Protein Kinase A Functions A Novel Upstream Kinase Of Microtubule Affinity-regulating Kinase 2 In Regulating Microtubule Stability And Neuronal Polarity

Alzheimer's disease is a kind of neurodegenerative disease, the main features neurofibrillary tangles were caused by Tau protein. In mammals, tau belongs to the microtubule-associated proteins (MAP) family of proteins, which also includes MAP 1/2, MAP2c and MAP4. Microtubule-affinity regulating kinases (MARKs) were originally named by their ability to phosphorylate tau protein and related (MAPs), regulating the microtubule stability. Phosphorylation by MARK2 (or other MARK family members) at the Lys-Xaa-Gly-Ser motifs that are present in the repeat domain of tau causes the detachment and destabilization of the MT. Enhanced phosphorylation of tau at multiple sites, including the KXGS motifs, is an early hallmark of Alzheimer's disease (AD), followed by abnormal aggregation of Tau protein to paired helical filaments (PHFs) and neurofibrillary tangles.Overexpression of MARK2 in cells disrupts the microtubule. Ectopic expression of MARK2 in hippocampal neurons results in an increase of tau phosphorylation at S262 and a loss of neuronal polarity; Reducing MARK2 levels in hippocampal neurons promotes outgrowth resulting neurons containing several axons. PKA-dependent phosphorylation of LKB1 in an undifferentiated neurite represented an early signal for axon initiation, Furthermore, PKA maintains microtubule stability by phosphorylatiing Stathmin. PKA and MARK2 may have a crosslink because of the similar biological function of them.We found PKA countacted MARK2 in axon formation when cooverexpression of PKA and MARK2 in primary hippocampal neurons. Then, we confirmed PKA and MARK2 directly interacted. The following was that the two kinases cound regulate and exist post-translation modification.Based on the primary structure of proteins, we compare the sequences of MARKs, we predict that PKA phosphorylates MARK2. Our results show that PKA phosphorylates MARK2 serine 409 in vitro and inhibits the activity of MARK2. The polarity defects caused by MARK2 mutant S409A were not rescued by expression PKA. We find that PKA as a new upstream kinase of MARK2 involves in microtubule stability and neuronal polarity.We summarizes many papers on microtubule and neuronal polarity, together with modern biological informatics resources. We presumed that PKA cound phosphorylate MARK2 serine 409 and inhibit the activity of MARK2 involving in regulating the functions of microtubule and neurons. We confirmed the hypothesis through cell biology and immunohistochemisty, PKA/MARK2 as a novel pathway regulates microtubule functions and axon formation, which plays a pivotal role during physiological processes. We provide a new thread for early hallmark of Alzheimer's disease which are charactered axon defects and NFT.