CCK-independent mTORC1 activation during dietary protein-induced exocrine pancreas growth

Am J Physiol Gastrointest Liver Physiol. 2010 Nov;299(5):G1154-63. doi: 10.1152/ajpgi.00445.2009. Epub 2010 Aug 26.

Abstract

Dietary protein can stimulate pancreatic growth in the absence of CCK release, but there is little data on the regulation of CCK-independent growth. To identify mechanisms whereby protein stimulates pancreatic growth in the absence of CCK release, C57BL/6 control and CCK-null male mice were fed normal-protein (14% casein) or high-protein (75% casein) chow for 7 days. The weight of the pancreas increased by 32% in C57BL/6 mice and 26% in CCK-null mice fed high-protein chow. Changes in pancreatic weight in control mice were due to both cell hypertrophy and hyperplasia since there was an increase in protein-to-DNA ratio, total DNA content, and DNA synthesis. In CCK-null mice pancreatic growth was almost entirely due to hypertrophy with both protein-to-DNA ratio and cell size increasing without significant increases in DNA content or DNA synthesis. ERK, calcineurin, and mammalian target of rapamycin complex 1 (mTORC1) are activated in models of CCK-induced growth, but there were no differences in ERK or calcineurin activation between fasted and fed CCK-null mice. In contrast, mTORC1 activation was increased after feeding and the duration of activation was prolonged in mice fed high-protein chow compared with normal-protein chow. Changes in pancreatic weight and RNA content were completely inhibited, and changes in protein content were partially abated, when the mTORC1 inhibitor rapamycin was administered during high-protein chow feeding. Prolonged mTORC1 activation is thus required for dietary protein-induced pancreatic growth in the absence of CCK.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Analysis of Variance
  • Animals
  • Blotting, Western
  • Calcineurin / metabolism
  • Cholecystokinin / genetics
  • Cholecystokinin / metabolism*
  • Dietary Proteins / metabolism*
  • Male
  • Mechanistic Target of Rapamycin Complex 1
  • Mice
  • Mice, Knockout
  • Multiprotein Complexes
  • Organ Size
  • Pancreas, Exocrine / growth & development*
  • Pancreas, Exocrine / metabolism
  • Phosphorylation
  • Proteins
  • Proto-Oncogene Proteins c-akt / metabolism
  • Signal Transduction
  • TOR Serine-Threonine Kinases
  • Transcription Factors / metabolism*

Substances

  • Dietary Proteins
  • Multiprotein Complexes
  • Proteins
  • Transcription Factors
  • Cholecystokinin
  • TOR Serine-Threonine Kinases
  • Mechanistic Target of Rapamycin Complex 1
  • Proto-Oncogene Proteins c-akt
  • Calcineurin