Ginger extract activates caspase independent paraptosis in cancer cells via ER stress, mitochondrial dysfunction, AIF translocation and DNA damage

Necrosis Links Neurodegeneration and Neuroinflammation in Neurodegenerative Disease

The mechanisms of neuronal cell death in neurodegenerative disease remain incompletely understood, although recent studies have made significant advances. Apoptosis was previously considered to be the only mechanism of neuronal cell death in neurodegenerative diseases. However, recent findings have challenged this dogma, identifying new subtypes of necrotic neuronal cell death. The present review provides an updated summary of necrosis subtypes and discusses their potential roles in neurodegenerative cell death. Among numerous necrosis subtypes, including necroptosis, paraptosis, ferroptosis, and pyroptosis, transcriptional repression-induced atypical cell death (TRIAD) has been identified as a potential mechanism of neuronal cell death. TRIAD is induced by functional deficiency of TEAD-YAP and self-amplifies via the release of HMGB1. TRIAD is a feasible potential mechanism of neuronal cell death in Alzheimer's disease and other neurodegenerative diseases. In addition to induction of cell death, HMGB1 released during TRIAD activates brain inflammatory responses, which is a potential link between neurodegeneration and neuroinflammation.

Paraptosis: a non-classical paradigm of cell death for cancer therapy

Due to the sustained proliferative potential of cancer cells, inducing cell death is a potential strategy for cancer therapy. Paraptosis is a mode of cell death characterized by endoplasmic reticulum (ER) and/or mitochondrial swelling and cytoplasmic vacuolization, which is less investigated. Considerable evidence shows that paraptosis can be triggered by various chemical compounds, particularly in cancer cells, thus highlighting the potential application of this non-classical mode of cell death in cancer therapy. Despite these findings, there remain significant gaps in our understanding of the role of paraptosis in cancer. In this review, we summarize the current knowledge on chemical compound-induced paraptosis. The ER and mitochondria are the two major responding organelles in chemical compound-induced paraptosis, which can be triggered by the reduction of protein degradation, disruption of sulfhydryl homeostasis, overload of mitochondrial Ca2+, and increased generation of reactive oxygen species. We also discuss the stumbling blocks to the development of this field and the direction for further research. The rational use of paraptosis might help us develop a new paradigm for cancer therapy.

Zearalenone Induces Blood-Testis Barrier Damage through Endoplasmic Reticulum Stress-Mediated Paraptosis of Sertoli Cells in Goats

Zearalenone (ZEA) is present worldwide as a serious contaminant of food and feed and causes male reproductive toxicity. The implication of paraptosis, which is a nonclassical paradigm of cell death, is unclear in ZEA-induced male reproductive disorders. In this study, the toxic effects of ZEA on the blood-testis barrier (BTB) and the related mechanisms of paraptosis were detected in goats. ZEA exposure, in vivo, caused a significant decrease in spermatozoon quality, the destruction of seminiferous tubules, and damage to the BTB integrity. Furthermore, ZEA exposure to Sertoli cells (SCs) in vitro showed similar dysfunction in structure and barrier function. Importantly, the formation of massive cytoplasmic vacuoles in ZEA-treated SCs corresponded to the highly swollen and dilative endoplasmic reticulum (ER), and paraptosis inhibition significantly alleviated ZEA-induced SC death and vacuolization, which indicated the important contribution of paraptosis in ZEA-induced BTB damage. Meanwhile, the expression of ER stress marker proteins was increased after ZEA treatment but decreased under the inhibition of paraptosis. The vacuole formation and SC death, induced by ZEA, were remarkably blocked by ER stress inhibition. In conclusion, these results facilitate the exploration of the mechanisms of the SC paraptosis involved in ZEA-induced BTB damage in goats.

