A HUWE1 Regulatory Helix Gates ASCL1 Degradation through Its C-Terminal Phospho-Degron in Small Cell Lung Cancer
Ontology highlight
ABSTRACT:
INSTRUMENT(S):
ORGANISM(S): Mus Musculus (mouse)
TISSUE(S): Cell Culture
SUBMITTER: 
Kevin Dong
LAB HEAD: Kevin Dong
PROVIDER: PXD071596 | Pride | 2026-08-03
REPOSITORIES: Pride
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Project description:ASCL1 is a lineage transcription factor dependency in small cell lung cancer (SCLC) and other high-grade neuroendocrine cancers, but remains undruggable. To uncover mechanisms that control ASCL1 abundance, we combined genome-wide CRISPR knockout and base-editor tiling screens with an endogenous ASCL1 reporter, quantitative proteomics, and structural modeling. We identify HUWE1 as the dominant E3 ligase for ASCL1 in SCLC and define a conserved C-terminal phospho-degron centered on Ser207 and terminal Trp/Phe residues that is necessary for HUWE1 binding and ASCL1 protein degradation. Disrupting this degron prevents HUWE1 binding and hyperstabilizes ASCL1, locks it on chromatin, and paradoxically impairs SCLC proliferation. These findings reveal a more generalizable phospho-degron recognition module in HUWE1 as a targetable regulatory switch for ASCL1 protein degradation.
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Project description:A subset of small cell lung cancer (SCLC) shows a clinical response to PARP inhibitors (PARPi) despite being proficient in homologous repair pathways. However, the underlying mechanism(s) of PARPi sensitivity is poorly understood. We performed quantitative proteomic analyses and identified proteomic changes that signify PARPi responses in a large panel of molecularly annotated patient-derived SCLC lines. We found that the toxicity of PARPi in SCLC is explained by the PARPi-induced degradation of key lineage-specific oncoproteins including ASCL1, NEUROD1, POU2F3, KDM4A, and KDM5B. Biochemical experiments showed that PARPi-induced activation of E3 ligases (e.g., HUWE1 and RNF8) mediated the ubiquitin-proteasome system (UPS)-dependent degradation of these oncoproteins. Interestingly, although PARPi resulted in a general DNA damage response, this signal is sensed by different SCLC cell lines to generate a cell-specific response. The dissection of the cell-specific oncoprotein degradation response led to the identification of potentially predictive biomarkers for PARPi in SCLC. The combination of PARPi and agents targeting these pathways led to dramatically improved cytotoxicity in SCLC. PARPi-induced degradation of lineage-specific oncoproteins therefore represents a novel mechanism to explain the efficacy of PARPi in tumors without homologous recombination deficiency.
2024-01-26 | PXD029968 | Pride
Project description:A subset of small cell lung cancer (SCLC) shows a clinical response to PARP inhibitors (PARPi) despite being proficient in homologous repair pathways. However, the underlying mechanism(s) of PARPi sensitivity is poorly understood. We performed quantitative proteomic analyses and identified proteomic changes that signify PARPi responses in a large panel of molecularly annotated patient-derived SCLC lines. We found that the toxicity of PARPi in SCLC is explained by the PARPi-induced degradation of key lineage-specific oncoproteins including ASCL1, NEUROD1, POU2F3, KDM4A, and KDM5B. Biochemical experiments showed that PARPi-induced activation of E3 ligases (e.g., HUWE1 and RNF8) mediated the ubiquitin-proteasome system (UPS)-dependent degradation of these oncoproteins. Interestingly, although PARPi resulted in a general DNA damage response, this signal is sensed by different SCLC cell lines to generate a cell-specific response. The dissection of the cell-specific oncoprotein degradation response led to the identification of potentially predictive biomarkers for PARPi in SCLC. The combination of PARPi and agents targeting these pathways led to dramatically improved cytotoxicity in SCLC. PARPi-induced degradation of lineage-specific oncoproteins therefore represents a novel mechanism to explain the efficacy of PARPi in tumors without homologous recombination deficiency.
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Project description:Neuroblastoma is a heterogeneous paediatric cancer arising from developmentally arrested neuronal precursors, where restoring differentiation offers therapeutic promise. ASCL1, a pro-neural transcription factor, is widely expressed in neuroblastoma and can drive either proliferation or differentiation depending on the cellular context. Here, we show that distinct MYCN-amplified neuroblastoma cell lines exhibit differing cell cycle and differentiation responses to ASCL1 overexpression. By comparing genome-wide ASCL1 chromatin binding, transcriptional changes, and protein-protein interactions, we found that ASCL1 binds more extensively to neuronal proteins in a cell line that is more susceptible to ASCL1-driven differentiation, but associates with cell cycle regulators in less responsive cells. We show that CDK2-Cyclin A2 bind ASCL1 in less responsive cells, with CDK-mediated phosphorylation of ASCL1 limiting the ability of ASCL1 to drive differentiation. Our study reveals that context-dependent interactions of ASCL1 with protein partners on the chromatin control its ability to re-engage a differentiation program in neuroblastoma.
