Rig-G is a growth inhibitory factor of lung cancer cells that suppresses STAT3 and NF-κB

The emerging roles of IFIT3 in antiviral innate immunity and cellular biology

The interferon-inducible protein with tetrapeptide repeats 3 (IFIT3) is one of the most important members in both the IFIT family and interferon-stimulated genes family. IFIT3 has typical features of the IFIT family in terms of gene and protein structures, and is able to be activated through the classical PRRs-IFN-JAK/STAT pathway. A variety of viruses can induce the expression of IFIT3, which in turn inhibits the replication of viruses, with the underlying mechanism showing its crucial role in antiviral innate immunity. Emerging studies have also identified that IFIT3 is involved in cellular biology changes, including cell proliferation, apoptosis, differentiation, and cancer development. In this review, we summarize the characteristics of IFIT3 with respect to molecular structure and regulatory pathways, highlighting the role of IFIT3 in antiviral innate immunity, as well as its diverse biological roles. We also discuss the potential of IFIT3 as a biomarker in disease diagnosis and therapy.

Chronic Inhalation Exposure to Antimony Trioxide Exacerbates the MAPK Signaling in Alveolar Bronchiolar Carcinomas in B6C3F1/N Mice

Antimony trioxide (AT) is used as a flame retardant in fabrics and plastics. Occupational exposure in miners and smelters is mainly through inhalation and dermal contact. Chronic inhalation exposure to AT particulates in B6C3F1/N mice and Wistar Han rats resulted in increased incidences and tumor multiplicities of alveolar/bronchiolar carcinomas (ABCs). In this study, we demonstrated Kras (43%) and Egfr (46%) hotspot mutations in mouse lung tumors (n = 80) and only Egfr (50%) mutations in rat lung tumors (n = 26). Interestingly, there were no differences in the incidences of these mutations in ABCs from rats and mice at exposure concentrations that did and did not exceed the pulmonary overload threshold. There was increased expression of p44/42 mitogen-activated protein kinase (MAPK) (Erk1/2) protein in ABCs harboring mutations in Kras and/or Egfr, confirming the activation of MAPK signaling. Transcriptomic analysis indicated significant alterations in MAPK signaling such as ephrin receptor signaling and signaling by Rho-family GTPases in AT-exposed ABCs. In addition, there was significant overlap between transcriptomic data from mouse ABCs due to AT exposure and human pulmonary adenocarcinoma data. Collectively, these data suggest chronic AT exposure exacerbates MAPK signaling in ABCs and, thus, may be translationally relevant to human lung cancers.

IFIT3 (interferon induced protein with tetratricopeptide repeats 3) modulates STAT1 expression in small extracellular vesicles

We have previously shown that the αvβ6 integrin plays a key role in promoting prostate cancer (PrCa) and it can be transferred to recipient cells via small extracellular vesicles (sEVs). Furthermore, we have reported in a proteomic analysis that αvβ6 integrin down-regulation increases the expression of IFIT3 (interferon induced protein with tetratricopeptide repeats 3) in PrCa cells and their derived sEVs. IFIT3 is a protein well known for being an antiviral effector, but recently its role in cancer has also been elucidated. To study the relationship between IFIT3 and STAT1 (signal transducer and activator of transcription 1), an upstream regulator of IFIT3, in PrCa cells and their released sEVs, we used CRISPR/Cas9 techniques to down-regulate the expression of the β6 integrin subunit, IFIT3 or STAT1. Our results show that IFIT3 and STAT1 are highly expressed in PrCa cells devoid of the β6 integrin subunit. However, IFIT3 but not STAT1, is present in sEVs derived from PrCa cells lacking the β6 integrin subunit. We demonstrate that loss of IFIT3 generates sEVs enriched in STAT1 but reduces the levels of STAT1 in the cells. As expected, IFIT3 is not detectable in STAT1 negative cells or sEVs. We thus propose that the observed STAT1 enrichment in sEVs is a compensatory mechanism for the loss of IFIT3. Overall, these results provide new insights into the intrinsic role of IFIT3 as a regulator of STAT1 expression in sEVs and in intercellular communication in PrCa.

Novel evidence for retinoic acid-induced G (Rig-G) as a tumor suppressor by activating p53 signaling pathway in lung cancer

Lung cancer is one of most common malignancies worldwide. We have previously identified retinoic acid-induced gene G (Rig-G) as a tumor suppressor in not only acute promyelocytic leukemia, but also in other solid tumors. However, the clinical significance of Rig-G and the underlying mechanism(s) for its biological function in lung cancer remain largely unexplored. Herein, we first compared the expression of Rig-G between lung cancer (n = 138) and normal tissues (n = 23), from public-available data sets and our patient cohort. We further analyzed the correlation of Rig-G expression with key clinico-pathological features and survival outcomes in a multi-site clinical cohort of 300 lung cancer patients. Functional studies for Rig-G were performed in cell lines, and an animal model to support clinical findings. We found that Rig-G was frequently downregulated in lung cancer tissues and cell lines, and correlated with poor prognosis in lung cancer patients. Overexpression of Rig-G led to significantly reduced cell growth and suppressed migration in A549 and NCI-H1944 cells, accompanied by reduced epithelial-mesenchymal transition. Likewise, restoration of Rig-G in Lewis lung carcinoma cells permitted development of fewer cancer metastases versus controls in an animal model. Gene expression profiling results identified p53 pathway as a key downstream target of Rig-G, and p53 inhibition by pifithrin-α caused abrogation of tumor-suppressive effects of Rig-G in lung cancer. In conclusion, we, for the first time, have identified Rig-G as a novel and important tumor suppressor, which may serve as a potential therapeutic target for restoring p53 expression in lung cancer patients.

