RNA Binding Protein HuR Promotes Autophagosome Formation by Regulating Expression of Autophagy-Related Proteins 5, 12, and 16 in Human Hepatocellular Carcinoma Cells

VEGF and ELAVL1/HuR protein levels are increased in dry and wet AMD patients. A new tile in the pathophysiologic mechanisms underlying RPE degeneration?

Age-related macular degeneration (AMD) is a common retinal pathology characterized by degeneration of macula's retinal pigment epithelium (RPE) and photoreceptors, visual impairment, or loss. Compared to wet AMD, dry AMD is more common, but lacks cures; therefore, identification of new potential therapeutic targets and treatments is urgent. Increased oxidative stress and declining antioxidant, detoxifying systems contribute to the pathophysiologic mechanisms underlying AMD. The present work shows that the Embryonic Lethal Abnormal Vision-Like 1/Human antigen R (ELAVL1/HuR) and the Vascular Endothelial Growth Factor (VEGF) protein levels are higher in the RPE of both dry and wet AMD patients compared to healthy subjects. Moreover, increased HuR protein levels are detected in the retina, and especially in the RPE layer, of a dry AMD model, the nuclear factor erythroid 2-related factor 2 (Nrf2) / peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) double knock-out mouse. The crosstalk among Nrf2, HuR and VEGF has been also studied in ARPE-19 cells in basal and stressful conditions related to the AMD context (i.e., oxidative stress, autophagy impairment, Nrf2 deficit), offering new evidence of the mutual influence between Nrf2 and HuR, of the dependence of VEGF expression and secretion by these two factors, and of the increased susceptibility of cells to stressful conditions in Nrf2- or HuR-impaired contexts. Overall, this study shows evidence of the interplay among Nrf2, HuR and VEGF, essential factors for RPE homeostasis, and represents an additional piece in the understanding of the complex pathophysiologic mechanisms underlying AMD.

FUS-Mediated Inhibition of Myogenesis Elicited by Suppressing TNNT1 Production

Myogenesis is a highly orchestrated process whereby muscle precursor cells, myoblasts, develop into muscle fibers to form skeletal muscle during embryogenesis and regenerate adult muscle. Here, we studied the RNA-binding protein FUS (fused in sarcoma), which has been implicated in muscular and neuromuscular pathologies but is poorly characterized in myogenesis. Given that FUS levels declined in human and mouse models of skeletal myogenesis, and that silencing FUS enhanced myogenesis, we hypothesized that FUS might be a repressor of myogenic differentiation. Interestingly, overexpression of FUS delayed myogenesis, accompanied by slower production of muscle differentiation markers. To identify the mechanisms through which FUS inhibits myogenesis, we uncovered RNA targets of FUS by ribonucleoprotein immunoprecipitation (RIP) followed by RNA-sequencing (RNA-seq) analysis. Stringent selection of the bound transcripts uncovered Tnnt1 mRNA, encoding troponin T1 (TNNT1), as a major effector of FUS influence on myogenesis. We found that in myoblasts, FUS retained Tnnt1 mRNA in the nucleus, preventing TNNT1 expression; however, reduction of FUS during myogenesis or by silencing FUS released Tnnt1 mRNA for export to the cytoplasm, enabling TNNT1 translation and promoting myogenesis. We propose that FUS inhibits myogenesis by suppressing TNNT1 expression through a mechanism of nuclear Tnnt1 mRNA retention.

Pro-survival signaling regulates lipophagy essential for multiple myeloma resistance to stress-induced death

Pro-survival metabolic adaptations to stress in tumorigenesis remain less well defined. We find that multiple myeloma (MM) is unexpectedly dependent on beta-oxidation of long-chain fatty acids (FAs) for survival under both basal and stress conditions. However, under stress conditions, a second pro-survival signal is required to sustain FA oxidation (FAO). We previously found that CD28 is expressed on MM cells and transduces a significant pro-survival/chemotherapy resistance signal. We now find that CD28 signaling regulates autophagy/lipophagy that involves activation of the Ca2+→AMPK→ULK1 axis and regulates the translation of ATG5 through HuR, resulting in sustained lipophagy, increased FAO, and enhanced MM survival. Conversely, blocking autophagy/lipophagy sensitizes MM to chemotherapy in vivo. Our findings link a pro-survival signal to FA availability needed to sustain the FAO required for cancer cell survival under stress conditions and identify lipophagy as a therapeutic target to overcome treatment resistance in MM.

Cellular Senescence and Extracellular Vesicles in the Pathogenesis and Treatment of Obesity-A Narrative Review

This narrative review explores the pathophysiology of obesity, cellular senescence, and exosome release. When exposed to excessive nutrients, adipocytes develop mitochondrial dysfunction and generate reactive oxygen species with DNA damage. This triggers adipocyte hypertrophy and hypoxia, inhibition of adiponectin secretion and adipogenesis, increased endoplasmic reticulum stress and maladaptive unfolded protein response, metaflammation, and polarization of macrophages. Such feed-forward cycles are not resolved by antioxidant systems, heat shock response pathways, or DNA repair mechanisms, resulting in transmissible cellular senescence via autocrine, paracrine, and endocrine signaling. Senescence can thus affect preadipocytes, mature adipocytes, tissue macrophages and lymphocytes, hepatocytes, vascular endothelium, pancreatic β cells, myocytes, hypothalamic nuclei, and renal podocytes. The senescence-associated secretory phenotype is closely related to visceral adipose tissue expansion and metaflammation; inhibition of SIRT-1, adiponectin, and autophagy; and increased release of exosomes, exosomal micro-RNAs, pro-inflammatory adipokines, and saturated free fatty acids. The resulting hypernefemia, insulin resistance, and diminished fatty acid β-oxidation lead to lipotoxicity and progressive obesity, metabolic syndrome, and physical and cognitive functional decline. Weight cycling is related to continuing immunosenescence and exposure to palmitate. Cellular senescence, exosome release, and the transmissible senescence-associated secretory phenotype contribute to obesity and metabolic syndrome. Targeted therapies have interrelated and synergistic effects on cellular senescence, obesity, and premature aging.

