Amino acid control of asparagine synthetase: relation to
asparaginase resistance in human leukemia cells.
Hutson, Richard G., Toshiyuki Kitoh, David A. Moraga Amador, Sanja
Cosic, Sheldon M. Schuster, and Michael S. Kilberg.
Department of Biochemistry and Molecular Biology, University of
Florida College of Medicine, Box 100245 JHMHC, Gainesville, Florida
32610-0245
APStracts 3:0405C, 1996.
Complete amino acid deprivation of mammalian cells causes a
significant enhancement in gene expression for a number of important
cellular activities, among these is included asparagine synthetase
(AS). The data presented demonstrate that in both non-leukemic (rat
Fao hepatoma cells) and human leukemia cells (MOLT-4, NALL-1, and
BALL-1), AS mRNA levels, protein content, and enzymatic activity is
induced following incubation in an otherwise complete tissue culture
medium that is deficient in a single amino acid or in medium that has
been depleted of the amino acid asparagine by the addition of
asparaginase. Complete amino acid deprivation results in a concerted
increase in AS mRNA, protein and enzymatic activity which, in
conjunction with previously published research, suggests that the
mechanism of this cellular response involves transcriptional control
of the AS gene. Asparaginase (ASNase) treatment is a standard
component of acute lymphoblastic leukemia therapy for which the
effectiveness is related to the inability of these cells to up
-regulate AS activity to a sufficient level. With regard to the ASNase
sensitivity of the three human leukemia cell lines, there was a trend
toward an inverse relation to the degree of AS expression. Selection
for ASNase-resistant MOLT-4 sublines resulted in enhanced AS mRNA and
protein content regardless of whether the cells had been selected by
ASNase treatment directly or asparagine removal from the culture
medium. Collectively, the data illustrate that further advances in
ASNase therapy will require additional knowledge of amino acid
-dependent regulation of AS gene expression and conversely, that
ASNase resistance represents a model system to investigate metabolite
control in a clinically relevant setting.
Received 4 September 1996; accepted in final form 3 December
1996.
APS Manuscript Number C515-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996