Connexin 32 dysfunction promotes ethanol-related hepatocarcinogenesis via activation of Dusp1-Erk axis

// Hiroyuki Kato 1 , Aya Naiki-Ito 1 , Taku Naiki 1 , Shugo Suzuki 1 , Yoriko Yamashita 1 , Shinya Sato 1 , Hiroyuki Sagawa 1, 2 , Akihisa Kato 1, 3 , Toshiya Kuno 1 , Satoru Takahashi 1 1 Department of Experimental Pathology and Tumor Biology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan 2 Department of Gastroenterological Surgery, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan 3 Department of Gastroenterology and Metabolism, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan Correspondence to: Aya Naiki-Ito, e-mail: ayaito@med.nagoya-cu.ac.jp Keywords: connexin 32, alcohol, hepatocarcinogenesis, Erk, Dusp1 Received: July 16, 2015      Accepted: November 21, 2015      Published: December 09, 2015 ABSTRACT There is abundant epidemiological evidence that heavy alcohol intake contributes to hepatocellular carcinoma (HCC) development. Previous reports indicated that connexin 32 (Cx32), which is a major hepatocyte gap junction protein, is down-regulated in chronic liver disease and has a protective role in hepatocarcinogenesis. However, functions of Cx32 in alcohol-related hepatocarcinogenesis have not been clarified. To evaluate them, 9-week-old Cx32 dominant negative transgenic (Tg) rats and their wild-type (Wt) littermates were given 1 % or 5 % ethanol (EtOH) or water ad libitum , for 16 weeks after an intraperitoneal injection of diethylnitrosamine (200 mg/kg). EtOH significantly increased the incidence and multiplicity of HCC and total tumors in a dose-dependent manner in Tg rats, but not in Wt rats. Although the number and area of glutathione S-transferase placental form (GST-P) positive foci were not significantly different between the groups, EtOH increased the Ki-67 labeling indices in GST-P positive foci only in Tg rats. EtOH up-regulated phosphorylated Erk1/2 with decrease of the Erk1/2 inhibitor, dual specificity protein phosphatase 1 (Dusp1) in whole livers of Tg and Wt rats. Immunofluorescence staining and quantitative RT-PCR revealed that EtOH significantly increased nucleolar localization of phosphorylated Erk1/2 and contrastingly reduced Dusp1 protein and mRNA expression in GST-P positive foci and HCC of Tg rats as compared to those of Wt rats. These findings suggest that Cx32 dysfunction like in chronic liver disease promoted EtOH-associated hepatocarcinogenesis through dysregulation of Erk-Dusp1 signaling.