Exosomes as carriers transporting long non‑coding RNAs: Molecular characteristics and their function in cancer (Review)

Research Progress of Exosomal Non-Coding RNAs in Cardiac Remodeling

Exosomes are vesicles with a size range of 50 to 200 nm and released by different cells, which are essential for the exchange of information between cells. They have attracted a lot of interest from medical researchers. Exosomal non-coding RNAs play an important part in pathological cardiac remodelings, such as cardiomyocyte hypertrophy, cardiomyocyte apoptosis, and cardiac fibrosis. This review summarizes the origins and functions of exosomes, the role of exosomal non-coding RNAs in the process of pathological cardiac remodeling, as well as their theoretical basis for clinical application.

The anti-immune dengue subgenomic flaviviral RNA is present in vesicles in mosquito saliva and is associated with increased infectivity

Mosquito transmission of dengue viruses to humans starts with infection of skin resident cells at the biting site. There is great interest in identifying transmission-enhancing factors in mosquito saliva in order to counteract them. Here we report the discovery of high levels of the anti-immune subgenomic flaviviral RNA (sfRNA) in dengue virus 2-infected mosquito saliva. We established that sfRNA is present in saliva using three different methods: northern blot, RT-qPCR and RNA sequencing. We next show that salivary sfRNA is protected in detergent-sensitive compartments, likely extracellular vesicles. In support of this hypothesis, we visualized viral RNAs in vesicles in mosquito saliva and noted a marked enrichment of signal from 3'UTR sequences, which is consistent with the presence of sfRNA. Furthermore, we show that incubation with mosquito saliva containing higher sfRNA levels results in higher virus infectivity in a human hepatoma cell line and human primary dermal fibroblasts. Transfection of 3'UTR RNA prior to DENV2 infection inhibited type I and III interferon induction and signaling, and enhanced viral replication. Therefore, we posit that sfRNA present in salivary extracellular vesicles is delivered to cells at the biting site to inhibit innate immunity and enhance dengue virus transmission.

Response of human macrophages to gamma radiation is mediated via expression of endogenous retroviruses

Ionizing radiation-induced tissue damage recruits monocytes into the exposed area where they are differentiated to macrophages. These implement phagocytic removal of dying cells and elicit an acute inflammatory response, but can also facilitate tumorigenesis due to production of anti-inflammatory cytokines. Using primary human monocyte-derived macrophages (MDMs) and the THP1 monocytic cell line, we demonstrate that gamma radiation triggers monocyte differentiation toward the macrophage phenotype with increased expression of type I interferons (IFN-I) and both pro- and anti-inflammatory macrophage activation markers. We found that these changes correlate with significantly upregulated expression of 622 retroelements from various groups, particularly of several clades of human endogenous retroviruses (HERVs). Elevated transcription was detected in both sense and antisense directions in the HERV subgroups tested, including the most genetically homogeneous clade HML-2. The level of antisense transcription was three- to five-fold higher than of the sense strand levels. Using a proximity ligation assay and immunoprecipitation followed by RNA quantification, we identified an increased amount of the dsRNA receptors MDA-5 and TLR3 bound to an equivalent number of copies of sense and antisense chains of HERVK HML-2 RNA. This binding triggered MAVS-associated signaling pathways resulting in increased expression of IFN-I and inflammation related genes that enhanced the cumulative inflammatory effect of radiation-induced senescence. HML-2 knockdown was accompanied with reduced expression and secretion of IFNα, pro-inflammatory (IL-1β, IL-6, CCL2, CCL3, CCL8, and CCL20) and anti-inflammatory (IL10) modulators in irradiated monocytes and MDMs. Taken together, our data indicate that radiation stress-induced HERV expression enhances the IFN-I and cytokine response and results in increased levels of pro-inflammatory modulators along with expression of anti-inflammatory factors associated with the macrophage tumorigenic phenotype.

Ionizing radiation is a powerful stressogenic factor that induces massive cell damage. The signals released from radiation-damaged tissues recruit the monocytes, which are differentiated into macrophages that remove dying cells via phagocytosis and facilitate inflammation but can also contribute to tumorigenesis through anti-inflammatory and regenerative activities. The mechanism of this dual response of macrophages to irradiation is not fully understood. Using primary human macrophages and a monocytic cell line, we demonstrated that gamma radiation doses activate expression of various human endogenous retroviruses (HERVs). At the molecular level, we have shown that increased numbers of sense and antisense transcripts of tested HERV subgroups bind to double-stranded RNA receptors inducing the expression of type I interferons, multiple pro-inflammatory and some anti-inflammatory factors. At the phenotypic level, polarized macrophages exhibit a potent inflammatory response along with potentially tumorigenic characteristics. Our data suggest that endogenous retroviruses represent an important contributor of the macrophage-mediated inflammation in response to radiation-induced stress but may also indirectly influence tumorigenesis via biased macrophage polarization.

