The mechanisms used by antisense transcripts to regulate their corresponding sense mRNAs are not fully understood. Herein, we have addressed this issue for the vimentin (VIM) gene, a member of the intermediate filament family involved in cell and tissue integrity that is deregulated in different types of cancer. VIM mRNA levels are positively correlated with the expression of a previously uncharacterized head-to-head antisense transcript, both transcripts being silenced in colon primary tumors concomitant with promoter hypermethylation. Furthermore, antisense transcription promotes formation of an R-loop structure that can be disfavored in vitro and in vivo by ribonuclease H1 overexpression, resulting in VIM down-regulation. Antisense knockdown and R-loop destabilization both result in chromatin compaction around the VIM promoter and a reduction in the binding of transcriptional activators of the NF-κB pathway. These results are the first examples to our knowledge of R-loop-mediated enhancement of gene expression involving head-to-head antisense transcription at a cancer-related locus.
Keywords: DNA methylation; R loop; antisense transcription; nucleosome occupancy; vimentin.