THE ROLE OF TRANSCRIPTION FACTORS IN LIVER METABOLISM

University Of Pennsylvania, Philadelphia PA

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Abstract

Diabetes mellitus is a significant health problem, affecting over 18 million people in the United States alone.[unreadable] Mutations in several hepatic nuclear factors have been linked to early onset non-insulin dependent diabetes[unreadable] mellitus (MODY), underscoring the importance of the hepatic transcription factors for glucose homeostasis.[unreadable] In the previous grant cycle, we have employed tissue-specific gene ablation to demonstrate the essential[unreadable] function of Foxa2 (previously known as HNF3(3) in the integration of the transcriptional response of the[unreadable] hepatocyte to fasting. In addition, Foxa2 has been proposed as a major mediator of insulin signaling in[unreadable] hepatocytes. We propose the following three Aims:[unreadable] In Aim 1, which is the direct result of the interactions within the PO1 with Dr. Birnbaum, we will test the[unreadable] hypothesis that Foxa2 is the major mediator of insulin signaling via AKT2 using genetic means. We will[unreadable] derive mice which are deficient for both AKT2 and Foxa2 in hepatocytes to test if Foxa2 is indeed required to[unreadable] establish the AKT2 mutant phenotype. In Aim 2, we will collaborate with Dr. Ahima to investigate the[unreadable] combined role of Foxa1 AND Foxa2 in hepatic metabolism. This aim is based on our discovery that Foxal[unreadable] and Foxa2 act jointly to enable the hepatogenic program during fetal devlopment. We hypothesize that the[unreadable] two genes also cooperate in transcription in the adult hepatocyte. We will use simulatenous conditional gene[unreadable] ablatation for Foxa1 and Foxa2 combined with physiological and genomics approaches to test our[unreadable] hypothesis that the two genes open chromatin to enable binding of hormone-dependent transcription factors[unreadable] like CREB and GR. In Aim 3, we will address a recent controversy concerning the regulation of hepatic[unreadable] gluconeogenesis by cAMP. Currently, two conflicting models exist regarding the regulation of the[unreadable] transcription factor CREB in hepatocyte. The first proposes that PKA-dependent phosphorylation of CREB is[unreadable] required for recruitment of the co-activator CBP/p300 and subsequent activation of target genes, while the[unreadable] second invokes PKA-dependent translocation of the novel co-activator TORC2 from the cytoplasm to the[unreadable] nucleus as the central regulator of CREB-dependent transcription. We will address the relative importance[unreadable] of both pathways in hepatic glucose homeostasis by genetic means. We will develop mouse models[unreadable] carrying a Ser/Ala mutation in the PKA-phosphorylation site of CREB or a hepatocyte-specific ablation of[unreadable] TORC2, and analyze the consequences to glucose metabolism both in vivo and in isolated hepatocytes.[unreadable] Together, these studies will further our understanding of the transcriptional regulation of hepatic metabolism[unreadable] and in insulin action.[unreadable]