Identification of genes that are regulated by the pro-diabetic transcription factor Foxo1a in liver cells

In patients with type-2-diabetes, fasting hyperglycemia is a common clinical symptom and it reflects an increased hepatic glucose production due to insulin resistance of the liver. The insulin-regulated forkhead transcription factor Foxo1a (also called FKHR) is a central mediator of the effects of insulin on hepatic glucose production and overexpression of Foxo1a has been described to result in a diabetic phenotype in transgenic mouse models. Therefore, Foxo1a and Foxo1a-regulated processes can be regarded as potential targets for anti-diabetic drugs and understanding the biological function and regulation of Foxo1a is an essential pre-requisite for the development of novel therapeutical strategies to treat diabetes. In order to identify Foxo1a-regulated processes in the liver, we have set up a cellular model based on a conditionally activatable version of Foxo1a (Foxo-ER) stably expressed in H4IIEC3-cells, a highly differentiated and insulin sensitive hepatoma cell line. The Foxo-ER-construct can be rapidly activated by the addition of 4-hydroxy-tamoxifen (OHT) and Foxo-ER transcriptional activity can be monitored by the use of a stably co-expressed Foxo1a-responsive reporter gene construct in this system. Microarray and real-time PCR analysis of the transcriptome led to the identification of clusters of Foxo1a-differentially transcribed genes not only relevant to glucose homeostasis but also to lipid metabolism and signal transduction processes.

In summary, our data suggest that Foxo1a has pleiotropic functions in liver cells in addition to its role in the regulation of hepatic glucose production.