The polypyrimidine tract binding protein, PTBP1, regulates selenium homeostasis via the Selenoprotein P 3′ untranslated region

2020 
Selenoproteins contain the 21st amino acid, selenocysteine (Sec), which is incorporated at select UGA codons when the encoding mRNA contains a specialized hairpin sequence in its 39 UTR. This hairpin, the so-called Sec insertion sequence (SECIS) element, is found in all selenoprotein mRNAs, but the sequence surrounding these elements is widely variable and in many cases of considerable length. In order to determine the function of one such SECIS context, we chose to focus on the plasma selenoprotein, SELENOP, that is required to maintain selenium homeostasis. It is unique in that its mRNA contains two SECIS elements that lie in the context of a highly conserved 843-nucleotide 39 UTR. Prior work has attempted to examine the functions of the SECIS context but none were identified. Here we have used CRISPR/Cas9 genome editing to delete the region between the two SECIS elements. We found that this sequence is required to mediate an increase in SELENOP synthesis under conditions of peroxide stress. Using RNA affinity chromatography, we have identified PTBP1 as the major RNA binding protein that specifically interacts with this region.
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