FoxO transcription factors are important targets of insulin action. To better understand the role of FoxO proteins in the liver, we created transgenic mice expressing constitutively active FoxO1 in the liver using the ␣1-antitrypsin promoter. Fasting glucose levels are increased, and glucose tolerance is impaired in transgenic (TGN) versus wild type (WT) mice. Interestingly, fasting triglyceride and cholesterol levels are reduced despite hyperinsulinemia, and post-prandial changes in triglyceride levels are markedly suppressed in TGN versus WT mice. Activation of pro-lipogenic signaling pathways (atypical protein kinase C and protein kinase B) and the ability to suppress ␤-hydroxybutyrate levels are not impaired in TGN. In contrast, de novo lipogenesis measured with 3 H 2 O is suppressed by ϳ70% in the liver of TGN versus WT mice after refeeding. Gene-array studies reveal that the expression of genes involved in gluconeogenesis, glycerol transport, and amino acid catabolism is increased, whereas genes involved in glucose utilization by glycolysis, the pentose phosphate shunt, lipogenesis, and sterol synthesis pathways are suppressed in TGN versus WT. Studies with adenoviral vectors in isolated hepatocytes confirm that FoxO1 stimulates expression of gluconeogenic genes and suppresses expression of genes involved in glycolysis, the shunt pathway, and lipogenesis, including glucokinase and SREBP-1c. Together, these results indicate that FoxO proteins promote hepatic glucose production through multiple mechanisms and contribute to the regulation of other metabolic pathways important in the adaptation to fasting and feeding in the liver, including glycolysis, the pentose phosphate shunt, and lipogenic and sterol synthetic pathways.FoxO 2 transcription factors are important targets of insulin and growth factor action, and they contribute to the regulation of cell growth, differentiation, and metabolism (1-3). FoxO proteins form a subgroup within the family of Forkhead box (or Fox) transcription factors (4). Early studies indicated that Forkhead proteins interact with insulin response sequences (IRSs) in the promoter of the IGF-binding protein-1 (IGFBP-1) and the phosphoenolpyruvate carboxykinase (PEPCK) genes (5, 6) and that signaling through phosphatidylinositol 3Ј-kinase and protein kinase B (PKB) mediates IRS-dependent effects of insulin on gene expression (7). Genetic studies of Caenorhabditis elegans revealed that DAF-16, a FoxO transcription factor, is a major target of insulin-like signaling (8, 9). DAF-16 plays an important role in the adaptation to environmental stress, including nutrient restriction, and signaling through phosphatidylinositol 3Ј-kinase and PKB suppresses the function of DAF-16. Subsequent studies revealed that FoxO proteins contain highly conserved PKB phosphorylation sites (corresponding to Thr-24, Ser-256, and Ser-319 in human FoxO1) (10 -12) and that phosphorylation at these sites suppresses transactivation and promotes nuclear exclusion of FoxO proteins through multiple mechanisms (13)...

This study identifies a novel crosstalk paradigm between the IGF1R and EGFR in colon cancer cells. IGF1R activation by ligand exposure in growth factor deprived cells induces Akt activation in the FET, CBS and GEO colon cancer cell lines. Investigation of IGF1R mediated signaling pathways using siRNA approaches indicated that, as expected, PI3K was activated by IGF1R. MAPK activity as reflected by phospho-Erk induction was not significantly activated until later times following release of these cells from growth factor deprivation stress. The appearance of phospho-Erk was proximal to EGFR activation. Treatment of cells with the PI3K inhibitor LY294002 prior to release from stress resulted in a concentration dependent loss of EGFR activation while treatment with the MAPK inhibitor PD98059 did not block EGFR activation indicating that EGFR activation was downstream of the IGF1R/PI3K pathway. PD98059 inhibition of MAPK was associated with a concentration dependent reduction in EGFR-mediated phospho-Erk. EGFR inhibitor blocked induction of phospho-Erk showing that MAPK activity was a consequence of EGFR mediated signaling. On the other hand, a small molecule IGF1R inhibitor, PQIP, blocked Akt phosphorylation. The divergent signaling functions of IGF1R and EGFR suggested the potential for synergism by a combination of therapy directed at the 2 receptors. Combination treatment with PQIP and EGFR inhibitor Tarceva resulted in synergistic effects as indicated by combination index analysis in all 3 cell lines tested.

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