Synergistic apoptotic effects of ethanolic extracts of ginger and Ganoderma lucidum in a colorectal cancer cell line

Current conventional therapy for colorectal cancer includes surgery, radiation and chemotherapy, all of which produce side effects. Herbal medicine can control the side effects of conventional treatments. We investigated the synergistic effect of a mixture of Zingiber officinale Roscoe (Ginger) and Ganoderma lucidum extracts on colorectal cancer cell apoptosis in vitro. We prepared ethanolic extracts of ginger (GEE) and G. lucidum (GLEE). Cytotoxicity was evaluated using MTT assay and the half-maximal inhibitory concentration (IC50) of each extract was calculated. The effect of these extracts on apoptosis in cancer cells was assessed using flow cytometry; Bax, Bcl2 and caspase-3 gene expression was evaluated using real-time PCR. GEE and GLEE decreased CT-26 cell viability significantly in a dose-dependent manner; however, the combined application of GEE + GLEE was most effective. Bax:Bcl-2 gene expression ratio, caspase-3 gene expression and the number of apoptotic cells were increased significantly in CT-26 cells treated at the IC50 level of each compound, especially in the GEE + GLEE treatment group. Combined ginger and Ganoderma lucidum extracts exhibited synergistic antiproliferative and apoptotic effects on colorectal cancer cells.

Polyploid cell dynamics and death before and after PEG-treatment of a NIH/3T3 derived culture: vinblastine effects on the regulation of cell subpopulations heterogeneity

BACKGROUND

Neoplastic subpopulations can include polyploid cells that can be involved in tumor evolution and recurrence. Their origin can be traced back to the tumor microenvironment or chemotherapeutic treatment, which can alter cell division or favor cell fusion, generating multinucleated cells. Their progeny, frequently genetically unstable, can result in new aggressive and more resistant to chemotherapy subpopulations. In our work, we used NIHs cells, previously derived from the NIH/3T3 line after serum deprivation, that induced a polyploidization increase with the appearance of cells with DNA content ranging from 4 to 24c. This study aimed to analyze the cellular dynamics of NIHs culture subpopulations before and after treatment with the fusogenic agent polyethylene glycol (PEG), which allowed us to obtain new giant polyploid cells. Successively, PEG-untreated and PEG-treated cultures were incubated with the antimicrotubular poison vinblastine. The dynamics of appearance, decrease and loss of cell subpopulations were evaluated by correlating cell DNA content to mono-multinuclearity resulting from cell fusion and division process alteration and to the peculiarities of cell death events.

RESULTS

DNA microfluorimetry and morphological techniques (phase contrast, fluorescence and TEM microscopies) indicated that PEG treatment induced a 4-24c cell increase and the appearance of new giant elements (64-140c DNA content). Ultrastructural analysis and autophagosomal-lysosomal compartment fluorochromization, which allowed us to correlate cytoplasmic changes to death events, indicated that cell depletion occurred through distinct mechanisms: apoptotic death involved 2c, 4c and 8c cells, while autophagic-like death involved intermediate 12-24c cells, showing nuclear (lobulation/micronucleation) and autophagic cytoplasm alterations. Death, spontaneously occurring, especially in intermediate-sized cells, was increased after vinblastine treatment. No evident cell loss by death events was detected in the 64-140c range.

CONCLUSIONS

PEG-treated NIHs cultures can represent a model of heterogeneous subpopulations originating from cell fusion and division process anomalies. Altogether, our results suggest that the different cell dynamics of NIHs subpopulations can affect the variability of responses to stimuli able to induce cell degeneration and death. Apoptptic, autophagic or hybrid forms of cell death can also depend on the DNA content and ability to progress through the cell cycle, which may influence the persistence and fate of polyploid cell descendants, also concerning chemotherapeutic agent action.

