Production of functional hepatocyte growth factor (HGF) in insect cells infected with an HGF-recombinant baculovirus in a serum-free medium

Three insect cell lines, SL-7B cells derived from Spodoptera litura, Sig, a nd High Five (Hi-5) cells, were used for the production of pro-hepatocyte g rowth factor (pro-HGF). Cells were cultured and then infected with a recomb inant HGF-containing baculovirus in a serum-free medium. In SL-7B cells, pr o-HGF is synthesized and excreted from the cells and late in infection is c onverted to a heterodimeric form of HGF even when the cells are grown in se rum free medium. Conversion of a single-chain form of HGF (pro-HGF) into an I-IGF heterodimer was unexpected as pro-HGF is normally cleaved by a serum protease called HGF activator. The proliferation activity of heparin-affin ity-purified HGF from serum-free culture supernatant of SL-7B cells is comp arable to that obtained from HGF converted by serum proteases, suggesting t hat SL-7B cells produce a functionally analogous protease to correctly proc ess pro-HGF. This work reports, for the first time, an the feasibility of p roperly processing pro-HGF to form functional HGF by proteases from inverte brate cells in serum-free media. Avoiding the supplementation of sera provi des the advantages of a low production cost, zero contamination of infectio us agents from sera, and simple downstream product purification. Experiment al results further demonstrate that the conversion of pro-HGF by insect cel ls is cell-line-dependent, because proteases in Hi-5 or Sf9 cells could not process pro-HGF as efficiently and properly as those in SL-7B cells.