AJP - Gastrointestinal and Liver Physiology, Vol 263, Issue 4 494-G501, Copyright © 1992 by American Physiological Society
Effect of putrescine on S-adenosylmethionine decarboxylase in a small intestinal crypt cell line
J. Y. Wang, M. J. Viar, S. A. McCormack and L. R. Johnson
Department of Physiology and Biophysics, University of Tennessee College of Medicine, Memphis 38163.
Two key enzymes in polyamine biosynthesis are ornithine decarboxylase (ODC)
and S-adenosylmethionine decarboxylase (SAMDC). SAMDC decarboxylates
S-adenosylmethionine, which then donates aminopropyl groups for spermidine
and spermine synthesis. The purpose of our study was to determine whether
putrescine, taken up from medium or synthesized endogenously by ODC, alters
SAMDC activity. Studies were conducted in the IEC-6 cell line derived from
rat small intestinal crypt cells. 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. Basal SAMDC activity
was increased significantly by > or = 10(-4) M of putrescine. Lower
doses had no significant effect. The same doses of putrescine decreased ODC
activity to near zero. Asparagine at 10 mM or 5% dFBS not only stimulated
ODC activity and the intracellular putrescine levels but also increased
significantly SAMDC activity as well. ODC activity peaked at 3 h, and the
maximum level of SAMDC occurred 3-4 h after exposure to asparagine or
serum. Treatment with DL-alpha-difluoromethylornithine (DFMO), a specific
ODC inhibitor, prevented the increases in both cellular putrescine levels
and SAMDC activity in asparagine- and serum-treated cells. In the presence
of DFMO, exogenous putrescine returned SAMDC activity toward control levels
but had no effect on ODC. A very slight increase of SAMDC half-life in
IEC-6 cells grown in the presence of putrescine was not statistically
significant.(ABSTRACT TRUNCATED AT 250 WORDS)
