Mechanisms of autophagy and apoptosis: Recent developments in breast cancer cells

The Function of Autophagy in the Initiation, and Development of Breast Cancer

Autophagy is a significant catabolic procedure that increases in stressful conditions. This mechanism is mostly triggered after damage to the organelles, the presence of unnatural proteins, and nutrient recycling in reaction to these stresses. One of the key points in this article is that cleaning and preserving damaged organelles and accumulated molecules through autophagy in normal cells helps prevent cancer. Since dysfunction of autophagy is associated with various diseases, including cancer, it has a dual function in tumor suppression and expansion. It has newly become clear that the regulation of autophagy can be used for the treatment of breast cancer, which has a promising effect of increasing the efficiency of anticancer treatment in a tissue- and cell-type-specific manner by affecting the fundamental molecular mechanisms. Regulation of autophagy and its function in tumorigenesis is a vital part of modern anticancer techniques. This study discusses the current advances related to the mechanisms that describe essential modulators of autophagy involved in the metastasis of cancers and the development of new breast cancer treatments.

Lysosomes as a Target of Anticancer Therapy

Lysosomes are organelles containing acidic hydrolases that are responsible for lysosomal degradation and the maintenance of cellular homeostasis. They play an important role in autophagy, as well as in various cell death pathways, such as lysosomal and apoptotic death. Various agents, including drugs, can induce lysosomal membrane permeability, resulting in the translocation of acidic hydrolases into the cytoplasm, which promotes lysosomal-mediated death. This type of death may be of great importance in anti-cancer therapy, as both cancer cells with disturbed pathways leading to apoptosis and drug-resistant cells can undergo it. Important compounds that damage the lysosomal membrane include lysosomotropic compounds, antihistamines, immunosuppressants, DNA-damaging drugs, chemotherapeutics, photosensitizers and various plant compounds. An interesting approach in the treatment of cancer and the search for ways to overcome the chemoresistance of cancer cells may also be combining lysosomotropic compounds with targeted modulators of autophagy to induce cell death. These compounds may be an alternative in oncological treatment, and lysosomes may become a promising therapeutic target for many diseases, including cancer. Understanding the functional relationships between autophagy and apoptosis and the possibilities of their regulation, both in relation to normal and cancer cells, can be used to develop new and more effective anticancer therapies.

Photothermal effect of albumin-modified gold nanorods diminished neuroblastoma cancer stem cells dynamic growth by modulating autophagy

Here, we investigated the photothermal effect of gold nanorods (GNRs) on human neuroblastoma CD133⁺ cancer stem cells (CSCs) via autophagic cell death. GNRs were synthesized using Cetyltrimethylammonium bromide (CTAB), covered with bovine serum albumin (BSA). CD133⁺ CSCs were enriched from human neuroblastoma using the magnetic-activated cell sorting (MACS) technique. Cells were incubated with GNRs coated with BSA and exposed to 808-nm near-infrared laser irradiation for 8 min to yield low (43 °C), medium (46 °C), and high (49 °C) temperatures. After 24 h, the survival rate and the percent of apoptotic and necrotic CSCs were measured using MTT assay and flow cytometry. The expression of different autophagy-related genes was measured using polymerase chain reaction (PCR) array analysis. Protein levels of P62 and LC3 were detected using an enzyme-linked immunosorbent assay (ELISA). The viability of CSC was reduced in GNR-exposed cells compared to the control group (p < 0.05). At higher temperatures (49 °C), the percent of apoptotic CSCs, but not necrotic cells, increased compared to the lower temperatures. Levels of intracellular LC3 and P62 were reduced and increased respectively when the temperature increased to 49 °C (p < 0.05). These effects were non-significant at low and medium temperatures (43 and 46 °C) related to the control CSCs (p > 0.05). The clonogenic capacity of CSC was also inhibited after photothermal therapy (p < 0.05). Despite these changes, no statistically significant differences were found in terms of CSC colony number at different temperatures regardless of the presence or absence of HCQ. Based on the data, the combination of photothermal therapy with HCQ at 49 °C can significantly abort the CSC clonogenic capacity compared to the control-matched group without HCQ (p < 0.0001). PCR array showed photothermal modulation of CSCs led to alteration of autophagy-related genes and promotion of co-regulator of apoptosis and autophagy signaling pathways. Factors related to autophagic vacuole formation and intracellular transport were significantly induced at a temperature of 49 °C (p < 0.05). We also note the expression of common genes belonging to autophagy and apoptosis signaling pathways at higher temperatures. Data showed tumoricidal effects of laser-irradiated GNRs by the alteration of autophagic response and apoptosis.

