GROWTH-INHIBITION OF HUMAN BREAST-CANCER CELLS BY 1,25-DIHYDROXYVITAMIN-D-3 IS ACCOMPANIED BY INDUCTION OF APOLIPOPROTEIN-D EXPRESSION

We have analyzed the effect of 1,25-dihydroxyvitamin D-3 on the expres sion of the gene encoding apolipoprotein D (apoD), a protein component of the human plasma lipid transport system that is overproduced by a specific subset of breast carcinomas. Northern blot analysis revealed that 1,25-dihydroxyvitamin D-3 strongly up-regulated apoD mRNA levels in T-47D human breast cancer cells in a time-and dose-dependent manner . The potency of this vitamin as an inducer of apoD expression was str onger than the effect observed for such steroid hormones as androgens and progesterone, described previously as hormonal up-regulators of ap oD expression in these cells. A time course study demonstrated that th e induction of apoD mRNA reached a level of 5-fold over the untreated cells after 48 h of incubation in the presence of 10(-7) M 1,25-dihydr oxyvitamin D-3. A dose-response analysis showed that a 10(-6) M concen tration of this vitamin consistently induced a maximal accumulation of 7-fold over the control cells. Similar up-regulatory effects on the a poD gene expression were obtained by treatment of T-47D cells with 1,2 5-dihydroxyvitamin D-3 analogues, including MC 903, which is relativel y devoid of hypercalcemic side effects in clinical applications. Weste rn blot analysis revealed that the inductive effect of 1,25-dihydroxyv itamin D-3 was also reflected at the protein level as an increase of i mmunoreactive protein in the conditioned media of vitamin-treated cell s. This increased expression of apoD was accompanied by an inhibition of cell growth and morphological changes in T-47D cells. By contrast, we did not detect any inductive effect of 1,25-dihydroxyvitamin D-3 on apoD gene expression in MDA-MB-231 cells, which are refractory to the growth-inhibitory effects of this compound. On the basis of these res ults, we propose 1,25-dihydroxyvitamin D-3 as an important regulator o f the expression of the apoD gene in breast carcinomas. We also sugges t that apoD may be of interest as a biochemical marker of the action o f 1,25-dihydroxyvitamin D-3 derivatives in current studies using these compounds as inhibitors of breast cancer cell growth or as chemothera peutic agents in the prevention of breast cancer.