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Depletion of eIF2·GTP·Met-tRNAi translation initiation complex up-regulates BRCA1 expression in vitro and in vivo.

Aktas BH, Bordelois P, Peker S, Merajver S, Halperin JA - Oncotarget (2015)

Bottom Line: Comparable tandem uORFs are characteristically seen in mRNAs whose translational efficiency paradoxically increases when the overall translation rate is decreased due to phosphorylation of eukaryotic translation initiation factor 2 α (eIF2α).Here we show fish oil derived eicosopanthenoic acid (EPA) that induces eIF2α phosphorylation translationally up-regulates the expression of BRCA1 in human breast cancer cells.We demonstrate further that a diet rich in EPA strongly induces expression of BRCA1 in human breast cancer xenografts.

View Article: PubMed Central - PubMed

Affiliation: Division of Hematology, Brigham and Women's Hospital, Boston, MA, USA.

ABSTRACT
Most sporadic breast and ovarian cancers express low levels of the breast cancer susceptibility gene, BRCA1. The BRCA1 gene produces two transcripts, mRNAa and mRNAb. mRNAb, present in breast cancer but not in normal mammary epithelial cells, contains three upstream open reading frames (uORFs) in its 5'UTR and is translationally repressed. Comparable tandem uORFs are characteristically seen in mRNAs whose translational efficiency paradoxically increases when the overall translation rate is decreased due to phosphorylation of eukaryotic translation initiation factor 2 α (eIF2α). Here we show fish oil derived eicosopanthenoic acid (EPA) that induces eIF2α phosphorylation translationally up-regulates the expression of BRCA1 in human breast cancer cells. We demonstrate further that a diet rich in EPA strongly induces expression of BRCA1 in human breast cancer xenografts.

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Related in: MedlinePlus

EPA-induced translational up-regulation of reporter genes fused to BRCA1 mRNAb 5′UTR is dependent on the presence of tandem uORFsThe plasmid encoding for F-luc fused to the 5′UTR of BRCA1 mRNAb with (BRCA1b 5′UTR Mut) and without (BRCA1b 5′UTR WT) mutations that replaced the three AUG codons for non-initiator AAG codons were transfected to MCF-7 cells. Cells were treated with EPA or DMSO and reporter activity was measured by dual luciferase assay. Bars indicate Mean ± SEM of F-Luc / R-Luc ratios in treated cells normalized to DMSO controls. *p < 0.01.
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Figure 6: EPA-induced translational up-regulation of reporter genes fused to BRCA1 mRNAb 5′UTR is dependent on the presence of tandem uORFsThe plasmid encoding for F-luc fused to the 5′UTR of BRCA1 mRNAb with (BRCA1b 5′UTR Mut) and without (BRCA1b 5′UTR WT) mutations that replaced the three AUG codons for non-initiator AAG codons were transfected to MCF-7 cells. Cells were treated with EPA or DMSO and reporter activity was measured by dual luciferase assay. Bars indicate Mean ± SEM of F-Luc / R-Luc ratios in treated cells normalized to DMSO controls. *p < 0.01.

Mentions: To confirm that these effects were due to the presence of uORF in the 5′UTR of BRCA1 mRNAb, we utilized a mutant of the BRCA1b 5′UTR where all three uAUGs in the uORFs (shown in Figure 1) were mutated to AAG (Mut-5′UTRb, kindly provided by Dr. Sobczak). Since AAG codon does not initiate translation, it removes the tandem uORFs in the 5′UTRb sequence. Figure 6 shows that fusion of the mutant BRCA1 mRNAb 5′UTR to F-luc abrogated EPA-induced up-regulation of this reporter (Figure 6). Taken together, these results provide strong support to our contention that structural features in the 5′UTR of BRCA1 mRNAb may contribute to its translational up-regulation by EPA through reduced availability of the ternary complex.


Depletion of eIF2·GTP·Met-tRNAi translation initiation complex up-regulates BRCA1 expression in vitro and in vivo.

Aktas BH, Bordelois P, Peker S, Merajver S, Halperin JA - Oncotarget (2015)

EPA-induced translational up-regulation of reporter genes fused to BRCA1 mRNAb 5′UTR is dependent on the presence of tandem uORFsThe plasmid encoding for F-luc fused to the 5′UTR of BRCA1 mRNAb with (BRCA1b 5′UTR Mut) and without (BRCA1b 5′UTR WT) mutations that replaced the three AUG codons for non-initiator AAG codons were transfected to MCF-7 cells. Cells were treated with EPA or DMSO and reporter activity was measured by dual luciferase assay. Bars indicate Mean ± SEM of F-Luc / R-Luc ratios in treated cells normalized to DMSO controls. *p < 0.01.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4466658&req=5

Figure 6: EPA-induced translational up-regulation of reporter genes fused to BRCA1 mRNAb 5′UTR is dependent on the presence of tandem uORFsThe plasmid encoding for F-luc fused to the 5′UTR of BRCA1 mRNAb with (BRCA1b 5′UTR Mut) and without (BRCA1b 5′UTR WT) mutations that replaced the three AUG codons for non-initiator AAG codons were transfected to MCF-7 cells. Cells were treated with EPA or DMSO and reporter activity was measured by dual luciferase assay. Bars indicate Mean ± SEM of F-Luc / R-Luc ratios in treated cells normalized to DMSO controls. *p < 0.01.
Mentions: To confirm that these effects were due to the presence of uORF in the 5′UTR of BRCA1 mRNAb, we utilized a mutant of the BRCA1b 5′UTR where all three uAUGs in the uORFs (shown in Figure 1) were mutated to AAG (Mut-5′UTRb, kindly provided by Dr. Sobczak). Since AAG codon does not initiate translation, it removes the tandem uORFs in the 5′UTRb sequence. Figure 6 shows that fusion of the mutant BRCA1 mRNAb 5′UTR to F-luc abrogated EPA-induced up-regulation of this reporter (Figure 6). Taken together, these results provide strong support to our contention that structural features in the 5′UTR of BRCA1 mRNAb may contribute to its translational up-regulation by EPA through reduced availability of the ternary complex.

Bottom Line: Comparable tandem uORFs are characteristically seen in mRNAs whose translational efficiency paradoxically increases when the overall translation rate is decreased due to phosphorylation of eukaryotic translation initiation factor 2 α (eIF2α).Here we show fish oil derived eicosopanthenoic acid (EPA) that induces eIF2α phosphorylation translationally up-regulates the expression of BRCA1 in human breast cancer cells.We demonstrate further that a diet rich in EPA strongly induces expression of BRCA1 in human breast cancer xenografts.

View Article: PubMed Central - PubMed

Affiliation: Division of Hematology, Brigham and Women's Hospital, Boston, MA, USA.

ABSTRACT
Most sporadic breast and ovarian cancers express low levels of the breast cancer susceptibility gene, BRCA1. The BRCA1 gene produces two transcripts, mRNAa and mRNAb. mRNAb, present in breast cancer but not in normal mammary epithelial cells, contains three upstream open reading frames (uORFs) in its 5'UTR and is translationally repressed. Comparable tandem uORFs are characteristically seen in mRNAs whose translational efficiency paradoxically increases when the overall translation rate is decreased due to phosphorylation of eukaryotic translation initiation factor 2 α (eIF2α). Here we show fish oil derived eicosopanthenoic acid (EPA) that induces eIF2α phosphorylation translationally up-regulates the expression of BRCA1 in human breast cancer cells. We demonstrate further that a diet rich in EPA strongly induces expression of BRCA1 in human breast cancer xenografts.

Show MeSH
Related in: MedlinePlus