title: LXR activation causes G1/S arrest through inhibiting SKP2 expression in MIN6 pancreatic beta cells.
abstract: Liver X receptors (LXRs) are nuclear hormone receptors with central roles in lipid homeostasis. We previously showed that LXR activation induced aberrant lipid metabolism and G1 cell cycle arrest in pancreatic beta cells. In this study, we aimed to identify the molecular target of LXR causing G1 arrest. LXR activation was induced by its agonist, T0901317. A series of luciferase reporters of truncated Skp2 promoter were analyzed in MIN6 cells. mRNA and protein levels of SKP2 and P27 were detected. Flow cytometry assay was used to determine the cell cycle distribution. MTT assay was used to evaluate cell viability. LXR activation increased cell distribution in G1 phase and lipid accumulation. Since dominant-negative Srebp1c could clear the deposited lipid rather than recover the G1 arrest, we identified S-phase kinase-associated protein 2 (Skp2) as a potential target gene of LXR. In deed, LXR activation significantly inhibited Skp2 gene expression and protein amount. We also observed that the luciferase activity of Skp2 promoter was suppressed by T0901317 and the potential LXR regulatory site was narrowed down to a region of nt -289 to -38. Silencing Lxrα and Lxrβ rescued SKP2 protein level and recovered the cellular growth repressed by LXR activation. Moreover, SKP2 overabundance reduced P27 protein level by promoting its degradation, consequently overcame the G1 arrest caused by T0901317. Our findings demonstrate that transrepressing Skp2 expression by LXR activation resulted in defective SKP2-mediated P27 degradation and inhibitory cell growth in beta cells.
authors.affiliation: Key Laboratory of Human Functional Genomics of Jiangsu Province, Department of Biochemistry and Molecular Biology, Nanjing Medical University, 140 Hanzhong Road, Nanjing, 210029, People's Republic of China.
authors.forename: Yating
authors.initials: Y
authors.lastname: Li
authors.affiliation: Key Laboratory of Human Functional Genomics of Jiangsu Province, Department of Biochemistry and Molecular Biology, Nanjing Medical University, 140 Hanzhong Road, Nanjing, 210029, People's Republic of China.
authors.forename: Changwen
authors.initials: C
authors.lastname: Jing
authors.affiliation: Key Laboratory of Human Functional Genomics of Jiangsu Province, Department of Biochemistry and Molecular Biology, Nanjing Medical University, 140 Hanzhong Road, Nanjing, 210029, People's Republic of China.
authors.forename: Xinyi
authors.initials: X
authors.lastname: Tang
authors.affiliation: Key Laboratory of Human Functional Genomics of Jiangsu Province, Department of Biochemistry and Molecular Biology, Nanjing Medical University, 140 Hanzhong Road, Nanjing, 210029, People's Republic of China.
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Key Laboratory of Human Functional Genomics of Jiangsu Province, Department of Biochemistry and Molecular Biology, Nanjing Medical University, 140 Hanzhong Road, Nanjing, 210029, People's Republic of China.
authors.forename: Xiao
authors.initials: X
authors.lastname: Han
authors.affiliation: Key Laboratory of Human Functional Genomics of Jiangsu Province, Department of Biochemistry and Molecular Biology, Nanjing Medical University, 140 Hanzhong Road, Nanjing, 210029, People's Republic of China. zhuyx@njmu.edu.cn.
authors.forename: Yunxia
authors.initials: Y
authors.lastname: Zhu
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000187:drug effects; D059447:Cell Cycle Checkpoints / Q000187:drug effects*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects*; D015870:Gene Expression / Q000187:drug effects; D006845:Hydrocarbons, Fluorinated / Q000494:pharmacology; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism; D000071518:Liver X Receptors / Q000819:agonists*; D051379:Mice; D011401:Promoter Regions, Genetic / Q000187:drug effects; D044786:S-Phase Kinase-Associated Proteins / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013449:Sulfonamides / Q000494:pharmacology; D005466:Fluorocarbons; D000096926:Benzenesulfonamides
chemical_list: D006845:Hydrocarbons, Fluorinated; D000071518:Liver X Receptors; D044786:S-Phase Kinase-Associated Proteins; D013449:Sulfonamides; C423915:T0901317; D005466:Fluorocarbons; D000096926:Benzenesulfonamides
keywords: Cell cycle arrest; Liver X receptors; Pancreatic beta cell; SKP2; Type 2 diabetes