Two-pore channel-2 and inositol trisphosphate receptors coordinate Ca2+ signals between lysosomes and the endoplasmic reticulum

Lysosomes and the endoplasmic reticulum (ER) are Ca2+ stores mobilized by the second messengers NAADP and IP3, respectively. Here, we establish Ca2+ signals between the two sources as fundamental building blocks that couple local release to global changes in Ca2+. Cell-wide Ca2+ signals evoked by activation of endogenous NAADP-sensitive channels on lysosomes comprise both local and global components and exhibit a major dependence on ER Ca2+ despite their lysosomal origin. Knockout of ER IP3 receptor channels delays these signals, whereas expression of lysosomal TPC2 channels accelerates them. High-resolution Ca2+ imaging reveals elementary events upon TPC2 opening and signals coupled to IP3 receptors. Biasing TPC2 activation to a Ca2+-permeable state sensitizes local Ca2+ signals to IP3. This increases the potency of a physiological agonist to evoke global Ca2+ signals and activate a downstream target. Our data provide a conceptual framework to understand how Ca2+ release from physically separated stores is coordinated.

Palladium (II) compounds containing oximes as promising antitumor agents for the treatment of osteosarcoma: An in vitro and in vivo comparative study with cisplatin

Drug resistance, evasion of cell death and metastasis are factors that contribute to the low cure rate and disease-free survival in osteosarcomas (OS). In this study, we demonstrated that a new class of oxime-containing organometallic complexes called Pd-BPO (O3) and Pd-BMO (O4) are more cytotoxic than cisplatin (CDDP) for SaOS-2 and U2OS cells using the MTT assay. Annexin-FITC/7-AAD staining demonstrated a greater potential for palladium-oxime complexes to induce death in SaOS-2 cells than CDDP, an event confirmed using the pan-caspase inhibitor Z-VAD-FMK. Compared to CDDP, only palladium-oxime complexes eradicated the clonogenicity of SaOS-2 cells after 7 days of treatment. The involvement of the lysosome-mitochondria axis in the cell death-inducing properties of the complexes was also evaluated. Using LysoTracker Red to label the acidic organelles of SaOS-2 cells treated with the O3 and O4 complexes, a decrease in the fluorescence intensity of this probe was observed in relation to CDDP and the control. Lysosomal membrane permeabilization (LMP) was also induced by the O3 and O4 complexes in an assay using acridine orange (A/O). The greater efficiency of the complexes in depolarizing the mitochondrial membrane compared to SaOS-2 cells treated with CDDP was also observed using TMRE (tetramethyl rhodamine, ethyl ester). For in vivo studies, C. elegans was used and demonstrated that both complexes reduce body bends and pharyngeal pumping after 24 h of treatment to the same extent as CDDP. We conclude that both palladium-oxime complexes are more effective than CDDP in inducing tumor cell death. The toxicity of these complexes to C. elegans was like that induced by CDDP. These results encourage preclinical studies aimed at developing more effective drugs for the treatment of osteosarcoma (OS). Furthermore, we propose palladium-oxime complexes as a new class of antineoplastic agents.

Artemisia vulgaris Induces Tumor-Selective Ferroptosis and Necroptosis via Lysosomal Ca2+ Signaling

OBJECTIVE

To evaluate the chemical composition and effects of Artemisia vulgaris (AV) hydroalcoholic extract (HEAV) on breast cancer cells (MCF-7 and SKBR-3), chronic myeloid leukemia (K562) and NIH/3T3 fibroblasts.

METHODS

Phytochemical analysis of HEAV was done by high-performance liquid chromatography-mass (HPLC) spectrometry. Viability and cell death studies were performed using trypan blue and Annexin/FITC-7AAD, respectively. Ferrostatin-1 (Fer-1) and necrostatin-1 (Nec-1) were used to assess the mode of HEAV-induced cell death and acetoxymethylester (BAPTA-AM) was used to verify the involvement of cytosolic calcium in this event. Cytosolic calcium measurements were made using Fura-2-AM.

