title: Malignant transformation of human fibroblasts previously immortalized with 60Co gamma rays.
abstract: Normal human fibroblasts obtained from a whole embryo were malignantly transformed with only 60Co gamma rays, but after extensive passage. The fibroblasts were exposed intermittently to 60Co gamma rays, 13 times, 2,800 rads in total, from the primary culture to the 40th passage level. At the 50th passage level the cells became morphologically changed, showing chromosomal abnormalities, and serial passages showed them to be immortalized. They were not tumorigenic on transplantation into nude mice, but became malignant after extensive passage; i.e., at the 547th passage level and 2,800 days after initiation of the culture. Our results indicate that several different genotypic changes are necessary for malignant transformation of human cells over long periods. No mutation at codons 12 and 61 of H-, K- and N-ras was detected in the malignant cells. Thus, this system may be useful to detect other cellular genes that may contribute to the malignant phenotypes of human fibroblasts.
authors.affiliation: Department of Cell Biology, Okayama University Medical School, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Mihara
authors.forename: L
authors.initials: L
authors.lastname: Bai
authors.forename: Y
authors.initials: Y
authors.lastname: Kano
authors.forename: M
authors.initials: M
authors.lastname: Miyazaki
authors.forename: M
authors.initials: M
authors.lastname: Namba
mesh_terms: D001483:Base Sequence; D002471:Cell Transformation, Neoplastic / Q000528:radiation effects*; D002478:Cells, Cultured / Q000528:radiation effects; D003037:Cobalt Radioisotopes; D005720:Gamma Rays; D011905:Genes, ras; D006801:Humans; D066298:In Vitro Techniques; D007621:Karyotyping; D008969:Molecular Sequence Data; D009154:Mutation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D016133:Polymerase Chain Reaction; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics
chemical_list: D003037:Cobalt Radioisotopes; D009838:Oligodeoxyribonucleotides; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)