TISSUE-SPECIFIC EXPRESSION, EVOLUTIONARY CONSERVATION AND LOCALIZATION OF THE CPH PROTOONCOGENE ON SYRIAN-HAMSTER CHROMOSOME-X

Treatment of Syrian hamster embryo fibroblasts with a single dose of 3 -methylcholanthrene caused the activation of the transforming potentia l of cellular sequences (Notario et al,, Oncogene 5: 1425-1430, 1990), which were subsequently isolated by cosmid rescue techniques, and fur ther identified as a novel oncogene, termed cph because of its involve ment in the carcinogenic progression of hamster embryo cells (Velasco ed al., Oncogene 9: 2065-2069, 1994), We have analysed the expression of the cph proto-oncogene in adult Syrian hamster tissues by northern hybridization using cph-specific genomic probes, The three cph transcr ipts expressed in normal and neoplastic Syrian hamster embryo cells in culture (5.0, 3.5 and 2.0 kb) were also present in most adult tissues , although different mRNA species, most likely resulting from alternat ive splicing events, were expressed in testes, The highest steady-stat e level of cph mRNA was found in kidney, whereas cph expression was ne arly undetectable in skin and skeletal muscle, Southern blot analyses of DNAs from other eucaryotic organisms were performed under moderate stringency conditions with a Syrian hamster-specific cph probe, Discre te cpk-hybridizing sequences were present in genomes from yeast to mam malian species, including humans, thus demonstrating that cph is a hig hly conserved gene in eucaryotic evolution, Using fluorescence in situ hybridization (FISH), we have determined also the chromosomal Idealiz ation of the cph proto-oncogene in the hamster genome, FISH experiment s demonstrated that cph is a single copy gene, localized on the euchro matic short arm of the X chromosome, at region Xpa7, Because chromosom e X is frequently involved in structural alterations in neoplastic Syr ian hamster cells transformed by chemical carcinogens and oncogenic vi ruses, the localization of the cph locus on this chromosome supports t he notion that the cph oncogene plays a role in the malignant conversi on of chemically transformed hamster fibroblasts, The wide range of ti ssue-specific expression and species-specific distribution of cph stro ngly suggest that the normal function of the cph protein product(s) ma y be essential for metabolic processes involved in the regulation of c ell proliferation and survival.