Tumor necrosis factor-alpha induced expression of matrix metalloproteinase-9 through p21-activated Kinase-1

Ling Zhou,Chunli Yan,Yuan-Ping Han,Roben G Gieling,Yujiro Kida,Warren Garner,Wei Li

doi:10.1186/1471-2172-10-15

Abstract

BackgroundExpressed in embryonic development, matrix metalloprotein-9 (MMP-9) is absent in most of developed adult tissues, but recurs in inflammation during tissue injury, wound healing, tumor formation and metastasis. Expression of MMP-9 is tightly controlled by extracellular cues including pro-inflammatory cytokines and extracellular matrix (ECM). While the pathologic functions of MMP-9 are evident, the intracellular signaling pathways to control its expression are not fully understood. In this study we investigated mechanism of cytokine induced MMP-9 with particular emphasis on the role of p21-activated-kinase-1 (PAK1) and the down stream signaling.ResultsIn response to TNF-alpha or IL-1alpha, PAK1 was promptly activated, as characterized by a sequential phosphorylation, initiated at threonine-212 followed by at threonine-423 in the activation loop of the kinase, in human skin keratinocytes, dermal fibroblasts, and rat hepatic stellate cells. Ectopic expression of PAK1 variants, but not p38 MAP kinase, impaired the TNF-alpha-induced MMP-9 expression, while other MMPs such as MMP-2, -3 and -14 were not affected. Activation of Jun N-terminal kinase (JNK) and NF-kappaB has been demonstrated to be essential for MMP-9 expression. Expression of inactive PAK1 variants impaired JNK but not NF-kappaB activation, which consequently suppressed the 5'-promoter activities of the MMP-9 gene. After the cytokine-induced phosphorylation, both ectopically expressed and endogenous PAK1 proteins were promptly accumulated even in the condition of suppressing protein synthesis, suggesting the PAK1 protein is stabilized upon TNF-alpha stimulation. Stabilization of PAK1 protein by TNF-alpha treatment is independent of the kinase catalytic activity and p21 GTPase binding capacities. In contrast to epithelial cells, mesenchymal cells require 3-dimensional type-I collagen in response to TNF-alpha to massively express MMP-9. The collagen effect is mediated, in part, by boost JNK activation in a way to cooperate the cytokine signaling.ConclusionWe identified a novel mechanism for MMP-9 expression in response to injury signals, which is mediated by PAK1 activation and stabilization leading JNK activation.

Highlights

Expressed in embryonic development, matrix metalloprotein-9 (MMP-9) is absent in most of developed adult tissues, but recurs in inflammation during tissue injury, wound healing, tumor formation and metastasis
Generation of active matrix metalloproteinases (MMPs)-9 within tissues is tightly monitored at the levels of gene expression, protein processing, and antagonization by inhibitors targeting at either proMMP-9 or converting enzyme
JNK1 is likely to be a downstream effector of PAK1 as demonstrated previously by others [22], and we showed here such moiety in the TNF-α signaling to control MMP-9 expression

Summary

Introduction

Matrix metalloprotein-9 (MMP-9) is absent in most of developed adult tissues, but recurs in inflammation during tissue injury, wound healing, tumor formation and metastasis. Expression of MMP-9 is tightly controlled by extracellular cues including pro-inflammatory cytokines and extracellular matrix (ECM). Degradation of extracellular matrix (ECM), as mediated by matrix metalloproteinases (MMPs) and antagonized by tissue inhibitors of matrix metalloproteinases (TIMPs), is critical for embryonic development and adult tissue homeostasis [1,2]. Not expressed in most of adult developed tissues, MMP-9 is promptly expressed in response to tissue damages under the control of pro-inflammatory cytokines [6,7]. We uncovered alpha-1antichymotrypsin (alpha-ACT) as a novel pathological inhibitor that directly antagonizes the proMMP-9 converting enzyme in skin tissues [9]. Generation of active MMP-9 within tissues is tightly monitored at the levels of gene expression, protein processing, and antagonization by inhibitors targeting at either proMMP-9 (by TIMP-1) or converting enzyme (by alpha-ACT)

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Conclusion