A novel Bcr-Abl-mTOR-eIF4A axis regulates IRES-mediated translation of LEF-1.
Internal ribosome entry sites (IRESs) in cellular mRNAs direct expression of growth-promoting factors through an alternative translation mechanism that has yet to be fully defined. Lymphoid enhancer factor-1 (LEF-1), a Wnt-mediating transcription factor important for cell survival and metastasis in cancer, is produced via IRES-directed translation, and its mRNA is frequently upregulated in malignancies, including chronic myeloid leukaemia (CML). In this study, we determined that LEF1 expression is regulated by Bcr-Abl, the oncogenic protein that drives haematopoietic cell transformation to CML. We have previously shown that the LEF1 5' untranslated region recruits a complex of proteins to its IRES, including the translation initiation factor eIF4A. In this report, we use two small molecule inhibitors, PP242 (dual mTOR (mammalian target of rapamycin) kinase inhibitor) and hippuristanol (eIF4A inhibitor), to define IRES regulation via a Bcr-Abl-mTOR-eIF4A axis in CML cell lines and primary patient leukaemias. We found that LEF1 and other IRESs are uniquely sensitive to the activities of Bcr-Abl/mTOR. Most notably, we discovered that eIF4A, an RNA helicase, elicits potent non-canonical effects on the LEF1 IRES. Hippuristanol inhibition of eIF4A stalls translation of IRES mRNA and triggers dissociation from polyribosomes. We propose that a combination drug strategy which targets mTOR and IRES-driven translation disrupts key factors that contribute to growth and proliferation in CML.
Department of Microbiology and Molecular Genetics, School of Medicine, University of California, Irvine, CA, USA.
Becky Pinjou
http://orcid.org/0000-0002-1995-802X
BP
Tsai
Department of Microbiology and Molecular Genetics, School of Medicine, University of California, Irvine, CA, USA.
Judith
J
Jimenez
Cancer and Stem Cell Biology Signature Research Program, Duke-NUS Graduate Medical School, Singapore Department of Haematology, Singapore General Hospital, Singapore.
Sharon
S
Lim
Department of Microbiology and Molecular Genetics, School of Medicine, University of California, Irvine, CA, USA.
Kerry D
KD
Fitzgerald
Division of Hematology/Oncology, Department of Medicine, School of Medicine, University of California, Irvine, CA, USA.
Min
M
Zhang
Cancer and Stem Cell Biology Signature Research Program, Duke-NUS Graduate Medical School, Singapore Department of Haematology, Singapore General Hospital, Singapore.
Charles T H
CT
Chuah
Department of Microbiology and Molecular Genetics, School of Medicine, University of California, Irvine, CA, USA.
Haley
H
Axelrod
Department of Microbiology and Molecular Genetics, School of Medicine, University of California, Irvine, CA, USA.
Luke
L
Wilson
Cancer and Stem Cell Biology Signature Research Program, Duke-NUS Graduate Medical School, Singapore Department of Haematology, Singapore General Hospital, Singapore Department of Medical Oncology, National Cancer Centre, Singapore Department of Medicine, Duke University Medical Center, Durham, NC, USA.
S Tiong
ST
Ong
Department of Microbiology and Molecular Genetics, School of Medicine, University of California, Irvine, CA, USA.
Bert L
BL
Semler
Department of Microbiology and Molecular Genetics, School of Medicine, University of California, Irvine, CA, USA marian.waterman@uci.edu.
Marian L
ML
Waterman
D000818:Animals; D002478:Cells, Cultured; D039601:Eukaryotic Initiation Factor-4A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016044:Fusion Proteins, bcr-abl / Q000378:metabolism*; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D019169:Jurkat Cells; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000378:metabolism*; D051821:Lymphoid Enhancer-Binding Factor 1 / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D011132:Polyribosomes / Q000378:metabolism; D014176:Protein Biosynthesis; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011687:Purines / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D013261:Sterols / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D007211:Indoles; C497573:LEF1 protein, human; D051821:Lymphoid Enhancer-Binding Factor 1; D047428:Protein Kinase Inhibitors; D011687:Purines; D012333:RNA, Messenger; D013261:Sterols; C510125:hippuristanol; D016044:Fusion Proteins, bcr-abl; D058570:TOR Serine-Threonine Kinases; D039601:Eukaryotic Initiation Factor-4A; C572919:PP242
Bcr-Abl; IRES; LEF-1; PP242; eIF4A; mTOR