Protein phosphatase 4 interacts with and down-regulates insulin receptor substrate 4 following tumor necrosis factor-alpha stimulation.
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.
Mihindukulasuriya
Kathie A
KA
Department of Immunology and Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030, USA.
Zhou
Guisheng
G
Qin
Jun
J
Tan
Tse-Hua
TH
D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D015153:Blotting, Western; D002460:Cell Line; D015536:Down-Regulation; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D047468:Immunoprecipitation; D055504:Insulin Receptor Substrate Proteins; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D019319:Okadaic Acid / Q000494:pharmacology; D010455:Peptides / Q000737:chemistry; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; C107686:IRS4 protein, human; D055504:Insulin Receptor Substrate Proteins; D010455:Peptides; D010750:Phosphoproteins; D014409:Tumor Necrosis Factor-alpha; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases; C080406:protein phosphatase 4