# Mechanisms of PIDDosome Signaling, a p53-Independent Apoptotic Response to DNA Damage

> **NIH NIH R01** · ICAHN SCHOOL OF MEDICINE AT MOUNT SINAI · 2021 · $346,946

## Abstract

Project Summary
 Mutations in p53 and attendant apoptotic pathways impair tumor cell responses to radiation and
chemotherapy in many human malignancies. Combining genetics, functional genomics and proteomics
in mammalian cells and zebrafish embryos these past 6 years, we identified a novel apoptotic pathway
that bypasses p53-dependent pathways altogether via activation of the PIDDosome (PIDD-RAIDD-
caspase-2) complex (Sidi et al., Cell 2008; Ando et al., Mol Cell 2012; Thompson et al., Mol Cell 2015;
Ando et al., J Cell Biol 2017). Unlike the mitochondrial apoptosome (cytc-Apaf1-caspase-9) and death
receptor complex (FAS-FADD-caspase-8), the PIDDosome does not require p53 for activation or
function. PIDDosome assembly can be activated by inhibiting its negative regulator, Chk1 kinase. As
such, Chk1 inhibitors restore radiosensitivity in p53 mutant zebrafish embryos, MEF, and human cancer
cell lines. The PIDDosome is also responsive to DNA damaging chemotherapies such as
topoisomerase inhibitors. Altogether, the PIDDosome pathway defines both a novel apoptotic axis and
a promising targeted strategy for overcoming treatment resistance in cancer.
 However, our molecular understanding of the PIDDosome remains very limited. To expand our
knowledge of the pathway and identify novel diagnostic tools and drug targets therein, this proposal will
focus on the mechanisms by which DNA damage triggers PIDDosome assembly in vertebrate cells.
Thus far, we have shown that DNA damage triggers PIDDosome formation via (i) ATM/ATR-mediated
phosphorylation of PIDD, which enables RAIDD recruitment to the platform (Mol Cell 2012); and (ii) the
binding of PIDD to nucleophosmin (NPM1), which provides a scaffold for PIDDosome assembly (JCB
2017). In Aim 1, we will elucidate the mechanism by which a newly identified PIDD interactor, the DNA
repair protein FANCI, recruits PIDD to DNA crosslinks and enables its phosphorylation by ATM at these
lesions. Notably, these experiments may identify FANCI as the first biochemically described
“repair/death” switch in vertebrates. In Aim 2, we will elucidate the mechanism by which NPM1 and two
newly identified nucleolar PIDD-binding proteins, NOLC1 and NCL, coordinately orchestrate
PIDDosome formation in response to IR. These experiments may ultimately outline the major apoptotic
branch in the nucleolar DNA damage response. Finally, using xenograft models of intrinsic tumor
radioresistance (Liu et al., Nat Cell Biol, accepted in principle), we will assess for the first time the
potential of PIDDosome targeting as a strategy to overcome radioresistance in TP53 mutant cancers.
 Altogether, these studies integrate the PIDDosome in the cellular responses to DNA repair
failure, replication stress and nucleolar stress. Our proposal is thus ideally positioned to reveal the role
of the PIDDosome in cancer etiology, one of the most hotly debated questions in the field of apoptosis.

## Key facts

- **NIH application ID:** 10153709
- **Project number:** 5R01CA178162-08
- **Recipient organization:** ICAHN SCHOOL OF MEDICINE AT MOUNT SINAI
- **Principal Investigator:** Samuel Sidi
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $346,946
- **Award type:** 5
- **Project period:** 2013-07-05 → 2024-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10153709

## Citation

> US National Institutes of Health, RePORTER application 10153709, Mechanisms of PIDDosome Signaling, a p53-Independent Apoptotic Response to DNA Damage (5R01CA178162-08). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10153709. Licensed CC0.

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