Cop1 constitutively regulates c-Jun protein stability and functions as a tumor suppressor in mice

Biochemical studies have suggested conflicting roles for the E3 ubiquitin ligase constitutive photomorphogenesis protein 1 (Cop 1; also known as Rfwd2) in tumorigenesis, providing evidence for both the oncoprotein c-Jun and the tumor suppressor p53 as its targets. Here we present what we believe to be the first in vivo investigation of the role of Cop1 in cancer etiology. Using an innovative genetic approach to generate an allelic series of Cop1, we found that Cop1 hypomorphic mice spontaneously developed malignancy at a high frequency in the first year of life and were highly susceptible to radiation-induced lymphomagenesis. Further analysis revealed that c-Jun was a key physiological target for Cop1 and that Cop1 constitutively kept c-Jun at low levels in vivo and thereby modulated c-Jun/AP-1 transcriptional activity. Importantly, Cop1 deficiency stimulated cell proliferation in a c-Jun-dependent manner. Focal deletions of COP1 were observed at significant frequency across several cancer types, and COP1 loss was determined to be one of the mechanisms leading to c-Jun upregulation in human cancer. We therefore conclude that Cop1 is a tumor suppressor that functions, at least in part, by antagonizing c-Jun oncogenic activity. In the absence of evidence for a genetic interaction between Cop1 and p53, our data strongly argue against the use of Cop1-inhibitory drugs for cancer therapy

The LKB1-salt-inducible kinase pathway functions as a key gluconeogenic suppressor in the liver

LKB1 is a master kinase that regulates metabolism and growth through adenosine monophosphate-activated protein kinase (AMPK) and 12 other closely related kinases. Liver-specific ablation of LKB1 causes increased glucose production in hepatocytes in vitro and hyperglycaemia in fasting mice in vivo. Here we report that the salt-inducible kinases (SIK1, 2 and 3), members of the AMPK-related kinase family, play a key role as gluconeogenic suppressors downstream of LKB1 in the liver. The selective SIK inhibitor HG-9-91-01 promotes dephosphorylation of transcriptional co-activators CRTC2/3 resulting in enhanced gluconeogenic gene expression and glucose production in hepatocytes, an effect that is abolished when an HG-9-91-01-insensitive mutant SIK is introduced or LKB1 is ablated. Although SIK2 was proposed as a key regulator of insulin-mediated suppression of gluconeogenesis, we provide genetic evidence that liver-specific ablation of SIK2 alone has no effect on gluconeogenesis and insulin does not modulate SIK2 phosphorylation or activity. Collectively, we demonstrate that the LKB1-SIK pathway functions as a key gluconeogenic gatekeeper in the liver

Acciones tempranas: venezuela hacia la integración liberadora. Rizoma entre políticas de estado e integración socio-educativa. Parte II

El propósito es abrirse a la discusión de las redes de integración dentro de un marco de referencia que incluye el compromiso de las políticas de Estado, nacionales e internacionales, con la integración en Educación Superior y en Investigación Científica. El punto de partida es el concepto de integración lanzado en la Doble Cumbre de Mar del Plata, en la que el Presidente Hugo Chávez (2005) presentó su eje estratégico, la lógica y práctica de la integración liberadora. Desde ese marco de referencia político-conceptual, se aproxima un diálogo con el tercer modelo de integración del MERCOSUR, tal como es descrito por Daniela Perrotta (2012). El presente artículo contrasta elementos de la lógica instrumental de funcionamiento tecnológico de las redes  y su modo de producción informacional (Castells, 1989) con la lógica y sentido de la tecnología como proceso-productivo-social, se vinculan esas dos lógicas a partir del enfoque de la geofilosofía y de la lógica del rizoma (Deleuze y Guattari, 1991). El estudio hace preguntas, argumenta y establece propuestas. En el proceso de análisis que subyace se descubre y se hace conocer el modo de concepción integral y modelo rizomático que sostiene --como plan de la nación-- el Programa de la Patria 2013-2019 (Chávez, 2012) quien trabaja la consolidación y ejercicio de la soberanía del territorio venezolano en cinco objetivos históricos, como políticas de Estado, en su conexión con la integración regional, en un mundo multicéntrico, multiétnico y pluricultural. Contribuyendo a la construcción de  una nueva hegemonía, el artículo presenta el paradigma de la integración socioeducativa (Córdova, 2010), en la geopolítica nacional e internacional, como posibilidad de redes de trabajo en movimiento hacia la integración liberadora. Rizoma de brotes nuevos en los procesos-productivos-sociales, con sujetos políticos, sujetos colectivos, saberes, ética, y valores humanos correspondientes.(Continuación de artículo. Primera Parte publicada en Revista Digital Integración y Conocimiento Nº2 - 2014

