title: A novel E2F/sphingosine kinase 1 axis regulates anthracycline response in squamous cell carcinoma.
abstract: OBJECTIVE
  Head and neck squamous cell carcinomas (HNSCC) are frequently drug resistant and have a mortality rate of 45%. We have previously shown that E2F7 may contribute to drug resistance in SCC cells. However, the mechanism and pathways involved remain unknown.
  
  
  METHODS
  We used transcriptomic profiling to identify candidate pathways that may contribute to E2F7-dependent resistance to anthracyclines. We then manipulated the activity/expression of the candidate pathway using overexpression, knockdown, and pharmacological inhibitors in in vitro and in vivo models of SCC to demonstrate causality. In addition, we examined the expression of E2F7 and a downstream effector in a tissue microarray (TMA) generated from HNSCC patient samples.
  
  
  RESULTS
  E2F7-deficient keratinocytes were selectively sensitive to doxorubicin and this was reversed by overexpressing E2F7. Transcriptomic profiling identified Sphingosine kinase 1 (Sphk1) as a potential mediator of E2F7-dependent drug resistance. Knockdown and overexpression studies revealed that Sphk1 was a downstream target of E2F7. TMA studies showed that E2F7 overexpression correlated with Sphk1 overexpression in human HNSCC. Moreover, inhibition of Sphk1 by shRNA or the Sphk1-specific inhibitor, SK1-I (BML-EI411), enhanced the sensitivity of SCC cells to doxorubicin in vitro and in vivo. Furthermore, E2F7-induced doxorubicin resistance was mediated via Sphk1-dependent activation of AKT in vitro and in vivo.
  
  
  CONCLUSIONS
  We identify a novel drugable pathway in which E2F7 directly increases the transcription and activity of the Sphk1/S1P axis resulting in activation of AKT and subsequent drug resistance. Collectively, this novel combinatorial therapy can potentially be trialed in humans using existing agents.
authors.affiliation: Epithelial Pathobiology Group, University of Queensland Diamantina Institute, Princess Alexandra Hospital, Translational Research Institute, Woolloongabba, Queensland, Australia.
authors.forename: Mehlika
authors.initials: M
authors.lastname: Hazar-Rethinam
authors.affiliation: Epithelial Pathobiology Group, University of Queensland Diamantina Institute, Princess Alexandra Hospital, Translational Research Institute, Woolloongabba, Queensland, Australia.
authors.forename: Lilia Merida
authors.initials: LM
authors.lastname: de Long
authors.affiliation: Epithelial Pathobiology Group, University of Queensland Diamantina Institute, Princess Alexandra Hospital, Translational Research Institute, Woolloongabba, Queensland, Australia.
authors.forename: Orla M
authors.initials: OM
authors.lastname: Gannon
authors.affiliation: Epithelial Pathobiology Group, University of Queensland Diamantina Institute, Princess Alexandra Hospital, Translational Research Institute, Woolloongabba, Queensland, Australia.
authors.forename: Eleni
authors.initials: E
authors.lastname: Topkas
authors.affiliation: Department of Pathology, Princess Alexandra Hospital, Woolloongabba, Queensland, Australia.
authors.forename: Samuel
authors.initials: S
authors.lastname: Boros
authors.affiliation: Department of Pathology, Princess Alexandra Hospital, Woolloongabba, Queensland, Australia.
authors.forename: Ana Cristina
authors.initials: AC
authors.lastname: Vargas
authors.affiliation: Department of Medical Oncology, Princess Alexandra Hospital, Woolloongabba, Queensland, Australia.
authors.forename: Marcin
authors.initials: M
authors.lastname: Dzienis
authors.affiliation: Epithelial Pathobiology Group, University of Queensland Diamantina Institute, Princess Alexandra Hospital, Translational Research Institute, Woolloongabba, Queensland, Australia.
authors.forename: Pamela
authors.initials: P
authors.lastname: Mukhopadhyay
authors.affiliation: Epithelial Pathobiology Group, University of Queensland Diamantina Institute, Princess Alexandra Hospital, Translational Research Institute, Woolloongabba, Queensland, Australia.
authors.forename: Fiona
authors.initials: F
authors.lastname: Simpson
authors.affiliation: Epithelial Pathobiology Group, University of Queensland Diamantina Institute, Princess Alexandra Hospital, Translational Research Institute, Woolloongabba, Queensland, Australia.
authors.forename: Liliana
authors.initials: L
authors.lastname: Endo-Munoz
authors.affiliation: Epithelial Pathobiology Group, University of Queensland Diamantina Institute, Princess Alexandra Hospital, Translational Research Institute, Woolloongabba, Queensland, Australia. nsaunders@uq.edu.au.
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Saunders
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004317:Doxorubicin / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm; D050702:E2F7 Transcription Factor / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D015603:Keratinocytes / Q000187:drug effects / Q000378:metabolism; D016688:Mice, Inbred NOD; D018345:Mice, Knockout; D016513:Mice, SCID; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays; D000099157:Sphingosine Kinase
chemical_list: D000970:Antineoplastic Agents; D004317:Doxorubicin; D050702:E2F7 Transcription Factor; D017853:Phosphotransferases (Alcohol Group Acceptor); D051057:Proto-Oncogene Proteins c-akt; D000099157:Sphingosine Kinase; C481054:E2F7 protein, human