title: miR-377-dependent BCL-xL regulation drives chemotherapeutic resistance in B-cell lymphoid malignancies.
abstract: BACKGROUND
  BCL-xL is an anti-apoptotic BCL-2 family protein that inhibits apoptosis and is overexpressed in many cancers. We have reported that acquired resistance to the BCL-2 inhibitor ABT-199 (venetoclax) is associated with increased BCL-xL expression. Yet, how BCL-xL mediates chemoresistance in hematopoietic malignancies is not clear. This finding may help in design of new strategies for therapeutic intervention to overcome acquired chemoresistance mediated by BCL-xL.
  
  
  RESULTS
  We now show that the increased BCL-xL expression was inversely correlated with that of miR-377 in ABT-199-resistant cells. This finding was also extended to a panel of B-cell lymphoid lines and primary chronic lymphocytic leukemia (CLL) cells. miR-377 suppressed BCL-xL expression by recognizing two binding sites in the BCL-xL 3'-UTR. Mutation of these two miR-377 consensus-binding sites completely abolished its regulatory effect. Expression of a miR-377 mimic downregulated BCL-xL protein expression and significantly increased apoptotic cell death. Expression of a miR-377 inhibitor restored BCL-xL protein expression and limited cell death caused by the hypomethylating agent 5-azacytidine. Thus, miR-377-dependent BCL-xL regulation drives acquired therapeutic resistance to ABT-199. We further show that CLL patients who received a diverse array of chemotherapy regimens also had significantly higher BCL-xL and lower miR377 expression, indicating that exposure to chemotherapy might trigger transcriptional silencing of miR-377, which results in high levels of BCL-xL. Importantly, CLL patients with high BCL-xL/low miR-377 expression had an advanced tumor stage. Moreover, the high BCL-xL expression correlated with short treatment-free survival in 76 CLL patients. miR-377 is located at 14q32 in the DLK1-DIO3 region, which encodes the largest tumor suppressor miRNA cluster in humans. Examination of five additional 14q32 miRNAs revealed that the majority were significantly down-regulated in most CLL patients as well as in ABT-199-resistant cell lines. Remarkably, four of these miRNAs had significantly decreased expression in chemotherapy-treated CLL patients as compared to those untreated. These findings indicate a reduced expression of multiple miRNAs that may reflect a global silencing of this miRNA cluster in therapy-resistant lymphoid cells.
  
  
  CONCLUSIONS
  These findings reveal a novel mechanism by which down-regulation of miR-377 increases BCL-xL expression, promoting chemotherapy resistance in B-cell lymphoid malignancies.
authors.affiliation: Departments of Cancer Biology, Cleveland, OH, 44195, USA.|Department of Human Cancer Genomic Research, King Faisal Specialist Hospital and Research Cancer, Riyadh, 11211, Saudi Arabia.
authors.forename: Sayer
authors.initials: S
authors.lastname: Al-Harbi
authors.affiliation: Departments of Cancer Biology, Cleveland, OH, 44195, USA.|Department of Pathology, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA.
authors.forename: Gaurav S
authors.initials: GS
authors.lastname: Choudhary
authors.affiliation: Department of Biological, Geological, and Environmental Sciences, Center for Gene Regulation in Health and Disease, Cleveland State University, Cleveland, OH, 44115, USA.
authors.forename: Jey Sabith
authors.initials: JS
authors.lastname: Ebron
authors.affiliation: Department of Hematology and Oncology, Cleveland Clinic, Taussig Cancer Institute, Cleveland, OH, 44195, USA.
authors.forename: Brian T
authors.initials: BT
authors.lastname: Hill
authors.affiliation: Genomic Medicine Institute, Cleveland, OH, 44195, USA.
authors.forename: Nagarajavel
authors.initials: N
authors.lastname: Vivekanathan
authors.affiliation: Genomic Medicine Institute, Cleveland, OH, 44195, USA.
authors.forename: Angela H
authors.initials: AH
authors.lastname: Ting
authors.affiliation: Quantitative Health Sciences, Lerner Research Institute, Cleveland, OH, 44195, USA.
authors.forename: Tomas
authors.initials: T
authors.lastname: Radivoyevitch
authors.affiliation: Department of Hematology and Oncology, Cleveland Clinic, Taussig Cancer Institute, Cleveland, OH, 44195, USA.
authors.forename: Mitchell R
authors.initials: MR
authors.lastname: Smith
authors.affiliation: Department of Biological, Geological, and Environmental Sciences, Center for Gene Regulation in Health and Disease, Cleveland State University, Cleveland, OH, 44115, USA.
authors.forename: Girish C
authors.initials: GC
authors.lastname: Shukla
authors.affiliation: Departments of Cancer Biology, Cleveland, OH, 44195, USA. almasaa@ccf.org.
authors.forename: Alex
authors.initials: A
authors.lastname: Almasan
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D001402:B-Lymphocytes / Q000378:metabolism*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002460:Cell Line; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000235:genetics / Q000378:metabolism*; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D013449:Sulfonamides / Q000494:pharmacology; D051020:bcl-X Protein / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D019086:Bridged Bicyclo Compounds, Heterocyclic; C534063:MIRN377 microRNA, human; D035683:MicroRNAs; D013449:Sulfonamides; D051020:bcl-X Protein; C579720:venetoclax