Poly(ADP-Ribosyl)ation Regulates the Cytoplasmic Localization, Cleavage, and Pro-Apoptotic Function of the RNA-Binding Protein HuR

Główne pojęcia

Poly(ADP-ribosyl)ation of the RNA-binding protein HuR by PARP1/2 regulates its subcellular localization and pro-apoptotic function.

Streszczenie

This study investigates the role of poly(ADP-ribosyl)ation (PARylation) in regulating the function of the RNA-binding protein HuR during apoptosis. The key findings are:

1. PARylation of HuR by PARP1/2 under normal conditions promotes its nuclear localization by facilitating its interaction with the nuclear import factor TRN2.

2. Depletion or inhibition of PARP1/2 leads to decreased PARylation of HuR, resulting in its cytoplasmic accumulation and cleavage by caspases, which enhances its pro-apoptotic function.

3. HuR contains a conserved PAR-binding motif (HuR-PBS) within its nucleocytoplasmic shuttling domain (HNS). Mutating this motif prevents PAR binding and causes HuR to accumulate in the cytoplasm, where it is cleaved and promotes apoptosis.

4. The non-covalent binding of PAR to the HuR-PBS regulates its association with the nuclear import factor TRN2, thereby controlling HuR's subcellular localization and pro-apoptotic function.

In summary, the study demonstrates that PARP1/2-mediated PARylation of HuR is a key regulatory mechanism that modulates its localization and pro-apoptotic activity, providing insights into how HuR function is controlled during cell death processes.

Statystyki

Treatment with staurosporine (STS) for 3 hours induces cleavage of both HuR and PARP1 in HeLa cells.
Depletion of PARP1 and/or PARP2 using siRNAs increases the cytoplasmic localization of HuR in untreated HeLa cells.
Knockdown of PARP1 and PARP2 together significantly increases the cleavage of HuR and caspase-3 in HeLa cells.
Expression of a HuR mutant (HuRPBmt) that cannot bind PAR leads to increased cytoplasmic localization, cleavage, and pro-apoptotic function of HuR compared to wild-type HuR.

Cytaty

"PARylation of HuR, via PARP1, regulates its localization and function during inflammation."
"Mutating the non-covalent PAR binding site on HuR prevents its association with the nuclear import factor TRN2, leading to its cytoplasmic accumulation and cleavage."
"The non-covalent binding of PAR to the HuR-PBS regulates its association with the nuclear import factor TRN2, thereby controlling HuR's subcellular localization and pro-apoptotic function."

Kluczowe wnioski z

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

by Ashour,K., H... o www.biorxiv.org 08-09-2023

https://www.biorxiv.org/content/10.1101/2023.08.07.552262v1

Głębsze pytania

How might the interplay between covalent and non-covalent PARylation of HuR regulate its function in other cellular processes beyond apoptosis?

The interplay between covalent and non-covalent PARylation of HuR could play a crucial role in regulating its function in various cellular processes beyond apoptosis. Covalent PARylation of HuR, typically mediated by PARP1, has been shown to impact its localization, stability, and interaction with mRNA targets. This modification can influence HuR's ability to bind to specific mRNA sequences, thereby affecting their stability, translation, and subcellular localization. On the other hand, non-covalent PAR binding to HuR through the identified PAR-binding motif (HuR-PBS) can regulate its nucleocytoplasmic shuttling and association with protein partners like TRN2 and PHAPI.
In processes such as inflammation, muscle cell differentiation, and stress responses, where HuR plays a critical role in post-transcriptional regulation, the interplay between covalent and non-covalent PARylation could modulate HuR's function. For instance, in muscle cell differentiation, PARylation of HuR by Tankyrase1 (TNKS1) has been shown to promote its cytoplasmic accumulation and cleavage, impacting its role in mRNA stabilization and translation. The balance between covalent and non-covalent PARylation may determine the subcellular localization of HuR and its interaction with mRNA targets, thereby influencing various cellular processes.

How might the interplay between covalent and non-covalent PARylation of HuR regulate its function in other cellular processes beyond apoptosis?

In addition to PARylation, other post-translational modifications of HuR could also modulate its localization and pro-apoptotic activity. Phosphorylation, for example, has been shown to regulate HuR's function by affecting its interaction with mRNA targets and protein partners. Phosphorylation of specific residues within HuR, such as S88, S100, and T118, can impact its binding to mRNA sequences and alter its subcellular localization. This modification can influence the stability and translation of HuR-targeted mRNAs, thereby affecting cellular processes like cell proliferation, differentiation, and apoptosis.
Furthermore, methylation and acetylation are other post-translational modifications that could potentially regulate HuR's activity. Methylation of HuR has been suggested to influence its RNA-binding ability and stability, while acetylation may impact its interaction with protein partners involved in mRNA regulation. These modifications could fine-tune HuR's function in different cellular contexts, including apoptosis, by modulating its localization, stability, and interaction with key signaling molecules.

Could targeting the PAR-binding motif of HuR be a potential therapeutic strategy to selectively induce apoptosis in cancer cells with dysregulated HuR function?

Targeting the PAR-binding motif of HuR could indeed be a promising therapeutic strategy to selectively induce apoptosis in cancer cells with dysregulated HuR function. By disrupting the non-covalent binding of HuR to PAR through the identified PAR-binding motif (HuR-PBS), it may be possible to alter HuR's subcellular localization and its interaction with key protein partners involved in apoptosis regulation. This disruption could lead to the cytoplasmic accumulation of HuR, its cleavage, and subsequent activation of pro-apoptotic pathways.
In cancer cells where HuR is overexpressed or aberrantly regulated, targeting the PAR-binding motif could specifically impact HuR's pro-survival functions and shift its role towards promoting apoptosis. By preventing the nuclear retention of HuR and promoting its cytoplasmic accumulation, the disruption of the PAR-binding motif could enhance the apoptotic potential of cancer cells. This targeted approach may offer a novel therapeutic strategy to induce apoptosis selectively in cancer cells while minimizing the impact on normal cells, making it a promising avenue for further exploration in cancer treatment.