The Effects Of PTPA On PP2A_c Y307 Phosphorylation Level And The Underlying Mechanisms

Alzheimer's disease (Alzheimer's disease, AD) is a progressive memory loss and cognitive impairment in neurodegenerative disease, the characteristic pathological changes in the brain is: neurofibrillary tangles (NFT) in neurons and senile plaques (senile plaques, SP). The main component of neurofibrillary tangles is the abnormal phosphorylated tau protein. 107 types of tyrosine phosphatases are in human body; PP2A belongs to PPP family, and plays an important role in tau phosphorylation. PP2A catalytic subunit is regulated by catalytic subunit level and posttranslational modification, for example methylation at Leu309 and phosphorylation at Tyr307. PTPA, exists in animal tissues and cells, could activate PP2A via changing PP2AC space conformation and increasing methylation level at Leu309 by PME. It's not clear whether PTPA has effects on Tyr307 phosphorylationai level.Objective: To explore the effects of PTPA on PP2AC Y307 phosphorylational level and the underlying mechanism.Materials and Methods: PTPA wild type plasmid (wt-PTPA) and siPTPA (pSUPER-siPTPA) were constructed and transfected into HEK293/tau cells. Proteins levels were detected by Western blotting and Immunofluorescence, PP2A actvity was detected by protein phosphatase activity assay kit, RT-PCR was used to deteced PTP1B mRNA.Results: (1) Overexpression of PTPA reduces tau phosphorylation level, knockdown of PTPA increases tau phosphorylation level; (2) Overexpression of PTPA increases PP2A activity, PTPA knockdown decreases PP2A activity; (3) PTPA regulates PP2AC Y307 phosphorylation and PP2Ac L309 methylation level, but has no obvious effects on other major enzymes which regulate tau phosphorylation; (4) Overexpression of PTPA increases PTP1B mRNA and protein levels; PTPA knockdown decreases PTP1B mRNA and protein levels.Conclusion: PTPA can regulate PP2AC Y307 phosphorylation level by changing PTP1B mRNA and protein level.