Camalexin-induced apoptosis in prostate cancer cells involves alterations of expression and activity of lysosomal protease cathepsin D

Combined effects of two phytoalexins, brassinin and camalexin, on the cells of colorectal origin

Brassinin and camalexin belong to phytoalexins, plant compounds generated in the response to stress. Both compounds are known to be cytotoxic to several cancer cell lines, mainly by inducing oxidative stress and subsequent apoptosis. In the presented study, cytotoxic effects of brassinin and camalexin, individually and, for the first time, after combined exposure, on the cells of normal (CCD-Co18) and cancer (Caco-2) lines originated from colorectal tissues and their proapoptotic impact on Caco-2 cells were studied. The determined IC50 values indicate a clearly higher sensitivity of cancer cells to the tested substances, as well as a stronger cytotoxic effect of camalexin than brassinin. The synergistic effect of both phytoalexins was also demonstrated. Caspase-dependent and independent mechanisms were involved in the final effects. Both tested phytoalexins caused evident, concentration-dependent symptoms of oxidative stress in cancer cells, leading to apoptosis, but in the highest concentrations, also to necrosis. In case of camalexin, signs of pyroptosis were additionally detected.

Larrea tridentata Extract Mitigates Oxidative Stress-Induced Cytotoxicity in Human Neuroblastoma SH-SY5Y Cells

Creosote bush (Larrea tridentata; LT) leaves extracts were tested for their potential efficacy to mitigate cellular oxidative stress on human SH-SY5Y cells. Here, the differential nuclear staining assay, a bioimager system, and flow cytometric protocols, concurrently with several specific chemicals, were used to measure the percentage of cell viability and several facets implicated in the cytoprotective mechanism of LT extracts. Initially, three LT extracts, prepared with different solvents, ethanol, ethanol:water (e/w), and water, were tested for their capacity to rescue the viability of cells undergoing aggressive H₂O₂-induced oxidative stress. Results indicate that the LT extract prepared with a mixture of ethanol:water (LT-e/w; 60:40% v/v) displayed the most effective cytoprotection rescue activity. Interestingly, by investigating the LT-e/w mechanism of action, it was found that LT-e/w extract decreases the levels of H₂O₂-provoked reactive oxidative species (ROS) accumulation, mitochondrial depolarization, phosphatidylserine externalization, caspase-3/7 activation, and poly (ADP-ribose) polymerase (PARP) cleavage significantly, which are hallmarks of apoptosis. Thus, out of the three LT extracts tested, our findings highlight that the LT-e/w extract was the most effective protective reagent on SH-SY5Y cells undergoing oxidative stress in vitro, functioning as a natural anti-apoptotic extract. These findings warrant further LT-e/w extract examination in a holistic context.

Human Cytomegalovirus Protein pUL38 Prevents Premature Cell Death by Binding to Ubiquitin-Specific Protease 24 and Regulating Iron Metabolism

Human cytomegalovirus (HCMV) protein pUL38 has been shown to prevent premature cell death by antagonizing cellular stress responses; however, the underlying mechanism remains unknown. In this study, we identified the host protein ubiquitin-specific protease 24 (USP24) as an interaction partner of pUL38. Mutagenesis analysis of pUL38 revealed that amino acids TFV at positions 227 to 230 were critical for its interaction with USP24. Mutant pUL38 TFV/AAA protein did not bind to USP24 and failed to prevent cell death induced by pUL38-deficient HCMV infection. Knockdown of USP24 suppressed the cell death during pUL38-deficient HCMV infection, suggesting that pUL38 achieved its function by antagonizing the function of USP24. We investigated the cellular pathways regulated by USP24 that might be involved in the cell death phenotype by testing several small-molecule compounds known to have a protective effect during stress-induced cell death. The iron chelators ciclopirox olamine and Tiron specifically protected cells from pUL38-deficient HCMV infection-induced cell death, thus identifying deregulated iron homeostasis as a potential mechanism. Protein levels of nuclear receptor coactivator 4 (NCOA4) and lysosomal ferritin degradation, a process called ferritinophagy, were also regulated by pUL38 and USP24 during HCMV infection. Knockdown of USP24 decreased NCOA4 protein stability and ferritin heavy chain degradation in lysosomes. Blockage of ferritinophagy by genetic inhibition of NCOA4 or Atg5/Atg7 prevented pUL38-deficient HCMV infection-induced cell death. Overall, these results support the hypothesis that pUL38 binds to USP24 to reduce ferritinophagy, which may then protect cells from lysosome dysfunction-induced cell death.IMPORTANCE Premature cell death is considered a first line of defense against various pathogens. Human cytomegalovirus (HCMV) is a slow-replicating virus that encodes several cell death inhibitors, such as pUL36 and pUL37x1, which allow it to overcome both extrinsic and intrinsic mitochondrion-mediated apoptosis. We previously identified HCMV protein pUL38 as another virus-encoded cell death inhibitor. In this study, we demonstrated that pUL38 achieved its activity by interacting with and antagonizing the function of the host protein ubiquitin-specific protease 24 (USP24). pUL38 blocked USP24-mediated ferritin degradation in lysosomes, which could otherwise be detrimental to the lysosome and initiate cell death. These novel findings suggest that iron metabolism is finely tuned during HCMV infection to avoid cellular toxicity. The results also provide a solid basis for further investigations of the role of USP24 in regulating iron metabolism during infection and other diseases.

