Krüppel Like Factor 5 (KLF5) Interacts with and Induces β-catenin Activity In vitro
¹Cassandra R. Williams, Nandan O. Mandayam, Beth B. McConnell, Vincent W. Yang
¹Division of Digestive Diseases, Emory University School of Medicine, Atlanta GA;

Abstract

The intestinal epithelium is a dynamic system in which proliferation of epithelial cells in the crypt region is stringently coupled with migration of cells along the crypt-to-villus axis and subsequent apoptosis after a cell reaches the apex of the intestine. Krüppel-like factor 5 (KLF5) has previously been shown to induce proliferation in intestinal epithelial cells. β-catenin is a cytoplasmic protein that can enter into the nucleus in response to Wnt signaling and activate Wnt target genes. This interaction also induces cellular proliferation in the crypt of the small and large intestine. Since KLF5 and β-catenin are both implicated in crypt cell proliferation, we hypothesize that the two factors may coordinate their effects on the crypt cells. Immunoprecipitation was used to examine protein-protein interactions between KLF5 and β-catenin. Luciferase assays were also conducted using as a reporter, TOPFLASH, to measure β-catenin activity. An increase in luciferase activity was seen in cells that overexpressed β-catenin or the combination of β-catenin and KLF5. These results suggest that KLF5 may be affecting β-catenin expression causing β-catenin transcription activity to be increased. KLF5 may also cause β-catenin to be stabilized. Lastly, KLF5 and β-catenin may be co-regulators of each other needing to bind to the same promoter region in order to induce a synergistic effect of cellular proliferation.

In Plain English

The small and large intestine have cells that proliferate from development. Wnt proteins are a part of the pathway that signals these cells to proliferate. There are two proteins that are targeted by Wnt to bind to genes that induce proliferation. These proteins are called beta-catenin and KLF5, and they are both transcription factors. The classical Wnt signaling pathway is dependent of beta-catenin not being degraded by a complex within the cell and being able to enter into the nucleus to bind to the genes that induce proliferation. When Wnt signaling is high, beta catenin activity is also high. This is the same for the protein levels of KLF5.

This research hypothesized that there may be an interaction between KLF5 and beta-catenin. If this interaction is true then it is expected that they may work together to cause the cells to proliferate. Knowing that these proteins interact will help in understanding cancers related to the small and large intestine. If we can understand what tells a cell to told to proliferate and make tumors, we might be able to make it stop.

Techniques

Luciferase Assay, Western Blotting, Immmunoprecipitation, Immunofluorescence, Transfections

Keywords

Cancer, mRNA, protein, signaling transduction, antibody, antigen, plasmid