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

Abstract

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.

Candidate DNA methylation drivers of acquired cisplatin resistance in ovarian cancer identified by methylome and expression profiling

“…ARMCX2 might have a role in tumour suppression based on the presence of an armadillo repeat motif, which is found in other proteins fulfilling functions in cell proliferation, migration, maintenance of tissue integrity and tumourigenesis, and has been involved in development (Smith et al, 2005). MEST, a maternally imprinted gene, has been implicated in embryonic growth and maternal behaviour (Lefebvre et al, 1998), and loss of MEST imprinting has been reported in breast and lung cancers (Pedersen et al, 2002;Nakanishi et al, 2004). Interestingly, it has recently been shown that MEST is a negative regulator of the Wnt pathway and that MEST knockdown might activate Wnt signalling (Jung et al, 2011).…”

Variable imprinting of the MEST gene in human preimplantation embryos

“…41 Subsequent reports have indicated that in certain tissues including breast, placenta and colon, isoform 2 may in fact be imprinted and, moreover, that the imprinting status (whether monoallelic or biallelic) may differ between individuals. 13,16,37,47 Isoform 2 has been observed to be preferentially paternally expressed in foetal placenta in other studies, and also in kidney and fibroblast lines, with polymorphic imprinting observed between different fibroblast lines. 48 Variable imprinting of MEST, including that of isoform 2, has also been reported between humanembryonic stem cell (hESCs) lines, raising concerns of the epigenetic stability of these cells.…”

“…48 Variable imprinting of MEST, including that of isoform 2, has also been reported between humanembryonic stem cell (hESCs) lines, raising concerns of the epigenetic stability of these cells. 40,49,50 In view of the observations of aberrant MEST methylation and imprinting with disease, 13,14,16 we considered it important to further characterise expression at the MEST locus in the embryos with expression arising from both alleles. Our data demonstrates that isoform 2 was the predominant MEST isoform detected in preimplantation embryos and show directly that imprinting of isoform 2 itself is variable between embryos (Figure 4d).…”

“…Alternatively, MEST PCR products were sequenced. For isoform-specific PCR (not spanning the AflIII polymorphism), exon A (5 0 -CCTGTAGGCAAGGTCTTACCTG-3 0 ) and exon 1 (5 0 -GCGGCGGGCGGCATGGGATA-3 0 ) specific primers 16 were used in conjunction with EXON 2 R1 5 0 -GAAGACTTCCATGAGTGAAGGGC-3 0 in the first round and the forward primers were then hemi-nested with EXON 2 R2 5 0 -ATGTGCAGGTACGCAGCAAG-3 0 in the second round. For isoform 2-specific PCR spanning the AflIII polymorphism, Exon A and R1 were used in the first round, with primer F1 and primer R2 in second.…”

“…14 LOI has also been reported in invasive breast cancer, 15 but the biallelic expression observed here is likely to be the result of a promoter usage switch between MEST isoforms. 16 Assisted reproductive technology (ART) and infertility may be associated with epigenetic defects. 17 There is a suggestive evidence that methylation and expression of the MEST gene may be affected by various forms of ART in humans, mice and non-human primates.…”