Epistructured catechins, EGCG and EC facilitate apoptosis induction through targeting de novo lipogenesis pathway in HepG2 cells

Background

Abnormally high expression of the mammalian de novo lipogenesis (DNL) pathway in various cancer cells promotes cell over-proliferation and resistance to apoptosis. Inhibition of key enzymes in the DNL pathway, namely, ATP citrate lyase, acetyl-CoA carboxylase, and fatty acid synthase (FASN) can increase apoptosis without cytotoxicity to non-cancerous cells, leading to the search for and presentation of novel selective and powerful targets for cancer therapy. Previous studies reported that epistructured catechins, epigallocatechin gallate (EGCG) and epicatechin (EC) exhibit different mechanisms regarding a strong inducer of apoptosis in various cancer cell lines. Thus, the current study investigated the growth inhibitory effect of EGCG and EC, on the enzyme expression and activity of the DNL pathway, which leads to the prominent activity of carnitine palmitoyl transferase-1 (CPT-1) mediating apoptosis in HepG2 cells.

Methods

The cytotoxicity on HepG2 cells of EGCG and EC was determined by MTT assay. Cell death caused by apoptosis, the dissipation of mitochondrial membrane potential (MMP), and cell cycle arrest were then detected by flow cytometry. We further investigated the decrease of fatty acid levels associated with DNL retardation, followed by evaluation of DNL protein expression. Then, the negative inhibitory effect of depleted fatty acid synthesis on malonyl-CoA synthesis followed by regulating of CPT-1 activity was investigated. Thereafter, we inspected the enhanced reactive oxygen species (ROS) generation, which is recognized as one of the causes of apoptosis in HepG2 cells.

Results

We found that EGCG and EC decreased cancer cell viability by increasing apoptosis as well as causing cell cycle arrest in HepG2 cells. Apoptosis was associated with MMP dissipation. Herein, EGCG and EC inhibited the expression of FASN enzymes contributing to decreasing fatty acid levels. Notably, this decrease consequently showed a suppressing effect on the CPT-1 activity. We suggest that epistructured catechin-induced apoptosis targets CPT-1 activity suppression mediated through diminishing the DNL pathway in HepG2 cells. In addition, increased ROS production was found after treatment with EGCG and EC, indicating oxidative stress mechanism-induced apoptosis. The strong apoptotic effect of EGCG and EC was specifically absent in primary human hepatocytes.

Conclusion

Our supportive evidence confirms potential alternative cancer treatments by EGCG and EC that selectively target the DNL pathway.

Cathepsin D protects renal tubular cells from damage induced by high glucose independent of its enzymatic activity

Although glomerular and vascular damage have been considered the main characteristics of diabetic kidney disease (DKD), accumulating data now indicate that tubular atrophy also plays a major role. Cathepsin D (CatD) is the major aspartate protease within lysosomes. The current study demonstrated that CatD expression was altered in the renal tubular epithelium in patients with diabetes mellitus (DM). In contrast to its low and uniform distribution in the tubular epithelium in normal kidney tissues, CatD demonstrated flecked and increased expression in tubules with relatively integral structures, and disappeared in disordered tubules in DM kidney tissues. In vitro studies demonstrated that CatD protected HK2 cells from the damage induced by high glucose and advanced glycation end-products (AGEs), independent of its enzymatic activity. In addition, the current study demonstrated that AGEs induced lysosome membrane permeabilization (LMP) and loss of mitochondrial membrane potential (MMP). Overexpression of CatD prevented LMP and maintained the MMP in HK2 cells exposed to AGEs. In addition, the catalytic activity of CatD was not required for its role in LMP prevention and MMP maintenance. These results indicate, for the first time that CatD may improve the viability of renal tubular cells in the presence of diabetic mediators independent of its enzymatic activity by preventing LMP and stabilizing the MMP.

