Autophagy plays a critical role in ChLym-1-induced cytotoxicity of non-hodgkin's lymphoma cells

Inhibition of Hedgehog signaling ameliorates foam cell formation by promoting autophagy in early atherosclerosis

Macrophages are the origin of most foam cells in the early stage of atherosclerotic plaques. However, the mechanism involved in the formation of macrophage-derived foam cell formation remains unclear. Here, we revealed that the hedgehog (Hh) signaling is critical in autophagy-lysosome pathway regulation and macrophage-derived foam cell formation. Inhibition of Hh signaling by vismodegib ameliorated lipid deposition and oxidative stress level in atherosclerotic plaques in high-fat diet-fed apoE-/- mice. For mechanistic study, how the Hh signaling modulate the process of foam cell formation were accessed afterward. Unexpectedly, we found that suppression of Hh signaling in apoE-/- mice had no significant impact on circulating cholesterol levels, indicating that Hh pathway modulate the procession of atherosclerotic plaque not through a traditional lipid-lowing mechanism. Instead, vismodegib was found to accelerate autophagosomes maturation as well as cholesterol efflux in macrophage-derived foam cell and in turn improve foam cell formation, while autophagy inhibitors (LY294002 or CQ) administration significantly attenuated vismodegib-induced cholesterol efflux and reversed the effect on foam cell formation. Therefore, our result demonstrated that inhibition of the Hh signaling pathway increases cholesterol efflux and ameliorates macrophage-derived foam cell formation by promoting autophagy in vitro. Our data thus suggested a novel therapeutic target of atherosclerosis and indicated the potential of vismodegib to treat atherosclerosis.

Autophagy in Hematological Malignancies

Simple Summary

Autophagy is a dynamic and tightly regulated process that seems to have dual effects in cancer. In some contexts, it can induce carcinogenesis and promote cancer cell survival, whereas in others, it acts preventing tumor cell growth and tumor progression. Thus, autophagy functions seem to strictly depend on cancer ontogenesis, progression, and type. Here, we will dive into the current knowledge of autophagy in hematological malignancies and will highlight the main genetic components involved in each cancer type.

Abstract

Autophagy is a highly conserved metabolic pathway via which unwanted intracellular materials, such as unfolded proteins or damaged organelles, are digested. It is activated in response to conditions of oxidative stress or starvation, and is essential for the maintenance of cellular homeostasis and other vital functions, such as differentiation, cell death, and the cell cycle. Therefore, autophagy plays an important role in the initiation and progression of tumors, including hematological malignancies, where damaged autophagy during hematopoiesis can cause malignant transformation and increase cell proliferation. Over the last decade, the importance of autophagy in response to standard pharmacological treatment of hematological tumors has been observed, revealing completely opposite roles depending on the tumor type and stage. Thus, autophagy can promote tumor survival by attenuating the cellular damage caused by drugs and/or stabilizing oncogenic proteins, but can also have an antitumoral effect due to autophagic cell death. Therefore, autophagy-based strategies must depend on the context to create specific and safe combination therapies that could contribute to improved clinical outcomes. In this review, we describe the process of autophagy and its role on hematopoiesis, and we highlight recent research investigating its role as a potential therapeutic target in hematological malignancies. The findings suggest that genetic variants within autophagy-related genes modulate the risk of developing hemopathies, as well as patient survival.

LOXL2 Upregulation in Gliomas Drives Tumorigenicity by Activating Autophagy to Promote TMZ Resistance and Trigger EMT

Glioma is the most prevalent primary brain tumor in adults and has an extremely unfavorable prognosis. As a member of the lysyl oxidase (LOX) family, lysyl-oxidase-like-2 (LOXL2) is known to play different roles in different tumors. However, the role of LOXL2 in glioma has not yet been fully elucidated. In the present study, we detected that LOXL2 was considerably upregulated in glioma and that LOXL2 upregulation was evidently related to glioma WHO grade, malignant molecular subtypes, and poor prognosis in glioma patients. Additionally, we found that LOXL2 not only promoted glioma cells proliferation, migration, invasion, and induced the epithelial-to-mesenchymal transition (EMT) process, but also reduced the sensitivity of glioma cells to temozolomide (TMZ). Furthermore, we identified that LOXL2 reduced TMZ sensitivity and induced EMT in glioma via the activation of autophagy. Mechanistically, LOXL2 enhanced Atg7 expression by promoting the phosphorylation of Erk1/2, leading to the activation of autophagy and regulation of EMT process and TMZ sensitivity through autophagy. Our study describes an LOXL2-Erk1/2-Atg7 signaling axis that influences glioma EMT and chemosensitivity through autophagy; moreover, LOXL2 may serve as a promising therapeutic target in the treatment of glioma.

Targeting PARP and autophagy evoked synergistic lethality in hepatocellular carcinoma

Hepatocellular carcinoma (HCC), one of the most lethal malignancies worldwide, has limited efficient therapeutic options. Here, we first demonstrated that simultaneously targeting poly (ADP-ribose) polymerase (PARP) and autophagy could evoke striking synergistic lethality in HCC cells. Specifically, we found that the PARP inhibitor Niraparib induced cytotoxicity accompanied by significant autophagy formation and autophagic flux in HCC cells. Further experiments showed that Niraparib induced suppression of the Akt/mTOR pathway and activation of the Erk1/2 cascade, two typical signaling pathways related to autophagy. In addition, the accumulation of reactive oxygen species was triggered, which was involved in Niraparib-induced autophagy. Blocking autophagy by chloroquine (CQ) in combination with Niraparib further enhanced cytotoxicity, induced apoptosis and inhibited colony formation in HCC cells. Synergistic inhibition was also observed in Huh7 xenografts in vivo. Mechanistically, we showed that autophagy inhibition abrogated Niraparib-induced cell-cycle arrest and checkpoint activation. Cotreatment with CQ and Niraparib promoted the formation of γ-H2AX foci while inhibiting the recruitment of the homologous recombination repair protein RAD51 to double-strand break sites. Thus, the present study developed a novel promising strategy for the management of HCC in the clinic and highlighted a potential approach to expand the application of PARP inhibitors.

Therapeutic Modulation of Autophagy in Leukaemia and Lymphoma

Haematopoiesis is a tightly orchestrated process where a pool of hematopoietic stem and progenitor cells (HSPCs) with high self-renewal potential can give rise to both lymphoid and myeloid lineages. The HSPCs pool is reduced with ageing resulting in few HSPC clones maintaining haematopoiesis thereby reducing blood cell diversity, a phenomenon called clonal haematopoiesis. Clonal expansion of HSPCs carrying specific genetic mutations leads to increased risk for haematological malignancies. Therefore, it comes as no surprise that hematopoietic tumours develop in higher frequency in elderly people. Unfortunately, elderly patients with leukaemia or lymphoma still have an unsatisfactory prognosis compared to younger ones highlighting the need to develop more efficient therapies for this group of patients. Growing evidence indicates that macroautophagy (hereafter referred to as autophagy) is essential for health and longevity. This review is focusing on the role of autophagy in normal haematopoiesis as well as in leukaemia and lymphoma development. Attenuated autophagy may support early hematopoietic neoplasia whereas activation of autophagy in later stages of tumour development and in response to a variety of therapies rather triggers a pro-tumoral response. Novel insights into the role of autophagy in haematopoiesis will be discussed in light of designing new autophagy modulating therapies in hematopoietic cancers.

Induction of anti-EGFR immune response with mimotopes identified from a phage display peptide library by panitumumab

The epidermal growth factor receptor (EGFR) is overexpressed in several epithelial tumors. Anti-EGFR humanized monoclonal antibodies, cetuximab and panitumumab, in combination with chemotherapy have improved the prognosis for patients with wild-type RAS tumors. To identify mimotopes of EGFR and develop mimotope-based EGFR vaccines, we screened a phage display peptide library with panitumumab. Two EGFR mimotopes P19 and P26, which could be recognized by panitumumab specifically, were isolated. To enhance the immune responses, we generated recombinant proteins of P19 or P26 fused to a heat-shock cognate protein 70 (Hsc70), and evaluated the efficacy of Hsc70-P19 and Hsc70-P26 as vaccines in vivo. Immunization with Hsc70-P19 or Hsc70-P26 fusion protein stimulated the immune system to produce specific antibodies against peptides as well as EGFR. Moreover, antibodies elicited against mimotopes could induce antibody-dependent cellular cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and inhibit the proliferation of EGFR-overexpressing A431 cells. Treatment with Hsc70-P19 and Hsc70-P26 significantly reduced tumor growth in BALB/c transplantable lung cancer models. Although there was no sequence homology between the phage-derived peptides and EGFR by alignments, both peptides mimic the conformational structure of EGFR binding to panitumumab. In conclusion, the mimotopes we identified from phage display peptide library could be promising candidate vaccines for active anti-EGFR immunotherapy against cancers.

Lym-1 Chimeric Antigen Receptor T Cells Exhibit Potent Anti-Tumor Effects against B-Cell Lymphoma

T cells expressing chimeric antigen receptors (CARs) recognizing CD19 epitopes have produced remarkable anti-tumor effects in patients with B-cell malignancies. However, cancer cells lacking recognized epitopes can emerge, leading to relapse and death. Thus, CAR T cells targeting different epitopes on different antigens could improve immunotherapy. The Lym-1 antibody targets a conformational epitope of Human Leukocyte Antigen-antigen D Related (HLA-DR) on the surface of human B-cell lymphomas. Lym-1 CAR T cells were thus generated for evaluation of cytotoxic activity towards lymphoma cells in vitro and in vivo. Human T cells from healthy donors were transduced to express a Lym-1 CAR, and assessed for epitope-driven function in culture and towards Raji xenografts in NOD-scidIL2Rgamma^null (NSG) mice. Lym-1 CAR T cells exhibited epitope-driven activation and lytic function against human B-cell lymphoma cell lines in culture and mediated complete regression of Raji/Luciferase-Green fluorescent protein (Raji/Luc-GFP) in NSG mice with similar or better reactivity than CD19 CAR T cells. Lym-1 CAR transduction of T cells is a promising immunotherapy for patients with Lym-1 epitope positive B-cell malignancies.

Blocking autophagy improves the anti-tumor activity of afatinib in lung adenocarcinoma with activating EGFR mutations in vitro and in vivo

Afatinib, a second-generation tyrosine kinase inhibitor (TKI), has been approved for the treatment of advanced EGFR-mutant non-small cell lung cancer (NSCLC). However, afatinib’s clinical application is still hampered by acquired resistance. Recently, autophagy is considered as an important mechanism of resistance to TKI. Herein, we investigated the autophagy induction as well as its influence on anti-lung adenocarcinoma activity of afatinib in two activating EGFR-mutants H1975 and H1650 cells. First, Growth inhibition and caspase-dependent apoptosis were observed in afatinib-treated H1975 and H1650 cells. Then we confirmed afatinib-induced autophagy in H1975 and H1650 cells. Importantly, autophagy inhibition using chloroquine (CQ) and 3-MA enhanced the cytotoxicity of afatinib, elucidating the cytoprotective role of autophagy in lung adenocarcinoma therapy with afatinib. Further study suggested that Akt/mTOR and Erk signaling pathways were involved in afatinib-induced autophagy, and reactive oxygen species (ROS) acted as an intracellular transducer regulating both autophagy and apoptosis in afatinib-treated H1975 and H1650 cells. Moreover, the in vivo experiment in xenograft model using H1975 cell line confirmed the enhanced anti-lung adenocarcinoma efficacy of afatinib when combined with autophagy inhibitor CQ. Thus, blocking autophagy may be a promising strategy to overcome resistance and increase sensitivity to afatinib in lung adenocarcinoma harboring activating EGFR mutations.

