title: Protein phosphatase 2A regulates interleukin-2 receptor complex formation and JAK3/STAT5 activation.
abstract: Reversible protein phosphorylation plays a key role in interleukin-2 (IL-2) receptor-mediated activation of Janus tyrosine kinase 3 (JAK3) and signal transducer and activator of transcription 5 (STAT5) in lymphocytes. Although the mechanisms governing IL-2-induced tyrosine phosphorylation and activation of JAK3/STAT5 have been extensively studied, the role of serine/threonine phosphorylation in controlling these effectors remains to be elucidated. Using phosphoamino acid analysis, JAK3 and STAT5 were determined to be serine and tyrosine-phosphorylated in response to IL-2 stimulation of the human natural killer-like cell line, YT. IL-2 stimulation also induced serine/threonine phosphorylation of IL-2Rbeta, but not IL-2Rgamma. To investigate the regulation of serine/threonine phosphorylation in IL-2 signaling, the roles of protein phosphatase 1 (PP1) and 2A (PP2A) were examined. Inhibition of phosphatase activity by calyculin A treatment of YT cells resulted in a significant induction of serine phosphorylation of JAK3 and STAT5, and serine/threonine phosphorylation of IL-2Rbeta. Moreover, inhibition of PP2A, but not PP1, diminished IL-2-induced tyrosine phosphorylation of IL-2Rbeta, JAK3, and STAT5, and abolished STAT5 DNA binding activity. Serine/threonine phosphorylation of IL-2Rbeta by a staurosporine-sensitive kinase also blocked its association with JAK3 and IL-2Rgamma in YT cells. Taken together, these data indicate that serine/threonine phosphorylation negatively regulates IL-2 signaling at multiple levels, including receptor complex formation and JAK3/STAT5 activation, and that this regulation is counteracted by PP2A. These findings also suggest that PP2A may serve as a therapeutic target for modulating JAK3/STAT5 activation in human disease.
authors.affiliation: From the Department of Biological Sciences, University of Texas, El Paso, Texas 79968.
authors.forename: Jeremy A
authors.initials: JA
authors.lastname: Ross
authors.affiliation: From the Department of Biological Sciences, University of Texas, El Paso, Texas 79968; the Department of Pathology, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, and.
authors.forename: Hanyin
authors.initials: H
authors.lastname: Cheng
authors.affiliation: From the Department of Biological Sciences, University of Texas, El Paso, Texas 79968.
authors.forename: Zsuzsanna S
authors.initials: ZS
authors.lastname: Nagy
authors.affiliation: the Department of Integrative Biology and Pharmacology, University of Texas Health Science Center, Houston, Texas 77030.
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Frost
authors.affiliation: From the Department of Biological Sciences, University of Texas, El Paso, Texas 79968. Electronic address: rkirken@utep.edu.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Kirken
mesh_terms: D015153:Blotting, Western; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D047468:Immunoprecipitation; D007376:Interleukin-2 / Q000494:pharmacology; D053616:Janus Kinase 3 / Q000378:metabolism*; D008214:Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D009841:Oligonucleotides / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000187:drug effects; D054645:Protein Phosphatase 1 / Q000378:metabolism; D054648:Protein Phosphatase 2 / Q000378:metabolism*; D015375:Receptors, Interleukin-2 / Q000378:metabolism*; D050799:STAT5 Transcription Factor / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
chemical_list: D007376:Interleukin-2; D009841:Oligonucleotides; D015375:Receptors, Interleukin-2; D050799:STAT5 Transcription Factor; C494092:STAT5A protein, human; C494095:STAT5B protein, human; D025521:Tumor Suppressor Proteins; D014443:Tyrosine; D012694:Serine; C507933:JAK3 protein, human; D053616:Janus Kinase 3; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2