Docosahexaenoic Acid Reverses Epithelial-Mesenchymal Transition and Drug Resistance by Impairing the PI3K/AKT/ Nrf2/GPX4 Signalling Pathway in Docetaxel-Resistant PC3 Prostate Cancer Cells

Drug resistance is a serious problem in cancer therapy. Growing evidence has shown that docosahexaenoic acid has anti-inflammatory and chemopreventive abilities. Studies have shown that autophagy inhibition and ferroptosis are promising therapeutic strategies for overcoming multidrug resistance. This study was aimed to examine whether docosahexaenoic acid (DHA) could reverse docetaxel resistance in prostate cancer cells. Cell survival was examined by MTT and colony formation. Protein expression was determined by Western blot. Reactive oxygen species (ROS) production was measured by flow cytometry. DHA displayed anti-cancer effects on proliferation, colony formation, migration, apoptosis, autophagy and epithelial mesenchymal transition. Glutathione-S-transferase π is an enzyme that plays an important role in drug resistance. DHA inhibited GSTπ protein expression and induced cytoprotective autophagy by regulating the PI3K/AKT signalling pathway in PC3R cells. DHA combined with PI3K inhibitor (LY294002) enhanced apoptosis by alleviating the expression of LC3B, (pro-) caspase- 3 and (uncleaved) PARP. DHA induced ferroptosis by attenuating the expression of glutathione peroxidase 4 (GPX4) and nuclear erythroid 2-related factor 2 (Nrf2). DHA-treated PC3R cells produced ROS. The ROS and cytotoxicity were reversed by treatment with ferrostatin-1. DHA combined with docetaxel inhibited EMT by regulating the expression of E-cadhein and N-cadherin. In summary, DHA reversed drug resistance and induced cytoprotective autophagy and ferroptosis by regulating the PI3K/AKT/Nrf2/GPX4 signalling pathway in PC3R cells. We propose that DHA could be developed as a chemosensitizer and that the PI3K/AKT /Nrf2/GPX4 signalling pathway might be a promising therapeutic target for overcoming cancer drug resistance.

Differential expression of Exaiptasia pallida GIMAP genes upon induction of apoptosis and autophagy suggests a potential role in cnidarian symbiosis and disease

Coral reefs, one of the world's most productive and diverse ecosystems, are currently threatened by a variety of stressors that result in increased prevalence of both bleaching and disease. Therefore, understanding the molecular mechanisms involved in these responses is critical to mitigate future damage to the reefs. One group of genes that is potentially involved in cnidarian immunity and symbiosis is GTPases of immunity associated proteins (GIMAP). In vertebrates, this family of proteins is involved in regulating the fate of developing lymphocytes and interacts with proteins involved in apoptosis and autophagy. As apoptosis, autophagy and immunity have previously been shown to be involved in cnidarian symbiosis and disease, the goal of this research was to determine the role of cnidarian GIMAPs in these processes using the anemone Exaiptasia pallida To do so, GIMAP genes were characterized in the E. pallida genome and changes in gene expression were measured using qPCR in response to chemical induction of apoptosis, autophagy and treatment with the immune stimulant lipopolysaccharide (LPS) in both aposymbiotic and symbiotic anemones. The results revealed four GIMAP-like genes in E. pallida, referred to as Ep_GIMAPs Induction of apoptosis and autophagy resulted in a general downregulation of Ep_GIMAPs, but no significant changes were observed in response to LPS treatment. This indicates that Ep_GIMAPs may be involved in the regulation of apoptosis and autophagy, and therefore could play a role in cnidarian-dinoflagellate symbiosis. Overall, these results increase our knowledge on the function of GIMAPs in a basal metazoan.

[Molecular pathways of autophagy regulation by BRCA1: Implications in cancer]

The BRCA1 protein contributes to maintain genomic integrity, through transcriptional regulation of proteins that control the cell cycle and DNA repair or by direct interaction with these proteins. The genetic instability caused by mutations that result in a deficit of BRCA1 activity, confers an increased risk of mainly breast and ovarian cancers. In recent years, it has been shown that autophagy has a dual role in tumor development, and chemical agents such as lucanthone, chloroquine, Z-ligustilide, spautin-1, tunicamycin, T-12, and olaparib, regulate tumor survival/death autophagy-dependent. Here we also review the different molecular pathways by which BRCA1 regulates (mostly negatively) autophagy, mainly in breast and ovarian cancers, and where the cellular redox state (ROS, GSH) and proteins mTOR, p53-Mdm2, STAT3, and Parkin, have been shown to play an essential role.

K092A and K092B, Two Peptides Isolated from the Dogfish (Scyliorhinus canicula L.), with Potential Antineoplastic Activity Against Human Prostate and Breast Cancer Cells

Cancer therapy is currently a major challenge within the research community, especially in reducing the side effects of treatments and to develop new specific strategies against cancers that still have a poor prognosis. In this context, alternative strategies using biotechnologies, such as marine peptides, have been developed based on their promise of effectivity associated with a low toxicity for healthy cells. The purpose of the present paper is to investigate the active mechanism of two peptides that were isolated from the epigonal tissue of the lesser spotted dogfish Scyliorhinus canicula L., identified NFDTDEQALEDVFSKYG (K092A) and EAPPEAAEEDEW (K092B) on the in vitro growth inhibition of ZR-75-1 mammary carcinoma cells and MDA-Pca-2b prostate cancer cells. The effects of the peptides on cell proliferation and cell death mechanisms were studied by the flow cytometry and immunofluorescence microscopy approaches. The results have shown the onset of both K092A- and K092B-induced early cytoskeleton changes, and then cell cycle perturbations followed by non-apoptotic cell death. Moreover, impedance perturbation and plasma membrane perforation in ZR-75-1 K092A-treated cell cultures and autophagy inhibition in MDA-Pca-2b K092B-treated cells have been observed. In conclusion, these two bioactive peptides from dogfish exhibit antineoplastic activity on the human prostate and breast cancer cells in vitro.

Ethanol extract of Chrysanthemum zawadskii Herbich induces autophagy and apoptosis in mouse colon cancer cells through the regulation of reactive oxygen species

Background

Recent research has suggested that autophagy can provide a better mechanism for inducing cell death than current therapeutic strategies. This study investigated the effects of using an ethanol extract of Chrysanthemum zawadskii Herbich (ECZ) to induce apoptosis and autophagy associated with reliable signal pathways in mouse colon cancer CT-26 cells.

Methods

Using ECZ on mouse colon cancer CT-26 cells, cell viability, annexin V/propidium iodide staining, acridine orange staining, reactive oxygen species (ROS) and western blotting were assayed.

Results

ECZ exhibited cytotoxicity in CT-26 cells in a dose-dependent manner. ECZ induced apoptosis was confirmed by caspase-3 activation, poly (ADP-ribose) polymerase cleavage, and increased production of reactive oxygen species (ROS). Furthermore, it was shown that ECZ induced autophagy via the increased conversion of microtubule-associated protein 1 light chain 3II, the degradation of p62, and the formation of acidic vesicular organelles. The inhibition of ROS production by N-Acetyl-L-cysteine resulted in reduced ECZ-induced apoptosis and autophagy. Furthermore, the inhibition of autophagy by 3-methyladenine resulted in enhanced ECZ-induced apoptosis via increased ROS generation.

Conclusion

These findings confirmed that ECZ induced ROS-mediated autophagy and apoptosis in colon cancer cells. Therefore, ECZ may serve as a novel potential chemotherapeutic candidate for colon cancer.

A Potential Antineoplastic Peptide of Human Prostate Cancer Cells Derived from the Lesser Spotted Dogfish (Scyliorhinus canicula L.)

The purpose of the present paper is to investigate the mechanism of action of a pyroglutamate-modified peptide (pE-K092D) on in vitro growth inhibition of MDA-Pca-2b prostate cancer cells. This peptide was derived from a peptide previously isolated from the testis of the lesser spotted dogfish and identified as QLTPEALADEEEMNALAAR (K092D). The effect of the peptide on cell proliferation and cell death mechanisms was studied by flow cytometry. Cellular morphology and cytoskeleton integrity of peptide-treated cells were observed by immunofluorescence microscopy. Results showed the onset of peptide induced early cytoskeleton perturbation, inhibition of autophagy, inhibition of cell proliferation and, at the end, non-apoptotic cell death mechanisms (membrane destabilization and necrosis). All those mechanisms seem to contribute to MDA-Pca-2b growth inhibition by a main cytostatic fate.

Natural products: An upcoming therapeutic approach to cancer

Cancer is one of the leading causes of death across the world. Different environmental and anthropogenic factors initiate mutations in different functional genes of growth factors and their receptors, anti-apoptotic proteins, self-renewal developmental proteins, tumor suppressors, transcription factors, etc. This phenomenon leads to altered protein homeostasis of the cell which in turn induces cancer initiation, development, progression and survival. From ancient times various natural products have been used as traditional medicine against different diseases. Natural products are readily applicable, inexpensive, accessible and acceptable therapeutic approach with minimum cytotoxicity. As most of the target-specific anticancer drugs failed to achieve the expected result so far, new multi-targeted therapies using natural products have become significant. In this review, we have summarized the efficacy of different natural compounds against cancer. They are capable of modulating cancer microenvironment and diverse cell signaling cascades; thus playing a major role in combating cancer. These compounds are found to be effective against several signaling pathways, mainly cell death pathways (apoptosis and autophagy) and embryonic developmental pathways (Notch pathway, Wnt pathway and Hedgehog pathway). This review article is expected to be helpful in understanding the recent progress of natural product research for the development of anticancer drug.

Lasalocid induces cytotoxic apoptosis and cytoprotective autophagy through reactive oxygen species in human prostate cancer PC-3 cells

Lasalocid is an antibiotic from the group of carboxylic ionophores, produced by Streptomyces lasaliensis. But there was limited information of lasalocid on human prostate cancer cells. In the present studies, to better understand its effect in human prostate cancer cells, apoptosis and autophagy associated with possible signal pathways in vitro was examined. Our study showed that lasalocid mediated cell cycle arrest in G₀/G₁ phase by reducing G₁ phase dependent proteins, indicating entering into apoptotic cell death pathway. Lasalocid-induced apoptosis was involved with reactive oxygen species (ROS) production, and mitochondrial hyperpolarization. In addition, lasalocid induced autophagy through microtubule-associated protein 1 light chain 3 (LC-3)-II conversion, acidic vesicular organelles formation and GFP-LC-3 punctuate, which was inhibited by 3-methyladenine (3-MA), a widely used pharmacological inhibitor of autophagy. Furthermore, the autophagic phenomena were mediated by production of ROS, confirming that inhibition of ROS with N-acetyl-l-cysteine, a ROS inhibitor, attenuated lasalocid-triggered autophagy. Inhibition of autophagy with 3-MA enhanced the lasalocid-induced apoptosis through enhanced ROS generation. Taken together, lasalocid should be useful in the search for new potential chemotherapeutic agents for understanding the molecular mechanisms of anticancer in prostate cancer cells.

Inhibiting autophagy increases epirubicin's cytotoxicity in breast cancer cells

Chemotherapy, radiotherapy, and endocrinotherapy are documented to induce autophagy among breast cancer cells, but the role of autophagy in this disease has been attributed as cytoprotective as well as tumor-suppressing. Thus we studied MDA-MB-231 and SK-BR-3 breast cancer cell lines treated with epirubicin (EPI) to assess autophagy and apoptosis. We found out that EPI induced apoptosis and autophagy in both cell lines. The lysosomal inhibitor bafilomycin A1 inhibited cellular autophagy and enhanced EPI-triggered apoptosis, perhaps due to inhibition of autolysosome formation, which then inhibited autophagic effects of engulfing and clearing damaged mitochondria. This inhibition increased mitochondrial cytochrome C release which augmented epirubicin-induced caspase-dependent apoptosis and cytotoxicity. In addition, the lysosomal neutralizing agent ammonia chloride (AC), and Atg7 knockdown by siRNA, could inhibit epirubicin-triggered autophagy, enhance cytotoxicity, and increase caspase-9- and caspase-3-dependent apoptosis. Thus, autophagy plays a prosurvival role in EPI-treated MDA-MB-231 and SK-BR-3 cells, and autophagy inhibition can potentially reverse this effect and increase the cytotoxicity of EPI.

Midazolam regulated caspase pathway, endoplasmic reticulum stress, autophagy, and cell cycle to induce apoptosis in MA-10 mouse Leydig tumor cells

PURPOSE

Midazolam is widely used as a sedative and anesthetic induction agent by modulating the different GABA receptors in the central nervous system. Studies have also shown that midazolam has an anticancer effect on various tumors. In a previous study, we found that midazolam could induce MA-10 mouse Leydig tumor cell apoptosis by activating caspase cascade. However, the detailed mechanism related to the upstream and downstream pathways of the caspase cascade, such as endoplasmic reticulum (ER) stress, autophagy, and p53 pathways plus cell cycle regulation in MA-10 mouse Leydig tumor cells, remains elusive.

METHODS

Flow cytometry assay and Western blot analyses were exploited.

RESULTS

Midazolam significantly decreased cell viability but increased sub-G1 phase cell numbers in MA-10 cells (P<0.05). Annexin V/propidium iodide double staining further confirmed that midazolam induced apoptosis. In addition, expressions of Fas and Fas ligand could be detected in MA-10 cells with midazolam treatments, and Bax translocation and cytochrome c release were also involved in midazolam-induced MA-10 cell apoptosis. Moreover, the staining and expression of LC3-II proteins could be observed with midazolam treatment, implying midazolam could induce autophagy to control MA-10 cell apoptosis. Furthermore, the expressions of p-EIF2α, ATF4, ATF3, and CHOP could be induced by midazolam, indicating that midazolam could stimulate apoptosis through ER stress in MA-10 cells. Additionally, the expressions of cyclin A, cyclin B, and CDK1 could be inhibited by midazolam, and the phosphorylation of p53, P27, and P21 could be adjusted by midazolam, suggesting that midazolam could manage cell cycle through the regulation of p53 pathway to induce apoptosis in MA-10 cells.