Camalexin-Induced Cell Membrane Scrambling and Cell Shrinkage in Human Erythrocytes

Background/Aims: The thaliana phytoalexin Camalexin has been proposed for the treatment of malignancy. Camalexin counteracts tumor growth in part by stimulation of suicidal death or apoptosis of tumor cells. Similar to apoptosis of nucleated cells, erythrocytes may enter suicidal death or eryptosis, which is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Cellular mechanisms contributing to the complex machinery executing eryptosis include increase of cytosolic Ca2+ activity ([Ca2+]i), oxidative stress, ceramide, protein kinase C and caspases. The present study explored, whether Camalexin induces eryptosis and, if so, to shed light on mechanisms involved. Methods: Phosphatidylserine exposure at the cell surface was estimated from annexin-V-binding, cell volume from forward scatter, [Ca2+]i from Fluo-3 fluorescence, ROS formation from DCFDA dependent fluorescence, and ceramide abundance utilizing specific antibodies. Results: A 48 hours exposure of human erythrocytes to Camalexin significantly increased the percentage of annexin-V-binding cells (≥ 10 µg/ml), significantly decreased forward scatter (≥ 5 µg/ml) and significantly increased Fluo-3-fluorescence (≥ 10 µg/ml), but did not significantly modify DCFDA fluorescence or ceramide abundance. The effect of Camalexin on annexin-V-binding was significantly blunted by removal of extracellular Ca2+, by kinase inhibitors staurosporine (1 µM) and chelerythrine (10 µM), as well as by caspase inhibitors zVAD (10 µM) and zIETD-fmk (50 µM). Conclusions: Camalexin triggers cell shrinkage and phospholipid scrambling of the erythrocyte cell membrane, an effect at least in part depending on Ca2+ entry, as well as staurosporine and chelerythrine sensitive kinase(s) as well as zVAD and zIETD-fmk sensitive caspase(s).

Antiproliferative Effect of Indole Phytoalexins

Indole phytoalexins from crucifers have been shown to exhibit significant anti-cancer, chemopreventive, and antiproliferative activity. Phytoalexins are natural low molecular antimicrobial compounds that are synthesized and accumulated in plants after their exposure to pathogenic microorganisms. Most interestingly, crucifers appear to be the only plant family producing sulfur-containing indole phytoalexins. The mechanisms underlying its anti-cancer properties are unknown. Isolation from cruciferous plants does not provide sufficient quantities of indole phytoalexins and, for biological screening, they are usually obtainable through synthesis. Understanding the molecular mechanism of the action of these substances and their structure-activity relationships is quite important in the development of new analogs with a more favorable profile of biological activities. In this review, we present the key features of indole phytoalexins, mainly their antiproliferative ativities.

A ROS-mediated lysosomal-mitochondrial pathway is induced by ginsenoside Rh2 in hepatoma HepG2 cells

Ginsenoside Rh2 (GRh2), isolated from Panax ginseng C. A. Meyer, has been proven as an anticancer compound both in vitro and in vivo. In the present study, we investigated the role of the lysosomes during the apoptosis of HepG2 cells induced by GRh2. The results showed that GRh2 significantly induced intracellular reactive oxygen species (ROS) generation in the HepG2 cells, which consequently resulted in early lysosomal membrane permeabilization with the release of cathepsin B (Cat B) to the cytosol. Western blot analysis showed that the released Cat B in the cytosol contributed to Bid cleavage. Subsequently mitochondrial damage was observed in the HepG2 cells. Interestingly, when the HepG2 cells were pre-treated with N-Acetyl-L-Cysteine (NAC) for 1 h, which inhibited ROS generation before being exposed to GRh2, the permeabilization of lysosomal membranes and the levels of Cat B in the cytosol were down-regulated. Moreover, mitochondrial damage was alleviated when the HepG2 cells were pre-treated with leupeptin (Leu). From the above results, it could be concluded that GRh2 induced apoptosis of the HepG2 cells through accumulation of ROS and activation of the lysosomal-mitochondrial apoptotic pathway involving the release of Cat B.

