Forschung
The tyrosine phosphatase Shp2 (PTPN11) directs Neuregulin-1/ErbB signaling throughout Schwann cell development.
Grossmann KS, Wende H, Paul FE, Cheret C, Garratt AN, Zurborg S, Feinberg K, Besser D, Schulz H, Peles E, Selbach M, Birchmeier W, Birchmeier C.
Proc Natl Acad Sci U S A. 2009 Sep 29;106(39):16704-9. Epub 2009 Sep 11.
The nonreceptor tyrosine phosphatase Shp2 (PTPN11) has been implicated in tyrosine kinase, cytokine, and integrin receptor signaling. We show here that conditional mutation of Shp2 in neural crest cells and in myelinating Schwann cells resulted in deficits in glial development that are remarkably similar to those observed in mice mutant for Neuregulin-1 (Nrg1) or the Nrg1 receptors, ErbB2 and ErbB3. In cultured Shp2 mutant Schwann cells, Nrg1-evoked cellular responses like proliferation and migration were virtually abolished, and Nrg1-dependent intracellular signaling was altered. Pharmacological inhibition of Src family kinases mimicked all cellular and biochemical effects of the Shp2 mutation, implicating Src as a primary Shp2 target during Nrg1 signaling. Together, our genetic and biochemical analyses demonstrate that Shp2 is an essential component in the transduction of Nrg1/ErbB signals.
A Colorectal Cancer Expression Profile that Includes Transforming Growth Factor ß Inhibitor BAMBI Predicts Metastatic Potential.
Fritzmann J, Morkel M, Besser D, Budczies J, Kosel F, Brembeck FH, Stein U, Fichtner I, Schlag PM, Birchmeier W.
Gastroenterology. 2009 Jul;137(1):165-75. Epub 2009 Mar 26.
Background & Aims: Much is known about the genes and mutations that cause colorectal cancer (CRC), yet only a few have been associated with CRC metastasis. We performed expression profiling experiments to identify genetic markers of risk and to elucidate the molecular mechanisms of CRC metastasis. Methods: We compared gene expression patterns between metastatic and non-metastatic, stage-matched human colorectal carcinomas by microarray analysis. Correlations between BAMBI and metastasis-free survival were examined by quantitative real-time PCR using an independent set of human colon carcinomas. Human colon cancer cell lines were analyzed for BAMBI regulation, cell motility and experimental metastasis. Results: We established a signature of 115 genes that differentiated metastatic from non-metastatic primary tumors. Among these, the transforming growth factor (TGF) ßinhibitor BAMBI was highly expressed in about half of metastatic primary tumors and metastases but not in non-metastatic tumors. BAMBI is a target of canonical Wnt signaling that involves the ß-catenin co-activator BCL9-2. We observed an inverse correlation between level of BAMBI expression and metastasis-free survival time of patients. BAMBI inhibits TGFß signaling and increases migration in colon cancer cells. In mice, overexpression of BAMBI caused colon cancer cells to form tumors that metastasized more frequently to liver and lymph nodes than control cancer cells. Conclusion: BAMBI regulates colorectal cancer metastasis by connecting the Wnt/ß -catenin and TGFß signaling pathways. The metastatic expression signature we describe, along with BAMBI levels, can be used in prognosis. Developmental signaling pathways appear to act in hierarchies and cooperate in tumor cell migration, invasion and metastasis.
Specific inhibitors of the protein tyrosine phosphatase Shp2 identified by high-throughput docking.
Hellmuth K, Grosskopf S, Lum CT, Würtele M, Röder N, von Kries JP, Rosario M, Rademann J, Birchmeier W.
Proc Natl Acad Sci U S A. 2008 May 20;105(20):7275-80. Epub 2008 May 14.
