Chromosome 18q is affected by loss of heterozygosity (LOH) in greater than 70 percent of colorectal cancers, and patients whose tumors have sustained 18q LOH have a markedly worse prognosis than those whose tumors have not. The DCC (deleted in colorectal cancer) gene was identified and cloned on the basis of localized genetic alterations affecting the common region of LOH on 18q, and several lines of evidence suggest DCC is a promising candidate colorectal tumor suppressor gene. Inactivation of DCC may also occur in some cancers of the breast, pancreas, stomach, uterus, prostate, brain, and cervix, as well as in some leukemias. The sequence of DCC predicts a 1447 amino acid transmembrane protein whose four immunoglobulin-like and six fibronectin type III-like extracellular domains show similarity to the neural cell adhesion molecule (N- CAM) family of cell surface proteins. The DCC cytoplasmic domain, however, shares little similarity with any other proteins. The structural similarity of DCC with the N-CAMs suggests it may function through specific cell-cell or cell-extracellular matrix interactions. Nevertheless, at present, many questions remain regarding the role of 18q and DCC alterations in tumorigenesis and the expression pattern and function of DCC in normal and neoplastic cells. For example, specific somatic genetic alterations in the DCC gene in tumors have not been well characterized. In addition, while DCC transcripts are present in most adult tissues at very low levels, with highest levels in brain tissues, DCC expression has not been fully characterized in normal and neoplastic tissues. Furthermore, the means by which DCC functions to regulate cell growth and differentiation is unknown. To address these and other questions four specific aims are proposed: 1) To identify somatic genetic alterations on chromosome 18q, and particularly those present in the DCC gene that inactivate it and/or account for the marked decrease in its expression in colon and other cancers. 2) To obtain detailed information on the structure and expression pattern of DCC transcripts and portein(s) in normal and neoplastic tissues, particularly those of the gastrointestinal tract, using RT-PCR to characterize DCC transcripts and immunoblotting, immunoprecipitation and immunohistochemical techniques to characterize the DCC protein(s). 3) To identify proteins which bind specifically to the cytoplastic domain of DCC. 4) To determine if DCC functions as a tumor suppressor gene in colorectal and other gastrointestinal cancer cell lines. The proposed studies will determine if DCC is the gene targeted for inactivation by 18q allelic losses in colon and other tumor types. In addition, the studies will begin to address the means by which DCC functions to regulate normal cell growth and suppress tumorigenesis. Finally, in addition to furthering the understanding of the pathogenesis of cancer, the studies in this application may provide novel insights and reagents for improving the diagnosis and management of patients with cancer.
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