Transcriptional Regulation of EGR1 by EGF and the ERK Signaling Pathway in Prostate Cancer Cells

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The early growth response gene 1, EGR1, is an important transcriptional regulator and acts as the convergent point between a variety of extracellular stimuli and activation of target genes. Unlike other tumor types, prostate tumors express high levels of EGR1 relative to normal tissues. However, the mechanism of EGR1 regulation in prostate tumor cells is unknown. As EGR1 expression and epidermal growth factor (EGF) signaling are frequently upregulated in prostate tumors, we tested the hypothesis that EGF induces EGR1 expression in prostate cancer cells. Using RT-PCR to quantify EGR1 transcripts, we found that EGF induced EGR1 expression in a dose- and time-dependent manner and the ERK pathway inhibitor, PD98059, abrogated the EGF-mediated EGR1 response in LNCaP and PC3 cells. Analysis of the EGR1 promoter using deletion constructs identified an EGF-responsive region in the proximal promoter (-771 to -245 bp) containing 3 potential serum response element (SRE) sites. In vivo chromatin immunoprecipitation assays demonstrated that Elk-1 binding at the SRE sites of the EGR1 promoter was enhanced by EGF treatment in PC3 cells. Overexpression of Elk-1 was sufficient to activate the EGF-responsive region of EGR1 promoter in PC3 cells and, similarly, a dominant-negative Elk-1 suppressed EGR1 promoter activity. Taken together, these results demonstrate for the first time that EGR1 expression in PC3 cells is mediated through an EGF-ERK-Elk-1 signaling cascade.