Hepatocyte growth factor-like protein is identical to macrophage stimulating protein

Although the hepatocyte growth factor-like protein (HLP) shares a 50% homology with the hepatocyte growth factor, the biological function of HLP has remained unknown. Addition of conditioned medium of COS-7 cells transfected with the expression plasmid for HLP cDNA to cultures of resident peritoneal macrophages induced specific activation of macrophages, and the factor which stimulates macrophages was purified from the conditioned medium. The purified protein showed M(r) of 85 kDa on SDS-PAGE, and this M(r) is in agreement with that of macrophage-stimulating protein (MSP) previously purified from human serum, as well as with the predicted M(r) of HLP. Amino acid composition of the purified protein coincided with the compositions of human HLP and MSP. Together with the finding that the partial amino acid sequences of MSP are highly homologous to that of HLP, we conclude that the biological function of HLP is to activate macrophages and that HLP and MSP are identical molecules.