Radiation-induced deletion of chromosomal regions containing tumor suppressor genes in human bronchial epithelial cells

Abstract

While several specific genetic alterations have been associated with malignant transformation of human bronchial epithelial cells, they are not all present in every tumor and there is reason to believe that additional genes important for loss of replication control in these cells remain to be identified. In an effort to develop a human bronchial epithelial cell model suitable for identification and functional analysis of genes involved in loss of replication control, and for studying the genetic basis of the multi-stage phenotypic changes associated with tumorigenesis, we treated multiple independent populations of the human papillomavirus (HPV)-immortalized human bronchial epithelial cell line BEP2D with ionizing radiation. Following irradiation, cell lines representing the radiated populations were established from single soft agar-selected colonies. These lines--R2B5SA, R3B5DSA, R2H9S, R2H16S, R2H18S and R3D7S--were compared cytogenetically to the parent cell line and found to have new chromosomal deletions involving putative or confirmed tumor suppressor genes, including chromosome 13 in most R2B5SA cells and all R3B5SA cells, chromosomes 11p and 22 in R216S, and 3p, 11p and 22 in R2H18S. The R2B5SA cells that have lost one copy of chromosome 13 overgrow the culture but are not tumorigenic, suggesting that loss of a single copy of chromosome 13 confers growth advantage but not tumorigenicity. The data confirm that ionizing radiation induces many large chromosomal alterations including chromosomal loss, translocation and deletion and that following radiation it is possible to isolate immortalized nontumorigenic cell lines monosomic for regions known or suspected to contain tumor suppressor genes. The cell lines described here provide powerful models for further investigation of putative tumor suppressor genes including identification, functional analysis and stage of transformation at which they are operative.