CHARACTERIZATION OF NUCLEAR RETINOIC ACID-BINDING ACTIVITY IN SENSITIVE LEUKEMIC-CELL LINES - CELL-SPECIFIC UPTAKE OF ATRA AND RAR-ALPHA PROTEIN MODULATION

The diverse effects of all-trans retinoic acid (ATRA) on growth, diffe rentiation and homeostasis of vertebrate organisms are mediated by thr ee distinct isoforms of retinoic acid receptors (RARs), Although it is not known to what extent each RAR contributes to the different effect s of ATRA, several studies have demonstrated that ATRA induced granulo cytic differentiation in human myeloid leukemic cell lines is mediated by RAR alpha. In this study, we investigated ATRA binding affinity of the endogenous nuclear receptors of HL-60 and NB4 leukemic cells, Sca tchard plot analysis yielded an apparent dissociation constant of 5+/- 0.3 nM and 1400+/-80 receptor sites per cell in HL-60 cells, whereas t he NB4 promyelocytic leukemic cell line showed a lower affinity (8.5+/ -0.5 nM and 900+/-30 receptor sites per cell). Modulation of RAR alpha protein (5 fold excess) was found in NB4 cells after 24 hours ATRA ex posure, whereas HL-60 cells required a 72-hour culture period to weakl y increase the RAR alpha protein level These data were closely related to the ATRA intracellular concentration and kinetics of terminal diff erentiation of the cells. (C) 1995 Academic Press, Inc.