Stromal Cell-derived Factor-1α Associates with Heparan Sulfates through the First β-Strand of the Chemokine

Abstract

Biological properties of chemokines are believed to be influenced by their association with glycosaminoglycans. Surface plasmon resonance kinetic analysis shows that the CXC chemokine stromal cell-derived factor-1␣ (SDF-1␣), which binds the CXCR4 receptor, associates with heparin with an affinity constant of 38.4 nM (k on ‫؍‬ 2.16 ؋ 10 6 M ؊1 s ؊1 and k off ‫؍‬ 0.083 ؋ s ؊1 ). A modified SDF-1␣ (SDF-1 3/6) was generated by combined substitution of the basic cluster of residues Lys 24 , His 25 , and Lys 27 by Ser. SDF-1 3/6 conserves the global native structure and functional properties of SDF-1␣, but it is unable to interact with sensor chip-immobilized heparin. The biological relevance of these in vitro findings was investigated. SDF-1␣ was unable to bind in a CXCR4-independent manner on epithelial cells that were treated with heparan sulfate (HS)-degrading enzymes or constitutively lack HS expression. The inability of SDF-1 3/6 to bind to cells underlines the importance of the identified basic cluster for the physiological interactions of SDF-1␣ with HS. Importantly, the amino-terminal domain of SDF-1␣ which is required for binding to, and activation of, CXCR4 remains exposed after binding to HS and is recognized by a neutralizing monoclonal antibody directed against the first residues of the chemokine. Overall, these findings indicate that the Lys 24 , His 25 , and Lys 27 cluster of residues forms, or is an essential part of, the HS-binding site which is distinct from that required for binding to, and signaling through, CXCR4.

Expression of Stromal Cell-Derived Factor-1 and of Its Receptor CXCR4 in Liver Regeneration from Oval Cells in Rat

“…Although it cannot be excluded that SDF-1 mRNA might have a very short half life, this result strongly suggests that SDF-1 is not synthesized by these cells but only bound to their surface, possibly through plasma membrane-associated heparan sulfates. 29 We also demonstrate that CXCR4 is expressed in the liver and that this expression is localized in oval cells. Indeed, in the AAF/PH model, CXCR4 mRNA hepatic expression varied in parallel with the number of oval cells, whereas it did not change in absence of oval cell accumulation (PH model).…”

“…22 However, in the latter study, it was not clear whether SDF-1 was synthesized by labeled cells or if it was of exogenous origin and bound to cell surface receptors or to plasma membrane-associated heparan sulfates. 29 Our in situ hybridization findings in oval cells suggest that ductal plate cells might indeed synthesize SDF-1. Contrasting with our results, it was found in a regeneration model similar to the present one that SDF-1 protein was mainly expressed by hepatocytes located at proximity of oval cells.…”

Induction of a CXCL8 binding site on endothelial syndecan‐3 in rheumatoid synovium

“…Different chemokines show variation in their affinities for glycosaminoglycans that are not solely based on charge considerations, suggesting selectivity in these interactions (14,17,18). Some of the structural domains of HS that bind chemokines have been described, including those for CXCL8, CXCL4, CXCL12, and CCL3 (19)(20)(21)(22).…”

Biliary Epithelial Cells Are Not the Predominant Source of Hepatic CXCL12

“…Because CXCL12 binds to cell surface heparan sulfates, it remains possible that the observed BEC expression of CXCL12 may be due to adherence of CXCL12 secreted by neighboring cells. 30 This is unlikely, however, given the robust staining pattern seen with CXCL12 antibody clone 79081, which is notably absent from BECs when stained with three additional commercially available antibodies (Supplemental Figure S3, AeJ), further suggesting a cross-reactive epitope specifically to clone 79081. We Cxcl12-expressing cells (green) can be seen directly adjacent to bile ducts in the PT (arrowheads pointing to bile duct) and around a CV, with more Cxcl12-expressing cells seen in the vicinity of the CV compared with the PT.…”