Regulation of CD40L expression by cyclic AMP: contrasting proinflammatory and inhibitory actions.

CD40L expression is well recognized to be of critical importance in initiation of the immune response. Because cAMP mediates actions of bronchodilators commonly used in asthma, the effects of cAMP in regulating the immune response are of major importance. Cyclic AMP was found to either inhibit or markedly increase CD40L expression dependent upon the mechanisms of T cell activation. Cyclic AMP inhibited CD40L expression induced by TCR activation. In contrast, cAMP enhanced CD40L induced by CD2-mediated T cell activation or by calcium-dependent mechanisms. While neither CD28 costimulation nor exogenous IL-2 or IL-4 prevented cAMP inhibition in TCR activated cells, addition of calcium ionophore to TCR activation prevented any inhibitory effects and caused cAMP to increase CD40L expression. Actions of cAMP to increase CD40L expression appeared independent of PKC and were not a reflection of generalized cellular activation since neither CD25 nor CD69 expression was affected. The markedly contrasting actions of cAMP to decrease or increase CD40L expression, an important control point in the immune response, could be relevant to actions of commonly used medications including bronchodilators.

CD40 is functionally expressed on human breast carcinomas: variable inducibility by cytokines and enhancement of Fas-mediated apoptosis.

The CD40 molecule, a member of the TNF receptor gene family, has been intensively studied with respect to regulation of B cell proliferation and survival. Although CD40 is also expressed on carcinoma cell lines, information concerning the biological function of CD40 on cells of epithelial origin is limited. In this study we detected constitutive CD40 on human breast carcinoma cell lines and an increase in CD40 expression following treatment with cytokines IL-1alpha and IFN-gamma. CD40 ligation was also found to increase MHC II expression in cells pretreated with IFN-gamma. In contrast to normal B cells, where CD40 signaling provides a potent survival signal, we observed that CD40 ligation in breast carcinoma cells results in growth inhibition and enhanced susceptibility to Fas-mediated apoptosis. Enhanced apoptosis appears to be attributable, at least in part, to an up-regulation of Fas expression caused by CD40 ligation. These results suggest a potentially important role for CD40 in breast tumor biology.

Pim-1 protein expression is regulated by its 5'-untranslated region and translation initiation factor elF-4E.

Expression of Pim-1, an oncogenic serine/threonine kinase, is highly regulated at the transcriptional, posttranscriptional, and posttranslational levels. Here, we report that expression of Pim-1 kinase is additionally regulated at the translational level. Pim-1 protein expression did not increase in Hut-78 lymphocytes in response to PMA1/ionomycin stimulation despite approximately 20-fold increases in mRNA levels, suggesting that translation was repressed. Sequence analysis of the 5'-untranslated region (UTR) indicated a long (400 nucleotide), 76% G + C-rich region, characteristics known to inhibit translation. Deletion of the 5'-UTR of pim-1 increased translation of the Pim-1 protein approximately 10-fold in vitro in reticulocyte lysates and approximately 1.6-fold in vivo in NIH-3T3 cells. When full-length 5'-UTR-containing pim-1 cDNA constructs were transfected into NIH-3T3 cells overexpressing eukaryotic translation initiation factor 4E (eIF-4E), approximately 6-fold higher levels of Pim-1 protein were produced, as compared to that produced in control NIH-3T3 cells. Moreover, eIF-4E overexpression had little effect in the absence of the 5'-UTR, suggesting that it relieved 5'-UTR-mediated inhibition of Pim-1 expression.