CONCLUSION

Midazolam could induce cell apoptosis through the activation of ER stress and the regulation of cell cycle through p53 pathway with the involvement of autophagy in MA-10 mouse Leydig tumor cells.

Lysosomal membrane stability plays a major role in the cytotoxic activity of the anti-proliferative agent, di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT)

The potent and selective anti-tumor agent, di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT), localizes in lysosomes and forms cytotoxic copper complexes that generate reactive oxygen species (ROS), resulting in lysosomal membrane permeabilization (LMP) and cell death. Herein, the role of lysosomal membrane stability in the anti-tumor activity of Dp44mT was investigated. Studies were performed using molecules that protect lysosomal membranes against Dp44mT-induced LMP, namely heat shock protein 70 (HSP70) and cholesterol. Up-regulation or silencing of HSP70 expression did not affect Dp44mT-induced LMP in MCF7 cells. In contrast, cholesterol accumulation in lysosomes induced by the well characterized cholesterol transport inhibitor, 3-β-[2-(diethyl-amino)ethoxy]androst-5-en-17-one (U18666A), inhibited Dp44mT-induced LMP and markedly and significantly (p<0.001) reduced the ability of Dp44mT to inhibit cancer cell proliferation (i.e., increased the IC(50)) by 140-fold. On the other hand, cholesterol extraction using methyl-β-cyclodextrin enhanced Dp44mT-induced LMP and significantly (p<0.01) increased its anti-proliferative activity. The protective effect of U18666A in increasing lysosomal cholesterol and preventing the cytotoxic activity of Dp44mT was not due to induced autophagy. Instead, U18666A was found to decrease lysosomal turnover, resulting in autophagosome accumulation. Moreover, preincubation with U18666A did not prevent the ability of Dp44mT to induce autophagosome synthesis, indicating that autophagic initiation via Dp44mT occurs independently of LMP. These studies demonstrate the significance of lysosomal membrane stability in relation to the ability of Dp44mT to execute tumor cell death and overcome pro-survival autophagy. Hence, lysosomal-dependent cell death induced by Dp44mT serves as an important anti-tumor strategy. These results are important for comprehensively understanding the mechanism of action of Dp44mT.

IKKβ/NFκBp65 activated by interleukin-13 targets the autophagy-related genes LC3B and beclin 1 in fibroblasts co-cultured with breast cancer cells

Interleukin-13 (IL-13), a Th2 cytokine, plays an important role in fibrosis, inflammation, tissue hyperresponsiveness and tumor development. Although studies have demonstrated that IL-13 exerts its roles through signal transducer and activator of transcription 6 (STAT6) signaling pathway, recent studies have revealed that I kappa B kinase (IKK)/nuclear factor kappa B (NFκB) pathway may also be involved in. The aim of this study was to investigate whether IL-13 delivers signals to IKKβ/NFκBp65 and whether autophagy genes are IL-13-induced the activation of NFκBp65 transcriptional targets in fibroblasts of breast tumor stroma. We examined the phosphorylation of IKKβ, the activation of NFκBp65 and NFκBp65-targeted autophagy genes in fibroblasts co-cultured with breast cancer cells under the condition of IL-13 stimulation. Results of this study showed that IL-13 induced IKKβ phosphorylation in the fibroblast line ESF co-cultured with breast cancer cell line BT474, and subsequently NFκBp65 was activated and aimed at beclin 1 and microtubule-associated protein 1 light chain 3 B (MAP1LC3B or LC3B) in these ESF cells. BMS345541, an inhibitor of IKK/NFκB pathway, significantly inhibited the IL-13-induced the activation of NFκB and also inhibited NFκB-targeted beclin 1 and LC3B expression. Our results suggest that IL-13 regulates beclin 1 and LC3B expression through IKKβ/NFκBp65 in fibroblasts co-cultured with breast cancer cells, and IL-13 plays role in activating IKKβ/NFκBp65.

