Clock gene Per2 as a controller of liver carcinogenesis

// Ali Mteyrek 1 , Elisabeth Filipski 1 , Catherine Guettier 2 , Alper Okyar 3 , Francis Levi 1, 2, 4 1 INSERM and Paris Sud University, UMRS 995, Team « Cancer Chronotherapy and Postoperative Liver », Campus CNRS, Villejuif F-94807, France 2 Assistance Publique-Hopitaux de Paris, Department of Medical Oncology and Laboratory of Anatomy and Pathologic Cytology, Hopital Paul Brousse, Villejuif F-94800, France 3 Istanbul University Faculty of Pharmacy, Department of Pharmacology, Beyazit TR-34116, Istanbul, Turkey 4 Warwick Medical School, Cancer Chronotherapy Unit, Coventry, CV4 7AL, United Kingdom Correspondence to: Francis Levi, email: F.Levi@warwick.ac.uk Keywords: Circadian rhythm, Per2 gene, Hepatocellular carcinoma, Molecular clock, Cell cycle genes Received: May 12, 2016     Accepted: July 13, 2016     Published: August 03, 2016 ABSTRACT Environmental disruption of molecular clocks promoted liver carcinogenesis and accelerated cancer progression in rodents. We investigated the specific role of clock gene Period 2 (Per2) for liver carcinogenesis and clock-controlled cellular proliferation, genomic instability and inflammation. We assessed liver histopathology, and determined molecular and physiology circadian patterns in mice on chronic diethylnitrosamine (DEN) exposure according to constitutive Per2 mutation. First, we found that Per2 m/m liver displayed profound alterations in proliferation gene expression, including c-Myc derepression, phase-advanced Wee1, and arrhythmic Ccnb1 and K-ras mRNA expressions, as well as deregulated inflammation, through arrhythmic liver IL-6 protein concentration, in the absence of any DEN exposure. These changes could then make Per2 m/m mice more prone to subsequently develop liver cancers on DEN. Indeed, primary liver cancers were nearly fourfold as frequent in Per2 m/m mice as compared to wild-type (WT), 4 months after DEN exposure. The liver molecular clock was severely disrupted throughout the whole carcinogenesis process, including the initiation stage, i.e. within the initial 17 days on DEN. Per2 m/m further exhibited increased c-Myc and Ccnb1 mean 24h expressions, lack of P53 response, and arrhythmic ATM, Wee1 and Ccnb1 expressions. DEN-induced tumor related inflammation was further promoted through increased protein concentrations of liver IL-6 and TNF-α as compared to WT during carcinogenesis initiation. Per2 mutation severely deregulated liver gene or protein expressions related to three cancer hallmarks, including uncontrolled proliferation, genomic instability, and tumor promoting inflammation, and accelerated liver carcinogenesis several-fold. Clock gene Per2 acted here as a liver tumor suppressor from initiation to progression.