V. J, Pal S, Nair BG, Kar R, Mishra N. Paraptosis: a unique cell death mode for targeting cancer

Programmed cell death (PCD) is the universal process that maintains cellular homeostasis and regulates all living systems' development, health and disease. Out of all, apoptosis is one of the major PCDs that was found to play a crucial role in many disease conditions, including cancer. The cancer cells acquire the ability to escape apoptotic cell death, thereby increasing their resistance towards current therapies. This issue has led to the need to search for alternate forms of programmed cell death mechanisms. Paraptosis is an alternative cell death pathway characterized by vacuolation and damage to the endoplasmic reticulum and mitochondria. Many natural compounds and metallic complexes have been reported to induce paraptosis in cancer cell lines. Since the morphological and biochemical features of paraptosis are much different from apoptosis and other alternate PCDs, it is crucial to understand the different modulators governing it. In this review, we have highlighted the factors that trigger paraptosis and the role of specific modulators in mediating this alternative cell death pathway. Recent findings include the role of paraptosis in inducing anti-tumour T-cell immunity and other immunogenic responses against cancer. A significant role played by paraptosis in cancer has also scaled its importance in knowing its mechanism. The study of paraptosis in xenograft mice, zebrafish model, 3D cultures, and novel paraptosis-based prognostic model for low-grade glioma patients have led to the broad aspect and its potential involvement in the field of cancer therapy. The co-occurrence of different modes of cell death with photodynamic therapy and other combinatorial treatments in the tumour microenvironment are also summarized here. Finally, the growth, challenges, and future perspectives of paraptosis research in cancer are discussed in this review. Understanding this unique PCD pathway would help to develop potential therapy and combat chemo-resistance in various cancer.

JI017 Induces Cell Autophagy and Apoptosis via Elevated Levels of Reactive Oxygen Species in Human Lung Cancer Cells

Lung cancer is one of the most common malignant tumors and a leading cause of cancer-related death in the worldwide. Various anticancer drugs, such as cisplatin and pemetrexed, have been developed for lung cancer treatment but due their drug resistance and side effects, novel treatments need to be developed. In this study, the efficacy of the natural drug JI017, which is known to have few side effects, was tested in lung cancer cells. JI017 inhibited A549, H460, and H1299 cell proliferation. JI017 induced apoptosis, regulated apoptotic molecules, and inhibited colony formation. Additionally, JI017 increased intracellular ROS generation. JI017 downregulated PI3K, AKT, and mTOR expression. JI017 increased the cytosolic accumulation of LC3. We found that JI017 promoted apoptosis through ROS-induced autophagy. Additionally, the xenograft tumor size was smaller in JI017-treated mice. We found that JI017 treatment increased MDA concentrations, decreased Ki-67 protein levels, and increased cleaved caspase-3 and LC3 levels in vivo. JI017 decreased cell proliferation and increased apoptosis by inducing autophagy signaling in H460 and H1299 lung cancer cells. Targeting JI017 and autophagy signaling could be useful in lung cancer treatment.

A Mini Review on Molecules Inducing Caspase-Independent Cell Death: A New Route to Cancer Therapy

Most anticancer treatments trigger tumor cell death through apoptosis, where initiation of proteolytic action of caspase protein is a basic need. But under certain circumstances, apoptosis is prevented by the apoptosis inhibitor proteins, survivin and Hsp70. Several drugs focusing on classical programmed death of the cell have been reported to have low anti-tumorogenic potency due to mutations in proteins involved in the caspase-dependent programmed cell death with intrinsic and extrinsic pathways. This review concentrates on the role of anti-cancer drug molecules targeting alternative pathways of cancer cell death for treatment, by providing a molecular basis for the new strategies of novel anti-cancer treatment. Under these conditions, active agents targeting alternative cell death pathways can be considered as potent chemotherapeutic drugs. Many natural compounds and other small molecules, such as inorganic and synthetic compounds, including several repurposing drugs, are reported to cause caspase-independent cell death in the system. However, few molecules indicated both caspase-dependent as well caspase-free cell death in specific cancer lines. Cancer cells have alternative methods of caspase-independent programmed cell death which are equally promising for being targeted by small molecules. These small molecules may be useful leads for rational therapeutic drug design, and can be of potential interest for future cancer-preventive strategies.

