title: RacGAP1 Is a Novel Downstream Effector of E2F7-Dependent Resistance to Doxorubicin and Is Prognostic for Overall Survival in Squamous Cell Carcinoma.
abstract: We have previously shown that E2F7 contributes to drug resistance in head and neck squamous cell carcinoma (HNSCC) cells. Considering that dysregulation of responses to chemotherapy-induced cytotoxicity is one of the major reasons for treatment failure in HNSCC, identifying the downstream effectors that regulate E2F7-dependent sensitivity to chemotherapeutic agents may have direct clinical impact. We used transcriptomic profiling to identify candidate pathways that contribute to E2F7-dependent resistance to doxorubicin. We then manipulated the expression of the candidate pathway using overexpression and knockdown in in vitro and in vivo models of SCC to demonstrate causality. In addition, we examined the expression of E2F7 and RacGAP1 in a custom tissue microarray (TMA) generated from HNSCC patient samples. Transcriptomic profiling identified RacGAP1 as a potential mediator of E2F7-dependent drug resistance. We validated E2F7-dependent upregulation of RacGAP1 in doxorubicin-insensitive SCC25 cells. Extending this, we found that selective upregulation of RacGAP1 induced doxorubicin resistance in previously sensitive KJDSV40. Similarly, stable knockdown of RacGAP1 in insensitive SCC25 cells induced sensitivity to doxorubicin in vitro and in vivo. RacGAP1 expression was validated in a TMA, and we showed that HNSCCs that overexpress RacGAP1 are associated with a poorer patient overall survival. Furthermore, E2F7-induced doxorubicin resistance was mediated via RacGAP1-dependent activation of AKT. Finally, we show that SCC cells deficient in RacGAP1 grow slower and are sensitized to the cytotoxic actions of doxorubicin in vivo. These findings identify RacGAP1 overexpression as a novel prognostic marker of survival and a potential target to sensitize SCC to doxorubicin.
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: 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: Natalia
authors.initials: N
authors.lastname: Saenz-Ponce
authors.affiliation: Epithelial Pathobiology Group, University of Queensland Diamantina Institute, Princess Alexandra Hospital, Translational Research Institute, Woolloongabba, Queensland, Australia.
authors.forename: Daniel D E
authors.initials: DD
authors.lastname: Dantzic
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. nsaunders@uq.edu.au.
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Saunders
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism* / Q000401:mortality; D045744:Cell Line, Tumor; D004195:Disease Models, Animal; D004317:Doxorubicin / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D050702:E2F7 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D005260:Female; D020690:GTPase-Activating Proteins / Q000235:genetics* / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011379:Prognosis; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: D000903:Antibiotics, Antineoplastic; D050702:E2F7 Transcription Factor; D020690:GTPase-Activating Proteins; C115995:mgcRacGAP; D004317:Doxorubicin; D006160:Guanosine Triphosphate; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D020830:rac1 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein