Abstract 1472: Alternate translation initiation regulation of PRDX5 mRNA by miR6855<->3p in basal<->like breast cancer cells

Abstract

Abstract Human peroxiredoxins (PRDXs) are a superfamily of six thiol<->dependent peroxidases that are able to reduce hydrogen peroxide, alkyl hydroperoxides and peroxynitrite. Apart from the classical, apparently redundant function of mitochondrial and often peroxisomal peroxide neutralization shared by other peroxiredoxins, PRDX5 was initially discovered as a DNA binding transcriptional repressor regulating the biosynthesis of cytotoxic Alu RNAs through a mitochondrial<->localization signal<->truncated mature form (SPRDX5] of this protein that is accumulated in the nucleus and binds to a 60 bp nucleotide sequence at the Alu gene promoters. Our data suggest that SPRDX5 also binds to the Alu<->sequence<->containing BRCA2 gene silencer to prevent the binding of SLUG at the silencer thus enhancing the BRCA2 gene expression leading to the genotoxin and radiation<->resistance of aggressive SLUG<->high basal<->like breast cancer cells. PRDX5 mRNA contains two in<->frame start codons (AUGs) that are conditionally used as alternate translation initiation sites. Translation from the first AUG would result in the synthesis of a larger 214<->residue protein (LPRDX5) whereas the use of the second AUG would result in the production of a shorter 162<->residue polypeptide (SPRDX5). Since SPRDX5 lacks the mitochondrial localization signal, it is accumulated in the nucleus via its C<->terminal bipartite nuclear localization signal. We present evidence here that a miRNA, miR<->6855<->3p, binds the primary PRDX5 transcript between the two AUG codons and prevents the translation of the mRNA from the first AUG codon but not that from the second AUG codon thus favoring the initiation of translation from the second AUG codon. To characterize the effect of miR<->6855<->3p on Prdx5 mRNA translation, we developed three different PRDX5<->FLAG constructs in pCV3XFLAG14 (Sigma) that has Prdx5 ORF with or without mutation on the first or second AUG codon. Transfection of these constructs into BT549 cells followed by treatments with miR<->6855<->3p mimic or antagomiR and subcellular fractionation further supported our notion. We propose here that miR<->6855<->3p acts as a tsmiR by promoting the biosynthesis of the transcriptional regulator protein SPRDX5 which enhances the expression of the tumor suppressor protein BRCA2 leading to the genotoxin and radiation<->resistance of aggressive SLUG<->high basal<->like breast cancer cells. Supported in part by DOD-CDMRP IDEA Expansion Grant# BC103645 and NIH/NCI grant 1R21CA181920 01 to GC and 1U54RR026140 to SM. Citation Format: Gautam Chaudhuri, Smita Misra. Alternate translation initiation regulation of PRDX5 mRNA by miR6855<->3p in basal<->like breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1472. doi:10.1158/1538-7445.AM2017-1472