Colorectal carcinogenesis is a multi-step process including both the activation of oncogenes and the loss of tumor suppressor genes. Most of the neoplastic lesions in the colon arise through the progression from normal to hyperproliferative epithelium, adenoma and carcinoma, It is hypothesized that cellular hyperproliferation resulting from either spontaneous mutation or increased in intestinal proliferation leads to clonal expansion and carcinogenesis. Although multiple genetic mutations have been described, the molecular events governing intestinal hyperproliferation is unknown. Recently, an eukaryotic zinc finger protein, gut-enriched Kruppel-like factor (GKLF/KLF4), has been identified to be an important factor in controlling growth arrest. Our laboratory has shown that GKLF gene expression is reduced in colon cancer tissue and that constitutive expression of an antisense GKLF DNA in a colon tumor cell line results in cell hyperproliferation. These data suggest that down-regulation of GKLF may lead to uninhibited cell growth. Furthermore, GKLF mRNA levels increased as colonic epithelium acquired more differentiated phenotype. We hypothesize that up-regulation of GKLF is essential for colonic epithelium to become differentiated and that down-regulation of GKLF will render colonic cells to become hyperproliferated and ultimately neoplastic transformation. The precise physiological function of GKLF in the colon is not clear and its up- and down-stream targets are currently unknown. The aims of the current study are: (1) to elucidate the physiological properties of GKLF by examining the effect of constitutive overexpression of sense, antisense or dominant-negative mutant GKLF DNA on cell growth and differentiation in normal colon epithelial; adenoma; and cancer cell lines; (2) to investigate the role of GKLF in cell cycle progression by examining its effect on cyclins, cyclin-dependent kinases (cdks) expression, and on transcriptional regulation of the cyclin D1 gene; and (3) to examine molecular mechanisms governing basal transcription of the GKLF gene as well as vit D3- or interferon-gama-promoted GKLF expression. Collectively, the information gained from this proposal will add to our understanding the contribution of GKLF to growth, differentiation, and malignant transformation of the colonic epithelial cells. Ultimately, if the GKLF down-regulation process can be manipulated, it may be possible to use inhibitors of this process for chemoprevention of cancer formation in the gastrointestinal tract.