title: Smad4 binds Hoxa9 in the cytoplasm and protects primitive hematopoietic cells against nuclear activation by Hoxa9 and leukemia transformation.
abstract: We studied leukemic stem cells (LSCs) in a Smad4(-/-) mouse model of acute myelogenous leukemia (AML) induced either by the HOXA9 gene or by the fusion oncogene NUP98-HOXA9. Although Hoxa9-Smad4 complexes accumulate in the cytoplasm of normal hematopoietic stem cells and progenitor cells (HSPCs) transduced with these oncogenes, there is no cytoplasmic stabilization of HOXA9 in Smad4(-/-) HSPCs, and as a consequence increased levels of Hoxa9 is observed in the nucleus leading to increased immortalization in vitro. Loss of Smad4 accelerates the development of leukemia in vivo because of an increase in transformation of HSPCs. Therefore, the cytoplasmic binding of Hoxa9 by Smad4 is a mechanism to protect Hoxa9-induced transformation of normal HSPCs. Because Smad4 is a potent tumor suppressor involved in growth control, we developed a strategy to modify the subcellular distribution of Smad4. We successfully disrupted the interaction between Hoxa9 and Smad4 to activate the TGF-β pathway and apoptosis, leading to a loss of LSCs. Together, these findings reveal a major role for Smad4 in the negative regulation of leukemia initiation and maintenance induced by HOXA9/NUP98-HOXA9 and provide strong evidence that antagonizing Smad4 stabilization by these oncoproteins might be a promising novel therapeutic approach in leukemia.
authors.affiliation: Molecular Medicine and Gene Therapy, Lund Stem Cell Center, Lund, Sweden.
authors.forename: Ronan
authors.initials: R
authors.lastname: Quéré
authors.forename: Göran
authors.initials: G
authors.lastname: Karlsson
authors.forename: Falk
authors.initials: F
authors.lastname: Hertwig
authors.forename: Marianne
authors.initials: M
authors.lastname: Rissler
authors.forename: Beata
authors.initials: B
authors.lastname: Lindqvist
authors.forename: Thoas
authors.initials: T
authors.lastname: Fioretos
authors.forename: Peter
authors.initials: P
authors.lastname: Vandenberghe
authors.forename: Marilyn L
authors.initials: ML
authors.lastname: Slovak
authors.forename: Jörg
authors.initials: J
authors.lastname: Cammenga
authors.forename: Stefan
authors.initials: S
authors.lastname: Karlsson
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D016026:Bone Marrow Transplantation; D002467:Cell Nucleus / Q000378:metabolism*; D002471:Cell Transformation, Neoplastic; D047369:Chromatin Immunoprecipitation; D003593:Cytoplasm / Q000378:metabolism*; D005434:Flow Cytometry; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics / Q000502:physiology*; D006801:Humans; D047468:Immunoprecipitation; D015470:Leukemia, Myeloid, Acute / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D028861:Nuclear Pore Complex Proteins / Q000235:genetics; D015514:Oncogene Proteins, Fusion / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051901:Smad4 Protein / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism
chemical_list: D018398:Homeodomain Proteins; C400441:NUP98-HOXA9 fusion protein, human; D028861:Nuclear Pore Complex Proteins; D015514:Oncogene Proteins, Fusion; D012333:RNA, Messenger; D051901:Smad4 Protein; C490810:Smad4 protein, mouse; D016212:Transforming Growth Factor beta; C097899:homeobox protein HOXA9