Antitumor activity of pachymic acid in cervical cancer through inducing endoplasmic reticulum stress, mitochondrial dysfunction, and activating the AMPK pathway

Pachymic acid has various pharmacological effects, including anti-inflammatory, antioxidant, immunomodulatory, and antitumor. However, the role of pachymic acid in cervical cancer remains unclear. So, we investigated the effects of pachymic acid in cervical cancer and elucidated the underlying mechanisms. We treated HeLa cells and normal cervical epithelial cells (HUCECs) with pachymic acid (0, 10, 20, 40, 80, or 160 μM) for 72 h, and found the cell activity was decreased in cells treated with 160 μM pachymic acid for 48 h or 80 μM pachymic acid for 72 h, while HUCECs viability without effect. Next, we observed that endoplasmic reticulum (ER) related gene expression, mitochondrial membrane potential (MMP) changes, ATP depletion, reactive oxygen species (ROS) generation and apoptosis were increased. Moreover, we observed that cytochrome C (Cytc) expression was increased and apoptosis-inducing factor (AIF) was decreased in the cytoplasm of pachymic acid-treated HeLa cells. Tauroursodeoxycholic acid (TUDCA) of ER stress inhibitor reversed the effects of pachymic acid on HeLa cells. Phosphorylation of AMPK and acetyl-CoA carboxylase (ACC) of the AMPK pathway key protein was upregulated in pachymic acid-induced HeLa cells. Finally, we subcutaneously implanted HeLa cells into female nude mice and treated them with pachymic acid (50 mg/kg) for 3 weeks (5 days/week), and observed in pachymic acid induced xenograft mice, tumor growth was suppressed, cell apoptosis, ER-related gene expression, and ROS levels in tumor tissues were increased. Therefore, these findings demonstrated that pachymic acid plays an anti-tumor activity in cervical cancer through inducing ER stress, mitochondrial dysfunction, and activating the AMPK pathway.

Methylmercury induced apoptosis of human neuroblastoma cells through the reactive oxygen species mediated caspase and poly ADP-ribose polymerase/apoptosis-inducing factor dependent pathways

Methylmercury (MeHg) is an environmental neurotoxic substance, which can easily cross the blood-brain barrier, causing irreversible damage to the human central nervous system. Reactive oxygen species (ROS) are involved in various ways of intracellular physiological or pathological processes including neuronal apoptosis. This study attempted to explore the role of ROS-mediated poly ADP-ribose polymerase (PARP)/apoptosis-inducing factor (AIF) apoptosis signaling pathway in the process of MeHg-induced cell death of human neuroblastoma cells (SH-SY5Y). Here, we found that SH-SY5Y cells underwent apoptosis in response to MeHg, which was accompanied by the increased levels of ROS and calcium ion, and the activation of caspase cascades and PARP. Inhibiting the production of ROS can reduce the apoptosis rate to a certain extent. PARP/AIF apoptotic pathway is independent of caspase dependent signaling pathway and regulates it. In conclusion, these results suggest that ROS mediated activation of caspase pathway and PARP/AIF signaling pathway are involved in MeHg induced apoptosis, and these two pathways interact with each other.

6-Shogaol Suppresses the Progression of Liver Cancer via the Inactivation of Wnt/[Formula: see text]-Catenin Signaling by Regulating TLR4

Liver cancer is a gastrointestinal malignant tumor with high lethality. The prognosis of liver cancer remains poor. Compounds derived from natural products have been confirmed to alleviate the progression of various diseases, including cancers. Additionally, 6-Shogaol has been reported to induce apoptosis in liver cancer cells. However, the mechanism by which 6-shogaol regulates apoptosis in liver cancer cells remains unclear. To investigate the function of 6-shogaol in liver cancer, RT-qPCR and western blotting were used to detect the expression of TLR4 and FOXO3a in liver cancer cells, respectively. The OD value of liver cancer cells was measured using the MTT assay. Flow cytometry was used to measure cell apoptosis. 6-Shogaol inhibited the growth of liver cancer cells. TLR4 and Wnt/[Formula: see text]-catenin were upregulated in liver cancer cells, and FOXO3a was inactivated, but 6-Shogaol reversed the expression of TLR4, Wnt/[Formula: see text]-catenin and FOXO3a in liver cancer cells. Additionally, TLR4 overexpression partially reversed the inhibitory effect of 6-shogaol on the progression of liver cancer cells via Wnt/[Formula: see text]-catenin signaling. Furthermore, the 6-shogaol-induced increase in FOXO3a expression in liver cancer was notably suppressed by TLR4 or Wnt/[Formula: see text]-catenin upregulation. Thus, 6-Shogaol suppresses the progression of liver cancer by mediating Wnt/[Formula: see text]-catenin signaling and is a potential agent for the treatment of liver cancer.

The Herbal Formula JI017 Induces ER Stress via Nox4 in Breast Cancer Cells

Chemotherapy is a powerful anti-tumor therapeutic strategy; however, resistance to treatment remains a serious concern. To overcome chemoresistance, combination therapy with anticancer drugs is a potential strategy. We developed a novel herbal extract, JI017, with lower toxicity and lesser side effects. JI017 induced programmed cell death and excessive unfolded protein response through the release of intracellular reactive oxygen species (ROS) and calcium in breast cancer cells. JI017 treatment increased the expression of endoplasmic reticulum (ER) stress markers, including p-PERK, p-eIF2α, ATF4, and CHOP, via the activation of both exosomal GRP78 and cell lysate GRP78. The ROS inhibitors diphenyleneiodonium and N-acetyl cysteine suppressed apoptosis and excessive ER stress by inhibiting Nox4 in JI017-treated breast cancer cells. Furthermore, in paclitaxel-resistant breast cancer cell lines, MCF-7R and MDA-MB-231R, a combination of JI017 and paclitaxel overcame paclitaxel resistance by blocking epithelial-mesenchymal transition (EMT) processes, such as the downregulation of E-cadherin expression and the upregulation of HIF-1α, vimentin, Snail, and Slug expression. These findings suggested that JI017 exerts a powerful anti-cancer effect in breast cancer and a combination therapy of JI017 and paclitaxel may be a potential cancer therapy for paclitaxel resistant breast cancer.

JI017, a Complex Herbal Medication, Induces Apoptosis via the Nox4-PERK-CHOP Axis in Ovarian Cancer Cells

Many anti-cancer drugs, including paclitaxel and etoposide, have originated and been developed from natural products, and traditional herbal medicines have fewer adverse effects and lesser toxicity than anti-tumor reagents. Therefore, we developed a novel complex herbal medicine, JI017, which mediates endoplasmic reticulum (ER) stress and apoptosis through the Nox4-PERK-CHOP signaling pathway in ovarian cancer cells. JI017 treatment increases the expression of GRP78, ATF4, and CHOP and the phosphorylation of PERK and eIF2α via the upregulation of Nox4. Furthermore, it increases the release of intracellular reactive oxygen species (ROS), the production of intracellular Ca2+, and the activation of exosomal GRP78 and cell lysate GRP78. Combination treatment using the sarco/endoplasmic reticulum Ca2+-ATPase inhibitor thapsigargin (TG) and JI017 reportedly induces increased ER stress and cell death in comparison to the control; however, knockdown experiments of PERK and CHOP indicated suppressed apoptosis and ER stress in JI017-treated ovarian cancer cells. Furthermore, targeting Nox4 using specific siRNA and pharmacological ROS inhibitors, including N-acetylcystein and diphenylene iodonium, blocked apoptosis and ER stress in JI017-treated ovarian cancer cells. In the radioresistant ovarian cancer model, when compared to JI017 alone, JI017 co-treatment with radiation induced greater cell death and resulted in overcoming radioresistance by inhibiting epithelial-mesenchymal-transition-related phenomena such as the reduction of E-cadherin and the increase of N-cadherin, vimentin, Slug, and Snail. These findings suggest that JI017 is a powerful anti-cancer drug for ovarian cancer treatment and that its combination treatment with radiation may be a novel therapeutic strategy for radioresistant ovarian cancer.

