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 cell ular resistance to the induction of differentiation by all-trans retinoic a cid (RA) we have generated and analyzed a mutant, RA-resistant HL-60 cell l ine. Molecular analysis of the retinoic acid receptor alpha (RAR alpha) cDN A 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 res triction endonuclease site previously described. As a consequence of this d eletion and translational frame-shift, a stop signal is created that trunca tes 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 cytoge netic analysis, fluorescent in situ hybridization (FISH) and comparative ge nomic hybridization (CGH) analysis revealed the presence of two RAR alpha l oci, and showed a composite karyotype with additional abnormalities with re spect to the parental line, including a chromosome 8 insertion in a chromos ome previously known as marker three. (C) 1999 Elsevier Science Ltd. All ri ghts reserved.