Activation Of Mitogen-activated Protein Kinase Phosphatase-1 Research Articles

MPT0E028, a novel pan-HDAC inhibitor, prevents pulmonary fibrosis through inhibition of TGF-β-induced CTGF expression in human lung fibroblasts: Involvement of MKP-1 activation

Histone deacetylase (HDAC) inhibitors are potential candidates for treating pulmonary fibrosis. MPT0E028, a novel pan-HDAC inhibitor, has been reported to exhibit antitumor activity in several cancer cell lines. In this study, we investigated the mechanism underlying the inhibitory effects of MPT0E028 on the expression of fibrogenic proteins in human lung fibroblasts (WI-38). Our results revealed that MPT0E028 inhibited transforming growth factor-β (TGF-β)-, thrombin-, and endothelin 1-induced connective tissue growth factor (CTGF) expression in a concentration-dependent manner. In addition, MPT0E028 suppressed TGF-β-stimulated expression of fibronectin, collagen I, and α-smooth muscle actin (α-SMA). Furthermore, MPT0E028 inhibited the TGF-β-induced phosphorylation of c-Jun N-terminal kinase (JNK), p38, and extracellular signal-regulated kinase (ERK). MPT0E028 reduced the increase in SMAD3 and c-Jun phosphorylation, and SMAD3-and activator protein-1 (AP-1)-luciferase activities under TGF-β stimulation. Transfection with mitogen-activated protein kinase phosphatase-1 (MKP-1) siRNA reversed the suppressive effects of MPT0E028 on TGF-β-induced increases in CTGF expression; JNK, p38, and ERK phosphorylation; and SMAD3 and AP-1 activation. Moreover, MPT0E028 increased MKP-1 acetylation and activity in WI-38 cells. Pretreatment with MPT0E028 reduced the fibrosis score and fibronectin, collagen, and α-SMA expression in bleomycin-induced pulmonary fibrosis mice. In conclusion, MPT0E028 induced MKP-1 acetylation and activation, which in turn inhibited TGF-β-stimulated JNK, p38, and ERK phosphorylation; SMAD3 and AP-1 activation; and subsequent CTGF expression in human lung fibroblasts. Thus, MPT0E028 may be a potential drug for treating pulmonary fibrosis.

Dietary 23-hydroxy ursolic acid protects against diet-induced weight gain and hyperglycemia by protecting monocytes and macrophages against nutrient stress-triggered reprogramming and dysfunction and preventing adipose tissue inflammation

The aim of this study was to determine whether the atheroprotective phytochemical 23-hydroxy ursolic acid protects against diet-induced obesity and hyperglycemia by preventing nutrient stress-induced monocyte reprogramming. After a two week run-in period on a defined, phytochemical-free low-fat maintenance diet, 12-week old female C57BL/6J mice were either kept on the maintenance diet for additional 13 weeks or switched to either a high-calorie diet, a high-calorie diet supplemented with either 0.05% 23-hydroxy ursolic acid or a high-calorie diet supplemented with 0.2% 23-hydroxy ursolic acid. Dietary supplementation with 23-hydroxy ursolic acid reduced weight gain and adipose tissue mass, prevented hyperglycemia, hyperleptinemia and adipose tissue inflammation, and preserved glucose tolerance. 23-Hydroxy ursolic acid also preserved blood monocyte mitogen-activated protein kinase phosphatase-1 activity, a biomarker of monocyte health, and reduced macrophage content in the adipose tissue. Targeted gene profiling by qRT-PCR using custom-designed TaqMan® Array Cards revealed that dietary 23-hydroxy ursolic acid converts macrophages into a transcriptionally hyperactive phenotype with enhanced antioxidant defenses and anti-inflammatory potential. In conclusion, our findings show that dietary 23-hydroxy ursolic acid exerts both anti-obesogenic effects through multiple mechanisms. These include improving glucose tolerance, preventing hyperleptinemia, maintaining blood monocyte function, reducing recruitment of monocyte-derived macrophages into adipose tissues during nutrient stress, and converting these macrophages into an anti-inflammatory, potentially inflammation-resolving phenotype, all contributing to reduced adipose tissue inflammation. Our data suggest that 23-hydroxy ursolic acid may serve as an oral therapeutic and dietary supplement suited for patients at risk for obesity, impaired glucose tolerance and cardiovascular disease.

Effects of Glucocorticoid-Induced Transcript 1 Gene Deficiency on Glucocorticoid Activation in Asthmatic Mice.

