Control of cell cycle regulatory protein expression by 1,25-dihydroxyvitamin D-3 in human promyelocytic HL-60 leukemic cells cultured in serum-free medium

1,25-Dihydroxyvitamin D-3 (herein referred to as vitamin D-3), the natural vitamin D-3 formed by successive hydroxylation of cholecalciferol at the 25 and 1 alpha position, and numerous vitamin D-3 analogs, have been reported to decrease proliferation and promote terminal differentiation from several types of human malignant cells, including the human promyelocytic HL-60 leukemic cells. The purpose of this study was to determine if and to what extent the cell culture conditions affect the sensitivity of the HL-60 cells to vitamin D-3, both in terms of cell growth, differentiation, and changes in expression of specific proteins. Addition of 10 nM and 100 nM vitamin D-3 to HL-60 cells cultured in the serum-free, chemically defined medium of insulin/transferrin/selenium (ITS) effected cell growth differently than cells maintained in a fetal bovine serum-supplemented medium. In addition to the greater degree of growth suppression by 100 nM vitamin D-3, cells maintained in serum-free medium also displayed significantly higher levels of monocytic differentiation. Furthermore, Western blot analysis showed that a pronounced arrest of cell cycling at the G(1)-to-S-phase transition, concomitant with a corresponding 36% down-regulation of cyclin D1 and, in parallel, a similar decreased hyperphosphorylation of pRb, was elicited by 100 nM vitamin D-3. These results indicate that the sensitivity of HL-60 cells to vitamin D-3 is dependent on the availability of serum.