The shedding of syndecan-4 and syndecan-1 from HeLa cells and human primary macrophages is accelerated by SDF-1/CXCL12 and mediated by the matrix metalloproteinase-9

We recently demonstrated that stromal cell-derived factor-1 (SDF-1/CXCL12) forms complexes with CXCR4, but also with syndecan-4 expressed by human primary lymphocytes and macrophages, and HeLa cells. We also suggested that syndecan-4 behaves as a SDF-1-signaling molecule. Here, we demonstrate that SDF-1 strongly accelerates the shedding of syndecan-4 ectodomains and to a lesser extent that of syndecan-1 from HeLa cells. The fact that this acceleration was not inhibited by the CXCR4 antagonist AMD3100, anti-CXCR4 mAb 12G5, and CXCR4 gene silencing suggests its CXCR4-independence. Pre-treating the cells with heparitinases I, III, or with the protein kinase C (PKC) inhibitor, bisindolylmaleimide, significantly inhibited this accelerated shedding, which suggests the involvement of both cell-surface heparan sulfate and PKC transduction pathway. In contrast, Map Kinase or NF-kB pathway inhibitors had no effect. Moreover, SDF-1 increases the matrix metalloproteinase-9 (MMP-9) mRNA level as well as MMP-9 activity in HeLa cells, and MMP-9 silencing by RNA interference strongly decreases the syndecan-1 and -4 ectodomain shedding accelerated by SDF-1. Finally, SDF-1 also accelerates in a CXCR4-independent manner, the shedding of syndecan-1 and -4 from human primary macrophages, which is significantly inhibited by anti-MMP-9 antibodies. This strongly indicates the role of MMP-9 in these events occurring in both a tumoral cell line and in human primary macrophages. Because MMP-9 plays a crucial role in extracellular matrix degradation during cancer cell metastasis and invasion, and shed ectodomains of syndecans may likely be involved in tumor cell proliferation, these data further indicate the multiplicity of the roles played by SDF-1 on tumor cell biology.