The protein tyrosine phosphatase Shp2 is a positive regulator of growth factor signaling. Gain-of-function mutations in several types of leukemia define Shp2 as a bona fide oncogene. We performed a high-throughput in silico screen for small-molecular-weight compounds that bind the catalytic site of Shp2. We have identified the phenylhydrazonopyrazolone sulfonate PHPS1 as a potent and cell-permeable inhibitor, which is specific for Shp2 over the closely related tyrosine phosphatases Shp1 and PTP1B. PHPS1 inhibits Shp2-dependent cellular events such as hepatocyte growth factor/scatter factor (HGF/SF)-induced epithelial cell scattering and branching morphogenesis. PHPS1 also blocks Shp2-dependent downstream signaling, namely HGF/SF-induced sustained phosphorylation of the Erk1/2 MAP kinases and dephosphorylation of paxillin. Furthermore, PHPS1 efficiently inhibits activation of Erk1/2 by the leukemia-associated Shp2 mutant, Shp2-E76K, and blocks the anchorage-independent growth of a variety of human tumor cell lines. The PHPS compound class is therefore suitable for further development of therapeutics for the treatment of Shp2-dependent diseases.
Distinct roles of Wnt/beta-catenin and Bmp signaling during early cardiogenesis.
Klaus A, Saga Y, Taketo MM, Tzahor E, Birchmeier W.
Proc Natl Acad Sci U S A. 2007 Nov 20;104(47):18531-6.
Heart formation requires the coordinated recruitment of multiple cardiac progenitor cell populations derived from both the first and second heart fields. In this study, we have ablated the Bmp receptor 1a and the Wnt effector beta-catenin in the developing heart of mice by using MesP1-cre, which acts in early mesoderm progenitors that contribute to both first and second heart fields. Remarkably, the entire cardiac crescent and later the primitive ventricle were absent in MesP1-cre; BmpR1a(lox/lox) mutants. Although myocardial progenitor markers such as Nkx2-5 and Isl1 and the differentiation marker MLC2a were detected in the small, remaining cardiac field in these mutants, the first heart field markers, eHand and Tbx-5, were not expressed. We conclude from these results that Bmp receptor signaling is crucial for the specification of the first heart field. In MesP1-cre; beta-catenin(lox/lox) mutants, cardiac crescent formation, as well as first heart field markers, were not affected, although cardiac looping and right ventricle formation were blocked. Expression of Isl1 and Bmp4 in second heart field progenitors was strongly reduced. In contrast, in a gain-of-function mutation of beta-catenin using MesP1-cre, we revealed an expansion of Isl1 and Bmp4 expressing cells, although the heart tube was not formed. We conclude from these results that Wnt/beta-catenin signaling regulates second heart-field development, and that a precise amount and/or timing of Wnt/beta-catenin signaling is required for proper heart tube formation and cardiac looping.
Distinct requirements for Gab1 in Met and EGF receptor signaling in vivo.
Schaeper U, Vogel R, Chmielowiec J, Huelsken J, Rosário M, Birchmeier W.
Proc Natl Acad Sci U S A. 2007 Sep 25;104(39):15376-81.
Gab1 is a multiadaptor protein that has been shown to be required for multiple processes in embryonic development and oncogenic transformation. Gab1 functions by amplifying signal transduction downstream of various receptor tyrosine kinases through recruitment of multiple signaling effectors, including phosphatidylinositol 3-kinase and Shp2. Until now, the functional significance of individual interactions in vivo was not known. Here we have generated knockin mice that carry point mutations in either the P13K or Shp2 binding sites of Gab1. We show that different effector interactions with Gab1 play distinct biological roles downstream of Gab1 during the development of different organs. Recruitment of phosphatidylinositol 3-kinase by Gab1 is essential for EGF receptor-mediated embryonic eyelid closure and keratinocyte migration, and the Gab1–Shp2 interaction is crucial for Met receptor-directed placental development and muscle progenitor cell migration to the limbs. Furthermore, we investigate the dual association of Gab1 with the Met receptor. By analyzing knockin mice with mutations in the Grb2 or Met binding site of Gab1, we show that the requirements for Gab1 recruitment to Met varies in different biological contexts. Either the direct or the indirect interaction of Gab1 with Met is sufficient for Met-dependent muscle precursor cell migration, whereas both modes of interaction are required and neither is sufficient for placenta development, liver growth, and palatal shelf closure. These data demonstrate that Gab1 induces different biological responses through the recruitment of distinct effectors and that different modes of recruitment for Gab1 are required in different organs.
