Selenoprotein mRNAs are particular in several aspects. They contain a specific secondary structure in their 3 UTR, called Secis (selenocysteine inserting sequence), which is indispensable for selenocysteine incorporation, and they are degraded under selenium-limiting conditions according to their ranking in the hierarchy of selenoproteins. In the familiy of selenium-dependent glutathione peroxidases (GPx) the ranking is GI-GPx > or = PHGPx > cGPx = pGPx. This phenomenon was studied by mutually combining the coding regions of GI-GPx, PHGPx and cGPx with their 3 UTRs. HepG2 cells were stably transfected with the resulting constructs. Expression of glutathione peroxidases was estimated by activity measurement and Western blotting, the selenium-dependent mRNA stability by real-time PCR. Whereas 3 UTRs from stable PHGPx and GI-GPx could be exchanged without loss of stability, they were not able to stabilize cGPx mRNA. cGPx 3 UTR rendered GI-GPx and PHGPx mRNA unstable. Thus, cGPx mRNA contains selenium-responsive instability elements in both the translated and the untranslated region, which cannot be compensated by one of the stable homologs. Stabilizing efficiency of an individual GPx 3 UTR did not correlate with the efficiency of selenocysteine incorporation. PHGPx 3 UTR was equally effective as cGPx 3 UTR in enhancing GPx activity in all constructs, while GI-GPx 3 UTR showed a markedly lower efficacy. We conclude that different mRNA sequences and/or RNA-binding proteins might regulate mRNA stability and translation of selenoprotein mRNA.
|Pages (from-to)||11 - 18|
|Number of pages||8|
|Publication status||Published - 2003|