Translational Regulation of CUG‐BP1 by Polyamines through the RNA‐binding Protein HuR

Abstract

All mammalian cells depend on polyamines for growth and division, but the exact roles of polyamines at the molecular level remain unclear. CUG‐BP1 protein interacts with CG‐rich element of many labile mRNAs and regulates decay and translation of its target transcripts. HuR modulates mRNA turnover and translation and its activity is tightly regulated by cellular polyamines. This study tests if polyamines regulate CUG‐BP1 expression through HuR in normal intestinal epithelial cells (IEC‐6 line).MethodsPolyamine levels were depleted by inhibiting ODC (key enzyme for polyamine biosynthesis) with DFMO but increased by overexpressing ODC gene. CUG‐BP1 expression was examined by newly translated protein and reporter assay using chimeric CUG‐BP1 3′‐UTR. RNA‐binding was examined by biotin pull‐down and RNP‐IP assays.ResultsDecreased polyamines by DFMO increased CUG‐BP1 protein, whereas elevated polyamines through ODC overexpression reduced CUG‐BP1 protein, neither intervention changed CUG‐BP1 mRNA levels. Polyamine depletion also increased CUG‐BP1 translation, but it failed to alter CUG‐BP1 protein stability. HuR bound the CUG‐BP1 mRNA and this association increased following polyamine depletion. HuR silencing repressed CUG‐BP1 translation in polyamine‐deficient cells, thus reducing CUG‐BP1 expression levels.ConclusionsThese results indicate that polyamines repress CUG‐BP1 translation by reducing HuR interaction with the CUG‐BP1 mRNA.