Apoptosis/differentiation-inducing effects of vitamin K-2 on HL-60 cells: dichotomous nature of vitamin K-2 in leukemia cells

We originally reported that vitamin K-2 (VK2) analogs, including menaquinon e 4 (MK4) but not vitamin K1, effectively induce apoptosis in various types of primary cultured leukemia cells and leukemia cell lines in vitro. It ha s also been reported by others that VK2 showed the differentiation-inducing activity in leukemia cell lines. To investigate the discrepancy between ap optosis- and differentiation-inductions of leukemia cells by VK2 treatment, we used bcl-2 gene transfected HL-60 cells (HL-60-bcl-2) which resulted in five-fold over-expression of BCL-2 protein, and then compared the effects of MK4 to the control HL-60-neo cells. Seventy-two hours of exposure to var ious concentrations of MK4 resulted in growth inhibition of these cells in a dose-dependent manner (0.1-50 muM), however, HL-60-bcl-2 was less sensiti ve against MK4. MK4 potently induced apoptosis of HL-60-neo cells along wit h the depolarization of mitochondrial membrane potential and caspase-3 acti vation. Notably, HL-60-bcl-2 was almost completely resistant to apoptosis i nduction in response to MK4, although cell growth inhibition was still obse rved. In spite of the abrogation of apoptosis induction, about 90% of HL-60 -bcl-2 cells were arrested in the G0/G1 phase within 48 h of exposure to 10 muM of MK4 accompanied by up-modulation of p27KIP1 expression. Concomitant ly, HL-60-bcl-2 cells underwent monocytic differentiation. These data sugge st that VK2 also shows the differentiation inducing effects on leukemia cel ls which are resistant against VK2-inducing apoptosis. The dichotomous natu re of VK2 against leukemia cells appears to have clinical benefits for the treatment of patients with leukemias and myelodysplastic syndromes.