Cell cycle arrest induced by the vitamin D-3 analog EB1089 in NCI-H929 myeloma cells is associated with induction of the cyclin-dependent kinase inhibitor p27

EB1089, a 1,25-dihydroxyvitamin D-3 analog, has been known to have potent a ntiproliferative properties in a variety of malignant cells in vitro and in vivo. In the present study, we analyzed the effect of EB1089 on human myel oma cell lines, EB1089 inhibited the proliferation of NCI-H929 cells and RP MI8226 cells in a dose-dependent manner among three myeloma cell lines test ed. The antiproliferative effect of EB1089 on myeloma cells was related to the expression level of vitamin D receptor, To investigate the mechanism of the antiproliferative effect of EB1089, cell cycle analysis was attempted in EB1089-sensitive NCI-H929 cells, EB1089 (1 x 10(-8) M) efficiently induc ed G(1), arrest of the cell cycle. Analysis of G(1) regulatory proteins dem onstrated that protein levels of CDK2, CDK4, cyclin D1, and cyclin A were d ecreased in a time-dependent manner, but not those of CDK6 and cyclin E, by EB1089, In addition, EB1089 (1 x 10(-8) M, 72 h) increased the protein lev el of the CDKI, p27 and markedly enhanced the binding of p27 with CDK2 comp ared to EB1089-untreated cells. Furthermore, the activity of CDK2-associate d cyclin kinase was decreased, which was accompanied by the reduction of cy clin-D1-, cyclin-E-, and cyclin-A-associated kinase activities, resulting i n the hypophosphorylation of Rb protein. These results suggest that EB1089 can inhibit the proliferation of human myeloma cells, especially NCI-H929 c ells, via a G(1), block in association with the induction of p27 and the re duction of CDK2 activity, (C) 2000 Academic Press.