FREQUENTLY ELEVATED CONTENT OF IMMUNOCHEMICALLY DEFINED WILD-TYPE P53PROTEIN IN COLORECTAL ADENOMAS

Mutations of the p53 tumour-suppressor gene are considered to be rare in human colorectal adenomas, a premalignant state of the digestive tr act. We have analysed a series of 32 exophytic tumours of the colon an d rectum for the presence of p53 protein. In 26 of the 28 pure adenoma s, the presence of significant levels of p53 proteins was established by a sensitive two-point enzyme-linked immunosorbent assay. The detect ability of p53 protein was frequently limited to PAb 1801, recognizing an N-terminal epitope. Immunoblotting of the fractions captured by th e monoclonal antibodies revealed that PAb 421 reacted exclusively with a 53-kDa species, whereas an additional 48-kDa band was detected afte r incubation with PAb 1801. In the adenomas, the mutant conformation-s pecific PAb 240 was always negative and no mutations were detected on exons 5-8 in three large and highly dysplastic lesions, selected for t heir high p53 protein content. The remaining four of the 32 tumours pr esented foci of cancer. Three of these were shown to contain 'mutant' PAb 240-reactive p53, and gene mutations were identified in two by den aturing gradient gel electrophoresis and sequencing of the amplified p roducts. Intense p53 nuclear immunohistochemical staining was associat ed with the malignant areas. We conclude that a novel mechanism affect ing the regulation of p53 protein could occur in colorectal adenomas