The STAT5A-Mediated Induction of Pyruvate Dehydrogenase Kinase 4 Expression by Prolactin or Growth Hormone in Adipocytes

Abstract

The purpose of this study was to determine whether pyruvate dehydrogenase kinase (PDK)4 was expressed in adipocytes and whether PDK4 expression was hormonally regulated in fat cells. Both Northern blot and Western blot analyses were conducted on samples isolated from 3T3-L1 adipocytes after various treatments with prolactin (PRL), growth hormone (GH), and/or insulin. Transfection of PDK4 promoter reporter constructs was performed. In addition, glucose uptake measurements were conducted. Our studies demonstrate that PRL and porcine GH can induce the expression of PDK4 in 3T3-L1 adipocytes. Our studies also show that insulin pretreatment can attenuate the ability of these hormones to induce PDK4 mRNA expression. In addition, we identified a hormone-responsive region in the murine PDK4 promoter and characterized a STAT5 binding site in this region that mediates the PRL (sheep) and GH (porcine) induction in PDK4 expression in 3T3-L1 adipocytes. PDK4 is a STAT5A target gene. PRL is a potent inducer of PDK4 protein levels, results in an inhibition of insulin-stimulated glucose transport in fat cells, and likely contributes to PRL-induced insulin resistance. Diabetes 56:1623-1629, 2007 I t is well known that growth hormone (GH) and prolactin (PRL) induce signaling via the JAK-STAT pathway. In particular, STAT5 proteins are potently activated by these hormones (rev. in 1). GH is known to have profound effects on lipid metabolism (rev. in 2). The effects of PRL have been well characterized in mammary tissues, yet there is also evidence demonstrating that this hormone can affect adipose tissue in mice and humans (3,4). Yet, few molecular targets for the STAT5-mediated actions of GH and PRL on adipocytes have been identified. Although multiple lines of recent evidence suggest that STAT5 proteins can modulate adipocyte function (5-11), very few studies have identified direct STAT5 target genes in adipocytes. We recently observed that the GH and PRL inhibition of fatty acid synthase (FAS) transcription was mediated by a STAT5A binding site in the rat FAS promoter (12). Hence, our current efforts have been to identify other genes associated with glucose or lipid metabolism that are directly modulated by STAT5 proteins in adipocytes. In this study, we present data demonstrating that pyruvate dehydrogenase kinase (PDK)4 is a STAT5A target gene.PDK is a family of kinases that negatively regulate the activity of the pyruvate dehydrogenase complex (PDC) (rev. in 13). There are four tissue-specific isoforms of PDK, PDK1-4, that have been identified in mammals, and each has different patterns of gene expression (14 -16). The specificity in distribution, expression, and activity of each PDK isoform contributes to the long-term regulation of PDC in a given tissue and thus, in part, regulates glucose metabolism. There are several conditions that result in the short-term regulation of PDC activity (17-19). The longterm regulation of PDK that occurs in starvation (18,20) and diabetes involves an increase in the amount of PDK protein, whi...

Orphan Nuclear Receptor Small Heterodimer Partner Negatively Regulates Growth Hormone-mediated Induction of Hepatic Gluconeogenesis through Inhibition of Signal Transducer and Activator of Transcription 5 (STAT5) Transactivation

“…GH down-regulates STAT5 occupancy on the fatty acid synthase gene promoter and up-regulates STAT5 recruitment on the pyruvate dehydrogenase kinase 4 promoter in adipocytes (38,39). Based on our current findings, we propose a molecular mechanism by which metformin induces SHP gene expression by activating AMPK and regulating GH-mediated hepatic gluconeogenesis through STAT5 transactivation in primary hepatocytes.…”

Hepatic Oxidative Stress Promotes Insulin-STAT-5 Signaling and Obesity by Inactivating Protein Tyrosine Phosphatase N2

“…Because HFF LTKO HET male mice gained more weight and exhibited greater insulin resistance than controls, we reasoned that the enhanced p-STAT-5 might be sufficient to drive the expression of genes that promote obesity and T2D. In particular, we focussed on two STAT-5 transcriptional targets, Igf-1 (Cui et al, 2007) and the gene encoding pyruvate dehydrogenase kinase 4 ( Pdk4 ) (White et al, 2007). PDK4 phosphorylates pyruvate dehydrogenase complex to conserve glucose and divert three carbon compounds for gluconeogenesis (Kim et al, 2012).…”

The modulation of adiponectin by STAT5-activating hormones

“…In addition, the promoter for acyl-CoA oxidase, the rate-limiting enzyme in peroxisomal fatty acid ␤-oxidation, contains a STAT5 binding site that increases its gene expression in fat cells as a result of treatment with GH (7). We also identified a STAT5 binding site in the murine pyruvate dehydrogenase kinase 4 (PDK4) promoter that mediates the PRL and GH induction of PDK4 expression in adipocytes (57). PDK4 expression is associated with decreased insulin-responsive glucose uptake in these cells (57) and may correlate with GHinduced systemic insulin resistance.…”

“…We also identified a STAT5 binding site in the murine pyruvate dehydrogenase kinase 4 (PDK4) promoter that mediates the PRL and GH induction of PDK4 expression in adipocytes (57). PDK4 expression is associated with decreased insulin-responsive glucose uptake in these cells (57) and may correlate with GHinduced systemic insulin resistance. Our current efforts are to identify other genes associated with glucose or lipid metabolism that are directly modulated by STAT5 proteins in fat cells.…”