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Motogenic and morphogenic activity of epithelial receptor tyrosine kinases
M Sachs1, K M Weidner, V Brinkmann
1Max-Delbrück-Center for Molecular Medicine, Berlin, Germany.
Abstract:
Receptor tyrosine kinases play essential roles in morphogenesis and differentiation of epithelia. Here we examined various tyrosine kinase receptors, which are preferentially expressed in epithelia (c-met, c-ros, c-neu, and the keratin growth factor [KGF] receptor), for their capacity to induce cell motility and branching morphogenesis of epithelial cells. We exchanged the ligand-binding domain of these receptors by the ectodomain of trkA and could thus control signaling by the new ligand, NGF. We demonstrate here that the tyrosine kinases of c-met, c-ros, c-neu, the KGF receptor, and trkA, but not the insulin receptor, induced scattering and increased motility of kidney epithelial cells in tissue culture. Mutational analysis suggests that SHC binding is essential for scattering and increased cell motility induced by trkA. The induction of motility in epithelial cells is thus an important feature of various receptor tyrosine kinases, which in vivo play a role in embryogenesis and metastasis. In contrast, only the c-met receptor promoted branching morphogenesis of kidney epithelial cells in three-dimensional matrices, which resemble the formation of tubular epithelia in development. Interestingly, the ability of c-met to induce morphogenesis could be transferred to trkA, when in a novel receptor hybrid COOH-terminal sequences of c-met (including Y14 to Y16) were fused to the trkA kinase domain. These data demonstrate that tubulogenesis of epithelia is a restricted activity of tyrosine kinases, as yet only demonstrated for the c-met receptor. We predict the existence of specific substrates that mediate this morphogenesis signal.
Insights
Various receptor tyrosine kinases, including c-met and KGF receptor, promote epithelial cell motility. However, only c-met induces branching morphogenesis, a process crucial for tubulogenesis and potentially transferable to other kinases like trkA.
Area of Science:
- Cell Biology
- Developmental Biology
- Molecular Biology
Background:
- Receptor tyrosine kinases (RTKs) are critical for epithelial development and differentiation.
- Specific RTKs like c-met, c-ros, c-neu, and the keratin growth factor (KGF) receptor are highly expressed in epithelial tissues.
Purpose of the Study:
- To investigate the roles of specific RTKs in inducing epithelial cell motility and branching morphogenesis.
- To determine if the signaling capabilities of these RTKs can be modulated by altering their ligand-binding domains.
Main Methods:
- Engineered chimeric receptors by exchanging ligand-binding domains of c-met, c-ros, c-neu, KGF receptor, and trkA with the ectodomain of trkA.
- Utilized kidney epithelial cells in tissue culture and three-dimensional matrices to assess cell scattering, motility, and branching morphogenesis.
- Performed mutational analysis to identify key domains involved in signaling, specifically SHC binding for trkA-induced motility.
Main Results:
- RTKs including c-met, c-ros, c-neu, KGF receptor, and trkA induced scattering and increased motility in kidney epithelial cells.
- SHC binding was identified as essential for trkA-mediated scattering and motility.
- Only the c-met receptor promoted branching morphogenesis in three-dimensional cultures, mimicking tubular epithelia formation.
- A hybrid receptor with c-met COOH-terminal sequences fused to the trkA kinase domain acquired the ability to induce morphogenesis, suggesting specific domains mediate this function.
Conclusions:
- Epithelial cell motility is a common response induced by various RTKs, highlighting their role in embryogenesis and metastasis.
- Branching morphogenesis, a key process in tubulogenesis, appears to be a specialized function primarily mediated by the c-met receptor.
- The study suggests the existence of specific downstream substrates responsible for mediating morphogenesis signals from RTKs.