Tumor exosome promotes Th17 cell differentiation by transmitting the lncRNA CRNDE-h in colorectal cancer

The T helper 17 (Th17) cells in tumor microenvironment play an important role in colorectal cancer (CRC) progression. This study investigated the mechanism of Th17 cell differentiation in CRC with a focus on the role of tumor exosome-transmitted long noncoding RNA (lncRNA). Exosomes were isolated from the CRC cells and serum of CRC patients. The role and mechanism of the lncRNA CRNDE-h transmitted by CRC exosomes in Th17 cell differentiation were assessed by using various molecular biological methods. The serum exosomal CRNDE-h level was positively correlated with the proportion of Th17 cells in the tumor-infiltrating T cells in CRC patients. CRC exosomes contained abundant CRNDE-h and transmitted them to CD4⁺ T cells to increase the Th17 cell proportion, RORγt expression, and IL-17 promoter activity. The underlying mechanism is that, CRNDE-h bound to the PPXY motif of RORγt and impeded the ubiquitination and degradation of RORγt by inhibiting its binding with the E3 ubiquitin ligase Itch. The in vivo experiments confirmed that the targeted silence of CRNDE-h in CD4⁺ T cells attenuated the CRC tumor growth in mice. The present findings demonstrated that the tumor exosome transmitted CRNDE-h promoted Th17 cell differentiation by inhibiting the Itch-mediated ubiquitination and degradation of RORγt in CRC, expanding our understanding of Th17 cell differentiation in CRC.

Caspase-3 Cleaves Extracellular Vesicle Proteins During Auditory Brainstem Development

Sound localization requires extremely precise development of auditory brainstem circuits, the molecular mechanisms of which are largely unknown. We previously demonstrated a novel requirement for non-apoptotic activity of the protease caspase-3 in chick auditory brainstem development. Here, we used mass spectrometry to identify proteolytic substrates of caspase-3 during chick auditory brainstem development. These auditory brainstem caspase-3 substrates were enriched for proteins previously shown to be cleaved by caspase-3, especially in non-apoptotic contexts. Functional annotation analysis revealed that our caspase-3 substrates were also enriched for proteins associated with several protein categories, including proteins found in extracellular vesicles (EVs), membrane-bound nanoparticles that function in intercellular communication. The proteome of EVs isolated from the auditory brainstem was highly enriched for our caspase-3 substrates. Additionally, we identified two caspase-3 substrates with known functions in axon guidance, namely Neural Cell Adhesion Molecule (NCAM) and Neuronal-glial Cell Adhesion Molecule (Ng-CAM), that were found in auditory brainstem EVs and expressed in the auditory pathway alongside cleaved caspase-3. Taken together, these data suggest a novel developmental mechanism whereby caspase-3 influences auditory brainstem circuit formation through the proteolytic cleavage of extracellular vesicle (EV) proteins.

Role of taurine, its haloamines and its lncRNA TUG1 in both inflammation and cancer progression. On the road to therapeutics? (Review)

For one century, taurine is considered as an end product of sulfur metabolism. In this review, we discuss the beneficial effect of taurine, its haloamines and taurine upregulated gene 1 (TUG1) long non‑coding RNA (lncRNA) in both cancer and inflammation. We outline how taurine or its haloamines (N‑Bromotaurine or N‑Chlorotaurine) can induce robust and efficient responses against inflammatory diseases, providing insight into their molecular mechanisms. We also provide information about the use of taurine as a therapeutic approach to cancer. Taurine can be combined with other chemotherapeutic drugs, not only mediating durable responses in various malignancies, but also circumventing the limitations met from chemotherapeutic drugs, thus improving the therapeutic outcome. Interestingly, the lncRNA TUG1 is regarded as a promising therapeutic approach, which can overcome acquired resistance of cancer cells to selected strategies. In this regard, we can translate basic knowledge about taurine and its TUG1 lncRNA into potential therapeutic options directed against specific oncogenic signaling targets, thereby bridging the gap between bench and bedside.

