Apaf-1- and Caspase-8-independent apoptosis

Paradoxical Roles of Leucine-Rich α2-Glycoprotein-1 in Cell Death and Survival Modulated by Transforming Growth Factor-Beta 1 and Cytochrome c

Leucine-rich α₂-glycoprotein-1 (LRG1) has been shown to impact both apoptosis and cell survival, pleiotropic effects similar to one of its known ligands, transforming growth factor-beta 1 (TGF-β1). Recent studies have given insight into the TGF-β1 signaling pathways involved in LRG1-mediated death versus survival signaling, i.e., canonical or non-canonical. Interaction of LRG1 with another ligand, extracellular cytochrome c (Cyt c), promotes cell survival, at least for lymphocytes. LRG1 has been shown to bind Cyt c with high affinity, higher than it binds TGF-β1, making it sensitive to small changes in the level of extracellular Cyt c within a microenvironment that may arise from cell death. Evidence is presented here that LRG1 can bind TGF-β1 and Cyt c simultaneously, raising the possibility that the ternary complex may present a signaling module with the net effect of signaling, cell death versus survival, determined by the relative extent to which the LRG1 binding sites are occupied by these two ligands. A possible role for LRG1 should be considered in studies where extracellular effects of TGF-β1 and Cyt c have been observed in media supplemented with LRG1-containing serum.

Gasdermins mediate cellular release of mitochondrial DNA during pyroptosis and apoptosis

Pyroptosis and intrinsic apoptosis are two forms of regulated cell death driven by active caspases where plasma membrane permeabilization is induced by gasdermin pores. Caspase-1 induces gasdermin D pore formation during pyroptosis, whereas caspase-3 promotes gasdermin E pore formation during apoptosis. These two types of cell death are accompanied by mitochondrial outer membrane permeabilization due to BAK/BAX pore formation in the external membrane of mitochondria, and to some extent, this complex also affects the inner mitochondrial membrane facilitating mitochondrial DNA relocalization from the matrix to the cytosol. However, the detailed mechanism responsible for this process has not been investigated. Herein, we reported that gasdermin processing is required to induce mitochondrial DNA release from cells during pyroptosis and apoptosis. Gasdermin targeted at the plasma membrane promotes a fast mitochondrial collapse along with the initial accumulation of mitochondrial DNA in the cytosol and then facilitates the DNA's release from the cell when the plasma membrane ruptures. These findings demonstrate that gasdermin action has a critical effect on the plasma membrane and facilitates the release of mitochondrial DNA as a damage-associated molecular pattern.

Raddeanin A Induces Apoptosis and Cycle Arrest in Human HCT116 Cells through PI3K/AKT Pathway Regulation In Vitro and In Vivo

This study aimed to investigate the in vitro and in vivo effects of Raddeanin A on apoptosis and the cell cycle in the human colorectal cell line, HCT116, and to explore the possible underlying mechanisms of action. We found the growth inhibition rate gradually increased as the drug concentration increased via the 3-(4,5)-dimethylthiahiazo(-z-y1)-3,5-di-phenytetrazoliumromide (MTT) assay, which indicated that Raddeanin A significantly inhibited the growth of HCT116 cells. Flow cytometry (FCM) showed that Raddeanin A concentration-dependently induced apoptosis in HCT116 cells. In addition, the percentage of cells in the G₀/G₁ phase was noticeably increased, which indicated that Raddeanin A blocked cell cycle progression in HCT116 cells and caused arrest in the G₀/G₁ phase. Moreover, the expression of proteins involved in the PI3K/AKT signaling pathway (e.g., p-PI3K and p-AKT) was decreased. The results showed that in vivo revealed that Raddeanin A significantly inhibited tumor growth in an HCT116-xenografted mouse model; apoptotic cells were also detected in the tumor tissue. The expression of the tissue proteins cyclinD1, cyclinE, p-PI3K, and p-AKT was decreased. The above results show that the Raddeanin A exerted a strong antitumor effect in the human colorectal cell line HCT116 both in vitro and in vivo. This effect may be caused by the induction of apoptosis and cycle arrest achieved through PI3K/AKT signaling pathway regulation.

