PKC and MEK pathways inhibit caspase-9/-3-mediated cytotoxicity in differentiated cells

Modulation of Dendritic Cell Apoptosis and CD8+ Cytotoxicity by Histamine: Role of Protein Kinase C

Dendritic cells (DC) are able to present extracellular antigens associated with the molecules of the major histocompatibility complex class I. In a previous work, we demonstrated that the histamine (HIS), acting through H1/H4 receptors, increases the cross-presentation of soluble ovalbumin by murine DC and can enhance the recruitment of specific CD8⁺ T lymphocytes during the development of chronic inflammatory responses. Here, we studied in more depth the mechanisms underlying this enhancement. We showed that the cytotoxicity of specific CD8⁺ lymphocytes is increased in HIS-treated DC and it is lost by inhibition of vacuolar-ATPase that prevents endosome acidification. It is known that HIS acts through G protein-coupled receptors. The H1/H4 receptors are associated with a G_q subunit, which involves PKC signaling, a pathway related to the apoptotic process. Interestingly, we demonstrated for the first time that HIS prevents DC apoptosis induced by heat shock through the inhibition of caspase-3, a mechanism dependent on PKC activation, since it is reversed by its inhibition. By contrast, cytolytic activity of T lymphocytes induced by HIS-stimulated DC was independent of PKC pathway.

Ascorbic acid inhibits TPA-induced HL-60 cell differentiation by decreasing cellular H₂O₂ and ERK phosphorylation

Retinoic acid (RA), vitamin D and 12-O‑tetradecanoyl phorbol-13-acetate (TPA) can induce HL-60 cells to differentiate into granulocytes, monocytes and macrophages, respectively. Similar to RA and vitamin D, ascorbic acid also belongs to the vitamin family. High‑dose ascorbic acid (>100 µM) induces HL‑60 cell apoptosis and induces a small fraction of HL‑60 cells to express the granulocyte marker, CD66b. In addition, ascorbic acid exerts an anti‑oxidative stress function. Oxidative stress is required for HL‑60 cell differentiation following treatment with TPA, however, the effect of ascorbic acid on HL‑60 cell differentiation in combination with TPA treatment remains to be fully elucidated. The aim of the present study was to investigate the cellular effects of ascorbic acid treatment on TPA-differentiated HL-60 cells. TPA-differentiated HL-60 cells were used for this investigation, this study and the levels of cellular hydrogen peroxide (H2O2), caspase activity and ERK phosphorylation were determined following combined treatment with TPA and ascorbic acid. The results demonstrated that low‑dose ascorbic acid (5 µM) reduced the cellular levels of H2O2 and inhibited the differentiation of HL‑60 cells into macrophages following treatment with TPA. In addition, the results of the present study further demonstrated that low‑dose ascorbic acid inactivates the ERK phosphorylation pathway, which inhibited HL‑60 cell differentiation following treatment with TPA.

Acetaminophen induces JNK/p38 signaling and activates the caspase-9-3-dependent cell death pathway in human mesenchymal stem cells

Acetaminophen (APAP) is a widely used analgesic and antipyretic drug. Generally, the therapeutic dose of APAP is clinically safe, however, high doses of APAP can cause acute liver and kidney injury. Therefore, the majority of previous studies have focussed on elucidating the mechanisms of APAP-induced hepatotoxicity and nephrotoxicity, in addition to examining ways to treat these conditions in clinical cases. However, few studies have reported APAP-induced intoxication in human stem cells. Stem cells are important in cell proliferation, differentiation and repair during human development, particularly during fetal and child development. At present, whether APAP causes cytotoxic effects in human stem cells remains to be elucidated, therefore, the present study aimed to investigate the cellular effects of APAP treatment in human stem cells. The results of the present study revealed that high-dose APAP induced more marked cytotoxic effects in human mesenchymal stem cells (hMSCs) than in renal tubular cells. In addition, increased levels of hydrogen peroxide (H2O2), phosphorylation of c-Jun N-terminal kinase and p38, and activation of caspase-9/-3 cascade were observed in the APAP-treated hMSCs. By contrast, antioxidants, including vitamin C reduced APAP-induced augmentations in H2O2 levels, but did not inhibit the APAP-induced cytotoxic effects in the hMSCs. These results suggested that high doses of APAP may cause serious damage towards hMSCs.