SIK2 regulates CRTCs, HDAC4 and glucose uptake in adipocytes

Salt-inducible kinase 2 (SIK2) is an AMP-activated protein kinase (AMPK) related kinase abundantly expressed in adipose tissue. Our aim was to identify molecular targets and functions of SIK2 in adipocytes, and to address the role of PKA-mediated phosphorylation of SIK2 on Ser358. Modulation of SIK2 in adipocytes resulted in altered phosphorylation of CREB-regulated transcription co-activator 2 (CRTC2), CRTC3 and class IIa histone deacetylase 4 (HDAC4). Furthermore, CRTC2, CRTC3, HDAC4 and protein phosphatase 2A (PP2A) interacted with SIK2, and the binding of CRTCs and PP2A to wild-type but not Ser358Ala SIK2, was reduced by cAMP elevation. Silencing of SIK2 resulted in reduced GLUT4 (also known as SLC2A4) protein levels, whereas cells treated with CRTC2 or HDAC4 siRNA displayed increased levels of GLUT4. Overexpression or pharmacological inhibition of SIK2 resulted in increased and decreased glucose uptake, respectively. We also describe a SIK2–CRTC2–HDAC4 pathway and its regulation in human adipocytes, strengthening the physiological relevance of our findings. Collectively, we demonstrate that SIK2 acts directly on CRTC2, CRTC3 and HDAC4, and that the cAMP–PKA pathway reduces the interaction of SIK2 with CRTCs and PP2A. Downstream, SIK2 increases GLUT4 levels and glucose uptake in adipocytes

O-GlcNAcylation Increases ChREBP Protein Content and Transcriptional Activity in the Liver

International audienceOBJECTIVE Carbohydrate-responsive element–binding protein (ChREBP) is a key transcription factor that mediates the effects of glucose on glycolytic and lipogenic genes in the liver. We have previously reported that liver-specific inhibition of ChREBP prevents hepatic steatosis in ob/ob mice by specifically decreasing lipogenic rates in vivo. To better understand the regulation of ChREBP activity in the liver, we investigated the implication of O-linked β-N-acetylglucosamine (O-GlcNAc or O-GlcNAcylation), an important glucose-dependent posttranslational modification playing multiple roles in transcription, protein stabilization, nuclear localization, and signal transduction. RESEARCH DESIGN AND METHODS O-GlcNAcylation is highly dynamic through the action of two enzymes: the O-GlcNAc transferase (OGT), which transfers the monosaccharide to serine/threonine residues on a target protein, and the O-GlcNAcase (OGA), which hydrolyses the sugar. To modulate ChREBPOG in vitro and in vivo, the OGT and OGA enzymes were overexpressed or inhibited via adenoviral approaches in mouse hepatocytes and in the liver of C57BL/6J or obese db/db mice. RESULTS Our study shows that ChREBP interacts with OGT and is subjected to O-GlcNAcylation in liver cells. O-GlcNAcylation stabilizes the ChREBP protein and increases its transcriptional activity toward its target glycolytic (L-PK) and lipogenic genes (ACC, FAS, and SCD1) when combined with an active glucose flux in vivo. Indeed, OGT overexpression significantly increased ChREBPOG in liver nuclear extracts from fed C57BL/6J mice, leading in turn to enhanced lipogenic gene expression and to excessive hepatic triglyceride deposition. In the livers of hyperglycemic obese db/db mice, ChREBPOG levels were elevated compared with controls. Interestingly, reducing ChREBPOG levels via OGA overexpression decreased lipogenic protein content (ACC, FAS), prevented hepatic steatosis, and improved the lipidic profile of OGA-treated db/db mice. CONCLUSIONS Taken together, our results reveal that O-GlcNAcylation represents an important novel regulation of ChREBP activity in the liver under both physiological and pathophysiological conditions

Activation of TORC1 transcriptional coactivator through MEKK1-induced phosphorylation

