Retinoic acid receptors in myeloid leukemia: characterization of receptors in retinoic acid-resistant K-562 cells

Although mRNA for the retinoic acid receptor alpha (RAR-alpha) is expressed in many different myeloid leukemias, most of these leukemia cells exhibit little if any phenotypic response when exposed to retinoic acid (RA). To determine whether such RA resistance is related to altered RA receptor structure or function, we performed a detailed analysis of nuclear RA receptors in RA-resistant K-562 cells. These cells exhibit RA receptors of the same approximate molecular weight and similar kd as those exhibited by the RA-sensitive HL-60 leukemia cell line, but the number of RA receptors in the RA-resistant K-562 cells (80 per cell) is significantly lower than that exhibited by RA- sensitive HL-60 cells (550 per cell). Retroviral-mediated transduction of RAR-alpha cDNA into K-562 significantly increased the number of RA receptors to 2,000 per cell. These RAR-alpha-transduced K-562 cells, when incubated with RA, exhibit diminished cell proliferation associated with decreased c-myc expression and an accumulation of cells in G0/G1. In addition, these RA-treated cells exhibit downregulation of the CD15 surface antigen and a slight increase in hemoglobin production but manifest no other evidence of significant erythroid, megakaryocytic, or myeloid differentiation. These results indicate that an elevated number of nuclear RA receptors can be involved in altering proliferation but not necessarily the differentiation of certain RA- treated myeloid leukemia cells.