Epidermal growth factor receptors (EGFRs) are inappropriately expressed or highly expressed in a variety of human tumors including breast, brain, prostate but also play a key role in normal cell growth and development. The critical role of EGFR in both normal and abnormal cell growth and development has lead to the development of therapeutic agents directed against the EGFR. Targeting the EGFR necessitates a clear understanding of the regulation of its' expression. We hypothesize that changes in transcription factors interacting with the EGFR promoter lead to increased expression in the absence of gene amplification. Our research focuses on two projects seeking to understand the factors that regulate EGFR expression during normal cell growth and in cancer. We seek to determine the transcription factors involved in EGFR gene regulation and to examine their role in cancer. We further seek to understand how GC-binding factor 2 (GCF2), a repressor of EGFR expression, decreases the activity of cellular and viral promoters.We characterized the EGFR promoter region as a GC-rich, TATA-less regulatory region and identified at least a dozen transcription factors that interact and effect changes in EGFR expression. These factors include well-characterized factors such as Sp1 and p53 and novel factors such as the transcriptional repressor GCF2. Recently we demonstrated that curcumin, the active ingredient of the rhizome of the plant turmeric (Curcuma longa Linn), suppressed the gene expression of EGFR in human colon cancer-derived cell lines, including Moser cells, Caco-2 and HT-29 cells. We utilized EGFR promoter deletions and site-directed mutagenesis to determine that the binding site for early growth response-1 (Egr-1) acted as a cis-activating element in regulating changes in the promoter activity associated with curcumin treatment in Moser cells. Gel shift assays and chromatin immuno-precipitation assays demonstrated that curcumin significantly reduced the DNA binding activity of Egr-1. We also showed that curcumin reduced the trans-activation activity of Egr-1 by suppressing its' gene expression and reducing the level of phosphorylated Egr-1, in which interruption of the ERK pathway was a necessity. Taken together, our results demonstrated that curcumin suppressed EGFR gene expression in colon cancer cells by reducing the trans-activating activity of Egr-1.We initially characterized GCF2 as a transcriptional repressor of the EGFR gene. We have also determined that GCF2 binds to a highly structured RNA element TAR (transactivation response element) that is located at the 5' end of nascent HIV transcripts. GCF2 inhibits activation of the HIV-1 LTR by a small regulatory protein, Tat, which is required for efficient transcription of genes linked to the HIV-1 LTR. We recently determined that GCF2 represses activation of the small GTPase RhoA by interacting with disheveled (Dvl). These findings implicate a role for GCF2 in the Wnt-noncanonical planar cell polarity pathway and possibly in cell migration or cytoskeleton development.