Background:Glucocorticoid (GC) is the first-line therapy for asthma, but some asthmatics are insensitive to it. Glucocorticoid-induced transcript 1 gene (GLCCI1) is reported to be associated with GCs efficiency in asthmatics, while its exact mechanism remains unknown.Methods:A total of 30 asthmatic patients received fluticasone propionate for 12 weeks. Forced expiratory volume in 1 s (FEV1) and GLCCI1 expression were detected. Asthma model was constructed in wild-type and GLCCI1 knockout (GLCCI1-/-) mice. Glucocorticoid receptor (GR) and mitogen-activated protein kinase phosphatase 1 (MKP-1) expression were detected by polymerase chain reaction and Western blotting (WB). The phosphorylation of p38 mitogen-activated protein kinase (MAPK) was also detected by WB.Results:In asthmatic patients, the change of FEV1 was well positively correlated with change of GLCCI1 expression (r = 0.430, P = 0.022). In animal experiment, GR and MKP-1 mRNA levels were significantly decreased in asthmatic mice than in control mice (wild-type: GR: 0.769 vs. 1.000, P = 0.022; MKP-1: 0.493 vs. 1.000, P < 0.001. GLCCI1-/-: GR: 0.629 vs. 1.645, P < 0.001; MKP-1: 0.377 vs. 2.146, P < 0.001). Hydroprednisone treatment significantly increased GR and MKP-1 mRNA expression levels than in asthmatic groups; however, GLCCI1-/- asthmatic mice had less improvement (wild-type: GR: 1.517 vs. 0.769, P = 0.023; MKP-1: 1.036 vs. 0.493, P = 0.003. GLCCI1-/-: GR: 0.846 vs. 0.629, P = 0.116; MKP-1: 0.475 vs. 0.377, P = 0.388). GLCCI1-/- asthmatic mice had more obvious phosphorylation of p38 MAPK than wild-type asthmatic mice (9.060 vs. 3.484, P < 0.001). It was still higher even though after hydroprednisone treatment (6.440 vs. 2.630, P < 0.001).Conclusions:GLCCI1 deficiency in asthmatic mice inhibits the activation of GR and MKP-1 and leads to more obvious phosphorylation of p38 MAPK, leading to a decremental sensitivity to GCs.Trial Registration:ChiCTR.org.cn, ChiCTR-RCC-13003634; http://www.chictr.org.cn/showproj.aspx?proj=5926.

NSC 95397 Suppresses Proliferation and Induces Apoptosis in Colon Cancer Cells through MKP-1 and the ERK1/2 Pathway.

NSC 95397, a quinone-based small molecule compound, has been identified as an inhibitor for dual-specificity phosphatases, including mitogen-activated protein kinase phosphatase-1 (MKP-1). MKP-1 is known to inactivate mitogen-activated protein kinases by dephosphorylating both of their threonine and tyrosine residues. Moreover, owing to their participation in tumorigenesis and drug resistance in colon cancer cells, MKP-1 is an attractive therapeutic target for colon cancer treatment. We therefore investigated the inhibitory activity of NSC 95397 against three colon cancer cell lines including SW480, SW620, and DLD-1, and their underlying mechanisms. The results demonstrated that NSC 95397 reduced cell viability and anchorage-independent growth of all the three colon cancer cell lines through inhibited proliferation and induced apoptosis via regulating cell-cycle-related proteins, including p21, cyclin-dependent kinases, and caspases. Besides, by using mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) inhibitor U0126, we provided mechanistic evidence that the antineoplastic effects of NSC 95397 were achieved via inhibiting MKP-1 activity followed by ERK1/2 phosphorylation. Conclusively, our results indicated that NSC 95397 might serve as an effective therapeutic intervention for colon cancer through regulating MKP-1 and ERK1/2 pathway.

166 - 23-Hydroxy Ursolic Acid Protects Atherosclerosis-prone Mice from Monocyte Dysfunction

