Targeting autophagy in lymphomas: a double-edged sword?

Basic Fibroblast Growth Factor Blockade Leads to Distinct Cellular Responses in Melanoma B16 Cells

Although bFGF is highly expressed in the melanoma tissues, its specific role in melanoma progression is still not completely clarified. Here, we investigated the consequent cellular responses in melanoma B16 cells after bFGF blocking by using a neutralizing monoclonal antibody (mAb). Results showed that bFGF mAb concentration dependent inhibited tumor cell growth. Meanwhile, cell viability suppression was accompanied by reduced levels of proangiogenic factors in low-concentration bFGF mAb-treated cancer cells and increased levels of proangiogenic factors in high-concentration bFGF mAb-treated cells. Furthermore, low-concentration bFGF mAb induced autophagy but not apoptosis; conversely, high-concentration bFGF mAb led to activation of autophagy and apoptosis. Finally, we found that different degrees of bFGF blockade-induced autophagy play distinct roles in promoting cell survival and cell death. Our findings revealed different adaptive responses to bFGF blockade in melanoma cells, which should be taken seriously when developing bFGF-targeting agents for melanoma treatment.

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.

Engineering Nanoplatform for Combined Cancer Therapeutics via Complementary Autophagy Inhibition

Despite advances in the development of tumor treatments, mortality from cancer continues to increase. Nanotechnology is expected to provide an innovative anti-cancer therapy, to combat challenges such as multidrug resistance and tumor recurrence. Nevertheless, tumors can greatly rely on autophagy as an alternative source for metabolites, and which desensitizes cancer cells to therapeutic stress, hindering the success of any current treatment paradigm. Autophagy is a conserved process by which cells turn over their own constituents to maintain cellular homeostasis. The multistep autophagic pathway provides potentially druggable targets to inhibit pro-survival autophagy under various therapeutic stimuli. In this review, we focus on autophagy inhibition based on functional nanoplatforms, which may be a potential strategy to increase therapeutic sensitivity in combinational cancer therapies, including chemotherapy, radiotherapy, phototherapy, sonodynamic therapy, and immunotherapy.

CD36 and LC3B initiated autophagy in B cells regulates the humoral immune response

Scavenger receptors are pattern recognition receptors that recognize both foreign and self-ligands, and initiate different mechanisms of cellular activation, often as co-receptors. The function of scavenger receptor CD36 in the immune system has mostly been studied in macrophages but it is also highly expressed by innate type B cells where its function is less explored. Here we report that CD36 is involved in macro-autophagy/autophagy in B cells, and in its absence, the humoral immune response is impaired. We found that CD36-deficient B cells exhibit a significantly reduced plasma cell formation, proliferation, mitochondrial mobilization and oxidative phosphorylation. These changes were accompanied by impaired initiation of autophagy, and we found that CD36 regulated autophagy and colocalized with autophagosome membrane protein MAP1LC3/LC3 (microtubule-associated protein 1 light chain 3). When we investigated T-cell-dependent immune responses, we found that mice with CD36 deficiency, specifically in B cells, exhibited attenuated germinal center responses, class switching, and antibody production as well as autophagosome formation. These findings establish a critical role for CD36 in B cell responses and may also contribute to our understanding of CD36-mediated autophagy in other cells as well as in B cell lymphomas that have been shown to express the receptor.Abbreviations: AICDA/AID: activation-induced cytidine deaminase; ATG5: autophagy related 5; ATP: adenosine triphosphate; BCR: B-cell receptor; CPG: unmethylated cytosine-guanosine; CQ: chloroquine; DC: dendritic cells; FOB: follicular B cells; GC: germinal center; Ig: immunoglobulin; LPS: lipopolysaccharide; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MFI: mean fluorescence intensity; MZB: marginal zone B cells; NP-CGG: 4-hydroxy-3-nitrophenylacetyl-chicken gamma globulin; OCR: oxygen consumption rate; oxLDL: oxidized low-density lipoprotein; PC: plasma cells; Rapa: rapamycin; SQSTM1/p62: sequestosome 1; SRBC: sheep red blood cells; Tfh: follicular helper T cells; TLR: toll-like receptor.

m6A mRNA Methylation Regulates LKB1 to Promote Autophagy of Hepatoblastoma Cells through Upregulated Phosphorylation of AMPK