RESULTS

HEAV decreased the viability of MCF-7, SKBR-3 and K562 cells (P<0.05). The viability of HEAV-treated K562 cells was reduced compared to HEAV-exposed fibroblasts (P<0.05). Treatment of K562 cells with HEAV induced cell death primarily by late apoptosis and necrosis in assays using annexin V-FITC/7-AAD (P<0.05). The use of Nec-1 and Fer-1 increased the viability of K562 cells treated with HEAV relative to cells exposed to HEAV alone (P<0.01). HEAV-induced Ca2+ release mainly from lysosomes in K562 cells (P<0.01). Furthermore, BAPTA-AM, an intracellular Ca2+ chelator, decreased the number of non-viable cells treated with HEAV (P<0.05).

CONCLUSIONS

HEAV is cytotoxic and activates several modalities of cell death, which are partially dependent on lysosomal release of Ca2+. These effects may be related to artemisinin and caffeoylquinic acids, the main compounds identified in HEAV.

Blocking autophagy by the two-pore channels antagonist tetrandrine improves sorafenib-induced death of hepatocellular carcinoma cells

Sorafenib, an oral multi-kinase inhibitor, used to treat hepatocellular carcinoma (HCC). However, drug resistance is still common in several HCC patients. This complex mechanism is not yet fully elucidated, driving the search for new therapeutic targets to potentiate the antitumoral effect of sorafenib. Recent findings have linked the expression of Two-Pore Channels (TPCs) receptors with the development and progression of cancer. TPCs receptors are stimulated by NAADP, a Ca²⁺ messenger, and inhibited by their antagonists Ned-19 and tetrandrine. Here, we investigate the participation of TPCs inhibition in cell death and autophagy in sorafenib-treated HCC cells. Here, we show that the association of sorafenib with tetrandrine increased sorafenib-induced cell death accompanied by increased lysotracker fluorescence intensity. In contrast, these effects were not observed after treating these cells with Ned-19. The pharmacological TPC antagonists by Ned-19 and tetrandrine or siRNA-mediated TPC1/2 inhibition decreased sorafenib-induced Ca²⁺ release, reinforcing the participation of TPCs in sorafenib HCC responses. Furthermore, the association tetrandrine and sorafenib blocked autophagy through ERK1/2 pathway inhibition, which represents a putative target for potentiating HCC cell death. Therefore, our study proposes the use of tetrandrine analogs with the aim of improving sorafenib therapy. Also, our data also allow us to suggest that TPCs may be a new target in anticancer therapies.

Cannabidiol Recovers Dopaminergic Neuronal Damage Induced by Reserpine or α-synuclein in Caenorhabditis elegans

Progressive neurodegenerative disorders such as Parkinson Disease (PD) lack curative or long-term treatments. At the same time, the increase of the worldwide elderly population and, consequently, the extension in the prevalence of age-related diseases have promoted research interest in neurodegenerative disorders. Caenorhabditis elegans is a free-living nematode widely used as an animal model in studies of human diseases. Here we evaluated cannabidiol (CBD) as a possible neuroprotective compound in PD using the C. elegans models exposed to reserpine. Our results demonstrated that CBD reversed the reserpine-induced locomotor alterations and this response was independent of the NPR-19 receptors, an orthologous receptor for central cannabinoid receptor type 1. Morphological alterations of cephalic sensilla (CEP) dopaminergic neurons indicated that CBD also protects neurons from reserpine-induced degeneration. That is, CBD attenuates the reserpine-induced increase of worms with shrunken soma and dendrites loss, increasing the number of worms with intact CEP neurons. Finally, we found that CBD also reduced ROS formation and α-syn protein accumulation in mutant worms. Our findings collectively provide new evidence that CBD acts as neuroprotector in dopaminergic neurons, reducing neurotoxicity and α-syn accumulation highlighting its potential in the treatment of PD.

