301. Protein phosphatase 4 interacts with and down-regulates insulin receptor substrate 4 following tumor necrosis factor-alpha stimulation.
- Author
-
Mihindukulasuriya KA, Zhou G, Qin J, and Tan TH
- Subjects
- Adaptor Proteins, Signal Transducing, Amino Acid Sequence, Blotting, Western, Cell Line, Electrophoresis, Polyacrylamide Gel, Humans, Immunoprecipitation, Insulin Receptor Substrate Proteins, Mass Spectrometry, Molecular Sequence Data, Okadaic Acid pharmacology, Peptides chemistry, Plasmids metabolism, Protein Binding, Signal Transduction, Time Factors, Transfection, Down-Regulation, Phosphoprotein Phosphatases metabolism, Phosphoproteins metabolism, Tumor Necrosis Factor-alpha metabolism
- Abstract
Protein phosphatase 4 (PP4; also named PPX or PPP4) is a PP2A-related protein serine/threonine phosphatase with important roles in a variety of cellular processes such as microtubule growth/organization, apoptosis, tumor necrosis factor (TNF)-alpha signaling, and activation of c-Jun N-terminal kinase and NF-kappaB. To further investigate the cellular functions of PP4, we isolated and identified PP4-interacting proteins using a proteomic approach. We found that insulin receptor substrate 4 (IRS-4) interacted with PP4 and that this interaction was enhanced following TNF-alpha stimulation. We also found that PP4, but not PP2A, down-regulated IRS-4 in a phosphatase activity-dependent manner. Pulse-chase analysis revealed that PP4 decreased the half-life of IRS-4 from 4 to 1 h. Moreover, we found that TNF-alpha stimulated a PP4-dependent degradation of IRS-4, as indicated by the blockage of the degradation by a potent PP4 inhibitor (okadaic acid) and a phosphatase-dead PP4 mutant (PP4-RL). Taken together, our studies indicate that IRS-4 is subject to regulation by TNF-alpha and that PP4 mediates TNF-alpha-induced degradation of IRS-4.
- Published
- 2004
- Full Text
- View/download PDF