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Monoamine-activated alpha 2-macroglobulin binds trk receptor and inhibits nerve growth factor-stimulated trk
1Department of Microbiology and Immunology, Northeastern Ohio Universities College of Medicine, Rootstown 44272-0095.
Abstract:
Monoamine-activated alpha 2-macroglobulin (alpha 2M) has been shown to inhibit beta-nerve growth factor (NGF)-promoted neurite outgrowth and the survival of embryonic sensory and forebrain neurons, whereas normal alpha 2M has little or no such activity. The objective of this study is to elucidate the mechanism of inhibition by monoamine-activated alpha 2M. Methylamine-activated alpha 2M (MA-alpha 2M) and serotonin-activated alpha 2M (5HT-alpha 2M) dose dependently inhibit NGF-promoted neurite outgrowth of the pheochromocytoma PC12 cell and its subline PC12(6-24) which overexpresses human trk protooncogene product, but have no effect on their viability, and this inhibition can be blocked by high concentrations of NGF. The binding of MA-alpha 2M to trk, which is a part of high-affinity NGF receptor, was studied with PC12(6-24) cells and NIH-3T3 fibroblasts expressing trk (trk-3T3). In each case MA-alpha 2M readily forms stable complexes with trk in vivo, whereas normal alpha 2M does not. Both 5HT-alpha 2M and MA-alpha 2M also dose dependently block NGF-promoted autophosphorylation of trk in vivo, whereas normal alpha 2M and plasmin-reacted alpha 2M are inactive or much less active. MA-alpha 2M also blocks NGF-promoted incorporation of 32P from [32P]ATP into trk receptors in vitro. Neither MA-alpha 2M, 5HT-alpha 2M, nor normal alpha 2M, however, blocks either platelet-derived growth factor-stimulated or epidermal growth factor-stimulated tyrosine phosphorylation of the respective receptors. Tyrosine phosphorylation of two of the intracellular substrates, phospholipase C-gamma 1 and extracellular signal-regulated kinase-2, in the NGF-promoted pathways is also dose dependently blocked by MA-alpha 2M. However, by comparison MA-alpha 2M is more effective in inhibiting the activation of phospholipase C-gamma 1 than trk. We conclude that monoamine-activated alpha 2M may block neurite outgrowth and neuronal survival by its specific binding to NGF receptors, thus inhibiting the NGF-promoted activation of intracellular second messenger pathways.
Insights
Monoamine-activated alpha 2-macroglobulin (alpha 2M) inhibits nerve growth factor (NGF)-promoted neurite outgrowth by binding to NGF receptors. This binding blocks crucial intracellular signaling pathways, impacting neuronal development and survival.
Area of Science:
- Neuroscience
- Molecular Biology
- Biochemistry
Background:
- Monoamine-activated alpha 2-macroglobulin (alpha 2M) inhibits beta-nerve growth factor (NGF)-promoted neurite outgrowth and neuronal survival.
- Normal alpha 2M exhibits minimal to no inhibitory activity on these processes.
- The precise mechanism by which activated alpha 2M exerts its inhibitory effects remains to be fully elucidated.
Purpose of the Study:
- To elucidate the mechanism of inhibition by monoamine-activated alpha 2M on NGF-promoted cellular processes.
- To investigate the interaction between monoamine-activated alpha 2M and the NGF receptor complex.
Main Methods:
- Utilized pheochromocytoma PC12 cells and NIH-3T3 fibroblasts expressing the trk protooncogene product (NGF receptor).
- Investigated the binding of methylamine-activated alpha 2M (MA-alpha 2M) to trk receptors in vivo and in vitro.
- Assessed the effects of MA-alpha 2M and serotonin-activated alpha 2M (5HT-alpha 2M) on NGF-promoted trk autophosphorylation and downstream substrate phosphorylation.
Main Results:
- MA-alpha 2M and 5HT-alpha 2M dose-dependently inhibit NGF-promoted neurite outgrowth without affecting cell viability.
- MA-alpha 2M forms stable complexes with trk receptors in vivo, unlike normal alpha 2M.
- Both MA-alpha 2M and 5HT-alpha 2M block NGF-promoted trk autophosphorylation and the phosphorylation of intracellular substrates phospholipase C-gamma 1 and extracellular signal-regulated kinase-2.
Conclusions:
- Monoamine-activated alpha 2M inhibits NGF signaling by specifically binding to NGF receptors (trk).
- This interaction disrupts the activation of intracellular second messenger pathways essential for neurite outgrowth and neuronal survival.
- The findings provide a mechanistic understanding of how activated alpha 2M modulates neuronal development.