In the past few years, significant advances have been made toward understanding the genetic basis for the development of colorectal cancer. These advances will almost certainly lead to better risk assessment and early diagnosis. However, in the foreseeable future, colorectal cancer will remain a significant disease, with the majority of patients presenting at late stages of the disease for which few major treatment advances have been made. For these patients, therapeutic treatments are likely to arise for a better understanding of the signal transduction pathways which regulate proliferation and differentiation of colonic epithelial cells, and whose alteration may lead to malignant transformation, tumor progression, and the development of metastases. One family of signal transduction enzymes, the non-receptor protein tyrosine kinases (PTKs) related to pp60c-src, is activated in nearly every colon tumor, resulting in specific activities of the enzymes equivalent to that observed for the retroviral oncogene homologues. Activation is first observed in an early stage of tumorigenesis, beginning with polyps of high malignant potential and persisting through subsequent stages of tumor progression. Additional increases in enzymatic activity occur between the primary tumor and development of metastasis. Two members of the src family, pp60c-src and pp62c-yes, are expressed in colonic epithelial cells, and both are activated in the majority of colon tumors. However, while these enzymes play redundant roles in normal growth regulation of colonic epithelial cells, they play distinct roles in aberrant growth of tumor cells. Thus, goals of this proposal are to define the specific and/or collective roles of pp60c-src and pp62c-yes in proliferation, tumorigenicity, and metastatic potential of colon tumor cells, and to attempt to elucidate the mechanism(s) by which these PTKs are activated. By specifically inhibiting and increasing the expression and activity of the c-src and/or c-yes kinases through antisense technology, the studies of this proposal will test the hypothesis that activation of either c- src or c-yes is critical for malignant transformation and/or progression.
The aims of the proposal include: (1) studying the effects of inhibition of these PTKs on proliferative kinetics and in vitro invasiveness of well characterized colon tumor cells, (2) generation of expression vectors for these antisense oligonucleotides; and (3) determining the tumorigenicity and metastatic potential of model colon tumor cell lines in which the expression and activity of these PTKs has been decreased via stable transfection of antisense-expression vectors, or increased via stable transfection of specific genetic constructs encoding wild type and """"""""activiated"""""""" forms of these enzymes. The studies will lead to a better understanding of the critical role these kinases play in growth control of colonic epithelial cells, and identify which of these enzymes may be a target for development of specific protein tyrosine kinase inhibitors.
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