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-1beta (IL-1beta). We found that MMP-1 mRNA levels were maximal following 16 hours of IL-1beta stimulation and that this correlated with the expression of the transcription factor CCAAT enhancer-binding protein-beta (CEBPB). Knockdown of CEBPB expression with short hairpin RNA abrogated the expression of MMP-1, MMP-3, and MMP-10 in IL-1beta-stimulated A549 cells. An established CEBP element in the MMP-1 promoter was found to be required for basal and IL-1beta-induced transcription. Electrophoresis mobility shift assays showed that CEBPB binds to this promoter element maximally 16 hours after IL-1beta stimulation. DNA affinity chromatography studies showed that the LAP1, LAP2, and LIP isoforms of CEBPB bind to the IL-1beta-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 Thr(235) peaked at 16 hours in IL-1beta-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.