MLL-AF6 fusion oncogene sequesters AF6 into the nucleus to trigger RAS activation in myeloid leukemia.
A rare location, t(6;11)(q27;q23) (MLL-AF6), is associated with poor outcome in childhood acute myeloid leukemia (AML). The described mechanism by which MLL-AF6, through constitutive self-association and in cooperation with DOT-1L, activates aberrant gene expression does not explain the biological differences existing between t(6;11)-rearranged and other MLL-positive patients nor their different clinical outcome. Here, we show that AF6 is expressed in the cytoplasm of healthy bone marrow cells and controls rat sarcoma viral oncogene (RAS)-guanosine triphosphate (GTP) levels. By contrast, in MLL-AF6-rearranged cells, AF6 is found localized in the nucleus, leading to aberrant activation of RAS and of its downstream targets. Silencing MLL-AF6, we restored AF6 localization in the cytoplasm, thus mediating significant reduction of RAS-GTP levels and of cell clonogenic potential. The rescue of RAS-GTP levels after MLL-AF6 and AF6 co-silencing confirmed that MLL-AF6 oncoprotein potentiates the activity of the RAS pathway through retention of AF6 within the nucleus. Exposure of MLL-AF6-rearranged AML blasts to tipifarnib, a RAS inhibitor, leads to cell autophagy and apoptosis, thus supporting RAS targeting as a novel potential therapeutic strategy in patients carrying t(6;11). Altogether, these data point to a novel role of the MLL-AF6 chimera and show that its gene partner, AF6, is crucial in AML development.
Women and Child Health Department, Hematology-Oncology Laboratory, Instituto di Ricerca Pediatrica, University of Padova, Padova, Italy;
Elena
E
Manara
Women and Child Health Department, Hematology-Oncology Laboratory, Instituto di Ricerca Pediatrica, University of Padova, Padova, Italy;
Emma
E
Baron
Women and Child Health Department, Hematology-Oncology Laboratory, Instituto di Ricerca Pediatrica, University of Padova, Padova, Italy;
Claudia
C
Tregnago
Women and Child Health Department, Hematology-Oncology Laboratory, Instituto di Ricerca Pediatrica, University of Padova, Padova, Italy;
Sanja
S
Aveic
Women and Child Health Department, Hematology-Oncology Laboratory, Instituto di Ricerca Pediatrica, University of Padova, Padova, Italy;
Valeria
V
Bisio
Women and Child Health Department, Hematology-Oncology Laboratory, Instituto di Ricerca Pediatrica, University of Padova, Padova, Italy;
Silvia
S
Bresolin
Clinica Pediatrica, Università di Bologna, Ospedale "S. Orsola," Bologna, Italy; and.
Riccardo
R
Masetti
Oncoematologia Pediatrica, IRCCS Ospedale Pediatrico Bambino Gesù, Roma, University of Pavia, Pavia, Italy.
Franco
F
Locatelli
Women and Child Health Department, Hematology-Oncology Laboratory, Instituto di Ricerca Pediatrica, University of Padova, Padova, Italy;
Giuseppe
G
Basso
Women and Child Health Department, Hematology-Oncology Laboratory, Instituto di Ricerca Pediatrica, University of Padova, Padova, Italy;
Martina
M
Pigazzi
D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism; D002648:Child; D002880:Chromosomes, Human, Pair 11; D002896:Chromosomes, Human, Pair 6; D020868:Gene Silencing; D006801:Humans; D016547:Kinesins / Q000235:genetics / Q000378:metabolism*; D007951:Leukemia, Myeloid / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D051788:Myeloid-Lymphoid Leukemia Protein / Q000235:genetics / Q000378:metabolism*; D009218:Myosins / Q000235:genetics / Q000378:metabolism*; D015514:Oncogene Proteins, Fusion / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics* / Q000378:metabolism*; D015533:Transcriptional Activation; D014178:Translocation, Genetic
C095516:AFDN protein, human; C447400:MLL-AF6 fusion protein, human; D015514:Oncogene Proteins, Fusion; D051788:Myeloid-Lymphoid Leukemia Protein; D009218:Myosins; D016547:Kinesins; D016283:Proto-Oncogene Proteins p21(ras)