Post-transcriptional regulation of urokinase mRNA. Identification of a novel urokinase mRNA-binding protein in human lung epithelial cells in vitro.
We sought to determine if urokinase expression is regulated at the post-transcriptional level in cultured lung epithelial cells. We also sought to determine if differences in urokinase expression by cultured human lung carcinoma and non-malignant lung epithelial subtypes were attributable to post-transcriptional regulatory mechanisms. Urokinase was expressed by phenotypically diverse lung carcinoma cell lines as well as non-malignant small airway epithelial cells and bronchial epithelial cells. Using gel mobility shift and UV cross-linking assays, we identified a 30-kDa urokinase mRNA-binding protein that selectively bound to a 66-nucleotide protein-binding fragment of urokinase mRNA. The urokinase mRNA-binding protein is found in the cytosolic but not nuclear extracts of non-malignant lung epithelial cells; whereas, it is found in the nuclear but not cytosolic extracts of selected malignant carcinoma-derived cells that express relatively large amounts of urokinase. Chimeric beta-globin/urokinase cDNA containing the urokinase mRNA-binding protein binding sequence destabilized otherwise stable beta-globin mRNA. Our results demonstrate that urokinase gene expression in lung epithelial and lung carcinoma-derived cells is regulated at the post-transcriptional level. The mechanism involves an interaction between a 66-nucleotide sequence of the urokinase mRNA 3'-untranslated region with a newly recognized urokinase mRNA-binding protein to regulate urokinase mRNA stability.
Shetty
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S
Department of Specialty Care Services, The University of Texas Health Center, Tyler, Texas 75708, USA.
Idell
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S
D001483:Base Sequence; D001667:Binding, Competitive; D002478:Cells, Cultured; D006801:Humans; D008168:Lung / Q000201:enzymology; D008969:Molecular Sequence Data; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000235:genetics*; D016601:RNA-Binding Proteins / Q000235:genetics*; D014568:Urokinase-Type Plasminogen Activator / Q000235:genetics*
D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D014568:Urokinase-Type Plasminogen Activator