Fructose 2,6-bisphosphate metabolism during megakaryocytic differentiation of K562 and MEG-01 cells.

Fructose 2,6-bisphosphate (Fru-2, 6-P2) represents the most powerful activator of 6-phosphofructo-1-kinase, rate-limiting enzyme of glycolysis. Fru-2,6-P2 content is tightly regulated and appears to be under the control of different hormones and growth factors, acting either through covalent modification of isoenzymatic forms of 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase (PFK-2/FBPase-2), the bifunctional enzyme responsible for the synthesis and the degradation of the compound, or through changes in transcription rate and/or in the expression of different isoforms of the enzyme. In the present study the metabolism of Fru-2,6-P2 was investigated during the differentiation toward megakaryocytes induced by phorbol 12-myristate 13-acetate (PMA) treatment of human leukemia K562 and MEG-01 cell lines. Fru-2,6-P2 content as well as PFK-2 activity were increased in a dose-dependent manner after 4 days of incubation with PMA. MEG-01 cells resulted more sensitive to the effect of the inducer, anyway in both cell types cytostatic concentrations of the phorbol ester were able to affect Fru-2,6-P2 metabolism. The effect of PMA was maximal at 4 days of incubation in both examined cell lines. Interestingly, the effect induced by the phorbol ester at 4 days was still appreciable subculturing K562 and MEG-01 cells for 3 days in the absence of the inducer and was associated with relevant changes in the molecular properties of PFK-2: namely increased Vmax and K(m). This latter finding suggests that the rise in Fru-2,6-P2 content during the differentiation process toward megakaryocytes might result from the expression of a novel PFK-2 isoform.