Autophagy Protects from Trastuzumab-Induced Cytotoxicity in HER2 Overexpressing Breast Tumor Spheroids

Multicellular tumor spheroids represent a 3D in vitro model that mimics solid tumor essential properties including assembly and development of extracellular matrix and nutrient, oxygen and proliferation gradients. In the present study, we analyze the impact of 3D spatial organization of HER2-overexpressing breast cancer cells on the response to Trastuzumab. We cultured human mammary adenocarcinoma cell lines as spheroids with the hanging drop method and we observed a gradient of proliferating, quiescent, hypoxic, apoptotic and autophagic cells towards the inner core. This 3D organization decreased Trastuzumab sensitivity of HER2 over-expressing cells compared to monolayer cell cultures. We did not observe apoptosis induced by Trastuzumab but found cell arrest in G0/G1 phase. Moreover, the treatment downregulated the basal apoptosis only found in tumor spheroids, by eliciting protective autophagy. We were able to increase sensitivity to Trastuzumab by autophagy inhibition, thus exposing the interaction between apoptosis and autophagy. We confirmed this result by developing a resistant cell line that was more sensitive to autophagy inhibition than the parental BT474 cells. In summary, the development of Trastuzumab resistance relies on the balance between death and survival mechanisms, characteristic of 3D cell organization. We propose the use of spheroids to further improve the understanding of Trastuzumab antitumor activity and overcome resistance.

Lysinibacillus sphaericus binary toxin induces apoptosis in susceptible Culex quinquefasciatus larvae

During sporulation, a Gram-positive bacterium Lysinibacillus sphaericus (Ls) produces the mosquito larvicidal binary toxin composed of 2 subunits, BinA and BinB. Full toxicity against Culex and Anopheles mosquito larvae is achieved when both subunits are administered together at equimolar amounts. Although cellular responses to Bin toxin have been reported in previous studies, it remains essential to extensively examine the cytopathic effects in vivo to define the underlying mechanism of larval death. In this study, 4th instar Culex quinquefasciatus larvae fed with different doses of Bin toxin were analyzed both for ultrastructural as well as biochemical effects. Typical morphological changes consistent with apoptosis were observed in mosquito larvae exposed to Bin toxin, including mitochondrial swelling, chromatin condensation, cytoplasmic vacuolization and apoptotic cell formation. Bin toxin also induced the activation of caspase-9 and caspase-3 in larval midgut cells. Our current observations thus suggest that Bin toxin triggers apoptosis via an intrinsic or mitochondrial pathway in vivo, possibly contributing to larval death.

The anticancer agent di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT) overcomes prosurvival autophagy by two mechanisms: persistent induction of autophagosome synthesis and impairment of lysosomal integrity

Autophagy functions as a survival mechanism during cellular stress and contributes to resistance against anticancer agents. The selective antitumor and antimetastatic chelator di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT) causes lysosomal membrane permeabilization and cell death. Considering the integral role of lysosomes in autophagy and cell death, it was important to assess the effect of Dp44mT on autophagy to further understand its mechanism of action. Notably, Dp44mT affected autophagy by two mechanisms. First, concurrent with its antiproliferative activity, Dp44mT increased the expression of the classical autophagic marker LC3-II as a result of induced autophagosome synthesis. Second, this effect was supplemented by a reduction in autophagosome degradation as shown by the accumulation of the autophagic substrate and receptor p62. Conversely, the classical iron chelator desferrioxamine induced autophagosome accumulation only by inhibiting autophagosome degradation. The formation of redox-active iron or copper Dp44mT complexes was critical for its dual effect on autophagy. The cytoprotective antioxidant N-acetylcysteine inhibited Dp44mT-induced autophagosome synthesis and p62 accumulation. Importantly, Dp44mT inhibited autophagosome degradation via lysosomal disruption. This effect prevented the fusion of lysosomes with autophagosomes to form autolysosomes, which is crucial for the completion of the autophagic process. The antiproliferative activity of Dp44mT was suppressed by Beclin1 and ATG5 silencing, indicating the role of persistent autophagosome synthesis in Dp44mT-induced cell death. These studies demonstrate that Dp44mT can overcome the prosurvival activity of autophagy in cancer cells by utilizing this process to potentiate cell death.

Role of Bcl-xL/Beclin-1 in interplay between apoptosis and autophagy in oxaliplatin and bortezomib-induced cell death

