MDH1 and MPP7 Regulate Autophagy in Pancreatic Ductal Adenocarcinoma

Physiology of malate dehydrogenase and how dysregulation leads to disease

Malate dehydrogenase (MDH) is pivotal in mammalian tissue metabolism, participating in various pathways beyond its classical roles and highlighting its adaptability to cellular demands. This enzyme is involved in maintaining redox balance, lipid synthesis, and glutamine metabolism and supports rapidly proliferating cells' energetic and biosynthetic needs. The involvement of MDH in glutamine metabolism underlines its significance in cell physiology. In contrast, its contribution to lipid metabolism highlights its role in essential biosynthetic processes necessary for cell maintenance and proliferation. The enzyme's regulatory mechanisms, such as post-translational modifications, underscore its complexity and importance in metabolic regulation, positioning MDH as a potential target in metabolic dysregulation. Furthermore, the association of MDH with various pathologies, including cancer and neurological disorders, suggests its involvement in disease progression. The overexpression of MDH isoforms MDH1 and MDH2 in cancers like breast, prostate, and pancreatic ductal adenocarcinoma, alongside structural modifications, implies their critical role in the metabolic adaptation of tumor cells. Additionally, mutations in MDH2 linked to pheochromocytomas, paragangliomas, and other metabolic diseases emphasize MDH's role in metabolic homeostasis. This review spotlights MDH's potential as a biomarker and therapeutic target, advocating for further research into its multifunctional roles and regulatory mechanisms in health and disease.

The acetylation of MDH1 and IDH1 is associated with energy metabolism in acute liver failure

The liver is the main organ associated with metabolism. In our previous studies, we identified that the metabolic enzymes malate dehydrogenase 1 (MDH1) and isocitrate dehydrogenase 1 (IDH1) were differentially expressed in ALF. The aim of this study was to explore the changes in the acetylation of MDH1 and IDH1 and the therapeutic effect of histone deacetylase (HDAC) inhibitor in acute liver failure (ALF). Decreased levels of many metabolites were observed in ALF patients. MDH1 and IDH1 were decreased in the livers of ALF patients. The HDAC inhibitor ACY1215 improved the expression of MDH1 and IDH1 after treatment with MDH1-siRNA and IDH1-siRNA. Transfection with mutant plasmids and adeno-associated viruses, identified MDH1 K118 acetylation and IDH1 K93 acetylation as two important sites that regulate metabolism in vitro and in vivo.

Proteomic characterization of epithelial ovarian cancer delineates molecular signatures and therapeutic targets in distinct histological subtypes

Clear cell carcinoma (CCC), endometrioid carcinoma (EC), and serous carcinoma (SC) are the major histological subtypes of epithelial ovarian cancer (EOC), whose differences in carcinogenesis are still unclear. Here, we undertake comprehensive proteomic profiling of 80 CCC, 79 EC, 80 SC, and 30 control samples. Our analysis reveals the prognostic or diagnostic value of dysregulated proteins and phosphorylation sites in important pathways. Moreover, protein co-expression network not only provides comprehensive view of biological features of each histological subtype, but also indicates potential prognostic biomarkers and progression landmarks. Notably, EOC have strong inter-tumor heterogeneity, with significantly different clinical characteristics, proteomic patterns and signaling pathway disorders in CCC, EC, and SC. Finally, we infer MPP7 protein as potential therapeutic target for SC, whose biological functions are confirmed in SC cells. Our proteomic cohort provides valuable resources for understanding molecular mechanisms and developing treatment strategies of distinct histological subtypes.

Tat-malate dehydrogenase fusion protein protects neurons from oxidative and ischemic damage by reduction of reactive oxygen species and modulation of glutathione redox system

Malate dehydrogenase (MDH) plays an important role in the conversion of malate to oxaloacetate during the tricarboxylic acid cycle. In this study, we examined the role of cytoplasmic MDH (MDH1) in hydrogen peroxide (H₂O₂)-induced oxidative stress in HT22 cells and ischemia-induced neuronal damage in the gerbil hippocampus. The Tat-MDH1 fusion protein was constructed to enable the delivery of MDH1 into the intracellular space and penetration of the blood-brain barrier. Tat-MDH1, but not MDH1 control protein, showed significant cellular delivery in HT22 cells in a concentration- and time-dependent manner and gradual intracellular degradation in HT22 cells. Treatment with 4 μM Tat-MDH1 significantly ameliorated 200 μM H₂O₂-induced cell death, DNA fragmentation, and reactive oxygen species formation in HT22 cells. Transient increases in MDH1 immunoreactivity were detected in the hippocampal CA1 region 6-12 h after ischemia, but MDH1 activity significantly decreased 2 days after ischemia. Supplementation of Tat-MDH1 immediately after ischemia alleviated ischemia-induced hyperlocomotion and neuronal damage 1 and 4 days after ischemia. In addition, treatment with Tat-MDH1 significantly ameliorated the increases in hydroperoxides, lipid peroxidation, and reactive oxygen species 2 days after ischemia. Tat-MDH1 treatment maintained the redox status of the glutathione system in the hippocampus 2 days after ischemia. These results suggest that Tat-MDH1 exerts neuroprotective effects by reducing oxidative stress and maintaining glutathione redox system in the hippocampus.

ACR-Based Probe for the Quantitative Profiling of Histidine Reactivity in the Human Proteome

The quantitative profiling of residue reactivity in proteins promotes the discovery of covalent druggable targets for precise therapy. Histidine (His) residues, accounting for more than 20% of the active sites in enzymes, have not been systematically characterized for their reactivity, due to lack of labeling probes. Herein, we report a chemical proteomics platform for the site-specific quantitative analysis of His reactivity by combination of acrolein (ACR) labeling and reversible hydrazine chemistry enrichment. Based on this platform, in-depth characterization of His residues was conducted for the human proteome, in which the rich content of His residues (>8200) was quantified, including 317 His hyper-reactive residues. Intriguingly, it was observed that the hyper-reactive residues were less likely to be the sites for phosphorylation, and the possible mechanism of this antagonistic effect still needs to be evaluated in further research. Based on the first comprehensive map of His residue reactivity, many more residues could be adopted as the bindable sites to disrupt the activities of a diverse number of proteins; meanwhile, ACR derivatives could also be used as a novel reactive warhead in the development of covalent inhibitors.

Elevated MPP6 expression correlates with an unfavorable prognosis, angiogenesis and immune evasion in hepatocellular carcinoma

Background

Membrane palmitoylated proteins (MPPs) are engaged in various biological processes, such as cell adhesion and cell polarity. Dysregulated MPP members have different effects on hepatocellular carcinoma (HCC) development. However, the role of MPP6 in HCC has been unknown.

Method

HCC transcriptome and clinical data from different public databases were downloaded and analyzed, and the results were further validated by qRT-PCR, Western blotting and immunohistochemistry (IHC) using HCC cell lines and tissues. The association between MPP6 and prognosis, potential pathogenic mechanisms, angiogenesis, immune evasion, tumor mutation burden (TMB) and treatment response in HCC patients was analyzed by bioinformatics and IHC staining.

Results

MPP6 was significantly overexpressed in HCC, and its expression was related to T stage, pathologic stage, histologic grade and adverse prognosis in HCC patients. Gene set enrichment analysis revealed that differentially expressed genes were mainly enriched in the synthesis of genetic materials and the WNT signaling pathway. GEPIA database analysis and IHC staining suggested that MPP6 expression had a positive correlation with angiogenesis. Single-cell dataset analysis indicated that MPP6 was associated with features of the tumor microenvironment. Additional analyses discovered that MPP6 expression was inversely related to immune cell infiltration and was involved in tumor immune evasion. MPP6 expression was positively associated with TMB, and patients with high TMB had an adverse prognosis. Immunotherapy was more effective in HCC patients with low MPP6 expression, whereas those with high MPP6 expression responded better to sorafenib, gemcitabine, 5-FU, and doxorubicin.

Conclusions

Elevated MPP6 expression is associated with an unfavorable prognosis, angiogenesis and immune evasion in HCC. Moreover, MPP6 has the potential to be used to assess TMB and treatment response. Therefore, MPP6 might serve as a novel prognostic biomarker and therapeutic target for HCC.

Exploration of spatial heterogeneity of tumor microenvironment in nasopharyngeal carcinoma via transcriptional digital spatial profiling

The heterogeneity of nasopharyngeal carcinoma (NPC) leads to mixed clinical outcomes. We collected 92 regions of interest from 41 biopsies of patients with untreated NPC and obtained their transcripts using GeoMx Digital Spatial Profiling (DSP) technology. Spatial heterogeneity was determined by measuring the expression of marker genes in tumor cell-enriched (PanCK-expressing), immune cell-enriched (CD45-expressing), and normal epithelial (Endo) regions. We screened 16 prognostic markers in tumor cell-enriched regions and 4 prognostic markers in immune cell-enriched regions. The levels of CD8⁺ T follicular helper T cells, activated NK cells, and M0 macrophage contents were higher in tumor cell-enriched regions than in immune cell-enriched regions. Conversely, plasma cell and M2 macrophage levels were lower. The follicular helper T cells in tumor cell-enriched regions were negatively correlated with resting NK cells and positively correlated with activated NK cells. In immune cell-enriched regions, this relationship was reversed. We also explored the heterogeneity of HLA gene families, immune checkpoints, and metabolism-related genes in the three regions. In tumor cell-enriched regions, we obtained 19 prognosis-related metabolism genes via univariate cox analysis. We used multiplex immunofluorescence to verify the elevated expression of SLC8A1 and MDH1 in immune cell-enriched regions and tumor cell-enriched regions, respectively, both of which were associated with prognosis of NPC. In conclusion, we explored the spatial heterogeneity of the NPC tumor environment and found specific diagnostic and prognostic markers that can be used to differentiate tumor cell-enriched regions from immune cell-enriched regions in NPC.

A novel refined pyroptosis and inflammasome-related genes signature for predicting prognosis and immune microenvironment in pancreatic ductal adenocarcinoma

Pyroptosis is an inflammatory form of cell death, which plays a key role in the development of auto-inflammation and cancer. This study aimed to construct a pyroptosis and inflammasome-related genes for predicting prognosis of the pancreatic ductal adenocarcinoma (PDAC). This study was based primarily on the one-way analysis of variance, univariate Cox regression analysis, Least absolute shrinkage and selection operator (LASSO) Cox regression, a risk-prognostic signature, gene set variation analysis (GSVA), and immune microenvironment analysis, using PDAC data from The Cancer Genome Atlas and International Cancer Genome Consortium databases for the analysis of the role of 676 pyroptosis and inflammasome-related genes in PDAC retrieved from the Reactome and GeneCards databases. Lastly, we collected six paired PDAC and matched normal adjacent tissue samples to verify the expression of signature genes by quantitative real-time PCR (qRT-PCR). We identified 18 candidate pyroptosis and inflammasome-related genes that differed significantly between pathologic grades (stages) of PDAC patients. The univariate Cox and LASSO analyses pointed to six genes as the best variables for constructing a prognostic signature, including ACTA2, C1QTNF9, DNAH8, GATM, LBP, and NGF. The results of the risk prognostic model indicated that the AUCs at 1, 3, and 5 years were greater than 0.62. GSVA revealed that 'GLYCOLYSIS', 'P53 PATHWAY', 'KRAS SIGNALING UP', and 'INFLAMMATORY RESPONSE' hallmark gene sets were associated with the risk score. The high-risk group was associated with poor prognosis and was characterized by a lower infiltration of cells involved in anti-tumor immunity; whereas the low-risk group with higher T cells, NK cells, and macrophages showed relatively better survival and significantly higher upregulation of cytolytic scores and inflammation scores. Additionally, crucial pyroptosis and inflammasome-related genes were further validated by qRT-PCR. Our study revealed the prognostic role of the pyroptosis and inflammasome-related genes in PDAC for the first time. Simultaneously, the biological and prognostic heterogeneity of PDAC had been demonstrated, deepening our molecular understanding of this tumor.

Autophagy and beyond: Unraveling the complexity of UNC-51-like kinase 1 (ULK1) from biological functions to therapeutic implications

UNC-51-like kinase 1 (ULK1), as a serine/threonine kinase, is an autophagic initiator in mammals and a homologous protein of autophagy related protein (Atg) 1 in yeast and of UNC-51 in Caenorhabditis elegans. ULK1 is well-known for autophagy activation, which is evolutionarily conserved in protein transport and indispensable to maintain cell homeostasis. As the direct target of energy and nutrition-sensing kinase, ULK1 may contribute to the distribution and utilization of cellular resources in response to metabolism and is closely associated with multiple pathophysiological processes. Moreover, ULK1 has been widely reported to play a crucial role in human diseases, including cancer, neurodegenerative diseases, cardiovascular disease, and infections, and subsequently targeted small-molecule inhibitors or activators are also demonstrated. Interestingly, the non-autophagy function of ULK1 has been emerging, indicating that non-autophagy-relevant ULK1 signaling network is also linked with diseases under some specific contexts. Therefore, in this review, we summarized the structure and functions of ULK1 as an autophagic initiator, with a focus on some new approaches, and further elucidated the key roles of ULK1 in autophagy and non-autophagy. Additionally, we also discussed the relationships between ULK1 and human diseases, as well as illustrated a rapid progress for better understanding of the discovery of more candidate small-molecule drugs targeting ULK1, which will provide a clue on novel ULK1-targeted therapeutics in the future.

Tumor Suppressor Role of Wild-Type P53-Dependent Secretome and Its Proteomic Identification in PDAC

The study of the cancer secretome is gaining even more importance in cancers such as pancreatic ductal adenocarcinoma (PDAC), whose lack of recognizable symptoms and early detection assays make this type of cancer highly lethal. The wild-type p53 protein, frequently mutated in PDAC, prevents tumorigenesis by regulating a plethora of signaling pathways. The importance of the p53 tumor suppressive activity is not only primarily involved within cells to limit tumor cell proliferation but also in the extracellular space. Thus, loss of p53 has a profound impact on the secretome composition of cancer cells and marks the transition to invasiveness. Here, we demonstrate the tumor suppressive role of wild-type p53 on cancer cell secretome, showing the anti-proliferative, apoptotic and chemosensitivity effects of wild-type p53 driven conditioned medium. By using high-resolution SWATH-MS technology, we characterized the secretomes of p53-deficient and p53-expressing PDAC cells. We found a great number of secreted proteins that have known roles in cancer-related processes, 30 of which showed enhanced and 17 reduced secretion in response to p53 silencing. These results are important to advance our understanding on the link between wt-p53 and cancer microenvironment. In conclusion, this approach may detect a secreted signature specifically driven by wild-type p53 in PDAC.

The Metabolism Reprogramming of microRNA Let-7-Mediated Glycolysis Contributes to Autophagy and Tumor Progression

Cancer is usually a result of abnormal glucose uptake and imbalanced nutrient metabolization. The dysregulation of glucose metabolism, which controls the processes of glycolysis, gives rise to various physiological defects. Autophagy is one of the metabolic-related cellular functions and involves not only energy regeneration but also tumorigenesis. The dysregulation of autophagy impacts on the imbalance of metabolic homeostasis and leads to a variety of disorders. In particular, the microRNA (miRNA) Let-7 has been identified as related to glycolysis procedures such as tissue repair, stem cell-derived cardiomyocytes, and tumoral metastasis. In many cancers, the expression of glycolysis-related enzymes is correlated with Let-7, in which multiple enzymes are related to the regulation of the autophagy process. However, much recent research has not comprehensively investigated how Let-7 participates in glycolytic reprogramming or its links to autophagic regulations, mainly in tumor progression. Through an integrated literature review and omics-related profiling correlation, this review provides the possible linkage of the Let-7 network between glycolysis and autophagy, and its role in tumor progression.

Regulation and function of autophagy in pancreatic cancer

Oncogenic KRAS mutation-driven pancreatic ductal adenocarcinoma is currently the fourth-leading cause of cancer-related deaths in the United States. Macroautophagy (hereafter "autophagy") is one of the lysosome-dependent degradation systems that can remove abnormal proteins, damaged organelles, or invading pathogens by activating dynamic membrane structures (e.g., phagophores, autophagosomes, and autolysosomes). Impaired autophagy (including excessive activation and defects) is a pathological feature of human diseases, including pancreatic cancer. However, dysfunctional autophagy has many types and plays a complex role in pancreatic tumor biology, depending on various factors, such as tumor stage, microenvironment, immunometabolic state, and death signals. As a modulator connecting various cellular events, pharmacological targeting of nonselective autophagy may lead to both good and bad therapeutic effects. In contrast, targeting selective autophagy could reduce potential side effects of the drugs used. In this review, we describe the advances and challenges of autophagy in the development and therapy of pancreatic cancer.Abbreviations: AMPK: AMP-activated protein kinase; CQ: chloroquine; csc: cancer stem cells; DAMP: danger/damage-associated molecular pattern; EMT: epithelial-mesenchymal transition; lncRNA: long noncoding RNA; MIR: microRNA; PanIN: pancreatic intraepithelial neoplasia; PDAC: pancreatic ductal adenocarcinoma; PtdIns3K: phosphatidylinositol 3-kinase; SNARE: soluble NSF attachment protein receptor; UPS: ubiquitin-proteasome system.

