Evidence that Expression of a Mutated p53 Gene Attenuates Apoptotic Cell Death in Human Gastric Intestinal‐type Carcinomas in vivo

To examine in vivo the validity of the results of experiments in vitro, we analyzed the relationship between p53 gene status and apoptotic cell death of human gastric intestinal‐type adenocarcinomas. Surgical specimens were classified into two categories: 18 gastric cancers with nuclear p53 protein (A), and 17 gastric cancers without nuclear p53 protein (B). Polyraerase chain reaction‐single strand conformation polymorphism disclosed a shifted band that corresponded to a mutation in the p53 gene in 13 cases (72%) in category A and 3 cases (18%) in category B, the frequency being significantly higher in the former (P<0.05). Apoptotic cells were identified from routinely stained sections and by terminal deoxynucleotidyl transferase‐mediated dUTP‐biotin nick end labeling (TUNEL). The TUNEL index [TI: (the number of TUNEL‐positive apoptotic cells/the total number of tumor cells) X100] was 3.8 ±1.4% in category A and 4.9 ±1.2% in category B, the value being significantly lower in the former (P< 0.05). The proliferating cell nuclear antigen index, defined similarly to the TI, was 56.4±16.3% in category A, and it was significantly higher than that in category B (P<0.05). The immunohistochemically detected expression of P21(CIP1/WAF1) did not differ between the two categories, while Bax‐positive tumor cells were more frequently detected in category A. These results indicate that (1) expression of a mutated p53 gene attenuates apoptotic cell death of gastric cancer, in accordance with the previous in vitro finding that p53 gene mutation provides a possible selective advantage for tumor cell proliferation, and (2) apoptosis is related not only to expression of p53 and the stage of the cell cycle, but also to p53‐independent and cell cycle‐independent events.