The N6-methyladenosine (m6A) RNA modification can regulate autophagy to modulate the growth and development of tumors, but the mechanism of m6A modification for the regulation of autophagy in hepatocellular carcinoma cells (HCC) remains unclear. In the study, the knockdown of the Wilms' tumor 1-associating protein (WTAP) was made in HCC to study the correlation between m6A modification and autophagy. A fluorescent confocal microscopy analysis showed that the knockdown of WTAP could facilitate the autophagy of HCC. A Western blot analysis showed that the level of p-AMPK was decreased in WTAP-knockdown HCC cells. Additionally, LKB1, the upstream kinase of AMPK, was regulated by WTAP and it could mediate the phosphorylation of AMPK in an m6A-dependent manner. Further studies revealed that the knockdown of WTAP could reduce the level of LKB1 mRNA with m6A. This could result in the increased stability of LKB1 mRNA to promote its expression. The knockdown of WTAP could upregulate the level of autophagy and inhibit HCC proliferation. However, the overexpression of WTAP could resist autophagic cell death.

Autophagy-related signaling pathways are involved in cancer (Review)

Autophagy is a self-digestion process in cells that can maintain energy homeostasis under normal circumstances. However, misfolded proteins, damaged mitochondria and other unwanted components in cells can be decomposed and reused via autophagy in some specific cases (including hypoxic stress, low energy states or nutrient deprivation). Therefore, autophagy serves a positive role in cell survival and growth. However, excessive autophagy may lead to apoptosis. Furthermore, abnormal autophagy may lead to carcinogenesis and promote tumorigenesis in normal cells. In tumor cells, autophagy may provide the energy required for excessive proliferation, promote the growth of cancer cells, and evade apoptosis caused by certain treatments, including radiotherapy and chemotherapy, resulting in increased treatment resistance and drug resistance. On the other hand, autophagy leads to an insufficient nutrient supply in cancer cells and the destruction of energy homeostasis, thereby inducing cancer cell apoptosis. Therefore, understanding the mechanism of the double-edged sword of autophagy is crucial for the treatment of cancer. The present review summarizes the signaling pathways and key factors involved in autophagy and cancer to provide possible strategies for treating tumors.

Epstein-Barr virus latent membrane protein-1 upregulates autophagy and promotes viability in Hodgkin lymphoma: Implications for targeted therapy

Hodgkin lymphoma (HL) is composed of neoplastic Hodgkin and Reed‐Sternberg cells in an inflammatory background. The neoplastic cells are derived from germinal center B cells that, in most cases, are infected by Epstein‐Barr virus (EBV), which may play a role in tumorigenesis. Given that EBV‐latent membrane protein 1 (LMP1) regulates autophagy in B cells, we explored the role of autophagy mediated by EBV or LMP1 in HL. We found that EBV‐LMP1 transfection in HL cells induced a modest increase in autophagy signals, attenuated starvation‐induced autophagic stress, and alleviated autophagy inhibition‐ or doxorubicin‐induced cell death. LMP1 knockdown leads to decreased autophagy LC3 signals. A xenograft mouse model further showed that EBV infection significantly increased expression of the autophagy marker LC3 in HL cells. Clinically, LC3 was expressed in 15% (19/127) of HL samples, but was absent in all cases of nodular lymphocyte‐predominant and lymphocyte‐rich classic HL cases. Although expression of LC3 was not correlated with EBV status or clinical outcome, autophagic blockade effectively eradicated LMP1‐positive HL xenografts with better efficacy than LMP1‐negative HL xenografts. Collectively, these results suggest that EBV‐LMP1 enhances autophagy and promotes the viability of HL cells. Autophagic inhibition may be a potential therapeutic strategy for treating patients with HL, especially EBV‐positive cases.

Chaetomugilin J Enhances Apoptosis in Human Ovarian Cancer A2780 Cells Induced by Cisplatin Through Inhibiting Pink1/Parkin Mediated Mitophagy

Purpose

The chemoresistance and toxicity of traditional chemotherapeutic drugs have become obstacles to their antitumor effects in ovarian cancers. Therefore, it is particularly important to develop new anticancer drugs to increase target sensitivity and reduce the toxicity of chemotherapy drugs. As key organelles, the endoplasmic reticulum and mitochondria play important role in chemoresistance. Cells become resistant to drugs by maintaining the homeostasis of the endoplasmic reticulum and mitochondria. Chaetomugilin J, a metabolite isolated from Polygonatum sibiricum, belongs to the Chaetomium family and exhibits potent cytotoxicity. In this study, we aimed to explore the mechanistic link between apoptosis and endoplasmic reticulum stress, mitophagy and mitochondrial dysfunction induced by chaetomugilin J combined with cisplatin in the ovarian cancer cell line A2780.

