CSA-19, A RADIATION-RESPONSIVE HUMAN GENE, IDENTIFIED BY AN UNBIASED 2-GEL CDNA LIBRARY SCREENING METHOD IN HUMAN CANCER-CELLS

A novel polymerase chain reaction (PCR)-based method was used to ident ify candidate genes whose expression is altered in cancer cells by ion izing radiation, Transcriptional induction of randomly selected genes in control versus irradiated human HL60 cells was compared, Among seve ral complementary DNA (cDNA) clones recovered by this approach, one cD NA clone (CL68-5) was downregulated in X-irradiated HL60 cells but una ffected by 12-O-tetradecanoyl phorbol-13-atetate, forskolin, or cyclos porin-A. DNA sequencing of the CL68-5 cDNA revealed 100% nucleotide se quence homology to the reported human Csa-19 gene, Northern blot analy sis of RNA from control and irradiated cells revealed the expression o f a single 0.7-kilobase (kb) messenger RNA (mRNA) transcript, This 0.7 -kb Csa-19 mRNA transcript was also expressed in a variety of human ad ult and corresponding fetal normal tissues, Moreover, when the effect of X- or fission neutron-irradiation on Csa-19 mRNA was compared in cu ltured human cells differing in p53 gene status (p53(-/-) ver sus p53( +/+)), downregulation of Csa-19 by X-rays or fission neutrons was simi lar in p53-wild type and p53-null cell lines, Our results provide the first known example of a radiation-responsive gene in human cancer cel ls whose expression is not-associated with p53, adenylate cyclase or p rotein kinase C.