IDENTIFICATION AND CHARACTERIZATION OF A GENE ENCODING A GUT-ENRICHEDKRUPPEL-LIKE FACTOR EXPRESSED DURING GROWTH ARREST

A cDNA clone, named gut-enriched Kruppel-like factor (GKLF), was isola ted from an NIH 3T3 library using a probe encoding the zinc finger reg ion of the immediate-early transcription factor zif/268. The deduced G KLF amino acid sequence contains three tandem zinc fingers that are re lated to members of the Kruppel family of transcription factors. By in direct immunofluorescence, GKLF is localized to the cell nucleus. In c ultured fibroblasts, GKLF mRNA is found in high levels in growth-arres ted cells and is nearly undetectable in cells that are in the exponent ial phase of proliferation. The growth-arresting nature of GKLF is dem onstrated by an inhibition of DNA synthesis in cells transfected with a GKLF-expressing plasmid construct. In the mouse, GKLF mRNA is presen t in select tissues and is most abundant in the colon, followed by the testis, lung, and small intestine. In situ hybridization experiments indicate that GKLF mRNA is enriched in epithelial cells located in the middle to upper crypt region of the colonic mucosa. Taken together, t hese results suggest that GKLF is potentially a negative regulator of cell growth in tissues such as the gut mucosa, where cell proliferatio n is intimately coupled to growth arrest and differentiation.