Novel histone deacetylase 8-selective inhibitor 1,3,4-oxadiazole-alanine hybrid induces apoptosis in breast cancer cells

Identification of isoform-specific histone deacetylase inhibitors (HDACi) is a significant advantage to overcome the adverse side effects of pan-HDACi for the treatment of various diseases, including cancer. We have designed, and synthesized novel 1,3,4 oxadiazole with glycine/alanine hybrids as HDAC8-specific inhibitors and preliminary evaluation has indicated that 1,3,4 oxadiazole with alanine hybrid [(R)-2-amino-N-((5-phenyl-1,3,4-oxadiazol-2-yl)methyl)propanamide (10b)] to be a potent HDAC8 inhibitor. In the present study, the in vitro efficacy of the molecule in inhibiting the cancer cell proliferation and the underlying molecular mechanism was studied. 10b inhibited the growth of MDA-MB-231 and MCF7 breast cancer cells, with a lower IC₅₀ of 230 and 1000 nM, respectively, compared to K562, COLO-205 and HepG2 cells and was not cytotoxic to normal breast epithelial cells, MCF10A. 10b was specific to HDAC8 and did not affect the expression of other class I HDACs. Further, a dose-dependent increase in H3K9 acetylation levels demonstrated the HDAC-inhibitory activity of 10b in MDA-MB-231 cells. Flow cytometric analysis indicated a dose-dependent increase and decrease in the percent apoptotic cells and mitochondrial membrane potential, respectively, when treated with 10b. Immunoblot analysis showed a modulation of Bax/Bcl2 ratio with a decrease in Bcl2 expression and no change in Bax expression. 10b treatment resulted in induction of p21 and inhibition of CDK1 proteins along with cytochrome c release from mitochondria, activation of caspases-3 and -9 and cleavage of poly ADP-ribose polymerase leading to apoptotic death of MDA-MB-231 and MCF7 cells. In conclusion, our results clearly demonstrated the efficacy of 10b as an anticancer agent against breast cancer.

Phloretin induces apoptosis of human esophageal cancer via a mitochondria-dependent pathway

2,4,6-trihydroxy-3-(4-hydroxyphenyl)-propiophenone (phloretin) is found in apple tree leaves and the Manchurian apricot, and is a potent compound that exhibits anti-inflammatory, antioxidant and antitumor activities. However, the effect of phloretin on esophageal cancer cells is not well-defined. The present study aimed to examine whether and how phloretin induced apoptosis in human esophageal cancer cells. EC-109 cells were cultured in Dulbecco's modified Eagle's medium and incubated with 60, 70, 80, 90 and 100 µg/ml phloretin for 6, 12, 24 and 48 h. Cell proliferation was measured by an MTT assay. Cell apoptosis rate was measured using flow cytometric analysis subsequent to propidium iodide (PI) staining. The protein expression levels were determined by western blot analysis. It was found that phloretin significantly decreased viable cell numbers in a dose- and time-dependent manner and induced apoptosis in EC-109 cells. Additionally, phloretin exhibited potent anticancer activity in vitro, as evidenced by the downregulation of the anti-apoptosis-associated molecule B-cell lymphoma 2 (bcl-2) and an increase in the levels of the apoptosis-associated molecules bcl-2-like protein 4 and tumor protein p53. Phloretin treatment also affected the expression of apoptotic protease activating factor-1, the protein product of the direct binding of the inhibitor of apoptosis protein with low PI to the X-linked inhibitor of apoptosis protein. The present results indicated that phloretin may inhibit EC-109 cell growth by inducing apoptosis, which may be mediated through a mitochondria-dependent pathway.

