A unique carboxy-terminus truncation mutant of the retinoic acid receptor alpha gene associated with a variant marker chromosome in a retinoic acid resistant HL-60 subline

In order to contribute to the study of the molecular basis of leukemic cellular resistance to the induction of differentiation by all-trans retinoic acid (RA) we have generated and analyzed a mutant, RA-resistant HL-60 cell line. Molecular analysis of the retinoic acid receptor alpha (RAR alpha) cDNA disclosed, in one of the two alleles, a novel mutation consisting of a 7-base deletion in the ligand binding domain that includes part of a FokI restriction endonuclease site previously described. As a consequence of this deletion and translational frame-shift, a stop signal is created that truncates the protein at codon 421, disrupting an essential functional component of the receptor. Transducing an epitope tagged RAR alpha into the mutant is sufficient to inhibit clonal growth in the presence of RA. Standard cytogenetic analysis, fluorescent in situ hybridization (FISH) and comparative genomic hybridization (CGH) analysis revealed the presence of two RAR alpha loci, and showed a composite karyotype with additional abnormalities with respect to the parental line, including a chromosome 8 insertion in a chromosome previously known as marker three. (C) 1999 Elsevier Science Ltd. All rights reserved.