An Assay for Transforming Growth Factor-β Using Cells Transfected with a Plasminogen Activator Inhibitor-1 Promoter-Luciferase Construct

Transforming growth factor-β (TGF-β) is a potent regulator of cellular differentiation, proliferation, migration, and protein expression. These properties have been exploited to create a variety of bioassays for detecting the mature growth factor. In this paper, we describe a highly sensitive and specific, nonradioactive quantitative bioassay for TGF-β based on its ability to induce plasminogen activator inhibitor-1 (PAI-1) expression. Mink lung epithelial cells (MLEC) were stably transfected with an expression construct containing a truncated PAI-1 promoter fused to the firefly luciferase reporter gene. Addition of TGF-β (0.2 to >30 pM) to the transfectants resulted in a dose-dependent increase in luciferase activity in the cell lysates. Although responsive to TGF-β, this promoter fragment was only minimally influenced by other known inducers of PAI-1 expression. When compared to the widely used MLEC assay, this assay demonstrated greater sensitivity and specificity, allowing quantification of TGF-β in complex biological solutions.