Cytoplasmic RAP1 mediates cisplatin resistance of non-small cell lung cancer

Cytotoxic chemotherapy agents (e.g., cisplatin) are the first-line drugs to treat non-small cell lung cancer (NSCLC) but NSCLC develops resistance to the agent, limiting therapeutic efficacy. Despite many approaches to identifying the underlying mechanism for cisplatin resistance, there remains a lack of effective targets in the population that resist cisplatin treatment. In this study, we sought to investigate the role of cytoplasmic RAP1, a previously identified positive regulator of NF-κB signaling, in the development of cisplatin resistance in NSCLC cells. We found that the expression of cytoplasmic RAP1 was significantly higher in high-grade NSCLC tissues than in low-grade NSCLC; compared with a normal pulmonary epithelial cell line, the A549 NSCLC cells exhibited more cytoplasmic RAP1 expression as well as increased NF-κB activity; cisplatin treatment resulted in a further increase of cytoplasmic RAP1 in A549 cells; overexpression of RAP1 desensitized the A549 cells to cisplatin, and conversely, RAP1 depletion in the NSCLC cells reduced their proliferation and increased their sensitivity to cisplatin, indicating that RAP1 is required for cell growth and has a key mediating role in the development of cisplatin resistance in NSCLC cells. The RAP1-mediated cisplatin resistance was associated with the activation of NF-κB signaling and the upregulation of the antiapoptosis factor BCL-2. Intriguingly, in the small portion of RAP1-depleted cells that survived cisplatin treatment, no induction of NF-κB activity and BCL-2 expression was observed. Furthermore, in established cisplatin-resistant A549 cells, RAP1 depletion caused BCL2 depletion, caspase activation and dramatic lethality to the cells. Hence, our results demonstrate that the cytoplasmic RAP1–NF-κB–BCL2 axis represents a key pathway to cisplatin resistance in NSCLC cells, identifying RAP1 as a marker and a potential therapeutic target for cisplatin resistance of NSCLC.

The Role of Deoxycytidine Kinase (dCK) in Radiation-Induced Cell Death

Deoxycytidine kinase (dCK) is a key enzyme in deoxyribonucleoside salvage and the anti-tumor activity for many nucleoside analogs. dCK is activated in response to ionizing radiation (IR)-induced DNA damage and it is phosphorylated on Serine 74 by the Ataxia-Telangiectasia Mutated (ATM) kinase in order to activate the cell cycle G2/M checkpoint. However, whether dCK plays a role in radiation-induced cell death is less clear. In this study, we genetically modified dCK expression by knocking down or expressing a WT (wild-type), S74A (abrogates phosphorylation) and S74E (mimics phosphorylation) of dCK. We found that dCK could decrease IR-induced total cell death and apoptosis. Moreover, dCK increased IR-induced autophagy and dCK-S74 is required for it. Western blotting showed that the ratio of phospho-Akt/Akt, phospho-mTOR/mTOR, phospho-P70S6K/P70S6K significantly decreased in dCK-WT and dCK-S74E cells than that in dCK-S74A cells following IR treatment. Reciprocal experiment by co-immunoprecipitation showed that mTOR can interact with wild-type dCK. IR increased polyploidy and decreased G2/M arrest in dCK knock-down cells as compared with control cells. Taken together, phosphorylated and activated dCK can inhibit IR-induced cell death including apoptosis and mitotic catastrophe, and promote IR-induced autophagy through PI3K/Akt/mTOR pathway.

Targeting Hedgehog signaling pathway and autophagy overcomes drug resistance of BCR-ABL-positive chronic myeloid leukemia

The frontline tyrosine kinase inhibitor (TKI) imatinib has revolutionized the treatment of patients with chronic myeloid leukemia (CML). However, drug resistance is the major clinical challenge in the treatment of CML. The Hedgehog (Hh) signaling pathway and autophagy are both related to tumorigenesis, cancer therapy, and drug resistance. This study was conducted to explore whether the Hh pathway could regulate autophagy in CML cells and whether simultaneously regulating the Hh pathway and autophagy could induce cell death of drug-sensitive or -resistant BCR-ABL(+) CML cells. Our results indicated that pharmacological or genetic inhibition of Hh pathway could markedly induce autophagy in BCR-ABL(+) CML cells. Autophagic inhibitors or ATG5 and ATG7 silencing could significantly enhance CML cell death induced by Hh pathway suppression. Based on the above findings, our study demonstrated that simultaneously inhibiting the Hh pathway and autophagy could markedly reduce cell viability and induce apoptosis of imatinib-sensitive or -resistant BCR-ABL(+) cells. Moreover, this combination had little cytotoxicity in human peripheral blood mononuclear cells (PBMCs). Furthermore, this combined strategy was related to PARP cleavage, CASP3 and CASP9 cleavage, and inhibition of the BCR-ABL oncoprotein. In conclusion, this study indicated that simultaneously inhibiting the Hh pathway and autophagy could potently kill imatinib-sensitive or -resistant BCR-ABL(+) cells, providing a novel concept that simultaneously inhibiting the Hh pathway and autophagy might be a potent new strategy to overcome CML drug resistance.

