Compensatory responses to pyruvate carboxylase suppression in islet beta-cells. Preservation of glucose-stimulated insulin secretion

J Biol Chem. 2006 Aug 4;281(31):22342-22351. doi: 10.1074/jbc.M604350200. Epub 2006 Jun 1.


We have previously reported that glucose-stimulated insulin secretion (GSIS) is tightly correlated with pyruvate carboxylase (PC)-catalyzed anaplerotic flux into the tricarboxylic acid cycle and stimulation of pyruvate cycling activity. To further evaluate the role of PC in beta-cell function, we constructed a recombinant adenovirus containing a small interfering RNA (siRNA) specific to PC (Ad-siPC). Ad-siPC reduced PC mRNA levels by 83 and 64% and PC protein by 56 and 35% in INS-1-derived 832/13 cells and primary rat islets, respectively. Surprisingly, this manipulation did not impair GSIS in rat islets. In Ad-siPC-treated 832/13 cells, GSIS was slightly increased, whereas glycolytic rate and glucose oxidation were unaffected. Flux through PC at high glucose was decreased by only 20%, suggesting an increase in PC-specific activity. Acetyl carnitine, a surrogate for acetyl-CoA, an allosteric activator of PC, was increased by 36% in Ad-siPC-treated cells, suggesting a mechanism by which PC enzymatic activity is maintained with suppressed PC protein levels. In addition, the NADPH:NADP ratio, a proposed coupling factor for GSIS, was unaffected in Ad-siPC-treated cells. We conclude that beta-cells activate compensatory mechanisms in response to suppression of PC expression that prevent impairment of anaplerosis, pyruvate cycling, NAPDH production, and GSIS.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetylcarnitine / analysis
  • Allosteric Regulation*
  • Animals
  • Cell Line
  • Glucose / pharmacology*
  • Insulin / metabolism*
  • Insulin Secretion
  • Insulin-Secreting Cells / metabolism*
  • Islets of Langerhans
  • NADP / biosynthesis
  • Pyruvate Carboxylase / antagonists & inhibitors
  • Pyruvate Carboxylase / physiology*
  • RNA, Small Interfering / pharmacology
  • Rats


  • Insulin
  • RNA, Small Interfering
  • NADP
  • Acetylcarnitine
  • Pyruvate Carboxylase
  • Glucose