Preparation of anti-ras Mr 21,000 protein monoclonal antibodies and immunohistochemical analyses on expression of ras genes in human stomach and thyroid cancers.

Sixteen clones (RASK-1 to -16) of murine monoclonal antibodies were raised against ras Mr 21,000 protein (p21). The p21 produced by Escherichia coli with inserted v-Ki-ras genes was used as immunogen. RASK-1 was found to be specific for Ki-ras p21, whereas RASK-2 to -16 reacted with the p21s of Ki-, N-, and Ha-ras genes in both enzyme-linked immunosorbent and immunoblotting assays. Binding inhibition assays with biotinylated monoclonal antibodies by enzyme-linked immunosorbent assay showed that the monoclonal antibodies of the 16 clones included those binding to several mutually distinct sites on p21. The expressions of ras p21 in human stomach and thyroid tissues were examined with RASK-3, which reacted with all the Ki-, N-, and Ha-ras p21s immunohistochemically by the avidin-biotin peroxidase complex method. Formalin-fixed, paraffin-embedded tissues of 101 cases of stomach cancer, 53 cases of noncancerous stomach, 74 cases of cancer of the thyroid, and 59 cases of noncancerous thyroid were analyzed. In both the stomach and thyroid, cancer cells expressed p21 predominantly. Cells of cases with various noncancerous disorders as well as certain types of normal cells were also p21 positive. These findings suggest that precaution is required in use of p21 as a cancer marker. Expression of p21 was noted in moderately to well-differentiated stomach cancer, intestinal metaplasia, and atypical hyperplasia. This finding suggests that the appearance of p21 in stomach cancer may be initiated before cytological transformation.