Apaf-1: Regulation and function in cell death

Apoptosis, a form of programmed cell death, is responsible for eliminating damaged or unnecessary cells in multicellular organisms. Various types of intracellular stress trigger apoptosis by induction of cytochrome c release from mitochondria into the cytosol. Apoptotic protease activating factor-1 (Apaf-1) is a key molecule in the intrinsic or mitochondrial pathway of apoptosis, which oligomerizes in response to cytochrome c release and forms a large complex known as apoptosome. Procaspase-9, an initiator caspase in the mitochondrial pathway, is recruited and activated by the apoptosome leading to downstream caspase-3 processing. Various cellular proteins and small molecules can modulate apoptosome formation and function directly or indirectly. Despite recent progress in understanding the mitochondrial pathway of apoptosis, numerous questions such as the molecular mechanism of Apaf-1 oligomerization and caspase-9 activation remain poorly understood. In addition, reports have emerged showing non-apoptotic functions for Apaf-1. The current review summarizes the latest findings regarding structure-function relationship of Apaf-1 as well as its modifiers.

Maternal-engineered nanomaterial exposure disrupts progeny cardiac function and bioenergetics

Nanomaterial production is expanding as new industrial and consumer applications are introduced. Nevertheless, the impacts of exposure to these compounds are not fully realized. The present study was designed to determine whether gestational nano-sized titanium dioxide exposure impacts cardiac and metabolic function of developing progeny. Pregnant Sprague-Dawley rats were exposed to nano-aerosols (~10 mg/m³, 130- to 150-nm count median aerodynamic diameter) for 7-8 nonconsecutive days, beginning at gestational day 5-6 Physiological and bioenergetic effects on heart function and cardiomyocytes across three time points, fetal (gestational day 20), neonatal (4-10 days), and young adult (6-12 wk), were evaluated. Functional analysis utilizing echocardiography, speckle-tracking based strain, and cardiomyocyte contractility, coupled with mitochondrial energetics, revealed effects of nano-exposure. Maternal exposed progeny demonstrated a decrease in E- and A-wave velocities, with a 15% higher E-to-A ratio than controls. Myocytes isolated from exposed animals exhibited ~30% decrease in total contractility, departure velocity, and area of contraction. Bioenergetic analysis revealed a significant increase in proton leak across all ages, accompanied by decreases in metabolic function, including basal respiration, maximal respiration, and spare capacity. Finally, electron transport chain complex I and IV activities were negatively impacted in the exposed group, which may be linked to a metabolic shift. Molecular data suggest that an increase in fatty acid metabolism, uncoupling, and cellular stress proteins may be associated with functional deficits of the heart. In conclusion, gestational nano-exposure significantly impairs the functional capabilities of the heart through cardiomyocyte impairment, which is associated with mitochondrial dysfunction.NEW & NOTEWORTHY Cardiac function is evaluated, for the first time, in progeny following maternal nanomaterial inhalation. The findings indicate that exposure to nano-sized titanium dioxide (nano-TiO₂) during gestation negatively impacts cardiac function and mitochondrial respiration and bioenergetics. We conclude that maternal nano-TiO₂ inhalation contributes to adverse cardiovascular health effects, lasting into adulthood.

Peritoneal expression of Matrilysin helps identify early post-operative recurrence of colorectal cancer

Recurrence of colorectal cancer (CRC) following a potentially curative resection is a challenging clinical problem. Matrix metalloproteinase-7 (MMP-7) is over-expressed by CRC cells and supposed to play a major role in CRC cell diffusion and metastasis. MMP-7 RNA expression was assessed by real-time PCR using specific primers in peritoneal washing fluid obtained during surgical procedure. After surgery, patients underwent a regular follow up for assessing recurrence. transcripts for MMP-7 were detected in 31/57 samples (54%). Patients were followed-up (range 20-48 months) for recurrence prevention. Recurrence was diagnosed in 6 out of 55 patients (11%) and two patients eventually died because of this. Notably, all the six patients who had relapsed were positive for MMP-7. Sensitivity and specificity of the test were 100% and 49% respectively. Data from patients have also been corroborated by computational approaches. Public available coloncarcinoma datasets have been employed to confirm MMP7 clinical impact on the disease. Interestingly, MMP-7 expression appeared correlated to Tgfb-1, and correlation of the two factors represented a poor prognostic factor. This study proposes positivity of MMP-7 in peritoneal cavity as a novel biomarker for predicting disease recurrence in patients with CRC.

