title: Forskolin-inducible cAMP pathway negatively regulates T-cell proliferation by uncoupling the interleukin-2 receptor complex.
abstract: Cytokine-mediated regulation of T-cell activity involves a complex interplay between key signal transduction pathways. Determining how these signaling pathways cross-talk is essential to understanding T-cell function and dysfunction. In this work, we provide evidence that cross-talk exists between at least two signaling pathways: the Jak3/Stat5 and cAMP-mediated cascades. The adenylate cyclase activator forskolin (Fsk) significantly increased intracellular cAMP levels and reduced proliferation of the human T-cells via inhibition of cell cycle regulatory genes but did not induce apoptosis. To determine this inhibitory mechanism, effects of Fsk on IL-2 signaling was investigated. Fsk treatment of MT-2 and Kit 225 T-cells inhibited IL-2-induced Stat5a/b tyrosine and serine phosphorylation, nuclear translocation, and DNA binding activity. Fsk treatment also uncoupled IL-2 induced association of the IL-2Rβ and γc chain, consequently blocking Jak3 activation. Interestingly, phosphoamino acid analysis revealed that Fsk-treated cells resulted in elevated serine phosphorylation of Jak3 but not Stat5, suggesting that Fsk can negatively regulate Jak3 activity possibly mediated through PKA. Indeed, in vitro kinase assays and small molecule inhibition studies indicated that PKA can directly serine phosphorylate and functionally inactivate Jak3. Taken together, these findings suggest that Fsk activation of adenylate cyclase and PKA can negatively regulate IL-2 signaling at multiple levels that include IL-2R complex formation and Jak3/Stat5 activation.
authors: Department of Biological Sciences, The University of Texas at El Paso, El Paso, Texas 79902, USA.
authors: Georgialina
authors: G
authors: Rodriguez
authors: Jeremy A
authors: JA
authors: Ross
authors: Zsuzsanna S
authors: ZS
authors: Nagy
authors: Robert A
authors: RA
authors: Kirken
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D005576:Colforsin / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D015870:Gene Expression / Q000187:drug effects; D057809:HEK293 Cells; D006801:Humans; D007376:Interleukin-2 / Q000494:pharmacology; D053646:Interleukin-2 Receptor beta Subunit / Q000378:metabolism*; D053616:Janus Kinase 3 / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding; D021122:Protein Subunits / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050799:STAT5 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013601:T-Lymphocytes / Q000187:drug effects* / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D007376:Interleukin-2; D053646:Interleukin-2 Receptor beta Subunit; D021122:Protein Subunits; D050799:STAT5 Transcription Factor; D005576:Colforsin; D000242:Cyclic AMP; C507933:JAK3 protein, human; D053616:Janus Kinase 3; D017868:Cyclic AMP-Dependent Protein Kinases; D015056:1-Methyl-3-isobutylxanthine