title: Hypoxia disrupts the expression levels of circadian rhythm genes in hepatocellular carcinoma.
abstract: Disturbance in the expression of circadian rhythm genes is a common feature in certain types of cancer, however the mechanisms mediating this disturbance remain to be elucidated. The present study aimed to investigate the effect of hypoxia on the expression of circadian rhythm genes in liver cancer cells and to identify the mechanisms underlying this effect in hepatocellular carcinoma (HCC). The HCC cell line, PLC/PRF/5. was treated with either a vehicle control or CoCl2 at 50, 100 or 200 µΜ for 24 h. Following treatment, the protein expression levels of hypoxia‑inducible factor (HIF)‑1α and HIF‑2α were detected by western blotting and the mRNA expression levels of circadian rhythm genes, including circadian locomotor output cycles kaput (Clock), brain and muscle Arnt‑like 1 (Bmal1), period (Per)1, Per2, Per3, cryptochrome (Cry)1, Cry2 and casein kinase Iε (CKIε), were detected by reverse transcription quantitative polymerase chain reaction (RT‑qPCR). Expression plasmids containing HIF‑1α or HIF‑2α were transfected into the PLC/PRF/5 cells using liposomes and RT‑qPCR was used to determine the effects of the transfections on the expression levels of circadian rhythm genes. Following treatment with CoCl2, the protein expression levels of HIF‑1α and HIF‑2α were upregulated in a CoCl2 concentration‑dependent manner. The mRNA expression levels of Clock, Bmal1 and Cry2 were increased, and the mRNA expression levels of Per1, Per2, Per3, Cry1 and CKIε were decreased following CoCl2 treatment (P<0.05). In the PLC/PRF/5 cells transfected with the plasmid containing HIF‑1α, the mRNA expression levels of Clock, Bmal1 and Cry2 were increased, and the mRNA expression levels of Per1, Per2, Per3, Cry1 and CKIε were decreased. In the PLC/PRF/5 cells transfected with the plasmid containing HIF‑2α, the mRNA expression levels of Clock, Bmal1, Per1, Cry1, Cry2 and CKIε were upregulated, and the mRNA expression levels of Per2 and Per3 were downregulated (P<0.05). A hypoxic microenvironment may contribute to the disturbance in the expression of circadian genes in HCC. HIF‑1α and HIF‑2α are involved in this process and have redundant, but not identical effects.
authors.affiliation: Department of Hepatobiliary Surgery, Affiliated Hospital of Guiyang Medical College, Guiyang, Guizhou 550001, P.R. China.
authors.forename: Chao
authors.initials: C
authors.lastname: Yu
authors.affiliation: Department of General Surgery, Liyuan Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430077, P.R. China.
authors.forename: Sheng-Li
authors.initials: SL
authors.lastname: Yang
authors.affiliation: Department of Pediatrics, College of Medicine, University of Florida, Gainesville, FL 32610, USA.
authors.forename: Xiefan
authors.initials: X
authors.lastname: Fang
authors.affiliation: Department of Hepatobiliary Surgery, Affiliated Hospital of Guiyang Medical College, Guiyang, Guizhou 550001, P.R. China.
authors.forename: Jian-Xin
authors.initials: JX
authors.lastname: Jiang
authors.affiliation: Department of Hepatobiliary Surgery, Affiliated Hospital of Guiyang Medical College, Guiyang, Guizhou 550001, P.R. China.
authors.forename: Cheng-Yi
authors.initials: CY
authors.lastname: Sun
authors.affiliation: Department of Pediatrics, Tianyou Hospital, Wuhan University of Science and Technology, Wuhan, Hubei 430064, P.R. China.
authors.forename: Tao
authors.initials: T
authors.lastname: Huang
mesh_terms: D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism; D006528:Carcinoma, Hepatocellular / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D002940:Circadian Rhythm / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D000860:Hypoxia; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D008113:Liver Neoplasms / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D000099162:Endothelial PAS Domain-Containing Protein 1