A novel therapeutic approach against B-cell non-Hodgkin's lymphoma through co-inhibition of Hedgehog signaling pathway and autophagy

B-cell non-Hodgkin's lymphoma (B-NHL) is one of the most common types of cancer in the world, with half of the patients dying due to the resistance or tolerance against the treatment. Thus, a novel therapeutic approach for B-NHL treatment was urgently needed. In this study, we investigated the potential of co-inhibition of Hedgehog signaling pathway (Hh) and autophagy in B-NHL therapy. We reported that vismodegib, an inhibitor of Hedgehog signaling pathway, could block the Hh pathway and induce cytotoxicity and apoptosis in B-NHL Raji cells. During this process, autophagy was activated as a response to Hh inhibition. Importantly, inhibition of autophagy potentiated the cytotoxicity and caspase 3-dependent apoptosis induced by vismodegib in B-NHL cells. Furthermore, clearance of ROS generation caused a decreased activity of autophagy and attenuated cytotoxicity in vismodegib-treated cells, while inhibition of autophagy accelerated the formation of ROS, indicating that ROS was required for vismodegib-induced autophagy and cytotoxicity in B-NHL cells. Our results demonstrated that co-inhibition of Hh pathway and autophagy could potently kill B-NHL cells and highlighted a novel approach for B-NHL therapy by co-inhibition of Hh pathway and cytoprotective autophagy.

Protective role of autophagy and autophagy-related protein 5 in early tumorigenesis

Autophagy, a fundamental cellular catabolic process, is involved in the development of numerous diseases including cancer. Autophagy seems to have an ambivalent impact on tumor development. While increasing evidence indicates a cytoprotective role for autophagy that can contribute to resistance against chemotherapy and even against the adverse, hypoxic environment of established tumors, relatively few publications focus on the role of autophagy in early tumorigenesis. However, the consensus is that autophagy is inhibitory for the genesis of tumors. To understand this apparent contradiction, more detailed information about the roles of the individual participants in autophagy is needed. This review will address this topic with respect to autophagy-related protein 5 (ATG5), which in several lines of investigation has been ascribed special significance in the autophagic pathway. Furthermore, it was recently shown that an ATG5 deficiency in melanocytes interferes with oncogene-induced senescence, thus promoting melanoma tumorigenesis. Similarly, an ATG5 deficiency resulted in tumors of the lung and liver in experimental mouse models. Taken together, these findings indicate that ATG5 and the autophagy to which it contributes are essential gatekeepers restricting early tumorigenesis in multiple tissues.

VAMP8 facilitates cellular proliferation and temozolomide resistance in human glioma cells

BACKGROUND

Malignant glioma is a common and lethal primary brain tumor in adults. Here we identified a novel oncoprotein, vesicle-associated membrane protein 8 (VAMP8), and investigated its roles in tumorigenisis and chemoresistance in glioma.

METHODS

The expression of gene and protein were determined by quantitative PCR and Western blot, respectively. Histological analysis of 282 glioma samples and 12 normal controls was performed by Pearson's chi-squared test. Survival analysis was performed using the log-rank test and Cox proportional hazards regression. Cell proliferation and cytotoxicity assay were conducted using Cell Counting Kit-8. Autophagy was detected by confocal microscopy and Western blot.

RESULTS

VAMP8 was significantly overexpressed in human glioma specimens and could become a potential novel prognostic and treatment-predictive marker for glioma patients. Overexpression of VAMP8 promoted cell proliferation in vitro and in vivo, whereas knockdown of VAMP8 attenuated glioma growth by arresting cell cycle in the G0/G1 phase. Moreover, VAMP8 contributed to temozolomide (TMZ) resistance by elevating the expression levels of autophagy proteins and the number of autophagosomes. Further inhibition of autophagy via siRNA-mediated knockdown of autophagy-related gene 5 (ATG5) or syntaxin 17 (STX17) reversed TMZ resistance in VAMP8-overexpressing cells, while silencing of VAMP8 impaired the autophagic flux and alleviated TMZ resistance in glioma cells.

CONCLUSION

Our findings identified VAMP8 as a novel oncogene by promoting cell proliferation and therapeutic resistance in glioma. Targeting VAMP8 may serve as a potential therapeutic regimen for the treatment of glioma.