[Growth factor and growth inhibitor for hepatocyte proliferation]

Using primary culture of adult rat hepatocytes, we recently purified a hepatotropic factor, named hepatocyte growth factor (HGF), from platelets of about 3,000 rats. HGF had MW of about 100 kD, which was composed of two subunits with MW of 69 kD and 34 kD. Platelets also contained two growth inhibitors for adult hepatocytes. One of these inhibitors is identical to TGF-beta 1, whereas another, named PDGI-alpha, is a new growth inhibitor unlike TGF-beta 1. We also showed that both TGF-beta 1 and PDGI-alpha are stored in and secreted from rat or human platelets in a latent form that is associated with a carrier protein, named masking protein. Recently we succeeded in purification and characterization of the masking protein from rat or human platelets and demonstrated that it is composed of two subunits with MW of 110 kD and 39 kD, and it may be a regulator of TGF-beta and PDGI-alpha.