FGF-receptor (FGFR) family, known as FGFR2IIIb. Previous mutational analysis suggested the importance of the beta4/beta5 loop of FGF7 in specific receptor recognition. Here a theoretical model of FGFR2IIIb/FGF7 complex showed that this loop interacts with the FGFR2IIIb unique exon. In addition, the model revealed new residues that either directly interact with the FGFR2IIIb unique exon (Asp63, Leu142) or facilitate this interaction (Arg65). Mutations in these residues reduced both receptor binding affinity and biological activity of FGF7. Altogether, these results provide the basis for understanding how receptor-binding specificity of FGF7 is conferred at the structural level.
    FEBS Letters 10/2003; 552(2-3):150-4. · 3.58 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Binding specificity between fibroblast growth factors (FGFs) and their receptors (FGFRs) is essential for mammalian development and is regulated primarily by two alternatively spliced exons, IIIb ("b") and IIIc ("c"), that encode the second half of Ig-like domain 3 (D3) of FGFRs. FGF7 and FGF10 activate only the b isoform of FGFR2 (FGFR2b). Here, we report the crystal structure of the ligand-binding portion of FGFR2b bound to FGF10. Unique contacts between divergent regions in FGF10 and two b-specific loops in D3 reveal the structural basis by which alternative splicing provides FGF10-FGFR2b specificity. Structure-based mutagenesis of FGF10 confirms the importance of the observed contacts for FGF10 biological activity. Interestingly, FGF10 binding induces a previously unobserved rotation of receptor Ig domain 2 (D2) to introduce specific contacts with FGF10. Hence, both D2 and D3 of FGFR2b contribute to the exceptional specificity between FGF10 and FGFR2b. We propose that ligand-induced conformational change in FGFRs may also play an important role in determining specificity for other FGF-FGFR complexes.
    Proceedings of the National Academy of Sciences 04/2003; 100(5):2266-71. · 9.81 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Fibroblast growth factors (FGFs) mediate a multitude of physiological and pathological processes by activating a family of tyrosine kinase receptors (FGFRs). Each FGFR binds to a unique subset of FGFs and ligand binding specificity is essential in regulating FGF activity. FGF-7 recognizes one FGFR isoform known as the FGFR2 IIIb isoform or keratinocyte growth factor receptor (KGFR), whereas FGF-2 binds well to FGFR1, FGFR2, and FGFR4 but interacts poorly with KGFR. Previously, mutations in FGF-2 identified a set of residues that are important for high affinity receptor binding, known as the primary receptor-binding site. FGF-7 contains this primary site as well as a region that restricts interaction with FGFR1. The sequences that confer on FGF-7 its specific binding to KGFR have not been identified. By utilizing domain swapping and site-directed mutagenesis we have found that the loop connecting the beta4-beta5 strands of FGF-7 contributes to high affinity receptor binding and is critical for KGFR recognition. Replacement of this loop with the homologous loop from FGF-2 dramatically reduced both the affinity of FGF-7 for KGFR and its biological potency but did not result in the ability to bind FGFR1. Point mutations in residues comprising this loop of FGF-7 reduced both binding affinity and biological potency. The reciprocal loop replacement mutant (FGF2-L4/7) retained FGF-2 like affinity for FGFR1 and for KGFR. Our results show that topologically similar regions in these two FGFs have different roles in regulating receptor binding specificity and suggest that specificity may require the concerted action of distinct regions of an FGF.
    Journal of Biological Chemistry 12/2000; 275(45):34881-6. · 4.65 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The fibroblast growth factor (FGF) family plays a key role in a multitude of physiological and pathological processes. The activities of FGFs are mediated by a family of tyrosine kinase receptors, designated FGFRs. The mechanism by which FGFs induce receptor activation is controversial. Despite their structural similarity, FGFs display distinct receptor binding characteristics and cell type specificity. Previous studies with FGF-2 identified a low affinity receptor binding site that is located within a loop connecting its 9th and 10th beta-strands. The corresponding residues in the other family members are highly variable, and it was proposed that the variability might confer on FGFs unique receptor binding characteristics. We studied the role of this loop in FGF-7 by both site-directed mutagenesis and loop replacement. Unlike the other members of the FGF family, FGF-7 recognizes only one FGFR isoform and is, therefore, ideal for studies of how the specificity in the FGF-FGFR interaction is conferred at the structural level. Point mutations in the loop of FGF-7 did not change receptor binding affinity but resulted in reduced mitogenic potency and reduced ability to induce receptor-mediated phosphorylation events. These results suggest that the loop of FGF-7 fulfills the role of low affinity binding site required for receptor activation. The observation that it is possible to uncouple FGF-7 receptor binding and biological activity favors a bivalent model for FGFR dimerization, and it may be clinically relevant to the design of FGF-7 antagonists. Reciprocal loop replacement between FGF-7 and FGF-2 had no effect on their known receptor binding affinities nor did it alter their known specificity in eliciting a mitogenic response. In conclusion, these results suggest that, despite the diversity in the loop structure of FGF-2 and FGF-7, the loop has a similar function in both growth factors.
    Journal of Biological Chemistry 01/2000; 274(49):35016-22. · 4.65 Impact Factor