The cGAS/STING signaling pathway: a cross-talk of infection, senescence and tumors

Cyclic GMP-AMP synthase recognizes the physical features of DNA

Cyclic GMP-AMP synthase (cGAS) is a major cytosolic DNA sensor that plays a significant role in innate immunity. Upon binding to double stranded DNA (dsDNA), cGAS utilizes GTP and ATP to synthesize the second messenger cyclic GMP-AMP (cGAMP). The cGAMP then binds to the adapter protein stimulator of interferon genes (STING) in the endoplasmic reticulum, resulting in the activation of the transcription factor interferon regulatory factor 3 (IRF3) and subsequent induction of type I interferon. An important question is how cGAS distinguishes between self and non-self DNA. While cGAS binds to the phosphate backbone of DNA without discrimination, its activation is influenced by physical features such as DNA length, inter-DNA distance, and mechanical flexibility. This suggests that the recognition of DNA by cGAS may depend on these physical features. In this article we summarize the recent progress in research on cGAS-STING pathway involved in antiviral defense, cellular senescence and anti-tumor response, and focus on DNA recognition mechanisms based on the physical features.

Recent advancements in cGAS-STING activation, tumor immune evasion, and therapeutic implications

The cGAS-STING signaling pathway is indeed a pivotal component of the immune system and serve as a crucial link between innate and adaptive immune responses. STING is involved in the cellular response to pathogen invasion and DNA damage, and which has important consequences for host defense mechanisms and cancer regulation. Ongoing research aiming to modulate the cGAS-STING pathway for improved clinical outcomes in cancer and autoimmune diseases is underway. Indeed, the interaction between the cGAS-STING pathway and immune evasion mechanisms is a complex and critical aspect of cancer biology. Pathogens and various host factors can exploit this pathway to reduce the effectiveness of cancer therapies, particularly immunotherapies. Thus, immunotherapies or combination therapies may assist in overcoming the immune suppression and improving clinical outcomes. This review explores recent advancements in understanding the cGAS-STING signaling pathway, with particular emphasis on its activation mechanisms and role in tumor immune evasion. The dual role of the pathway in boosting immune responses while simultaneously enabling tumors to evade the immune system makes it a crucial target for innovative cancer treatment approaches.Please confirm if the author names are presented accurately and in the correct sequence (given name, middle name/initial, family name). Author 2 Given name: [Md Mazedul] Last name [Islam], Author 3 Given name: [Mst Rubaiat Nazneen] Last name [Akhand] and Author 5 Given name: [Md Rashedunnabi] Last name [Akanda]. Also, kindly confirm the details in the metadata are correct.AQ1: Here Author 4 given name: [Byung-Yong] Last name [Park] is missing. Metadata are correct.

Ozone exposure affects corneal epithelial fate by promoting mtDNA leakage and cGAS/STING activation

Ozone is a common air pollutant associated with various human diseases. The human ocular surface is frequently exposed to ozone in the troposphere, but the mechanisms by which ozone affects the ocular surface health remain unclear. This study aimed to establish a mouse model to investigate the effects of ozone exposure on the ocular surface and the corneal epithelium. The findings revealed that ozone exposure disrupted corneal epithelial homeostasis and differentiation, resulting in corneal squamous metaplasia. Further, ozone exposure induced oxidative damage and cytoplasmic leakage of mitochondrial DNA (mtDNA), thereby activating the cGAS/STING signaling pathway. The activation of the cGAS/STING signaling pathway triggered the activation of downstream NF-κB and TRAF6 signaling pathways, causing corneal inflammation, thereby promoting corneal inflammation and squamous metaplasia. Finally, C-176, a selective STING inhibitor, effectively prevented and treated corneal inflammation and squamous metaplasia caused by ozone exposure. This study revealed the role of mtDNA leakage-mediated cGAS/STING activation in corneal squamous epithelial metaplasia caused by ozone exposure. It also depicted the abnormal expression pattern of corneal epithelial keratin using three-dimensional images, providing new targets and strategies for preventing and treating corneal squamous metaplasia and other ocular surface diseases.

Bioinformatics analysis of immune characteristics in tumors with alternative carcinogenesis pathways induced by human papillomaviruses

BACKGROUND

Human papillomaviruses (HPVs) induce a subset of head and neck squamous cell carcinomas (HNSCC) and anogenital cancers, particularly cervical cancer (CC). The major viral proteins that contribute to tumorigenesis are the E6 and E7 oncoproteins, whose expression is usually enhanced after the integration of viral DNA into the host genome. Recently, an alternative tumorigenesis pathway has been suggested in approximately half of HNSCC and CC cases associated with HPV infection. This pathway is characterized by extrachromosomal HPV persistence and increased expression of the viral E2, E4, and E5 genes. The E6, E7, E5, and E2 proteins have been shown to modify the expression of numerous cellular immune-related genes. The antitumor immune response is a critical factor in the prognosis of HPV-driven cancers, and its characterization may contribute to the prediction and personalization of the increasingly used cancer immunotherapy.