Rapamycin Improves the Response of Effector and Memory CD8+ T Cells Induced by Immunization With ASP2 of Trypanosoma cruzi

Deficiency in memory formation and increased immunosenescence are pivotal features of Trypanosoma cruzi infection proposed to play a role in parasite persistence and disease development. The vaccination protocol that consists in a prime with plasmid DNA followed by the boost with a deficient recombinant human adenovirus type 5, both carrying the ASP2 gene of T. cruzi, is a powerful strategy to elicit effector memory CD8+ T-cells against this parasite. In virus infections, the inhibition of mTOR, a kinase involved in several biological processes, improves the response of memory CD8+ T-cells. Therefore, our aim was to assess the role of rapamycin, the pharmacological inhibitor of mTOR, in CD8+ T response against T. cruzi induced by heterologous prime-boost vaccine. For this purpose, C57BL/6 or A/Sn mice were immunized and daily treated with rapamycin for 34 days. CD8+ T-cells response was evaluated by immunophenotyping, intracellular staining, ELISpot assay and in vivo cytotoxicity. In comparison with vehicle-injection, rapamycin administration during immunization enhanced the frequency of ASP2-specific CD8+ T-cells and the percentage of the polyfunctional population, which degranulated (CD107a+) and secreted both interferon gamma (IFNγ) and tumor necrosis factor (TNF). The beneficial effects were long-lasting and could be detected 95 days after priming. Moreover, the effects were detected in mice immunized with ten-fold lower doses of plasmid/adenovirus. Additionally, the highly susceptible to T. cruzi infection A/Sn mice, when immunized with low vaccine doses, treated with rapamycin, and challenged with trypomastigote forms of the Y strain showed a survival rate of 100%, compared with 42% in vehicle-injected group. Trying to shed light on the biological mechanisms involved in these beneficial effects on CD8+ T-cells by mTOR inhibition after immunization, we showed that in vivo proliferation was higher after rapamycin treatment compared with vehicle-injected group. Taken together, our data provide a new approach to vaccine development against intracellular parasites, placing the mTOR inhibitor rapamycin as an adjuvant to improve effective CD8+ T-cell response.

ACE2 OVEREXPRESSION CHANGES THE SARS-COV-2 INFECTION PROFILE IN BEAS-2B CELLS

Background

Aims

Methods

Results

Conclusion

Angiotensin II modulates the murine hematopoietic stem cell and progenitors cocultured with stromal S17 cells

Although the existence of the renin-angiotensin system (RAS) in the bone marrow is clear, the exact role of this system in hematopoiesis has not yet been fully characterized. Here the direct role of angiotensin II (AngII) in hematopoietic stem cells (HSCs), common myeloid progenitors (CMPs), granulocyte/monocyte progenitors (GMPs), and megakaryocytes/erythroid progenitors (MEPs), using a system of coculture with stromal S17 cells. Flow cytometry analysis showed that AngII increases the percentage of HSC and GMP, while reducing CMP with no effect on MEP. According to these data, AngII increased the total number of mature Gr-1⁺ /Mac-1⁺ cells without changes in Terr119⁺ cells. AngII does not induce cell death in the population of LSK cells. In these populations, treatment with AngII decreases the expression of Ki67⁺ protein with no changes in the Notch1 expression, suggesting a role for AngII on the quiescence of immature cells. In addition, exposure to AngII from murine bone marrow cells increased the number of CFU-GM and BFU-E in a clonogenic assay. In conclusion, our data showed that AngII is involved in the regulation of hematopoiesis with a special role in HSC, suggesting that AngII should be evaluated in coculture systems, especially in cases that require the expansion of these cells in vitro, still a significant challenge for therapeutic applications in humans.

