Human Glucocorticoid Receptor Gene Deletion following Exposure to Cancer

The sensitivity of the human glucocorticoid receptor (hGR) gene to mutagenesis by the cancer chemotherapeutic drugs adriamycin, bleomycin, and chlorambucil was evaluated using glucocorticoid-sensitive (dex s) subciones of the human leukemic cell line CEM-C7. Treatment of cells with either bleomycin or chlorambucil increased the frequency of glucocorticoid-resistant (dex r) clones 3.3and 10-fold, respectively. Measurement of steroid-binding activity in intact dex r cells demonstrated that the predominant phenotype of drug-induced dex r clones was receptorless (r-). dex s CEM cells express only one functional hGR allele and, in addition, are heterozygous for a Bcll restriction fragment length polymorphism in the hGR gene (L. A. Palmer and J. M. Harmon, Cancer Res., 51: 5224-5231, 1991). To determine the basis of the rphenotype, Bcll digests of genomic DNA isolated from r + and rcell lines were examined for the presence of the polymorphic 2.4and 4.4-kilobase digestion products. A deletion of all or part of the hGR gene was demonstrated by the absence of the 4.4-kilobase fragment in one of two bleomycin-induced dex r clones, as well as the ICR191-induced dex r cell line ICR27TK.3. Cytogenetic analysis of ICR27TK.3 showed that the distal portion of the long arm of one chromosome 5 had been replaced with a portion of chromosome 15. Thus, in at least two dex r cell lines, deletions and/or chromosome breaks in the hGR locus appear to account for the rphenotype.