Knockout of Mkp-1 exacerbates colitis in Il-10-deficient mice.

Il-10-deficient mice develop colitis associated with exaggerated Th1/Th17 responses and are a valuable model of inflammatory bowel disease. Mkp-1 is a major negative regulator of MAPKs, and its expression is enhanced by IL-10. To understand the role of Mkp-1 in the regulation of intestinal mucosal immune responses, we studied the effect of Mkp-1 deletion on the pathogenesis of colitis in Il-10(-/-) mice. We found that knockout of Mkp-1 on an Il-10(-/-) background accelerated the development of colitis. Compared with Il-10(-/-) mice, colitis not only appeared earlier but also was more severe in Il-10(-/-)/Mkp-1(-/-) mice. Il-10(-/-) mice exhibited a mild intestinal inflammation in the specific pathogen-free environment, and rectal prolapse rarely appeared before 6 mo of age. In contrast, the majority of Il-10(-/-)/Mkp-1(-/-) mice developed severe colitis rapidly and presented with rectal prolapse after only 2-3 mo. The colon of Il-10(-/-)/Mkp-1(-/-) mice showed diffuse transmural chronic inflammation and mucosal hyperplasia, with significantly more proliferating crypt epithelial cells than those of Il-10(-/-) mice. In addition to the severe colitis, Il-10(-/-)/Mkp-1(-/-) mice also developed conjunctivitis and blepharitis. The colon of Il-10(-/-)/Mkp-1(-/-) mice contained significantly higher levels of proinflammatory cytokines and exhibited greater MAPK activities than did the colon of Il-10(-/-) mice. Splenocytes and lymphocytes from Il-10(-/-)/Mkp-1(-/-) mice produced higher levels of Th1 cytokines ex vivo upon activation than did cells from Il-10(-/-) mice. Our studies support a pivotal role of Mkp-1 as a negative regulator of mucosal immune responses and highlight its protective function against inflammatory bowel disease.

Triptolide induces anti-inflammatory cellular responses.

Tripterygium wilfordii Hook F. has been used for centuries in traditional Chinese medicine to treat rheumatoid arthritis, an autoimmune disease associated with increased production of the pro-inflammatory cytokine, tumor necrosis factor (TNF)-alpha. Triptolide is a compound originally purified from T. wilfordii Hook F. and has potent anti-inflammatory and immunosuppressant activities. In this study, we investigated the effect of triptolide on the global gene expression patterns of macrophages treated with lipopolysaccharide (LPS). We found that LPS stimulation resulted in >5-fold increase in expression of 117 genes, and triptolide caused a >50% inhibition in 47 of the LPS-inducible 117 genes. A large portion of the genes that were strongly induced by LPS and significantly inhibited by triptolide were pro-inflammatory cytokine and chemokine genes, including TNF-alpha, IL-1beta, and IL-6. Interestingly, LPS also induced the expression of micro-RNA-155 (miR-155) precursor, BIC, which was inhibited by triptolide. Confirming the cDNA array results, we demonstrated that triptolide blocked the induction of these pro-inflammatory cytokines as well as miR-155 in a dose-dependent manner. Profound inhibition of pro-inflammatory cytokine expression was observed at concentrations as low as 10-50 nM. However, triptolide neither inhibited the phosphorylation or degradation of IkappaBalpha after LPS stimulation, nor affected the DNA-binding activity of NF-kappaB. Surprisingly, we found that triptolide not only inhibited NF-kappaB-regulated reporter transcription, but also dramatically blocked the activity of other transcription factors. Our study offers a plausible explanation of the therapeutic mechanism of T. wilfordii Hook F.

Inducible nitric-oxide synthase expression is regulated by mitogen-activated protein kinase phosphatase-1.

Inducible nitric-oxide (NO) synthase (iNOS) plays a critical role in the eradication of intracellular pathogens. However, the excessive production of NO by iNOS has also been implicated in the pathogenesis of septic shock syndrome. Previously, we have demonstrated that mice deficient in mitogen-activated protein kinase phosphatase-1 (MKP-1) exhibit exaggerated inflammatory responses and rapidly succumb to lipopolysaccharide (LPS). In response to LPS, MKP-1(-/-) mice produce greater amounts of inflammatory cytokines and NO than do wild-type mice, and the MKP-1(-/-) mice exhibit severe hypotension. To understand the molecular basis for the increase in NO production, we studied the role of MKP-1 in the regulation of iNOS expression. We found that LPS challenge elicited a stronger iNOS induction in MKP-1 knock-out mice than in wild-type mice. Likewise, LPS treatment also resulted in greater iNOS expression in macrophages from MKP-1(-/-) mice than in macrophages from wild-type mice. Both accelerated gene transcription and enhanced mRNA stability contribute to the increases in iNOS expression in LPS-stimulated MKP-1(-/-) macrophages. We found that STAT-1, a transcription factor known to mediate iNOS induction by interferon-gamma, was more potently activated by LPS in MKP-1(-/-) macrophages than in wild-type cells. MicroRNA array analysis indicated that microRNA (miR)-155 expression was increased in MKP-1-deficient macrophages compared with wild-type macrophages. Transfection of miR-155 attenuated the expression of Suppressor of Cytokine Signal (SOCS)-1 and enhanced the expression of iNOS. Our results suggest that MKP-1 may negatively regulate iNOS expression by controlling the expression of miR-155 and consequently the STAT pathway via SOCS-1.

