Altered function of KLF5 is associated with intestinal tumor progression

Abstract

Members of the kroppel-like family of transcription factors (KLFs) have been linked to the regulation of cell growth and tumorigenesis in a number of systems. In the normal intestinal epithelium, KLF5 (intestinal-kruppel like factor/BTEB2) is expressed m growing cells of the lower crypt but is downregulated in non-dividing ceils of the upper crypt and villus/surface mucosa, suggesting that it has a growth promoting role in this tissue. In support of this idea, a direct positive growth regulatory role for KLF5 in fibrobfasts and vascular smooth muscle ceils has been reported. To evaluate the expression of KLF5 during intestinal tumorigenesis, RT-PCR was performed on laser-capture microdissected samples from intestinal adenomas and normal epithelium. This analysis showed reduced expression of KLF5 mRNA in rain mouse and human adenomatons polyposis adenornas; thus, while KLF5 may be growth promoting in the normal intestinal epithelium, it may also have a tumor suppressive function in this tissue. This possibility was further investigated using a normalintestinal crypt epithelial cell line (1EC-18) and colon tumor cell lines (Ward and DLD-1). Overexpression of KLF5 inhibited colony formation in the colon tumor cell lines but enhanced colony number in IEC-18 cells, indicating that KLF5 has opposing effects on cell growth and/or survival in normal and tumor-derived intestinal epithelial cells. Differences in the effects of KLF5 were also seen in transient transfection assays, where KLF5 enhanced expression of growthrelated genes in [EC-18 cells but not DLD-1 or Ward cells. Furthermore, while phorbol ester-induced growth arrest of IEC-18 cells led to downregulation of KLF5, consistent with the posiuve relationship between this factor and cell growth in the normal intestinal epithelium, growth arrest of tumor cell lines led to an upregulation of KLF5, indicating that this factor is negatively associated with growth in tumor cells. Collectively, these data indicate that KLF5 is growth promoting in the normal intestinal epithelium but is associated with growth inhibition in tumor cells. Thus, intestinal tumor progression appears to be associated with a change in the growth-related functions of KLF5. Supported by the Roswell Park Alliance Foundation and by NIH grants CA16056 and DK54909.