Fig. 7. Schematic model showing the potential role of bacitracin in inhibiting glioma cell invasion. Oxidized protein disulfide isomerase (PDI) and reduced PDI interconvert under the bacitracin-free condition. During the transformation process, PDI alters the conformation of integrin to a high affinity state and integrin binds tightly with the extracellular matrix (ECM) (integrin activation). Then, focal adhesion kinase (FAK), one of the downstream molecules of integrin, is phosphorylated, which increases matrix metalloproteinase-2 (MMP-2) production. Finally, the cell secretes MMP-2, resulting in increased cell invasion. The PDI cycle was disturbed after the cells were treated with bacitracin. Bacitracin binding with reduced PDI led to lack of oxidation of reduced PDI. Only reduced PDI was present on the cell membrane after extending the bacitracin treatment time. Then, integrin was not activated, resulting in decreased FAK phosphorylation and MMP-2 production. Finally, MMP-2 secretion decreased, which disturbed cell invasion.