α-Synuclein Overexpression Induces Lysosomal Dysfunction and Autophagy Impairment in Human Neuroblastoma SH-SY5Y

Although the etiology of Parkinson's disease (PD) is multifactorial, it has been linked to abnormal accumulation of α-synuclein (α-syn) in dopaminergic neurons, which could lead to dysfunctions on intracellular organelles, with potential neurodegeneration. Patients with familial early-onset PD frequently present mutation in the α-syn gene (SNCA), which encodes mutant α-syn forms, such as A30P and A53T, which potentially regulate Ca2+ unbalance. Here we investigated the effects of overexpression of wild-type α-syn (WT) and the mutant forms A30P and A53T, on modulation of lysosomal Ca2+ stores and further autophagy activation. We found that in α-syn-overexpressing cells, there was a decrease in Ca2+ released from endoplasmic reticulum (ER) which is related to the increase in lysosomal Ca2+ release, coupled to lysosomal pH alkalization. Interestingly, α-syn-overexpressing cells showed lower LAMP1 levels, and a disruption of lysosomal morphology and distribution, affecting autophagy. Interestingly, all these effects were more evident with A53T mutant isoform when compared to A30P and WT α-syn types, indicating that the pathogenic phenotype for PD is potentially related to impairment of α-syn degradation. Taken together, these events directly impact PD-related dysfunctions, being considered possible molecular targets for neuroprotection.

Estrogen receptors localization and signaling pathways in DU-145 human prostate cancer cells

The aim of the present study was to investigate the subcellular localization of estrogen receptors ERα and ERβ in androgen-independent prostate cancer cell line DU-145, and the possible role of exportin CRM1 on ERs distribution. In addition, we evaluated the ERs contribution to activation of ERK1/2 and AKT. Immunostaining of ERα and ERβ was predominantly found in the extranuclear regions of DU-145 cells. CRM1 inhibitor Leptomycin B reduced drastically the presence of ERα and ERβ in the extranuclear regions and increased in the nuclei, indicating the possible involvement of CRM1 on ERs nuclear-cytoplasmic shuttling. 17β-estradiol (E2), ERα-selective agonist PPT and ERβ-selective agonist DPN induced a rapid increase on ERK1/2 phosphorylation. E2-induced ERK1/2 activation was partially inhibited when cells were pretreated with ERα- or ERβ-selective antagonists, and blocked by simultaneous pretreatment with both antagonists, suggesting ERα/β heterodimers formation. Furthermore, E2 treatment did not activate AKT pathway. Therefore, we highlighted a possible crosstalk between extranuclear and nuclear ERs and their upstream and downstream signaling molecules as an important mechanism to control ER function as a potential therapeutic target in prostate cancer cells.

Medicinal properties of Angelica archangelica root extract: Cytotoxicity in breast cancer cells and its protective effects against in vivo tumor development

OBJECTIVE

Although Angelica archangelica is a medicinal and aromatic plant with a long history of use for both medicinal and food purposes, there are no studies regarding the antineoplastic activity of its root. This study aimed to evaluate the cytotoxicity and antitumor effects of the crude extract of A. archangelica root (CEAA) on breast cancer.

METHODS

The cytotoxicity of CEAA against breast adenocarcinoma cells (4T1 and MCF-7) was evaluated by a 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay. Morphological and biochemical changes were detected by Hoechst 33342/propidium iodide (PI) and annexin V/PI staining. Cytosolic calcium mobilization was evaluated in cells staining with FURA-4NW. Immunoblotting was used to determine the effect of CEAA on anti- and pro-apoptotic proteins (Bcl-2 and Bax, respectively). The 4T1 cell-challenged mice were used for in vivo assay.

RESULTS

Using ultra-high-performance liquid chromatography-mass spectrometry analysis, angelicin, a constituent of the roots and leaves of A. archangelica, was found to be the major constituent of the CEAA evaluated in this study (73 µg/mL). The CEAA was cytotoxic for both breast cancer cell lines studied but not for human fibroblasts. Treatment of 4T1 cells with the CEAA increased Bax protein levels accompanied by decreased Bcl-2 expression, in the presence of cleaved caspase-3 and cytosolic calcium mobilization, suggesting mitochondrial involvement in breast cancer cell death induced by the CEAA in this cell line. No changes on the Bcl-2/Bax ratio were observed in CEAA-treated MCF7 cells. Gavage administration of the CEAA (500 mg/kg) to 4T1 cell-challenged mice significantly decreased tumor growth when compared with untreated animals.

