title: Activated KRAS Cooperates with MLL-AF4 to Promote Extramedullary Engraftment and Migration of Cord Blood CD34+ HSPC But Is Insufficient to Initiate Leukemia.
abstract: The MLL-AF4 (MA4) fusion gene is the genetic hallmark of an aggressive infant pro-B-acute lymphoblastic leukemia (B-ALL). Our understanding of MA4-mediated transformation is very limited. Whole-genome sequencing studies revealed a silent mutational landscape, which contradicts the aggressive clinical outcome of this hematologic malignancy. Only RAS mutations were recurrently detected in patients and found to be associated with poorer outcome. The absence of MA4-driven B-ALL models further questions whether MA4 acts as a single oncogenic driver or requires cooperating mutations to manifest a malignant phenotype. We explored whether KRAS activation cooperates with MA4 to initiate leukemia in cord blood-derived CD34(+) hematopoietic stem/progenitor cells (HSPC). Clonogenic and differentiation/proliferation assays demonstrated that KRAS activation does not cooperate with MA4 to immortalize CD34(+) HSPCs. Intrabone marrow transplantation into immunodeficient mice further showed that MA4 and KRAS(G12V) alone or in combination enhanced hematopoietic repopulation without impairing myeloid-lymphoid differentiation, and that mutated KRAS did not cooperate with MA4 to initiate leukemia. However, KRAS activation enhanced extramedullary hematopoiesis of MA4-expressing cell lines and CD34(+) HSPCs that was associated with leukocytosis and central nervous system infiltration, both hallmarks of infant t(4;11)(+) B-ALL. Transcriptional profiling of MA4-expressing patients supported a cell migration gene signature underlying the mutant KRAS-mediated phenotype. Collectively, our findings demonstrate that KRAS affects the homeostasis of MA4-expressing HSPCs, suggesting that KRAS activation in MA4(+) B-ALL is important for tumor maintenance rather than initiation. Cancer Res; 76(8); 2478-89. ©2016 AACR.
authors.affiliation: Josep Carreras Leukemia Research Institute and Department of Biomedicine, School of Medicine, University of Barcelona, Barcelona, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Prieto
authors.affiliation: Pediatric Oncology/Hematology, Erasmus MC-Sophia Children's Hospital, Rotterdam, the Netherlands.
authors.forename: Ronald W
authors.initials: RW
authors.lastname: Stam
authors.affiliation: Josep Carreras Leukemia Research Institute and Department of Biomedicine, School of Medicine, University of Barcelona, Barcelona, Spain. Institute of Biomedicine and Biotechnology of Cantabria (IBBTEC-CSIC-UNIVERSIDAD DE CANTABRIA-SODERCAN), Santander, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Agraz-Doblas
authors.affiliation: Pediatric Hematology Department, A. Trousseau Hospital, Paris, France.
authors.forename: Paola
authors.initials: P
authors.lastname: Ballerini
authors.affiliation: Hematology Laboratory, Hospital Sant Joan de Deu, Barcelona, Spain.
authors.forename: Mireia
authors.initials: M
authors.lastname: Camos
authors.affiliation: Josep Carreras Leukemia Research Institute and Department of Biomedicine, School of Medicine, University of Barcelona, Barcelona, Spain.
authors.forename: Julio
authors.initials: J
authors.lastname: Castaño
authors.affiliation: Institute Pharmaceutical Biology, Goethe-University, Frankfurt/Main, Germany.
authors.forename: Rolf
authors.initials: R
authors.lastname: Marschalek
authors.affiliation: Institute Pharmaceutical Biology, Goethe-University, Frankfurt/Main, Germany.
authors.forename: Aldeheid
authors.initials: A
authors.lastname: Bursen
authors.affiliation: Institute of Biomedicine and Biotechnology of Cantabria (IBBTEC-CSIC-UNIVERSIDAD DE CANTABRIA-SODERCAN), Santander, Spain.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Varela
authors.affiliation: Josep Carreras Leukemia Research Institute and Department of Biomedicine, School of Medicine, University of Barcelona, Barcelona, Spain. pmenendez@carrerasresearch.org cbueno@carrerasresearch.org.
authors.forename: Clara
authors.initials: C
authors.lastname: Bueno
authors.affiliation: Josep Carreras Leukemia Research Institute and Department of Biomedicine, School of Medicine, University of Barcelona, Barcelona, Spain. Instituciò Catalana Recerca i Estudis Avançats (ICREA), Barcelona, Spain. pmenendez@carrerasresearch.org cbueno@carrerasresearch.org.
authors.forename: Pablo
authors.initials: P
authors.lastname: Menendez
mesh_terms: D000818:Animals; D018952:Antigens, CD34 / Q000097:blood*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005312:Fetal Blood / Q000276:immunology*; D011905:Genes, ras; D006412:Hematopoietic Stem Cells / Q000473:pathology*; D064593:Heterografts; D006801:Humans; D007938:Leukemia / Q000235:genetics* / Q000473:pathology; D051379:Mice; D051788:Myeloid-Lymphoid Leukemia Protein / Q000378:metabolism*; D035602:Transcriptional Elongation Factors / Q000378:metabolism*
chemical_list: D018952:Antigens, CD34; D004268:DNA-Binding Proteins; D035602:Transcriptional Elongation Factors; D051788:Myeloid-Lymphoid Leukemia Protein; C081449:AFF1 protein, human