Anticancer effect of deoxypodophyllotoxin induces apoptosis of human prostate cancer cells

Deoxypodophyllotoxin (DPPT) is extracted and separated from citrus-related plants, including Podophyllum (P.) peltatum, P. pleianthum, P. emodi (also called P. hexandrum) and Diphylleia grayi. DPPT has significant antitumor and antiviral activity. However, due to its strong toxicity and side effects, its use is limited in practical applications. The in vitro antitumor efficacy of DPPT on human prostate cancer (PCa) cells remains to be determined. The present study investigated the anticancer effect of DPPT on human PCa cells and its potential mechanism. The data revealed that DPPT markedly reduced cell proliferation and activated the caspase-3 expression level by an increase in apoptotic cell death in DU-145 cells. In addition, treatment with DPPT markedly downregulated the levels of phosphorylated Akt and activated the p53/B-cell lymphoma 2 associated X protein (Bax)/phosphatase and tensin homolog (PTEN) signaling pathway in DU-145 cells, suggesting that caspase-mediated pathways were involved in DPPT-induced apoptosis. The present study suggested the role of DPPT as a novel chemotherapeutic drug for human PCa, which may function through the Akt/p53/Bax/PTEN signaling pathway.

Deciphering the role of phytoalexins in plant-microorganism interactions and human health

Phytoalexins are low molecular weight antimicrobial compounds that are produced by plants as a response to biotic and abiotic stresses. As such they take part in an intricate defense system which enables plants to control invading microorganisms. In this review we present the key features of this diverse group of molecules, namely their chemical structures, biosynthesis, regulatory mechanisms, biological activities, metabolism and molecular engineering.

The selective target of capsaicin on FASN expression and de novo fatty acid synthesis mediated through ROS generation triggers apoptosis in HepG2 cells

The inhibition of the mammalian de novo synthesis of long-chain saturated fatty acids (LCFAs) by blocking the fatty acid synthase (FASN) enzyme activity in tumor cells that overexpress FASN can promote apoptosis, without apparent cytotoxic to non-tumor cells. The present study aimed to focus on the potent inhibitory effect of capsaicin on the fatty acid synthesis pathway inducing apoptosis of capsaicin in HepG2 cells. The use of capsaicin as a source for a new FASN inhibitor will provide new insight into its possible application as a selective anti-cancer therapy. The present findings showed that capsaicin promoted apoptosis as well as cell cycle arrest in the G0/G1 phase. The onset of apoptosis was correlated with a dissipation of mitochondrial membrane potential (ΔΨm). Apoptotic induction by capsaicin was mediated by inhibition of FASN protein expression which was accompanied by decreasing its activity on the de novo fatty acid synthesis. The expression of FASN was higher in HepG2 cells than in normal hepatocytes that were resistant to undergoing apoptosis following capsaicin administration. Moreover, the inhibitory effect of capsaicin on FASN expression and activity was found to be mediated by an increase of intracellular reactive oxygen species (ROS) generation. Treatment of HepG2 cells with capsaicin failed to alter ACC and ACLY protein expression, suggesting ACC and ACLY might not be the specific targets of capsaicin to induce apoptosis. An accumulation of malonyl-CoA level following FASN inhibition represented a major cause of mitochondrial-dependent apoptotic induction instead of deprivation of fatty acid per se. Here, we also obtained similar results with C75 that exhibited apoptosis induction by reducing the levels of fatty acid without any change in the abundance of FASN expression along with increasing ROS production. Collectively, our results provide novel evidence that capsaicin exhibits a potent anti-cancer property by targeting FASN protein in HepG2 cells.

ROS-dependent antiproliferative effect of brassinin derivative homobrassinin in human colorectal cancer Caco2 cells

This study was designed to examine the in vitro antiproliferative effect of brassinin and its derivatives on human cancer cell lines. Among seven tested compounds, homobrassinin (K1; N-[2-(indol-3-yl)ethyl]-S-methyldithiocarbamate) exhibited the most potent activity with IC₅₀ = 8.0 μM in human colorectal Caco2 cells and was selected for further studies. The flow cytometric analysis revealed a K1-induced increase in the G₂/M phase associated with dysregulation of α-tubulin, α₁-tubulin and β₅-tubulin expression. These findings suggest that the inhibitory effect of K1 can be mediated via inhibition of microtubule formation. Furthermore, simultaneously with G₂/M arrest, K1 also increased population of cells with sub-G₁ DNA content which is considered to be a marker of apoptotic cell death. Apoptosis was also confirmed by annexin V/PI double staining, DNA fragmentation assay and chromatin condensation assay. The apoptosis was associated with the loss of mitochondrial membrane potential (MMP), caspase-3 activation as well as intracellular reactive oxygen species (ROS) production. Moreover, the antioxidant Trolox blocked ROS production, changes in MMP and decreased K1 cytotoxicity, which confirmed the important role of ROS in cell apoptosis. Taken together, our data demonstrate that K1 induces ROS-dependent apoptosis in Caco2 cells and provide the rationale for further in vivo anticancer investigation.