CCAAT enhancer binding protein-β regulates matrix metalloproteinase-1 expression in interleukin-1β-stimulated A549 lung carcinoma cells

Abstract

Matrix metalloproteinase-1 (MMP-1) is an inflammation-inducible neutral protease that mediates extracellular matrix remodeling and promotes tumor invasion. In this study, we examined the activation of MMP-1 gene expression in A549 lung carcinoma cells stimulated with the inflammatory cytokine interleukin-1β (IL-1β). We found that MMP-1 mRNA levels were maximal following 16 hours of IL-1β stimulation and that this correlated with the expression of the transcription factor CCAAT enhancer-binding protein-β (CEBPB). Knockdown of CEBPB expression with short hairpin RNA abrogated the expression of MMP-1, MMP-3, and MMP-10 in IL-1β-stimulated A549 cells. An established CEBP element in the MMP-1 promoter was found to be required for basal and IL-1β-induced transcription. Electrophoresis mobility shift assays showed that CEBPB binds to this promoter element maximally 16 hours after IL-1β stimulation. DNA affinity chromatography studies showed that the LAP1, LAP2, and LIP isoforms of CEBPB bind to the IL-1β-responsive CEBPB site in the MMP-1 promoter. Exogenous expression of the LAP1 and LAP2 isoforms stimulated the MMP-1 promoter, whereas LIP had no effect. Phosphorylation of CEBPB at Thr235 peaked at 16 hours in IL-1β-stimulated cells. The MEK inhibitor U0126 inhibited this phosphorylation and reduced MMP-1 gene induction. These studies establish CEBPB as an important mediator of metalloproteinase gene activation during inflammatory responses in lung cancer cells and highlight the different regulatory roles of CEBPB isoforms. Copyright © 2009 American Association for Cancer Research.