Differential expression of amino acid transport systems A and ASC during erythroleukemia cell differentiation

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.