The neurite outgrowth multiadaptor RhoGAP, NOMA-GAP, regulates neurite extension through SHP2 and Cdc42.
Rosário M, Franke R, Bednarski C, Birchmeier W.
J Cell Biol 178(3): 503-516. (2007-07-30)
Neuronal differentiation involves the formation and extension of neuronal processes. We have identified a novel regulator of neurite formation and extension, the neurite outgrowth multiadaptor, NOMA-GAP, which belongs to a new family of multiadaptor proteins with RhoGAP activity. We show that NOMA-GAP is essential for NGF-stimulated neuronal differentiation and for the regulation of the ERK5 MAP kinase and the Cdc42 signaling pathways downstream of NGF. NOMA-GAP binds directly to the NGF receptor, TrkA, and becomes tyrosine phosphorylated upon receptor activation, thus enabling recruitment and activation of the tyrosine phosphatase SHP2. Recruitment of SHP2 is required for the stimulation of neuronal process extension and for sustained activation of ERK5 downstream of NOMA-GAP. In addition, we show that NOMA-GAP promotes neurite outgrowth by tempering activation of the Cdc42/PAK signaling pathway in response to NGF. NOMA-GAP, through its dual function as a multiadaptor and RhoGAP protein, thus plays an essential role downstream of NGF in promoting neurite outgrowth and extension.
c-Met is essential for wound healing in the skin.
Chmielowiec J, Borowiak M, Morkel M, Stradal T, Munz B, Werner S, Wehland J, Birchmeier C, Birchmeier W.
J Cell Biol. 177: 151-162 (2007-04-09)
Wound healing of the skin is a crucial regenerative process in adult mammals. We examined wound healing in conditional mutant mice, in which the c-Met gene that encodes the receptor of hepatocyte growth factor/scatter factor was mutated in the epidermis by cre recombinase. c-Met-deficient keratinocytes were unable to contribute to the reepithelialization of skin wounds. In conditional c-Met mutant mice, wound closure was slightly attenuated, but occurred exclusively by a few (5%) keratinocytes that had escaped recombination. This demonstrates that the wound process selected and amplified residual cells that express a functional c-Met receptor. We also cultured primary keratinocytes from the skin of conditional c-Met mutant mice and examined them in scratch wound assays. Again, closure of scratch wounds occurred by the few remaining c-Met-positive cells. Our data show that c-Met signaling not only controls cell growth and migration during embryogenesis but is also essential for the generation of the hyperproliferative epithelium in skin wounds, and thus for a fundamental regenerative process in the adult.
Bmp and Wnt/beta-catenin signals control expression of the transcription factor Olig3 and the specification of spinal cord neurons.
Zechner D, Muller T, Wende H, Walther I, Taketo MM, Crenshaw EB 3rd, Treier M, Birchmeier W, Birchmeier C.
Dev Biol. 2007 Mar 1;303(1):181-90.
In the developing spinal cord, signals of the roof plate pattern the dorsal progenitor domain and control the specification of three neuron types, dorsal interneurons dI1, dI2, and dI3. Bmp and Wnt/beta-catenin signals as well as transcription factors like Olig3 or Ngn1/2 are essential in this process. We have studied the epistatic relationship between Bmp and Wnt/beta-catenin signals and the transcription factor Olig3 in dorsal spinal cord patterning. Using beta-catenin gain-of-function and compound beta-catenin gain-of-function/Olig3 loss-of-function mutations in mice, we could show that Wnt/beta-catenin signals act upstream of Olig3 in the specification of dI2 and dI3 neurons. The analysis of such compound mutant mice allowed us to distinguish between the two functions of Wnt/beta-catenin signaling in proliferation and patterning of dorsal progenitors. Using electroporation of chick spinal cords, we further demonstrate that Bmp signals act upstream of Wnt/beta-catenin in the regulation of Olig3 and that Wnt/beta-catenin signals play an instructive role in controlling Olig3 expression. We conclude that Wnt/beta-catenin and BMP signals coordinately control the specification of dorsal neurons in the spinal cord.
