Epidermal growth factor receptors (EGFR) play an important role in cell growth and development. Signaling from the EGFR has many effects including cell growth and division, proliferation and angiogenesis. EGFRs are inappropriately expressed or highly expressed in a variety of human tumors including breast, brain, prostate and others. Overexpression of the EGFR has been associated with advanced tumor stage, resistance to standard therapies and, in some tumors, with poor patient prognosis. 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 leads 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 initially characterized the EGFR promoter region as a GC-rich, TATA-less regulatory region with multiple transcription initiation sites and specificity protein 1 (Sp1) binding sites. Many DNA-binding factors have been identified that interact with the promoter region including p53, activator protein 1 (AP1), AP2 and interferon regulated factor 1 (IRF-1). We found that the p53 homologue, p63, repressed EGFR expression through protein-protein interactions with Sp1, an activator of EGFR expression. Egr-1 was determined to increase endogenous EGFR expression. Furthermore, we were able to show that upregulation of egr-1 during hypoxia leads to increased EGFR expression. 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. EGFR promoter deletions and site-directed mutagenesis indicated that the binding site for the transcription factor early growth response-1 (Egr-1) in the promoter of EGFR gene acted as a cis-activating element in regulating the promoter activity of the gene in Moser cells. Gel shift assays and chromatin immuno-precipitation assays demonstrated that curcumin significantly reduced the DNA binding activity of the transcription factor Egr-1. Further studies showed that curcumin reduced the trans-activation activity of Egr-1 by suppressing the 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 have cloned and characterized GCF2, a transcriptional repressor. We have determined the GCF2 binding site in the EGFR promoter and shown that GCF2 can partially inhibit AP2 activation of EGFR promoter activity. In addition, we have shown that GCF2 was able to bind 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 further determined that the amino terminal region of GCF2 was required to repress the Tat-mediated enhancement of the HIV-1 LTR and that GCF2 can also decrease basal HIV-1 LTR activity. We have also identified two additional members of the GCF2 family, GCF2-SK (skeletal muscle) and GCF2-SM (smooth muscle). ?