CONCLUSION

Altogether, our data show the antitumor potential of the CEAA against breast cancer cells in vitro and in vivo. Further research is necessary to better elucidate the pharmacological application of the CEAA in breast cancer therapy.

Glutamate induces autophagy via the two-pore channels in neural cells

NAADP (nicotinic acid adenine dinucleotide phosphate) has been proposed as a second messenger for glutamate in neuronal and glial cells via the activation of the lysosomal Ca²⁺ channels TPC1 and TPC2. However, the activities of glutamate that are mediated by NAADP remain unclear. In this study, we evaluated the effect of glutamate on autophagy in astrocytes at physiological, non-toxic concentration. We found that glutamate induces autophagy at similar extent as NAADP. By contrast, the NAADP antagonist NED-19 or SiRNA-mediated inhibition of TPC1/2 decreases autophagy induced by glutamate, confirming a role for NAADP in this pathway. The involvement of TPC1/2 in glutamate-induced autophagy was also confirmed in SHSY5Y neuroblastoma cells. Finally, we show that glutamate leads to a NAADP-dependent activation of AMPK, which is required for autophagy induction, while mTOR activity is not affected by this treatment. Taken together, our results indicate that glutamate stimulates autophagy via NAADP/TPC/AMPK axis, providing new insights of how Ca²⁺ signalling glutamate-mediated can control the cell metabolism in the central nervous system.

Cafestol, a diterpene molecule found in coffee, induces leukemia cell death

To evaluate the antitumor properties of Cafestol four leukemia cell lines were used (NB4, K562, HL60 and KG1). Cafestol exhibited the highest cytotoxicity against HL60 and KG1 cells, as evidenced by the accumulation of cells in the sub-G1 fraction, mitochondrial membrane potential reduction, accumulation of cleaved caspase-3 and phosphatidylserine externalization. An increase in CD11b and CD15 differentiation markers with attenuated ROS generation was also observed in Cafestol-treated HL60 cells. These results were similar to those obtained following exposure of the same cell line to cytarabine (Ara-C), an antileukemic drug. Cafestol and Ara-C reduced the clonogenic potential of HL60 cells by 100%, but Cafestol spared murine colony forming unit- granulocyte/macrophage (CFU-GM), which retained their clonogenicity. The co-treatment of Cafestol and Ara-C reduced HL60 cell viability compared with both drugs administered alone. In conclusion, despite the distinct molecular mechanisms involved in the activity of Cafestol and Ara-C, a similar cytotoxicity towards leukemia cells was observed, which suggests a need for prophylactic-therapeutic pre-clinical studies regarding the anticancer properties of Cafestol.

Autophagy regulates Selumetinib (AZD6244) induced-apoptosis in colorectal cancer cells

OBJECTIVE

As Selumetinib is a MEK1/2 inhibitor that has gained interest as an anti-tumor agent, the present study was designed to investigate autophagy involvement on Selumetinib-induced apoptosis in colorectal cancer (CRC) cells.

METHODS

CRC cells death and cycle studies were assessed by AnnexinV-FITC and PI staining, respectively. Autophagy flux was analysed by Western Blot (LC3II and p62 protein levels) and retroviral infection of SW480 cells for siBecn1 RNA interference experiments. Confocal microscopy was used to determine mCherry-EGFP-LC3 distribution.

KEY FINDINGS

The Selumetinib effects were concentration-dependent in SW480 cell line. Whereas 1 μM exerted an arrest in the cell cycle (G1 phase), higher concentrations (10 μM) induced cell death, which was accompanied by autophagy blockage in its last stages. Autophagy induction by Rapamycin (RAPA) increased cell survival, whereas pharmacology autophagy inhibition by Bafilomycin A1 (BAF), Chloroquine (CQ) or 3-Methyladenine (3-MA) increased Selumetinib-induced CRC cells death.

