Deregulation of AhR function by the human acute leukemia TEL‐ARNT fusion protein
Authors: Florence Nguyen‐Khac, Véronique Della Valle, Rodolphe G. Lopez, Jacques Ghysdael, Olivier A. Bernard
Journal: American Journal of Hematology (2014)

To the Editor: The Aryl Hydrocarbon Receptor (AhR) is a member of the conserved Per/ARNT/SIM family of transcription factors. AhR is known since 1992 as a subunit of the dimeric transcription factor AhR-Aryl Receptor Nuclear Translocator (ARNT), involved in the transcriptional response to xenobiotics through specific binding to the xenobiotic response element (XRE). Only recently, an endogenous ligand and its function in the control of hematopoietic stem/progenitor cells growth and differentiation have been elucidated 1. Smith et al. recently reported a role for the AhR in both hematopoietic progenitor expansion and erythroid and megakaryocytic differentiation 2. In addition to AhR, ARNT also interacts with HIF1A and HIF2A, two major actors in the cellular transcriptional response to low oxygen tension. We and others described a t(1;12)(q21;p13) chromosomal translocation in human acute leukemia that recombines the TEL (aka ETV6) and ARNT genes, and results in the expression of a TEL-ARNT fusion protein 3, 4. Functional analyses showed that TEL-ARNT interacts with HIF1A, impairs its transcriptional activity and in turn the cellular response to low oxygen tension 5. In our initial report, we showed transcription of AhR in the primary leukemic sample 3. We wondered whether TEL-ARNT would impact on AhR function. To address this question, we first investigated the interactions between TEL-ARNT and AhR proteins. As shown in Fig. 1A, coimmunoprecipitation experiments using in vitro translated proteins clearly demonstrated their physical interaction. We next tested the capacity of the AhR/TEL-ARNT complex to bind the specific XRE nucleotide sequence. In electrophoretic mobility shift assay, AhR/TEL-ARNT complexes were able to specifically bind a radiolabeled XRE probe (Fig. 1B). To investigate the transcriptional properties of AhR/TEL-ARNT (Fig. 1C), we transiently transfected expression vectors for both AhR and TEL-ARNT together with a XRE-dependent promoter luciferase reporter construct. In contrast to the transcriptional activation observed in response to B naphtoflavone (BnF, an AhR ligand) in cells coexpressing ARNT and AhR, no transactivation of the XRE-based reporter was seen in TEL-ARNT-expressing cells (Fig. 1D). Instead, the TEL-ARNT fusion protein exerted a dominant-negative effect upon the activity of wild-type ARNT (Fig. 1E). Although performed essentially in vitro, our data indicate that TEL-ARNT impairs the normal functions of ARNT. Thus, TEL-ARNT likely contributes to leukemogenesis by directly interfering with transcriptional programs induced in response to low oxygen tension and xenobiotics. F.N-K. performed the research reported here, analyzed data, and wrote the paper. V.D.V. and R.G.L. performed the research. J.G. analyzed data, and wrote the paper. O.A.B. designed research, analyzed data, and wrote the paper. Florence Nguyen-Khac1,2,3 Véronique Della Valle4 Rodolphe G. Lopez5,6,7 Jacques Ghysdael5,6,7 Olivier A. Bernard4 1Service d'Hématologie Biologique, Hôpital Pitié-Salpêtrière, Paris, France; 2INSERM U872, Centre de Recherche des Cordeliers, Paris, France; 3UPMC, Paris, France; 4INSERM U985, Institut Gustave Roussy, Villejuif, France; 5Institut Curie, Centre Universitaire, Orsay, France; 6Centre National de la Recherche Scientifique UMR 3306, Orsay, France; 7Institut National de la Santé et de la Recherche Médicale U1005, Orsay, France