The RNA-binding protein Msi2 regulates autophagy during myogenic differentiation

Skeletal muscle development is a highly ordered process orchestrated transcriptionally by the myogenic regulatory factors. However, the downstream molecular mechanisms of myogenic regulatory factor functions in myogenesis are not fully understood. Here, we identified the RNA-binding protein Musashi2 (Msi2) as a myogenin target gene and a post-transcriptional regulator of myoblast differentiation. Msi2 knockdown in murine myoblasts blocked differentiation without affecting the expression of MyoD or myogenin. Msi2 overexpression was also sufficient to promote myoblast differentiation and myocyte fusion. Msi2 loss attenuated autophagosome formation via down-regulation of the autophagic protein MAPL1LC3/ATG8 (LC3) at the early phase of myoblast differentiation. Moreover, forced activation of autophagy effectively suppressed the differentiation defects incurred by Msi2 loss. Consistent with its functions in myoblasts in vitro, mice deficient for Msi2 exhibited smaller limb skeletal muscles, poorer exercise performance, and muscle fiber-type switching in vivo. Collectively, our study demonstrates that Msi2 is a novel regulator of mammalian myogenesis and establishes a new functional link between muscular development and autophagy regulation.

Revealing the mechanism of Zanthoxylum armatum DC. extract-induced liver injury in mice based on lipidomics

ETHNOPHARMACOLOGICAL RELEVANCE

Zanthoxylum armatum DC. (Z. armatum) is an herbal medicine with various active ingredients and pharmacological effects. However, modern studies found that Z. armatum is hepatotoxic. The liver is the target organ for toxic effects and an important site for lipid metabolism. The effects of Z. armatum on lipid level and metabolism in the liver are still unclear.

AIM OF THE STUDY

This study aimed to analyze hepatic lipid levels, lipid metabolites and metabolic pathways of action of Z. armatum based on lipidomics, to investigate the potential hepatotoxic mechanism of Z. armatum.

MATERIALS AND METHODS

Different doses (62, 96, and 150 mg/kg) of the methanolic extract of Z. armatum (MZADC) were administered to ICR mice by gavage. The hepatotoxicity of MZADC was assessed by the liver index, serum biochemical measurements, and histopathological examination. Lipid levels measured by the serum lipid index were evaluated in the mice. Lipidomics was used to screen for differential lipid metabolism markers and lipid metabolism pathways in the liver. Western blot analysis was performed to investigate the effects of MZADC on the liver.

RESULTS

Liver index values and serum alanine transaminase and aspartate transaminase levels were increased in the MZADC group. Histopathology examination revealed hepatocyte necrosis, watery degeneration of the hepatocytes, and hepatic cord rupture in the livers of mice. Serum levels of low-density lipoprotein cholesterol, cholesterol, and triglycerides were elevated, and high-density lipoprotein cholesterol levels were decreased. Lipidomics screening for markers of differential lipid metabolism in the liver, and altered profiles of differential metabolites indicated that glycerophospholipid metabolism, linoleic acid metabolism, alpha-linolenic acid metabolism, glycosylphosphatidylinositol-anchored biosynthesis, sphingolipid metabolism and arachidonic acid metabolic pathways were significantly associated with MZADC-induced liver injury. Western blots confirmed that the protein expression of LC3, Beclin-1, ATG5, ATG12 and ATG16L1 was decreased, and p62 was increased in the MZADC group. The proportion of p-PI3K/PI3K and p-AKT/AKT was increased.

CONCLUSIONS

The liver injury induced by MZADC involved many different lipid metabolites and lipid metabolic pathways, which may be related to autophagy. This study provides a new perspective on the hepatotoxicity study of Z. armatum and provides a reference for the safe application of Z. armatum in the medicine and food fields.

The significance of long non-coding RNAs in the pathogenesis, diagnosis and treatment of inflammatory bowel disease

Inflammatory bowel diseases (IBD) are a group of chronic relapsing gastrointestinal inflammatory diseases with significant global incidence. Although the pathomechanism of IBD has been extensively investigated, several aspects of its pathogenesis remain unclear. Long non-coding RNAs (lncRNAs) are transcripts with more than 200 nucleotides in length that have potential protein-coding functions. LncRNAs play important roles in biological processes such as epigenetic modification, transcriptional regulation and post-transcriptional regulation. In this review, we summarize recent advances in research on IBD-related lncRNAs from the perspective of the overall intestinal microenvironment, as well as their potential roles as immune regulators, diagnostic biomarkers and therapeutic targets or agents for IBD.

Post-transcriptional dynamics and RNA homeostasis in autophagy and cancer

Autophagy is an essential recycling and quality control pathway which preserves cellular and organismal homeostasis. As a catabolic process, autophagy degrades damaged and aged intracellular components in response to conditions of stress, including nutrient deprivation, oxidative and genotoxic stress. Autophagy is a highly adaptive and dynamic process which requires an intricately coordinated molecular control. Here we provide an overview of how autophagy is regulated post-transcriptionally, through RNA processing events, epitranscriptomic modifications and non-coding RNAs. We further discuss newly revealed RNA-binding properties of core autophagy machinery proteins and review recent indications of autophagy's ability to impact cellular RNA homeostasis. From a physiological perspective, we examine the biological implications of these emerging regulatory layers of autophagy, particularly in the context of nutrient deprivation and tumorigenesis.

Regulation of autophagy gene expression and its implications in cancer

Autophagy is a catabolic cellular process that targets and eliminates superfluous cytoplasmic components via lysosomal degradation. This evolutionarily conserved process is tightly regulated at multiple levels as it is critical for the maintenance of homeostasis. Research in the past decade has established that dysregulation of autophagy plays a major role in various diseases, such as cancer and neurodegeneration. However, modulation of autophagy as a therapeutic strategy requires identification of key players that can fine tune the induction of autophagy without complete abrogation. In this Review, we summarize the recent discoveries on the mechanism of regulation of ATG (autophagy related) gene expression at the level of transcription, post transcription and translation. Furthermore, we briefly discuss the role of aberrant expression of ATG genes in the context of cancer.