METHODS

We analyzed the immune characteristics of HPV-dependent tumors and their association with carcinogenesis types. Transcriptomic HNSCC and CC datasets from The Cancer Genome Atlas were used for this analysis.

RESULTS

Clustering with immune-related genes resulted in two clusters of HPV16-positive squamous cell carcinomas in both tumor types: cluster 1 had higher activation of immune responses, including stimulation of the antigen processing and presentation pathway, which was associated with higher immune cell infiltration and better overall survival, and cluster 2 was characterized by keratinization. In CC, the distribution of tumor samples into clusters 1 and 2 did not depend on the level of E2/E5 expression, but in HNSCC, most E2/E5-high tumors were localized in cluster 1 and E2/E5-low tumors in cluster 2. Further analysis did not reveal any association between the E2/E5 levels and the expression of immune-related genes.

CONCLUSIONS

Our results suggest that while the detection of immune responses associated with preserved expression of genes encoding components of antigen processing and presentation machinery in HPV-driven tumors may be markers of better prognosis and an important factor in therapy selection, the type of carcinogenesis does not seem to play a decisive role in the induction of antitumor immunity.

COVID-19. Biology, pathophysiology, and immunology: a pathologist view

Even if the SARS-CoV-2 pandemic has been declared over, several risks and clinical problems remain to be faced, including long-COVID sequelae and possible outbreaks of pathogenic variants. Intense research on COVID-19 has provided in these few years a striking amount of data covering different fields and disciplines, which can help to provide a knowledge shield against new potential infective spreads, and may also potentially be applied to other fields of medicine, including oncology and neurology. Nevertheless, areas of uncertainty still remain regarding the pathogenic mechanisms that subtend the multifaceted manifestations of the disease. To better clarify the pathogenesis of the disease, a systematic multidisciplinary evaluation of the many mechanisms involved in COVID-19 is mandatory, including clinical, physiological, radiological, immunological and pathological studies. In COVID-19 syndrome the pathological studies have been mainly performed on autopsy cases, and only a few studies are available on biopsies. Nevertheless, these studies have provided relevant information that can substantially contribute to decipher the complex scenario characterizing the different forms of COVID-19 and long-COVID-19. In this review the data provided by pathological investigations are recapitulated and discussed, in the light of different hypothesis and data provided by clinical, physiological and immunological data.

Innate immune response restarts adaptive immune response in tumors

The imbalance of immune response plays a crucial role in the development of diseases, including glioblastoma. It is essential to comprehend how the innate immune system detects tumors and pathogens. Endosomal and cytoplasmic sensors can identify diverse cancer cell antigens, triggering the production of type I interferon and pro-inflammatory cytokines. This, in turn, stimulates interferon stimulating genes, enhancing the presentation of cancer antigens, and promoting T cell recognition and destruction of cancer cells. While RNA and DNA sensing of tumors and pathogens typically involve different receptors and adapters, their interaction can activate adaptive immune response mechanisms. This review highlights the similarity in RNA and DNA sensing mechanisms in the innate immunity of both tumors and pathogens. The aim is to enhance the anti-tumor innate immune response, identify regions of the tumor that are not responsive to treatment, and explore new targets to improve the response to conventional tumor therapy and immunotherapy.

Crosstalk between cGAS-STING pathway and autophagy in cancer immunity

The cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway is critical in cancer immunity. Autophagy is a highly conserved process that is responsible for the degradation of cytoplasmic material and is involved in both innate and adaptive immunity. Recently, cGAS-STING and autophagy have been shown to be interconnected, which may influence the progression of cancer. Although cGAS-STING and autophagy have been shown to be interrelated in innate immunity, little has been reported about cancer immunity. As cancer immunity is key to treating tumors, it is essential to summarize the relationship and interactions between the two. Based on this, we systematically sorted out the recent findings of cGAS-STING and autophagy in cancer immunity and explored the interactions between cGAS-STING and autophagy, although these interactions have not been extensively studied. Lastly, we provide an outlook on how cGAS-STING and autophagy can be combined, with the hope that our research can help people better understand their potential roles in cancer immunity and bring light to the treatment of cancer.