Activation of the protein kinase A increases the DNA-binding and transcriptional activity of c-Rel in T cells.
Cyclic AMP (cAMP)-dependent protein kinase A (PKA) is known to have both negative and positive effects on the activation mechanisms of T lymphocytes. The authors have analysed the effect of increased cAMP on the activation of NF-kappa B transcription factor. This factor controls the expression of several genes (e.g. IL-2 and IL-2 receptor) involved in the activation and proliferation of T cells. The authors found that elevation of intracellular cAMP in Jurkat T leukaemia cells activated with phorbol ester (PDBu)/calcium ionophore (A23187) increased the DNA-binding of NF-kappa B as detected by the electrophoretic mobility shift assay (EMSA). Analysis of the subunit composition of the DNA-binding complex indicated that the amount of c-Rel was enhanced while RelA was decreased. Analysis of the effect of elevated cAMP on the degradation of I kappa B-alpha and I kappa B-beta did not reveal an essential change in degradation kinetics of these inhibitor proteins. The elevation of cAMP did not increase the synthesis of c-Rel, but it enhanced the nuclear localization of this protein. Transfection of Jurkat cells with a plasmid kB/TK10-CAT indicated that the increased DNA-binding of c-Rel containing complexes seen in EMSA was also functional. These data imply that the strong and long-lasting c-Rel nuclear localization and DNA-binding induced by protein kinase A is not due to increased c-Rel synthesis or enhanced degradation of the I kappa B inhibitors. Therefore, a direct phosphorylation of the c-Rel protein is the most plausible explanation for these observations. Taken together, these results suggest that cAMP is able to regulate the expression of NF-kappa B-dependent genes in T cells by modifying the composition and subunit activity of NF-kappa B.
Lahdenpohja
N
N
Department of Microbiology and Immunology, University of Tampere Medical School, Finland.
Henttinen
T
T
Hurme
M
M
D001483:Base Sequence; D002451:Cell Compartmentation; D002467:Cell Nucleus; D016384:Consensus Sequence; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000378:metabolism*; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D020569:Proto-Oncogene Proteins c-rel; D051841:Transcription Factor RelB; D014157:Transcription Factors; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; D016328:NF-kappa B; D011518:Proto-Oncogene Proteins; D020569:Proto-Oncogene Proteins c-rel; C497593:RELB protein, human; D014157:Transcription Factors; D051841:Transcription Factor RelB; D017868:Cyclic AMP-Dependent Protein Kinases