ISG15: A link between innate immune signaling, DNA replication, and genome stability

Identification of MUC1-C as a Target for Suppressing Progression of Head and Neck Squamous Cell Carcinomas

The MUC1-C protein is aberrantly expressed in adenocarcinomas of epithelial barrier tissues and contributes to their progression. Less is known about involvement of MUC1-C in the pathogenesis of squamous cell carcinomas (SCC). Here, we report that the MUC1 gene is upregulated in advanced head and neck SCCs (HNSCC). Studies of HNSCC cell lines demonstrate that the MUC1-C subunit regulates expression of (i) RIG-I and MDA5 pattern recognition receptors, (ii) STAT1 and IFN regulatory factors, and (iii) downstream IFN-stimulated genes. MUC1-C integrates chronic activation of the STAT1 inflammatory pathway with induction of the ∆Np63 and SOX2 genes that are aberrantly expressed in HNSCCs. In extending those dependencies, we demonstrate that MUC1-C is necessary for NOTCH3 expression, self-renewal capacity, and tumorigenicity. The findings that MUC1 associates with ∆Np63, SOX2 and NOTCH3 expression by single-cell RNA sequencing analysis further indicate that MUC1-C drives the HNSCC stem cell state and is a target for suppressing HNSCC progression.

SIGNIFICANCE

This work reports a previously unrecognized role for MUC1-C in driving STAT1-mediated chronic inflammation with the progression of HNSCC and identifies MUC1-C as a druggable target for advanced HNSCC treatment.

Protocol for the quantitative identification of endogenously ISGylated proteins from mammalian cell lines

Ubiquitin-like protein ISG15 plays an important role in an array of cellular functions via its covalent attachment to target proteins (ISGylation). Here, we present a protocol for the identification of ISGylated proteins that avoids the caveats associated with ISG15 overexpression and minimizes the likelihood of false positives. We describe steps for the tagging of endogenous ISG15, followed by genotyping and clone selection. We then detail steps for ISGylation induction, the isolation of ISGylated proteins, and their identification via quantitative mass spectrometry. For complete details on the use and execution of this protocol, please refer to Wardlaw and Petrini.1.

Single-cell and bulk transcriptional profiling of mouse ovaries reveals novel genes and pathways associated with DNA damage response in oocytes

Immature oocytes enclosed in primordial follicles stored in female ovaries are under constant threat of DNA damage induced by endogenous and exogenous factors. Checkpoint kinase 2 (CHEK2) is a key mediator of the DNA damage response in all cells. Genetic studies have shown that CHEK2 and its downstream targets, p53 and TAp63, regulate primordial follicle elimination in response to DNA damage, however the mechanism leading to their demise is still poorly characterized. Single-cell and bulk RNA sequencing were used to determine the DNA damage response in wildtype and Chek2-deficient ovaries. A low but oocyte-lethal dose of ionizing radiation induces a DNA damage response in ovarian cells that is solely dependent on CHEK2. DNA damage activates multiple ovarian response pathways related to apoptosis, p53, interferon signaling, inflammation, cell adhesion, and intercellular communication. These pathways are differentially employed by different ovarian cell types, with oocytes disproportionately affected by radiation. Novel genes and pathways are induced by radiation specifically in oocytes, shedding light on their sensitivity to DNA damage, and implicating a coordinated response between oocytes and pre-granulosa cells within the follicle. These findings provide a foundation for future studies on the specific mechanisms regulating oocyte survival in the context of aging, as well as therapeutic and environmental genotoxic exposures.

Chronic Interferon Stimulated Gene Transcription Promotes Oncogene Induced Breast Cancer

The Mre11 complex (comprising Mre11, Rad50, Nbs1) is integral to the maintenance of genome stability. We previously showed that a hypomorphic Mre11 mutant mouse strain ( Mre11 ATLD1/ATLD1 ) was highly susceptible to oncogene induced breast cancer. Here we used a mammary organoid system to examine which Mre11 dependent responses are tumor suppressive. We found that Mre11 ATLD1/ATLD1 organoids exhibited an elevated interferon stimulated gene (ISG) signature and sustained changes in chromatin accessibility. This Mre11 ATLD1/ATLD1 phenotype depended on DNA binding of a nuclear innate immune sensor, IFI205. Ablation of Ifi205 in Mre11 ATLD1/ATLD1 organoids restored baseline and oncogene-induced chromatin accessibility patterns to those observed in WT . Implantation of Mre11 ATLD1/ATLD1 organoids and activation of oncogene led to aggressive metastatic breast cancer. This outcome was reversed in implanted Ifi205 -/- Mre11 ATLD1/ATLD1 organoids. These data reveal a connection between innate immune signaling and tumor suppression in mammary epithelium. Given the abundance of aberrant DNA structures that arise in the context of genome instability syndromes, the data further suggest that cancer predisposition in those contexts may be partially attributable to tonic innate immune transcriptional programs.

The Multiple Faces of the MRN Complex: Roles in Medulloblastoma and Beyond

Hypomorphic mutations in MRN complex genes are frequently found in cancer, supporting their role as oncosuppressors. However, unlike canonical oncosuppressors, MRN proteins are often overexpressed in tumor tissues, where they actively work to counteract DSBs induced by both oncogene-dependent RS and radio-chemotherapy. Moreover, at the same time, MRN genes are also essential genes, since the constitutive KO of each component leads to embryonic lethality. Therefore, even though it is paradoxical, MRN genes may work as oncosuppressive, oncopromoting, and essential genes. In this review, we discussed how alterations in the MRN complex impact the physiopathology of cancer, in light of our recent discoveries on the gene-dosage-dependent effect of NBS1 in Medulloblastoma. These updates aim to understand whether MRN complex can be realistically used as a prognostic/predictive marker and/or as a therapeutic target for the treatment of cancer patients in the future.