Identification and characterization of nuclear retinoic acid-binding activity in human myeloblastic leukemia HL-60 cells.

Specific [3H]retinoic acid (RA)-binding sites in nuclear and cytosolic extracts prepared from human myeloblastic leukemia HL-60 cells have been detected by sucrose density gradient sedimentation and size-exclusion highperformance liquid chromatography (HPLC) analyses. This RA-binding activity migrated as a single peak with an apparent molecular weight of 50,000 and >95% of the total binding activity was associated with the nuclear extract. Nuclear extracts prepared from COS-1 cells transfected with an expression vector for the nuclear RA receptors RARa or RARE were enriched (20- to 100-fold) with a RA-binding activity that coeluted by size-exclusion HPLC with the putative RAR from HL-60 cells. The HL-60 nuclear receptor exhibited high affinity binding ofRA and its benzoic acid analogs ChS5, Ch3O, Ro 13-7410, and SRI 6409-40 and low-affinity binding of retinol, Ro 8-8717, and SRI 5442-60, correlating well with the biological activity of these compounds in HL-60 cells. Saturation binding and Scatchard plot analyses of the binding of RA to the nuclear HL-60 receptor yielded an apparent dissociation constant of -0.46 nM and 1400 ± 100 receptor sites per cell. Northern blot analyses of poly(A)+ RNA with cDNA probes specific for RARa and RARf indicated that HL-60 cells contain predominantly transcripts encoded by the RARa gene. Our results suggest that the observed nuclear RA-binding activity in HL-60 cells might mediate the action of RA in these cells.