Targeting Drug Chemo-Resistance in Cancer Using Natural Products

Cancer is one of the leading causes of death globally. The development of drug resistance is the main contributor to cancer-related mortality. Cancer cells exploit multiple mechanisms to reduce the therapeutic effects of anticancer drugs, thereby causing chemotherapy failure. Natural products are accessible, inexpensive, and less toxic sources of chemotherapeutic agents. Additionally, they have multiple mechanisms of action to inhibit various targets involved in the development of drug resistance. In this review, we have summarized the basic research and clinical applications of natural products as possible inhibitors for drug resistance in cancer. The molecular targets and the mechanisms of action of each natural product are also explained. Diverse drug resistance biomarkers were sensitive to natural products. P-glycoprotein and breast cancer resistance protein can be targeted by a large number of natural products. On the other hand, protein kinase C and topoisomerases were less sensitive to most of the studied natural products. The studies discussed in this review will provide a solid ground for scientists to explore the possible use of natural products in combination anticancer therapies to overcome drug resistance by targeting multiple drug resistance mechanisms.

Three cytosolic NAD-malate dehydrogenase isoforms of Arabidopsis thaliana: on the crossroad between energy fluxes and redox signaling

In yeast and animal cells, mitochondrial disturbances resulting from imbalances in the respiratory chain require malate dehydrogenase (MDH) activities for re-directing fluxes of reducing equivalents. In plants, in addition to mitochondria, plastids use malate valves to counterbalance and maintain redox-homeostasis. Arabidopsis expresses three cytosolic MDH isoforms, namely cyMDH1, cyMDH2, and cyMDH3, the latter possessing an N-terminal extension carrying a unique cysteine residue C2. In this study, redox-effects on activity and structure of all three cyMDH isoforms were analyzed in vitro. cyMDH1 and cyMDH2 were reversibly inactivated by diamide treatment, accompanied by dimerization via disulfide-bridge formation. In contrast, cyMDH3 forms dimers and higher oligomers upon oxidation, but its low specific activity is redox-independent. In the presence of glutathione, cyMDH1 and cyMDH2 are protected from dimerization and inactivation. In contrast, cyMDH3 still dimerizes but does not form oligomers any longer. From analyses of single and double cysteine mutants and structural modeling of cyMDH3, we conclude that the presence of C2 and C336 allows for multiple cross-links in the higher molecular mass complexes comprising disulfides within the dimer as well as between monomers of two different dimers. Furthermore, nuclear localization of cyMDH isoforms was significantly increased under oxidizing conditions in isolated Arabidopsis protoplasts, in particular of isoform cyMDH3. The unique cyMDH3 C2-C2-linked dimer is, therefore, a good candidate as a redox-sensor taking over moonlighting functions upon disturbances of energy metabolism, as shown previously for the glycolytic enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH) where oxidative modification of the sensitive catalytic cysteine residues induces nuclear translocation.

MPP7 promotes the migration and invasion of breast cancer cells via EGFR/AKT signaling

Metastasis is a major cause of breast cancer death. MPP7 is a cell polarity controller highly linked to cell migration; however, the function of MPP7 in breast cancer remains unknown. In this study, we reported that MPP7 expression was upregulated in breast cancer tissues and high MPP7 expression predicted poor survival in patients with breast cancer. Ectopic expression of MPP7 markedly enhanced the migration and invasion in breast cancer cells. In contrast, depletion of MPP7 resulted in impaired cell mobility and metastasis. Moreover, we demonstrated that MPP7 exerted its promotional effect via modulation of EMT and activation of the EGFR/AKT cascade. Our study reveals an oncogenic role of MPP7 in breast cancer and suggests that MPP7 may serve as a potential target for exploring novel therapeutic strategies against breast cancer metastasis.