Methods

Chaetomugilin J was identified by chemical methods. Cell viability was measured by an MTT assay. The apoptosis, mitochondrial membrane potential, and intracellular reactive oxygen species (ROS) were examined by flow cytometry. Mitochondrial ROS was measured by a fluorescence microscope with MitoSox staining. Further, the related proteins and overexpression of parkin were detected by Western blot.

Results

Chaetomugilin J combined with low-dose cisplatin decreased cell viability and increased apoptosis in A2780 cells. In addition, intracellular ROS and mitochondrial ROS were increased, while the mitochondrial membrane potential was reduced. The expressions of grp78 and chop were decreased after treatment by chaetomugilin J combined with low-dose cisplatin. Overexpression of parkin attenuated chaetomugilin J combined with cisplatin-induced apoptosis.

Conclusion

Chaetomugilin J combined with cisplatin inhibited pink1/parkin mediated mitophagy increased mitochondrial dysfunction in the A2780 cells and enhanced apoptosis induced by cisplatin in the ovarian cancer cell line A2780. But this process was not related to endoplasmic reticulum apoptotic pathway.

MiR-28-5p mediates the anti-proliferative and pro-apoptotic effects of curcumin on human diffuse large B-cell lymphoma cells

OBJECTIVE

To investigate the anti-proliferative and pro-apoptotic effects of curcumin on diffuse large B-cell lymphoma (DLBCL) cells and explore the mechanism.

METHODS

OCI-LY7 cells were treated with curcumin (2.5, 5, 10, 20, and 40 μM) for 24, 48, or 72 hours. Cell viability and apoptosis were determined using the 3-(4, 5-dimethylthiazol-2-yl)-2, 5 diphenyl tetrazolium bromide assay and TdT-mediated dUTP nick-end labeling staining, respectively. MiR-28-5p expression was detected via qRT-PCR. The binding site of miR-28-5p was predicted using online databases and verified using the dual-luciferase reporter assay. MiR-28-5p overexpression and inhibition were achieved via transfection with an miR-28-5p mimic and inhibitor, respectively.

RESULTS

Curcumin decreased the viability of OCI-LY7 cells in a concentration- and time-dependent manner, and these effects were attenuated by miR-28-5p inhibition. MiR-28-5p expression was upregulated by curcumin. Curcumin increased the numbers of apoptotic cells and upregulated cleaved caspase-3 expression, and these effects were attenuated by miR-28-5p inhibition. The dual-luciferase reporter assay confirmed that miR-28-5p directly targets the 3'-untranslated region of BECN1. Curcumin downregulated BECN1 and microtubule-associated protein 1 light chain 3 beta-II/I expression and upregulated p62 expression.

CONCLUSIONS

Our results described the curcumin exerted anti-proliferative and pro-apoptotic effects on OCI-LY7 cells through a mechanism potentially involving miR-28-5p.

Drug Resistance in Non-Hodgkin Lymphomas

Non-Hodgkin lymphomas (NHL) are lymphoid tumors that arise by a complex process of malignant transformation of mature lymphocytes during various stages of differentiation. The WHO classification of NHL recognizes more than 90 nosological units with peculiar pathophysiology and prognosis. Since the end of the 20^th century, our increasing knowledge of the molecular biology of lymphoma subtypes led to the identification of novel druggable targets and subsequent testing and clinical approval of novel anti-lymphoma agents, which translated into significant improvement of patients’ outcome. Despite immense progress, our effort to control or even eradicate malignant lymphoma clones has been frequently hampered by the development of drug resistance with ensuing unmet medical need to cope with relapsed or treatment-refractory disease. A better understanding of the molecular mechanisms that underlie inherent or acquired drug resistance might lead to the design of more effective front-line treatment algorithms based on reliable predictive markers or personalized salvage therapy, tailored to overcome resistant clones, by targeting weak spots of lymphoma cells resistant to previous line(s) of therapy. This review focuses on the history and recent advances in our understanding of molecular mechanisms of resistance to genotoxic and targeted agents used in clinical practice for the therapy of NHL.

Effect of Ganoderma applanatum polysaccharides on MAPK/ERK pathway affecting autophagy in breast cancer MCF-7 cells

Fungal polysaccharides have become hotspots in the field of health foods due to their antitumor activity in recent years. In this experiment, antitumor effect of the medicinal fungus Ganoderma applanatum polysaccharide (GAP) was investigated in human breast cancer MCF-7 cells, as well as the molecular mechanism of its effect on autophagy. Results showed that GAP contains three polysaccharides with molecular weights of 6.36 × 10⁵ Da, 4.25 × 10⁵ Da, and 2.53 × 10⁵ Da and which composed of rhamnose, glucose, arabinose, fucose in the molar ratio of 1:22:16.1:3.2. GAP inhibited the proliferation and migration of MCF-7 cells in a time-dose-dependent manner, the maximum inhibition rate reached 50.2% at 500 μg/mL in 48 h. Flow cytometry analysis showed that GAP could induce apoptosis, treatment of cells with GAP could result in up-regulation of gene and protein levels of autophagy-associated markers LC3 and Beclin-1; addition of autocrine late inhibitor CQ significantly raised the protein expression level of LC3II. The mitogen-activated protein kinases (MAPK) signaling pathway was not only related to the apoptotic pathway but also to the autophagy pathway; Western blot analysis showed that MAPK signaling pathway is involved in GAP-induced autophagy in MCF-7 cells. Detection of the relevant signaling pathway protein showed that the expression of p-ERK1/2 protein was down-regulated, however the expression of p-p38 and p-JNK protein was up-regulated. These results indicate that GAP could induce early autophagy in MCF-7 cells via the MAPK/ERK pathway. In conclusion, GAP showed strong antitumor activity by inducing apoptosis and autophagy through MAPK signaling pathway in MCF-7 cells, suggesting the molecular mechanism of fungal polysaccharide on its antitumor activity.

Autophagy inhibits the mesenchymal stem cell aging induced by D-galactose through ROS/JNK/p38 signalling

Autophagy and cellular senescence are two critical responses of mammalian cells to stress and may have a direct relationship given that they respond to the same set of stimuli, including oxidative stress, DNA damage, and telomere shortening. Mesenchymal stem cells (MSCs) have emerged as reliable cell sources for stem cell transplantation and are currently being tested in numerous clinical trials. However, the effects of autophagy on MSC senescence and corresponding mechanisms have not been fully evaluated. Several studies demonstrated that autophagy level increases in aging MSCs and the downregulation of autophagy can delay MSC senescence, which is inconsistent with most studies that showed autophagy could play a protective role in stem cell senescence. To further study the relationship between autophagy and MSC senescence and explore the effects and mechanisms of premodulated autophagy on MSC senescence, we induced the up- or down-regulation of autophagy by using rapamycin (Rapa) or 3-methyladenine, respectively, before MSC senescence induced by D-galactose (D-gal). Results showed that pretreatment with Rapa for 24 hours remarkably alleviated MSC aging induced by D-gal and inhibited ROS generation. p-Jun N-terminal kinases (JNK) and p-38 expression were also clearly decreased in the Rapa group. Moreover, the protective effect of Rapa on MSC senescence can be abolished by enhancing the level of ROS, and p38 inhibitor can reverse the promoting effect of H₂ O₂ on MSC senescence. In summary, the present study indicates that autophagy plays a protective role in MSC senescence induced by D-gal, and ROS/JNK/p38 signalling plays an important mediating role in autophagy-delaying MSC senescence.

An mTORC1/2 dual inhibitor, AZD2014, acts as a lysosomal function activator and enhances gemtuzumab ozogamicin-induced apoptosis in primary human leukemia cells

Gemtuzumab ozogamicin (GO), an anti-CD33 antibody linked to calicheamicin via an acid-labile linker, is the first antibody-drug conjugate (ADC). The acidic environment inside lysosomes of target cells is an important intracellular determinant of the cytocidal action of GO, as the linker is hydrolyzed under acidic conditions. However, lysosomal activity in acute myeloid leukemia (AML) blasts in GO therapy has been insufficiently evaluated. It has been suggested that lysosome activity is suppressed in AML due to hyperactivation of the phosphoinositide 3-kinase/Akt pathway. We therefore hypothesized that agents which activate lysosomal function would potentiate the cytotoxicity of GO. Here, we found that a clinically useful mTORC1/2 dual inhibitor, AZD2014, reduced pH in the acidic organelles, including lysosomes, as shown by increased LysoTracker fluorescent intensity, and synergistically enhanced the cytotoxic effect of GO in primary leukemia cells. GO-induced cytotoxicity appeared to be enhanced with the increase in lysosomal activity by AZD2014. These results indicate that AZD2014 activated lysosomal function in primary leukemia cells, which in turn enhanced the cytotoxicity of GO. Enhancement of lysosomal activity may represent a new therapeutic strategy in the treatment of GO and other ADCs, particularly in cases with low lysosomal activity.

