Pharmacological modulation of c-fos mRNA expression in the HL60 and U937 cell lines

Opposing regulatory effects of protein kinase C on the cAMP cascade in human HL-60 promyelocytic leukemia cells

The functional role of protein kinase C in the cAMP signaling cascade was investigated in human promyelocytic leukemia (HL-60) cells. Protein kinase C activation after short exposure to 100 nM phorbol 12-myristate 13-acetate (PMA) increased the intracellular cAMP level up to 3- to 5-fold after 30 min. Such enhancement was almost completely blocked by the selective protein kinase C inhibitor bisindolylmaleimide (GF 109203X). In addition, PMA, but not 4-alpha-PMA, synergistically elevated cAMP levels when adenylyl cyclase was activated directly by forskolin or indirectly by G protein activation after cholera toxin treatment or guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) treatment in digitonin-permeabilized cells. The results indicate that protein kinase C directly increases adenylyl cyclase activity and synergistically enhances it, when it is simultaneously activated otherwise. On the other hand, a 10-min treatment with PMA cut the cAMP accumulation induced by histamine, prostaglandin E2, or isoproterenol by 50-70%. However, the binding affinity and total binding of [3H]histamine to membrane receptors was not effected by PMA, suggesting that the site of protein kinase C's action is not at the receptor level. Western blot analysis of protein kinase C isozymes revealed that PMA (100 nM) caused translocation of cytosolic protein kinase C such as alpha, beta and epsilon to the particulate/membrane fraction. Treatment with a lower concentration of PMA (10 nM) translocated the protein kinase C-epsilon within 2 min, while it had little effect on the translocation of protein kinase C-alpha and -beta up to 20 min. However, simultaneous treatment with 10 nM PMA plus histamine for 5 min significantly inhibited the histamine-mediated cAMP generation, indicating that the protein kinase C-epsilon could be involved in the inhibition of receptor-mediated cAMP generation. Taken together, we conclude that PMA, through the activation of protein kinase C, has two opposite effects on the cAMP signaling cascade in HL-60 cells: a direct activation of adenylyl cyclase and an inhibition of receptor-mediated signal transduction.

Histamine modulates the expression of c-fos through cyclic AMP production via the H2 receptor in the human promonocytic cell line U937

We examined the effects of histamine and its agonists on the expression of the c-fos and c-myc proto-oncogenes at the transcriptional and translational levels in the human promonocytic U937 cell line. Histamine transiently increased cAMP and c-fos expression through H2 receptors. Dibutyryl cAMP also increased c-fos mRNA and protein, and levels remained elevated even after 12 hr of treatment. Dose-dependence studies using histamine and dimaprit showed that the EC50 values for cAMP production and c-fos increase were similar, suggesting that cAMP might be involved in c-fos induction via H2 receptors. Furthermore, studies carried out using H7, a protein kinase A/protein kinase C inhibitor, blocked c-fos induction, whereas no effect was observed with bisindolylmaleimide, a specific protein kinase C inhibitor. No modification of c-myc expression could be detected on treatment with histamine or its analogues. Nevertheless, dibutyryl cAMP induced a down-regulation of the levels of this proto-oncogene. In addition, dibutyryl cAMP inhibited cell growth in a dose-dependent manner, whereas histamine failed to affect proliferation and differentiation of U937 cells. Cells pretreated with dimaprit showed a decrease in the cAMP response to subsequent addition of H2 agonists, whereas the cAMP response to prostaglandin E2 remained unaltered. This homologous mechanism of H2 receptor desensitization was time dependent. These results indicate that histamine activates several mechanisms involved in the induction of differentiation, such as cAMP and c-fos production, but fails to promote differentiation of U937 cells, apparently due to the rapid desensitization of H2 receptors.

Increase in interleukin (IL)-1 beta and IL-6 in bronchoalveolar lavage fluid obtained from infants with chronic lung disease of prematurity

Chronic lung disease (CLD) of prematurity is associated with an initial increase in pulmonary neutrophils followed by pulmonary fibrosis. We determined whether the proinflammatory cytokines, IL-1 beta and IL-6, were increased in the bronchoalveolar lavage fluid obtained from nine infants (median gestation 25 wk, birthweight 820 g) who developed CLD, seven (28 wk, 1110 g) who recovered from the respiratory distress syndrome (RDS), and four (38 wk, 2690 g) control infants. IL-1 beta and IL-6 protein were both increased in the bronchoalveolar lavage fluid from the CLD groups when compared with the RDS and control groups. This difference for both the cytokines was most marked on d 10 of age, when results from infants with and without CLD were compared (IL-1 beta, 4.6 versus 1.1 ng/mL, p < 0.05; and IL-6, 9.5 versus 1.5 ng/mL, p < 0.05). Immunocytochemistry of lavage cells for IL-1 beta, IL-6, and IL-8 protein showed alveolar macrophages to contain all three cytokines, with lesser staining evident in neutrophils, and in epithelial cells occasionally obtained by lavage. The contribution of alveolar macrophages and luminal cells to the increase in IL-6 and IL-1 was determined by performing semiquantitative reverse transcription-polymerase chain reactions on RNA extracted from lavage cells. IL-6 mRNA expression was increased in lavage cells from the CLD infants when compared with the RDS group. However, the expression for IL-1 beta and IL-8 mRNA was similar in both groups. These results suggest that IL-1 beta, IL-6, and IL-8 may contribute to the pathogenesis of CLD, and that, in CLD, IL-6 may be produced by cells within the air spaces.