| |
[摘要]：Hepatocyte growth factor (HGF), a heterodimer composed of the alpha-chain and beta-chain, exerts multifunctional actions for tissue repair and homeostasis via its receptor, MET. HGF is cleaved by proteases secreted from inflammatory cells, and NK4 and beta-chain remnant (HGF-beta) are generated. Here, we provide evidence that HGF-beta binds to a new receptor other than MET for promoting a host cell clearance system. By an affinity cross-linking, radiolabeled HGF-beta was bound to liver non-parenchymal cells, particularly to Kupffer cells and sinusoidal endothelial cells, but not to parenchymal hepatocytes. The cross-linked complex was immunoprecipitated by anti-HGF antibody, but not anti-MET antibody, implying that HGF-beta binds to non-parenchymal cells at a site distinct from MET. Mass spectrometric detection of the ligand receptor complex revealed that the binding site of HGF-beta was the mannose receptor (MR). Actually, an ectopic expression of MR in COS-7 cells, which express no endogenous MR or MET, enabled HGF-beta to bind these cells at a K-D of 89 nM, demonstrating that MR is the new receptor for HGF-beta. Interaction of HGF-beta and MR was diminished by EGTA, and by an enzymatic digestion of HGF-beta sugar chains, suggesting that MR may recognize the glycosylation site(s) of HGF-beta in a Ca2+-dependent fashion. Notably, HGF-beta, but not other MR ligands, enhanced the ingestion of latex beads, or of apoptotic neutrophils, by Kupffer cells, possibly via an F-actin-dependent pathway. Thus, the HGF-beta center dot MRcomplex may provide a new pathway for the enhancement of cell clearance systems, which is associated with resolution of inflammation. |
|
