pADP-ribosylation Regulates the Cytoplasmic Localization, Cleavage and Pro-apoptotic Function of HuR

HuR (ElavL1) is one of the main posttranscriptional regulators that determines cell fate. While the role of HuR in apoptosis is well-established, the posttranslational modifications that governs this function remain elusive. In this study we show that PARP1/2-mediated poly(ADP)-ribosylation (PARylation) is instrumental in the pro-apoptotic function of HuR. During apoptosis or in cells depleted of PARP1/2 enzymes, a substantial reduction in HuR PARylation is observed. This results in the cytoplasmic accumulation and the cleavage of HuR, both of which are essential events for apoptosis. These effects are mediated by a pADP-ribose (PAR) binding motif within the HuR-HNS region (HuR PAR Binding Site (HuR-PBS)). Under normal conditions, the association of HuR-PBS with PAR is responsible for the nuclear retention of HuR. Mutations within this motif prevents the binding of HuR to its import factor TRN2, leading to its cytoplasmic accumulation and cleavage. Collectively, our findings underscore the role of PARylation in controlling the proapoptotic function of HuR, offering insight into the mechanism by which PARP1/2 enzymes regulate cell fate and adaptation to various assaults.