We showed that ursolic acid (UA), a pentacyclic triterpenoid with anti-inflammatory properties, reduces atherosclerotic lesion size and improves kidney function in diabetic mice. We proposed that the atheroprotective effects of UA are due to its ability to protect monocytes against metabolic stress-induced dysfunction or “priming”, i.e. the hyper-responsiveness to chemokine-induced cell adhesion and migration. Based on structure-function analyses of UA’s naturally occurring analogs, we identified and synthesized a compound, 23-hydroxy ursolic acid (23-OHUA), with a structural feature that we predicted to enhance both bioavailability and the protective effects of UA against monocyte dysfunction in vitro and in dyslipidemia atherosclerosis-prone mice. 23-OHUA protected monocytes from metabolic priming and dysfunction with a similar efficacy to UA. Both phytochemicals protected monocytes from metabolic stress by preventing the degradation of MAPK phosphatase-1 (MKP-1), a master regulator of monocyte chemotaxis and macrophage function. To test the efficacy of 23-OHUA in protecting mice against monocyte dysfunction and atherogenesis, we fed atherosclerosis-prone LDLR-/- mice a high fat diet (HFD) or a HFD supplemented with either 0.05% UA or 0.05% 23-OHUA. Monocytes were primed and hyper-sensitive to chemokines as early as 6 weeks after initiating HFD-feeding as shown by our in vivo chemotaxis assay. After 20 weeks, mice fed 23-OHUA showed 11% less weight gain compared to HFD-fed control mice and 40% reduced atherosclerotic plaque formation. Both dietary UA and 23-OHUA reduced metabolic priming and prevented the decrease in MKP-1 activity, suggesting that both compounds exert their anti-inflammatory, anti-obesogenic and anti-atherogenic effects through a novel but common mechanism involving the protection of blood monocytes against metabolic stress-induced priming and dysfunction. Our results suggest 23-OHUA and UA are viable candidates for dietary supplements for the prevention of chronic inflammatory diseases associated with metabolic disorders.

Regulation of mitogen-activated protein kinase by protein kinase C and mitogen-activated protein kinase phosphatase-1 in vascular smooth muscle

Vascular smooth muscle contraction is primarily regulated by phosphorylation of myosin light chain. There are also modulatory pathways that control the final level of force development. We tested the hypothesis that protein kinase C (PKC) and mitogen-activated protein (MAP) kinase modulate vascular smooth muscle activity via effects on MAP kinase phosphatase-1 (MKP-1). Swine carotid arteries were mounted for isometric force recording and subjected to histamine stimulation in the presence and absence of inhibitors of PKC [bisindolylmaleimide-1 (Bis)], MAP kinase kinase (MEK) (U0126), and MKP-1 (sanguinarine) and flash frozen for measurement of MAP kinase, PKC-potentiated myosin phosphatase inhibitor 17 (CPI-17), and caldesmon phosphorylation levels. CPI-17 was phosphorylated in response to histamine and was inhibited in the presence of Bis. Caldesmon phosphorylation levels increased in response to histamine stimulation and were decreased in response to MEK inhibition but were not affected by the addition of Bis. Inhibition of PKC significantly increased p42 MAP kinase, but not p44 MAP kinase. Inhibition of MEK with U0126 inhibited both p42 and p44 MAP kinase activity. Inhibition of MKP-1 with sanguinarine blocked the Bis-dependent increase of MAP kinase activity. Sanguinarine alone increased MAP kinase activity due to its effects on MKP-1. Sanguinarine increased MKP-1 phosphorylation, which was inhibited by inhibition of MAP kinase. This suggests that MAP kinase has a negative feedback role in inhibiting MKP-1 activity. Therefore, PKC catalyzes MKP-1 phosphorylation, which is reversed by MAP kinase. Thus the fine tuning of vascular contraction is due to the concerted effort of PKC, MAP kinase, and MKP-1.

WMJ-S-001, a novel aliphatic hydroxamate derivative, exhibits anti-inflammatory properties via MKP-1 in LPS-stimulated RAW264.7 macrophages.

Hydroxamate derivatives have attracted considerable attention because of their broad pharmacological properties. Recent studies reported their potential use in the treatment of cardiovascular diseases, arthritis and infectious diseases. However, the mechanisms of the anti-inflammatory effects of hydroxamate derivatives remain to be elucidated. In an effort to develop a novel pharmacological agent that could suppress abnormally activated macrophages, we investigated a novel aliphatic hydroxamate derivative, WMJ-S-001, and explored its anti-inflammatory mechanisms. RAW264.7 macrophages were exposed to LPS in the absence or presence of WMJ-S-001. COX-2 expression and signalling molecules activated by LPS were assessed. LPS-induced COX-2 expression was suppressed by WMJ-S-001. WMJ-S-001 inhibited p38MAPK, NF-κB subunit p65 and CCAAT/enhancer-binding protein (C/EBP)β phosphorylation in cells exposed to LPS. Treatment of cells with a p38MAPK inhibitor (p38MAPK inhibitor III) markedly inhibited LPS-induced p65 and C/EBPβ phosphorylation and COX-2 expression. LPS-increased p65 and C/EBPβ binding to the COX-2 promoter region was suppressed in the presence of WMJ-S-001. In addition, WMJ-S-001 suppression of p38MAPK, p65 and C/EBPβ phosphorylation, and subsequent COX-2 expression were restored in cells transfected with a dominant-negative (DN) mutant of MAPK phosphatase-1 (MKP-1). WMJ-S-001 also caused an increase in MKP-1 activity in RAW264.7 macrophages. WMJ-S-001 may activate MKP-1, which then dephosphorylates p38MAPK, resulting in a decrease in p65 and C/EBPβ binding to the COX-2 promoter region and COX-2 down-regulation in LPS-stimulated RAW264.7 macrophages. The present study suggests that WMJ-S-001 may be a potential drug candidate for alleviating LPS-associated inflammatory diseases.

