title: Role of RhoA-specific guanine exchange factors in regulation of endomitosis in megakaryocytes.
abstract: Polyploidization can precede the development of aneuploidy in cancer. Polyploidization in megakaryocytes (Mks), in contrast, is a highly controlled developmental process critical for efficient platelet production via unknown mechanisms. Using primary cells, we demonstrate that the guanine exchange factors GEF-H1 and ECT2, which are often overexpressed in cancer and are essential for RhoA activation during cytokinesis, must be downregulated for Mk polyploidization. The first (2N-4N) endomitotic cycle requires GEF-H1 downregulation, whereas subsequent cycles (>4N) require ECT2 downregulation. Exogenous expression of both GEF-H1 and ECT2 prevents endomitosis, resulting in proliferation of 2N Mks. Furthermore, we have shown that the mechanism by which polyploidization is prevented in Mks lacking Mkl1, which is mutated in megakaryocytic leukemia, is via elevated GEF-H1 expression; shRNA-mediated GEF-H1 knockdown alone rescues this ploidy defect. These mechanistic insights enhance our understanding of normal versus malignant megakaryocytopoiesis, as well as aberrant mitosis in aneuploid cancers.
authors.affiliation: Department of Laboratory Medicine, Yale University, New Haven, CT 06520, USA.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Gao
authors.forename: Elenoe
authors.initials: E
authors.lastname: Smith
authors.forename: Elmer
authors.initials: E
authors.lastname: Ker
authors.forename: Phil
authors.initials: P
authors.lastname: Campbell
authors.forename: Ee-chun
authors.initials: EC
authors.lastname: Cheng
authors.forename: Siying
authors.initials: S
authors.lastname: Zou
authors.forename: Sharon
authors.initials: S
authors.lastname: Lin
authors.forename: Lin
authors.initials: L
authors.lastname: Wang
authors.forename: Stephanie
authors.initials: S
authors.lastname: Halene
authors.forename: Diane S
authors.initials: DS
authors.lastname: Krause
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D015536:Down-Regulation; D055785:Gene Knockdown Techniques; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000502:physiology*; D007947:Leukemia, Megakaryoblastic, Acute / Q000503:physiopathology; D008533:Megakaryocytes / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008938:Mitosis; D011123:Polyploidy; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000502:physiology*; D064067:Rho Guanine Nucleotide Exchange Factors
chemical_list: C577402:Arhgef2 protein, mouse; C080509:Ect2 protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D011518:Proto-Oncogene Proteins; D064067:Rho Guanine Nucleotide Exchange Factors