Inhibitory Role of Plasminogen Activator Inhibitor‐1 in Invasion and Proliferation of HLE Hepatocellular Carcinoma Cells

Plasminogen activator inhibitor (PAI)‐1, a serine protease inhibitor, inactivates urokinase‐type plasminogen activator (uPA) and regulates degradation of the extracellular matrix; whether it functions for or against tumor progression, however, has been the subject of controversy. To assess the role of PAI‐1 in invasion and proliferation of hepatocellular carcinoma (HCC) cells, HLE cells were transfected with a vector capable of expressing an antisense PAI‐1 transcript. Analysis of seven stably transfected clones (PAI‐1(−)) showed reductions of 81% in PAI‐1 mRNA by northern blot analysis and 63% in the cellular PAI‐1 antigen level by enzyme‐linked immunosorbent assay(ELISA). There was no change in the levels of secreted PAI‐1 or PAI‐2. The activity of cellular uPA increased by 54%, without change in the protein level or the secreted uPA activity evaluated by ELISA. Morphologically, PAI‐1 antisense induced a spindle shape with narrower cytoplasmic processes in HLE cells. The forced inhibition of PAI‐1 increased the invasion and the growth of PAI‐1(−) cells by 75% and 82%, respectively. These results suggest that PAI‐1 plays a role in inhibiting invasion and proliferation, and the balance between uPA and PAI‐1 expression is important to assess the invasiveness of HCC cells.