Identification of a novel nucleus protein involved in the regulation of urokinase in 95D cells.

The urokinase-type plasminogen activator (uPA) plays an important role in cellular invasion. By using the downstream part of a 74 bp DNA region called the cooperation mediator (COM) of the uPA promoter as a bait sequence in the yeast one-hybrid screen, a gene called PBK1 was previously cloned from the cDNA library of the 95D lung cancer cell strain. In this study, the intracellular distribution of PBK1 was studied by using the transient transfection of pEGFP-C3-PBK1, and PBK1 was found to be localized in the nucleus. Co-transfection of pEGFP-C3-PBK1 and the deletion mutants of the pGL3-uPA promoter indicated that PBK1 can increase the uPA promoter activity by about 25% and this effect is uPA enhancer-dependent. Western blotting and Enzyme-linked immunoadsordent assay further confirmed that PBK1 can upregulate the expression of uPA. Our results suggest that PBK1 is involved in the regulation of uPA expression, which might provide a new clue to further understanding the regulation mechanism of uPA expression.