Protein handling, modification and folding in the endoplasmic reticulum (ER) are tightly regulated processes that determine cell function, fate and survival. In several tumour types, diverse oncogenic, transcriptional and metabolic abnormalities cooperate to generate hostile microenvironments that disrupt ER homeostasis in malignant and stromal cells, as well as infiltrating leukocytes. These changes provoke a state of persistent ER stress that has been demonstrated to govern multiple pro-tumoural attributes in the cancer cell while dynamically reprogramming the function of innate and adaptive immune cells. Aberrant activation of ER stress sensors and their downstream signalling pathways have therefore emerged as key regulators of tumour growth and metastasis as well as response to chemotherapy, targeted therapies and immunotherapy. In this Review, we discuss the physiological inducers of ER stress in the tumour milieu, the interplay between oncogenic signalling and ER stress response pathways in the cancer cell and the profound immunomodulatory effects of sustained ER stress responses in tumours.

Endoplasmic reticulum stress signals in the tumour and its microenvironment

Gastric cancer is the fourth most common malignancy and the third leading cause of cancer-related deaths worldwide. Advanced gastric cancer patients can notably benefit from chemotherapy including adriamycin, platinum drugs, 5-fluorouracil, vincristine, and paclitaxel as well as targeted therapy drugs. Nevertheless, primary drug resistance or acquisition drug resistance eventually lead to treatment failure and poor outcomes of the gastric cancer patients. The detailed mechanisms involved in gastric cancer drug resistance have been revealed. Interestingly, different noncoding RNAs (ncRNAs), such as microRNAs (miRNAs), long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs), are critically involved in gastric cancer development. Multiple lines of evidences demonstrated that ncRNAs play a vital role in gastric cancer resistance to chemotherapy reagents and targeted therapy drugs. In this review, we systematically summarized the emerging role and detailed molecular mechanisms of ncRNAs impact drug resistance of gastric cancer. Additionally, we propose the potential clinical implications of ncRNAs as novel therapeutic targets and prognostic biomarkers for gastric cancer.

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Noncoding RNAs in gastric cancer: implications for drug resistance

Hepatocellular carcinoma (HCC) is the most commonmalignancy. Exsome plays a significant role in the elucidation of signal transduction pathways between hepatoma cells, angiogenesis and early diagnosis of HCC. Exosomes are small vesicular structures that mediate interaction between different types of cells, and contain a variety of components (including DNA, RNA, and proteins). Numerous studies have shown that these substances in exosomes are involved in growth, metastasis and angiogenesis in liver cancer, and then inhibited the growth of liver cancer by blocking the signaling pathway of liver cancer cells. In addition, the exosomal substances could also be used as markers for screening early liver cancer. In this review, we summarized to reveal the significance of exosomes in the occurrence, development, diagnosis and treatment of HCC, which in turn might help us to further elucidate the mechanism of exosomes in HCC, and promote the use of exosomes in the clinical diagnosis and treatment of HCC.

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The significance of exosomes in the development and treatment of hepatocellular carcinoma

MicroRNAs (miRNAs) are small, non-coding RNAs that post-transcriptionally regulate gene expression by binding to specific mRNA targets and promoting their degradation and/or translational inhibition. miRNAs regulate both physiological and pathological liver functions. Altered expression of miRNAs is associated with liver metabolism dysregulation, liver injury, liver fibrosis and tumour development, making miRNAs attractive therapeutic strategies for the diagnosis and treatment of liver diseases. Here, we review recent advances regarding the regulation and function of miRNAs in liver diseases with a major focus on miRNAs that are specifically expressed or enriched in hepatocytes (miR-122, miR-194/192), neutrophils (miR-223), hepatic stellate cells (miR-29), immune cells (miR-155) and in circulation (miR-21). The functions and target genes of these miRNAs are emphasised in alcohol-associated liver disease, non-alcoholic fatty liver disease, drug-induced liver injury, viral hepatitis and hepatocellular carcinoma, as well liver fibrosis and liver failure. We touch on the roles of miRNAs in intercellular communication between hepatocytes and other types of cells via extracellular vesicles in the pathogenesis of liver diseases. We provide perspective on the application of miRNAs as biomarkers for early diagnosis, prognosis and assessment of liver diseases and discuss the challenges in miRNA-based therapy for liver diseases. Further investigation of miRNAs in the liver will help us better understand the pathogeneses of liver diseases and may identify biomarkers and therapeutic targets for liver diseases in the future.

