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Formation of signal transfer complexes between stem cell and platelet-derived growth factor receptors and SH2 domain
R Herbst1, M S Shearman, B Jallal
1Department of Molecular Biology, Max-Planck-Institut für Biochemie, Martinsried, Germany.
Abstract:
Cellular growth and differentiation signals are generated and defined by the interaction of specific phosphotyrosine residues of activated receptor tyrosine kinases (RTKs) and src homology-2 (SH2) domain-containing intracellular signal transducers. This appears to involve for both the p145c-kit and beta platelet-derived growth factor receptor (PDGF-R) cytoplasmic domains the formation of multiprotein signal transfer complexes, which include combinations of noncatalytic and enzymatically active subunits of phosphatidylinositol 3'-kinase (PI3'-K), phospholipase C-gamma (PLC gamma), and guanosine trisphosphatase activating protein (GAP). In vitro association experiments indicate that PLC gamma and PI3'-K bind the beta PDGF-R simultaneously, while these two SH2 proteins compete for association to p145c-kit binding sites, with p85/PI3'-K exhibiting higher affinity. Interestingly, GAP and p85/PI3'-K binding to distinct p145c-kit phosphotyrosines is cooperative, enhancing formation of a heterotetrameric signaling complex, which may include different combinations of p85 alpha and p85 beta with p110, p112, and p116 by interaction with the same tyrosine 721 docking site. The diversity of molecular interactions observed for PDGF-R and p145c-kit suggests a new mode of signal definition and modulation.
Insights
Receptor tyrosine kinases (RTKs) signal through protein complexes. Different interactions with platelet-derived growth factor receptor (PDGF-R) and p145c-kit reveal novel signaling mechanisms for cell growth and differentiation.
Area of Science:
- Cellular signaling pathways
- Molecular biology
- Biochemistry
Background:
- Cellular growth and differentiation are regulated by receptor tyrosine kinases (RTKs).
- Activated RTKs interact with intracellular signal transducers containing src homology-2 (SH2) domains.
- These interactions form multiprotein complexes that define cellular signals.
Purpose of the Study:
- To investigate the molecular interactions of phosphatidylinositol 3'-kinase (PI3'-K), phospholipase C-gamma (PLC gamma), and guanosine trisphosphatase activating protein (GAP) with p145c-kit and beta platelet-derived growth factor receptor (PDGF-R).
- To elucidate the formation and composition of signaling complexes involving these transducers.
- To understand how these interactions modulate cellular signals.
Main Methods:
- In vitro association experiments were used to study protein binding.
- Analysis of binding affinities and competition between SH2 domain-containing proteins.
Main Results:
- PLC gamma and PI3'-K bind simultaneously to the beta PDGF-R.
- PLC gamma and PI3'-K compete for binding sites on p145c-kit, with p85/PI3'-K showing higher affinity.
- Binding of GAP and p85/PI3'-K to distinct p145c-kit phosphotyrosines is cooperative, forming a heterotetrameric complex.
Conclusions:
- The binding diversity of signaling proteins to PDGF-R and p145c-kit suggests a novel mechanism for signal definition.
- Cooperative binding enhances the formation of specific signaling complexes.
- These findings offer new insights into the modulation of cellular growth and differentiation signals.