Swainsonine Triggers Paraptosis via ER Stress and MAPK Signaling Pathway in Rat Primary Renal Tubular Epithelial Cells

Swainsonine (SW), an indolizidine alkaloid extracted from locoweeds, was shown toxic effects in multiple studies, but the underlying action mechanism remains unclear. SW is known to cause autophagy and apoptosis, but there has been no report on paraptosis mediated cell death. Here, we showed that SW induced rat primary renal tubular epithelial cells (RTECs) death accompanied by vacuolation in vitro. The fluorescence with the endoplasmic reticulum (ER)-Tracker Red and transmission electron microscopy (TEM) results indicated that the vacuoles were of ER origin, typical of paraptosis. The level of ER stress markers, such as polyubiquitinated proteins, Bip, CHOP and cytoplasmic concentration of Ca²⁺ have drastically increased. Interestingly, autophagy inhibitor could not interrupt but enhanced the induction of cytoplasmic vacuolization. Furthermore, MAPK pathways were activated by SW and inhibitors of ERK and JNK pathways could prevent the formation of cytoplasmic vacuolization. In this study, we confirmed that SW induced cell paraptosis through ER stress and MAPK signaling pathway, thus further laying a theoretical foundation for the study of SW toxicity mechanism.

Programmed cell death, redox imbalance, and cancer therapeutics

Cancer cells are disordered by nature and thus featured by higher internal redox level than healthy cells. Redox imbalance could trigger programmed cell death if exceeded a certain threshold, rendering therapeutic strategies relying on redox control a possible cancer management solution. Yet, various programmed cell death events have been consecutively discovered, complicating our understandings on their associations with redox imbalance and clinical implications especially therapeutic design. Thus, it is imperative to understand differences and similarities among programmed cell death events regarding their associations with redox imbalance for improved control over these events in malignant cells as well as appropriate design on therapeutic approaches relying on redox control. This review addresses these issues and concludes by bringing affront cold atmospheric plasma as an emerging redox controller with translational potential in clinics.

Antioxidant and anticancer potentials of edible flowers: where do we stand?

Edible flowers are attracting special therapeutic attention and their administration is on the rise. Edible flowers play pivotal modulatory roles on oxidative stress and related interconnected apoptotic/inflammatory pathways toward the treatment of cancer. In this review, we highlighted the phytochemical content and therapeutic applications of edible flowers, as well as their modulatory potential on the oxidative stress pathways and apoptotic/inflammatory mediators, resulting in anticancer effects. Edible flowers are promising sources of phytochemicals (e.g., phenolic compounds, carotenoids, terpenoids) with several therapeutic effects. They possess anti-inflammatory, anti-diabetic, anti-microbial, anti-depressant, anxiolytic, anti-obesity, cardioprotective, and neuroprotective effects. Edible flowers potentially modulate oxidative stress by targeting erythroid nuclear transcription factor-2/extracellular signal-regulated kinase/mitogen-activated protein kinase (Nrf2/ERK/MAPK), reactive oxygen species (ROS), nitric oxide (NO), malondialdehyde (MDA) and antioxidant response elements (AREs). As the interconnected pathways to oxidative stress, inflammatory mediators, including tumor necrosis factor (TNF)-α, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), interleukins (ILs) as well as apoptotic pathways such as Bcl-2-associated X protein (Bax), Bcl-2, caspase and cytochrome C are critical targets of edible flowers in combating cancer. In this regard, edible flowers could play promising anticancer effects by targeting oxidative stress and downstream dysregulated pathways.

In vitro Anticancer Effects of JI017 on Two Prostate Cancer Cell Lines Involve Endoplasmic Reticulum Stress Mediated by Elevated Levels of Reactive Oxygen Species

