AJP - Cell Physiology, Vol 260, Issue 3 C392-C399, Copyright © 1991 by American Physiological Society
Differential expression of amino acid transport systems A and ASC during erythroleukemia cell differentiation
J. V. Vadgama, M. N. Chan and J. M. Wu
Department of Pediatrics, Harbor-UCLA Medical Center, Torrance.
The human erythroleukemic cell K-562 serves as an in vitro model to study
changes in cell surface antigens and mechanisms regulating globin gene
expression associated with in vivo erythropoiesis. In this report we have
examined the regulation of amino acid transport systems, in particular,
systems A and ASC, during differentiation of erythroleukemic cells. For
additional comparison we examined the uptake of leucine,
3-aminoendobicyclo-(3,2,1)-octane-3-carboxylic acid (BCO), arginine, and
glutamate. Hexamethylene-bis-acetamide (HMBA), dimethyl sulfoxide, and
butyrate induce cell differentiation with a block in G1-G0 phase of the
cell cycle. These agents caused a significant downregulation of
2-(methylamino)isobutyric acid uptake by system A. In contrast, the
Na(+)-dependent threonine uptake by system ASC remained unaltered. The
uptake of leucine, BCO, arginine, and glutamate by as yet unidentified
systems was, however, stimulated after HMBA treatment. Hemin, a potent
inducer of hemoglobin synthesis in K-562 cells, does not block cell cycle
events and, interestingly, had no significant effect on both systems A and
ASC. These differences in inducer actions suggest that system A activity
may be related to specific stages of cell differentiation and perhaps to
other cellular signals.
