title: The impact of S6K1 kinase on neuroblastoma cell proliferation is independent of GLI1 signaling.
abstract: BACKGROUND
  The crosstalk between Hedgehog (HH) signaling and other signal transduction cascades has been extensively studied in different cancers. In neuroblastoma, mTOR/S6K1 signaling is known to have a role in the development of this disease and recent evidence also implicates the HH pathway. Moreover, S6K1 kinase has been shown to phosphorylate GLI1, the effector of HH signaling, promoting GLI1 transcriptional activity and oncogenic function in esophageal adenocarcinoma. In this study, we examined the possible interplay of S6K1 and GLI1 signaling in neuroblastoma.
  
  
  METHODS
  siRNA knockdowns were used to suppress S6K1 and GLI1 expression, and the siRNA effects were validated by real-time PCR and Western blotting. Cell proliferation analysis was performed with the EdU incorporation assay. Cytotoxic analysis with increasing concentrations of PI3K/mTOR and GLI inhibitors, individually and in combination, was used to determine drug response.
  
  
  RESULTS
  Although knockdown of either S6K1 or GLI1 reduces the cellular proliferation of neuroblastoma cells, there is little effect of S6K1 on the expression of GLI1 mRNA and protein and on the capacity of GLI1 to activate target genes. No detectable phosphorylation of GLI1 is observed prior or following S6K1 knockdown. GLI1 overexpression can not rescue the reduced proliferation elicited by S6K1 knockdown. Moreover, inhibitors of PI3K/mTOR and GLI signaling reduced neuroblastoma cell growth, but no additional growth inhibitory effects were detected when the two classes of drugs were combined.
  
  
  CONCLUSIONS
  Our results demonstrate that the impact of S6K1 kinase on neuroblastoma cells is not mediated through modulation of GLI1 expression/activity.
authors.forename: Yumei
authors.initials: Y
authors.lastname: Diao
authors.forename: Mohammed Ferdous-Ur
authors.initials: MF
authors.lastname: Rahman
authors.forename: Victoria E
authors.initials: VE
authors.lastname: Villegas
authors.forename: Malin
authors.initials: M
authors.lastname: Wickström
authors.forename: John I
authors.initials: JI
authors.lastname: Johnsen
authors.affiliation: Department of Biosciences and Nutrition, Karolinska Institutet, Huddinge, Sweden. peter.zaphiropoulos@ki.se.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Zaphiropoulos
mesh_terms: D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D053823:Hedgehog Proteins / Q000378:metabolism; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D009447:Neuroblastoma / Q000378:metabolism / Q000473:pathology*; D010766:Phosphorylation; D011725:Pyridines / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D011804:Quinolines / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000494:pharmacology; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism*; D000071676:Zinc Finger Protein GLI1
chemical_list: C551027:GANT 61; C400551:GLI1 protein, human; D053823:Hedgehog Proteins; D007093:Imidazoles; D011725:Pyridines; D011743:Pyrimidines; D011804:Quinolines; D034741:RNA, Small Interfering; D014157:Transcription Factors; D000071676:Zinc Finger Protein GLI1; D038762:Ribosomal Protein S6 Kinases, 70-kDa; C448901:ribosomal protein S6 kinase, 70kD, polypeptide 1; C531198:dactolisib