Jun Zhang

Linear ubiquitination and deubiquitination represent critical regulatory mechanisms in inflammation and cell death, yet their roles in RIG-I-like receptor (RLR)-dependent signaling remain unclear. Here, we identified OTU deubiquitinase with linear linkage specificity (OTULIN) as a negative regulator of RIG-I-dependent type I IFN (IFN-I) signaling. Overexpression of OTULIN markedly attenuated NF-κB and IFNβ reporter activation triggered by RNA viruses or synthetic analogs, suppressed downstream gene expression, impaired IFN-I production, and diminished phosphorylation of IκBα, TBK1, and IRF3, thereby facilitating viral replication. Conversely, knockout of OTULIN in HeLa and iBMDM cells enhanced these antiviral signaling events and restricted viral replication. Critically, reintroducing OTULIN into OTULIN -KO cells via lentiviral transduction reversed this enhanced phenotype, restoring the suppression of IFN-I signaling. Mechanistically, RNA virus infection induced linear ubiquitination of TRAF6 at K104, K142, and K371. LUBAC promoted antiviral innate immune signaling by enhancing the linear ubiquitination of TRAF6, which was antagonized by OTULIN. Notably, the linear ubiquitination of TRAF6 facilitated its K63-linked ubiquitination and strengthened its association with MAVS, amplifying the antiviral response. Furthermore, Otulin ^+/− mice exhibited enhanced antiviral immunity and more efficient viral clearance than wild-type littermates. Collectively, these findings unveil a regulatory role of OTULIN in attenuating RIG-I-dependent IFN-I signaling through removal of linear ubiquitination from TRAF6, highlighting the essential equilibrium between linear ubiquitination and deubiquitination in antiviral innate immunity and immune homeostasis.

Tumor immune evasion is intricately linked to malignant tumor progression and contributes to the failure of anti‐cancer immunotherapy. Serine/threonine protein kinase 25 (STK25) has been previously implicated in the progression of various neoplastic diseases. However, the function of STK25 in the colorectal cancer (CRC) microenvironment remains unclear. Here, it is demonstrated that STK25 global knockout (STK25 ^−/− ) mice and STK25‐knockout tumor‐bearing mice exhibited enhanced effectiveness of anti‐PD‐1 immunotherapy, which leads to significant tumor suppression with increased recruitment of CD8 ⁺ T cells. Mechanistically, STK25 deficiency increased PD‐L1 protein levels by regulating PD‐L1 K48‐linked ubiquitination in a NEDD4‐dependent manner. Moreover, CRC patients with low STK25 expression are more responsive to immune checkpoint blockade (ICB) therapy compared to those with high STK25 levels. Taken together, the findings reveal a critical role of STK25 for regulating PD‐L1 protein stability in tumor immune evasion, and suggest that targeting STK25 may provide a potential approach to increase sensitivity to the ICB treatment in patients with CRC.

In an initial screening of virus-induced differentially expressed circRNAs, circHOMER1 was significantly upregulated. However, its role in antiviral innate immunity remained unclear. circHOMER1 was upregulated in response to a range of stimuli, including RNA viruses, DNA viruses, as well as type I IFNs. Overexpression of circHOMER1 reduced the virus-induced type I IFN signaling pathway and promoted viral replication. Consistently, knockdown of circHOMER1 yielded opposite consequence. Mechanistically, circHOMER1 acted as a competitive endogenous RNA (ceRNA) for miR-145-3p, controlling the mRNA level of OTU domain-containing protein 7B (OTUD7B), thereby downregulating interferon regulatory factor 3 (IRF3) expression. Furthermore, circHOMER1 was found to disrupt the interaction between Ras GTPase-activating protein-binding protein 1 (G3BP1) and retinoic-acid-inducible protein I (RIG-I), impairing the detection of viral RNAs by RIG-I. Notably, the concordant immunosuppressive effects of circHOMER1 were observed in mouse infection models. These findings identify circHOMER1 as a novel interferon-stimulated circRNA that serves as a negative modulator of the antiviral innate immune response and is essential for immune homeostasis. IMPORTANCE: A growing body of evidence suggests that circRNAs are involved in various physiological or pathological processes. Through circRNA microarray screening of virus-induced differentially expressed circRNAs, we identified an upregulated circRNA, circHOMER1. circHOMER1 is abundantly expressed in the brain. The known functions of circHOMER1 have been focused on the nervous systems and the related diseases. Its functions in the immune system are not discovered. In this study, we found that circHOMER1 is upregulated by viral infection, interferon treatment, etc. circHOMER1 can negatively modulate virus-induced type I IFN signaling by acting as a ceRNA or other mechanism. The regulatory function of circHOMER1 in innate immunity is critical for immune homeostasis. The dysregulation of circHOMER1 may be associated with virus encephalitis or other related diseases. circHOMER1 may be a potential therapeutic target of virus-induced infections and autoimmune diseases.

