title: Essential role for SphK1/S1P signaling to regulate hypoxia-inducible factor 2α expression and activity in cancer.
abstract: The sphingosine kinase-1/sphingosine 1-phosphate (SphK1/S1P) signaling pathway has been reported to modulate the expression of the canonical transcription factor hypoxia-inducible HIF-1α in multiple cell lineages. HIF-2α is also frequently overexpressed in solid tumors but its role has been mostly studied in clear cell renal cell carcinoma (ccRCC), the most common form of kidney cancer, where HIF-2α has been established as a driver of a more aggressive disease. In this study, the role of SphK1/S1P signaling with regard to HIF-2α was investigated in various cancer cell models including ccRCC cells. Under hypoxic conditions or in ccRCC lacking a functional von Hippel-Lindau (VHL) gene and expressing high levels of HIF-2α, SphK1 activity controls HIF-2α expression and transcriptional activity through a phospholipase D (PLD)-driven mechanism. SphK1 silencing promotes a VHL-independent HIF-2α loss of expression and activity and reduces cell proliferation in ccRCC. Importantly, downregulation of SphK1 is associated with impaired Akt and mTOR signaling in ccRCC. Taking advantage of a monoclonal antibody neutralizing extracellular S1P, we show that inhibition of S1P extracellular signaling blocks HIF-2α accumulation in ccRCC cell lines, an effect mimicked when the S1P transporter Spns2 or the S1P receptor 1 (S1P1) is silenced. Here, we report the first evidence that the SphK1/S1P signaling pathway regulates the transcription factor hypoxia-inducible HIF-2α in diverse cancer cell lineages notably ccRCC, where HIF-2α has been established as a driver of a more aggressive disease. These findings demonstrate that SphK1/S1P signaling may act as a canonical regulator of HIF-2α expression in ccRCC, giving support to its inhibition as a therapeutic strategy that could contribute to reduce HIF-2 activity in ccRCC.
authors.affiliation: CNRS, Institut de Pharmacologie et de Biologie Structurale, Toulouse, France.|Université de Toulouse, UPS, IPBS, Toulouse, France.|Equipe Labellisée Ligue contre le Cancer, Toulouse, France.
authors.forename: P
authors.initials: P
authors.lastname: Bouquerel
authors.affiliation: CNRS, Institut de Pharmacologie et de Biologie Structurale, Toulouse, France.|Université de Toulouse, UPS, IPBS, Toulouse, France.|Equipe Labellisée Ligue contre le Cancer, Toulouse, France.
authors.forename: C
authors.initials: C
authors.lastname: Gstalder
authors.affiliation: Equipe Labellisée Ligue contre le Cancer, Toulouse, France.|Laboratoire d'Excellence Toulouse Cancer (TOUCAN), INSERM UMR-1037, Cancer Research Center of Toulouse (CRCT), Université de Toulouse, Toulouse, France.
authors.forename: D
authors.initials: D
authors.lastname: Müller
authors.affiliation: CNRS, Institut de Pharmacologie et de Biologie Structurale, Toulouse, France.|Université de Toulouse, UPS, IPBS, Toulouse, France.|Equipe Labellisée Ligue contre le Cancer, Toulouse, France.
authors.forename: J
authors.initials: J
authors.lastname: Laurent
authors.affiliation: CNRS, Institut de Pharmacologie et de Biologie Structurale, Toulouse, France.|Université de Toulouse, UPS, IPBS, Toulouse, France.|Equipe Labellisée Ligue contre le Cancer, Toulouse, France.
authors.forename: L
authors.initials: L
authors.lastname: Brizuela
authors.affiliation: Lpath Inc, San Diego, CA, USA.
authors.forename: R A
authors.initials: RA
authors.lastname: Sabbadini
authors.affiliation: CNRS, Institut de Pharmacologie et de Biologie Structurale, Toulouse, France.|Université de Toulouse, UPS, IPBS, Toulouse, France.|Equipe Labellisée Ligue contre le Cancer, Toulouse, France.|Institut Universitaire du Cancer Toulouse Oncopôle, Toulouse, France.
authors.forename: B
authors.initials: B
authors.lastname: Malavaud
authors.affiliation: Equipe Labellisée Ligue contre le Cancer, Toulouse, France.|Laboratoire d'Excellence Toulouse Cancer (TOUCAN), INSERM UMR-1037, Cancer Research Center of Toulouse (CRCT), Université de Toulouse, Toulouse, France.
authors.forename: S
authors.initials: S
authors.lastname: Pyronnet
authors.affiliation: Laboratoire d'Excellence Toulouse Cancer (TOUCAN), INSERM UMR-1037, Cancer Research Center of Toulouse (CRCT), Université de Toulouse, Toulouse, France.
authors.forename: Y
authors.initials: Y
authors.lastname: Martineau
authors.affiliation: CNRS, Institut de Pharmacologie et de Biologie Structurale, Toulouse, France.|Université de Toulouse, UPS, IPBS, Toulouse, France.|Equipe Labellisée Ligue contre le Cancer, Toulouse, France.
authors.forename: I
authors.initials: I
authors.lastname: Ader
authors.affiliation: CNRS, Institut de Pharmacologie et de Biologie Structurale, Toulouse, France.|Université de Toulouse, UPS, IPBS, Toulouse, France.|Equipe Labellisée Ligue contre le Cancer, Toulouse, France.
authors.forename: O
authors.initials: O
authors.lastname: Cuvillier