POTENTIATION OF SODIUM BUTYRATE-INDUCED APOPTOSIS BY VANADATE IN HUMAN PROMYELOCYTIC LEUKEMIA-CELL LINE HL-60

Vanadate (10 mu M), a potent inhibitor of tyrosine phosphatase, added simultaneously potentiated the sodium butyrate (BuONa)-induced growth inhibition. Furthermore, at 1 mM BuONa alone, after 96 h of incubation , about 20 +/- 5% of cells exhibited the morphological characteristic of apoptosis, as established by nuclear changes (condensed and fragmen ted nuclei) and decrease in cell size. After treatment of cells with 1 mM BuONa in the presence of 10 mu M vanadate, apoptotic cells became more abundant; 90 +/- 3% of cells presented morphological characterist ics of apoptosis after 96 h of incubation. Flow cytometric measurement of DNA content demonstrated the accumulation of cells in G(1) phase a fter 72 h of incubation with 1 mM BuONa alone. In the presence of vana date (10 mu M), accumulation of cells in G(1) phase appeared after sho rter times of incubation (48 h) with BuONa. A substantial increase in the proportion of cells with degraded DNA characteristic of apoptosis was observed after 48- to 72-h incubation with BuONa in the presence o f vanadate. BuONa-induced apoptosis was accompanied by the increase of tyrosine phosphorylation of cellular proteins pp37 and pp97. Our resu lts raised the possibility that regulation of tyrosine phosphorylation of pp37 and pp97 is an important event that heralds the BuONa-induced apoptosis. (C) 1996 Academic Press, Inc.