PLAC8 inhibits oral squamous cell carcinogenesis and epithelial-mesenchymal transition via the Wnt/β-catenin and PI3K/Akt/GSK3β signaling pathways

Placenta-specific 8 (PLAC8) is closely associated with the proliferation, apoptosis and autophagy of several tumor cells. However, the expression and function of PLAC8 in oral squamous cell carcinoma (OSCC) remain unknown. Therefore, the present study investigated the function and mechanism of PLAC8 in OSCC. Reverse transcription-quantitative PCR and western blot analyses were performed to quantify the expression of PLAC8 in OSCC cell lines. The function of PLAC8 in OSCC was investigated via transfection, the Transwell and Cell Counting Kit-8 assays, immunofluorescence staining and western blotting. The results demonstrated that PLAC8 exspression was downregulated in OSCC cell lines. PLAC8 inhibited the cell proliferation in OSCC. In addition, PLAC8 restrained invasion and epithelial-mesenchymal transition of OSCC cells. Furthermore, β-catenin helped to repress PLAC8 expression by regulating the Wnt/β-catenin and PI3K/Akt/GSK3β signaling pathways in OSCC cells. Collectively, the results of the present study suggest that PLAC8 acts as a tumor suppressor in OSCC by downregulating β-catenin.

2-(6-Hydroxyhexylthio)-5,8-dimethoxy-1,4-naphthoquinone Induces Apoptosis through ROS-Mediated MAPK, STAT3, and NF-κB Signalling Pathways in Lung Cancer A549 Cells

Two novel compounds, 2-(2-hydroxyethylthio)-5,8-dimethoxy-1,4-naphthoquinone (HEDMNQ) and 2-(6-hydroxyhexylthio)-5,8-dimethoxy-1,4-naphthoquinone (HHDMNQ), were synthesized to investigate the kill effects and mechanism of 1,4-naphthoquinone derivatives in lung cancer cells. The results of the CCK-8 assay showed that HEDMNQ and HHDMNQ had significant cytotoxic effects on A549, NCI-H23, and NCI-H460 NSCLC cells. Flow cytometry and western blot results indicated that HHDMNQ induced A549 cell cycle arrest at the G2/M phase by decreasing the expression levels of cyclin-dependent kinase 1/2 and cyclin B1. Fluorescence microscopy and flow cytometry results indicated that HHDMNQ could induce A549 cell apoptosis, and western blot analysis showed that HHDMNQ induced apoptosis through regulating the mitochondria pathway, as well as the MAPK, STAT3, and NF-κB signalling pathways. Flow cytometry results showed that intracellular reactive oxygen species (ROS) levels were increased after HHDMNQ treatment, and western blot showed that ROS could modulate the intrinsic pathway and MAPK, STAT3, and NF-κB signalling pathways. These effects were blocked by the ROS inhibitor N-acetyl-L-cysteine in A549 cells. Our findings suggest that compared with HEDMNQ, HHDMNQ had the stronger ability to inhibit the cell viability of lung cancer cells and induce apoptosis by regulating the ROS-mediated intrinsic pathway and MAPK/STAT3/NF-κB signalling pathways. Thus, HHDMNQ might be a potential antitumour compound for treating lung cancer.

Inflammation and tissue homeostasis: the NF-κB system in physiology and malignant progression

Disruption of tissue function activates cellular stress which triggers a number of mechanisms that protect the tissue from further damage. These mechanisms involve a number of homeostatic modules, which are regulated at the level of gene expression by the transactivator NF-κB. This transcription factor shifts between activation and repression of discrete, cell-dependent gene expression clusters. Some of its target genes provide feedback to NF-κB itself, thereby strengthening the inflammatory response of the tissue and later terminating inflammation to facilitate restoration of tissue homeostasis. Disruption of key feedback modules for NF-κB in certain cell types facilitates the survival of clones with genomic aberrations, and protects them from being recognized and eliminated by the immune system, to enable thereby carcinogenesis.

Better together: the role of IFIT protein-protein interactions in the antiviral response

The interferon-induced proteins with tetratricopeptide repeats (IFITs) are a family of antiviral proteins conserved throughout all vertebrates. IFIT1 binds tightly to non-self RNA, particularly capped transcripts lacking methylation on the first cap-proximal nucleotide, and inhibits their translation by out-competing the cellular translation initiation apparatus. This exerts immense selection pressure on cytoplasmic RNA viruses to maintain mechanisms that protect their messenger RNA from IFIT1 recognition. However, it is becoming increasingly clear that protein-protein interactions are necessary for optimal IFIT function. Recently, IFIT1, IFIT2 and IFIT3 have been shown to form a functional complex in which IFIT3 serves as a central scaffold to regulate and/or enhance the antiviral functions of the other two components. Moreover, IFITs interact with other cellular proteins to expand their contribution to regulation of the host antiviral response by modulating innate immune signalling and apoptosis. Here, we summarize recent advances in our understanding of the IFIT complex and review how this impacts on the greater role of IFIT proteins in the innate antiviral response.