PARTIAL CHARACTERIZATION OF A PLASMINOGEN-ACTIVATOR INHIBITOR-1 STIMULATING FACTOR PRODUCED BY HUMAN HEPATOMA-CELLS

We have previously shown that constitutive plasminogen activator inhib itor 1 (PAI-1) biosynthesis in human Hep G2 hepatoma cells is maintain ed by an autocrine factor. In the present paper we demonstrate that th is factor is capable of stimulating PAI-1 mRNA expression in human HT- 1080 fibrosarcoma cells, implying that it has also a paracrine role. T he partial characterisation of this factor shows that it is acid and h eat stable, resistant to proteolytic degradation by trypsin and protei nase K and has a very low molecular weight, probably lower than 500. T hese characteristics suggest that the PAI-1 stimulating factor in Hep G2 cell-conditioned medium is distinct from the many factors known to induce PAI-1 biosynthesis in endothelial cells, hepatocytes or other c ell types.