title: Internal Tandem Duplication in FLT3 Attenuates Proliferation and Regulates Resistance to the FLT3 Inhibitor AC220 by Modulating p21Cdkn1a and Pbx1 in Hematopoietic Cells.
abstract: Internal tandem duplication (ITD) mutations in the Fms-related tyrosine kinase 3 (FLT3) gene (FLT3-ITD) are associated with poor prognosis in patients with acute myeloid leukemia (AML). Due to the development of drug resistance, few FLT3-ITD inhibitors are effective against FLT3-ITD+ AML. In this study, we show that FLT3-ITD activates a novel pathway involving p21Cdkn1a (p21) and pre-B cell leukemia transcription factor 1 (Pbx1) that attenuates FLT3-ITD cell proliferation and is involved in the development of drug resistance. FLT3-ITD up-regulated p21 expression in both mouse bone marrow c-kit+-Sca-1+-Lin- (KSL) cells and Ba/F3 cells. The loss of p21 expression enhanced growth factor-independent proliferation and sensitivity to cytarabine as a consequence of concomitantly enriching the S+G2/M phase population and significantly increasing the expression of Pbx1, but not Evi-1, in FLT3-ITD+ cells. This enhanced cell proliferation following the loss of p21 was partially abrogated when Pbx1 expression was silenced in FLT3-ITD+ primary bone marrow colony-forming cells and Ba/F3 cells. When FLT3-ITD was antagonized with AC220, a selective inhibitor of FLT3-ITD, p21 expression was decreased coincident with Pbx1 mRNA up-regulation and a rapid decline in the number of viable FLT3-ITD+ Ba/F3 cells; however, the cells eventually became refractory to AC220. Overexpressing p21 in FLT3-ITD+ Ba/F3 cells delayed the emergence of cells that were refractory to AC220, whereas p21 silencing accelerated their development. These data indicate that FLT3-ITD is capable of inhibiting FLT3-ITD+ cell proliferation through the p21/Pbx1 axis and that treatments that antagonize FLT3-ITD contribute to the subsequent development of cells that are refractory to a FLT3-ITD inhibitor by disrupting p21 expression.
authors.affiliation: Department of Pediatrics, Shimane University School of Medicine, Izumo, Shimane, Japan.
authors.forename: Mariko
authors.initials: M
authors.lastname: Abe
authors.affiliation: Department of Microbiology/Immunology, Indiana University School of Medicine, Indianapolis, Indiana, United States of America.
authors.forename: Louis M
authors.initials: LM
authors.lastname: Pelus
authors.affiliation: Department of Microbiology/Immunology, Indiana University School of Medicine, Indianapolis, Indiana, United States of America.
authors.forename: Pratibha
authors.initials: P
authors.lastname: Singh
authors.affiliation: Department of Pediatrics, Shimane University School of Medicine, Izumo, Shimane, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Hirade
authors.affiliation: Department of Oncology/Hematology, Shimane University School of Medicine, Izumo, Shimane, Japan.
authors.forename: Chie
authors.initials: C
authors.lastname: Onishi
authors.affiliation: Department of Pediatrics, Shimane University School of Medicine, Izumo, Shimane, Japan.
authors.forename: Jamiyan
authors.initials: J
authors.lastname: Purevsuren
authors.affiliation: Department of Pediatrics, Shimane University School of Medicine, Izumo, Shimane, Japan.|Division of Blood Transfusion, Shimane University Hospital, Izumo, Shimane, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Taketani
authors.affiliation: Department of Pediatrics, Shimane University School of Medicine, Izumo, Shimane, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Yamaguchi
authors.affiliation: Department of Pediatrics, Shimane University School of Medicine, Izumo, Shimane, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Fukuda
mesh_terms: D000818:Animals; D000906:Antibodies / Q000737:chemistry; D052160:Benzothiazoles / Q000737:chemistry*; D019070:Cell Lineage; D049109:Cell Proliferation; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism*; D016207:Cytokines / Q000378:metabolism; D005260:Female; D017353:Gene Deletion; D005786:Gene Expression Regulation; D020868:Gene Silencing; D006412:Hematopoietic Stem Cells / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D010641:Phenotype; D010671:Phenylurea Compounds / Q000737:chemistry*; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D015398:Signal Transduction; D020080:Tandem Repeat Sequences; D014157:Transcription Factors / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D051941:fms-Like Tyrosine Kinase 3 / Q000235:genetics*
chemical_list: D000906:Antibodies; D052160:Benzothiazoles; C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016207:Cytokines; D018398:Homeodomain Proteins; C481797:Pbx1 protein, mouse; D010671:Phenylurea Compounds; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; C544967:quizartinib; C497970:FLT3 protein, human; C497971:Flt3 protein, mouse; D051941:fms-Like Tyrosine Kinase 3; D017868:Cyclic AMP-Dependent Protein Kinases