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. Author manuscript; available in PMC: 2012 Feb 1.
Published in final edited form as: Exp Hematol. 2010 Nov 22;39(2):151–166.e1. doi: 10.1016/j.exphem.2010.11.007

Figure 5. Model of CXCL12 bound to annexin 2.

Figure 5

A model for how annexin 2 regulates CXCL12 presentation to HSCs. HSC homing and engraftment is dependent on CXCL12 and annexin 2 expression in marrow. The two CXCL12 receptors (CXCR4 and CXCR7) function to localize to the endosteal niche and annexin 2 and its receptor (anxa2r) serve as binding factors. That CXCL12 and annexin 2 directly bind to one and another, and this interaction facilitates HSCs migration in response to CXCL12. Yet the binding of CXCL12 to annexin 2 does not prevent degredation of CXCL12 under HSC mobilizating conditions, as both CXCL12 are degraded by enzymes activated by G-CSF during mobilization. Together these results demonstrate that annexin 2 expressed by osteoblasts is critical for the HSC localization, homing, and mobilization of HSCs from the marrow and provides an important link with CXCL12 function in the marrow.