Development of in vitro PIK3C3/VPS34 complex protein assay for autophagy-specific inhibitor screening

Overcoming radio-resistance in esophageal squamous cell carcinoma via hypermethylation of PIK3C3 promoter region mediated by KDM5B loss

Many patients with esophageal squamous cell carcinoma (ESCC) are inoperable because of old age or the advanced stage of the disease; thus radio- and chemotherapy are believed as the standard treatments for these patients. However, due to the radio-resistance of tumor cells that may develop during radiotherapy, results remain unsatisfactory. In this article, the possible relationship between the expression of lysine demethylase 5B (KDM5B) and ESCC radio-resistance is clarified, and the underlying mechanism is evaluated. Using the GSE75241 microarray, we identified KDM5B as a potential oncogene in ESCC. KDM5B was overexpressed in ESCC patients and cells. Inhibition of KDM5B enhanced the H3K4me3 methylation of phosphatidylinositol 3-kinase catalytic subunit type 3 (PIK3C3) promoter and induced the expression of PIK3C3. Knockdown of KDM5B or overexpression of PIK3C3 in KYSE-150 and TE-10 cells promoted apoptosis, cell cycle arrest, autophagy, and increased sensitivity to radiotherapy. Silencing of PIK3C3 attenuated the promoting effect of sh-KDM5B on the sensitivity of ESCC cells to radiotherapy. The inhibition of sh-KDM5B in radio-resistance of ESCC cells was also reproduced in vivo. Taken together, our findings provide evidence that reduced expression of KDM5B has a critical role in promoting ESCC radio-sensitivity by upregulating PIK3C3, suggesting KDM5B may function as an oncogene in ESCC.

An alcoholic extract of Thuja orientalis L. leaves inhibits autophagy by specifically targeting pro-autophagy PIK3C3/VPS34 complex

Autophagy is a lysosome-dependent degradation program to maintain cellular homeostasis in response to a variety of stressful conditions, such as long-lived or non-functional subcellular organelles, protein aggregates, nutrient limitation, and virus/bacteria infection. Accordingly, dysregulation of autophagy is closely associated with many human pathophysiological conditions, such as neurodegenerative diseases, aging, and cancer, and autophagy is highlighted as an important therapeutic target for these human diseases. In autophagy process, PIK3C3/VPS34 complex plays important roles in autophagosome biogenesis. Accumulating evidences that inhibition of PIK3C3/VPS34 complex successfully blocks autophagy make the complex as an attractive target for the development of autophagy-specific inhibitors. However, considering that various forms of PIK3C3/VPS34 complex exist and they are involved in many different cellular functions, the targeting of the pro-autophagy PIK3C3/VPS34 complex is required to specifically inhibit autophagy. To identify autophagy inhibitors targeting the pro-autophagy complex, we have performed the screening of a customized natural product library consisting of 35 herbal extracts which are widely used in the oriental medicine as anti-inflammation and/or anti-tumor reagents. We discovered that an alcoholic extract of Thuja orientalis L. leaves inhibits pro-autophagy complex formation by disrupting the interaction between autophagy-specific factor, ATG14L, and the complex core unit Vps34-Beclin 1 in vitro. Also, it inhibits the nutrient starvation induced autophagy and diminished pro-autophagy PIK3C3/VPS34 complex containing either ATG14L or UVRAG in several cell lines. Our results strongly suggest that Thuja orientalis L. leave extract functions as an autophagy-specific inhibitor not decreasing the complex activity nor the protein level, but preventing protein-protein interaction between autophagy-specific factor (ATG14L and UVRAG) and PIK3C3/VPS34 complex core unit, Vps34-Beclin 1, thereby specifically depleting the pro-autophagy complex to inhibit autophagy.

PIK3C3 Acts as a Tumor Suppressor in Esophageal Squamous Cell Carcinoma and Was Regulated by MiR-340-5p

BACKGROUND Esophageal squamous cell carcinoma (ESCC), a major histological subtype of esophageal cancer, is a common cause of tumor-related deaths in the world. Due to the lack of understanding of the pathogenesis of ESCC, its clinical treatment is still a big challenge. In the present study, we aimed to identify an ESCC-related gene in the GEO dataset, and to explore its function and mechanism in ESCC. MATERIAL AND METHODS The GSE dataset (GSE100492) consisting of 10 samples was analyzed using GEO2R for identifying the differentially expressed genes between ESCC and normal samples. Expression levels of mRNA and miRNA in ESCC tissues and cells were detected via quantitative real-time polymerase chain reaction. Protein expression was analyzed by western blot. Cell proliferation viability was determined through MTT and colony formation. Cell distribution and apoptosis was detected by flow cytometry. MiRNA target prediction was analyzed by bioinformatics. The interplay between miR-340-5p and PIK3C3 was validated by dual-luciferase reporter assay. RESULTS PIK3C3 was lowly expressed in ESCC tissue and indicated a poor prognosis in patents. Overexpression of PIK3C3 in vitro repressed cell proliferation of KYSE-150 and TE-12 cells. Moreover, PIK3C3 overexpression was demonstrated to enhance the sensitivity of KYSE-150 and TE-12 cells to irradiation. In addition, miR-340-5p was revealed to directly bind and negatively modulate PIK3C3 expression in ESCC. Blockage of miR-340-5p promoted ESCC cell proliferation, while rescue of PIK3C3 reversed this effect. MiR-340-5p was highly expressed in ESCC tissue and it exhibited a negative correlation with PIK3C3 expression. CONCLUSIONS MiR-340-5p functioned as an oncogene of ESCC by directly binding and repressing the expression of PIK3C3.

