title: Calpain 2 activation of P-TEFb drives megakaryocyte morphogenesis and is disrupted by leukemogenic GATA1 mutation.
abstract: Megakaryocyte morphogenesis employs a "hypertrophy-like" developmental program that is dependent on P-TEFb kinase activation and cytoskeletal remodeling. P-TEFb activation classically occurs by a feedback-regulated process of signal-induced, reversible release of active Cdk9-cyclin T modules from large, inactive 7SK small nuclear ribonucleoprotein particle (snRNP) complexes. Here, we have identified an alternative pathway of irreversible P-TEFb activation in megakaryopoiesis that is mediated by dissolution of the 7SK snRNP complex. In this pathway, calpain 2 cleavage of the core 7SK snRNP component MePCE promoted P-TEFb release and consequent upregulation of a cohort of cytoskeleton remodeling factors, including α-actinin-1. In a subset of human megakaryocytic leukemias, the transcription factor GATA1 undergoes truncating mutation (GATA1s). Here, we linked the GATA1s mutation to defects in megakaryocytic upregulation of calpain 2 and of P-TEFb-dependent cytoskeletal remodeling factors. Restoring calpain 2 expression in GATA1s mutant megakaryocytes rescued normal development, implicating this morphogenetic pathway as a target in human leukemogenesis.
authors.affiliation: Department of Pathology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
authors.forename: Kamaleldin E
authors.initials: KE
authors.lastname: Elagib
authors.affiliation: Department of Pathology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: Rubinstein
authors.affiliation: Department of Pathology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
authors.forename: Lorrie L
authors.initials: LL
authors.lastname: Delehanty
authors.affiliation: Department of Pathology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
authors.forename: Valerie S
authors.initials: VS
authors.lastname: Ngoh
authors.affiliation: Department of Pathology and Molecular Medicine, Queen's University, Kingston, Ontario K7L 3N6, Canada.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Greer
authors.affiliation: Department of Public Health Sciences, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
authors.forename: Shuran
authors.initials: S
authors.lastname: Li
authors.affiliation: Department of Public Health Sciences, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
authors.forename: Jae K
authors.initials: JK
authors.lastname: Lee
authors.affiliation: Division of Hematology/Oncology, Children's Hospital Boston, Harvard Stem Cell Institute, Harvard Medical School, Boston, MA 02115, USA; Department of Pediatric Oncology, Dana-Farber Cancer Institute, Harvard Stem Cell Institute, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Li
authors.affiliation: Division of Hematology/Oncology, Children's Hospital Boston, Harvard Stem Cell Institute, Harvard Medical School, Boston, MA 02115, USA; Department of Pediatric Oncology, Dana-Farber Cancer Institute, Harvard Stem Cell Institute, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Stuart H
authors.initials: SH
authors.lastname: Orkin
authors.affiliation: Department of Pathology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
authors.forename: Ivailo S
authors.initials: IS
authors.lastname: Mihaylov
authors.affiliation: Department of Pathology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA. Electronic address: ang3x@virginia.edu.
authors.forename: Adam N
authors.initials: AN
authors.lastname: Goldfarb
mesh_terms: D000185:Actinin / Q000235:genetics / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002154:Calpain / Q000502:physiology*; D002454:Cell Differentiation; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic / Q000378:metabolism / Q000473:pathology*; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000378:metabolism; D005434:Flow Cytometry; D050982:GATA1 Transcription Factor / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D007938:Leukemia / Q000378:metabolism / Q000473:pathology*; D008533:Megakaryocytes / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009024:Morphogenesis; D009154:Mutation / Q000235:genetics*; D042925:Positive Transcriptional Elongation Factor B / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017411:Ribonucleoproteins, Small Nuclear / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D050982:GATA1 Transcription Factor; D012333:RNA, Messenger; D017411:Ribonucleoproteins, Small Nuclear; D000185:Actinin; D042925:Positive Transcriptional Elongation Factor B; D002154:Calpain; C112682:Capn1 protein, mouse