Extracellular vesicle long non-coding RNA-mediated crosstalk in the tumor microenvironment: Tiny molecules, huge roles

Emerging evidence has shown that dynamic crosstalk among cells in the tumor microenvironment modulates the progression and chemotherapeutic responses of cancer. Extracellular vesicles comprise a crucial form of intracellular communication through horizontal transfer of bioactive molecules, including long non-coding RNA (lncRNA), to neighboring cells. Three main types of extracellular vesicles are exosomes, microvesicles and apoptotic bodies, exhibiting a wide range of sizes and different biogenesis. Over the last decade, dysregulation of extracellular vesicle lncRNA has been revealed to remodel the tumor microenvironment and induce aggressive phenotypes of tumor cells, thereby facilitating tumor growth and development. This review will focus on extracellular vesicle lncRNA-mediated crosstalk between tumor cells and recipient cells, including tumor cells as well as stromal cells in the tumor microenvironment, and overview the mechanisms by which lncRNA are selectively sorted into extracellular vesicles, which may pave the way for their clinical application in cancer diagnosis and treatment.

lncRNA ZNF649-AS1 Induces Trastuzumab Resistance by Promoting ATG5 Expression and Autophagy

The regulatory mechanism of long non-coding RNAs (lncRNAs) in trastuzumab resistance is not well established to date. In this research, we identified differentially expressed lncRNA and investigated its regulatory role in trastuzumab resistance of breast cancer. HiSeq sequencing and quantitative real-time PCR were performed to identify the dysregulated lncRNAs. Mass spectrometry, RNA fluorescence in situ hybridization (RNA-FISH), and immunoprecipitation assays were performed to identify the direct interactions between ZNF649-AS1 and other associated targets, such as polypyrimidine tract binding protein 1 (PTBP1) and autophagy related 5 (ATG5). Our results showed that ZNF649-AS1 was more highly expressed in trastuzumab-resistant cells compared to sensitive cells. Increased expression of ZNF649-AS1 was associated with a poorer response and shorter survival time of breast cancer patients. ZNF649-AS1 was upregulated by H3K27ac modification at the presence of trastuzumab treatment, and knockdown of ZNF649-AS1 reversed trastuzumab resistance via modulating ATG5 expression and autophagy. Mechanically, ZNF649-AS1 was associated with PTBP1 protein, which further promoted the transcription activity of the ATG5 gene. In conclusion, we demonstrated that H3K27ac modification-induced upregulation of ZNF649-AS1 could cause autophagy and trastuzumab resistance through associating with PTBP1 and promoting ATG5 transcription.

Advances in the role of exosomal non-coding RNA in the development, diagnosis, and treatment of gastric cancer (Review)

Exosomes are small vesicles secreted by a variety of cells that contain vrious biological macromolecules, including RNA, non-coding RNA and protein. An increasing number of studies have demonstrated that exosomes and particularly the non-coding RNAs they contain, serve important roles in many cellular processes, including the transmission of information. It is well established that the occurrence and development of gastric cancer, one of the four most common malignant tumors worldwide, involves the transmission of information. Based on the urgent need for the elucidation of the mechanism involved in this process, as well as advances in the diagnosis and treatment of gastric cancer, numerous reports have assessed the association between non-coding RNAs in exosomes and gastric cancer. The purpose of the present review was to summarize recent evidence on certain non-coding RNAs associated with the development, diagnosis and treatment of gastric cancer.

Exosomes: From Potential Culprits to New Therapeutic Promise in the Setting of Cardiac Fibrosis

Fibrosis is a significant global health problem associated with many inflammatory and degenerative diseases affecting multiple organs, individually or simultaneously. Fibrosis develops when extracellular matrix (ECM) remodeling becomes excessive or uncontrolled and is associated with nearly all forms of heart disease. Cardiac fibroblasts and myofibroblasts are the main effectors of ECM deposition and scar formation. The heart is a complex multicellular organ, where the various resident cell types communicate between themselves and with cells of the blood and immune systems. Exosomes, which are small extracellular vesicles, (EVs), contribute to cell-to-cell communication and their pathophysiological relevance and therapeutic potential is emerging. Here, we will critically review the role of endogenous exosomes as possible fibrosis mediators and discuss the possibility of using stem cell-derived and/or engineered exosomes as anti-fibrotic agents.