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Cell transformation by fibroblast growth factors can be suppressed by truncated fibroblast growth factor receptors
Y Li1, C Basilico, A Mansukhani
1Department of Microbiology and Kaplan Cancer Center, New York University School of Medicine, New York 10016.
Abstract:
Ligand-induced dimerization and transphosphorylation are thought to be important events by which receptor tyrosine kinases generate cellular signals. We have investigated the ability of signalling-defective, truncated fibroblast growth factor (FGF) receptors (FGFR-1 and FGFR-2) to block the FGF response in cells that express both types of endogenous FGF receptors. When these dominant negative receptors are expressed in NIH 3T3 cells transformed by the secreted FGF-4, the transformed properties of the cells can be reverted to various degrees, with better reversion phenotype correlating with higher levels of truncated receptor expression. Furthermore, truncated FGFR-2 is significantly more efficient at producing reversion than FGFR-1, indicating that FGF-4 preferentially utilizes the FGFR-2 signalling pathway. NIH 3T3 clones expressing these truncated receptors are more resistant to FGF-induced mitogenesis and also exhibit reduced tyrosine phosphorylation upon treatment with FGF. The block in FGF-signalling, however, can be overcome by the addition of excess growth factor. The truncated receptors have binding affinities that are four- to eightfold lower than those of wild-type receptors, as measured by Scatchard analysis. We also observed a partial specificity in the responses of truncated-receptor-expressing clones to FGF-2 or FGF-4. Our results suggest that the block to signal transduction produced by kinase-negative FGF receptors is achieved through a combination of dominant negative effects and competition for growth factor binding with functional receptors.
Insights
Dominant-negative fibroblast growth factor (FGF) receptors block FGF signaling by interfering with functional receptors. This suggests a dual mechanism involving dominant negative effects and competition for growth factor binding.
Area of Science:
- Cellular signaling
- Receptor tyrosine kinases
- Fibroblast growth factor signaling
Background:
- Receptor tyrosine kinases (RTKs) mediate cellular signals through ligand-induced dimerization and transphosphorylation.
- Fibroblast growth factors (FGFs) are crucial signaling molecules that bind to FGF receptors (FGFRs), a subclass of RTKs.
- Understanding the mechanisms of FGF signaling is vital for comprehending cellular growth, differentiation, and development.
Purpose of the Study:
- To investigate the dominant-negative effects of signaling-defective, truncated fibroblast growth factor receptors (FGFRs) on FGF signaling.
- To determine the relative efficiencies of truncated FGFR-1 and FGFR-2 in blocking FGF responses.
- To elucidate the mechanisms by which truncated FGFRs inhibit FGF-induced cellular responses.
Main Methods:
- Expression of dominant-negative, truncated FGFR-1 and FGFR-2 in NIH 3T3 cells.
- Assessment of cellular reversion phenotypes in FGF-4 transformed NIH 3T3 cells.
- Measurement of resistance to FGF-induced mitogenesis and tyrosine phosphorylation.
- Scatchard analysis to determine binding affinities of truncated receptors.
- Evaluation of responses to FGF-2 and FGF-4 in truncated receptor-expressing clones.
Main Results:
- Truncated FGFRs reverted transformed properties of NIH 3T3 cells, with higher expression correlating with better reversion.
- Truncated FGFR-2 was more efficient than FGFR-1 in blocking FGF-4 response, suggesting preferential signaling via FGFR-2.
- Cells expressing truncated receptors showed reduced mitogenesis and tyrosine phosphorylation upon FGF treatment.
- The inhibitory effect could be overcome by excess FGF, and truncated receptors had lower binding affinities than wild-type receptors.
- Partial specificity was observed in responses to FGF-2 versus FGF-4.
Conclusions:
- Signaling-defective FGFRs act as dominant-negative inhibitors of FGF signal transduction.
- The inhibition is achieved through a combination of dominant-negative effects and competition for FGF binding.
- FGF-4 preferentially utilizes the FGFR-2 signaling pathway.
- Truncated FGFRs offer a tool to dissect FGF signaling pathways and receptor utilization.