title: G-quadruplex-mediated regulation of telomere binding protein POT1 gene expression.
abstract: BACKGROUND
  Telomere is protected by its G-quadruplex, T-loop structure, telomerase, and binding protein complex. Protein POT1 (protection of telomeres 1) is one subunit of telomere binding protein complex Shelterin. POT1 acts as a regulator of telomerase-dependent telomere length, and it can help telomere to form D-loop structure to stabilize telomere. POT1 protects telomere ends from ATR-dependent DNA damage response as well.
  
  
  METHODS
  Extensive methods were used, including CD, EMSA, ITC, PCR stop assay, luciferase reporter assay, quantitative real-time PCR, Western blot, chromatin immunoprecipitation (Ch-IP), cloning, expression and purification of proteins.
  
  
  RESULTS
  We found a new G-rich 30-base-pair long sequence (P-pot1 G18) located from -165 to -136 base pairs upstream of the translation starting site of protein POT1. This sequence in the promoter region of pot1 gene formed G-quadruplex resulting in down-regulation of pot1 gene transcription. This G-rich sequence is close to a binding site "TCCC" for transcription factor hnRNP K (heterogeneous nuclear ribonucleoprotein K), and its conversion to G-quadruplex prevented the access of hnRNP K to this binding site. The binding of hnRNP K could up-regulate pot1 gene transcription. TMPyP4 (meso-tetra(N-methyl-4-pyridyl)porphine) has been widely used as G-quadruplex binding ligand, which stabilized the G-quadruplex in vitro and in cellulo, resulting in down-regulation of pot1 gene transcription.
  
  
  CONCLUSIONS
  This G-quadruplex might become a potentially new drug target for antitumor agents.
  
  
  CONCLUSIONS
  Our results first demonstrated that G-quadruplex formation can affect the binding of transcription factor to its nearby binding site, and thus making additional influence to gene transcription.
authors.affiliation: School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou University City, 132 Waihuan East Road, Guangzhou 510006, PR China.
authors.forename: Qingqing
authors.initials: Q
authors.lastname: He
authors.affiliation: School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou University City, 132 Waihuan East Road, Guangzhou 510006, PR China.
authors.forename: Ping
authors.initials: P
authors.lastname: Zeng
authors.affiliation: School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou University City, 132 Waihuan East Road, Guangzhou 510006, PR China.
authors.forename: Jia-Heng
authors.initials: JH
authors.lastname: Tan
authors.affiliation: School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou University City, 132 Waihuan East Road, Guangzhou 510006, PR China.
authors.forename: Tian-Miao
authors.initials: TM
authors.lastname: Ou
authors.affiliation: School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou University City, 132 Waihuan East Road, Guangzhou 510006, PR China.
authors.forename: Lian-Quan
authors.initials: LQ
authors.lastname: Gu
authors.affiliation: School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou University City, 132 Waihuan East Road, Guangzhou 510006, PR China.
authors.forename: Zhi-Shu
authors.initials: ZS
authors.lastname: Huang
authors.affiliation: School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou University City, 132 Waihuan East Road, Guangzhou 510006, PR China. Electronic address: liding@mail.sysu.edu.cn.
authors.forename: Ding
authors.initials: D
authors.lastname: Li
mesh_terms: D001665:Binding Sites; D004277:DNA, Single-Stranded / Q000235:genetics; D054856:G-Quadruplexes / Q000187:drug effects*; D005786:Gene Expression Regulation; D006801:Humans; D011166:Porphyrins / Q000494:pharmacology; D011485:Protein Binding; D000089804:Shelterin Complex; D019098:Telomerase / Q000235:genetics / Q000378:metabolism; D016615:Telomere / Q000235:genetics*; D034501:Telomere-Binding Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics*
chemical_list: D004277:DNA, Single-Stranded; C440849:POT1 protein, human; D011166:Porphyrins; D000089804:Shelterin Complex; D034501:Telomere-Binding Proteins; C021096:tetra(4-N-methylpyridyl)porphine; D019098:Telomerase
keywords: Cancer; G-quadruplex; POT1; Shelterin; Telomere; hnRNP K