Anti-inflammatory effects of glutamine on LPS-stimulated human dental pulp cells correlate with activation of MKP-1 and attenuation of the MAPK and NF-κB pathways.

To evaluate the anti-inflammatory effects of glutamine and the underlying signal pathway mechanisms in lipopolysaccharide (LPS)-stimulated human dental pulp cells (HDPCs). Human dental pulp cells were exposed to 10 μg mL(-1) LPS and various concentrations of glutamine for 24 h. The production of PGE2 and nitric oxide was determined by enzyme-linked immunosorbent assay (ELISA) and Griess reagent kit, respectively. Cytokines were examined by ELISA, reverse transcriptase-polymerase chain reaction (RT-PCR) and real-time PCR. iNOS and COX protein expression as well as signal pathways were accessed by Western blot. The data were analysed by anova with Bonferroni's test (α = 0.05). Glutamine reduced LPS-induced iNOS and COX-2 protein expression as well as production of NO and PGE2 in a dose-dependent fashion. Additionally, glutamine suppressed the production and mRNA expression of inflammatory cytokines including interleukin-1β (IL-1β), TNF-α, and IL-8. Furthermore, glutamine attenuated phosphorylation of extracellular signal-regulated kinase (ERK), p38, c-Jun N-terminal kinase (JNK) and IκB-α, and nuclear translocation of NF-κB p65, but enhanced mitogen-activated protein kinase phosphatase-1 (MKP-1) expression in LPS-treated HDPCs. Glutamine exerted an anti-inflammatory effect via activation of MKP-1 and inhibition of the NF-κB and MAPK pathways in LPS-treated HDPCs.

The water-soluble triptolide derivative PG490-88 protects against cisplatin-induced acute kidney injury.

Triptolide, a traditional Chinese medicine, has anti-inflammatory, antiproliferative, and proapoptotic properties. As interstitial inflammation and tubular apoptosis are features of cisplatin-induced acute kidney injury (AKI), we determined the effect of the water-soluble triptolide derivative 14-succinyl triptolide sodium salt (PG490-88) in a mouse model of cisplatin-induced AKI. PG490-88 resulted in a significant decrease in blood urea nitrogen (BUN), serum creatinine, and acute tubular necrosis (ATN) score, and a nonsignificant increase in tubular apoptosis score in AKI. The mitogen-activated protein kinase (MAPK) pathway is activated in AKI. On immunoblot analysis, phosphoextracellular signal-regulated kinase (p-ERK) was increased 3.6-fold in AKI and 2.0-fold inhibited by PG490-88. Phospho-c-Jun N-terminal kinase (p-JNK) was increased in AKI. PG490-88 resulted in a nonsignificant decrease in p-JNK. Phospho-p38 was not affected by cisplatin or PG490-88. MAPK phosphatase-1 (MKP-1) that negatively regulates MAPK signaling has not previously been studied in AKI. MKP-1 activity was not affected by cisplatin or PG490-88. Changes in p-ERK, p-JNK, and MKP-1 were confirmed on reverse protein phase analysis. The ERK inhibitor U0126 resulted in lower BUN and serum creatinine, suggesting a mechanistic role of ERK in AKI. The increase in interleukin-1α (IL-1α), IL-1β, IL-6, CXCL1, and IL-33 in the kidney in AKI was unaffected by PG490-88. In summary, PG490-88 protects against AKI and ATN despite no decrease in tubular apoptosis. The protection of PG490-88 against AKI was associated with a decrease in p-ERK and was independent of MKP-1 and proinflammatory cytokines. In conclusion, PG490-88 protects against cisplatin-induced AKI possibly by decreasing p-ERK.