Not Just Another Scaffolding Protein Family: The Multifaceted MPPs

Membrane palmitoylated proteins (MPPs) are a subfamily of a larger group of multidomain proteins, namely, membrane-associated guanylate kinases (MAGUKs). The ubiquitous expression and multidomain structure of MPPs provide the ability to form diverse protein complexes at the cell membranes, which are involved in a wide range of cellular processes, including establishing the proper cell structure, polarity and cell adhesion. The formation of MPP-dependent complexes in various cell types seems to be based on similar principles, but involves members of different protein groups, such as 4.1-ezrin-radixin-moesin (FERM) domain-containing proteins, polarity proteins or other MAGUKs, showing their multifaceted nature. In this review, we discuss the function of the MPP family in the formation of multiple protein complexes. Notably, we depict their significant role for cell physiology, as the loss of interactions between proteins involved in the complex has a variety of negative consequences. Moreover, based on recent studies concerning the mechanism of membrane raft formation, we shed new light on a possible role played by MPPs in lateral membrane organization.

Comprehensive analysis of prognostic tumor microenvironment-related genes in osteosarcoma patients

Background

Tumor microenvironment (TME) plays an important role in malignant tumors. Our study aimed to investigate the effect of the TME and related genes in osteosarcoma patients.

Methods

Gene expression profiles and clinical data of osteosarcoma patients were downloaded from the TARGET dataset. ESTIMATE algorithm was used to quantify the immune score. Then, the association between immune score and prognosis was studied. Afterward, a differential analysis was performed based on the high- and low-immune scores to determine TME-related genes. Additionally, Cox analyses were performed to construct two prognostic signatures for overall survival (OS) and disease-free survival (DFS), respectively. Two datasets obtained from the GEO database were used to validate signatures.

Results

Eighty-five patients were included in our research. The survival analysis indicated that patients with higher immune score have a favorable OS and DFS. Moreover, 769 genes were determined as TME-related genes. The unsupervised clustering analysis revealed two clusters were significantly related to immune score and T cells CD4 memory fraction. In addition, two signatures were generated based on three and two TME-related genes, respectively. Both two signatures can significantly divide patients into low- and high-risk groups and were validated in two GEO datasets. Afterward, the risk score and metastatic status were identified as independent prognostic factors for both OS and DFS and two nomograms were generated. The C-indexes of OS nomogram and DFS nomogram were 0.791 and 0.711, respectively.

Conclusion

TME was associated with the prognosis of osteosarcoma patients. Prognostic models based on TME-related genes can effectively predict OS and DFS of osteosarcoma patients.

Integrated Analysis of RNA-Binding Proteins in Glioma

RNA-binding proteins (RBPs) play important roles in many cancer types. However, RBPs have not been thoroughly and systematically studied in gliomas. Global analysis of the functional impact of RBPs will provide a better understanding of gliomagenesis and new insights into glioma therapy. In this study, we integrated a list of the human RBPs from six sources-Gerstberger, SONAR, Gene Ontology project, Poly(A) binding protein, CARIC, and XRNAX-which covered 4127 proteins with RNA-binding activity. The RNA sequencing data were downloaded from The Cancer Genome Atlas (TCGA) (n = 699) and Chinese Glioma Genome Atlas (CGGA) (n = 325 + 693). We examined the differentially expressed genes (DEGs) using the R package DESeq2, and constructed a weighted gene co-expression network analysis (WGCNA) of RBPs. Furthermore, survival analysis was also performed based on the univariate and multivariate Cox proportional hazards regression models. In the WGCNA analysis, we identified a key module involved in the overall survival (OS) of glioblastomas. Survival analysis revealed eight RBPs (PTRF, FNDC3B, SLC25A43, ZC3H12A, LRRFIP1, HSP90B1, HSPA5, and BNC2) are significantly associated with the survival of glioblastoma patients. Another 693 patients within the CGGA database were used to validate the findings. Additionally, 3564 RBPs were classified into canonical and non-canonical RBPs depending on the domains that they contain, and non-canonical RBPs account for the majority (72.95%). The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that some non-canonical RBPs may have functions in glioma. Finally, we found that the knockdown of non-canonical RBPs, PTRF, or FNDC3B can alone significantly inhibit the proliferation of LN229 and U251 cells. Simultaneously, RNA Immunoprecipitation (RIP) analysis indicated that PTRF may regulate cell growth and death- related pathways to maintain tumor cell growth. In conclusion, our findings presented an integrated view to assess the potential death risks of glioblastoma at a molecular level, based on the expression of RBPs. More importantly, we identified non-canonical RNA-binding proteins PTRF and FNDC3B, showing them to be potential prognostic biomarkers for glioblastoma.

