Inhibition of MMP-9 mRNA expression by EGR-1. The HT1080 fibrosarcoma cells were treated with different doses of EGF for (A) 0.5 hours or (B) 18 hours. Total RNA was extracted and the subjected to RT-PCR to quantify EGR-1 and MMP-9 expression, respectively. (C) pCMV6-XL5-EGR-1 (2 μg) or empty vector pCDNA3.1 (2 μg) was transiently transfected as described in “Transient transfections and luciferase assays.” Cells were either not stimulated or stimulated with recombinant human tumor necrosis factor α (50 ng/mL) for 18 hours. HT1080 cells were collected, total RNA was extracted and then subjected to RT-PCR to quantify MMP-9 expression. Densitometry was conducted for MMP-9 and the results are presented normalized relative to GAPDH expression. (D) Levels of MT1-MMP transcripts are shown as a specificity control. Results are representative of 3 independent experiments. Bars represent SD; *P ≤ .05.