Prostate cancer is the second most commonly diagnosed cancer, and prostate cancer is the second most common cause of cancer death in United States men after lung cancer. Many therapies are used to treat prostate cancer, and chemotherapy is one of the most relevant treatments. However, chemotherapy has many side effects, and repeated administration of chemotherapeutic agents leads to acquired resistance. Thus, new drugs with few side effects are needed. We investigated the molecular mechanism of action of JI017 in human prostate cancer cells. We identified an endoplasmic reticulum (ER) stress pathway that depended on the reactive oxygen species (ROS) pathway and played a crucial role in JI017-induced apoptosis. We measured cell viability by the MTS assay to determine the effect of JI017. Analysis of apoptosis, mitochondrial dysfunction, and cell cycle features was performed by flow cytometry. We used western blot and RT-PCR to measure the levels of the proteins of the unfolded protein response (UPR) pathway and apoptosis markers. Immunoprecipitation assay and transfection were used to determine the expression levels of proteins interacting with the pathways influenced by JI017 in prostate cancer cells. The anticancer effects induced by JI017 were evaluated. JI017 induced cell death that regulated apoptotic molecules and caused cell cycle arrest that inhibited the proliferation of cancer cells. Moreover, JI017 generated ROS. Accumulation of ROS caused ER stress through the PERK-eIF2α-CHOP and IRE1α-CHOP pathways. Furthermore, persistent activation of the UPR pathway induced by JI017 treatment triggered mitochondrial dysfunction, including dissipation of mitochondrial membrane potential, which activated intrinsic apoptotic pathway in human prostate cancer cells. The data indicated that N-acetyl-L-cysteine diminished apoptosis. We demonstrated that JI017 induced ER stress and cell death. Anticancer properties of JI017 in prostate cancer cells and in a human prostate cancer model involved ROS-mediated ER stress. Thus, JI017 treatment provides a new strategy for chemotherapy of prostate cancer.

Intracellular Ca2 + Imbalance Critically Contributes to Paraptosis

Paraptosis is a type of programmed cell death that is characterized by dilation of the endoplasmic reticulum (ER) and/or mitochondria. Since paraptosis is morphologically and biochemically different from apoptosis, understanding its regulatory mechanisms may provide a novel therapeutic strategy in malignant cancer cells that have proven resistant to conventional pro-apoptotic treatments. Relatively little is known about the molecular basis of paraptosis, but perturbations of cellular proteostasis and ion homeostasis appear to critically contribute to the process. Ca²⁺ transport has been shown to be important in the paraptosis induced by several natural products, metal complexes, and co-treatment with proteasome inhibitors and certain Ca²⁺-modulating agents. In particular, the Ca²⁺-mediated communication between the ER and mitochondria plays a crucial role in paraptosis. Mitochondrial Ca²⁺ overload from the intracellular Ca²⁺-flux system located at the ER–mitochondrial axis can induce mitochondrial dilation during paraptosis, while the accumulation of misfolded proteins within the ER lumen is believed to exert an osmotic force and draw water from the cytoplasm to distend the ER lumen. In this process, Ca²⁺ release from the ER also critically contributes to aggravating ER stress and ER dilation. This review focuses on the role of Ca²⁺ transport in paraptosis by summarizing the recent findings related to the actions of Ca²⁺-modulating paraptosis-inducing agents and discussing the potential cancer therapeutic strategies that may effectively induce paraptosis via Ca²⁺ signaling.

Proteasomal dysfunction and ER stress triggers 2'-hydroxy-retrochalcone-induced paraptosis in cancer cells

Chalcones are biologically active class of compounds, known for their anticancer activities. Here we show for the first time that out of the six synthetic derivatives of chalcone tested, 2'-hydroxy-retrochalcone (HRC) was the most effective in inducing extensive cytoplasmic vacuolation mediated death called paraptosis in malignant breast and cervical cancer cells. The cell death by HRC is found to be nonapoptotic in nature due to the absence of DNA fragmentation, PARP cleavage, and phosphatidylserine externalization. It was also found to be nonautophagic as there was an increase in the levels of autophagic markers LC3I, LC3II and p62. Immunofluorescence with the endoplasmic reticulum (ER) marker protein calreticulin showed that the cytoplasmic vacuoles formed were derived from the ER. This ER dilation was due to ER stress as evidenced from the increase in polyubiquitinated proteins, Bip and CHOP. Docking studies revealed that HRC could bind to the Thr1 residue on the active site of the chymotrypsin-like subunit of the proteasome. The inhibition of proteasomal activity was further confirmed by the fluorescence based assay of the chymotrypsin-like subunit of the 26S proteasome. The cell death by HRC was also triggered by the collapse of mitochondrial membrane potential and depletion of ATP. Pretreatment with thiol antioxidants and cycloheximide were able to inhibit this programmed cell death. Thus our data suggest that HRC can effectively kill cancer cells via paraptosis, an alternative death pathway and can be a potential lead molecule for anticancer therapy.