Apoptotic protease activating factor-1 and tumors

Apoptotic protease activating factor-1 (Apaf-1) functions as a core apoptosis factor in the mitochondrial apoptosis pathway. Apaf-1 promoter methylation and loss of heterozygosity are the main causes of cancer, and lower expression of Apaf-1 is closely related to malignant tumors. Apaf-1 expression deletion and methylation can be used as markers for deeper tumor invasion, frequent lymph node metastasis, tumor differentiation and poor prognosis. Apaf-1 can be used as a molecular target for anticancer therapy and prognosis prediction. Further research on Apaf-1 will contribute to the development of effective anti-tumor drugs. In this paper, we will review the biochemical structure and function of Apaf-1, Apaf-1 signal transduction pathway, expression of Apaf-1 in a variety of tumors, as well as its role in tumor occurrence, drug resistance and treatment.

Phospholipid scrambling on the plasma membrane

Phospholipids are asymmetrically distributed at plasma membrane in normal cells, and scrambled in various biological situations such as blood clotting and apoptotic cell death. Recent studies revealed that phospholipid scrambling is mediated by at least two independent mechanisms. An eight transmembrane-containing protein TMEM16F Ca(2+)-dependently promotes the phospholipid scrambling, which is required for the PS exposure in activated platelets during blood clotting. On the other hand, a six transmembrane-containing protein Xk-related family protein 8 is activated by caspases during apoptosis and promotes the phospholipid scrambling, thus exposing PS as an "eat-me-signal." In this chapter, we describe procedures for assaying phospholipid scrambling.

Induction of apoptosis in HCT-116 colon cancer cells by polysaccharide of Larimichthys crocea swim bladder

Larimichthys crocea swim bladder is a traditional food and medicine widely used in China. The in vitro anticancer effects of polysaccharide of L. crocea swim bladder (PLCSB) in HCT-116 human colon cancer cells was investigated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. At concentrations ranging between 0 and 800 μg/ml PLCSB, cancer cell viability was decreased by PLCSB in a concentration-dependent manner. In particular, 400 μg/ml PLCSB significantly (P<0.05) induced apoptosis, which was demonstrated by 4,6-diamidino-2-phenylindole staining and flow cytometry analysis. To elucidate the mechanisms underlying the anticancer effect of PLCSB in HCT-116 cancer cells, the expression of apoptosis and metastasis-associated genes was analyzed by reverse transcription-polymerase chain reaction and western blot analysis. A total of 400 μg/ml PLCSB significantly induced apoptosis in HCT-116 cells (P<0.05) via the upregulation Bax, p53, p21, apoptotic protease activating factor 1, caspase-3, -8, and -9, as well as Fas and the downregulation of B-cell lymphoma 2 (Bcl-2), Bcl-extra large and Fas ligand (L). The results of this study demonstrated that PLCSB exhibits an anticancer effect on HCT-116 colon cancer cells, in vitro.

Chemotherapeutic drugs induce ATP release via caspase-gated pannexin-1 channels and a caspase/pannexin-1-independent mechanism

