Dexamethasone suppresses interleukin-1beta-induced human beta-defensin 2 mRNA expression: involvement of p38 MAPK, JNK, MKP-1, and NF-kappaB transcriptional factor in A549 cells.

Human beta-defensin (HBD)-2 is an inducible antimicrobial peptide that plays an important role in innate immunity. Glucocorticoids, on the other hand, exert immunosuppressive and anti-inflammatory actions. We have previously reported that interleukin (IL)-1beta induces HBD-2 mRNA expression through the activation of nuclear factor-kappaB (NF-kappaB) transcriptional factor, as well as p38 mitogen-activated protein kinase (MAPK), c-Jun N-terminal kinase (JNK), or phosphatidylinositol-3-kinase/AKT in A549 cells. In this study, we further investigated whether dexamethasone (Dex) controls IL-1beta-induced HBD-2 mRNA expression in A549 cells and the molecular mechanism associated with it. Dex suppressed IL-1beta-induced HBD-2 mRNA expression, which is mediated by a glucocorticoid receptor, at the transcriptional level. Interestingly, Dex attenuated IL-1beta-mediated activation of p38 MAPK and JNK, but not of AKT. Dex increased the expression of MAPK phosphatase (MKP)-1, which dephosphorylated p38 MAPK, but not JNK, by IL-1beta. However, although Dex did not inhibit the nuclear translocation of p65 NF-kappaB in response to IL-1beta, it profoundly inhibited NF-kappaB promoter- and HBD-2 promoter-driven luciferase activities. These results suggest that Dex acts to inhibit IL-1beta-induced HBD-2 mRNA expression through blockage of the nuclear transcriptional activation of p65 NF-kappaB as well as through inactivation of p38 MAPK and JNK. Specifically, Dex-induced MKP-1 expression is responsible for the inactivation of p38 MAPK, but not JNK, in response to IL-1beta in A549 cells.

Triptolide suppresses interleukin-1beta-induced human beta-defensin-2 mRNA expression through inhibition of transcriptional activation of NF-kappaB in A549 cells.

The immunosuppressive effect of triptolide has been associated with suppression of T-cell activation. However, the immunosuppressive effects of triptolide on innate immunity in the epithelial barrier remain to be elucidated. Human beta-defensin (HBD)-2 is an inducible antimicrobial peptide and plays an important role in the innate immunity. We have previously demonstrated that IL-1beta induced HBD-2 mRNA expression in A549 cells through activation of nuclear factor-kappaB (NF-kappaB) transcriptional factor as well as p38 mitogen-activated protein kinase (MAPK), c-Jun N-terminal kinase (JNK), or phosphatidylinositol-3-kinase (PI3K). In this study, we investigated effects of triptolide on IL-1beta-induced HBD-2 mRNA expression in A549 cells. Triptolide inhibited IL-1beta-induced HBD-2 mRNA expression in a dose-dependent manner. Addition of triptolide did not suppress activation of p38 MAPK, JNK, or PI3K in response to IL-1beta. Triptolide inhibited IL-1beta-induced MAPK phosphatase-1 expression at the transcriptional level and resulted in sustained phosphorylation of JNK or p38 MAPK, explaining the little effect of triptolide on IL-1beta-induced phosphorylation of these kinases. Although triptolide partially suppressed IL-1beta-mediated degradation of IkappaB-alpha and nuclear translocation of p65 NF-kappaB, triptolide potently inhibited NF-kappaB promoter-driven luciferase activity in A549 cells. These results collectively suggest that the inhibitory effect of triptolide on IL-1beta-induced HBD-2 mRNA expression in A549 cells seems to be at least in part mediated through nuclear inhibition of NF-kappaB transcriptional activity, but not inhibition of p38 MAPK, JNK, or PI3K. This inhibition may explain the ability of triptolide to diminish innate immune response.