CREB is a prototypic bZIP transcription factor and a master regulator of glucose metabolism, synaptic plasticity, cell growth, apoptosis, and tumorigenesis. Transducers of regulated CREB activity (TORCs) are essential transcriptional coactivators of CREB and an important point of regulation on which various signals converge. In this study, we report on the activation of TORC1 through MEKK1-mediated phosphorylation. MEKK1 potently activated TORC1, and this activation was independent of downstream effectors MEK1/MEK2, ERK2, JNK, p38, protein kinase A, and calcineurin. MEKK1 induced phosphorylation of TORC1 both in vivo and in vitro. Expression of the catalytic domain of MEKK1 alone in cultured mammalian cells sufficiently caused phosphorylation and subsequent activation of TORC1. MEKK1 physically interacted with TORC1 and stimulated its nuclear translocation. An activation domain responsive to MEKK1 stimulation was mapped to amino acids 431-650 of TORC1. As a physiological activator of CREB, interleukin 1α triggered MEKK1-dependent phosphorylation of TORC1 and its consequent recruitment to the cAMP response elements in the interleukin 8 promoter. Taken together, our findings suggest a new mechanism for regulated activation of TORC1 transcriptional coactivator and CREB signaling. © 2008 by The American Society for Cell Biology.published_or_final_versio

Acciones tempranas: Venezuela hacia la integración liberadora. Rizoma entre políticas de Estado e integración socio-educativa (Parte I)

El propósito es abrirse a la discusión de las redes de integración dentro de un marco de referencia que incluye elcompromiso de las políticas de estado, nacionales e internacionales, con la integración en Educación Superior y eninvestigación científica. El punto de partida es el concepto de integración lanzado en la Doble Cumbre de Mar delPlata, en las que el Presidente Hugo Chávez (2005) presentó su eje estratégico, la lógica y práctica de la integraciónliberadora. Desde ese marco de referencia político-conceptual, se aproxima un diálogo con el tercer modelo deintegración del MERCOSUR, tal como es descrito por Daniela Perrotta (2012). El artículo contrasta elementos de lalógica instrumental de funcionamiento tecnológico de las redes y su modo de producción informacional (Castells,1989), con la lógica y sentido de la tecnología como proceso-productivo-social; se vinculan esas dos lógicas a partirdel enfoque de la geo-filosofía y de la lógica del Rizoma (Deleuze y Guattari, 1991). El estudio hace preguntas,argumenta y establece propuestas. En el proceso de análisis que subyace se descubre y se hace conocer el modo deconcepción integral y modelo rizomático que sostiene -como Plan de la Nación- el Programa de la Patria 2013-2019 (Chávez, 2012). Allí se trabajan la consolidación y ejercicio de la soberanía del territorio venezolano, en cincoobjetivos históricos, como políticas de estado, en su conexión con la integración regional, en un mundomulticéntrico, multiétnico y pluricultural. Contribuyendo a la construcción de una nueva hegemonía, el artículopresenta el paradigma de la integración socioeducativa (Córdova, 2010), en la geopolítica nacional e internacional,como posibilidad de redes de trabajo en movimiento hacia la integración liberadora. Rizoma de brotes nuevos enlos procesos productivos-sociales, con sujetos políticos, sujetos colectivos, saberes, ética, y los valores humanoscorrespondientes.Palabras claves: integración liberadora, modelo rizomático, políticas de estado, integración socioeducativa, nuevahegemonía conceptual

Glycerol-3-Phosphate Acyltransferase 1 Deficiency in ob/ob Mice Diminishes Hepatic Steatosis but Does Not Protect Against Insulin Resistance or Obesity

OBJECTIVEHepatic steatosis is strongly associated with insulin resistance, but a causal role has not been established. In ob/ob mice, sterol regulatory element binding protein 1 (SREBP1) mediates the induction of steatosis by upregulating target genes, including glycerol-3-phosphate acyltransferase-1 (Gpat1), which catalyzes the first and committed step in the pathway of glycerolipid synthesis. We asked whether ob/ob mice lacking Gpat1 would have reduced hepatic steatosis and improved insulin sensitivity.RESEARCH DESIGN AND METHODSHepatic lipids, insulin sensitivity, and hepatic insulin signaling were compared in lean (Lep+/?), lean-Gpat1−/−, ob/ob (Lepob/ob), and ob/ob-Gpat1−/− mice.RESULTSCompared with ob/ob mice, the lack of Gpat1 in ob/ob mice reduced hepatic triacylglycerol (TAG) and diacylglycerol (DAG) content 59 and 74%, respectively, but increased acyl-CoA levels. Despite the reduction in hepatic lipids, fasting glucose and insulin concentrations did not improve, and insulin tolerance remained impaired. In both ob/ob and ob/ob-Gpat1−/− mice, insulin resistance was accompanied by elevated hepatic protein kinase C-ε activation and blunted insulin-stimulated Akt activation.CONCLUSIONSThese results suggest that decreasing hepatic steatosis alone does not improve insulin resistance, and that factors other than increased hepatic DAG and TAG contribute to hepatic insulin resistance in this genetically obese model. They also show that the SREBP1-mediated induction of hepatic steatosis in ob/ob mice requires Gpat1