Interleukin-4 gene expression in activated human T lymphocytes is regulated by the cyclic adenosine monophosphate-dependent signaling pathway

In the present study, we have investigated the involvement of the cyclic adenosine monophosphate (cAMP)-dependent signaling pathway on interleukin-4 (IL-4) gene expression in freshly isolated human T lymphocytes. 2′–0-dibutyryl cAMP (db-cAMP) and prostaglandin E2 (PGE2) were used to directly and indirectly activate the protein kinase A pathway. Northern analysis showed that concanavalin A (Con A)-, anti- CD3 (alpha CD3)-, or anti-CD3 plus anti-CD28 (alpha CD3/alpha CD28)- induced accumulation of IL-4 mRNA was inhibited by db-cAMP (10(-3) mol/L). Db-cAMP showed a steep dose-dependent inhibition; concentrations or = 10(-4) mol/L did not affect IL-4 mRNA accumulation. In contrast, GM-CSF mRNA expression showed a wider dose- dependent range; 10(-5) mol/L db-cAMP still affected GM-CSF accumulation. PGE2 inhibited the Con A- and alpha CD3/alpha CD28- induced accumulation of IL-4 mRNA in a dose-dependent fashion. Con A- induced IL-4 mRNA was inhibited by 10(-4) to 10(-7) mol/L PGE2; alpha CD3/alpha CD28-induced IL-4 mRNA was inhibited by 10(-5) to 10(-8) mol/L PGE2. Nuclear run-on experiments showed that the inhibitory effects of db-cAMP and PGE2 were accomplished at transcriptional level in Con A-activated T cells, whereas changes at transcriptional and posttranscriptional level were involved in alpha CD3/alpha CD28- activated T lymphocytes. In contrast to Con A and alpha CD3/alpha CD28 activation, phorbol myristate acetate plus A23187-induced IL-4 mRNA expression was insensitive to the inhibitory effect of db-cAMP and PGE2. Moreover, it appeared that the sensitivity for cAMP-mediated downregulation could not be blocked by stimulation T lymphocytes with alpha CD3/alpha CD28 in the presence of IL-2, IL-7, IL-10, IL-12, or a combination of these cytokines. Finally, it was shown that, in accordance with the mRNA studies, db-cAMP and PGE2 suppressed the IL-4 secretion in Con A- and alpha CD3/alpha CD28-activated T cells. In conclusion, these data show that IL-4 expression is negatively regulated by the protein kinase A-dependent signaling pathway by transcriptional and posttranscriptional mechanisms that depend on costimulatory signals.