Diversin regulates heart formation and gastrulation movements in development.
Moeller H, Jenny A, Schaeffer HJ, Schwarz-Romond T, Mlodzik , Hammerschmidt M, Birchmeier W.
Proc Natl Acad Sci U S A. 2006 Oct 24;103(43):15900-5.
Canonical and non-canonical Wnt signaling regulate crucial events in the development of vertebrates and invertebrates. In this work we show that vertebrate Diversin, a potential orthologue of Drosophila Diego, controls fusion of heart precursors and gastrulation movements in zebrafish embryogenesis. These events are regulated by non-canonical Wnt signaling, which is independent of ß-catenin. We found that Diversin directly interacts with Dishevelled, and that this interaction is necessary and sufficient to mediate signals of the non-canonical Wnt pathway to downstream effectors like Rho family GTPases and Jun N-terminal kinase. The ankyrin repeats of Diversin are required for the interaction with Dishevelled, for the activation of non-canonical Wnt signaling and for the biological responses. The mutation K446M in the DEP domain of vertebrate Dishevelled, which mimics a classical Drosophila loss of function mutation, prevents functional interaction with Diversin's ankyrin repeats. Diversin also affects planar cell polarity in Drosophila, which is controlled by the non-canonical Wnt signaling pathway. Our data thus demonstrate that Diversin and Dishevelled function together in a mutually dependent fashion in zebrafish gastrulation and organ formation.
The neuronal scaffold protein Shank3 mediates signaling and biological function of the receptor tyrosine kinase Ret in epithelial cells.
Schuetz G, Rosário M, Grimm J, Boeckers TM, Gundelfinger ED, Birchmeier W.
J Cell Biol 167: 945-952. (2004-12-06)
Shank proteins, initially also described as ProSAP proteins, are scaffolding adaptors that have been previously shown to integrate neurotransmitter receptors into the cortical cytoskeleton at postsynaptic densities. We show here that Shank proteins are also crucial in receptor tyrosine kinase signaling. The PDZ domain–containing Shank3 protein was found to represent a novel interaction partner of the receptor tyrosine kinase Ret, which binds specifically to a PDZ-binding motif present in the Ret9 but not in the Ret51 isoform. Furthermore, we show that Ret9 but not Ret51 induces epithelial cells to form branched tubular structures in three-dimensional cultures in a Shank3-dependent manner. Ret9 but not Ret51 has been previously shown to be required for kidney development. Shank3 protein mediates sustained Erk–MAPK and PI3K signaling, which is crucial for tubule formation, through recruitment of the adaptor protein Grb2. These results demonstrate that the Shank3 adaptor protein can mediate cellular signaling, and provide a molecular mechanism for the biological divergence between the Ret9 and Ret51 isoform.
Requirement of plakophilin 2 for heart morphogenesis and cardiac junction formation.
Grossmann KS, Grund C, Huelsken J, Behrend M, Erdmann B, Franke WW, Birchmeier W.
J Cell Biol 167: 149-160. (2004-10-11)
Plakophilins are proteins of the armadillo family that function in embryonic development and in the adult, and when mutated can cause disease. We have ablated the plakophilin 2 gene in mice. The resulting mutant mice exhibit lethal alterations in heart morphogenesis and stability at mid-gestation (E10.5-E11), characterized by reduced trabeculation, disarrayed cytoskeleton, ruptures of cardiac walls, and blood leakage into the pericardiac cavity. In the absence of plakophilin 2, the cytoskeletal linker protein desmoplakin dissociates from the plaques of the adhering junctions that connect the cardiomyocytes and forms granular aggregates in the cytoplasm. By contrast, embryonic epithelia show normal junctions. Thus, we conclude that plakophilin 2 is important for the assembly of junctional proteins and represents an essential morphogenic factor and architectural component of the heart.
