Rac1, a small GTPase, regulates macrophage MMP (matrix metalloproteinase)-9 in an ERK (extracellular-signal-regulated kinase)- and SP (specificity protein)-1-dependent manner. SP-1 contains a PEST (Pro-Glu-Ser-Thr) domain that may modulate protein stability. We hypothesize that Thr578, Ser586 and/or Ser587 in the PEST domain are required for SP-1 stability and MMP-9 expression secondary to activation of ERK, a serine/threonine kinase. We determined the effects of Rac1 and ERK on MMP-9 expression driven by SP-1WT (wild-type) and the SP-1 mutants T578A, S586A and S587A. Expression of WT and mutant SP-1 increased MMP9 promoter activity in alveolar macrophages. However, constitutively active Rac1 suppressed MMP9 promoter activity in cells expressing SP-1WT, SP-1T578A and SP-1S587A, but not SP-1S586A. Furthermore, constitutive ERK activation, which was inhibited by Rac1, significantly increased MMP9 transcription in cells expressing SP-1WT, but not SP-1S586A. As Rac1 activation and ERK inactivation increased degradation of SP-1WT and not SP-1S586A, the results of the present study suggest that SP-1 stability mediated at Ser586 regulates MMP9 transcription. Ex vivo, alveolar macrophages obtained from patients with asbestosis had less MMP-9 expression that was associated with decreased SP-1 expression and ERK activation. These observations demonstrate that Ser586 in the PEST domain of SP-1 is important for MMP9 gene expression in alveolar macrophages and highlight the importance of these proteins in pulmonary fibrosis.
Research Article| June 27 2012
SP-1 regulation of MMP-9 expression requires Ser586 in the PEST domain
Alan J. Ryan;
A. Brent Carter
A. Brent Carter 1
*Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, IA 52242, U.S.A.
†Department of Free Radical and Radiation Biology, University of Iowa Carver College of Medicine, Iowa City, IA 52242, U.S.A.
‡Department of Human Toxicology, College of Public Health, University of Iowa, Iowa City, IA 52242, U.S.A.
§Iowa City Veterans Affairs Medical Center, Iowa City, IA 52242, U.S.A.
1To whom correspondence should be addressed (email email@example.com).
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Shubha Murthy, Alan J. Ryan, A. Brent Carter; SP-1 regulation of MMP-9 expression requires Ser586 in the PEST domain. Biochem J 15 July 2012; 445 (2): 229–236. doi: https://doi.org/10.1042/BJ20120053
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