title: Inhibition of RhoA GTPase activity enhances hematopoietic stem and progenitor cell proliferation and engraftment.
abstract: Ras-related Rho GTPases regulate actin cytoskeletal organization, adhesion, gene transcription, and cell-cycle progression. The Rac subfamily of Rho GTPases and Cdc42 has been shown to play essential roles in hematopoietic stem cell (HSC) engraftment and mobilization. Here, we study the role of RhoA, a related Rho GTPase, in HSC functions. Using retrovirus-mediated gene transfer of a dominant-negative (DN) mutant of RhoA (RhoAN19), we demonstrate that down-regulation of RhoA activity resulted in increased HSC engraftment and self-renewal as measured by competitive repopulation and serial transplantation assays. However, overexpression of RhoAN19 resulted in decreased migration toward SDF-1alpha and alpha(4)beta(1)- and alpha(5)beta(2)-integrin-mediated adhesion of hematopoietic progenitor cells in vitro. Low RhoA activity was associated with higher proliferation rate of hematopoietic progenitor cells and increased cells in active phases of cell cycle, most likely via decreasing p21Cip/Waf expression and increasing cyclin D1 levels. Thus, reducing RhoA activity by optimizing the balance between adhesion/migration and proliferation/self-renewal results in a net increase in HSC engraftment. This mechanism could provide a novel therapeutic target to enhance HSC therapies.
authors.affiliation: Division of Experimental Hematology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, MLC 7013, Cincinnati, OH 45229, USA.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Ghiaur
authors.forename: Andrew
authors.initials: A
authors.lastname: Lee
authors.forename: Jeff
authors.initials: J
authors.lastname: Bailey
authors.forename: Jose A
authors.initials: JA
authors.lastname: Cancelas
authors.forename: Yi
authors.initials: Y
authors.lastname: Zheng
authors.forename: David A
authors.initials: DA
authors.lastname: Williams
mesh_terms: D000818:Animals; D002448:Cell Adhesion; D002453:Cell Cycle; D002465:Cell Movement; D049109:Cell Proliferation; D019938:Cyclin D1 / Q000378:metabolism; D015536:Down-Regulation; D006085:Graft Survival; D006410:Hematopoiesis; D018380:Hematopoietic Stem Cell Transplantation; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000378:metabolism*; D066298:In Vitro Techniques; D051379:Mice; D008810:Mice, Inbred C57BL; D020742:rhoA GTP-Binding Protein / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism
chemical_list: D019938:Cyclin D1; D020742:rhoA GTP-Binding Protein