PARylation regulates stress granule dynamics, phase separation, and neurotoxicity of disease-related RNA-binding proteins

Abstract

Mutations in RNA-binding proteins (RBPs) localized in ribonucleoprotein (RNP) granules, such as hnRNP A1 and TDP-43, promote aberrant protein aggregation, which is a pathological hallmark of various neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Protein posttranslational modifications (PTMs) are known to regulate RNP granules. In this study, we investigate the function of poly(ADP-ribosyl)ation (PARylation), an important PTM involved in DNA damage repair and cell death, in RNP granule-related neurodegeneration. We reveal that PARylation levels are a major regulator of the assembly-disassembly dynamics of RNP granules containing disease-related RBPs, hnRNP A1 and TDP-43. We find that hnRNP A1 can both be PARylated and bind to PARylated proteins or poly(ADP-ribose) (PAR). We further uncover that PARylation of hnRNP A1 at K298 controls its nucleocytoplasmic transport, whereas PAR-binding via the PAR-binding motif (PBM) of hnRNP A1 regulates its association with stress granules. Moreover, we reveal that PAR not only dramatically enhances the liquid-liquid phase separation of hnRNP A1, but also promotes the co-phase separation of hnRNP A1 and TDP-43 in vitro and their interaction in vivo. Finally, both genetic and pharmacological inhibition of PARP mitigates hnRNP A1-and TDP-43-mediated neurotoxicity in cell and Drosophila models of ALS. Together, our findings suggest a novel and crucial role for PARylation in regulating the dynamics of RNP granules, and that dysregulation in PARylation and PAR levels may contribute to ALS disease pathogenesis by promoting protein aggregation.

Changing faces of stress: Impact of heat and arsenite treatment on the composition of stress granules

“…Arsenite stress leads to the specific modification of TDP-43 by lysine acetylation, a PTM that impairs mRNA binding and promotes TDP-43 aggregation (Cohen, Hwang, Restrepo, et al, 2015;Cohen, Hwang, Unger, Trojanowski, & Lee, 2012). The covalent modification of proteins by poly(ADP-ribose) (PAR) and the noncovalent binding of proteins to PAR have been shown to assist SG formation (Duan et al, 2019;Leung et al, 2011;McGurk et al, 2018). McGurk et al suggested that TDP-43 is recruited to SGs via binding to PAR and can therefore be protected from phosphorylation under short-term arsenite stress.…”

Paip2 cooperates with Cbp80 at an active promoter and participates in RNA Polymerase II phosphorylation in Drosophila

“…Our tests indicate that Paip2 is probably modified by this enzyme, which may result in the formation of the upper Paip2 band. Interestingly, PARylation in living cells was found to play an important role in transcription and translation . Since Paip2 is involved in both processes, this modification may be important for its functioning both in the nucleus and the cytoplasm.…”

The Potential Contribution of Dysfunctional RNA-Binding Proteins to the Pathogenesis of Neurodegeneration in Multiple Sclerosis and Relevant Models

“…Extensive activation of PARP is related to cell death while inhibition has been found to attenuate inflammation and improve neuronal survival [116]. PARP can also induce Poly ADP-ribosylation (PARylation), a major regulator of SG assembly and disassembly [117]. For example, PARylation of hnRNP A1 contributes to its nucleocytoplasmic mislocalization and association within SGs, while inhibition of PARP was found to mitigate hnRNP A1 mediated neurotoxicity [117].…”