Up-regulation of human beta-defensin 2 by interleukin-1beta in A549 cells: involvement of PI3K, PKC, p38 MAPK, JNK, and NF-kappaB.

Induction of human beta-defensin 2 (HBD-2) by interleukin-1beta (IL-1beta) in epithelial cells has been reported. However, the mechanism by which IL-1beta up-regulates HBD-2 remains poorly understood. In this study, we investigated the effect of IL-1beta on induction of HBD-2 in A549 cells. IL-1beta markedly increased HBD-2 mRNA expression in concentration- and time-dependent manners. HBD-2 mRNA expression in response to IL-1beta was attenuated by pretreatment of GF109203X, Go6976, and staurosporine [inhibitors of protein kinase C (PKC)], SB203580 [an inhibitor of p38 mitogen-activated protein kinase (MAPK)], SP600125 [an inhibitor of c-Jun N-terminal kinase (JNK)], and LY294002 [an inhibitor of phosphatidylinositol-3-kinase (PI3K)], but not PD98059 [an inhibitor of extracellular signal-regulated kinase (ERK)], suggesting involvement of PKC, p38 MAPK, JNK, and PI3K in this response. Interestingly, IL-1beta induced nuclear factor-kappaB (NF-kappaB) activation in A549 cells, which was shown by increased nuclear translocation of p65 NF-kappaB and degradation of IkappaB-alpha. Importantly, IL-1beta-induced HBD-2 mRNA expression was inhibited by blockage of NF-kappaB activation using NF-kappaB inhibitors, including pyrrolidine dithiocarbamate and MG132. Specifically, IL-1beta-induced nuclear translocation of NF-kappaB was in part attenuated by LY294002, but not by GF109203X, SB203580, and SP600125, suggesting PI3K-dependent nuclear translocation of NF-kappaB in response to IL-1beta. Together, these results suggest that IL-1beta induces HBD-2 mRNA expression in A549 cells, and the induction seems to be at least in part mediated through activation of NF-kappaB transcription factor as well as activation of signaling proteins of PKC, p38 MAPK, JNK, and PI3K, but not ERK.

Tetrandrine-induced apoptosis is mediated by activation of caspases and PKC-delta in U937 cells.

Tetrandrine, which is isolated from Chinese herb Stephania tetrandrae, possesses anti-inflammatory, immunosuppressive, and cytoprotective properties. Though it was previously shown that tetrandrine causes a G1 blockade and apoptosis in various cell types, however, the mechanism by which tetrandrine initiates apoptosis remains poorly understood. In present study, we investigated the mechanisms of apoptosis induced by tetrandrine in U937 leukemia cells. Tetrandrine inhibited U937 cell growth by inducing apoptosis. After treatment of U937 cells with tetrandrine (10microM) for 24h, alteration of cell morphology, chromatin fragmentation, cytochrome c release, and caspase activation were observed. Tetrandrine also induced early oxidative stress, which resulted in activation of JNK, but not ERK and p38 MAPK. A broad-spectrum caspase inhibitor and antioxidants significantly blocked tetrandrine-induced caspase-3 activation. However, inhibition of the JNK activity with SP600125 did not block tetrandrine-induced apoptosis. Tetrandrine-induced apoptosis of U937 cells also required activity of PKC-delta, because pretreatment with a specific PKC-delta inhibitor greatly blocked tetrandrine-induced caspase-3 activation. In addition, the apoptotic response to tetrandrine was significantly attenuated in dominant-negative PKC-delta transfected MCF-7 cells, suggesting that PKC-delta plays an important role in tetrandrine-induced apoptosis and can induce caspase activation. These results suggest that tetrandrine induces oxidative stress, JNK activation, and caspase activation. However, JNK activation by ROS is not involved in the tetrandrine-induced apoptosis. In addition, tetrandrine induces caspase-dependent generation of a catalytically active fragment of PKC-delta, and this fragment also appears to play a role in the activation of caspases.