PP2A regulates upstream members of the c-jun N-terminal kinase mitogen-activated protein kinase signaling pathway.
We have previously demonstrated that inhibition of the serine-threonine phosphatase PP2A resulted in increased c-jun N-terminal kinase (JNK) activity, and that the regulatory subunit, A/alpha of PP2A, was physically associated with the JNK. Because there exists additional examples of phosphatases serving as negative regulators of multiple members of mitogen-activated protein kinase (MAPK) pathways in Drosophila and yeast, we hypothesized that PP2A may serve a homologous function in mammalian cells affording the regulation of additional upstream kinases in the JNK pathway. In human monocytes, activation of JNK by LPS proceeds through the MAPK kinase kinase MEKK-1 and, subsequently, the MAPK kinases MKK4 and/or MKK7. Using the human monocyte cell line THP-1, we show that pharmacological manipulation of the activity of PP2A seemed to regulate not only JNK but also the upstream kinases MKK4 and MEKK-1. Using coimmunoprecipitation, overexpression of tagged recombinant JNK, and bacterial two-hybrid strategies, evidence for physical interactions between the structural subunit, PP2A-A/alpha and MEKK-1, MKK4, and JNK was observed. These studies suggest that the target of regulation by PP2A includes upstream kinases in the JNK MAPK pathway. Furthermore, PP2A-A/alpha seems to serve as a structural protein to foster protein-protein interactions affording specificity of the regulation among members of this MAP kinase pathway.
Zhao
Bin
B
Division of Pediatric Critical Care Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA.
Sun
Lei
L
Haas
Michael
M
Denenberg
Alvin G
AG
Wong
Hector R
HR
Shanley
Thomas P
TP
D015153:Blotting, Western; D045744:Cell Line, Tumor; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D047468:Immunoprecipitation; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D048670:MAP Kinase Kinase 4 / Q000235:genetics / Q000378:metabolism; D048688:MAP Kinase Kinase 7 / Q000235:genetics / Q000378:metabolism; D048728:MAP Kinase Kinase Kinase 1 / Q000235:genetics / Q000378:metabolism; D048055:Mitogen-Activated Protein Kinase 8 / Q000235:genetics / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D010080:Oxazoles / Q000494:pharmacology; D011485:Protein Binding; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D020798:Two-Hybrid System Techniques
D007527:Isoenzymes; D010080:Oxazoles; D048031:JNK Mitogen-Activated Protein Kinases; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; D048670:MAP Kinase Kinase 4; D048688:MAP Kinase Kinase 7; C517189:PPP2CA protein, human; D054648:Protein Phosphatase 2