PARP14-dependent ADP-ribosylation of cytoplasmic SQSTM1/p62 foci supports innate immune signaling

Abstract

Interferon-induced ADP-ribosyltransferases are emerging regulators of cellular innate immunity, yet the relevant substrates and downstream effects remain incompletely defined. Here, we mapped the PARP14-dependent ADP-ribosylome in lung epithelial cancer cells and identified the selective autophagy adaptor SQSTM1/p62, along with multiple innate immune regulators, as IFN-dependent MARylation substrates. Site-resolved analysis revealed that PARP14-dependent MARylation is strongly enriched on cysteine residues, including defined cysteine acceptor sites within p62. PARP14-dependent MARylation is localized to cytoplasmic p62 foci that colocalize with diverse ubiquitin species. Furthermore, our results indicate that TRIM21 limits the autophagic degradation of p62, suggesting that the identified p62 foci may have degradation-independent roles. Consistent with this, both PARP14 and p62 support inflammatory gene expression, linking PARP14-dependent MARylation to innate immune regulation. Together, our findings identify p62 foci as sites of PARP14-dependent ADP-ribosylation and suggest a functional link between interferon signaling, ubiquitin-associated protein assemblies, and MARylation-dependent innate immune regulation.