SYNTHESIS OF PLASMINOGEN-ACTIVATOR INHIBITOR-1 BY BOVINE MAMMARY EPITHELIAL AND MYOEPITHELIAL CELL-LINES

Conversion of plasminogen to plasmin provides an important source of p roteolytic activity in the bovine mammary gland. Plasminogen activator inhibitor 1 (PAI-1.) plays a key role in limiting plasminogen activat ion. The PAI-1 biosynthetic capabilities of various bovine mammary cel ls mere determined. The immortalized epithelial cell lines MAC-T and B ME-UV and the myoepithelial cell Line BMM-UV were used as model system s. Northern blot analysis indicated that both epithelial and myoepithe lial cells contained PAI-1. mRNA. Bovine PAI-1 was encoded by a single mRNA species similar to 3.0 kb long. BME-UV cells contained 2.0-fold (P < 0.01) the PAI-1. mRNA of MAC-T or BMM-UV cells. Reverse zymograph y indicated that both epithelial and myoepithelial cells synthesized P AI-1 protein with a molecular mass of similar to 50 kDa.