1,25-dihydroxyvitamin D-3 induces differentiation of a retinoic acid-resistant acute promyelocytic leukemia cell line (UF-1) associated with expression of p21(WAF1/CIP1) and p27(KIP1)

Retinoic acid (RA) resistance is a serious problem for patients with acute promyelocytic leukemia (APL) who are receiving all-trans RA. However, the m echanisms and strategies to overcome RA resistance by APL cells are still u nclear. The biologic effects of RA are mediated by two distinct families of transcriptional factors: RA receptors (RARs) and retinoid X receptors (RXR s). RXRs heterodimerize with 1,25-dihydroxyvitamin D-3 [1,25(OH)(2)D-3] rec eptor (VDR), enabling their efficient transcriptional activation. The cycli n-dependent kinase (cdk) inhibitor p21(WAF1/CIP1) has a vitamin D-3-respons ive element (VDRE) in its promoter, and 1,25(OH)(2)D-3 enhances the express ion of p21(WAF1/CIP1) and induces differentiation of selected myeloid leuke mic cell lines. We have recently established a novel APL cell line (UF-1) w ith features of RA resistance. 1,25(OH)(2)D-3 can induce growth inhibition and G1 arrest of UF-1 cells, resulting in differentiation of these cells to ward granulocytes. This 1,25(OH)(2)D-3-induced G1 arrest is enhanced by all -trans RA. Also, 1,25(OH)(2)D-3 (10(-10) to 10(-7) mol/L) in combination wi th RA markedly inhibits cellular proliferation in a dose- and time-dependen t manner. Associated with these findings, the levels of p21(WAF1/CIP1) and p27(KIP1) mRNA and protein increased in these cells. Northern blot analysis showed that p21(WAF1/CIP1) and p27(KIP1) mRNA and protein increased in the se cells. Northern blot analysis showed that p21(WAF1/CIP1) and p27(KIP1) t ranscripts were induced after 6 hours' exposure to 1,25(OH)(2)D-3 and then decreased to basal levels over 48 hours. Western blot experiments showed th at p21(WAF1/CIP1) protein levels increased and became detectable after 12 h ours of 1,25(OH)(2)D-3 treatment and induction of p27(KIP1) protein was muc h more gradual and sustained in UF-1 cells. Interestingly, the combination of 1,25(OH)(2)D-3 and RA markedly enhanced the levels of p27(KIP1) transcri pt and protein as compared with levels induced by 1,25(OH)(2)D-3 alone. In addition, exogenous p27(KIP1) expression can enhance the level of CD11b ant igen in myeloid leukemic cells. In contrast, RA alone can induce G1 arrest of UF-1 cells; however, it did not result in an increase of p21(WAF1/CIP1) and p27(KIP1) transcript and protein expression in RA-resistant cells. Take n together, we conclude that 1,25(OH)(2)D-3 induces increased expression of cdk inhibitors, which mediates a G1 arrest, and this may be associated wit h differentiation of HA-resistant UF-1 cells toward mature granulocytes. (C ) 1999 by The American Society of Hematology.