Regulation And Mechanism Research Of CDK5 Activator Protein P35/p25 On EGFR-GSK3β Pathway

CDK5 is a proline-directed serine/threonine kinase and is one of the well-known large protein family Cyclin-Dependent-Kinases(CDKs).The main function is to participate in the migration and differentiation of nerve cells,axon guidance,synapse production and transmission,and neuronal survival through phosphorylation of a large number of substrate proteins.Activation of CDK5 relies primarily on two activators specifically expressed in the nervous system:p35 and p39.Under some pathological conditions or under external stimuli(such as cerebral ischemia.excitatory amino acid(Glutamate)and oxidative stress(H2O2)etc.),calpain is activated,and p35 is cleaved by calpain to form p25.p25 is more stable than p35 and can over-activate CDK5,thereby inducing neuronal apoptosis and synaptic dysfunction.In this article,we focus on the regulation and mechanism of the CDK5 activator protein p35/p25 on the EGFR-GSK3β pathway.Alzheimer disease(AD),also known as senile dementia,is a serious neurodegenerative disease whose main pathology is the formation of amyloid plaques formed by β-amyloid and neurofibrillary tangles(NFTs)formed by hyperphosphorylation of tau.Glycogen Synthase Kinase 3β(GSK3β)and CDK5 proteins are two important kinases in the development of Alzheimer’s disease.They have similar structures and functions,and can induce excessive phosphorylation of tau protein,resulting in neurofibrillary tangles(NFTs).Since GSK3β is highly similar to CDK5,we question whether CDK5 activator can also modulate the activity of GSK3β to cause changes in its activity leading to Alzheimer’s disease.We studied the interaction between GSK3βand p35 or p25,and found that p25,but not p35,binds tightly to GSK3β.Our further study found that p25 binds to GSK3β and significantly activates its protein activity.Next,through the protein fragmentation binding assay,it was found that the N-terminus and the C-terminus of p25 and GSK3β can be combined,indicating that the interaction between p25 and GSK3β is very tightly bound and is not easily broken,which further confirms the regulation effect of the binding of p25 and GSK3β.In the study of how p25 activates the GSK3β signaling pathway,the EGFR-GSK3β signaling pathway has attracted our attention.Epidermal growth factor(EGFR)is a transmembrane tyrosine kinase receptor.Our study found that overexpression of p25 significantly increased EGFR protein levels compared to p35 protein.We further validated the above results in neurons.At the same time,we also found that p25 can bind to EGFR and increase the protein level of EGFR.Next,we examined the molecular pathways described above in a mouse model of AD and stroke,respectively.We found that EGFR protein levels and GSK3β activity were significantly elevated in the AD mouse model cortex,consistent with our previous in vitro studies;in the stroke model,AKT and GSK3β proteins were significantly reduced.This prepares us for the intervention and treatment of neurodegenerative diseases later.In conclusion,we found that p25 can regulate both EGFR and GSK3β protein molecules.This finding gives us a deeper understanding of the role of EGFR and GSK3β in regulating neuronal apoptosis.Our results validate the previous role of the CDK5 activator protein p35/p25 in neurodegenerative diseases and how p25 affects the activity of EGFR and the downstream protein GSK3β,which provides a new theoretical foundation and drug development targets for future prevention and treatment of Alzheimer’s disease.