Essential role of BCL9-2 in the switch between beta-catenin's adhesive and transcriptional functions.
Brembeck FH, Schwarz-Romond T, Bakkers J, Wilhelm S, Hammerschmidt M, Birchmeier W.
Genes Dev 18: 2225-2230. (2004-09-15)
beta-Catenin controls both cadherin-mediated cell adhesion and activation of Wnt target genes. We demonstrate here that the beta-catenin-binding protein BCL9-2, a homolog of the human proto-oncogene product BCL9, induces epithelial-mesenchymal transitions of nontransformed cells and increases beta-catenin-dependent transcription. RNA interference of BCL9-2 in carcinoma cells induces an epithelial phenotype and translocates beta-catenin from the nucleus to the cell membrane. The switch between beta-catenin's adhesive and transcriptional functions is modulated by phosphorylation of Tyr 142 of beta-catenin, which favors BCL9-2 binding and precludes interaction with alpha-catenin. During zebrafish embryogenesis, BCL9-2 acts in the Wnt8-signaling pathway and regulates mesoderm patterning.
Beta-Catenin regulates Cripto- and Wnt3-dependent gene expression programs in mouse axis and mesoderm formation.
Morkel M, Huelsken J, Wakamiya M, Ding J, Van De Wetering M, Clevers H, Taketo MM, Behringer RR, Shen MM, Birchmeier W.
Development. 2003 Dec;130(25):6283-6294.
Gene expression profiling of beta-catenin, Cripto and Wnt3 mutant mouse embryos has been used to characterise the genetic networks that regulate early embryonic development. We have defined genes whose expression is regulated by beta-catenin during formation of the anteroposterior axis and the mesoderm, and have identified Cripto, which encodes a Nodal co-receptor, as a primary target of beta-catenin signals both in embryogenesis as well as in colon carcinoma cell lines and tissues. We have also defined groups of genes regulated by Wnt3/beta-catenin signalling during primitive streak and mesoderm formation. Our data assign a key role to beta-catenin upstream of two distinct gene expression programs during anteroposterior axis and mesoderm formation.
Beta-Catenin mediated signalling is essential for AER induction and dorsal-ventral patterning of limbs.
Natalia Sochnikova, Dietmar Zechner, Joerg Hülsken1, Makoto M. Taketo, E. Bryan Crenshaw III and Walter Birchmeier
Genes Dev 17: 1963-1968. (2003-01-01)
Distinct signalling centres direct the formation and outgrowth of vertebrate limbs. The apical ectodermal ridge (AER) controls proximal-distal outgrowth and patterning of limbs, and FGFs are key molecules that regulate these events. Dorsal-ventral patterning is controlled by ectodermally derived signals such as Wnt-7a and BMPs. We found that beta-catenin, an essential downstream effector of the canonical Wnt signalling pathway, is a key regulator of both AER induction and dorsal-ventral patterning of the limbs. Conditional inactivation of beta-catenin in the limb ectoderm of mice using Brn4Cre results in severe limb abnormalities. No AER is formed, and expression of signalling molecules like Bmp2, Bmp4 and Fgf8 is blocked. Conversely, dominant-active beta-catenin induces ectopic expression of these genes. These findings suggest that ectodermal beta-catenin acts genetically upstream of BMPs to initiate AER formation and to activate Fgf8 expression. Moreover, ablation of beta-catenin results in a loss of En-1 expression in the ventral ectoderm, and leads to a dorsalisation of distal limb structures. Taken together, our data demonstrate that beta-catenin-mediated signalling in the ectoderm of limbs is essential for both, AER induction and dorsal-ventral patterning.
