S. Shetty et S. Idell, Post-transcriptional regulation of urokinase mRNA - Identification of a novel urokinase mRNA-binding protein in human lung epithelial cells in vitro, J BIOL CHEM, 275(18), 2000, pp. 13771-13779
We sought to determine if urokinase expression is regulated at the post-tra
nscriptional level in cultured lung epithelial cells. We also sought to det
ermine if differences in urokinase expression by cultured human lung carcin
oma and non-malignant lung epithelial subtypes were attributable to post-tr
anscriptional regulatory mechanisms. Urokinase was expressed by phenotypica
lly diverse lung carcinoma cell lines as well as nonmalignant small airway
epithelial cells and bronchial epithelial cells. Using gel mobility shift a
nd UV crosslinking assays, we identified a 30-kDa urokinase mRNA-binding pr
otein that selectively bound to a 66-nucleotide protein-binding fragment of
urokinase mRNA. The urokinase mRNA-binding protein is found in the cytosol
ic but not nuclear extracts of non-malignant lung epithelial cells; whereas
, it is found in the nuclear but not cytosolic extracts of selected maligna
nt carcinoma-derived cells that express relatively large amounts of urokina
se. Chimeric beta-globin/urokinase cDNA containing the urokinase mRNA-bindi
ng 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 l
evel. The mechanism involves an interaction between a bs-nucleotide sequenc
e of the urokinase mRNA 3'-untranslated region with a newly recognized urok
inase mRNA-binding protein to regulate urokinase mRNA stability.