Emerging mechanistic insights of selective autophagy in hepatic diseases

Macroautophagy (hereafter referred to as autophagy), a highly conserved metabolic process, regulates cellular homeostasis by degrading dysfunctional cytosolic constituents and invading pathogens via the lysosomal system. In addition, autophagy selectively recycles specific organelles such as damaged mitochondria (via mitophagy), and lipid droplets (LDs; via lipophagy) or eliminates specialized intracellular pathogenic microorganisms such as hepatitis B virus (HBV) and coronaviruses (via virophagy). Selective autophagy, particularly mitophagy, plays a key role in the preservation of healthy liver physiology, and its dysfunction is connected to the pathogenesis of a wide variety of liver diseases. For example, lipophagy has emerged as a defensive mechanism against chronic liver diseases. There is a prominent role for mitophagy and lipophagy in hepatic pathologies including non-alcoholic fatty liver disease (NAFLD), hepatocellular carcinoma (HCC), and drug-induced liver injury. Moreover, these selective autophagy pathways including virophagy are being investigated in the context of viral hepatitis and, more recently, the coronavirus disease 2019 (COVID-19)-associated hepatic pathologies. The interplay between diverse types of selective autophagy and its impact on liver diseases is briefly addressed. Thus, modulating selective autophagy (e.g., mitophagy) would seem to be effective in improving liver diseases. Considering the prominence of selective autophagy in liver physiology, this review summarizes the current understanding of the molecular mechanisms and functions of selective autophagy (mainly mitophagy and lipophagy) in liver physiology and pathophysiology. This may help in finding therapeutic interventions targeting hepatic diseases via manipulation of selective autophagy.

Upstream open reading frames mediate autophagy-related protein translation

Macroautophagy/autophagy, a highly conserved catabolic pathway that maintains proper cellular homeostasis is stringently regulated by numerous autophagy-related (Atg) proteins. Many studies have investigated autophagy regulation at the transcriptional level; however, relatively little is known about translational control. Here, we report the upstream open reading frame (uORF)-mediated translational control of multiple Atg proteins in Saccharomyces cerevisiae and in human cells. The translation of several essential autophagy regulators in yeast, including Atg13, is suppressed by canonical uORFs under nutrient-rich conditions, and is activated during nitrogen-starvation conditions. We also found that the predicted human ATG4B and ATG12 non-canonical uORFs suppress downstream coding sequence translation. These results demonstrate that uORF-mediated translational control is a widely used mechanism among ATG genes from yeast to human and suggest a model for how some ATG genes bypass the general translational suppression that occurs under stress conditions to maintain a proper level of autophagy.Abbreviations: 5' UTR, 5' untranslated region; Atg, autophagy-related; CDS, coding sequence; Cvt, cytoplasm-to-vacuole targeting; HBSS, Hanks' balanced salt solution; PA, protein A; PE, phosphati-dylethanolamine; PIC, preinitiation complex; PtdIns3K, phosphatidylinositol 3-kinase; qRT-PCR, quantitative reverse transcription PCR; Ubl, ubiquitin-like; uORF, upstream open reading frame; WT, wild-type.

Epidermal growth factor regulates autophagy activity and endocytosis of yak cumulus cells in a concentration-dependent manner

Introduction

Autophagy and endocytosis are crucial biological activities in mammalian follicle development and oocyte maturation, which are easily affected by external environmental factors. Epidermal growth factor (EGF), as an important component of follicular fluid, regulates the growth and apoptosis of follicular cells. However, its regulatory mechanism of autophagy and endocytosis in mammals, especially in large domestic animals such as plateau yak, remains unclear. This study aimed to investigate the regulatory mechanism of EGF on autophagy and endocytosis in yak cumulus cells.

Methods

Yak cumulus cells were treated with different concentrations of EGF and appropriate concentrations of EGFR inhibitor gefitinib (10 μM). The dynamic expression levels of Atg5, Beclin1, LC3, Cav1 and Cav2 were detected by immunofluorescence staining, qRT-PCR and Western-blot.

Results

EGF inhibited autophagy in yak cumulus cells by down-regulating the expression of Atg5, Beclin1, and LC3. The level of autophagy varied with the concentration of ligands, and the inhibition was most significant at 100 ng/mL. Noteworthy, EGF can promote endocytosis by regulating the expression of Cav1 and Cav2, but the EGFR-mediated signaling pathway is not the main way to regulate the expression of these proteins.

Discussion

These results provide a reference for further exploring the effects of growth factors on livestock germ cells and the regulatory role of autophagy-endocytosis crosstalk mechanism in follicle development and oocyte maturation, to improve the fecundity of yaks.

Hu Antigen R (HuR) Protein Structure, Function and Regulation in Hepatobiliary Tumors

Simple Summary

Hepatobiliary tumors are a group of primary malignancies encompassing the liver, the intra- and extra-hepatic biliary tracts, and the gall bladder. Within the liver, hepatocellular carcinoma (HCC) is the most common type of primary cancer, which is, also, representing the third-most recurrent cause of cancer-associated death and the sixth-most prevalent type of tumor worldwide, nowadays. Although less frequent, cholangiocarcinoma (CCA) is, currently, a fatal cancer with limited therapeutic options. Here, we review the regulatory role of Hu antigen R (HuR), a ubiquitous member of the ELAV/Hu family of RNA-binding proteins (RBPs), in the pathogenesis, progression, and treatment of HCC and CCA. Overall, HuR is proposed as a valuable diagnostic and prognostic marker, as well as a therapeutic target in hepatobiliary cancers. Therefore, novel therapeutic approaches that can selectively modulate HuR function appear to be highly attractive for the clinical management of these types of tumors.

