The role of PIWI-interacting RNAs and LINE-1 retrotransposons in cancer epigenetics

Small non-coding RNAs (ncRNAs) are key regulators of gene expression that function at both transcriptional and posttranscriptional levels by binding to complementary sequences. In mammalian germline cells, short ncRNAs known as PIWI-interacting RNAs (piRNAs) were found to be involved in the epigenetic control of LINE-1 retrotransposons and thus in maintaining genome stability against the uncontrolled activity of mobile elements. The piRNA pathway plays a central role in suppressing LINE-1 activity, which is considered to be a major risk factor for cancer, and aberrant expression of piRNAs has indeed been detected in tumor cells. Moreover, experiments involving the inactivation of the components of the PIWI-piRNA machinery also support a link between the dysregulation of this pathway and the tumorigenic state.