Attenuation of TNF production and experimentally induced inflammation by PDE4 inhibitor rolipram is mediated by MAPK phosphatase‐1

3',5'-Cyclic nucleotide PDE4 is expressed in several inflammatory and immune cells, and PDE4 catalyses the hydrolysis of cAMP to 5'AMP, down-regulating cAMP signalling in cells. MAPK phosphatase-1 (MKP-1) is an endogenous p38 MAPK signalling suppressor and limits inflammatory gene expression and inflammation. In the present study, we investigated the effect of a PDE4 inhibitor rolipram on MKP-1 expression and whether MKP-1 is involved in the anti-inflammatory effects of rolipram. The effect of rolipram on TNF production was investigated in J774 mouse macrophage cell line and in primary mouse peritoneal macrophages (PM) from wild-type (WT) and MKP-1(-/-) mice. We also investigated the effect of rolipram on carrageenan-induced paw inflammation in WT and MKP-1(-/-) mice. MKP-1 expression was enhanced by rolipram, by a non-selective PDE inhibitor IBMX and by a cAMP analogue 8-Br-cAMP in J774 cells and in PM. Enhanced MKP-1 mRNA expression by rolipram was reversed by a PKA inhibitor. Rolipram, IBMX and 8-Br-cAMP also inhibited TNF production in activated macrophages. Accordingly, rolipram inhibited TNF production in PMs from WT mice but, interestingly, not in PMs from MKP-1(-/-) mice. Furthermore, rolipram attenuated carrageenan-induced paw inflammation in WT but not in MKP-1(-/-) mice. PDE4 inhibitor rolipram was found to enhance the expression of MKP-1, and MKP-1 mediated, at least partly, the anti-inflammatory effects of PDE4 inhibition. The results suggest that compounds that enhance MKP-1 expression and/or MKP-1 activity hold potential as novel anti-inflammatory drugs.

Mitogen-Activated Protein Kinase Phosphatase (MKP)-1 as a Neuroprotective Agent: Promotion of the Morphological Development of Midbrain Dopaminergic Neurons

A greater understanding of the mechanisms that promote the survival and growth of dopaminergic neurons is essential for the advancement of cell replacement therapies for Parkinson's disease (PD). Evidence supports a role for the mitogen-activated protein kinase p38 in the demise of dopaminergic neurons, while mitogen-activated protein kinase phosphatase-1 (MKP-1), which negatively regulates p38 activity, has not yet been investigated in this context. Here, we show that MKP-1 is expressed in dopaminergic neurons cultured from E14 rat ventral mesencephalon (VM). When dopaminergic neurons were transfected to overexpress MKP-1, they displayed a more complex morphology than their control counterparts in vitro. Specifically, MKP-1-transfection induced significant increases in neurite length and branching with a maximum increase observed in primary branches. We demonstrate that inhibition of dopaminergic neurite growth induced by treatment of rat VM neurons with the dopaminergic neurotoxin 6-hydroxydopamine (6-OHDA) in vitro is mediated by p38 and is concomitant with a significant and selective decrease in MKP-1 expression in these neurons. We further show that overexpression of MKP-1 in dopaminergic neurons contributes to neuroprotection against the effects of 6-OHDA. Collectively, we report that MKP-1 can promote the growth and elaboration of dopaminergic neuronal processes and can help protect them from the neurotoxic effects of 6-OHDA. Thus, we propose that strategies aimed at augmenting MKP-1 expression or activity may be beneficial in protecting dopaminergic neurons and may provide potential therapeutic approaches for PD.

Differences in oxidative stress status and expression of MKP-1 in dorsal medulla of transgenic rats with altered brain renin-angiotensin system

ANG II-stimulated production of reactive oxygen species (ROS) through NADPH oxidase is suggested to activate MAPK pathways, which are implicated in neurally mediated pressor effects of ANG II. Emerging evidence suggests that ANG-(1-7) up regulates MAPK phosphatases to reduce MAPK signaling and attenuate actions of ANG II. Whether angiotensin peptides participate in long-term regulation of these systems in the brain is not known. Therefore, we determined tissue and mitochondrial ROS, as well as expression and activity of MAPK phosphatase-1 (MKP-1) in brain dorsal medullary tissue of hypertensive transgenic (mRen2)27 rats exhibiting higher ANG II/ANG-(1-7) tone or hypotensive transgenic rats with targeted decreased glial expression of angiotensinogen, ASrAOGEN (AS) exhibiting lower ANG II/ANG-(1-7) tone compared with normotensive Sprague-Dawley (SD) rats that serve as the control strain. Transgenic (mRen2)27 rats showed higher medullary tissue NADPH oxidase activity and dihydroethidium fluorescence in isolated mitochondria vs. SD or AS rats. Mitochondrial uncoupling protein 2 was lower in AS and unchanged in (mRen2)27 compared with SD rats. MKP-1 mRNA and protein expression were higher in AS and unchanged in (mRen2)27 compared with SD rats. AS rats also had lower phosphorylated ERK1/2 and JNK consistent with higher MKP-1 activity. Thus, an altered brain renin-angiotensin system influences oxidative stress status and regulates MKP-1 expression. However, there is a dissociation between these effects and the hemodynamic profiles. Higher ROS was associated with hypertension in (mRen2)27 and normal MKP-1, whereas the higher MKP-1 was associated with hypotension in AS, where ROS was normal relative to SD rats.