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Project description:HUWE1 is a large, enigmatic HECT domain ubiquitin ligase implicated in the degradation of numerous substrates and regulating diverse pathways including DNA repair, apoptosis, and differentiation. However, the mechanism by which HUWE1 acts in a pleiotropic manner to regulate a myriad of substrates is unknown. Recent work has established a physical and genetic interaction between HUWE1 and C16orf72/HAPSTR1, suggesting that HAPSTR1 positively regulates HUWE1 function. Here, we show that HAPSTR1 is both a HUWE1 substrate, and is required to localize HUWE1 to the nucleus. Quantitative proteomics across diverse cell types reveals that HUWE1 substrates are largely context specific. Transcriptomics following HUWE1 or HAPSTR1 loss of function reveals a broad transcriptional stress response. We show that nuclear HUWE1 impacts stress signaling pathways, including p53 and NFkB-mediated signaling, and is required for cell proliferation. Together, these data define a critical role for nuclear HUWE1 function that is dependent on HAPSTR1.
2023-05-14 | PXD041591 | Pride
Project description:HUWE1 is a large, enigmatic HECT domain ubiquitin ligase implicated in the degradation of numerous substrates and regulating diverse pathways including DNA repair, apoptosis, and differentiation. However, the mechanism by which HUWE1 acts in a pleiotropic manner to regulate a myriad of substrates is unknown. Recent work has established a physical and genetic interaction between HUWE1 and C16orf72/HAPSTR1, suggesting that HAPSTR1 positively regulates HUWE1 function. Here, we show that HAPSTR1 is both a HUWE1 substrate, and is required to localize HUWE1 to the nucleus. Quantitative proteomics across diverse cell types reveals that HUWE1 substrates are largely context specific. Transcriptomics following HUWE1 or HAPSTR1 loss of function reveals a broad transcriptional stress response. We show that nuclear HUWE1 impacts stress signaling pathways, including p53 and NFkB-mediated signaling, and is required for cell proliferation. Together, these data define a critical role for nuclear HUWE1 function that is dependent on HAPSTR1.
2023-05-14 | PXD041590 | Pride
Project description:Deregulated expression of MYC is a driver of colorectal carcinogenesis, necessitating novel strategies to inhibit MYC function. The ubiquitin ligase HUWE1 (HECTH9, ARFBP1, MULE) associates with both MYC and the MYC-associated protein MIZ1. We show here that HUWE1 is required for growth of colorectal cancer cells in culture and in orthotopic xenograft models. Using high throughput screening, we identify small molecule inhibitors of HUWE1, which inhibit MYC-dependent transactivation in colorectal cancer cells, but not in stem and normal colon epithelial cells. Inhibition of HUWE1 stabilizes MIZ1. MIZ1 globally accumulates on MYC target genes and contributes to repression of MYC-activated target genes upon HUWE1 inhibition. Our data show that transcriptional activation by MYC in colon cancer cells requires the continuous degradation of MIZ1 and identify a novel principle that allows for inhibition of MYC function in tumor cells. MIZ1 and MYC ChIPseq experiments in HUWE1 inhibitor-treated Ls174T cells as well as RNAseq experiments in HUWE1- or MIZ1-depleted Ls174T cells after HUWE1 inhibitor treatment. Sequencing was performed on an Illumina Genome Analyzer IIx.
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Project description:FOXO transcription factors are central regulators of longevity from worms to humans. FOXO3 – the FOXO isoform associated with exceptional human longevity – preserves adult neural stem cell pools. Here we identify FOXO3 direct targets genome-wide in primary cultures of adult neural progenitor cells (NPCs). Interestingly, FOXO3-bound sites are enriched for motifs for bHLH transcription factors and FOXO3 shares common targets with the pro-neuronal bHLH transcription factor ASCL1/MASH1 in NPCs. Analysis of the chromatin landscape reveals that FOXO3 and ASCL1 are particularly enriched at the enhancers of genes involved in neurogenic pathways. Intriguingly, FOXO3 inhibits ASCL1-dependent neurogenesis in NPCs and direct neuronal conversion in fibroblasts. FOXO3 also restrains neurogenesis in vivo. Our study identifies a genome-wide interaction between the pro-longevity transcription factor FOXO3 and the cell fate determinant ASCL1, and raises the possibility that FOXO3’s ability to restrain ASCL1-dependent neurogenesis may help preserve the neural stem cell pool. ChIP-seq profiles of two transcription factors (FOXO3 and ASCL1) and three histone marks (H3K4me1, H3K4me3 and H3K27me3) in adult mouse neural progenitor cells.
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Project description:The ubiquitin system regulates eukaryotic physiology by modifying specific substrate proteins. Substrate recognition and the assembly of ubiquitin signals are determined by ubiquitin ligases, some of which also modify non-protein biomolecules. Here we expand this substrate realm, revealing that the human ligase HUWE1 can target drug-like small molecules. We demonstrate that compounds previously reported as HUWE1 inhibitors present substrates of their target ligase. Compound ubiquitination is driven by the canonical catalytic cascade, linking ubiquitin to the compound’s primary amino group. In vitro, the modification is selectively catalyzed by HUWE1, allowing the compounds to compete with protein substrates. We establish cellular detection methods, confirming HUWE1 promotes — but does not exclusively drive — compound ubiquitination in cells.
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