An investigation of the potential for epigenetic inactivation by transcription read-through in a sporadic colorectal cancer.

Aberrant transcription read-through of a gene promoter as a result of genetic structural rearrangements can cause the epigenetic inactivation of a neighbouring gene. All reported cases have involved copy number alterations that remove the 3' poly(A) transcription terminator sequence of a gene leading to transcription read-through (TRT) and methylation of the gene promoter of a downstream gene. We aimed to determine whether deletion of poly (A) transcription terminator sequences was associated with the methylation of neighbouring genes in a CRC with extensive copy number alterations. We performed a high resolution CGH array and methylation analysis on a CRC specimen to identify such alterations. Analysis of the CRC using high-resolution CGH identified 6 genes with deletions in the 3' part of the gene that encompassed the poly(A) transcription terminator sequence. Bisulphite sequencing of the promoter region of neighbouring (affected) genes at these six regions showed all candidate genes were unmethylated. Considering the fact that six TRT affected genes in a CRC with multiple deletions show no signs of hypermethylated promoters, it would be fairly appropriate to suggest that epigenetic inactivation by TRT might be a rare phenomenon in sporadic CRCs.

Pervasive transcription read-through promotes aberrant expression of oncogenes and RNA chimeras in renal carcinoma.

Aberrant expression of cancer genes and non-canonical RNA species is a hallmark of cancer. However, the mechanisms driving such atypical gene expression programs are incompletely understood. Here, our transcriptional profiling of a cohort of 50 primary clear cell renal cell carcinoma (ccRCC) samples from The Cancer Genome Atlas (TCGA) reveals that transcription read-through beyond the termination site is a source of transcriptome diversity in cancer cells. Amongst the genes most frequently mutated in ccRCC, we identified SETD2 inactivation as a potent enhancer of transcription read-through. We further show that invasion of neighbouring genes and generation of RNA chimeras are functional outcomes of transcription read-through. We identified the BCL2 oncogene as one of such invaded genes and detected a novel chimera, the CTSC-RAB38, in 20% of ccRCC samples. Collectively, our data highlight a novel link between transcription read-through and aberrant expression of oncogenes and chimeric transcripts that is prevalent in cancer.