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Reciprocal modulation of TrkA and p75NTR affinity states is mediated by direct receptor interactions
G M Ross1, I L Shamovsky, G Lawrance
1Department of Medicine, Kingston General Hospital, Ontario, Canada.
Abstract:
Equilibrium binding of 125I-nerve growth factor (125I-NGF) to cells coexpressing the tyrosine kinase receptor A (TrkA) and common neurotrophin receptor (p75NTR), cells coexpressing both receptors where p75NTR is occupied, and cells expressing only p75NTR, revealed reciprocal modulation of receptor affinity states. Analysis of receptor affinity states in PC12 cells, PC12 cells in the presence of brain-derived neurotrophic factor (BDNF), and PC12nnr5 cells suggested that liganded and unliganded p75NTR induce a higher affinity state within TrkA, while TrkA induces a lower affinity state within p75NTR. These data are consistent with receptor allosterism, and prompted a search for TrkA/p75NTR complexes in the absence of NGF. Chemical crosslinking studies revealed high molecular weight receptor complexes that specifically bound 125I-NGF, and were immunoprecipitated by antibodies to both receptors. The heteroreceptor complex of TrkA and p75NTR alters conformation and/or dissociates in the presence of NGF, as indicated by the ability of low concentrations of NGF to prevent heteroreceptor crosslinking. These data suggest a new model of receptor interaction, whereby structural changes within a heteroreceptor complex are induced by ligand binding.
Insights
Nerve growth factor (NGF) binding to TrkA and p75NTR receptors modulates their affinity states. These neurotrophin receptors form complexes that change conformation upon NGF binding, suggesting a new interaction model.
Area of Science:
- Neuroscience
- Molecular Biology
- Cell Biology
Background:
- Neurotrophin receptors, including tyrosine kinase receptor A (TrkA) and the common neurotrophin receptor (p75NTR), play critical roles in neuronal development and function.
- The interaction between TrkA and p75NTR is complex and influences cellular responses to neurotrophins like nerve growth factor (NGF).
- Understanding the precise mechanisms of TrkA and p75NTR interaction is crucial for deciphering signaling pathways in the nervous system.
Purpose of the Study:
- To investigate the reciprocal modulation of receptor affinity states between TrkA and p75NTR.
- To identify and characterize TrkA/p75NTR complexes.
- To elucidate the impact of ligand binding on the TrkA/p75NTR heteroreceptor complex structure and function.
Main Methods:
- Equilibrium binding assays using radiolabeled 125I-nerve growth factor (125I-NGF).
- Analysis of receptor affinity states in various cell lines (PC12, PC12nnr5) under different conditions.
- Chemical crosslinking studies to detect receptor complexes.
- Immunoprecipitation using antibodies against TrkA and p75NTR.
Main Results:
- Binding of 125I-NGF revealed reciprocal affinity modulation between TrkA and p75NTR.
- Liganded and unliganded p75NTR increased TrkA affinity, while TrkA decreased p75NTR affinity, suggesting receptor allosterism.
- Chemical crosslinking identified high molecular weight TrkA/p75NTR heteroreceptor complexes.
- NGF binding induced conformational changes or dissociation of the TrkA/p75NTR complex, preventing crosslinking.
Conclusions:
- A novel model of TrkA and p75NTR interaction is proposed, involving ligand-induced structural changes within a heteroreceptor complex.
- The affinity states of TrkA and p75NTR are dynamically regulated through their physical association.
- These findings provide new insights into the molecular mechanisms governing neurotrophin signaling.