Induction of apoptosis by vitamin D3 analogue EB1089 in NCI-H929 myeloma cells via activation of caspase 3 and p38 MAP kinase

EB1089, a novel 1,25-dihydroxyvitamin D-3 analogue, has been known to have potent antiproliferative properties in a variety of malignant cells both in vitro and in vivo. In the present study we analysed the effect of EB1089 on NCI-H929 human myeloma cells. EB1089 inhibited cell growth of NCI-H929 and efficiently induced the G(1) phase arrest of the cell cycle in a dose-dependent manner. We could also detect apoptosis in NCI-H929 cells exposed to EB1089 (1 x 10(-7) M for 72 h) using the sub-G(1) group of the cell cycle by FAGS and annexin V binding assays. Induction of apoptosis by EB1089 was associated with down-regulation of the Bcl-2 protein without change of the Bar protein. Regarding caspase activity, which plays a crucial role in apoptosis, EB1089-treated NCI-H929 cells revealed an increased activity of caspase 3 protease accompanied by degradation of the PARP protein in a dose- and time-dependent manner, In addition, EB1089 caused the down-regulation of p44 extracellular signal-related kinase (ERK) activity and up-regulation of the p38 kinase activity during apoptosis of NCI-H929 cells, These results suggest that EB1089 inhibits growth of NCI-H929 cells via G(1) cell cycle arrest as well as apoptosis by activating p38 kinase and suppressing ERK activity.