Insulin-receptor substrate-2 (irs-2) is required for maintaining glucokinase and glucokinase regulatory protein expression in mouse liver

PLoS One. 2013;8(4):e58797. doi: 10.1371/journal.pone.0058797. Epub 2013 Apr 1.

Abstract

Insulin receptor substrate (IRS) proteins play important roles in hepatic nutrient homeostasis. Since glucokinase (GK) and glucokinase regulatory protein (GKRP) function as key glucose sensors, we have investigated the expression of GK and GKRP in liver of Irs-2 deficient mice and Irs2(-/-) mice where Irs2 was reintroduced specifically into pancreatic β-cells [RIP-Irs-2/IRS-2(-/-)]. We observed that liver GK activity was significantly lower (p<0.0001) in IRS-2(-/-) mice. However, in RIP-Irs-2/IRS-2(-/-) mice, GK activity was similar to the values observed in wild-type animals. GK activity in hypothalamus was not altered in IRS-2(-/-) mice. GK and GKRP mRNA levels in liver of IRS-2(-/-) were significantly lower, whereas in RIP-Irs-2/IRS-2(-/-) mice, both GK and GKRP mRNAs levels were comparable to wild-type animals. At the protein level, the liver content of GK was reduced in IRS-2(-/-) mice as compared with controls, although GKRP levels were similar between these experimental models. Both GK and GKRP levels were lower in RIP-Irs-2/IRS-2(-/-) mice. These results suggest that IRS-2 signalling is important for maintaining the activity of liver GK. Moreover, the differences between liver and brain GK may be explained by the fact that expression of hepatic, but not brain, GK is controlled by insulin. GK activity was restored by the β-cell compensation in the RIP-Irs-2/IRS-2 mice. Interestingly, GK and GKRP protein expression remained low in RIP-Irs-2/IRS-2(-/-) mice, perhaps reflecting different mRNA half-lives or alterations in the process of translation and post-translational regulation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing
  • Animals
  • Carrier Proteins / genetics*
  • Carrier Proteins / metabolism
  • Gene Expression Regulation
  • Genetic Complementation Test
  • Glucokinase / genetics*
  • Glucokinase / metabolism
  • Glucose / metabolism*
  • Hypothalamus / metabolism
  • Insulin / metabolism*
  • Insulin Receptor Substrate Proteins / deficiency
  • Insulin Receptor Substrate Proteins / genetics*
  • Insulin-Secreting Cells / cytology
  • Insulin-Secreting Cells / metabolism
  • Intracellular Signaling Peptides and Proteins
  • Liver / metabolism*
  • Mice
  • Mice, Knockout
  • Organ Specificity
  • RNA, Messenger / genetics
  • Signal Transduction
  • Transfection

Substances

  • Adaptor Proteins, Signal Transducing
  • Carrier Proteins
  • Gckr protein, mouse
  • Insulin
  • Insulin Receptor Substrate Proteins
  • Intracellular Signaling Peptides and Proteins
  • Irs2 protein, mouse
  • RNA, Messenger
  • Glucokinase
  • Glucose

Grants and funding

This work was supported by grants from MICINN (SAF2006-0475 and SAF2009-11297), Ayudas del Programa de Creación y Consolidación de Grupos de Investigación UCM-Banco Santander (GR58/08, GR35/10A, GR35/10B and GR42/10), Fundación de Investigación Médica Mutua Madrileña and IODURE project, CIBER de Diabetes y Enfermedades Metabólicas Asociadas, an initiative of ISCIII (Ministerio de Ciencia e Innovación). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.