Abstract

Hu antigen R (HuR) is a 36-kDa ubiquitous member of the ELAV/Hu family of RNA-binding proteins (RBPs), which plays an important role as a post-transcriptional regulator of specific RNAs under physiological and pathological conditions, including cancer. Herein, we review HuR protein structure, function, and its regulation, as well as its implications in the pathogenesis, progression, and treatment of hepatobiliary cancers. In particular, we focus on hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), tumors where the increased cytoplasmic localization of HuR and activity are proposed, as valuable diagnostic and prognostic markers. An overview of the main regulatory axes involving HuR, which are associated with cell proliferation, invasion, metastasis, apoptosis, and autophagy in HCC, is provided. These include the transcriptional, post-transcriptional, and post-translational modulators of HuR function, in addition to HuR target transcripts. Finally, whereas studies addressing the relevance of targeting HuR in CCA are limited, in the past few years, HuR has emerged as a potential therapeutic target in HCC. In fact, the therapeutic efficacy of some pharmacological inhibitors of HuR has been evaluated, in early experimental models of HCC. We, further, discuss the major findings and future perspectives of therapeutic approaches that specifically block HuR interactions, either with post-translational modifiers or cognate transcripts in hepatobiliary cancers.

ULK1 Signaling in the Liver: Autophagy Dependent and Independent Actions

Liver is the primary organ for energy metabolism and detoxification in the human body. Not surprisingly, a derangement in liver function leads to several metabolic diseases. Autophagy is a cellular process, which primarily deals with providing molecules for energy production, and maintains cellular health. Autophagy in the liver has been implicated in several hepatic metabolic processes, such as, lipolysis, glycogenolysis, and gluconeogenesis. Autophagy also provides protection against drugs and pathogens. Deregulation of autophagy is associated with the development of non-alcoholic fatty liver disease (NAFLD) acute-liver injury, and cancer. The process of autophagy is synchronized by the action of autophagy family genes or autophagy (Atg) genes that perform key functions at different steps. The uncoordinated-51-like kinases 1 (ULK1) is a proximal kinase member of the Atg family that plays a crucial role in autophagy. Interestingly, ULK1 actions on hepatic cells may also involve some autophagy-independent signaling. In this review, we provide a comprehensive update of ULK1 mediated hepatic action involving lipotoxicity, acute liver injury, cholesterol synthesis, and hepatocellular carcinoma, including both its autophagic and non-autophagic functions.

Circular RNA HECTD1 Mitigates Ulcerative Colitis by Promoting Enterocyte Autophagy Via miR-182-5p/HuR Axis

OBJECTIVE

Ulcerative colitis (UC) is a chronic colitis with unknown etiology. Circular RNA (circRNA) has shown regulatory effect in many diseases, but the role of circRNA in UC is barely known. This study uncovers the function and regulatory mechanism of circRNA HECTD1 (circHECTD1) in UC.

METHODS

Colonic mucosal tissues of 60 patients with active UC and 30 healthy controls were collected for H&E staining. Lipopolysaccharide (LPS) and dextran sulfate sodium (DSS) were used to induce inflammation and UC in Caco-2 cells and C57BL/6 mice where modification of circHECTD1, miR-182-5p and/or human antigen R (HuR) took place. The Caco-2 cells and the colon tissues of DSS-treated mice were collected for analysis of the expression levels of inflammatory cytokines, NLRP3 inflammasome, and autophagy-related proteins. The interactions among circHECTD1, miR-182-5p, and HuR were verified.

RESULTS

The colonic mucosal tissues of UC patients showed impaired autophagy and decreased expressions of circHECTD1 and HuR. Overexpression of circHECTD1 or HuR or inhibition of miR-182-5p suppressed inflammation and promoted autophagy of LPS-induced Caco-2 cells. The expression of HuR was promoted by circHECTD1 via miR-182-5p in Caco-2 cells. Overexpression of circHECTD1 reduced colonic injuries and inflammation by promoting autophagy in DSS-treated mice.

CONCLUSION

Overexpression of circHECTD1 alleviates UC by promoting HuR-dependent autophagy via miR-182-5p. This study highlights the therapeutic potential of circHECTD1 for UC and adds to the knowledge of circRNA in the pathogenesis of UC.

CCAT2 enhances autophagy-related invasion and metastasis via regulating miR-4496 and ELAVL1 in hepatocellular carcinoma

Autophagy is thought to contribute to the pathogenesis of many diseases, including cancer. Long non‐coding RNA (lncRNA) CCAT2 functions as an oncogene in a variety of tumours. However, it is still unknown whether CCAT2 is involved in autophagy and metastasis of hepatocellular carcinoma (HCC). In our study, we found that lncRNA CCAT2 expression was significantly increased in HCC tissue and was correlated with advanced stage and venous invasion. Further experiments revealed that CCAT2 induced autophagy and promoted migration and invasion in vitro and in vivo. Mechanistic investigations found that CCAT2 involved in HCC by regulating miR‐4496/Atg5 in cytoplasm. In nucleus, CCAT2 bound with ELAVL1/HuR to facilitate HCC progression. Our findings suggest that CCAT2 is an oncogenic factor in the progression of HCC with different regulatory mechanisms and may serve as a target for HCC therapy.

Differential regulation of autophagy by STAU1 in alveolar rhabdomyosarcoma and non-transformed skeletal muscle cells

PURPOSE

Recent work has highlighted the therapeutic potential of targeting autophagy to modulate cell survival in a variety of diseases including cancer. Recently, we found that the RNA-binding protein Staufen1 (STAU1) is highly expressed in alveolar rhabdomyosarcoma (ARMS) and that this abnormal expression promotes tumorigenesis. Here, we asked whether STAU1 is involved in the regulation of autophagy in ARMS cells.

METHODS

We assessed the impact of STAU1 expression modulation in ARMS cell lines (RH30 and RH41), non-transformed skeletal muscle cells (C2C12) and STAU1-transgenic mice using complementary techniques.

RESULTS

We found that STAU1 silencing reduces autophagy in the ARMS cell lines RH30 and RH41, while increasing their apoptosis. Mechanistically, this inhibitory effect was found to be caused by a direct negative impact of STAU1 depletion on the stability of Beclin-1 (BECN1) and ATG16L1 mRNAs, as well as by an indirect inhibition of JNK signaling via increased expression of Dual specificity phosphatase 8 (DUSP8). Pharmacological activation of JNK or expression silencing of DUSP8 was sufficient to restore autophagy in STAU1-depleted cells. By contrast, we found that STAU1 downregulation in non-transformed skeletal muscle cells activates autophagy in a mTOR-dependent manner, without promoting apoptosis. A similar effect was observed in skeletal muscles obtained from STAU1-overexpressing transgenic mice.

CONCLUSIONS

Together, our data indicate an effect of STAU1 on autophagy regulation in ARMS cells and its differential role in non-transformed skeletal muscle cells. Our findings suggest a cancer-specific potential of targeting STAU1 for the treatment of ARMS.

Emerging Roles of Impaired Autophagy in Fatty Liver Disease and Hepatocellular Carcinoma

Autophagy is a conserved catabolic process that eliminates dysfunctional cytosolic biomolecules through vacuole-mediated sequestration and lysosomal degradation. Although the molecular mechanisms that regulate autophagy are not fully understood, recent work indicates that dysfunctional/impaired autophagic functions are associated with the development and progression of nonalcoholic fatty liver disease (NAFLD), alcoholic fatty liver disease (AFLD), and hepatocellular carcinoma (HCC). Autophagy prevents NAFLD and AFLD progression through enhanced lipid catabolism and decreasing hepatic steatosis, which is characterized by the accumulation of triglycerides and increased inflammation. However, as both diseases progress, autophagy can become impaired leading to exacerbation of both pathological conditions and progression into HCC. Due to the significance of impaired autophagy in these diseases, there is increased interest in studying pathways and targets involved in maintaining efficient autophagic functions as potential therapeutic targets. In this review, we summarize how impaired autophagy affects liver function and contributes to NAFLD, AFLD, and HCC progression. We will also explore how recent discoveries could provide novel therapeutic opportunities to effectively treat these diseases.

RNA-binding proteins and long noncoding RNAs in intestinal epithelial autophagy and barrier function

The intestinal autophagy and barrier function are crucial for maintaining the epithelium homeostasis and tightly regulated through well-controlled mechanisms. RNA-binding proteins (RBPs) and long noncoding RNAs (lncRNAs) modulate gene expression at the posttranscription level and are intimately involved in different physiological processes and diverse human diseases. In this review, we first highlight the roles of several RBPs and lncRNAs in the regulation of intestinal epithelial autophagy and barrier function, particularly focusing on the emerging evidence of RBPs and lncRNAs in the control of mRNA stability and translation. We additionally discuss recent findings that the interactions between RBPs and lncRNAs alter the fate of their target transcripts and thus influence gut epithelium host defense in response to stressful environments. These exciting advances in understanding the posttranscriptional control of the epithelial autophagy and barrier function by RBPs and lncRNAs provide a strong rationale for developing new effective therapeutics based on targeting RBPs and/or lncRNAs to preserve the intestinal epithelial integrity in patients with critical illnesses.

HuR Protein in Hepatocellular Carcinoma: Implications in Development, Prognosis and Treatment

Hu-antigen R (HuR) is a post-transcriptional regulator that belongs to the embryonic lethal abnormal vision Drosophila-like family (ELAV). HuR regulates the stability, translation, subcellular localization, and degradation of several target mRNAs, which are implicated in carcinogenesis and could affect therapeutic options. HuR protein is consistently highly expressed in hepatocellular carcinoma (HCC) compared to the adjacent normal liver tissue and is involved in the post-transcriptional regulation of various genes implicated in liver malignant transformation. Additionally, HuR protein seems to be a putative prognosticator in HCC, predicting worse survival. This review summarizes the recent evidence regarding the role of HuR in primary liver tumors, as presented in clinical studies, in vitro experiments and in vivo animal models. In conclusion, our review supports the consistent role of HuR protein in the development, prognosis, and treatment of HCC. Additional studies are expected to expand current information and exploit its putative employment as a future candidate for more personalized treatment in these tumors.

The multifunctional RNA-binding protein Staufen1: an emerging regulator of oncogenesis through its various roles in key cellular events

The double-stranded multifunctional RNA-binding protein (dsRBP) Staufen was initially discovered in insects as a regulator of mRNA localization. Later, its mammalian orthologs have been described in different organisms, including humans. Two human orthologues of Staufen, named Staufen1 (STAU1) and Staufen2 (STAU2), share some structural and functional similarities. However, given their different spatio-temporal expression patterns, each of these orthologues plays distinct roles in cells. In the current review, we focus on the role of STAU1 in cell functions and cancer development. Since its discovery, STAU1 has mostly been studied for its involvement in various aspects of RNA metabolism. Given the pivotal role of RNA metabolism within cells, recent studies have explored the mechanistic impact of STAU1 in a wide variety of cell functions ranging from cell growth to cell death, as well as in various disease states. In particular, there has been increasing attention on the role of STAU1 in neuromuscular disorders, neurodegeneration, and cancer. Here, we provide an overview of the current knowledge on the role of STAU1 in RNA metabolism and cell functions. We also highlight the link between STAU1-mediated control of cellular functions and cancer development, progression, and treatment. Hence, our review emphasizes the potential of STAU1 as a novel biomarker and therapeutic target for cancer diagnosis and treatment, respectively.

ELAVL1 Role in Cell Fusion and Tunneling Membrane Nanotube Formations with Implication to Treat Glioma Heterogeneity

Homotypic and heterotypic cell fusions via permanent membrane fusions and temporal tunneling nanotube formations in the glioma microenvironment were recently documented in vitro and in vivo and mediate glioma survival, plasticity, and recurrence. Chronic inflammation, a hypoxic environment, aberrant mitochondrial function, and ER stress due to unfolded protein accumulation upregulate cell fusion events, which leads to tumor heterogeneity and represents an adaptive mechanism to promote tumor cell survival and plasticity in cytotoxic, nutrient-deprived, mechanically stressed, and inflammatory microenvironments. Cell fusion is a multistep process, which consists of the activation of the cellular stress response, autophagy formation, rearrangement of cytoskeletal architecture in the areas of cell-to-cell contacts, and the expression of proinflammatory cytokines and fusogenic proteins. The mRNA-binding protein of ELAV-family HuR is a critical node, which orchestrates the stress response, autophagy formation, cytoskeletal architecture, and the expression of proinflammatory cytokines and fusogenic proteins. HuR is overexpressed in gliomas and is associated with poor prognosis and treatment resistance. Our review provides a link between the HuR role in the regulation of cell fusion and tunneling nanotube formations in the glioma microenvironment and the potential suppression of these processes by different classes of HuR inhibitors.

mRNA Post-Transcriptional Regulation by AU-Rich Element-Binding Proteins in Liver Inflammation and Cancer

AU-rich element-binding proteins (AUBPs) represent important post-transcriptional regulators of gene expression. AUBPs can bind to the AU-rich elements present in the 3'-UTR of more than 8% of all mRNAs and are thereby able to control the stability and/or translation of numerous target mRNAs. The regulation of the stability and the translation of mRNA transcripts by AUBPs are highly complex processes that occur through multiple mechanisms depending on the cell type and the cellular context. While AUBPs have been shown to be involved in inflammatory processes and the development of various cancers, their important role and function in the development of chronic metabolic and inflammatory fatty liver diseases (FLDs), as well as in the progression of these disorders toward cancers such as hepatocellular carcinoma (HCC), has recently started to emerge. Alterations of either the expression or activity of AUBPs are indeed significantly associated with FLDs and HCC, and accumulating evidence indicates that several AUBPs are deeply involved in a significant number of cellular processes governing hepatic metabolic disorders, inflammation, fibrosis, and carcinogenesis. Herein, we discuss our current knowledge of the roles and functions of AUBPs in liver diseases and cancer. The relevance of AUBPs as potential biomarkers for different stages of FLD and HCC, or as therapeutic targets for these diseases, are also highlighted.

Human Antigen R (HuR): A Regulator of Heme Oxygenase-1 Cytoprotection in Mouse and Human Liver Transplant Injury

BACKGROUND AND AIMS

Ischemia-reperfusion injury (IRI) represents a risk factor in liver transplantation (LT). We have shown that overexpression of heme oxygenase-1 (HO-1) mitigates hepatic IRI in LT recipients. Here, we hypothesized that human antigen R (HuR), the stabilizer of adenylate-uridylate (AU)-rich mRNAs, is required for hepatoprotection in LT.

APPROACH AND RESULTS

In an experimental arm, HuR/HO-1 protein expression was correlated with hepatic IRI phenotype. In an in vitro inflammation mimic model of hepatic warm IRI, induction of HuR/HO-1 and cytoplasmic localization following cytokine preconditioning were detected in primary hepatocyte cultures, whereas HuR silencing caused negative regulation of HO-1, followed by enhanced cytotoxicity. Using the HuR-inhibitor, we showed that HuR likely regulates HO-1 through its 3' untranslated region and causes neutrophil activation (CD69+/lymphocyte antigen 6 complex locus G [Ly6-G]). HuR silencing in bone marrow-derived macrophages decreased HO-1 expression, leading to the induction of proinflammatory cytokines/chemokines. RNA sequencing of HuR silenced transcripts under in vitro warm IRI revealed regulation of genes thymus cell antigen 1 (THY1), aconitate decarboxylase 1 (ACOD1), and Prostaglandin E Synthase (PTGES). HuR, but not hypoxia-inducible protein alpha, positively regulated HO-1 in warm, but not cold, hypoxia/reoxygenation conditions. HuR modulated HO-1 in primary hepatocytes, neutrophils, and macrophages under reperfusion. Adjunctive inhibition of HuR diminished microtubule-associated proteins 1A/1B light chain 3B (LC3B), a marker for autophagosome, under HO-1 regulation, suggesting a cytoprotective mechanism in hepatic IR. In a clinical arm, hepatic biopsies from 51 patients with LT were analyzed at 2 hours after reperfusion. Graft HuR expression was negatively correlated with macrophage (CD80/CD86) and neutrophil (Cathepsin G) markers. Hepatic IRI increased HuR/HO-1 expression and inflammatory genes. High HuR-expressing liver grafts showed lower serum alanine aminotransferase/serum aspartate aminotransferase levels and improved LT survival.

CONCLUSIONS

This translational study identifies HuR as a regulator of HO-1-mediated cytoprotection in sterile liver inflammation and a biomarker of ischemic stress resistance in LT.

Identification of an autophagy-related gene signature that can improve prognosis of hepatocellular carcinoma patients

Background

Autophagy is a programmed cell degradation mechanism that has been associated with several physiological and pathophysiological processes, including malignancy. Improper induction of autophagy has been proposed to play a pivotal role in the progression of hepatocellular carcinoma (HCC).

Methods

Univariate Cox regression analysis of overall survival (OS) was performed to identify risk-associated autophagy-related genes (ARGs) in HCC data set from The Cancer Genome Atlas (TCGA). Multivariate cox regression was then performed to develop a risk prediction model for the prognosis of 370 HCC patients. The multi-target receiver operating characteristic (ROC) curve was used to determine the model’s accuracy. Besides, the relationship between drug sensitivity and ARGs expression was also examined.

Results

A total of 62 differentially expressed ARGs were identified in HCC patients. Univariate and multivariate regression identified five risk-associated ARGs (HDAC1, RHEB, ATIC, SPNS1 and SQSTM1) that were correlated with OS in HCC patients. Of importance, the risk-associated ARGs were independent risk factors in the multivariate risk model including clinical parameters such as malignant stage (HR = 1.433, 95% CI = 1.293–1.589, P < 0.001). In addition, the area under curve for the prognostic risk model was 0.747, which indicates the high accuracy of the model in prediction of HCC outcomes. Interestingly, the risk-associated ARGs were also correlated with drug sensitivity in HCC cell lines.

Conclusion

We developed a novel prognostic risk model by integrating the molecular signature and clinical parameters of HCC, which can effectively predict the outcomes of HCC patients.

Role of long noncoding RNA-mediated competing endogenous RNA regulatory network in hepatocellular carcinoma

Long noncoding RNAs (lncRNAs) and microRNAs (miRNAs) are noncoding RNAs (ncRNAs) that occupy over 90% of the human genome, and their main function is to directly or indirectly regulate messenger RNA (mRNA) expression and participate in the tumorigenesis and progression of malignances. In particular, some lncRNAs can interact with miRNAs as competing endogenous RNAs (ceRNAs) to modulate mRNA expression. Accordingly, these RNA molecules are interrelated and coordinate to form a dynamic lncRNA-mediated ceRNA regulatory network. Mounting evidence has revealed that lncRNAs that act as ceRNAs are closely related to tumorigenesis. To date, numerous studies have established many different regulatory networks in hepatocellular carcinoma (HCC), and perturbations in these ceRNA interactions may result in the initiation and progression of HCC. Herein, we emphasize recent advances concerning the biological function of lncRNAs as ceRNAs in HCC, with the aim of elucidating the molecular mechanism underlying these HCC-related RNA molecules and providing novel insights into the diagnosis and treatment of HCC.

The RNA-binding protein, HuD regulates proglucagon biosynthesis in pancreatic α cells

Glucagon is a peptide hormone generated by pancreatic α cells. It is the counterpart of insulin and plays an essential role in the regulation of blood glucose level. Therefore, a tight regulation of glucagon levels is pivotal to maintain homeostasis of blood glucose. However, little is known about the mechanisms regulating glucagon biosynthesis. In this study, we demonstrate that the RNA-binding protein HuD regulates glucagon expression in pancreatic α cells. HuD was found in α cells from mouse pancreatic islet and mouse glucagonoma αTC1 cell line. Ribonucleoprotein immunoprecipitation analysis, followed by RT-qPCR showed the association of HuD with glucagon mRNA. Knockdown of HuD resulted in a reduction in both proglucagon expression and cellular glucagon level by decreasing its de novo synthesis. Reporter analysis using the EGFP reporter containing 3' untranslated region (3'UTR) of glucagon mRNA showed that HuD regulates proglucagon expression via its 3'UTR. In addition, the relative level of glucagon in the islets and plasma was lower in HuD knockout (KO) mice compared to age-matched control mice. Taken together, these results suggest that HuD is a novel factor regulating the biosynthesis of proglucagon in pancreatic α cells.

Modulation of the Autophagy-lysosomal Pathway in Hepatocellular Carcinoma Using Small Molecules

Hepatocellular carcinoma (HCC) accounts for approximately 90% of all cases of primary liver cancer; it is the third most frequent cause of cancer-related death worldwide. In early-stage disease, surgical resection and liver transplantation are considered curative treatments. However, the majority of HCC patients present with advanced-stage disease that is treated using palliative systemic therapy. Since HCC is heterogeneous owing to its multiple etiologies, various risk factors, and inherent resistance to chemotherapy, the development of an effective systemic treatment strategy for HCC remains a considerable challenge. Autophagy is a lysosome-dependent catabolic degradation pathway that is essential for maintaining cellular energy homeostasis. Autophagy dysfunction is closely linked with the pathogenesis of various cancers; therefore, the discovery of small molecules that can modulate autophagy has attracted considerable interest in the development of a systemic treatment strategy for advanced HCC. Here, we reviewed the roles of autophagy in HCC and the recent advances regarding small molecules that target autophagy regulatory mechanisms.

Autophagy Regulation by the Translation Machinery and Its Implications in Cancer

Various metabolic pathways and molecular processes in the cell act intertwined, and dysregulating the interplay between some of them may lead to cancer. It is only recently that defects in the translation process, i.e., the synthesis of proteins by the ribosome using a messenger (m)RNA as a template and translation factors, have begun to gain strong attention as a cause of autophagy dysregulation with effects in different maladies, including cancer. Autophagy is an evolutionarily conserved catabolic process that degrades cytoplasmic elements in lysosomes. It maintains cellular homeostasis and preserves cell viability under various stress conditions, which is crucial for all eukaryotic cells. In this review, we discuss recent advances shedding light on the crosstalk between the translation and the autophagy machineries and its impact on tumorigenesis. We also summarize how this interaction is being the target for novel therapies to treat cancer.

Interaction between HuR and circPABPN1 Modulates Autophagy in the Intestinal Epithelium by Altering ATG16L1 Translation

Intestinal epithelial autophagy is crucial for host defense against invasive pathogens, and defects in this process occur frequently in patients with inflammatory bowel disease (IBD) and other mucosal disorders, but the exact mechanism that activates autophagy is poorly defined. Here, we investigated the role of RNA-binding protein HuR (human antigen R) in the posttranscriptional control of autophagy-related genes (ATGs) in the intestinal epithelium. We found that targeted deletion of HuR in intestinal epithelial cells (IECs) specifically decreased the levels of ATG16L1 in the intestinal mucosa. Intestinal mucosa from patients with IBD exhibited reduced levels of both HuR and ATG16L1. HuR directly interacted with Atg16l1 mRNA via its 3' untranslated region and enhanced ATG16L1 translation, without affecting Atg16l1 mRNA stability. Circular RNA circPABPN1 blocked HuR binding to Atg16l1 mRNA and lowered ATG16L1 production. HuR silencing in cultured IECs also prevented rapamycin-induced autophagy, which was abolished by overexpressing ATG16L1. These findings indicate that HuR regulates autophagy by modulating ATG16L1 translation via interaction with circPABPN1 in the intestinal epithelium.

Human antigen R: A potential therapeutic target for liver diseases

Human antigen R (HuR), also known as HuA and embryonic lethal abnormal vision-like 1 (ELAVL1), is a ubiquitously expressed RNA binding protein and functions as an RNA regulator and mediates the expression of various proteins by diverse post-transcriptional mechanisms. HuR has been well characterized in the inflammatory responses and in the development of various cancers. The importance of HuR-mediated roles in cell signaling, inflammation, fibrogenesis and cancer development in the liver has attracted a great deal of attention. However, there is still a substantial gap between the current understanding of the potential roles of HuR in the progression of liver disease and whether HuR can be targeted for the treatment of liver diseases. In this review, we introduce the function and mechanistic characterization of HuR, and then focus on the physiopathological roles of HuR in the development of different liver diseases, including hepatic inflammation, alcoholic liver diseases, non-alcoholic fatty liver diseases, viral hepatitis, liver fibrosis and liver cancers. We also summarize existing approaches targeting HuR function. In conclusion, although characterizing the liver-specific HuR function and demonstrating the multi-level regulative networks of HuR in the liver are still required, emerging evidence supports the notion that HuR represents a potential therapeutic target for the treatment of chronic liver diseases.

Psp2, a novel regulator of autophagy that promotes autophagy-related protein translation

Macroautophagy/autophagy defines an evolutionarily conserved catabolic process that targets cytoplasmic components for lysosomal degradation. The process of autophagy from initiation to closure is tightly executed and controlled by the concerted action of autophagy-related (Atg) proteins. Although substantial progress has been made in characterizing transcriptional and post-translational regulation of ATG/Atg genes/proteins, little is known about the translational control of autophagy. Here we report that Psp2, an RGG motif protein, positively regulates autophagy through promoting the translation of Atg1 and Atg13, two proteins that are crucial in the initiation of autophagy. During nitrogen starvation conditions, Psp2 interacts with the 5' UTR of ATG1 and ATG13 transcripts in an RGG motif-dependent manner and with eIF4E and eIF4G2, components of the translation initiation machinery, to regulate the translation of these transcripts. Deletion of the PSP2 gene leads to a decrease in the synthesis of Atg1 and Atg13, which correlates with reduced autophagy activity and cell survival. Furthermore, deactivation of the methyltransferase Hmt1 constitutes a molecular switch that regulates Psp2 arginine methylation status as well as its mRNA binding activity in response to starvation. These results reveal a novel mechanism by which Atg proteins become upregulated to fulfill the increased demands of autophagy activity as part of translational reprogramming during stress conditions, and help explain how ATG genes bypass the general block in protein translation that occurs during starvation.

UBL4A inhibits autophagy-mediated proliferation and metastasis of pancreatic ductal adenocarcinoma via targeting LAMP1

BACKGROUND

Ubiquitin-like protein 4A (UBL4A) plays a significant role in protein metabolism and the maintenance of cellular homeostasis. In cancer, UBL4A represses tumorigenesis and is involved in various signaling pathways. Pancreatic ductal adenocarcinoma (PDAC) is still a major cause of cancer-related death and the underlying molecular mechanism of UBL4A and PDAC remains unknown.

METHODS

First, the prognostic role of UBL4A and its expression in human PDAC patients and in pancreatic cancer cell lines were detected by survival analysis and qRT-PCR, western blotting, and immunohistochemistry. Next, the effects of UBL4A on proliferation and metastasis in pancreatic cancer were evaluated by functional assays in vitro and in vivo. In addition, chloroquine was introduced to determine the role of autophagy in UBL4A-related tumor proliferation and metastasis. Ultimately, coimmunoprecipitation was used to confirm the interaction between UBL4A and lysosome associated membrane protein-1 (LAMP1), and western blotting was performed to explore the UBL4A mechanism.

RESULTS

We found that UBL4A was decreased in PDAC and that high levels of UBL4A correlated with a favorable prognosis. We observed that UBL4A inhibited tumor proliferation and metastasis through suppression of autophagy, a critical intracellular catabolic process that reportedly protects cells from nutrient starvation and other stress conditions. UBL4A caused impaired autophagic degradation in vitro, a crucial process in autophagy, by disturbing the function of lysosomes and contributing to autophagosome accumulation. We found a positive correlation between UBL4A and LAMP1. Furthermore, UBL4A caused lysosomal dysfunction by directly interacting with LAMP1, and LAMP1 overexpression reversed the antitumor effects of UBL4A in pancreatic cancer. In addition, we demonstrated that UBL4A suppressed tumor growth and metastasis in a pancreatic orthotopic tumor model.

CONCLUSIONS

These findings suggest that UBL4A exerts an antitumor effect on autophagy-related proliferation and metastasis in PDAC by directly targeting LAMP1. Herein, we describe a novel mechanism of UBL4A that suppresses the progression of pancreatic cancer. UBL4A might be a promising target for the treatment and prognostication of PDAC.

New insights into autophagy in hepatocellular carcinoma: mechanisms and therapeutic strategies

Autophagy is a mechanism by which cellular substances are transported to lysosomes for degradation, allowing the basic transformation of cellular components, and providing energy and macromolecular precursors. In cancer, the contradictory role of autophagy in tumor suppression and promotion has been widely acknowledged. Activation and suppression of autophagy have been proposed as cancer therapies, resulting in targeted treatment of cancer by autophagy being considered ambiguous. The dynamic effect of autophagy can also be applied to hepatocellular carcinoma (HCC), a malignant tumor with high incidence and a low survival rate. In this review, we introduce characteristics of different types of autophagy and summarize which genes, non-coding RNAs, and related signaling pathways are involved in autophagy and the regulation of the formation and progress of HCC. More importantly, we discuss the role of autophagy in the treatment of HCC, such as in traditional chemotherapy, molecular targeted drugs, and natural products.