Recent studies indicate that a complex relationship exists between autophagy and apoptosis. In this study we investigated a regulatory relationship between autophagy and apoptosis in colorectal cancer cells utilizing molecular and biochemical approaches. For this study, human colorectal carcinoma HCT116 and CX-1 cells were treated with two chemotherapeutic agents-oxaliplatin, which induces apoptosis, and bortezomib, which triggers both apoptosis and autophagy. A combinatorial treatment of oxaliplatin and bortezomib caused a synergistic induction of apoptosis which was mediated through an increase in caspase activation. The combinational treatment of oxaliplatin and bortezomib promoted the JNK-Bcl-xL-Bax pathway which modulated the synergistic effect through the mitochondria-dependent apoptotic pathway. JNK signaling led to Bcl-xL phosphorylation at serine 62, oligomerization of Bax, alteration of mitochondrial membrane potential, and subsequent cytochrome c release. Overexpression of dominant-negative mutant of Bcl-xL (S62A), but not dominant-positive mutant of Bcl-xL (S62D), suppressed cytochrome c release and synergistic death effect. Interestingly, Bcl-xL also affected autophagy through alteration of interaction with Beclin-1. Beclin-1 was dissociated from Bcl-xL and initiated autophagy during treatment with oxaliplatin and bortezomib. However, activated caspase 8 cleaved Beclin-1 and suppressed Beclin-1-associated autophagy and enhanced apoptosis. A combinatorial treatment of oxaliplatin and bortezomib-induced Beclin-1 cleavage was abolished in Beclin-1 double mutant (D133AA/D149A) knock-in HCT116 cells, restoring the autophagy-promoting function of Beclin-1 and suppressing the apoptosis induced by the combination therapy. In addition, the combinatorial treatment significantly inhibited colorectal cancer xenografts' tumor growth. An understanding of the molecular mechanisms of crosstalk between apoptosis and autophagy will support the application of combinatorial treatment to colorectal cancer.

Epoxyeicosatrienoic acids protect cardiac cells during starvation by modulating an autophagic response

Epoxyeicosatrienoic acids (EETs) are cytochrome P450 epoxygenase metabolites of arachidonic acid involved in regulating pathways promoting cellular protection. We have previously shown that EETs trigger a protective response limiting mitochondrial dysfunction and reducing cellular death. Considering it is unknown how EETs regulate cell death processes, the major focus of the current study was to investigate their role in the autophagic response of HL-1 cells and neonatal cardiomyocytes (NCMs) during starvation. We employed a dual-acting synthetic analog UA-8 (13-(3-propylureido)tridec-8-enoic acid), possessing both EET-mimetic and soluble epoxide hydrolase (sEH) inhibitory properties, or 14,15-EET as model EET molecules. We demonstrated that EETs significantly improved viability and recovery of starved cardiac cells, whereas they lowered cellular stress responses such as caspase-3 and proteasome activities. Furthermore, treatment with EETs resulted in preservation of mitochondrial functional activity in starved cells. The protective effects of EETs were abolished by autophagy-related gene 7 (Atg7) short hairpin RNA (shRNA) or pharmacological inhibition of autophagy. Mechanistic evidence demonstrated that sarcolemmal ATP-sensitive potassium channels (pmK_ATP) and enhanced activation of AMP-activated protein kinase (AMPK) played a crucial role in the EET-mediated effect. Our data suggest that the protective effects of EETs involve regulating the autophagic response, which results in a healthier pool of mitochondria in the starved cardiac cells, thereby representing a novel mechanism of promoting survival of cardiac cells. Thus, we provide new evidence highlighting a central role of the autophagic response in linking EETs with promoting cell survival during deep metabolic stress such as starvation.

A novel binuclear palladacycle complex inhibits melanoma growth in vitro and in vivo through apoptosis and autophagy

Malignant melanoma is an aggressive skin cancer and it is reported to be the most treatment-resistant human cancer. Here we describe the anti-tumour activity of a novel binuclear palladacycle complex (AJ-5) in vertical growth phase (ME1402) and metastatic (WM1158) melanoma cell lines. We show that compared to normal control cell lines, AJ-5 is more effective in inhibiting the proliferation of ME1402 and WM1158 melanoma cells with IC50 values of 0.19 and 0.20μM, respectively. Flow cytometry analyses showed that AJ-5 induced apoptosis (sub-G1 peak) which was confirmed by Annexin V-FITC/propidium iodide double-staining, nuclear fragmentation and an increase in the levels of PARP cleavage. Furthermore, AJ-5 was shown to induce both intrinsic and extrinsic apoptotic pathways as measured by PUMA, Bax and active caspases. Interestingly, AJ-5 treatment also simultaneously induced the formation of autophagosomes and led to an increase in the autophagy markers LC3II and Beclin1. Inhibition of autophagy reduced AJ-5 cytotoxicity suggesting that AJ-5 induced autophagy was a cell death and not cell survival mechanism. Moreover we show that AJ-5 induces the ATM-CHK2 DNA damage pathway and that its anti-tumour function is mediated by the p38 and ERK1/2 signalling pathways. Importantly, AJ-5 treatment efficiently reduced tumour growth in melanoma bearing mice and induced high levels of autophagy and apoptosis markers. Together these findings suggest that AJ-5 may be an effective chemotherapeutic drug in the treatment of melanoma, a highly aggressive and intractable cancer.

