Epidermal growth factor receptor (EGFR) is critically involved in the genesis and progression of human cancers and is considered as an attractive target for anti-cancer therapy. However, clinical success with anti-EGFR therapy remains limited in part due to our incomplete knowledge of the EGFR pathway. Accumulating evidences revealed a novel mode of EGFR signaling in which EGF ligand shuttles EGFR into the nucleus, leading to cyclin D1 gene activation. Patients with breast tumors that contain high nuclear EGFR survived poorly compared to those with no/low levels. However, the nature and pathological significance of this novel EGFR network remain largely unknown. We will test the hypothesis that nuclear EGFR functions as both a transcriptional regulator and a tyrosine kinase and that de-regulated nuclear EGFR pathway contributes to a more aggressive biology of human tumors. Preminary data indicate a novel nuclear interaction between EGFR and the oncogenic transcription factor, signal transducer and activator of transcription-3, STATS, leading to increased expression of inducible nitric oxide synthase (iNOS).
Aim 1 will characterize nuclear EGFR/STAT3 interaction and determine its role in iNOS gene regulation. Moreover, whether nuclear EGFR also functions as a tyrosine kinase remains unknown. Interestingly, preliminary results suggest that nuclear EGFR phosphorylates c-jun. In addition, we found that EGF activates expression of TWIST, a mediator for epithelial-mesenchymal transition (EMT)/metastasis and that TWIST gene promoter can be regulated by EGFR, c-jun and STATS.
Aim 2 will thus determine the effect of EGFR/ c-jun/STAT3 interplay on TWIST gene activation and TWIST-mediated EMT/tumor progression. A role of nuclear EGFR in Taxol/5-Fu resistance is suggested by our preliminary data.
Aim 3 will determine the significance and mechanisms for nuclear EGFR-mediated chemoresistance. This proposal is highly relevant to public health and its outcome will shed light into the nuclear EGFR signaling network in human cancers.
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