Inducible Nitric-oxide Synthase Expression Is Regulated by Mitogen-activated Protein Kinase Phosphatase-1

Xianxi Wang,Qun Zhao,Ranyia Matta,Xiaomei Meng,Xiuping Liu,Chang-Gong Liu,Leif D Nelin,Yusen Liu

doi:10.1074/jbc.m109.051235

Abstract

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.

Highlights

We have identified mitogen-activated protein (MAP) kinase phosphatase-1 (MKP-1) as a crucial negative regulator of the inflammatory response during bacterial infection
Upon LPS Challenge, mitogen-activated protein kinase phosphatase-1 (MKP-1) Knock-out Mice Exhibit Profoundly Greater MAP Kinase Activities and Inducible nitric-oxide (NO) synthase (iNOS) Expression Than Do Wild-type Mice—NO is an important mediator in host defense during microbial infection, serving as both a potent microbicide and a powerful vasodilator. iNOS is the primary producer of NO during sepsis
We found that iNOS was more robustly induced by LPS in MKP-1 knock-out mice than in wild-type mice and enhanced iNOS induction was associated with elevated activities of the MAP kinases (Fig. 1)

Summary

Introduction

We have identified mitogen-activated protein (MAP) kinase phosphatase-1 (MKP-1) as a crucial negative regulator of the inflammatory response during bacterial infection. At 24 h post-LPS challenge, markedly elevated levels of iNOS protein were observed in the lungs from both wild-type and MKP-1 knock-out mice (Fig. 1A). In the lungs iNOS mRNA levels were significantly increased after LPS treatment in both wild-type and MKP-1 knock-out mice (Fig. 2).

Results

Conclusion