MicroRNAs as regulators, biomarkers and therapeutic targets in liver diseases.

Programmed death-ligand 1 (PD-L1) on cancer cells engages with programmed cell death-1 (PD-1) on immune cells, contributing to cancer immune escape. For multiple cancer types, the PD-1/PD-L1 axis is the major speed-limiting step of the anti-cancer immune response. In this context, blocking PD-1/PD-L1 could restore T cells from exhausted status and eradicate cancer cells. However, only a subset of PD-L1 positive patients benefits from α-PD-1/PD-L1 therapies. Actually, PD-L1 expression is regulated by various factors, leading to the diverse significances of PD-L1 positivity. Understanding the mechanisms of PD-L1 regulation is helpful to select patients and enhance the treatment effect. In this review, we focused on PD-L1 regulators at the levels of transcription, post-transcription, post-translation. Besides, we discussed the potential applications of these laboratory findings in the clinic.

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Regulation of PD-L1 expression in the tumor microenvironment.

Endoplasmic Reticulum Stress Causes Liver Cancer Cells to Release Exosomal miR-23a-3p and Up-regulate Programmed Death Ligand 1 Expression in Macrophages.

BACKGROUND Long noncoding RNAs (lncRNAs) play important roles in cancer development and therapeutic resistance. However, the role of small nucleolar RNA host gene 16 (SNHG16) in the development of hepatocellular carcinoma (HCC) remains largely unknown. MATERIAL AND METHODS In situ hybridization (ISH) staining was performed to detect the expression level of SNHG16 in HCC tissues and adjacent non-cancerous tissues. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the level of SNHG16 in HCC samples, adjacent non-cancerous tissues and HCC cell lines. Transwell assay was performed to investigate the migration and invasion ability of HCC cells. Cell viability assays were performed to determine the ability of proliferation and sorafenib resistance of HCC cells. RESULTS We found that SNHG16 was upregulated in HCC tissues and cell lines and that it was negatively correlated with survival time in HCC patients. Univariate and multivariate analyses revealed that SNHG16 was a significant and independent predictor for the overall survival of HCC patients. Furthermore, downregulation of SNHG16 inhibited proliferation, migration, invasion, and sorafenib resistance in hepatocellular carcinoma cell lines. CONCLUSIONS Our findings revealed that lncRNA SNHG16 could be used as an oncogene to predict the outcome of hepatocellular carcinoma.

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Long Noncoding RNA (lncRNA) Small Nucleolar RNA Host Gene 16 (SNHG16) Predicts Poor Prognosis and Sorafenib Resistance in Hepatocellular Carcinoma.

Endoplasmic reticulum (ER) stress has been reported to be transmitted from tumor cells to immune cells via exosome and implicated in immune escape. However, the influence of ER stress on monocytes in chronic lymphocytic leukemia (CLL) cells is largely unknown. Here, we observed the expression of ER stress markers (GRP78, ATF6, PERK, IRE1a, and XBP1s) in CLL cells. The increasing mRNA expression of these ER stress response components was positively correlated with more aggressive disease. Exosome from ER stress inducer tunicamycin (TM)‐primed CLL cells (ERS‐exo) up‐regulated the expression of ER stress marker on monocytes, indicating ER stress is transmissible in vitro via exosome. Treatment with ERS‐exo promoted the survival of monocytes and induced phenotypic changes with a significantly larger percentage of CD14+CD16+monocytes. Finally, we identified exosome‐mediated transfer of extracellular nicotinamide phosphoribosyltransferase (eNAMPT) from ER stressed CLL cells into monocytes as a novel mechanism through which ERS‐exo regulated monocytes. Exosomal eNAMPT up‐regulated nicotinamide adenine dinucleotide (NAD+) production which subsequently activated SIRT1‐C/EBPβ signaling pathway in monocytes. Our results suggest the role of ER stress in mediating immunological dysfunction in CLL.

Ju Zhang

Papers

Endoplasmic Reticulum Stress Causes Liver Cancer Cells to Release Exosomal miR-23a-3p and Up-regulate Programmed Death Ligand 1 Expression in Macrophages.

Long Noncoding RNA (lncRNA) Small Nucleolar RNA Host Gene 16 (SNHG16) Predicts Poor Prognosis and Sorafenib Resistance in Hepatocellular Carcinoma.

Exosomal NAMPT from chronic lymphocytic leukemia cells orchestrate monocyte survival and phenotype under endoplasmic reticulum stress