Doxorubicin-induced loss of DNA topoisomerase II and DNMT1- dependent suppression of MiR-125b induces chemoresistance in ALK-positive cells

// Annabelle Congras 1, 2, 3, 7, * , Nina Caillet 1, 2, 3, 7, * , Nouritza Torossian 1, 2, 3 , Cathy Quelen 1, 2, 3, 7 , Camille Daugrois 1, 2, 3 , Pierre Brousset 1, 2, 3, 4, 5, 6, 7 , Laurence Lamant 1, 2, 3, 4, 5, 6, 7 , Fabienne Meggetto 1, 2, 3, 4, 5, 6, 7 and Coralie Hoareau-Aveilla 1, 2, 3, 7 1 Inserm, UMR1037 CRCT, F-31000 Toulouse, France 2 Universite Toulouse III-Paul Sabatier, UMR1037 CRCT, F-31000 Toulouse, France 3 CNRS, ERL5294 CRCT, F-31000 Toulouse, France 4 Institut Carnot Lymphome-CALYM, 31024, Toulouse, France 5 Laboratoire d’Excellence Toulouse Cancer-TOUCAN, 31024, Toulouse, France 6 European Research Initiative on ALK-related malignancies (ERIA) ( http://www.erialcl.net/ ) 7 Equipe Labelisee LIGUE 2017 * Co–first authors Correspondence to: Fabienne Meggetto, email: fabienne.meggetto@inserm.fr Keywords: miR-125b; chemoresistance; doxorubicin; DNA topoisomerase II; DNMT1 Received: November 11, 2017      Accepted: November 20, 2017      Epub: February 08, 2018      Published: March 06, 2018 ABSTRACT Systemic anaplastic large-cell lymphoma (ALCL) is a childhood T cell neoplasm defined by the presence or absence of translocations that lead to the ectopic expression of anaplastic lymphoma kinase (ALK), with nucleophosmin-ALK (NPM-ALK) fusions being the most common. Polychemotherapy involving doxorubicin is the standard first-line treatment but for the 25 to 35% of patients who relapse and develop resistance the prognosis remains poor. We studied the potential role of the microRNA miR-125b in the development of resistance to doxorubicin in NPM-ALK(+) ALCL. Our results show that miR-125b expression is repressed in NPM-ALK(+) cell lines and patient samples through hypermethylation of its promoter. NPM-ALK activity, in cooperation with DNA topoisomerase II (Topo II) and DNA methyltransferase 1 (DNMT1), is responsible for miR-125b repression through DNA hypermethylation. MiR-125b repression was reversed by the inhibition of DNMTs with decitabine or the inhibition of DNA topoisomerase II with either doxorubicin or etoposide. In NPM-ALK(+) cell lines, doxorubicin treatment led to an increase in miR-125b levels by inhibiting the binding of DNMT1 to the MIR125B1 promoter and downregulating the pro-apoptotic miR-125b target BAK1. Reversal of miR-125b silencing, increased miR-125b levels and reduced BAK1 expression also led to a lower efficacy of doxorubicin, suggestive of a pharmacoresistance mechanism. In line with this, miR-125b repression and increased BAK1 expression correlated with early relapse in human NPM-ALK(+) ALCL primary biopsies. Collectively our findings suggest that miR-125b could be used to predict therapeutic outcome in NPM-ALK(+) ALCL.