Hypomethylation-Linked Activation of PLCE1 Impedes Autophagy and Promotes Tumorigenesis through MDM2-Mediated Ubiquitination and Destabilization of p53

Esophageal squamous cell carcinoma (ESCC) is one of the deadliest malignant diseases. Multiple studies with large clinic-based cohorts have revealed that variations of phospholipase C epsilon 1 (PLCE1) correlate with esophageal cancer susceptibility. However, the causative role of PLCE1 in ESCC has remained elusive. Here, we observed that hypomethylation-mediated upregulation of PLCE1 expression was implicated in esophageal carcinogenesis and poor prognosis in ESCC cohorts. PLCE1 inhibited cell autophagy and suppressed the protein expression of p53 and various p53-targeted genes in ESCC. Moreover, PLCE1 decreased the half-life of p53 and promoted p53 ubiquitination, whereas it increased the half-life of mouse double minute 2 homolog (MDM2) and inhibited its ubiquitination, leading to MDM2 stabilization. Mechanistically, the function of PLCE1 correlated with its direct binding to both p53 and MDM2, which promoted MDM2-dependent ubiquitination of p53 and subsequent degradation in vitro. Consequently, knockdown of PLCE1 combined with transfection of a recombinant adenoviral vector encoding wild-type p53 resulted in significantly increased levels of autophagy and apoptosis of esophageal cancer in vivo. Clinically, the upregulation of PLCE1 and mutant p53 protein predicted poor overall survival of patients with ESCC, and PLCE1 was positively correlated with p53 in ESCC cohorts. Collectively, this work identified an essential role for PLCE1- and MDM2-mediated ubiquitination and degradation of p53 in inhibiting ESCC autophagy and indicates that targeting the PLCE1-MDM2-p53 axis may provide a novel therapeutic approach for ESCC. SIGNIFICANCE: These findings identify hypomethylation-mediated activation of PLCE1 as a potential oncogene that blocks cellular autophagy of esophageal carcinoma by facilitating the MDM2-dependent ubiquitination of p53 and subsequent degradation. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/11/2175/F1.large.jpg.

The Role of Autophagy in Pancreatic Cancer-Recent Advances

Pancreatic ductal adenocarcinoma (PDAC) remains one of the deadliest cancers with a 5-year survival rate of only 9%, despite ongoing efforts to improve treatment. This dismal prognosis is due to the difficulty of early stage diagnosis, drug resistance, and likelihood of metastasis development. It is therefore of great importance to identify appropriate therapeutic targets and gain a greater understanding of PDAC biology. Autophagy is a membrane-mediated degradation and recycling mechanism, which is crucial for cell homeostasis. There is evidence for both a tumor-suppressive and a tumor-promoting role of autophagy in cancer, and this is likely context dependent. Within PDAC, a large body of evidence points towards autophagy being required for tumor survival and metabolism. In this review, we describe the recent advances in the understanding of the role and regulation of autophagy in PDAC.

Targeting Autophagy in Cancer: Recent Advances and Future Directions

Autophagy, a multistep lysosomal degradation pathway that supports nutrient recycling and metabolic adaptation, has been implicated as a process that regulates cancer. Although autophagy induction may limit the development of tumors, evidence in mouse models demonstrates that autophagy inhibition can limit the growth of established tumors and improve response to cancer therapeutics. Certain cancer genotypes may be especially prone to autophagy inhibition. Different strategies for autophagy modulation may be needed depending on the cancer context. Here, we review new advances in the molecular control of autophagy, the role of selective autophagy in cancer, and the role of autophagy within the tumor microenvironment and tumor immunity. We also highlight clinical efforts to repurpose lysosomal inhibitors, such as hydroxychloroquine, as anticancer agents that block autophagy, as well as the development of more potent and specific autophagy inhibitors for cancer treatment, and review future directions for autophagy research. SIGNIFICANCE: Autophagy plays a complex role in cancer, but autophagy inhibition may be an effective therapeutic strategy in advanced cancer. A deeper understanding of autophagy within the tumor microenvironment has enabled the development of novel inhibitors and clinical trial strategies. Challenges and opportunities remain to identify patients most likely to benefit from this approach.