Growth factor receptors play a central role in cell proliferation, differentiation and regulated death. Poor regulation of specific signals from these receptors is an important mechanism of cancer pathogenesis and progression. The epidermal growth factor receptor (EGFR) and other members of ErbB tyrosine kinase family are important in human neoplasia, particularly in breast, cervical, ovary, stomach, bladder and lung carcinomas, and in neuroblastomas/glioblastomas. These receptors have become major targets for cancer prevention and therapy. The EGFR has been used as a prognostic marker in several types of cancer, and an antibody to EGFRs has been tested as an anti-cancer therapy. However, general limitations of antibody therapy and the presence of EGFRs in normal tissue pose a need for new approaches to specifically inhibit EGFRs in tumor cells and to use the EGFR as a marker of the various stages of cancer. Activation of EGFRs by ligand normally results in the rapid endocytosis and down-regulation of EGFRs. By down-regulating EGFRs, endocytosis serves as the major regulator of the duration and intensity of signaling by the EGFR. The rate-limiting step of this process is receptor internalization via clathrin-coated pits. In contrast, the internalization and down-regulation of EGFRs is negligible in many types of cancer cells that overexpress EGFRs. We hypothesize that the endocytic pathway of EGFRs via coated pits is saturable because its capacity is limited by the low amount of specific proteins responsible for recruitment of activated EGFRs into coated pits. The goal of the proposal is to identify these coated pit """"""""recruiters"""""""" (CPRs) and to characterize how they participate in down-regulation of EGFR in cancer cells. The functional characterization of CPRs will be accomplished using novel protein-protein interaction assays in living cells that we have developed. A longer-term goal is to define the expression and regulation of CPRs in tumors where EGFR is important in the transformation. Our prediction is that CPRs are differentially expressed in normal and tumor cells. For instance, low levels of expression of CPRs in cancer tissue may be a primary reason of the maintenance of large amounts of activated EGFR in these cells. Therefore, CPRs may well be important new targets for cancer prevention and therapy. CPR molecules will be evaluated in benign cervical mucosa, squamous intraepithelial lesions, and squamous cell carcinomas to determine if CPR analysis could play a role in the determination of prognosis and in guiding therapy of patients with potentially premalignant or malignant lesions of the cervical mucosa.
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