Natural antisense transcripts drive a regulatory cascade controlling c-MYC transcription

<i>Cis</i>-natural antisense transcripts (<i>cis-</i>NATs) are long noncoding RNAs transcribed from the opposite strand and overlapping coding and noncoding genes on the sense strand. <i>cis-</i>NATs are widely present in the human genome and can be involved in multiple mechanisms of gene regulation. Here, we describe the presence of <i>cis-</i>NATs in the 3′ distal region of the c-MYC locus and investigate their impact on transcriptional regulation of this key oncogene in human cancers. We found that <i>cis-</i>NATs are produced as consequence of the activation of cryptic transcription initiation sites in the 3′ distal region downstream of the c-MYC 3′UTR. The process is tightly regulated and leads to the formation of two main transcripts, NAT6531 and NAT6558, which differ in their ability to fold into stem-loop secondary structures. NAT6531 acts as a substrate for DICER and as a source of small RNAs capable of modulating c-MYC transcription. This complex system, based on the interplay between <i>cis</i>-NATs and NAT-derived small RNAs, may represent an important layer of epigenetic regulation of the expression of c-MYC and other genes in human cells.