Sp1 and Sp3 regulate glucokinase gene transcription in the liver of gilthead sea bream (Sparus aurata)

Abstract

To better understand the transcriptional machinery that governs glucokinase (GCK) expression, we have cloned and characterized the proximal promoter region of GCK from gilthead sea bream (Sparus aurata). The 5 0 -flanking region of GCK was isolated by chromosome walking. SMART RACE-PCR allowed us to locate the transcription start site 98 bp (bp) upstream from the translational start. Transfection analysis in HepG2 cells revealed the presence of a functional promoter in the 1397 bp 5 0 -flanking isolated fragment (positions K1321 to C76 relative to the transcription start site).Sequential 5 0 -deletion analysis indicated a core functional promoter for basal transcription within the 288 bp upstream from the transcription start site. Transient transfection experiments performed in HepG2 cells and electrophoretic mobility shift assays denoted that Sp1 binds and transactivates GCK promoter, whereas Sp3 repressed Sp1-mediated activation of GCK by competing for the same binding site. Mutations in the Sp binding site completely abolished the enhancing effect of Sp1. Treatment with insulin stimulated GCK expression, and increased Sp1 levels in S. aurata liver. We propose a new mechanism that involves Sp1 and Sp3 to mediate insulin activation of GCK transcription.

Insulin-induced hypoglycaemia is co-ordinately regulated by liver and muscle during acute and chronic insulin stimulation in rainbow trout (Oncorhynchus mykiss)

“…For example, we found that while GK transcript levels were strongly down-regulated, G6Pase transcripts were upregulated in insulin-injected trout. Although in other fish (Egea et al, 2007) and mammals (Iynedjian, 2009) GK is always upregulated by insulin, in the present study its repression could be related to the counter-regulation during hypoglycaemia, blocking the large glucose entrance and phosphorylation. In the same sense, the increased G6Pase transcript level probably improves glucose export to the bloodstream, as observed in the mammalian liver under hypoglycaemic conditions (Bady et al, 2002).…”

Insulin-Dependent Leptin Expression in Breast Cancer Cells

“…15). Sp1 is a ubiquitous nuclear factor that mediates the effects of insulin in different cell types, regulating such processes as glucose metabolism, lipid biosynthesis (16)(17)(18). The abundance of nuclear Sp1 has been shown to be increased by insulin and can be posttranslationally regulated by phosphatidylinositol-3-OH kinase (PI-3K) and extracellular signal-regulated kinase (ERK)1/2 pathways in some cell models (19)(20)(21).…”

Efecto del tratamiento con leptina sobre la actividad del sistema glucosensor y la expresión de neuropéptidos implicados en la regulación de la ingesta de alimento en trucha arcoíris (Onchorhynchus mykiss)

“…Los promotores "upstream" desencadenan la expresión de GK en tejidos no hepáticos, incluido el páncreas y el cerebro (Iynedjian, 2009). En peces, estudios realizados en dorada (Sparus aurata) revelan la presencia de un promotor de GK en el hígado (Egea et al, 2007).La expresión génica de GK en el conjunto del cerebro ha sido estudiada en dos especies de peces como son la trucha arco iris (Panserat et al, 2000) y el pez zebra (González-Álvarez et al, 2009). Además, la actividad/expresión génica de GK se ha descrito en cinco áreas específicas del cerebro tales como el telencéfalo, cerebro posterior, cerebro medio, hipotálamo (Soengas et al, 2006) e hipófisis (Polakof, comunicación personal).…”

“…Los promotores "upstream" desencadenan la expresión de GK en tejidos no hepáticos, incluido el páncreas y el cerebro (Iynedjian, 2009). En peces, estudios realizados en dorada (Sparus aurata) revelan la presencia de un promotor de GK en el hígado (Egea et al, 2007).…”