Annexin-2 is a regulator of stromal cell-derived factor-1/CXCL12 function in the hematopoietic stem cell endosteal niche.
OBJECTIVE
Previously, we reported that annexin-2 (anxa2) plays an important role in hematopoietic stem cell (HSC) localization to the endosteal/osteoblastic marrow niche. This study explored the role that annexin-2 plays in presenting stromal cell-derived factor-1 (or CXCL12) to HSCs.


METHODS
Competitive long-term bone marrow transplant assays were used to determine if HSC engraftment is altered in annexin-2-deficient animals. Colony-forming cell assays, CXCL12 enzyme-linked immunosorbent assay, and real-time reverse transcription polymerase chain reaction analyses were used to determine stem or progenitor cell mobilization by granulocyte colony-stimulating factor. Immunohistochemistry, immunoprecipitation, binding assays, and chemotactic assays were employed to determine if annexin-2 is associated with CXCL12. Degradation assays were also used to determine if annexin-2 and CXCL12 protect each other from proteolytic degradation.


RESULTS
Anxa2(-/-) animals had fewer HSCs in their marrow, and the HSCs in anxa2(-/-) animals express less CXCR4 and CXCR7, suggesting a cell intrinsic defect. Transplantation studies of wild-type marrow into anxa2(-/-) animals demonstrated a cell-extrinsic defect in the anxa2(-/-) animals. CXCL12 binds directly to annexin-2, and this interaction facilitates presentation of CXCL12 to HSCs. Yet the binding of CXCL12 to annexin-2 did not protect CXCL12 from proteolytic cleavage after stem or progenitor cell mobilization by granulocyte colony-stimulating factor.


CONCLUSIONS
These results suggest that annexin-2 serves as an anchor for CXCL12 to help in the localization of HSCs to the niche.
Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, 1011 North University Avenue, Ann Arbor, MI 48109-1078, USA.
Younghun
Y
Jung
Yusuke
Y
Shiozawa
Jingcheng
J
Wang
Lalit R
LR
Patel
Aaron M
AM
Havens
Junhui
J
Song
Paul H
PH
Krebsbach
G David
GD
Roodman
Russell S
RS
Taichman
D000818:Animals; D017306:Annexin A2 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D054377:Chemokine CXCL12 / Q000378:metabolism*; D005786:Gene Expression Regulation; D006412:Hematopoietic Stem Cells / Q000378:metabolism*; D007150:Immunohistochemistry; D051379:Mice; D018345:Mice, Knockout; D011485:Protein Binding; D055153:Stem Cell Niche / Q000378:metabolism*
D017306:Annexin A2; D054377:Chemokine CXCL12