1. ¹Department of Gastroenterology and Hepatology, Graduate School of Medicine, Kyoto University, Kyoto, Japan
2. ²Department of Neurology, Graduate School of Medicine, Kyoto University, Kyoto, Japan
3. ³Laboratory for Motor System Neurodegeneration, RIKEN Brain Science Institute, Saitama, Japan
4. ⁴Laboratory for Structural Neuropathology, RIKEN Brain Science Institute, Saitama, Japan

Correspondence: Dr H Marusawa, Department of Gastroenterology and Hepatology, Graduate School of Medicine, Kyoto University, 54 Kawara-cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan. E-mail: maru@kuhp.kyoto-u.ac.jp; Professor R Takahashi, Department of Neurology, Graduate School of Medicine, Kyoto University, 54 Kawara-cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan. E-mail: ryosuket@kuhp.kyoto-u.ac.jp

⁵These authors contributed equally to this work.

Received 4 December 2007; Revised 9 April 2008; Accepted 1 May 2008; Published online 23 June 2008.

Abstract

The parkin was first identified as a gene implicated in autosomal recessive juvenile Parkinsonism. Deregulation of the parkin gene, however, has been observed in various human cancers, suggesting that the parkin gene may be important in tumorigenesis. To gain insight into the physiologic role of parkin, we generated parkin-/- mice lacking exon 3 of the parkin gene. We demonstrated here that parkin-/- mice had enhanced hepatocyte proliferation and developed macroscopic hepatic tumors with the characteristics of hepatocellular carcinoma. Microarray analyses revealed that parkin deficiency caused the alteration of gene expression profiles in the liver. Among them, endogenous follistatin is commonly upregulated in both nontumorous and tumorous liver tissues of parkin-deficient mice. Parkin deficiency resulted in suppression of caspase activation and rendered hepatocytes resistant to apoptosis in a follistatin-dependent manner. These results suggested that parkin deficiency caused enhanced hepatocyte proliferation and resistance to apoptosis, resulting in hepatic tumor development, partially through the upregulation of endogenous follistatin. The finding that parkin-deficient mice are susceptible to hepatocarcinogenesis provided the first evidence showing that parkin is indeed a tumor suppressor gene.