Autophagy modulators for the treatment of oral and esophageal squamous cell carcinomas

Oral squamous cell carcinomas (OSCC) and esophageal squamous cell carcinomas (ESCC) exhibit a survival rate of less than 60% and 40%, respectively. Late-stage diagnosis and lack of effective treatment strategies make both OSCC and ESCC a significant health burden. Autophagy, a lysosome-dependent catabolic process, involves the degradation of intracellular components to maintain cell homeostasis. Targeting autophagy has been highlighted as a feasible therapeutic strategy with clinical utility in cancer treatment, although its associated regulatory mechanisms remain elusive. The detection of relevant biomarkers in biological fluids has been anticipated to facilitate early diagnosis and/or prognosis for these tumors. In this context, recent studies have indicated the presence of specific proteins and small RNAs, detectable in circulating plasma and serum, as biomarkers. Interestingly, the interplay between biomarkers (eg, exosomal microRNAs) and autophagic processes could be exploited in the quest for targeted and more effective therapies for OSCC and ESCC. In this review, we give an overview of the available biomarkers and innovative targeted therapeutic strategies, including the application of autophagy modulators in OSCC and ESCC. Additionally, we provide a viewpoint on the state of the art and on future therapeutic perspectives combining the early detection of relevant biomarkers with drug discovery for the treatment of OSCC and ESCC.

Excessive ER stress and the resulting autophagic flux dysfunction contribute to fluoride-induced neurotoxicity

Fluoride is capable of inducing neurotoxicity, but its mechanisms remain elusive. This study aimed to explore the roles of endoplasmic reticulum (ER) stress and autophagy in sodium fluoride (NaF)-induced neurotoxicity, focusing on the regulating role of ER stress in autophagy. The in vivo results demonstrated that NaF exposure impaired the learning and memory capabilities of rats, and resulted in histological and ultrastructural abnormalities in rat hippocampus. Moreover, NaF exposure induced excessive ER stress and associated apoptosis, as manifested by elevated IRE1α, GRP78, cleaved caspase-12 and cleaved-caspase-3, as well as defective autophagy, as shown by increased Beclin1, LC3-II and p62 expression in hippocampus. Consistently, the in vitro results further verified the findings of in vivo study that NaF induced excessive ER stress and defective autophagy in SH-SY5Y cells. Notably, inhibition of autophagy in NaF-treated SH-SY5Y cells with Wortmannin or Chloroquine decreased, while induction of autophagy by Rapamycin increased the cell viability. These results were correlated well with the immunofluorescence observations, thus confirming the pivotal role of autophagic flux dysfunction in NaF-induced cell death. Importantly, mitigation of ER stress by 4-phenylbutyrate in NaF-treated SH-SY5Y cells inhibited the expressions of autophagy markers, and decreased cell apoptosis. Taken together, these data suggest that neuronal death resulted from excessive ER stress and autophagic flux dysfunction contributes to fluoride-elicited neurotoxicity. Moreover, the autophagic flux dysfunction was mediated by excessive ER stress, which provided novel insight into a better understanding of fluoride-induced neurotoxicity.

Design of Small Molecule Autophagy Modulators: A Promising Druggable Strategy

Autophagy is a lysosome-dependent mechanism of intracellular degradation for maintaining cellular homeostasis. Dysregulation of autophagy has been verified to be closely linked to a number of human diseases. Consequently, targeting autophagy has been highlighted as a novel therapeutic strategy for clinical utility. Mounting efforts have been done in recent years to elucidate the mechanisms of autophagy regulation and to identify potential modulators of autophagy. However, most of the compounds target complex and multifaceted pathway and proteins, which may limit the evaluation of therapeutic value and in depth studies as chemical tools. Therefore, the development of specific and active autophagy modulators becomes most desirable. Here, we briefly review the regulation of autophagy and then summarize the recent development of small molecules targeting the core autophagic machinery. Finally, we put forward our viewpoints on the current problems, with the aim to provide reference for future drug discovery and potential therapeutic perspectives on novel, potent, selective autophagy modulators.