MKP-1: a negative feedback effector that represses MAPK-mediated pro-inflammatory signaling pathways and cytokine secretion in human airway smooth muscle cells.

Publication Type:
Journal Article
Citation:
Cellular signalling, 2012, 24 (4), pp. 907 - 913
Issue Date:
2012-04
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Airway smooth muscle (ASM) plays an important immunomodulatory role in airway inflammation in asthma. In our previous in vitro studies in ASM cells delineating the pro-inflammatory mitogen-activated protein kinase (MAPK) signaling pathways activated by tumor necrosis factor α (TNFα), we observed that TNFα concomitantly induces the rapid, but transient, upregulation of the anti-inflammatory protein-mitogen-activated protein kinase phosphatase 1 (MKP-1). As this was suggestive of a negative feedback loop, the aim of this study was to investigate the molecular mechanisms of MKP-1 upregulation by TNFα and to determine whether MKP-1 is a negative feedback effector that represses MAPK-mediated pro-inflammatory signaling pathways and cytokine secretion in ASM cells. Herein, we show that TNFα increases MKP-1 mRNA expression and protein upregulation in a p38 MAPK-dependent manner. TNFα does not increase MKP-1 transcription (measured by MKP-1 promoter activity); rather, we found that TNFα-induced MKP-1 mRNA stability is regulated by the p38 MAPK pathway. Inhibiting MKP-1 upregulation (with triptolide) demonstrated the precise temporal control exerted on MAPK signaling by MKP-1. In the absence of MKP-1, downstream phosphoprotein targets of MAPKs (such as MSK-1 and histone H3) are not turned off at the right time, allowing pro-inflammatory pathways to continue in an unrestrained manner. This is confirmed by knocking-down MKP-1 by siRNA where enhanced secretion of the neutrophil chemoattractant cytokine-interleukin 8 was detected in the absence of MKP-1. Thus, by activating p38 MAP kinase, TNFα concomitantly upregulates the MAPK deactivator MKP-1 to serve as an important negative feedback effector, limiting the extent and duration of pro-inflammatory MAPK signaling and cytokine secretion in ASM cells.
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