title: The endoplasmic reticulum chaperone protein GRP94 is required for maintaining hematopoietic stem cell interactions with the adult bone marrow niche.
abstract: Hematopoietic stem cell (HSC) homeostasis in the adult bone marrow (BM) is regulated by both intrinsic gene expression products and interactions with extrinsic factors in the HSC niche. GRP94, an endoplasmic reticulum chaperone, has been reported to be essential for the expression of specific integrins and to selectively regulate early T and B lymphopoiesis. In GRP94 deficient BM chimeras, multipotent hematopoietic progenitors persisted and even increased, however, the mechanism is not well understood. Here we employed a conditional knockout (KO) strategy to acutely eliminate GRP94 in the hematopoietic system. We observed an increase in HSCs and granulocyte-monocyte progenitors in the Grp94 KO BM, correlating with an increased number of colony forming units. Cell cycle analysis revealed that a loss of quiescence and an increase in proliferation led to an increase in Grp94 KO HSCs. This expansion of the HSC pool can be attributed to the impaired interaction of HSCs with the niche, evidenced by enhanced HSC mobilization and severely compromised homing and lodging ability of primitive hematopoietic cells. Transplanting wild-type (WT) hematopoietic cells into a GRP94 null microenvironment yielded a normal hematology profile and comparable numbers of HSCs as compared to WT control, suggesting that GRP94 in HSCs, but not niche cells, is required for maintaining HSC homeostasis. Investigating this, we further determined that there was a near complete loss of integrin α4 expression on the cell surface of Grp94 KO HSCs, which showed impaired binding with fibronectin, an extracellular matrix molecule known to play a role in mediating HSC-niche interactions. Furthermore, the Grp94 KO mice displayed altered myeloid and lymphoid differentiation. Collectively, our studies establish GRP94 as a novel cell intrinsic factor required to maintain the interaction of HSCs with their niche, and thus regulate their physiology.
authors.affiliation: Department of Biochemistry and Molecular Biology and the USC Norris Comprehensive Cancer Center, University of Southern California Keck School of Medicine, Los Angeles, California, United States of America.
authors.forename: Biquan
authors.initials: B
authors.lastname: Luo
authors.forename: Ben S
authors.initials: BS
authors.lastname: Lam
authors.forename: Sung Hyung
authors.initials: SH
authors.lastname: Lee
authors.forename: Shiuan
authors.initials: S
authors.lastname: Wey
authors.forename: Hui
authors.initials: H
authors.lastname: Zhou
authors.forename: Miao
authors.initials: M
authors.lastname: Wang
authors.forename: Si-Yi
authors.initials: SY
authors.lastname: Chen
authors.forename: Gregor B
authors.initials: GB
authors.lastname: Adams
authors.forename: Amy S
authors.initials: AS
authors.lastname: Lee
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology*; D002450:Cell Communication / Q000235:genetics; D002454:Cell Differentiation / Q000235:genetics; D002465:Cell Movement / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005260:Female; D005353:Fibronectins / Q000378:metabolism; D005786:Gene Expression Regulation / Q000235:genetics; D055786:Gene Knockout Techniques; D018840:HSP70 Heat-Shock Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000378:metabolism*; D006706:Homeostasis / Q000235:genetics; D039441:Integrin alpha4 / Q000378:metabolism; D008214:Lymphocytes / Q000166:cytology; D008297:Male; D008565:Membrane Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D022423:Myeloid Cells / Q000166:cytology; D016192:Resting Phase, Cell Cycle / Q000235:genetics; D055153:Stem Cell Niche / Q000166:cytology* / Q000378:metabolism
chemical_list: D005353:Fibronectins; D018840:HSP70 Heat-Shock Proteins; D008565:Membrane Proteins; C018551:glucose-regulated proteins; D039441:Integrin alpha4