Transposons acting as ceRNAs (TAC) hypothesis: initial evidence from in-silico analyses of LINE1 overexpression contexts

LINE1 are transposable elements that can replicate within the genome by passing through RNA intermediates. The vast majority of LINE1 copies in the human genome are inactive and just between 100/150 copies are full length and still potentially capa-ble to mobilize. During the evolution, they could have been positively selected for cel-lular beneficial functions. Nonetheless, LINE1 deregulation can be detrimental to the cell causing diseases like cancer. The activity of miRNAs represents a fundamental mechanism for controlling transcript levels in somatic cells. These are a class of small non-coding RNAs that cause degradation or translational inhibition of their target tran-scripts. Beyond this, competitive endogenous RNAs (ceRNAs), mostly made by circu-lar and non-coding RNAs, have been observed to compete for the binding of the same set of miRNAs targeting protein coding genes. In my PhD project, I have explored the possibility that autonomously transcribed LINE1s may act as ceRNAs. I observed that genes sharing miRNA target sites with LINE1 have a tendency to be upregulated when LINE1 are overexpressed suggesting that LINE1 might act as ceRNAs. This finding will help in the interpretation of transcriptomic responses in contexts characterized by specific activation of transposons.