ERK and p38 MAPK signaling pathways negatively regulate CIITA gene expression in dendritic cells and macrophages.

The CIITA is a master regulator for MHC class II expression, but the signaling events that control CIITA expression remain poorly understood. In this study, we report that both constitutive and IFN-gamma-inducible expression of CIITA in mouse bone marrow-derived dendritic cells (DC) and macrophages, respectively, are regulated by MAPK signals. In DC, the inhibitory effect of LPS on CIITA expression was prevented by MyD88 deficiency or pharmacological MAPK inhibitors specific for MEK (U0126) and p38 (SB203580), but not JNK (SP600125). In macrophages, LPS inhibited IFN-gamma-inducible CIITA and MHC class II expression without affecting expression of IFN regulatory factor-1 and MHC class I. Blocking ERK and p38 by MAPK inhibitors not only rescued LPS-mediated inhibition, but also augmented IFN-gamma induction of CIITA. Moreover, the induction of CIITA by IFN-gamma was enhanced by overexpressing MAPK phosphatase-1 that inactivates MAPK. Conversely, CIITA expression was attenuated in the absence of MAPK phosphatase-1. The down-regulation of CIITA gene expression by ERK and p38 was at least partly due to decreased histone acetylation of the CIITA promoter. Our study indicates that both MAPK and phosphatase play an important role for CIITA regulation in DC and macrophages.

Mechanism of triptolide-induced apoptosis: Effect on caspase activation and Bid cleavage and essentiality of the hydroxyl group of triptolide.

Triptolide is a compound extracted from the Chinese herb Tripterygium wilfordii Hook. f. Triptolide has potent anticancer activity. However, the mechanisms by which triptolide exerts its anticancer activities remain unclear. To explore the molecular mechanisms involved in the anticancer activity of triptolide, we have examined the effect of triptolide on the growth of pancreatic carcinoma PANC-1 and cervical adenocarcinoma HeLa cells. We found that treatment of both HeLa and PANC-1 cells with triptolide potently suppressed cell growth and induced apoptosis, indicated by nuclear fragmentation and blebbing. In both HeLa and PANC-1 cells, apoptosis induced by triptolide was associated with activation of both caspase-3 and caspase-8, and cleavage of poly(ADP-ribose) polymerase and Bid. Moreover, in HeLa cells, caspase-9 is also significantly activated in response to triptolide. Overexpression of Bcl-2 in HeLa cells substantially attenuated triptolide-induced apoptosis. Interestingly, substitution of the 14-OH of triptolide with an acetyl group abrogated both its anticancer and its antiinflammatory activities. Our studies suggest that triptolide may exert its anticancer effects by initiating apoptosis through both death-receptor- and mitochondria-mediated pathways. Our results indicate that both the apoptosis-promoting and the antiinflammatory activities of triptolide depend on the 14-OH group.

MAP kinase phosphatase 1 controls innate immune responses and suppresses endotoxic shock.

Septic shock is a leading cause of morbidity and mortality. However, genetic factors predisposing to septic shock are not fully understood. Excessive production of proinflammatory cytokines, particularly tumor necrosis factor (TNF)-alpha, and the resultant severe hypotension play a central role in the pathophysiological process. Mitogen-activated protein (MAP) kinase cascades are crucial in the biosynthesis of proinflammatory cytokines. MAP kinase phosphatase (MKP)-1 is an archetypal member of the dual specificity protein phosphatase family that dephosphorylates MAP kinase. Thus, we hypothesize that knockout of the Mkp-1 gene results in prolonged MAP kinase activation, augmented cytokine production, and increased susceptibility to endotoxic shock. Here, we show that knockout of Mkp-1 substantially sensitizes mice to endotoxic shock induced by lipopolysaccharide (LPS) challenge. We demonstrate that upon LPS challenge, Mkp-1-/- cells exhibit prolonged p38 and c-Jun NH2-terminal kinase activation as well as enhanced TNF-alpha and interleukin (IL)-6 production compared with wild-type cells. After LPS challenge, Mkp-1 knockout mice produce dramatically more TNF-alpha, IL-6, and IL-10 than do wild-type mice. Consequently, Mkp-1 knockout mice develop severe hypotension and multiple organ failure, and exhibit a remarkable increase in mortality. Our studies demonstrate that MKP-1 is a pivotal feedback control regulator of the innate immune responses and plays a critical role in suppressing endotoxin shock.