Correction: BAG3 promotes tumour cell proliferation by regulating EGFR signal transduction pathways in triple negative breast cancer.

[This corrects the article DOI: 10.18632/oncotarget.24590.].

BAG3 promotes tumour cell proliferation by regulating EGFR signal transduction pathways in triple negative breast cancer.

Triple-negative breast cancer (TNBC), is a heterogeneous disease characterised by absence of expression of the estrogen receptor (ER), progesterone receptor (PR) and lack of amplification of human epidermal growth factor receptor 2 (HER2). TNBC patients can exhibit poor prognosis and high recurrence stages despite early response to chemotherapy treatment. In this study, we identified a pro-survival signalling protein BCL2- associated athanogene 3 (BAG3) to be highly expressed in a subset of TNBC cell lines and tumour tissues. High mRNA expression of BAG3 in TNBC patient cohorts significantly associated with a lower recurrence free survival. The epidermal growth factor receptor (EGFR) is amplified in TNBC and EGFR signalling dynamics impinge on cancer cell survival and disease recurrence. We found a correlation between BAG3 and EGFR expression in TNBC cell lines and determined that BAG3 can regulate tumour cell proliferation, migration and invasion in EGFR expressing TNBC cells lines. We identified an interaction between BAG3 and components of the EGFR signalling networks using mass spectrometry. Furthermore, BAG3 contributed to regulation of proliferation in TNBC cell lines by reducing the activation of components of the PI3K/AKT and FAK/Src signalling subnetworks. Finally, we found that combined targeting of BAG3 and EGFR was more effective than inhibition of EGFR with Cetuximab alone in TNBC cell lines. This study demonstrates a role for BAG3 in regulation of distinct EGFR modules and highlights the potential of BAG3 as a therapeutic target in TNBC.

Alpha-T-catenin (CTNNA3) displays tumour specific monoallelic expression in urothelial carcinoma of the bladder.

CTNNA3 (alpha-T-catenin) is imprinted with preferential monoallelic expression of the maternal allele in placental tissue. The allelic expression pattern of CTNNA3 in adult human cancer is unknown and warrants investigation as CTNNA3 stabilizes cellular adherence, a feature which if compromised could enable cells to acquire an increased capability to detach and invade. We document the frequency of monoallelic versus biallelic expression of CTNNA3 in urothelial carcinoma of the bladder (UCB) samples and compare the observed patterns with that found in the paired normal sample. DNA PCR reactions encompassing a transcribable SNP polymorphism within exon 12 of CTNNA3 were sequence analyzed to identify heterozygous cases. A total of 96 samples were analyzed and included 22 paired normal and tumor UCB cases, 38 formalin fixed paraffin embedded (FFPE) UCB samples consisting of 18 noninvasive pTa tumors and 20 lamina propria invasive pT1 tumors and 14 cell lines of various lineages. RT-PCR analysis of 35 heterozygous samples followed by sequence analysis allowed monoallelic versus biallelic patterns to be assigned. We have provided the first demonstration that CTNNA3 displays differing allelic expression patterns in UCB. Specifically, 35% (7/20) of informative UCB, showed monoallelic expression, a feature confined to the tumor, with normal urothelial samples displaying biallelic expression. Real time RT-PCR analyses, demonstrated a significantly lower (P = 0.00039) level of CTNNA3 in the tumor samples compared with the paired normals, all of which displayed biallelic expression. In conclusion, monoallelic and biallelic CTNNA3 expression patterns are demonstrable in tumor bladder tissue, whereas normal cases show only biallelic expression.

Promoter switch: a novel mechanism causing biallelic PEG1/MEST expression in invasive breast cancer.

We have previously reported on the biallelic expression of the imprinted PEG1/MEST gene in infiltrating carcinomas of the breast. Putative loss of imprinting (LOI) of PEG1/MEST has subsequently also been implicated in the aetiology of lung adenocarcinomas and colon cancer. Taking advantage of our previous study, identifying seven infiltrating carcinomas of the breast, displaying biallelic PEG1/MEST expression, we have analysed the allelic usage of the two alternative PEG1/MEST transcripts encoding isoforms 1 and 2, separately. In addition, expression levels of the two transcripts have been measured by real-time RT-PCR, in order to elucidate the mechanism behind the switch from monoallelic transcription in normal breast tissue to biallelic expression in invasive cancer. The isoform 1 transcript is imprinted in both the paired normal tissue and the breast carcinomas. In contrast, the isoform 2 transcript is biallelically expressed, or in one case expressed from the opposite allele to isoform 1, raising the possibility that isoform 2 is polymorphically imprinted in normal breast tissue. In all the paired normal samples, isoform 1 is predominantly expressed, explaining the monoallelic profiles of these samples. However, in four of the seven biallelic carcinomas, isoform 2 is expressed at higher levels than isoform 1, indicating that a switch in expression from isoform 1 to isoform 2 is responsible for the biallelic profiles in these samples. Our results not only suggest a novel mechanism leading to biallelic expression detected when analysing the common 3'-UTR of the PEG1/MEST transcriptional unit, they are also indicative of the existence of further alternative PEG1/MEST transcripts.