title: Interferon-inducible IFI16, a negative regulator of cell growth, down-regulates expression of human telomerase reverse transcriptase (hTERT) gene.
abstract: BACKGROUND
  Increased levels of interferon (IFN)-inducible IFI16 protein (encoded by the IFI16 gene located at 1q22) in human normal prostate epithelial cells and diploid fibroblasts (HDFs) are associated with the onset of cellular senescence. However, the molecular mechanisms by which the IFI16 protein contributes to cellular senescence-associated cell growth arrest remain to be elucidated. Here, we report that increased levels of IFI16 protein in normal HDFs and in HeLa cells negatively regulate the expression of human telomerase reverse transcriptase (hTERT) gene.
  
  
  RESULTS
  We optimized conditions for real-time PCR, immunoblotting, and telomere repeat amplification protocol (TRAP) assays to detect relatively low levels of hTERT mRNA, protein, and telomerase activity that are found in HDFs. Using the optimized conditions, we report that treatment of HDFs with inhibitors of cell cycle progression, such as aphidicolin or CGK1026, which resulted in reduced steady-state levels of IFI16 mRNA and protein, was associated with increases in hTERT mRNA and protein levels and telomerase activity. In contrast, knockdown of IFI16 expression in cells increased the expression of c-Myc, a positive regulator of hTERT expression. Additionally, over-expression of IFI16 protein in cells inhibited the c-Myc-mediated stimulation of the activity of hTERT-luc-reporter and reduced the steady-state levels of c-Myc and hTERT.
  
  
  CONCLUSIONS
  These data demonstrated that increased levels of IFI16 protein in HDFs down-regulate the expression of hTERT gene. Our observations will serve basis to understand how increased cellular levels of the IFI16 protein may contribute to certain aging-dependent diseases.
authors.affiliation: Department of Environmental Health, Cincinnati, Ohio, United States of America.
authors.forename: Lynda Li
authors.initials: LL
authors.lastname: Song
authors.forename: Larissa
authors.initials: L
authors.lastname: Ponomareva
authors.forename: Hui
authors.initials: H
authors.lastname: Shen
authors.forename: Xin
authors.initials: X
authors.lastname: Duan
authors.forename: Fatouma
authors.initials: F
authors.lastname: Alimirah
authors.forename: Divaker
authors.initials: D
authors.lastname: Choubey
mesh_terms: D002455:Cell Division / Q000502:physiology*; D002460:Cell Line; D015536:Down-Regulation / Q000502:physiology*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D055785:Gene Knockdown Techniques; D016259:Genes, myc; D006367:HeLa Cells; D006801:Humans; D009687:Nuclear Proteins / Q000502:physiology*; D010750:Phosphoproteins / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics; D019098:Telomerase / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic / Q000235:genetics
chemical_list: D009687:Nuclear Proteins; D010750:Phosphoproteins; D012333:RNA, Messenger; C076700:IFI16 protein, human; C509186:TERT protein, human; D019098:Telomerase