Mutation in p53 and de-regulation of p53-related gene expression in three human cell lines immortalized with 4-nitroquinoline 1-oxide or 60Co gamma rays.
In vitro models of malignant transformation of human cells may provide considerable insight into the mechanisms of multi-step carcinogenesis. It is well established that normal human cells must be immortalized before they can be malignantly transformed; however, they are stringently destined for aging and are rarely immortalized. The mechanism of cellular aging and immortalization is still unknown. We detected expression of only mutated p53 mRNA by direct sequencing of the reverse-transcribed mRNA in 3 human cell lines immortalized either with 4-nitroquinoline 1-oxide or with 60Co gamma rays. Consequently, only the mutated pS3 protein was expressed in each immortalized cell line. The expression of sdiI/p21 and mdm2, both of which are positively regulated by wild-type p53, was significantly down-regulated in the immortalized cell lines, resulting in over-expression of cdk2 and cdk4. Introduction of the sdiI/p21 gene into these cells was followed by a remarkable decrease in their ability to synthesize DNA. These results indicate that the p53 cascade may play an important role in the immortalization of human cells.
Iijima
M
M
Department of Cell Biology, Institute of Molecular and Cellular Biology, Okayama University Medical School, Japan.
Mihara
K
K
Kondo
T
T
Tsuji
T
T
Ishioka
C
C
Namba
M
M
D015112:4-Nitroquinoline-1-oxide / Q000494:pharmacology*; D001483:Base Sequence; D015152:Blotting, Northern; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002273:Carcinogens / Q000494:pharmacology*; D002460:Cell Line; D002471:Cell Transformation, Neoplastic / Q000235:genetics*; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects / Q000528:radiation effects; D005347:Fibroblasts / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D005720:Gamma Rays; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000528:radiation effects; D018816:Genes, cdc; D016158:Genes, p53 / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D016133:Polymerase Chain Reaction; D006656:Protamine Kinase / Q000378:metabolism; D014158:Transcription, Genetic
C493956:CDKN1A protein, human; D002273:Carcinogens; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D015112:4-Nitroquinoline-1-oxide; D006656:Protamine Kinase; D016203:CDC2 Protein Kinase