Anti-tumor immune responses have been linked to the regulated release of ATP from apoptotic cancer cells to engage P2 purinergic receptor signaling cascades in nearby leukocytes. We used the Jurkat T cell acute lymphocytic leukemia model to characterize the role of pannexin-1 (Panx1) channels in the release of nucleotides during chemotherapeutic drug-induced apoptosis. Diverse pro-apoptotic drugs, including topoisomerase II inhibitors, kinase inhibitors, and proteosome inhibitors, induced functional activation of Panx1 channels via caspase-3-mediated cleavage of the Panx1 autoinhibitory C-terminal domain. The caspase-activated Panx1 channels mediated efflux of ATP, but also ADP and AMP, with the latter two comprising >90% of the released adenine nucleotide pool as cells transitioned from the early to late stages of apoptosis. Chemotherapeutic drugs also activated an alternative caspase- and Panx1-independent pathway for ATP release from Jurkat cells in the presence of benzyloxycarbonyl-VAD, a pan-caspase inhibitor. Comparison of Panx1 levels indicated much higher expression in leukemic T lymphocytes than in normal, untransformed T lymphoblasts. This suggests that signaling roles for Panx1 may be amplified in leukemic leukocytes. Together, these results identify chemotherapy-activated pannexin-1 channels and ATP release as possible mediators of paracrine interaction between dying tumor cells and the effector leukocytes that mediate immunogenic anti-tumor responses.

Antrodia camphorata induces G1 cell-cycle arrest in human premyelocytic leukemia (HL-60) cells and suppresses tumor growth in athymic nude mice

Antrodia camphorata is a well-known medicinal mushroom in Taiwan.

Overexpression of 4EBP1, p70S6K, Akt1 or Akt2 differentially promotes Coxsackievirus B3-induced apoptosis in HeLa cells

Our previous studies have shown that the inhibition of phosphatidylinositol 3-kinase (PI3K) or mTOR complex 1 can obviously promote the Coxsackievirus B3 (CVB3)-induced apoptosis of HeLa cells by regulating the expression of proapoptotic factors. To further illustrate it, Homo sapiens eIF4E-binding protein 1 (4EBP1), p70S6 kinase (p70S6K), Akt1 and Akt2 were transfected to HeLa cells, respectively. And then, we established the stable transfected cell lines. Next, after CVB3 infection, apoptosis in different groups was determined by flow cytometry; the expressions of Bim, Bax, caspase-9 and caspase-3 were examined by real-time fluorescence quantitative PCR and western blot analysis; the expression of CVB3 mRNA and viral capsid protein VP1 were also analyzed by real-time fluorescence quantitative PCR, western blot analysis and immunofluorescence, respectively. At the meantime, CVB3 replication was observed by transmission electron microscope. We found that CVB3-induced cytopathic effect and apoptosis in transfected groups were more obvious than that in controls. Unexpectedly, apoptosis rate in Akt1 group was higher than others at the early stage after viral infection and decreased with the viral-infected time increasing, which was opposite to other groups. Compared with controls, the expression of CVB3 mRNA was increased at 3, 6, 12 and 24 h postinfection (p. i.) in all groups. At the meantime, VP1 expression in 4EBP1 group was higher than control during the process of infection, while the expressions in the other groups were change dynamically. Moreover, overexpression of 4EBP1 did not affect the mRNA expressions of Bim, Bax, caspase-9 and caspase-3; while protein expressions of Bim and Bax were decreased, the self-cleavages of caspase-9 and caspase-3 were stimulated. Meanwhile, overexpression of p70S6K blocked the CVB3-induced Bim, Bax and caspase-9 expressions but promoted the self-cleavage of caspase-9. In the Akt1 group, it is noteworthy that the expressions of Bim protein were higher than controls at 3 and 6 h p. i. but lower at 24 h p. i., and the expression of Bax protein were higher at 6 and 24 h p. i., while their mRNA expressions were all decreased. Furthermore, overexpression of Akt1 stimulated the procaspase-9 and procaspase-3 expression but blocked their self-cleavages. Overexpression of Akt2, however, had little effect on Bim, Bax and caspase-3, while prevented caspase-9 from self-cleavage at the late stage of CVB3 infection. As stated above, our results demonstrated that overexpression of 4EBP1, p70S6K, Akt1 or Akt2 could promote the CVB3-induced apoptosis in diverse degree via different mediating ways in viral replication and proapoptotic factors in BcL-2 and caspase families. As 4EBP1, p70S6K and Akt are the important substrates of PI3K and mammalian target of rapamycin (mTOR), we further illustrated the role of PI3K/Akt/mTOR signaling pathway in the process of CVB3-induced apoptosis.

