Expression of the ornithine decarboxylase gene in response to
asparagine in intestinal epithelial cells.
Wang, Jian-Ying, Mary Jane Viar, Patrick M. Blanner, and Leonard R.
Johnson.
Department of Surgery, University of Maryland Medical School and
Baltimore
APStracts 3:0029G, 1996.
Refeeding fasted rats significantly stimulates mucosal growth and
ornithine decarboxylase (ODC), the rate-limiting enzyme in the
biosynthesis of polyamines, but the exact mechanism responsible for
induction of ODC at the molecular level is unknown. Of normal dietary
constituents the amino acid asparagine markedly increases ODC
activity and mucosal growth when administered intragastrically. The
current study examined the expression of the ODC gene in IEC-6 cells
(a line of normal rat small intestinal crypt cells) after exposure to
asparagine. Cells were grown in Dulbecco's minimal essential medium
containing 5% dialyzed fetal bovine serum (dFBS). They were deprived
of serum for 24 h before experiments. Exposure to asparagine at the
dose of 10 mM resulted in the rapid increase in ODC mRNA levels. The
increased expression of the ODC gene began 1 h and peaked between 3
and 5 h after treatment with asparagine. Maximum increases in ODC
mRNA levels were approximately 5-fold the normal value. Increased
levels of ODC mRNA in cells exposed to asparagine were paralleled by
increases in ODC protein and enzyme activity and cellular polyamine
levels. The half-life of mRNA for ODC in unstimulated IEC-6 cells was
30 min and increased to more than 2 h in cells exposed to 10 mM
asparagine. The half-life of ODC activity also was increased in
asparagine-treated cells. When cellular protein synthesis was
inhibited by of cycloheximide, asparagine superinduced ODC mRNA
levels. Furthermore, asparagine also significantly stimulated DNA
synthesis in IEC-6 cell line. These results indicate that 1)
asparagine stimulates ODC in IEC-6 cells through multiple pathways,
and 2) increased ODC mRNA levels result partly from a delay in the
rate of degradation. These findings suggest that luminal amino acids
stimulate gut mucosal growth in the association with their ability to
regulate ODC gene expression.
Received 21 August 1995; accepted in final form 19 January 1996.
APS Manuscript Number G363-5.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 February 96