Activation of p21CIP1/WAF1 gene expression and inhibition of cell proliferation by overexpression of hepatocyte nuclear factor-4α

The F9 murine embryonal carcinoma cell line provides an attractive system for studying epithelial differentiation and antiproliferative processes. We have recently established F9 cells expressing doxycycline-inducible hepatocyte nuclear factor (HNF)-4α and shown that HNF-4α triggers the gene expression of tight-junction molecules, occludin, claudin-6, and claudin-7, as well as formation of functional tight junctions and polarized epithelial morphology (Exp. Cell Res. 286, [2003] 288). Since these events were very similar to those induced by retinoids, we investigated whether HNF-4α, like retinoid receptors, was involved in the control of cell proliferation. We herein show that HNF-4α up-regulates expression of the p21 gene, but not the p15, p16, p18, p19, or p27 gene, in a p53-independent manner, and inhibits cell growth in F9 cells. Similar results were observed in rat lung endothelial cells, in which expression of HNF-4α is conditionally induced by doxycycline. Furthermore, we demonstrate, by reporter assay, that HNF-4α significantly elevates the transcriptional activity of the p21 promoter. Since, HNF-4α is expressed not only in the liver but also in organs containing epithelial cells, such as kidney, intestine, pancreas, and stomach, it might also play critical roles in the regulation of epithelial morphogenesis and proliferation in these organs.