Both PI3K- and mTOR-signaling pathways take part in CVB3-induced apoptosis of Hela cells

This work illustrated the mechanism contributing to the process of Phosphatidylinostiol 3-kinase (PI3K)/protein kinase B (PKB)/mammalian target of rapamycin (mTOR) signaling pathway, which has been demonstrated to play an important role in virus-induced apoptosis, which contributes to the Viral Myocarditis (VMC) pathogeneses. We examined the expression of Bax, Bim, caspase-3, caspase-9, and viral replication after Coxsackievirus B3 (CVB3) infection using the mTOR inhibitor and PI3K inhibitor pretreated HeLa cells, respectively. Apoptosis in different groups was determined by flow cytometry. Bax, Bim, caspase-9, and caspase-3 were examined by semiquantitative polymerase chain reaction (PCR) and Western blot analysis. The expression of CVB3 mRNA and viral capsid protein VP1 were analyzed by semiquantitative PCR and Western blot analysis distinctively. We found that rapamycin and LY294002 promote CVB3-induced cytopathic effect (CPE) and apoptosis. CVB3 replication in host cells is mediated in mRNA and protein expression by rapamycin and LY294002. Moreover, comparing with controls, at 12 and 24 h of postinfection (p.i.), Bim and Bax expression increased in cells after treated with rapamycin or LY294002, which also stimulates the activation of procaspase-9, and the CVB3-induced caspase-3 self-cleavage. However, in the meantime, the mRNA expression of caspase-9 and caspase-3 did not have an obvious change. In summary, our results demonstrated that the mTOR-signaling pathway plays an important role in CVB3-induced CPE and apoptosis, which is indispensable in VMC, via regulating Bim, Bax, caspase-9, caspase-3, and viral replication. Our findings may provide a new perspective and a deeper understanding of the mechanism of CVB3-induced apoptosis which, in turn, may help with the development of new therapy for the CVB3 infection.

Calcium-dependent phospholipid scramblase activity of TMEM16 protein family members

BACKGROUND

TMEM16A and 16B work as Cl(-) channel, whereas 16F works as phospholipid scramblase. The function of other TMEM16 members is unknown.

RESULTS

Using TMEM16F(-/-) cells, TMEM16C, 16D, 16F, 16G, and 16J were shown to be lipid scramblases.

CONCLUSION

Some TMEM16 members are divided into two Cl(-) channels and five lipid scramblases.

SIGNIFICANCE

Learning the biochemical function ofTMEM16family members is essential to understand their physiological role. Asymmetrical distribution of phospholipids between the inner and outer plasma membrane leaflets is disrupted in various biological processes. We recently identified TMEM16F, an eight-transmembrane protein, as a Ca(2+)-dependent phospholipid scramblase that exposes phosphatidylserine (PS) to the cell surface. In this study, we established a mouse lymphocyte cell line with a floxed allele in the TMEM16F gene. When TMEM16F was deleted, these cells failed to expose PS in response to Ca(2+) ionophore, but PS exposure was elicited by Fas ligand treatment. We expressed other TMEM16 proteins in the TMEM16F(-/-) cells and found that not only TMEM16F, but also 16C, 16D, 16G, and 16J work as lipid scramblases with different preference to lipid substrates. On the other hand, a patch clamp analysis in 293T cells indicated that TMEM16A and 16B, but not other family members, acted as Ca(2+)-dependent Cl(-) channels. These results indicated that among 10 TMEM16 family members, 7 members could be divided into two subfamilies, Ca(2+)-dependent Cl(-) channels (16A and 16B) and Ca(2+)-dependent lipid scramblases (16C, 16D, 16F, 16G, and 16J).