title: Osteopontin regulates actin cytoskeleton and contributes to cell proliferation in primary erythroblasts.
abstract: Erythropoietin and stem cell factor are the key cytokines that regulate early stages of erythroid differentiation. However, it remains undetermined whether additional cytokines also play a role in the differentiation program. Here, we report that osteopontin (OPN) is highly expressed and secreted by erythroblasts during differentiation. We also demonstrate that OPN-deficient human and mouse erythroblasts exhibit defects in F-actin filaments, and addition of exogenous OPN to OPN-deficient erythroblasts restored the F-actin filaments in these cells. Furthermore, our studies demonstrate that OPN contributes to erythroblast proliferation. OPN knock-out male mice exhibit lower hematocrit and hemoglobin levels compared with their wild-type counterparts. We also show that OPN mediates phosphorylation or activation of multiple proteins including Rac-1 GTPase and the actin-binding protein, adducin, in human erythroblasts. In addition, we show that the OPN effects include regulation of intracellular calcium in human erythroblasts. Finally, we demonstrate that human erythroblasts express CD44 and integrins beta1 and alpha4, three known receptors for OPN, and that the integrin beta1 receptor is involved in transmitting the proliferative signal. Together these results provide evidence for signal transduction by OPN and contribution to multiple functions during the erythroid differentiation program in human and mouse.
authors.affiliation: Department of Medicine, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Jeong-Ah
authors.initials: JA
authors.lastname: Kang
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhou
authors.forename: Tahlia L
authors.initials: TL
authors.lastname: Weis
authors.forename: Hui
authors.initials: H
authors.lastname: Liu
authors.forename: Jodie
authors.initials: J
authors.lastname: Ulaszek
authors.forename: Nilesh
authors.initials: N
authors.lastname: Satgurunathan
authors.forename: Li
authors.initials: L
authors.lastname: Zhou
authors.forename: Koen
authors.initials: K
authors.lastname: van Besien
authors.forename: John
authors.initials: J
authors.lastname: Crispino
authors.forename: Amit
authors.initials: A
authors.lastname: Verma
authors.forename: Philip S
authors.initials: PS
authors.lastname: Low
authors.forename: Amittha
authors.initials: A
authors.lastname: Wickrema
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D002454:Cell Differentiation; D049109:Cell Proliferation; D003599:Cytoskeleton / Q000378:metabolism*; D004912:Erythrocytes / Q000166:cytology* / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D018960:Hyaluronan Receptors / Q000096:biosynthesis; D039441:Integrin alpha4 / Q000378:metabolism; D019012:Integrin beta1 / Q000378:metabolism; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008954:Models, Biological; D053495:Osteopontin / Q000235:genetics* / Q000378:metabolism*; D019089:Stem Cell Factor / Q000378:metabolism
chemical_list: D000199:Actins; D018960:Hyaluronan Receptors; D019012:Integrin beta1; D019089:Stem Cell Factor; D053495:Osteopontin; D039441:Integrin alpha4