The ankyrin repeat protein Diversin recruits Casein kinase Ie to the ß-catenin degradation complex and acts in both canonical Wnt and Wnt/JNK signaling.
Thomas Schwarz-Romond, Christian Asbrand, Jeroen Bakkers*, Michael Kühl†, Hans-Joerg Schaeffer, Jörg Huelsken, Jürgen Behrens‡, Matthias Hammerschmidt*, and Walter Birchmeier
Genes Dev 16: 2073-2084. (2002-01-01)
Wnt signals control decisive steps in development and can induce the formation of tumors. Canonical Wnt signals control the formation of the embryonic axis, and are mediated by stabilization and interaction of b-catenin with Lef/Tcf transcription factors. An alternative branch of the Wnt pathway employs JNK to establish planar cell polarity in Drosophila and gastrulation movements in vertebrates. We describe here the vertebrate protein Diversin that interacts with two components of the canonical Wnt pathway, Casein kinase Ie (CKIe) and Axin/Conductin. Diversin recruits CKIe to the b-catenin degradation complex that consists of Axin/Conductin and GSK3b and allows efficient phosphorylation of b-catenin, thereby inhibiting b-catenin/Tcf signals. Morpholino-based gene ablation in zebrafish demonstrates that Diversin is crucial for axis formation, which depends on b-catenin signaling. Diversin is also involved in JNK activation and gastrulation movements in zebrafish. Diversin is distantly related to Diego of Drosophila, that functions only in the pathway that controls planar cell polarity. Our data demonstrate that Diversin is an essential component of the Wnt signaling pathway and acts as a molecular switch, which suppresses Wnt signals mediated by the canonical b-catenin pathway and stimulates signaling via JNK (Schwarz-Romond et al., 2002)
Requirement of ß-catenin in anterior-posterior axis formation and in hair development in mice.
Jörg Hülsken, Markus Morkel, and Regina Vogel. In cooperation with Carmen Birchmeier (MDC).
J Cell Biol 148: 567-578. (2000-02-07)
Cell 105: 533-545. (2001-05-18)
We recently generated beta-catenin-deficient mice and observed a defect in anterior-posterior axis formation at embryonic day 5.5, as visualized by the absence of the markers Hex and Hesx1 and the mislocation of Cerberus-like and Lim1 expression. Subsequently, no mesoderm and head structures are generated. Intercellular adhesion is maintained since plakoglobin substitutes for b-catenin. Our data demonstrate that beta-catenin function is essential in anterior-posterior axis formation in the mouse, and experiments with chimeric embryos show that this function is required in the embryonic ectoderm (Huelsken et al., 2000).
To study the role of beta-catenin in development of the skin and skin appendages, we introduced a conditional mutation of the gene in the epidermis and hair follicles using the Cre/loxP technology. When beta-catenin is mutated in the ectoderm during embryogenesis, formation of the epithelial placodes that generate hair follicles is blocked. We show that beta-catenin is required genetically downstream of tabby/downless and upstream of bmp and shh in the formation of hair follicles. If beta-catenin is mutated after hair follicles have formed, hair is completely lost after the first hair cycle, and the regressing hair follicles are transformed into epidermal cysts. Further analysis demonstrates that beta-catenin is essential for fate decisions of stem cells in the skin: in the absence of beta-catenin, stem cells do not differentiate into follicular keratinocytes, but instead adopt an epidermal fate (Huelsken et al., 2001).
Hakai, a c-Cbl-like protein, ubiquitinates and induces endocytosis of the E-cadherin complex.