MKP-1 antagonizes C/EBP β activity and lowers the apoptotic threshold after ischemic injury

The dual specificity phosphatase MAPK phosphatase-1 (MKP-1) feeds back on MAP kinase signaling to regulate metabolic, inflammatory and survival responses. MKP-1 is widely expressed in the central nervous system (CNS) and induced after ischemic stress, although its function in these contexts remains unclear. Here we report that MKP-1 activated several cell death factors, including BCL2 and adenovirus E1B 19 kDa interacting protein 3, and caspases 3 and 12 culminating in apoptotic cell death in vitro. MKP-1 also exerted inhibitory effects on the bZIP transcription factor CCAAT/enhancer-binding protein (C/EBPβ), previously shown to have neuroprotective properties. These effects included reduced expression of the full-length C/EBPβ variant and hypo-phosphorylation at the MEK-ERK1/2-sensitive Thr(188) site. Notably, enforced expression C/EBPβ rescued cells from MKP-1-induced toxicity. Studies performed in knock-out mice indicate that the MKP-1 activity is required to exclude C/EBPβ from the nucleus basally, and that MKP-1 antagonizes C/EBPβ expression after global forebrain ischemia, particularly within the vulnerable CA1 sector of the hippocampus. Overall, MKP-1 appears to lower the cellular apoptotic threshold by inhibiting C/EBPβ and enhancing both BH3 protein expression and cellular caspase activity. Thus, although manipulation of the MKP-1-C/EBPβ axis could have therapeutic value in ischemic disorders, our observations using MKP-1 catalytic mutants suggest that approaches geared towards inhibiting MKP-1's phosphatase activity alone may be ineffective.

S-Nitrosylation of mitogen activated protein kinase phosphatase-1 suppresses radiation-induced apoptosis

Radiotherapy is a key modality for head and neck cancer (HNC) treatment. Mitogen activated protein kinase phosphatase-1 (MKP-1) protein levels are elevated in various tumors and are negatively correlated with efficacy of chemo- or radio-therapy. However, the mechanisms underlying the moderate radiosensitivity of HNC and the increased MKP-1 protein levels are still dismal. Here we show that S-nitrosylation of MKP-1 on Cysteine 258 enhances MKP-1 protein stability, phosphatase activity, and MKP-1-mediated anti-apoptotic effect on HNC radiotherapy. Co-culturing MKP-1 transfected HNC cell lines with activated macrophages for mimicking the microenvironment of the irradiated cancer cells further confirms that S-nitrosylation-mediated increase of MKP-1 activity correlates with decrease of HNC radiosensitivity. Therefore, S-nitrosylation of MKP-1 presents a novel mechanism underlying the enhanced MKP-1 expression levels and MKP-1-mediated radio-resistance in head and neck cancer.

Abstract 3838: Mitogen-activated protein kinase phosphatase-1 deficiency increases susceptibility to 4-nitroquinoline 1-oxide-induced neoplasia in murine squamous oral epithelium

Abstract Background: Cytokines and pro-inflammatory factors have critical roles in shaping the malignant transformation that gives rise to head and neck squamous cell carcinoma (HNSCC). Mitogen-activated protein kinases (MAPKs), such as p38, JNK, and ERK, relay information from extracellular signals to control the diverse cellular processes of carcinogenesis. These kinases are negatively regulated by MAPK phosphatases (MKPs), the founding member being mitogen-activated protein kinase phosphatase-1 (MKP-1). Initial studies demonstrated significant over-expression of MKP-1 in human epithelial tumors only in the early phases of disease with levels falling progressively in tumors of higher histological grade and in metastases. We hypothesize low levels of MKP-1 in the HNSCC tumor microenvironment generate high levels of inflammation which promote tumor development and progression. Methods: To address how regulation of inflammatory cytokine expression via MKP-1 activity may affect HNSCC development and progression, we examined the effects of MKP-1 deficiency on a well characterized model for oral squamous cell carcinoma (OSCC), a subset of HNSCC. MKP-1-/- and wild-type mice were treated with 4-nitroquinoline 1-oxide (4NQO), a surrogate for tobacco exposure, in drinking water for 16 weeks and monitored by oral examination for an additional 16 weeks. Tumor size was assessed by volumetric measurement. Histological grading of the tumors and inflammation were performed in a blinded manner by two collaborating pathologists. Results: Our studies demonstrated significantly earlier onset of 4NQO-induced OSCC in MKP-1-/- mice compared with wild-type controls. Tumor size and histological grade were found to be more severe in the MKP-1-/- mice. In addition, tissues surrounding the tumors demonstrated a significantly higher degree of inflammation in MKP-1-/- mice. Remarkably, development of esophageal squamous carcinomas was dramatically enhanced in MKP-1-/- mice treated with 4NQO. Conclusion: These studies demonstrate increased susceptibility of MKP-1-/- mice to 4NQO-induced neoplasia, suggesting an important role for MKP-1 as a negative regulator of HNSCC development. Further work will be done to characterize mechanisms of regulation by assessing levels of MAPK activity and characterizing the pro- and anti-inflammatory milieu of the tumor tissues and supportive stroma. Elucidating the regulation of inflammatory mediators in the tumor microenvironment may reveal critical tumor suppressive interactions mediated by MKP-1 which are lost during cancer initiation and progression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3838. doi:10.1158/1538-7445.AM2011-3838