Non‑covalent proteasome inhibitor PI‑1840 induces apoptosis and autophagy in osteosarcoma cells

Osteosarcoma (OS) is the predominant form of primary bone malignancy in children and adolescents. Although the combination of chemotherapy and modified surgical therapy leads to marked improvements in the survival rate, the therapeutic outcomes remain unsatisfactory. Therefore, the identification of novel drugs with higher efficacy and fewer side‑effects is urgently required. Proteasome inhibitors have been approved by the Food and Drug Administration (FDA) for the treatment of certain cancers, although none of them are directed against OS. Non‑covalent proteasome inhibitors, such as PI‑1840, are superior to covalent ones in numerous respects in view of their chemical structure; however, to date, no studies have been published on the effects of non‑covalent proteasome inhibitors on OS cells. In the present study, the antineoplastic effects of PI‑1840 were systematically evaluated in the OS cell lines, MG‑63 and U2‑OS. Cell viability and morphological changes were assessed by Cell Counting Kit‑8 (CCK‑8) and live/dead assays. The cell cycle was analyzed using flow cytometry (FCM) and western blot analysis (assessing the levels of the proteins p21, p27, and the tyrosine kinase, WEE1). The extent of cell apoptosis and autophagy were assessed by FCM, western blot analysis [of the apoptosis‑associated proteins, microtubule‑associated protein 1 light chain 3 α (LC3) and Beclin1], and mRFP‑GFP‑LC3 adenovirus transfection assay. Transwell and wound healing assays, and western blot analysis of the matrix metalloproteinases (MMPs)2 and 9 were performed to preliminarily evaluate the migration and invasion capability of the cells. In the present study, our results revealed that PI‑1840 inhibited the proliferation of OS cells and induced apoptosis, partly due to attenuation of the nuclear factor‑κB (NF‑κB) pathway. In addition, PI‑1840‑induced autophagy was detected, and inhibiting the autophagy of the OS cells led to an increase in the survival rate of the U2‑OS cells rather than of the MG‑63 cells. Furthermore, PI‑1840 attenuated the migration and invasion capabilities of the OS cells. In conclusion, the present study revealed PI‑1840 to be a promising drug for the treatment of OS.

The Autophagy-Lysosomal Pathways and Their Emerging Roles in Modulating Proteostasis in Tumors

In normal physiological condition, the maintenance of cellular proteostasis is a prerequisite for cell growth, functioning, adapting to changing micro-environments, and responding to extracellular stress. Cellular proteostasis is maintained by specific proteostasis networks (PNs) to prevent protein misfolding, aggregating, and accumulating in subcellular compartments. Commonly, the PNs are composed of protein synthesis, molecular chaperones, endoplasmic reticulum (ER), unfolded protein response (UPR), stress response pathways (SRPs), secretions, ubiquitin proteasome system (UPS), and autophagy-lysosomal pathways (ALPs). Although great efforts have been made to explore the underlying detailed mechanisms of proteostasis, there are many questions remain to explore, especially in proteostasis regulated by the ALPs. Proteostasis out-off-balance is correlated with various human diseases such as diabetes, stroke, inflammation, hypertension, pulmonary fibrosis, and Alzheimer’s disease. Enhanced regulation of PNs is observed in tumors, thereby indicating that proteostasis may play a pivotal role in tumorigenesis and cancer development. Recently, inhibitors targeting the UPS have shown to be failed in solid tumor treatment. However, there is growing evidence showing that the ALPs play important roles in regulation of proteostasis alone or with a crosstalk with other PNs in tumors. In this review, we provide insights into the proteostatic process and how it is regulated by the ALPs, such as macroautophagy, aggrephagy, chaperone-mediated autophagy, microautophagy, as well as mitophagy during tumor development.