Yasuyuki Fujita, Dietmar Zechner, Hugo E. Molina Leddy, in cooperation with Thomas Sommer (MDC), Gerd Krause, FMP Berlin, Martin Scheffner, University of Köln, Jürgen Behrens, University of Erlangen
Nature Cell Biology 4: 222-231. (2002-01-01)
In epithelial cells, tyrosine kinases induce tyrosine phosphorylation and ubiquitination of the E-cadherin complex, which induces endocytosis of E-cadherin. With a modified yeast 2-hybrid system, we isolated Hakai, an E-cadherin binding protein, which we have identified as an E3 ubiquitin-ligase. Hakai contains SH2, RING, zinc-finger and proline-rich domains, and interacts with E-cadherin in a tyrosine phosphorylation-dependent manner, inducing ubiquitination of the E-cadherin complex. Expression of Hakai in epithelial cells disrupts cell-cell contacts and enhances endocytosis of E-cadherin and cell motility. Through dynamic recycling of E-cadherin, Hakai can thus modulate cell adhesion, and could participate in the regulation of epithelial-mesenchymal transitions in development or metastasis (Fujita et al., 2002)
Novel p62dok family members, dok-4 and dok-5, are substrates of the c-Ret receptor tyrosine kinase and mediate neuronal differentiation.
Jan Grimm, in collaboration with Stefan Britsch (MDC) and Kari Alitalo, University of Helsinki
J Cell Biol 154: 345-354. (2001-01-01)
We found that p62dok family members act as substrates for the c-Ret receptor tyrosine kinase. In addition to dok-1, dok-2, and dok-3, we identified two new family members, dok-4, and dok-5, that can directly associate with Y1062 of c-Ret. Dok-4 and dok-5 constitute a subgroup of dok family members that is coexpressed with c-Ret in various neuronal tissues. Activated c-Ret promotes neurite outgrowth of PC12 cells; for this activity, Y1062 in c-Ret is essential. Ret/dok fusion proteins, in which Y1062 of c-Ret is deleted and replaced by the sequences of dok-4 or dok-5, induce ligand-dependent axonal outgrowth of PC12 cells, whereas a c-Ret fusion containing dok-2 sequences does not elicit this response. Dok-4 and dok-5 do not associate with rasGAP or Nck, in contrast to p62dok and dok-2. Moreover, dok-4 and dok-5 enhance c-Ret-dependent activation of mitogen-activated protein kinase. Thus, we have identified a subclass of p62dok proteins that are putative links with downstream effectors of c-Ret in neuronal differentiation (Grimm et al., 2001).
Coupling of Gab1 to c-Met and downstream effectors mediate biological responses.
Martin Sachs, Ute Schaeper, Dietmar Zechner, Renate Franke and Ingrid Walther. In collaboration with Henning Brohmann, Thomas Müller and Carmen Birchmeier (MDC)
J Cell Biol 149: 1419-1432. (2000-01-01)
The docking protein Gab1 binds phosphorylated c-Met receptor tyrosine kinase directly and mediates signals of c-Met in cell culture. Gab1 is phosphorylated by c-Met and by other receptor and non-receptor tyrosine kinases (Schaeper et al., 2000). We performed a functional analysis of Gab1 by targeted mutagenesis in the mouse, and compared the phenotypes of the Gab1 and c-Met mutations. Gab1 is essential for several steps in development: migration of myogenic precursor cells into the limb anlage is impaired in Gab1 -/- embryos. As a consequence, extensor muscle groups of the forelimbs are virtually absent, and the flexor muscles reach less far. Fewer hindlimb muscles exist, which are smaller and disorganized. Muscles in the diaphragm, which also originate from migratory precursors, are missing. Moreover, Gab1-/- embryos die in a broad time window between embryonic day 13.5 and 16.5, and display reduced liver size and placental defects. The labyrinth layer but not the spongiotrophoblast layer of the placenta is severely reduced, resulting in impaired communication between maternal and fetal circulation. Thus, extensive similarities between the phenotypes of Gab1, c-Met and SF/HGF mutant mice exist, and the muscle migration phenotype is even more pronounced in Gab1-/-: c-Met+/- compound mutants. This is genetic evidence that Gab1 is essential for c-Met signaling in vivo. Analogy exists to signal transmission by insulin and IGF receptors, which require IRS1 and IRS2 as specific docking proteins (Sachs et al., 2000).