Multiple biological responses are induced by glycosylation-deficient hepatocyte growth factor

Abstract

HGF (hepatocyte growth factor), a heterodimeric glycoprotein composed of α- and β-chains, exerts biological activities through the c-Met receptor tyrosine kinase. The α-chain has three glycosylation sites, while the β-chain has two; however, the role of sugar chains on HGF is still unknown. To address the significance of glycosylation of HGF, three different types of glycosylation-deficient HGFs, i.e. non-glycosylated in the α-chain, the β-chain, and in both the α- and β-chains, were respectively expressed in COS-7 cells and then purified from culture supernatants. Unexpectedly, glycosylation-deficient HGFs induced tyrosine phosphorylation of the c-Met receptor and subsequent phosphorylation of ERK (extracellular-signal-regulated kinase) and Akt in rat hepatocytes with the same potency as glycosylated HGF. Consistent with this, glycosylation-deficient HGFs strongly stimulated DNA synthesis of hepatocytes equal to glycosylated HGF. Likewise, glycosylation-deficient HGFs induced cell scattering and branching tubulogenesis in MDCK (Madin–Darby canine kidney) cells, and thus were indistinguishable from glycosylated HGF in biological activities. Glycosylation also did not affect stability, protease sensitivity and tissue distribution, although the plasma clearance of HGF was slightly prolonged by glycosylation deficiency. Glycosylation deficiency resulted in a decrease in post-transcriptional biosynthesis of HGF in the cells, whereas extracellularly secreted HGFs were efficiently activated to a two-chain form. These results indicate that glycosylation influences post-transcriptional biosynthesis of HGF, whereas biological activities and basic physicochemical characteristics are retained, even in completely non-glycosylated HGF. Hence, non-glycosylated HGF is promising as an alternative for glycosylated HGF in clinical applications.