CONCLUSIONS

Altogether, these results suggest that autophagy plays a fundamental role in CRC cells response to Selumetinib. In addition, the combination of Selumetinib with autophagy inhibitors may be a useful therapeutic strategy to enhance its activity against colorectal tumours.

Bothropoides pauloensis venom effects on isolated perfused kidney and cultured renal tubular epithelial cells

Snake envenomation (Bothrops genus) is common in tropical countries and acute kidney injury is one of the complications observed in Bothrops snakebite with relevant morbidity and mortality. Here, we showed that Bothropoides pauloensis venom (BpV) decreased cell viability (IC50 of 7.5 μg/mL). Flow cytometry with annexin V and propidium iodide showed that cell death occurred predominantly by apoptosis and late apoptosis, through caspases 3 and 7 activation, mitochondrial membrane potential collapse and ROS overproduction. BpV reduced perfusion pressure, renal vascular resistance, urinary flow, glomerular filtration rate, percentage of sodium, chloride or potassium tubular transportation. These findings demonstrated that BpV cytotoxicity on renal epithelial cells might be responsible for the nephrotoxicity observed in isolated kidney.

L-Aminoacid Oxidase from Bothrops leucurus Venom Induces Nephrotoxicity via Apoptosis and Necrosis

Acute renal failure is a common complication caused by Bothrops viper envenomation. In this study, the nefrotoxicity of a main component of B. leucurus venom called L-aminoacid oxidase (LAAO-Bl) was evaluated by using tubular epithelial cell lines MDCK and HK-2 and perfused kidney from rats. LAAO-Bl exhibited cytotoxicity, inducing apoptosis and necrosis in MDCK and HK-2 cell lines in a concentration-dependent manner. MDCK apoptosis induction was accompanied by Ca²⁺ release from the endoplasmic reticulum, reactive oxygen species (ROS) generation and mitochondrial dysfunction with enhanced expression of Bax protein levels. LAAO-Bl induced caspase-3 and caspase-7 activation in both cell lines. LAAO-Bl (10 μg/mL) exerts significant effects on the isolated kidney perfusion increasing perfusion pressure and urinary flow and decreasing the glomerular filtration rate and sodium, potassium and chloride tubular transport. Taken together our results suggest that LAAO-Bl is responsible for the nephrotoxicity observed in the envenomation by snakebites. Moreover, the cytotoxic of LAAO-Bl to renal epithelial cells might be responsible, at least in part, for the nephrotoxicity observed in isolated kidney.

Comparative study of autophagy inhibition by 3MA and CQ on Cytarabine‑induced death of leukaemia cells

BACKGROUND

As the molecular mechanisms of Cytarabine,one of the most important drugs used in the leukaemia’s treatment, are only partially understood and the role of autophagy on leukaemia development and treatment is only recently being investigated, in this study, by using Chloroquine (CQ) and 3-methyladenine (3MA) as autophagy inhibitors, we aim to evaluate the contribution of an autophagic mechanism to Cytarabine (AraC)-induced death of HL60 leukaemia cells.

METHODS

Trypan blue exclusion and AnnexinV/PI assays were used to evaluate HL60 cell death under AraC treatment in the presence or absence of 3MA and CQ. Western blotting and immunofluorescence experiments were performed to show the involvement of apoptosis and autophagy protein expressions. Phenotypic characterization of HL60-treated cells was performed by using immunophenotyping. Clonogenic assays were applied to analyse clonal function of HL60-treated cells.

RESULTS

We observed that although autophagy inhibition by 3MA, but not CQ, increased the death of HL60 AraC cells after 24 h of treatment, no significant differences between AraC and AraC + 3MA-treated groups were observed by using clonogenic assay. In addition, increased number of immature (CD34(+)/CD38(−)Lin(−/low)) HL60 cells was found in AraC and AraC-3MA groups when compared with control untreated cells.

CONCLUSIONS

Although AraC anti-leukaemia effects could be potentiated by 3MA autophagy inhibition after 24 h of exposure, leukaemia cell resistance, the main causes of treatment failure, is also promoted by autophagy initial stage impairment by 3MA, denoting the complex role of autophagy in leukaemia cells’ response to chemotherapy.