Regulation of JNK activity in the apoptotic response of intestinal epithelial cells

We have studied apoptosis of gastrointestinal epithelial cells by examining the receptor-mediated and DNA damage-induced pathways using TNF-α and camptothecin (CPT), respectively. TNF-α requires inhibition of antiapoptotic protein synthesis by cycloheximide (CHX). CHX also results in high levels of active JNK, which are necessary for TNF-induced apoptosis. While CPT induces apoptosis, the increase in JNK activity was not proportional to the degree of apoptosis. Thus the mechanism of activation of JNK and its role in apoptosis are unclear. We examined the course of JNK activation in response to a combination of TNF-α and CPT (TNF + CPT), which resulted in a three- to fourfold increase in apoptosis compared with CPT alone, indicating an amplification of apoptotic signaling pathways. TNF + CPT caused apoptosis by activating JNK, p38, and caspases-8, -9, and -3. TNF-α stimulated a transient phosphorylation of JNK1/2 and ERK1/2 at 15 min, which returned to basal by 60 min and remained low for 4 h. CPT increased JNK1/2 activity between 3 and 4 h. TNF + CPT caused a sustained and robust JNK1/2 and ERK1/2 phosphorylation by 2 h, which remained high at 4 h, suggesting involvement of MEKK4/7 and MEK1, respectively. When administered with TNF + CPT, SP-600125, a specific inhibitor of MEKK4/7, completely inhibited JNK1/2 and decreased apoptosis. However, administration of SP-600125 at 1 h after TNF + CPT failed to prevent JNK1/2 phosphorylation, and the protective effect of SP-600125 on apoptosis was abolished. These results indicate that the persistent activation of JNK might be due to inhibition of JNK-specific MAPK phosphatase 1 (MKP1). Small interfering RNA-mediated knockdown of MKP1 enhanced TNF + CPT-induced activity of JNK1/2 and caspases-9 and -3. Taken together, these results suggest that MKP1 activity determines the duration of JNK1/2 and p38 activation and, thereby, apoptosis in response to TNF + CPT.

Curcumin Protects Intestinal Mucosal Barrier Function of Rat Enteritis via Activation of MKP-1 and Attenuation of p38 and NF-κB Activation

BackgroundIntestinal mucosa barrier (IMB) dysfunction results in many notorious diseases for which there are currently few effective treatments. We studied curcumin's protective effect on IMB and examined its mechanism by using methotrexate (MTX) induced rat enteritis model and lipopolysaccharide (LPS) treated cell death model.Methodology/Principal FindingsCurcumin was intragastrically administrated from the first day, models were made for 7 days. Cells were treated with curcumin for 30 min before exposure to LPS. Rat intestinal mucosa was collected for evaluation of pathological changes. We detected the activities of D-lactate and diamine oxidase (DAO) according to previous research and measured the levels of myeloperoxidase (MPO) and superoxide dismutase (SOD) by colorimetric method. Intercellular adhesion molecule-1 (ICAM-1), tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β) were determined by RT-PCR and IL-10 production was determined by ELISA. We found Curcumin decreased the levels of D-lactate, DAO, MPO, ICAM-1, IL-1β and TNF-α, but increased the levels of IL-10 and SOD in rat models. We further confirmed mitogen-activated protein kinase phosphatase-1 (MKP-1) was activated but phospho-p38 was inhibited by curcumin by western blot assay. Finally, NF-κB translocation was monitored by immunofluorescent staining. We showed that curcumin repressed I-κB and interfered with the translocation of NF-κB into nucleus.Conclusions/SignificanceThe effect of curcumin is mediated by the MKP-1-dependent inactivation of p38 and inhibition of NF-κB-mediated transcription. Curcumin, with anti-inflammatory and anti-oxidant activities may be used as an effective reagent for protecting intestinal mucosa barrier and other related intestinal diseases.

