Development of glutathione S‐transferase‐P‐negative foci accompanying nuclear factor‐erythroid 2‐related factor 2 expression during early stage of rat hepatocarcinogenesis

Glutathione S-transferase P (GST-P), a marker for rat hepatic preneoplastic lesions, is suggested to bind to Jun N-terminal kinase (JNK) to repress stress response, and GST-P gene expression is regulated by a transcription factor, nuclear factor-erythroid 2-related factor 2 (Nrf2). In this study, we examined by immunohistochemistry whether JNK2, p38 mitogen-activated protein kinase, and Nrf2 were expressed in GST-P-positive foci induced by the Solt–Farber protocol. At 2 weeks after partial hepatectomy, all GST-P-positive foci were negative for p38, and 86.4 ± 5.6% and 64.7 ± 6.3% of GST-P-positive foci were negative for JNK2 and Nrf2, respectively. Western blot analysis showed decreased p38 mitogen-activated protein kinase and JNK2 expression in livers treated with the protocol. In immunohistochemistry, besides GST-P-positive foci, GST-P-negative foci were detected as p38-negative foci in the surrounding tissues positive for p38. In contrast to GST-P-positive foci, most GST-P-negative foci showed enhanced Nrf2 expression. The number of GST-P-negative foci was 76 ± 18/10 mm2 of liver section at 2 weeks, but was undetectable at 1 week. The area of GST-P-negative foci was 0.09 ± 0.05 mm2, smaller than that of GST-P-positive ones (0.29 ± 0.23). After treatment with carbon tetrachloride, small vacuoles due to liver injury were frequently observed inside GST-P-negative foci but less frequently in GST-P-positive foci. However, this treatment resulted in expression of JNK2, p38, and Nrf2 in both foci. These results showed development of GST-P-negative foci during the early stage of hepatocarcinogenesis and suggested that Nrf2 is not responsible for GST-P expression in rat hepatic preneoplastic foci. (Cancer Sci 2008; 99: 497–501)