Cathepsin l expression is up-regulated by hypoxia in human melanoma cells: role of its 5‘-untranslated region
Résumé
Overexpression of cathepsin L, a cysteine protease and consequently procathepsin L secretion switch the phenotype of human melanoma cells to highly tumorigenic and strongly metastatic. This led us to identify the DNA regulatory sequences involved in the regulation of cathepsin L expression in highly metastatic human melanoma cells. Data demonstrated presence of inhibitory sequences in the 3' region downstream of cathepsin L gene and in the 3'- and 5'-flanking region of GC/CCAAT sites of its promoter. In addition, we established that the 5'-untranslated region (5'-UTR) was the most important region for cathepsin L expression. This 5'-UTR integrated an alternative promoter and sequences involved in post-transcriptionnal regulation. Transfection experiments of bicistronic reporter vectors and RNAs demonstrated that cathepsin L 5'-UTR contained a functional internal ribosome entry site (IRES). This complete IRES was present only in one of the three splice variants, which differed in their 5'-UTR. Then, we analyzed cathepsin L expression in this human melanoma cell line grown under hypoxia. We demonstrated that under moderate hypoxic conditions (1% O2) intracellular expression of cathepsin L was up-regulated. Hypoxia increased significantly only the expression of the transcript which contains the complete IRES but inhibited promoter activity. These data suggested that presence of an IRES allowed cathepsin L mRNA translation to be efficient under hypoxic conditions. Altogether, our results emphasized that in vivo tumor hypoxic environment up-regulates cathepsin L expression which promotes tumor progression.
Domaines
Sciences du Vivant [q-bio]
Origine : Fichiers produits par l'(les) auteur(s)
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