NAADP-sensitive two-pore channels are present and functional in gastric smooth muscle cells

Nicotinic acid adenine dinucleotide phosphate (NAADP) has been identified as an important modulator of Ca(2+) release from the endo-lysosomal system in a variety of cells by a new and ubiquitous class of endo-lysosomal ion channels known as the two-pore channels (TPCs). However, the role of TPCs in NAADP action in smooth muscle is not known. In the present work, we investigated the effects of NAADP in gastric smooth muscle cells and its ability to release Ca(2+) by TPCs. We show that Ca(2+) signals mediated by NAADP were inhibited by disrupting Ca(2+) handling by either acidic organelles (using bafilomycin A1) or the Endoplasmic Reticulum (using thapsigargin, ryanodine or 2-APB). Transcripts for endogenous TPC1 and TPC2 were readily detected and recombinant TPCs localized to the endosomes and/or lysosomes. Overexpression of wild-type TPCs but not pore mutants enhanced NAADP-mediated cytosolic Ca(2+) signals. Desensitizing the NAADP pathway inhibited Ca(2+)-responses to extracellular stimulation with carbachol but not ATP. Taken together, these results indicate that NAADP likely induces Ca(2+) release from the endolysosomal system through TPCs which is subsequently amplified via the ER in an agonist-specific manner. Thus, we suggest a second messenger role for NAADP in smooth muscle cells.

Interplay between apoptosis and autophagy, a challenging puzzle: new perspectives on antitumor chemotherapies

Autophagy is a mechanism of protection against various forms of human diseases, such as cancer, in which autophagy seems to have an extremely complex role. In cancer, there is evidence that autophagy may be oncogenic in some contexts, whereas in others it clearly contributes to tumor suppression. In addition, studies have demonstrated the existence of a complex relationship between autophagy and cell death, determining whether a cell will live or die in response to anticancer therapies. Nevertheless, we still need to complete the autophagy-apoptosis puzzle in the tumor context to better address appropriate chemotherapy protocols with autophagy modulators. Generally, tumor cell resistance to anticancer induced-apoptosis can be overcome by autophagy inhibition. However, when an extensive autophagic stimulus is activated, autophagic cell death is observed. In this review, we discuss some details of autophagy and its relationship with tumor progression or suppression, as well as role of autophagy-apoptosis in cancer treatments.

The role of calcium stores in apoptosis and autophagy

The mechanisms that regulate programmed cell death, such as apoptosis, and the cellular "self-eating" phenomenon of autophagy, share many regulatory systems and common pathways. These mechanisms have been extensively investigated over the last few years. Some intracellular structures may determine and control the autophagic fate of the cell such as the endoplasmic reticulum, mitochondria, and lysosomes. The coordination and interrelation of these organelles are crucial in maintaining calcium levels and general cellular homeostasis, as well as in regulating cell life and death under physiological and pathological conditions, including cancer, neurodegeneration, and aging. In this review, we discuss the crosstalk between the aforementioned organelles and their influence in apoptotic and autophagic processes.

Nicotinic acid adenine dinucleotide phosphate (NAADP) regulates autophagy in cultured astrocytes

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a potent Ca(2+)-mobilizing messenger that in many cells releases Ca(2+) from the endolysosomal system. Recent studies have shown that NAADP-induced Ca(2+) mobilization is mediated by the two-pore channels (TPCs). Whether NAADP acts as a messenger in astrocytes is unclear, and downstream functional consequences have yet to be defined. Here, we show that intracellular delivery of NAADP evokes Ca(2+) signals from acidic organelles in rat astrocytes and that these signals are potentiated upon overexpression of TPCs. We also show that NAADP increases acidic vesicular organelle formation and levels of the autophagic markers, LC3II and beclin-1. NAADP-mediated increases in LC3II levels were reduced in cells expressing a dominant-negative TPC2 construct. Our data provide evidence that NAADP-evoked Ca(2+) signals mediated by TPCs regulate autophagy.