MKP-1 inhibits high NaCl-induced activation of p38 but does not inhibit the activation of TonEBP/OREBP: Opposite roles of p38α and p38δ

High NaCl rapidly activates p38 MAPK by phosphorylating it, the phosphorylation presumably being regulated by a balance of kinases and phosphatases. Kinases are known, but the phosphatases are uncertain. Our initial purpose was to identify the phosphatases. We find that in HEK293 cells transient overexpression of MAPK phosphatase-1 (MKP-1), a dual-specificity phosphatase, inhibits high NaCl-induced phosphorylation of p38, and that overexpression of a dominant negative mutant of MKP-1 does the opposite. High NaCl lowers MKP-1 activity by increasing reactive oxygen species, which directly inhibit MKP-1, and by reducing binding of MKP-1 to p38. Because inhibition of p38 is reported to reduce hypertonicity-induced activation of the osmoprotective transcription factor, TonEBP/OREBP, we anticipated that MKP-1 expression might also. However, overexpression of MKP-1 has no significant effect on Ton EBP/OREBP activity. This paradox is explained by opposing effects of p38alpha and p38delta, both of which are activated by high NaCl and inhibited by MKP-1. Thus, we find that overexpression of p38alpha increases high NaCl-induced TonEBP/OREBP activity, but overexpression of p38delta reduces it. Also, siRNA-mediated knockdown of p38delta enhances the activation of TonEBP/OREBP. We conclude that high NaCl inhibits MKP-1, which contributes to the activation of p38. However, opposing actions of p38alpha and p38delta negate any effect on TonEBP/OREBP activity. Thus, activation of p38 isoforms by hypertonicity does not contribute to activation of TonEBP/OREBP because of opposing effects of p38alpha and p38delta, and effects of inhibitors of p38 depend on which isoform is affected, which can be misleading.

Astragali Radix elicits anti-inflammation via activation of MKP-1, concomitant with attenuation of p38 and Erk

Although Astragali Radix (Astragalus, AR), the root of Astragalus membranaceus (Fisch) Bunge, is widely used in oriental medicine for tonifying the immune response and improving circulation, the underlying mechanism(s) by which these effects are induced remains unclear. Here, we report that AR displays anti-inflammatory effects in zymosan air–pouch mice by reducing the expression of iNOS, COX-2, IL-6, IL-1β and TNF-α and by decreasing the production of nitric oxide (NO). In a similar manner, AR reduces the expression of IL-6, iNOS, and COX-2 in lipopolysaccharide (LPS)-treated Raw 264.7 cells. We further demonstrate that AR attenuates the activity of p38 and Erk1/2 and stimulates mitogen-activated protein kinase phosphatase-1 (MKP-1) in LPS-treated Raw 264.7 cells. Additionally, AR interferes with the translocation of NFκB to the nucleus, subsequently resulting in NFκB-dependent transcriptional repression. Taken together, these data reveal that AR has an anti-inflammatory effect that is mediated by the MKP-1-dependent inactivation of p38 and Erk1/2 and inhibition of NFκB-mediated transcription. These results imply that the AR herb has a potential anti-inflammatory activity.

Role of MAPK Phosphatase-1 in the Induction of Monocyte Chemoattractant Protein-1 during the Course of Adipocyte Hypertrophy

Monocyte chemoattractant protein-1 (MCP-1), an important chemokine whose expression is increased during the course of obesity, plays a role in macrophage infiltration into obese adipose tissue. This study was designed to elucidate the role of mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1) in the induction of MCP-1 during the course of adipocyte hypertrophy. We examined the time course of MKP-1 and MCP-1 mRNA expression and extracellular signal-regulated kinase (ERK) phosphorylation in the adipose tissue from mice rendered mildly obese by a short term high fat diet. We also studied the role of MKP-1 in the induction of MCP-1 in 3T3-L1 adipocytes during the course of adipocyte hypertrophy. MCP-1 mRNA expression was increased, followed by ERK activation and down-regulation of MKP-1, an inducible dual specificity phosphatase to inactivate ERK, in the adipose tissue at the early stage of obesity induced by a short term high fat diet, when macrophages are not infiltrated. Down-regulation of MKP-1 preceded ERK activation and increased production of MCP-1 in 3T3-L1 adipocytes in vitro during the course of adipocyte hypertrophy. Adenovirus-mediated restoration of MKP-1 in hypertrophied 3T3-L1 adipocytes reduced the otherwise increased ERK phosphorylation, thereby leading to the significant reduction of MCP-1 mRNA expression. This study provides evidence that the down-regulation of MKP-1 is critical for increased production of MCP-1 during the course of adipocyte hypertrophy.