title: cAMP regulates IL-10 production by normal human T lymphocytes at multiple levels: a potential role for MEF2.
abstract: Signal transduction by the cAMP/cAMP-dependent protein kinase A (PKA) pathway is triggered through multiple receptors and is important for many processes in a variety of cells. In T cells, the engagement of the TCR-CD3 complex induces cAMP, a second messenger that controls immune response. IL-10, produced by a variety of lymphocyte subpopulations, is an important regulator of this response exerting a wide range of immunomodulatory actions. Elevation of cAMP has been shown to increase IL-10 production by monocytes. However, the mechanism of cAMP mediated regulation of IL-10 production by T lymphocytes remains unclear. In this study using normal peripheral T lymphocytes stimulated either through the TCR-CD3 complex or the TCR-CD3 and the CD28 molecule, we show that IL-10 is produced mainly by memory T lymphocytes after either way of stimulation and is drastically inhibited (70-90%) by cAMP elevating agents. cAMP mediated inhibition was reversed by the use of the specific PKA inhibitor Rp-8-Br-cAMP but not by the addition of exogenous rhIL-2, indicating that the inhibitory effect depends on PKA activation and is not secondary to IL-2 inhibition. Inhibition is taking place at both transcriptional and posttranscriptional level. Transfection of a luciferase reporter plasmid carrying the IL-10 promoter in T cells, revealed that TCR/CD28-induced activation was inhibited by 60% by cAMP elevation. The most sensitive part to cAMP mediated inhibition was a fragment of 135 bp upstream of TATA box, which contains multiple binding sites for MEF-2. Overexpression of MEF-2 in the same cells increased IL-10 promoter activity by 2.5-fold. Stimulation through TCR/CD28 increased MEF-2 binding in its corresponding binding sites which was inhibited by 80% in the presence of cAMP elevating agents. These results suggest that the inhibitory effect of cAMP on IL-10 production by normal peripheral T lymphocytes is cell type and stimulus specific, exerted on multiple levels and involves MEF2 transcription factor.
authors.affiliation: Department of Microbiology, School of Medicine, University of Patras, Patras, Greece.
authors.forename: Kassiani
authors.initials: K
authors.lastname: Liopeta
authors.forename: Stavroula
authors.initials: S
authors.lastname: Boubali
authors.forename: Laura
authors.initials: L
authors.lastname: Virgilio
authors.forename: George
authors.initials: G
authors.lastname: Thyphronitis
authors.forename: George
authors.initials: G
authors.lastname: Mavrothalassitis
authors.forename: George
authors.initials: G
authors.lastname: Dimitracopoulos
authors.forename: Fotini
authors.initials: F
authors.lastname: Paliogianni
mesh_terms: D001483:Base Sequence; D018106:CD28 Antigens / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D016753:Interleukin-10 / Q000096:biosynthesis* / Q000235:genetics; D007376:Interleukin-2 / Q000096:biosynthesis; D008213:Lymphocyte Activation / Q000187:drug effects; D026161:MADS Domain Proteins / Q000378:metabolism*; D064326:MEF2 Transcription Factors; D018006:Myogenic Regulatory Factors / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D015398:Signal Transduction / Q000187:drug effects; D013601:T-Lymphocytes / Q000187:drug effects* / Q000201:enzymology / Q000276:immunology*; D016385:TATA Box / Q000235:genetics
chemical_list: D018106:CD28 Antigens; D007376:Interleukin-2; D026161:MADS Domain Proteins; D064326:MEF2 Transcription Factors; C578035:MEF2A protein, human; D018006:Myogenic Regulatory Factors; D012333:RNA, Messenger; D011948:Receptors, Antigen, T-Cell; D016753:Interleukin-10; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases