FBXW7-Induced MTOR Degradation Forces Autophagy to Counteract Persistent Prion Infection

Xiaojianzhong decoction prevents gastric precancerous lesions in rats by inhibiting autophagy and glycolysis in gastric mucosal cells

BACKGROUND

Gastric precancerous lesions (GPL) precede the development of gastric cancer (GC). They are characterized by gastric mucosal intestinal metaplasia and dysplasia caused by various factors such as inflammation, bacterial infection, and injury. Abnormalities in autophagy and glycolysis affect GPL progression, and their effective regulation can aid in GPL treatment and GC prevention. Xiaojianzhong decoction (XJZ) is a classic compound for the treatment of digestive system diseases in ancient China which can inhibit the progression of GPL. However, its specific mechanism of action is still unclear.

AIM

To investigate the therapeutic effects of XJZ decoction on a rat GPL model and the mechanisms underlying its effects on autophagy and glycolysis regulation in GPLs.

METHODS

Wistar rats were randomly divided into six groups of five rats each and all groups except the control group were subjected to GPL model construction for 18 wk. The rats’ body weight was monitored every 2 wk starting from the beginning of modeling. Gastric histopathology was examined using hematoxylin-eosin staining and Alcian blue-periodic acid-Schiff staining. Autophagy was observed using transmission electron microscopy. The expressions of autophagy, hypoxia, and glycolysis related proteins in gastric mucosa were detected using immunohistochemistry and immunofluorescence. The expressions of the following proteins in gastric tissues: B cell lymphoma/Leukemia-2 and adenovirus E1B19000 interacting protein 3 (Bnip-3), microtubule associated protein 1 light chain 3 (LC-3), moesin-like BCL2-interacting protein 1 (Beclin-1), phosphatidylinositol 3-kimase (PI3K), protein kinase B (AKT), mammalian target of rapamycin (mTOR), p53, AMP-activated protein kinase (AMPK), and Unc-51 like kinase 1 (ULK1) were detected using western blot. The relative expressions of autophagy, hypoxia, and glycolysis related mRNA in gastric tissues was detected using reverse transcription-polymerase chain reaction.

RESULTS

Treatment with XJZ increased the rats’ body weight and improved GPL-related histopathological manifestations. It also decreased autophagosome and autolysosome formation in gastric tissues and reduced Bnip-3, Beclin-1, and LC-3II expressions, resulting in inhibition of autophagy. Moreover, XJZ down-regulated glycolysis-related monocarboxylate transporter (MCT1), MCT4, and CD147 expressions. XJZ prevented the increase of autophagy level by decreasing gastric mucosal hypoxia, activating the PI3K/AKT/mTOR pathway, inhibiting the p53/AMPK pathway activation and ULK1 Ser-317 and Ser-555 phosphorylation. In addition, XJZ improved abnormal gastric mucosal glucose metabolism by ameliorating gastric mucosal hypoxia and inhibiting ULK1 expression.

CONCLUSION

This study demonstrates that XJZ may inhibit autophagy and glycolysis in GPL gastric mucosal cells by improving gastric mucosal hypoxia and regulating PI3K/AKT/mTOR and p53/ AMPK/ULK1 signaling pathways, providing a feasible strategy for the GPL treatment.

Activation of Innate Immunity and Autophagy in Brain Tissues with Prion Disease and Degradation of Abnormal PrPs in Cells - China's Studies

Unlike infectious diseases caused by conventional microbes, there are no detectable specific humoral or cellular immunoresponses to prion infection. However, extensive and active gliosis is observable in affected brain regions along with significant deposits of scrapie-like prion protein (PrP^Sc). Here, we summarize our studies of vibrant activation of host non-specific immune components and autophagy in the microenvironment of prion infected brains. Activation of the brain's innate immunity and autophagy upon prion infection reflect non-specific host defense systems attempt to dispose of accumulated prions. Vibrant elevation of neuroinflammation leads to neuron injury.

E3 Ligase FBXW7 Facilitates Mycobacterium Immune Evasion by Modulating TNF-α Expression

Tumor necrosis factor alpha (TNF-α) is a crucial factor in the control of Mycobacterium tuberculosis (Mtb) infection. Pathogenic mycobacteria can inhibit and/or regulate host cell TNF-α production in a variety of ways to evade antituberculosis (anti-TB) immunity as well as facilitate immune escape. However, the mechanisms by which TNF-α expression in host cells is modulated to the benefit of mycobacteria is still an interesting topic and needs further study. Here, we report that macrophages infected with Mycobacterium marinum (Mm)—a close relative of Mtb—upregulated the expression of E3 ubiquitin ligase FBXW7. Specific silencing FBXW7 with small interfering RNA (siRNA) significantly elevates TNF-α expression and eventually promotes the elimination of intracellular bacteria. In turn, overexpression of FBXW7 in Raw264.7 macrophages markedly decreased TNF-α production. Furthermore, partial inhibition of FBXW7 in an Mm-infected murine model significantly reduced TNF-α tissue content, alleviated tissue damage as well as reduced the bacterial load of mouse tails. Finally, FBXW7 could decrease TNF-α in a K63-linked ubiquitin signaling dependent manner. Taken together, our study uncovered a previously unknown role of FBXW7 in regulating TNF-α dynamics during mycobacterial infection, which provides new insights into understanding the role of FBXW7 in anti-tuberculosis immunity and its related clinical significance.

FBXW7 and the Hallmarks of Cancer: Underlying Mechanisms and Prospective Strategies

FBXW7, a member of the F-box protein family within the ubiquitin–proteasome system, performs an indispensable role in orchestrating cellular processes through ubiquitination and degradation of its substrates, such as c-MYC, mTOR, MCL-1, Notch, and cyclin E. Mainly functioning as a tumor suppressor, inactivation of FBXW7 induces the aberrations of its downstream pathway, resulting in the occurrence of diseases especially tumorigenesis. Here, we decipher the relationship between FBXW7 and the hallmarks of cancer and discuss the underlying mechanisms. Considering the interplay of cancer hallmarks, we propose several prospective strategies for circumventing the deficits of therapeutic resistance and complete cure of cancer patients.

Physiological Functions of FBW7 in Metabolism

FBW7 is the recognition subunit of the SCF (Skp1-Cullin1-F-box proteins) E3 ubiquitin ligase complex, and it determines the specificity of the SCF substrate. SCFFBW7 is a recognized tumor suppressor because of its ability to degrade many proto-oncogenic substrates. Recent studies have shown that FBW7 plays a key role in metabolism by targeting the degradation of critical regulators involved in cellular metabolism in a ubiquitin-dependent manner. Here, we review recent studies, which highlight the important role of FBW7 in metabolism.

MiR-25 enhances autophagy and promotes sorafenib resistance of hepatocellular carcinoma via targeting FBXW7

Sorafenib resistance is a major challenge in the treatment of patients with advanced hepatocellular carcinoma (HCC). MicroRNAs (miRNAs) are a large family of non-coding RNA molecules, which is an important mechanism of drug resistance. We previously found that knockdown of miR-25 increased the sensitivity of TRAIL-induced apoptosis in liver cancer stem cells. We aimed to study the effects of miR-25 on sorafenib resistance of HCC and the underlying mechanisms. In the present study, we analyzed the expression of miR-25 between HCC and normal tissues and predicted miR-25 target genes through databases. After transfecting miR-25 mimics, inhibitor or FBXW7 Plasmid, CCK-8 and flow cytometry assay was performed to determine the sorafenib resistance. We performed LC3-dual-fluorescence assay and Western blotting to detect the autophagy levels. The expression of miR-25 was upregulated in human HCC tissues and was associated with tumor pathological grade, clinic staging, and lymphatic metastasis. MiR-25 enhanced sorafenib resistance of HCC cells and autophagy. FBXW7 is the direct target of miR-25. Overexpression of FBXW7 could reverse the increase of sorafenib resistance caused by miR-25 mimics. Our results suggested that miR-25 increased the sorafenib resistance of HCC via inducing autophagy. In addition, miR-25 decreases the expression of FBXW7 protein to regulate autophagy. Therefore, miR-25 may represent a novel therapeutic target for the treatment of HCC.

Overexpression of hsa_circ_0022742 suppressed hyperglycemia-induced endothelial dysfunction by targeting the miR-503-5p/FBXW7 axis

Type I and II diabetes adversely affect the microvasculature of several organs, although the regulatory mechanisms remain unclear. Previous studies have found that differentially expressed circRNAs associated with hyperglycemia (HG) induce endothelial dysfunction. In the present study, high-throughput sequencing was employed to assess abnormal circRNA expression in human umbilical vein endothelial cells (HUVECs) after HG treatment. Then, bioinformatics analysis, luciferase reporting analysis, angiogenic differentiation analysis, flow cytometry, and qRT-PCR analysis were performed to investigate the underlying regulatory mechanism and targets. The results demonstrate that hsa_circ_0022742 expression in HUVECs was decreased by HG treatment and overexpression of hsa_circ_0022742 suppressed HG-induced endothelial dysfunction. Luciferase analysis showed that miR-503-5p and FBXW7 were downstream targets of hsa_circ_0022742. Both overexpression of FBXW7 and inhibition of miR-503-5p reversed the protective effect of hsa_circ_0022742 against HG-induced endothelial dysfunction, including apoptosis, abnormal vascular differentiation, and secretion of inflammatory factors, indicating that hsa_circ_0022742 enhanced FBXW7 expression by sponging miR-503-5p. Taken together, these findings demonstrate that overexpression of hsa_circ_0022742 suppressed HG-induced endothelial dysfunction by targeting the miR-503-5p/FBXW7 axis.

Attenuating glucose metabolism by Fbxw7 promotes Taxol sensitivity of colon cancer cells through downregulating NADPH oxidase 1 (Nox1)

Background

Colorectal cancer (CRC), one of the most common malignancies worldwide, is associated with poor survival and has a high mortality rate. Taxol is a chemotherapeutic agent that has been clinically applied as a first-line drug against diverse cancers. Yet, development of drug resistance has become the major challenge for anti-cancer treatments. F-box and WD40 domain protein 7 (Fbxw7) is a known tumor suppressor which is frequently downregulated in cancers. However, the biological roles and mechanisms of Fbxw7 in Taxol resistance are still under investigation.

Methods

We report that Fbxw7 is significantly inactivated in CRC tumors and cell lines compared with normal tissues and colon cells. Expressions of Fbxw7 and Nox1 were detected from human colon tumors and cells by qRT-PCR and Western blot. Glycolysis rate was assessed by glucose uptake and lactate product assay. Interactions between Fbxw7 and Nox1 were determined by co-immunoprecipitation (Co-IP). Chemosensitivity and resistance of colon cancer cells were determined by MTT assay and Annexin V-FITC assay.

Results

Overexpression of Fbxw7 sensitized colon cancer cells to Taxol. Moreover, we observed a negative correlation between Fbxw7 and glucose metabolism. From the established Taxol-resistant (TR) cell line from HCT-116, Fbxw7 was found to be markedly downregulated in HCT-116 TR cells. We detected that NADPH oxidase 1 (Nox1), a superoxide-generating NADPH oxidase, is negatively regulated by Fbxw7. The Co-IP assay showed that Fbxw7 interacted with Nox1, which was observed to be significantly upregulated in CRC tissues. Nox1 therefore promotes the Taxol resistance and glucose metabolism of colon cancer cells. Finally, rescue experiments demonstrated that the Fbxw7-promoted Taxol sensitivity was partially through the Nox1-glycolysis axis. Restoration of Nox1 in Fbxw7-overexpressed TR colon cancer cells significantly recovered the Taxol resistance, which could be further overridden by glycolysis inhibition.

Conclusions

Collectively, this study uncovered that targeting the Fbxw7-Nox1-glucose metabolism axis could be an effective strategy against chemoresistant colon cancer.

Rhein Suppresses Colorectal Cancer Cell Growth by Inhibiting the mTOR Pathway In Vitro and In Vivo

Colorectal cancer (CRC) is one of the leading causes of mortality and morbidity in the world. Rhein has demonstrated therapeutic effects in various cancer models. However, its effects and underlying mechanisms of action in CRC remain poorly understood. We investigated the potential anticancer activity and underlying mechanisms of rhein in CRC in vitro and in vivo. Cell viability and anchorage-independent colony formation assays were performed to examine the antigrowth effects of rhein on CRC cells. Wound-healing and Transwell assays were conducted to assess cell migration and invasion capacity. Cell cycle and apoptosis were investigated by flow cytometry and verified by immunoblotting. A tissue microarray was used to detect mTOR expression in CRC patient tissues. Gene overexpression and knockdown were done to analyze the function of mTOR in CRC. The anticancer effect of rhein in vivo was assessed in a CRC xenograft mouse model. The results show that rhein significantly inhibited CRC cell growth by inducing S-phase cell cycle arrest and apoptosis. Rhein inhibited CRC cell migration and invasion through the epithelial-mesenchymal transition (EMT) process. mTOR was highly expressed in CRC cancer tissues and cells. Overexpression of mTOR promoted cell growth, migration, and invasion, whereas mTOR knockdown diminished these phenomena in CRC cells in vitro. In addition, rhein directly targeted mTOR and inhibited the mTOR signaling pathway in CRC cells. Rhein promoted mTOR degradation through the ubiquitin-proteasome pathway. Intraperitoneal administration of rhein inhibited HCT116 xenograft tumor growth through the mTOR pathway. In conclusion, rhein exerts anticancer activity in vitro and in vivo by targeting mTOR and inhibiting the mTOR signaling pathway in CRC. Our results indicate that rhein is a potent anticancer agent that may be useful for the prevention and treatment of CRC.

Downregulation of long non-coding RNA AIRN promotes mitophagy in alcoholic fatty hepatocytes by promoting ubiquitination of mTOR

Long non-coding RNAs (lncRNAs) are crucial in chronic liver diseases, but the specific molecular mechanism of lncRNAs in alcoholic fatty liver (AFL) remains unclear. In this study, we investigated the in-depth regulatory mechanism of mTOR affected by AIRN non-protein coding RNA (lncRNA-AIRN) in the development of AFL. LncRNA-AIRN was highly expressed in the liver tissues of AFL C57BL/6mice and oleic acid+alcohol (O+A)treated AML-12cells by using quantitative real-timePCR. RNA pull-down and RNA immunoprecipitation experiments demonstrated that there was an interaction between lncRNA-AIRN and mTOR, and that interference with lncRNA-AIRN could promote the mTOR protein level. Results ofcycloheximide-chase assay showed that the proteinlevel of mTOR was decreased with the treatment time after the knockdown of lncRNA-AIRN. Furthermore, the knockdown of lncRNA-AIRN reducedmTOR protein level by promoting the E3 ubiquitin ligase FBXW7-mediated ubiquitination.The lncRNA-AIRN/mTORaxis was involved in the regulation of the mitophagy of O+A treated hepatocytes, which was confirmed by the cell transfection and the MTT assay.SPSS 16.0 was used for analyzing data. The difference between the two groups was analyzed by performing Student's t-test, and ANOVA was used to analyze the difference when more than two groups. P values < 0.05 were considered to be significantly different.Our findings demonstrated that the knockdown of lncRNA-AIRN influencedmitophagy in AFL by promoting mTOR ubiquitination.

The Roles of Post-Translational Modifications on mTOR Signaling

The mechanistic target of rapamycin (mTOR) is a master regulator of cell growth, proliferation, and metabolism by integrating various environmental inputs including growth factors, nutrients, and energy, among others. mTOR signaling has been demonstrated to control almost all fundamental cellular processes, such as nucleotide, protein and lipid synthesis, autophagy, and apoptosis. Over the past fifteen years, mapping the network of the mTOR pathway has dramatically advanced our understanding of its upstream and downstream signaling. Dysregulation of the mTOR pathway is frequently associated with a variety of human diseases, such as cancers, metabolic diseases, and cardiovascular and neurodegenerative disorders. Besides genetic alterations, aberrancies in post-translational modifications (PTMs) of the mTOR components are the major causes of the aberrant mTOR signaling in a number of pathologies. In this review, we summarize current understanding of PTMs-mediated regulation of mTOR signaling, and also update the progress on targeting the mTOR pathway and PTM-related enzymes for treatment of human diseases.

A Destiny for Degradation: Interplay between Cullin-RING E3 Ligases and Autophagy

Autophagy and the ubiquitin-proteasome system (UPS) are two major pathways for protein degradation. The cullin-RING E3 ligases (CRLs) are the largest E3 ligase family and have key biological functions in maintaining protein homeostasis. We provide an updated review of the interactions between CRLs and autophagy, focusing on the regulatory effects of CRLs on the core autophagy machinery that consists of several autophagy-related protein (ATG) complexes and their key upstream signaling pathways. The involvement of such functional interactions in health and disease is also discussed. Understanding the role of CRLs in autophagy is helpful for the development of therapeutic strategies for diseases in which CRLs and autophagy are dysregulated, such as cancer and neurodegenerative conditions.

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)1

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field.

Age-related copy number variations and expression levels of F-box protein FBXL20 predict ovarian cancer prognosis

About 70% of ovarian cancer (OvCa) cases are diagnosed at advanced stages (stage III/IV) with only 20–40% of them survive over 5 years after diagnosis. A reliably screening marker could enable a paradigm shift in OvCa early diagnosis and risk stratification. Age is one of the most significant risk factors for OvCa. Older women have much higher rates of OvCa diagnosis and poorer clinical outcomes. In this article, we studied the correlation between aging and genetic alterations in The Cancer Genome Atlas Ovarian Cancer dataset. We demonstrated that copy number variations (CNVs) and expression levels of the F-Box and Leucine-Rich Repeat Protein 20 (FBXL20), a substrate recognizing protein in the SKP1-Cullin1-F-box-protein E3 ligase, can predict OvCa overall survival, disease-free survival and progression-free survival. More importantly, FBXL20 copy number loss predicts the diagnosis of OvCa at a younger age, with over 60% of patients in that subgroup have OvCa diagnosed at age less than 60 years. Clinicopathological studies further demonstrated malignant histological and radiographical features associated with elevated FBXL20 expression levels. This study has thus identified a potential biomarker for OvCa prognosis.

An Update on Autophagy in Prion Diseases

Autophagy is a dynamic intracellular mechanism involved in protein and organelle turnover through lysosomal degradation. When properly regulated, autophagy supports normal cellular and developmental processes, whereas defects in autophagic degradation have been associated with several pathologies, including prion diseases. Prion diseases, or transmissible spongiform encephalopathies (TSE), are a group of fatal neurodegenerative disorders characterized by the accumulation of the pathological misfolded isoform (PrP^Sc) of the physiological cellular prion protein (PrP^c) in the central nervous system. Autophagic vacuoles have been described in experimental models of TSE and in the natural disease in humans. The precise connection of this process with prion-related neuropathology, or even whether autophagy is completely beneficial or pathogenic during neurodegeneration, is poorly understood. Thus, the biological role of autophagy in these diseases is still open to debate. During the last years, researchers have used a wide range of morphological, genetic and biochemical methods to monitor and manipulate the autophagic pathway and thus determine the specific role of this process in TSE. It has been suggested that PrP^c could play a crucial role in modulating the autophagic pathway in neuronal cells, and the presence of abnormal autophagic activity has been frequently observed in several models of TSE both in vitro and in vivo, as well as in human prion diseases. Altogether, these findings suggest that autophagy is implicated in prion neuropathology and points to an impairment or failure of the process, potentially contributing to the pathogenesis of the disease. Additionally, autophagy is now emerging as a host defense response in controlling prion infection that plays a protective role by facilitating the clearance of aggregation-prone proteins accumulated within neurons. Since autophagy is one of the pathways of PrP^Sc degradation, and drug-induced stimulation of autophagic flux (the dynamic process of autophagic degradation activity) produces anti-prion effects, new treatments based on its activation have been tested to develop therapeutic strategies for prion diseases. In this review, we summarize previous and recent findings concerning the role of autophagy in TSE.

MiR-223 regulates autophagy associated with cisplatin resistance by targeting FBXW7 in human non-small cell lung cancer

Background

Cisplatin is widely used as a first-line treatment for non-small cell lung cancer (NSCLC), but chemoresistance remains a major clinical obstacle for efficient use. As a microRNA, miR-223 was reported to promote the doxorubicin resistance of NSCLC. However, whether miR-223 is also involved in cisplatin resistance of NSCLC and the mechanism miR-223 involved in drug resistance is unclear. Accumulated evidence has shown that abnormal autophagy is associated with tumor chemoresistance. The study aimed to study the role of miR-223 on cisplatin sensitivity in NSCLC and uncover the potential mechanisms.

Methods

NSCLC cells transfected with mimic or inhibitor for miR-223 was assayed for chemoresistance in vitro. MiR-223 expression was assessed by quantitative real-time PCR (qRT-PCR). Western blot were used to study the expression level of F-box/WD repeat-containing protein 7 (FBXW7) and autophagy-related protein. The effect of miR-223 on cisplatin sensitivity was examined by using CCK-8, EdU assays and Autophagic flux assay. Luciferase assays, EdU assays and small interfering RNA were performed to identify the targets of miR-223 and the mechanism by which it promotes treatment resistance. Xenograft models were established to investigate the effect of mir-223 on cisplatin sensitivity.

Results

In the present study, we found that the level of miR-223 was significantly positively correlated with cisplatin resistance. MiR-223 overexpression made NSCLC cells resistant to cisplatin treatment. We further found that autophagy mediated miR-223-mediated cisplatin resistance in NSCLC cells. Further mechanistic research demonstrated that miR-223 directly targeted FBXW7. The overexpression of miR-223 could inhibit the level of FBXW7 protein expression, thus promoting autophagy and making NSCLC cells resistant to cisplatin. Finally, we confirmed the increased effect of cisplatin sensitivity by miR-223 Antagomir in xenograft models of NSCLC.

Conclusions

Our results demonstrate that miR-223 could enhance autophagy by targeting FBXW7 in NSCLC cells. Inhibition of autophagy by miR-223 knockdown provides a novel treatment strategy to alleviate cisplatin resistance in NSCLC.

Enhanced Mitophagy Activity in Prion-Infected Cultured Cells and Prion-Infected Experimental Mice via a Pink1/Parkin-Dependent Mitophagy Pathway

Mitophagy is an important process for removing damaged mitochondria in cells, the dysfunction of which has been directly linked to an increasing number of neurodegenerative disorders. However, the details of mitophagy in prion diseases still need to be deeply explored. In this study, we identified more autophagosomes and large swelling mitochondria structures in the prion-infected cultured cell line SMB-S15 by transmission electron microscopy, accompanying the molecular evidence of activated autophagic flux. Western blots illustrated that the levels of Pink1 and Parkin, particularly in the mitochondrial fraction, were increased in SMB-S15 cells, whereas the levels of mitochondrial membrane proteins TIMM44, TOMM20, and TIMM23 were decreased. The amount of whole polyubiquitinated proteins decreased, but that of phosphor-polyubiquitinated proteins increased in SMB-S15 cells. The level of MFN2 in SMB-S15 cells were down-regulated, but its polyubiquitinated form was up-regulated. Knockdown of the expressions of Pink1 and Parkin by the individual SiRNAs in SMB-S15 cells reduced autophagic activity but did not seem to influence the expressions of TOMM20 and TIMM23. Moreover, we also demonstrated that the brain levels of Pink1 and Parkin in the mice infected with scrapie strains 139A and ME7 were remarkably increased at the terminal stage of the disease by Western blot and immunohistochemical (IHC) assays. Immunofluorescent assays revealed that Pink1 signals widely colocalized with GAFP-, Iba1-, and NeuN-positive cells in the brains of scrapie-infected mice. IHC assays with serial sections of the brain tissues infected with agents 139A and ME7 showed more Pink1- and Parkin-positive cells located at the areas with more PrP^Sc deposit. These results suggest an activated mitophagy in prion-infected cells and prion-infected experimental mice, probably via an enhanced Pink-Parkin pathway.

Impairment of autophagy in scrapie-infected transgenic mice at the clinical stage

Autophagy appears to play a role in the etiology and progress of misfolded protein disorders. Although this process is dysregulated in prion diseases, it is unknown whether this impairment is a cause or a consequence of prion neuropathology. The study of autophagy during the progress of the disease could elucidate its role. For this purpose, we have investigated its regulation at different stages of the disease in Tg338 mice, a transgenic murine model that overexpresses the highly susceptible ovine VRQ prion protein allele. Mice were intracerebrally inoculated with mouse-adapted classical scrapie and euthanized at the preclinical and clinical stages of the disease. Regulation of autophagy was investigated analyzing the distribution of LC3-B and p62 proteins by immunohistochemistry. Moreover, the expression of genes involved in autophagy regulation was quantified by real-time PCR. LC3-B and p62 proteins were downregulated and upregulated, respectively, in the central nervous system of infected mice with clinical signs of scrapie. Accumulation of p62 correlated with scrapie-related lesions, suggesting an impairment of autophagy in highly prion-affected areas. In addition, Gas5 (growth arrest-specific 5), Atg5 (autophagy-related 5), and Fbxw7 (F-box and WD repeat domain containing 7) transcripts were downregulated in mesencephalon and cervical spinal cord of the same group of animals. The impairment of autophagic machinery seems to be part of the pathological process of scrapie, but only during the late stage of prion infection. Similarities between Tg338 mice and the natural ovine disease make them a reliable in vivo model to study prion infection and autophagy side by side.

FBW7 Regulates the Autophagy Signal in Mesangial Cells Induced by High Glucose

Aims

Abnormal regulation of autophagy participates in the development of diabetic nephropathy. mTOR is the most common negative regulator of the autophagy signaling pathway. FBW7 constitutes the SCF (Skp1-Cullin1-F-box protein) recognition subunit of E3 ubiquitin ligase, and mTOR is a substrate of FBW7 that can be modified by ubiquitination and be degraded via proteasomes. In this study, we explored the relationship between FBW7 and autophagy and examined the effects of FBW7 on the occurrence of diabetic nephropathy in vitro.

Materials and Methods

We cultured mesangial cells induced by high glucose in vitro and used rapamycin as a specific mTOR inhibitor, performed FBW7 gene overexpression, and detected the expression of autophagy signal and inflammatory factors by WB, ELISA, RT-PCR, and immunofluorescence.

Results

High glucose can downregulate the expression of FBW7 and activate mTOR signal, which leads to diminished autophagy in renal mesangial cells, as well as renal inflammatory cytokines and fibrotic factors. RAPA, as a specifically inhibitor of mTOR, can decrease inflammatory cytokines and fibrotic factors by inhibiting mTOR. Moreover, FBW7 gene overexpression can increase autophagy by inhibiting mTOR signal; at the same time, the inflammatory cytokines and fibrotic factors were decreased in mesangial cells.

Conclusions

FBW7 was decreased in renal mesangial cells induced by high glucose, and FBW7 gene overexpression can increase autophagy by inhibiting mTOR signaling and ameliorate inflammation and fibrosis.

Cell biology of prion infection

The development of multiple cell culture models of prion infection over the last two decades has led to a significant increase in our understanding of how prions infect cells. In particular, new techniques to distinguish exogenous from endogenous prions have allowed us for the first time to look in depth at the earliest stages of prion infection through to the establishment of persistent infection. These studies have shown that prions can infect multiple cell types, both neuronal and nonneuronal. Once in contact with the cell, they are rapidly taken up via multiple endocytic pathways. After uptake, the initial replication of prions occurs almost immediately on the plasma membrane and within multiple endocytic compartments. Following this acute stage of prion replication, persistent prion infection may or may not be established. Establishment of a persistent prion infection in cells appears to depend upon the achievement of a delicate balance between the rate of prion replication and degradation, the rate of cell division, and the efficiency of prion spread from cell to cell. Overall, cell culture models have shown that prion infection of the cell is a complex and variable process which can involve multiple cellular pathways and compartments even within a single cell.

Decrease of RyR2 in the prion infected cell line and in the brains of the scrapie infected mice models and the patients of human prion diseases

The levels of ryanodine receptors (RyRs) are usually increased in the brains of human Alzheimer disease (AD) and AD animal models. To evaluate the underlying alteration of brain RyRs in prion disease, scrapie infected cell line SMB-S15 and its infected mice were tested. RyR2 specific Western blots revealed markedly decreased RyR2 levels both in the cells and in the brains of infected mice. Assays of the brain samples of other scrapie (agents 139A and ME7) infected mice collected at different time-points during incubation period showed time-dependent decreases of RyR2. Immunofluorescent assays (IFA) verified that the expression of RyR2 locates predominantly in cytoplasm of SMB cells and overlapped with the neurons in the brain slices of mice. Furthermore, significant down-regulation of RyR2 was also detected in the postmortem cortical brains of the patients of various types of human prion diseases, including sporadic Creutzfeldt-Jakob disease (sCJD), fatal familial insomnia (FFI) and G114V-genetic CJD. Our data here propose the evidences of remarkably decreased brain RyR2 at terminal stages of both human prion diseases and prion infected rodent models. It also highlights that the therapeutic strategy with antagonist of RyRs in AD may not be suitable for prion disease.

Reduction of NF-κB (p65) in Scrapie-Infected Cultured Cells and in the Brains of Scrapie-Infected Rodents

Transcription factor NF-κB functions as a pleiotropic regulator of target genes controlling physiological function as well as pathological processes of many different diseases, including some neurodegenerative diseases. However, the role of NF-κB in the pathogenesis of prion disease remains ambiguous. In this study, the status of NF-κB (p65) in a prion-infected cell line SMB-S15 was first evaluated. Significantly lower levels of p65 and the phosphorylated form of p65 (p-p65) were detected in SMB-S15 cells, compared with its normal partner cell line SMB-PS. Markedly slower responses of the NF-κB system to the stimulation of TNF-α were observed in SMB-S15 cells. Removal of PrP^Sc replication in SMB-S15 cells rescued the expression and activity of NF-κB. However, overexpression of p65 in SMB-S15 cells did not influence the propagation of PrP^Sc. Moreover, significant decline of p65 level was also observed in the brain tissues of mice infected with the lysates of SMB-S15 cells and hamsters infected with scrapie agent 263K at terminal stage. Immunofluorescence assays (IFAs) on brain sections from either normal or scrapie-infected rodents revealed colocalization of p65 with neuronal nuclear (NeuN) protein positive cells but not with glial fibrillary acidic protein (GFAP) positive cells. Assays of the agents involving in the regulation of NF-κB showed down-regulated phosphoinositide 3-kinase (PI3K) and protein kinase B (PKB/Akt) both in SMB-S15 cells and in the brains of scrapie-infected rodents. Those data indicate a remarkable repression of the classical NF-κB pathway during prion infection both in vitro and in vivo. The alteration of NF-κB (p65) shows close association with the replication and accumulation of PrP^Sc in the cells.

Role of the AMPK pathway in promoting autophagic flux via modulating mitochondrial dynamics in neurodegenerative diseases: Insight into prion diseases

Neurons are highly energy demanding cells dependent on the mitochondrial oxidative phosphorylation system. Mitochondria generate energy via respiratory complexes that constitute the electron transport chain. Adenosine triphosphate depletion or glucose starvation act as a trigger for the activation of adenosine monophosphate-activated protein kinase (AMPK). AMPK is an evolutionarily conserved protein that plays an important role in cell survival and organismal longevity through modulation of energy homeostasis and autophagy. Several studies suggest that AMPK activation may improve energy metabolism and protein clearance in the brains of patients with vascular injury or neurodegenerative disease. Mild mitochondrial dysfunction leads to activated AMPK signaling, but severe endoplasmic reticulum stress and mitochondrial dysfunction may lead to a shift from autophagy towards apoptosis and perturbed AMPK signaling. Hence, controlling mitochondrial dynamics and autophagic flux via AMPK activation might be a useful therapeutic strategy in neurodegenerative diseases to reinstate energy homeostasis and degrade misfolded proteins. In this review article, we discuss briefly the role of AMPK signaling in energy homeostasis, the structure of AMPK, activation mechanisms of AMPK, regulation of AMPK, the role of AMPK in autophagy, the role of AMPK in neurodegenerative diseases, and finally the role of autophagic flux in prion diseases.

Diminished DYRK2 sensitizes hormone receptor-positive breast cancer to everolimus by the escape from degrading mTOR

Mammalian target of rapamycin (mTOR) inhibitor, everolimus, provides benefit for metastatic hormone receptor positive breast cancer after failure of the endocrine therapy. The present report highlights Dual Specificity Tyrosine Phosphorylation Regulated Kinase 2 (DYRK2) as a predictive marker for everolimus sensitivity. The key node and KEGG pathway analyses revealed that mTORC1 pathway is activated in DYRK2-depleted cells. Everolimus was more effective in DYRK2-depleted cells compared with control cells. In xenograft model, everolimus treatment significantly inhibited tumor growth compared with vehicle or eribulin treatment. In clinical analysis, patients with low DYRK2 expression acquired longer treatment period and had higher clinical benefit rate than those with high DYRK2 expression (171 vs 82 days; P < 0.05 and 50% vs 12.5%, respectively). We further investigated the underlying mechanism by which DYRK2 regulates mTORC1 pathway. The ectopic expression of DYRK2 promoted phosphorylation of Thr631 for the ubiquitination and degradation of mTOR. DYRK2 expression levels may thus predict clinical responses to everolimus.

Autophagy modulators from traditional Chinese medicine: Mechanisms and therapeutic potentials for cancer and neurodegenerative diseases

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicine (TCM), an ancient yet still alive medicinal system widely used in East Asia, has played an essential role in health maintenance and diseases control, for a wide range of human chronic diseases like cancers and neurodegenerative diseases. TCM-derived compounds and extracts attract wide attention for their potential application as therapeutic agents against above mentioned diseases.

AIM OF REVIEW

Recent years the enthusiasm in searching for autophagy regulators for human diseases has yielded many positive hits. TCM-derived compounds as important sources for drug discovery have been widely tested in different models for autophagy modulation. Here we summarize the current progress in the discovery of natural autophagy regulators from TCM for the therapeutic application in cancer and neurodegenerative disease models, aiming to provide the direct link from traditional use to new pharmacological application.

METHODS

The present review collected the literature published during the recent 10 years which studied the effect of TCM-derived compounds or extracts on autophagy regulation from PubMed, Web of Science, Google Scholar and Science Direct. The names of chemical compounds studied in this article are corresponding to the information in journal plant list.

RESULTS

In this review, we give a brief introduction about the autophagy and its roles in cancer and neurodegenerative disease models and describe the molecular mechanisms of autophagy modulation. We also make comprehensive lists to summarize the effects and underlying mechanisms of TCM-derived autophagy regulators in cancer and neurodegenerative disease models. In the end of the review, we discuss the current strategies, problems and future direction for TCM-derived autophagy regulators in the treatment of human diseases.

CONCLUSIONS

A number of data from in vivo and in vitro models indicated TCM derived compounds and extracts hold great potential for the treatment of human diseases including cancers and neurodegenerative diseases. Autophagy, as a novel and promising drug target involved in a wide range of human diseases, can be modulated by many TCM derived agents, indicating autophagy modulation may be an important mechanism underlying the therapeutic effect of TCM in treating diseases. Furthermore, we look forward to seeing the discovery of ideal autophagy modulators from TCM with considerably higher selectivity for the treatment of human diseases.

Overexpression of PLK3 Mediates the Degradation of Abnormal Prion Proteins Dependent on Chaperone-Mediated Autophagy

Polo-like kinase 3 (PLK3) is the main cause of cell cycle reentry-related neuronal apoptosis which has been implicated in the pathogenesis of prion diseases. Previous work also showed the regulatory activity of exogenous PLK3 on the degradation of PrP (prion protein) mutants and pathogenic PrP^Sc; however, the precise mechanisms remain unknown. In this study, we identified that the overexpression of PLK3-mediated degradation of PrP mutant and PrP^Sc was repressed by lysosome rather than by proteasomal and macroautophagy inhibitors. Core components of chaperone-mediated autophagy (CMA) effectors, lysosome-associated membrane protein type 2A (LAMP2a), and heat shock cognate protein 70 (Hsc70) are markedly decreased in the HEK293T cells expressing PrP mutant and scrapie-infected cell line SMB-S15. Meanwhile, PrP mutant showed ability to interact with LAMP2a and Hsc70. Overexpression of PLK3 sufficiently increased the cellular levels of LAMP2a and Hsc70, accompanying with declining the accumulations of PrP mutant and PrP^Sc. The kinase domain (KD) of PLK3 was responsible for elevating LAMP2a and Hsc70. Knockdown of endogenous PLK3 enhanced the activity of macroautophagy in the cultured cells. Moreover, time-dependent reductions of LAMP2a and Hsc70 were also observed in the brain tissues of hamster-adapted scrapie agent 263K-infected hamsters, indicating an impairment of CMA during prion infection. Those data indicate that the overexpression of PLK3-mediated degradation of abnormal PrP is largely dependent on CMA pathway.

Activation of the AMPK-ULK1 pathway plays an important role in autophagy during prion infection

AMPK is a serine/threonine protein kinase that acts as a positive regulator of autophagy, by phosphorylating ULK1 at specific sites. A previous study demonstrated activation of the macroautophagic system in scrapie-infected experimental rodents and in certain human prion diseases, in which the essential negative regulator mTOR is severely inhibited. In this study, AMPK and ULK1 in the brains of hamsters infected with scrapie strain 263 K and in the scrapie-infected cell line SMB-S15 were analysed. The results showed an up-regulated trend of AMPK and AMPK-Thr172, ULK1 and ULK1-Ser555. Increases in brain AMPK and ULK1 occurred at an early stage of agent 263 K infection. The level of phosphorylated ULK1-Ser757 decreased during mid-infection and was only negligibly present at the terminal stage, a pattern that suggested a close relationship of the phosphorylated protein with altered endogenous mTOR. In addition, the level of LKB1 associated with AMPK activation was selectively increased at the early and middle stages of infection. Knockdown of endogenous ULK1 in SMB-S15 cells inhibited LC3 lipidation. These results showed that, in addition to the abolishment of the mTOR regulatory pathway, activation of the AMPK-ULK1 pathway during prion infection contributes to autophagy activation in prion-infected brain tissues.

Strain-Dependent Effect of Macroautophagy on Abnormally Folded Prion Protein Degradation in Infected Neuronal Cells

Prion diseases are neurodegenerative disorders caused by the accumulation of abnormal prion protein (PrP^Sc) in the central nervous system. With the aim of elucidating the mechanism underlying the accumulation and degradation of PrP^Sc, we investigated the role of autophagy in its degradation, using cultured cells stably infected with distinct prion strains. The effects of pharmacological compounds that inhibit or stimulate the cellular signal transduction pathways that mediate autophagy during PrP^Sc degradation were evaluated. The accumulation of PrP^Sc in cells persistently infected with the prion strain Fukuoka-1 (FK), derived from a patient with Gerstmann–Sträussler–Scheinker syndrome, was significantly increased in cultures treated with the macroautophagy inhibitor 3-methyladenine (3MA) but substantially reduced in those treated with the macroautophagy inducer rapamycin. The decrease in FK-derived PrP^Sc levels was mediated, at least in part, by the phosphatidylinositol 3-kinase/MEK signalling pathway. By contrast, neither rapamycin nor 3MA had any apparently effect on PrP^Sc from either the 22L or the Chandler strain, indicating that the degradation of PrP^Sc in host cells might be strain-dependent.

FBXW7 overexpression suppresses renal cancer cell proliferation and induces apoptosis

FBXW7 gene (F-box and WD-40 domain protein 7) is also named HCDC4 and is a significant tumor suppressor gene, which can regulate human cell cycle, proliferation and differentiation. In this study, we tend to investigate protein expression and related biological functions of FBXW7 gene. FBXW7 expression level in renal cell carcinoma (RCC) tissues is highly related to its clinical pathologic grade (P = 0.0094) and TNM phase (P = 0.0080) and is highly lower than in paracancerous normal tissues through immunohistochemistry study. FBXW7 high-expression patients have overall better prognosis than low-expression patients (P < 0.001). After transfected with FBXW7 plasmid, the RCC cell lines ACHN and A704 showed a depressed proliferation activity and high proportion of apoptosis through CCK8, colony formation and flow cytometry assay studies. By Western blot analysis, expression of cell proliferation-activating protein c-Myc and c-Jun is downregulated in FBXW7 high-expression RCC compared with negative control. These data suggested that FBXW7 is a significant tumor suppressor gene in RCC.