Regulation of autophagy by glucose in Mammalian cells

Autophagy is an evolutionarily conserved process that contributes to maintain cell homeostasis. Although it is strongly regulated by many extracellular factors, induction of autophagy is mainly produced by starvation of nutrients. In mammalian cells, the regulation of autophagy by amino acids, and also by the hormone insulin, has been extensively investigated, but knowledge about the effects of other autophagy regulators, including another nutrient, glucose, is more limited. Here we will focus on the signalling pathways by which environmental glucose directly, i.e., independently of insulin and glucagon, regulates autophagy in mammalian cells, but we will also briefly mention some data in yeast. Although glucose deprivation mainly induces autophagy via AMPK activation and the subsequent inhibition of mTORC1, we will also comment other signalling pathways, as well as evidences indicating that, under certain conditions, autophagy can be activated by glucose. A better understanding on how glucose regulates autophagy not only will expand our basic knowledge of this important cell process, but it will be also relevant to understand common human disorders, such as cancer and diabetes, in which glucose levels play an important role.

Sirtinol, a class III HDAC inhibitor, induces apoptotic and autophagic cell death in MCF-7 human breast cancer cells

Sirtuins (SIRTs), NAD+-dependent class III histone deacetylases (HDACs), play an important role in the regulation of cell division, survival and senescence. Although a number of effective SIRT inhibitors have been developed, little is known about the specific mechanisms of their anticancer activity. In this study, we investigated the anticancer effects of sirtinol, a SIRT inhibitor, on MCF-7 human breast cancer cells. Apoptotic and autophagic cell death were measured. Sirtinol significantly inhibited the proliferation of MCF-7 cells in a concentration-dependent manner. The IC50 values of sirtinol were 48.6 µM (24 h) and 43.5 µM (48 h) in MCF-7 cells. As expected, sirtinol significantly increased the acetylation of p53, which has been reported to be a target of SIRT1/2. Flow cyto-metry analysis revealed that sirtinol significantly increased the G1 phase of the cell cycle. The upregulation of Bax, downregulation of Bcl-2 and cytochrome c release into the cytoplasm, which are considered as mechanisms of apoptotic cell death, were observed in the MCF-7 cells treated with sirtinol. The annexin V-FITC assay was used to confirm sirtinol-induced apoptotic cell death. Furthermore, the expression of LC3-II, an autophagy-related molecule, was significantly increased in MCF-7 cells after sirtinol treatment. Autophagic cell death was confirmed by acridine orange and monodansylcadaverine (MDC) staining. Of note, pre-treatment with 3-methyladenine (3-MA) increased the sirtinol-induced MCF-7 cell cytotoxicity, which is associated with blocking autophagic cell death and increasing apoptotic cell death. Based on our results, the downregulation of SIRT1/2 expression may play an important role in the regulation of breast cancer cell death; thus, SIRT1/2 may be a novel molecular target for cancer therapy and these findings may provide a molecular basis for targeting SIRT1/2 in future cancer therapy.

Molecular mechanism of SAHA on regulation of autophagic cell death in tamoxifen-resistant MCF-7 breast cancer cells

OBJECTIVE

Tamoxifen is currently used for the treatment of estrogen receptor-positive breast cancer patients, but acquired resistance to tamoxifen is a critical problem in breast cancer therapy. Suberoylanilide hydroxamic acid (SAHA) is a prototype of the newly developed HDAC inhibitor. The aim of this study is to investigate the anticancer effects of SAHA in tamoxifen-resistant MCF-7 (TAMR/MCF-7) cells.

METHODS

Cytotoxicity, apoptosis and autophagic cell death induced by SAHA were studied. A TAMR/MCF-7 cells xenograft model was established to investigate the inhibitory effect of SAHA on tumor growth in vivo.

RESULTS

SAHA inhibited the proliferation of TAMR/MCF-7 cells in a dose-dependent manner. SAHA significantly reduced the expression of HDAC1, 2, 3, 4 and 7 and increased acetylated histone H3 and H4. Although SAHA induced G2/M phase arrest of cell cycle, apoptotic cell death was very low, which is correlated with the slight change in the activation of caspases and PARP cleavage. Interestingly, expression of the autophagic cell death markers, LC3-II and beclin-1, was significantly increased in TAMR/MCF-7 cells treated with SAHA. Autophagic cell death induced by SAHA was confirmed by acridine orange staining and transmission electron microscopy (TEM) in TAMR/MCF-7 cells. In mice bearing the TAMR/MCF-7 cell xenografts, SAHA significantly reduced the tumor growth and weight, without apparent side effects.

CONCLUSION

These results suggest that SAHA can induce caspase-independent autophagic cell death rather than apoptotic cell death in TAMR/MCF-7 cells. SAHA-mediated autophagic cell death is a promising new strategy to treatment of tamoxifen-resistant human breast cancer.