Caspase dependent cleavage of the mono-ADP-ribosyltransferase ARTD10 interferes with its pro-apoptotic function

Intracellular communication at the molecular level is mainly dependent on posttranslational modifications and interplay between those. ADP-ribosylation, the transfer of ADP-ribose from NAD+ to substrates and especially its polymerization, is involved in processes like signal transduction, gene transcription and DNA damage repair. The latter is mainly mediated by ARTD1/PARP1, the founding member of the group of ADP-ribosyltransferases (ARTs). Its functions through poly-ADP-ribosylation have been studied well. Mono-ADP-ribosyltransferase activity however was previously only reported for bacterial toxins and extracellular ARTs. Yet although evidence for intracellular ADP-ribosylation is still missing, ARTD10 was recently shown to possess mono-ADP-ribosylation activity in vitro. First attempts to obtain insight into its physiological relevance revealed that the enzyme is implicated in transformation and proliferation. In this work we expanded on these findings and generated stable HeLa cell lines, which inducibly express ARTD10 or different constructs thereof. The expression of the wild-type protein confirmed prior observations, as it inhibited proliferation. By follow-up experiments this effect could be linked to the induction of apoptosis in those cells. This was dependent on catalytic activity, as ARTD10-G888W, a catalytic inactive mutant, was not cytotoxic. In addition, we could observe cleavage of ARTD10 during apoptosis, an observation also made for ARTD1. Processing at 'I A M D406 S' resulted in a catalytically active fragment, which was no longer able to stimulate apoptosis. Moreover, the inflammatory caspase-1 also processed ARTD10 in vitro at 'W T P D581 S' potentially linking ARTD10 cleavage to a second cellular pathway involving caspases. In both cases the RNA recognition motif as well as a glycine-rich region were separated from the catalytic center. The loss of pro-apoptotic activity alongside the separation of these domains hints towards an important function of ARTD10 in an RRM-linked process, like ...