To study why the human teratocarcinoma cell line PA-1 maintains a stable near-diploid karyotype even after it has been cultured for more than twenty years, p53 gene status of the cell line in 407-445 passages were investigated in detail by DNA sequence analysis and a yeast function status assay. Direct sequence analysis of RT-PCR products showed both wild and mutated bands (p53 codon 239 mutation). Consistent with the above results, the functional assay showed that one allele of the p53 gene was active (wild), while the other was inactive (mutant). In addition, the PA-1 cells expressed the p21 protein to a lesser extent than normal human fibroblasts. Though many lines of evidence have shown that mutant p53 works dominant-negatively, our results suggest that mutation in a p53 allele alone can not induce cytogenetic instability.

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