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SP-1 regulation of MMP-9 expression requires Ser586 in the PEST domain

Shubha Murthy1, Alan J Ryan, A Brent Carter

  • 1Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, IA 52242, USA.

The Biochemical Journal
|April 24, 2012
PubMed

Insights

Rac1 and ERK signaling impact matrix metalloproteinase-9 (MMP-9) expression in macrophages. Serine 586 in SP-1 is crucial for MMP-9 gene expression and protein stability, particularly in pulmonary fibrosis.

Area of Science:

  • Cellular and Molecular Biology
  • Pulmonary Medicine
  • Biochemistry

Background:

  • Rac1, a small GTPase, influences macrophage matrix metalloproteinase-9 (MMP-9) expression.
  • This regulation is dependent on extracellular-signal-regulated kinase (ERK) and specificity protein-1 (SP-1).
  • SP-1 has a PEST domain, suggesting a role in protein stability.

Purpose of the Study:

  • To investigate the role of specific sites within the SP-1 PEST domain (Thr578, Ser586, Ser587) in SP-1 stability and MMP-9 expression.
  • To determine how Rac1 and ERK signaling affect MMP-9 expression mediated by wild-type (SP-1WT) and mutant SP-1.
  • To explore the relevance of these pathways in alveolar macrophages from patients with asbestosis.

Main Methods:

  • Utilized wild-type (SP-1WT) and mutant SP-1 constructs (T578A, S586A, S587A) in alveolar macrophage models.
  • Assessed MMP-9 promoter activity under conditions of Rac1 and ERK activation/inhibition.
  • Examined protein degradation of SP-1 variants.
  • Analyzed ex vivo alveolar macrophages from asbestosis patients.

Main Results:

  • Expression of both WT and mutant SP-1 increased MMP9 promoter activity.
  • Constitutively active Rac1 suppressed MMP9 promoter activity for SP-1WT, SP-1T578A, and SP-1S587A, but not SP-1S586A.
  • Constitutive ERK activation increased MMP9 transcription for SP-1WT but not SP-1S586A; Rac1 inhibited ERK.
  • Rac1 activation and ERK inactivation accelerated SP-1WT degradation, but not SP-1S586A degradation.
  • Alveolar macrophages from asbestosis patients showed reduced MMP-9, SP-1, and ERK activation.

Conclusions:

  • SP-1 stability, specifically at Ser586 within its PEST domain, is critical for regulating MMP-9 transcription.
  • Rac1 and ERK signaling pathways converge on SP-1 stability to control MMP-9 expression in alveolar macrophages.
  • These findings highlight the significance of the SP-1 Ser586 site in pulmonary fibrosis pathogenesis.

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