ADP-ribosylation of RNA in mammalian cells is mediated by TRPT1 and multiple PARPs

RNA function relies heavily on posttranscriptional modifications. Recently, it was shown that certain PARPs and TRPT1 can ADP-ribosylate RNA in vitro. Traditionally, intracellular ADP-ribosylation has been considered mainly as a protein posttranslational modification. To date, it is not clear whether RNA ADP-ribosylation occurs in cells. Here we present evidence that different RNA species are ADP-ribosylated in human cells. The modification of cellular RNA is mediated by several transferases such as TRPT1, PARP10, PARP11, PARP12 and PARP15 and is counteracted by different hydrolases including TARG1, PARG and ARH3. In addition, diverse cellular stressors can modulate the content of ADP-ribosylated RNA in cells. We next investigated potential consequences of ADP-ribosylation for RNA and found that ADPr-capped mRNA is protected against XRN1 mediated degradation but is not translated. T4 RNA ligase 1 can ligate ADPr-RNA in absence of ATP, resulting in the incorporation of an abasic site. We thus provide the first evidence of RNA ADP-ribosylation in mammalian cells and postulate potential functions of this novel RNA modification.