Differential Changes in Expression of Gap Junction Proteins Connexin 26 and 32 during Hepatocarcinogenesis in Rats

We examined expressions of the gap junction proteins, connexin 26 (C×26) and 32 (C×32), in preneoplastic and neoplastic lesions during rat hepatocarcinogenesis. A marked reduction in the numher of C×32‐positive gap junctions was observed in 17% of the glutathione S‐transferase placental form‐positive foci, whereas 44% of the foci showed increased expression of C×26. Most hyperplastic nodules exhibited decreased expression of C×32, whereas 16% of the nodules showed increased expression of C×26. In hepatocellular carcinomas, expressions of both C×32 and C×26 were significantly reduced. These results suggest that the expressions of C×32 and 26 are differentially regulated during hepatocarcinogenesis, and that the decrease in C×32 expression occurs earlier, whereas reduction in C×26 expression occurs later in association with promotion and progression of carcinogenesis.