I1PP2A affects tau phosphorylation via association with the catalytic subunit of protein phosphatase 2A.
In Alzheimer disease (AD) brain, the level of I (1)(PP2A), a 249-amino acid long endogenous inhibitor of protein phosphatase 2A (PP2A), is increased, the activity of the phosphatase is decreased, and the microtubule-associated protein Tau is abnormally hyperphosphorylated. However, little is known about the detailed regulatory mechanism by which PP2A activity is inhibited by I (1)(PP2A) and the consequent events in mammalian cells. In this study, we found that both I (1)(PP2A) and its N-terminal half I (1)(PP2A(1-120)), but neither I (1)(PP2A(1-163)) nor I (1)(PP2A(164-249)), inhibited PP2A activity in vitro, suggesting an autoinhibition by amino acid residues 121-163 and its neutralization by the C-terminal region. Furthermore, transfection of NIH3T3 cells produced a dose-dependent inhibition of PP2A activity by I (1)(PP2A)(1). I (PP2A) and PP2A were found to colocalize in PC12 cells. I (1)(PP2A) could only interact with the catalytic subunit of PP2A (PP2Ac) and had no interaction with the regulatory subunits of PP2A (PP2A-A or PP2A-B) using a glutathione S-transferase-pulldown assay. The interaction was further confirmed by coimmunoprecipitation of I (1)(PP2A) and PP2Ac from lysates of transiently transfected NIH3T3 cells. The N-terminal isotype specific region of I (1)(PP2A) was required for its association with PP2Ac as well as PP2A inhibition. In addition, the phosphorylation of Tau was significantly increased in PC12/Tau441 cells transiently transfected with full-length I (1)(PP2A) and with PP2Ac-interacting I (1)(PP2A) deletion mutant 1-120 (I (1)(PP2A)DeltaC2). Double immunofluorescence staining showed that I (1)(PP2A) and I (1)(PP2A)DeltaC2 increased Tau phosphorylation and impaired the microtubule network and neurite outgrowth in PC12 cells treated with nerve growth factor.
Chen
She
S
Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, New York 10314, USA.
Li
Bin
B
Grundke-Iqbal
Inge
I
Iqbal
Khalid
K
D000818:Animals; D020134:Catalytic Domain; D017353:Gene Deletion; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry* / Q000502:physiology; D051379:Mice; D041681:NIH 3T3 Cells; D020932:Nerve Growth Factor / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D009687:Nuclear Proteins; D016716:PC12 Cells; D010766:Phosphorylation; D054648:Protein Phosphatase 2 / Q000737:chemistry* / Q000378:metabolism; D017434:Protein Structure, Tertiary; D016601:RNA-Binding Proteins; D051381:Rats; D014162:Transfection; D016875:tau Proteins / Q000737:chemistry / Q000502:physiology*
C087425:ANP32A protein, human; D047908:Intracellular Signaling Peptides and Proteins; C489131:Mapt protein, rat; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; D016875:tau Proteins; D020932:Nerve Growth Factor; D054648:Protein Phosphatase 2