The cellular protein p53 in human tumours.

Tumour tissue from patients with colorectal and mammary tumours has been assayed for the cellular protein p53 using a specific radioimmune assay. The levels of p53 in normal tissues are not detectable with this assay but a substantial number of the tumours showed detectable p53, i.e. the amounts of this protein were significantly increased, to levels which varied from 0.3% to 10% of that found in simian virus 80 (SV80), an SV40 transformed human fibroblast cell line. Sera from the same patients were also assayed for the presence of anti-p53 antibodies and found to be positive in about 12% of the patients. The presence of increased amounts of p53 is not peculiar to malignant tumours since 4 out of 19 fibroadenomas (benign breast tumours) showed detectable amounts of p53 protein. The DNA from tumours was examined by Southern blotting using a variety of restriction enzymes. The arrangement of the p53 gene was not detectably altered in comparison with that in normal human foetal liver DNA. No alteration was observed which could be correlated with the increased levels of p53 in the positive tumours.