Hypoxia inducible factor-1 mediates the expression of the immune checkpoint HLA-G in glioma cells through hypoxia response element located in exon 2

// Layale Yaghi 1, 2, 3 , Isabelle Poras 1, 2 , Renata T. Simoes 1, 2, 4 , Eduardo A. Donadi 5 , Jorg Tost 6, 7 , Antoine Daunay 6 , Bibiana Sgorla de Almeida 1, 2, 5 , Edgardo D. Carosella 1, 2 , Philippe Moreau 1, 2 1 Commissariat a l’Energie Atomique et aux Energies Alternatives, Institut des Maladies Emergentes et des Therapies Innovantes, Service de Recherches en Hemato-Immunologie, Hopital Saint-Louis, Paris, France 2 Universite Paris-Diderot, Sorbonne Paris-Cite, UMR E5, Institut Universitaire d’Hematologie, Hopital Saint-Louis, Paris, France 3 Lebanese University, School of Medicine, Hadath, Lebanon 4 Instituto de Ensino e Pesquisa da Santa Casa de Belo Horizonte, IEP/SCBH, Belo Horizonte, Minas Gerais, Brasil 5 Divisao de Imunologia Clinica, Departamento de Clinica Medica, Faculdade de Medicina de Ribeirao Preto, Universidade de Sao Paulo, Ribeirao Preto, Sao Paulo, Brasil 6 Centre d’Etude du Polymorphisme Humain, Fondation Jean-Dausset, Laboratory for Functional Genomics, Paris, France 7 Commissariat a l’Energie Atomique et aux Energies Alternatives, Centre National de Genotypage, Laboratory for Epigenetics and Environment, Evry, France Correspondence to: Philippe Moreau, email: philippe.moreau@cea.fr Keywords: HLA-G, HIF-1, exon 2 HRE, glioma Received: July 02, 2016      Accepted: August 20, 2016      Published: August 26, 2016 ABSTRACT HLA-G is an immune checkpoint molecule with specific relevance in cancer immunotherapy. It was first identified in cytotrophoblasts, protecting the fetus from maternal rejection. HLA-G tissue expression is very restricted but induced in numerous malignant tumors such as glioblastoma, contributing to their immune escape. Hypoxia occurs during placenta and tumor development and was shown to activate HLA-G . We aimed to elucidate the mechanisms of HLA-G activation under conditions combining hypoxia-mimicking treatment and 5-aza-2’deoxycytidine, a DNA demethylating agent used in anti-cancer therapy which also induces HLA-G . Both treatments enhanced the amount of HLA-G mRNA and protein in HLA-G negative U251MG glioma cells. Electrophoretic Mobility Shift Assays and luciferase reporter gene assays revealed that HLA-G upregulation depends on Hypoxia Inducible Factor-1 (HIF-1) and a hypoxia responsive element (HRE) located in exon 2. A polymorphic HRE at –966 bp in the 5’UT region may modulate the magnitude of the response mediated by the exon 2 HRE. We suggest that therapeutic strategies should take into account that HLA-G expression in response to hypoxic tumor environment is dependent on HLA-G gene polymorphism and DNA methylation state at the HLA-G locus.