Differential interaction between DARC and SDF-1 on erythrocytes and their precursors

Abstract

The Duffy Antigen Receptor for Chemokines (DARC) is expressed on erythrocytes and on endothelium of postcapillary venules and splenic sinusoids. Absence of DARC on erythrocytes, but not on endothelium, is referred to as the Duffy negative phenotype and is associated with neutropenia. Here we provide evidence that stromal cell-derived factor 1 (SDF-1), the chemokine that restricts neutrophil precursors to the bone marrow, binds to erythrocyte progenitors in a DARC-dependent manner. Furthermore, we show that SDF-1 binding to DARC is dependent on the conformation of DARC, which gradually changes during erythroid development, resulting in the absence of SDF-1 binding to mature erythrocytes. However, SDF-1 binding to erythrocytes was found to be inducible by pre-treating erythrocytes with IL-8 or with antibodies recognizing specific epitopes on DARC. Taken together, these novel findings identify DARC on erythrocyte precursors as a receptor for SDF-1, which may be of interest in beginning to understand the development of neutropenia in situations where DARC expression is limited.

The dimeric form of CXCL12 binds to atypical chemokine receptor 1

“…The recombinant ACKR1 fragment produced in bacteria lacks those modifications, which are more likely to enhance CXCL12 binding than to diminish or alter it. Our findings not only confirm a recent report that CXCL12 is an ACKR1 ligand ( 55 ) but also importantly modify its conclusions as monomeric CXCL12 is not a potent ligand of ACKR1. Our data open a possibility that other chemokines that apparently fail to compete with canonical ACKR1 ligands for binding might still bind ACKR1 in physiologically relevant contexts.…”

“…CXCL12-WT and, to a greater extent, CXCL12-LD lead to broadening of additional ACKR1 N-term peaks with many of these located in the 50s region of ACKR1 N-term residues. Previous reports provide contradicting claims regarding the interaction or lack thereof of CXCL12 with ACKR1 ( 54 , 55 ). Our analysis of the ACKR1 N-term spectra suggests that ACKR1 N-term can bind CXCL12-LM, CXCL12-WT, and CXCL12-LD with potentially substantial differences in affinity and stoichiometry.…”

“…CXCL12 forms an extensive protein-protein interface with the flexible N-terminal domain of its receptors CXCR4 and ACKR3 ( 44 , 51 , 65 ). ACKR1 has the longest N-terminal domain in the chemokine receptor family (60 amino acids) and binds a multitude of inflammatory chemokines but apparently not homeostatic chemokines like CXCL12 ( 54 ), a notion that was recently contested by Klei et al ( 55 ). While most chemokines form dimers at micromolar concentrations or in the presence of glycosaminoglycans ( 66 – 68 ), they are generally understood to bind their GPCRs as monomers ( 69 , 70 ).…”

In Vitro Erythropoiesis at Different pO2 Induces Adaptations That Are Independent of Prior Systemic Exposure to Hypoxia

“…During reticulocyte maturation a spectrum of different morphological configurations occurs. These processes are as yet ill-defined mechanistically but involve restructuring of membrane protein complexes and their dynamic interaction with the underlying spectrin cytoskeleton, as well as regulation by post-translational protein modifications, loss of specific proteins through vesicle release (e.g., AQP1 and CD71) and shear stress signaling [ 36 , 37 , 38 , 39 ]. The presence of proto-biconcave cells, meaning a large biconcave cell with irregular borders, suggests a more advanced maturation stage of the reticulocytes formed at three percent O 2 .…”

“…In addition, HSPC mobilization is tightly controlled by an interplay between cell–cell interactions and chemokines (e.g., SDF1) and also regulated by atypical chemokine receptor (DARC, containing the duffy antigen) expression on erythroid cells [ 43 ]. We have recently shown that DARC expressed on nucleated erythroblast binds SDF1 but that this is lost upon reticulocyte maturation [ 39 ]. Increased erythroid mass due to hypoxia-induced stress erythropoiesis may signal mobilization of HSPC.…”