Spermatogenesis-associated protein 2 (SPATA2) is primarily named for its important role in spermatogenesis. Its function in tumorigenesis remains elusive. Here, we used various bioinformatic tools to systematically analyze the expression patterns of SPATA2 in cancers, the correlation of SPATA2 expression with clinical parameters, genetic variation, methylation, phosphorylation, immune infiltration and immune therapy. SPATA2 is significantly upregulated in multiple cancers and its expression was associated with tumor stage, grade and serve as a potential prognostic marker in LIHC. Notably, SPATA2 was also linked to immune suppression, exhibiting positive correlations with immune checkpoint genes and immune suppressive cells such as regulatory T cells and MDSCs. Furthermore, SPATA2 interacted and co-expressed with proteins involved in DNA repair mechanisms, indicating its potential role in maintaining genomic stability. Finally, we conducted biological experiments to investigate the role of SPATA2 in LIHC. SPATA2 knockdown enhances the migration and proliferation capabilities of Hep-G2 and HuH7 cell lines. These findings underscore the significance of SPATA2 in cancer biology, suggests its role in both the tumor microenvironment and the tumor cell level and its potential as a prognostic marker and therapeutic target in oncology, particularly in LIHC.

Type I and type II IFNs are important immune modulators in both innate and adaptive immunity. They transmit signaling by activating JAK-STAT pathways. Sirtuin 1 (SIRT1), a class III NAD ⁺ -dependent deacetylase, has multiple functions in a variety of physiological processes. Here, we characterized the novel functions of SIRT1 in the regulation of type I and type II IFN-induced signaling. Overexpression of SIRT1 inhibited type I and type II IFN-induced interferon-stimulated response element activation. In contrast, knockout of SIRT1 promoted type I and type II IFN-induced expression of ISGs and inhibited viral replication. Treatment with SIRT1 inhibitor EX527 had similar positive effects. SIRT1 physically associated with STAT1 or STAT3, and this interaction was enhanced by IFN stimulation or viral infection. By deacetylating STAT1 at K673 and STAT3 at K679/K685/K707/K709, SIRT1 downregulated the phosphorylation of STAT1 (Y701) and STAT3 (Y705). Sirt1 ^+/− primary peritoneal macrophages and Sirt1 ^+/− mice exhibited enhanced IFN-induced signaling and antiviral activity. Thus, SIRT1 is a novel negative regulator of type I and type II IFN-induced signaling through its deacetylase activity. IMPORTANCE: SIRT1 has been reported in the precise regulation of antiviral (RNA and DNA) immunity. However, its functions in type I and type II IFN-induced signaling are still unclear. In this study, we deciphered the important functions of SIRT1 in both type I and type II IFN-induced JAK-STAT signaling and explored the potential acting mechanisms. It is helpful for understanding the regulatory roles of SIRT1 at different levels of IFN signaling. It also consolidates the notion that SIRT1 is an important target for intervention in viral infection, inflammatory diseases, or even interferon-related therapies.

The inflammasomes play crucial roles in inflammation and cancer development, while the PD-1/PD-L1 pathway is critical for immune suppression in the tumor microenvironment (TME). Recent research indicates a reciprocal regulatory relationship between inflammasomes and PD-1/PD-L1 signaling in cancer development and PD-1 blockade treatment. By activating in diverse cells in tumor tissues, inflammasome upregulates PD-L1 level in the TME. Moreover, the regulation of PD-1/PD-L1 activity by inflammasome activation involves natural killer cells, tumor-associated macrophages and myeloid-derived suppressor cells. Conversely, PD-1 blockade can activate the inflammasome, potentially influencing treatment outcomes. The interplay between inflammasomes and PD-1/PD-L1 has profound and intricate effects on cancer development and treatment. In this review, we discuss the crosstalk between inflammasomes and PD-1/PD-L1 in cancers, exploring their implications for tumorigenesis, metastasis and immune checkpoint inhibitor (ICI) resistance. The combined therapeutic strategies targeting both inflammasomes and checkpoint molecules hold promising potential as treatments for cancer.