Tissue-specific expression, evolutionary conservation and localization of the cph proto-oncogene on Syrian hamster chromosome X

Abstract

Treatment of Syrian hamster embryo fibroblasts with a single dose of 3-methylcholanthrene caused the activation of the transforming potential of cellular sequences (Notario et al, Oncogene 5: 1425-1430, 1990), which were subsequently isolated by cosmid rescue techniques, and further identified as a novel oncogene, termed cph because of its involvement in the carcinogenic progression of hamster embryo cells (Velasco et 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 transcripts 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 alternative splicing events, were expressed in testes. The highest steady-state level of cph mRNA was found in kidney, whereas cph expression was nearly 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. Discrete cph-hybridizing sequences were present in genomes from yeast to mammalian species, including humans, thus demonstrating that cph is a highly conserved gene in eucaryotic evolution. Using fluorescence in situ hybridization (FISH), we have determined also the chromosomal localization of the cph proto-oncogene in the hamster genome. FISH experiments demonstrated that cph is a single copy gene, localized on the euchromatic short arm of the X chromosome, at region Xpa7. Because chromosome X is frequently involved in structural alterations in neoplastic Syrian hamster cells transformed by chemical carcinogens and oncogenic viruses, the localization of the cph locus on this chromosome supports the notion that the cph oncogene plays a role in the malignant conversion of chemically transformed hamster fibroblasts. The wide range of tissue-specific expression and species-specific distribution of cph strongly suggest that the normal function of the cph protein product(s) may be essential for metabolic processes involved in the regulation of cell proliferation and survival.