The fraction of
glucose metabolized to
lactate is dramatically reduced during erythroid differentiation of mouse
erythroleukemia (MEL) cells induced by
dimethyl sulfoxide (
DMSO),
hexamethylene bisacetamide (
HMBA), or
sodium butyrate treatment. In order to determine the mechanism of the reduction in
lactate production, several enzymatic steps in
glucose catabolism were investigated. No changes in glycolytic
enzyme levels were found during differentiation that could account for the alteration in
lactate production and alterations in
pyruvate kinase activity are known not to occur during MEL cell differentiation. Further, utilizing D-
mannoheptulose, a specific inhibitor of hepatic-/
tumor-specific
glucokinase, no dependence on the activity of this
enzyme for growth or differentiation was observed. Therefore, the possibility was entertained that the decrease in
lactate production reflected a decrease in
fructose 2,6-bisphosphate (F-2,6-P-2) which is a major regulator of the
lactate production due to its ability to allosterically stimulate
phosphofructokinase-1 (PFK-1) activity. PFK-1 cannot function in the absence of F-2,6-P-2 when only a suboptimal concentration of one of its substrates,
fructose-6-phosphate (F-6-P), is present. When assayed under limiting F-6-P concentrations, it was found that following
DMSO- or
HMBA-induced differentiation, PFK-1 activity was decreased 7-20-fold. This finding suggested that F-2,6-P-2 levels might be controlling
lactate production in this system. In keeping with this idea, marked decreases in F-2,6-P-2 levels were found to occur during
DMSO- or
HMBA-induced differentiation. These data suggest that decreasing F-2,6-P-2 levels account for the decrease in
lactate accumulation that occurs during MEL cell differentiation.