Rana catesbeiana ribonuclease induces cell apoptosis via the caspase-9/-3 signaling pathway in human glioblastoma DBTRG, GBM8901 and GBM8401 cell lines

Human glioblastoma multiforme is one of the most aggressive malignant brain tumor types, and the mean survival time of patients with a brain tumor is <2 years when traditional therapies are administered. Thus, numerous studies have focused on the development of novel treatments for brain tumors. Frog ribonucleases, such as Onconase and Rana catesbeiana ribonuclease (RC-RNase), exert antitumor effects on various tumor cells, including cervical cancer, breast cancer, hepatoma, leukemia, pancreatic cancer and prostate cancer cells. In addition, frog Onconase has been applied as a treatment in clinical trials. However, the antitumor effects of frog ribonucleases on brain tumors are unclear. Previous studies have indicated that RC-RNase demonstrates a decreased cytotoxic effect in normal cells compared with Onconase. Therefore, the present study investigated the ability of RC-RNase to exert antitumor activities on human glioblastoma. It was found that RC-RNase inhibits the growth of the human glioblastoma DBTRG, GBM8901 and GBM8401 cells. In addition, the present study revealed that RC-RNase induces caspase-9/-3 activity and triggers the apoptotic cell death pathway in human glioblastoma cells. Notably, it was also demonstrated that RC-RNase effectively inhibits the growth of human glioblastoma tumors in a nude mouse model. Overall, the present study indicates that RC-RNase may be a potential agent for the treatment of human glioblastoma.

Vitamin C enhances anticancer activity in methotrexate‑treated Hep3B hepatocellular carcinoma cells

Methotrexate (MTX) has been widely used for rheumatoid arthritis therapy for a long time. MTX is also used as an anticancer drug for various tumors. However, many studies have shown that high-dose MTX treatment for cancer therapy may cause liver and renal damage. Alhough the mechanisms involved in MTX-induced liver and renal damage require further research, many studies have indicated that MTX-induced cytotoxicity is associated with increases in oxidative stress and caspase activation. In order to reduce MTX-induced side-effects and increase anticancer efficiency, currently, combination treatments of low-dose MTX and other anticancer drugs are considered and applied for various tumor treatments. The present study showed that MTX induces increases in H₂O₂ levels and caspase-9/-3 activation leading to cell death in hepatocellular carcinoma Hep3B cells. Importantly, this study is the first to demonstrate that vitamin C can efficiently aid low-dose MTX in inducing cell death in Hep3B cells. Therefore, the present study provides a possible powerful therapeutic method for tumors using a combined treatment of vitamin C and low-dose MTX.

Dual role of acetaminophen in promoting hepatoma cell apoptosis and kidney fibroblast proliferation

Acetaminophen (APAP), is a safe analgesic and antipyretic drug at therapeutic dose, and is widely used in the clinic. However, high doses of APAP can induce hepatotoxicity and nephrotoxicity. Most studies have focused on high‑dose APAP‑induced acute liver and kidney injury. So far, few studies have investigated the effects of the therapeutic dose (1/10 of the high dose) or of the low dose (1/100 of the high dose) of APAP on the cells. The aim of this study was to investigate the cellular effects of therapeutic- or low‑dose APAP treatment on hepatoma cells and kidney fibroblasts. As expected, high‑dose APAP treatment inhibited while therapeutic and low‑dose treatment did not inhibit cell survival of kidney tubular epithelial cells. In addition, therapeutic-dose treatment induced an increase in the H2O2 level, activated the caspase‑9/‑3 cascade, and induced cell apoptosis of hepatoma cells. Notably, APAP promoted fibroblast proliferation, even at low doses. This study demonstrates that different cellular effects are exerted upon treatment with different APAP concentrations. Our results indicate that treatment with the therapeutic dose of APAP may exert an antitumor activity on hepatoma, while low‑dose treatment may be harmful for patients with fibrosis, since it may cause proliferation of fibroblasts.

RC-6 ribonuclease induces caspase activation, cellular senescence and neuron-like morphology in NT2 embryonal carcinoma cells

Frog ribonucleases have been demonstrated to have anticancer activities. However, whether RC-6 ribonuclease exerts anticancer activity on human embryonal carcinoma cells remains unclear. In the present study, RC-6 induced cytotoxicity in NT2 cells (a human embryonal carcinoma cell line) and our studies showed that RC-6 can exert anticancer effects and induce caspase-9 and -3 activities. Moreover, to date, there is no evidence that frog ribonuclease-induced cytotoxicity effects are related to cellular senescence. Therefore, our studies showed that RC-6 can increase p16 and p21 protein levels and induce cellular senescence in NT2 cells. Notably, similar to retinoic acid-differentiated NT2 cells, neuron-like morphology was found on some remaining live cells after RC-6 treatment. In conclusion, our study is the first to demonstrate that RC-6 can induce cytotoxic effects, caspase-9/-3 activities, cellular senescence and neuron-like morphology in NT2 cells.

Protein kinase C protects from DNA damage-induced necrotic cell death by inhibiting poly(ADP-ribose) polymerase-1

The goal of the current study, conducted in freshly isolated thymocytes was (1) to investigate the possibility that the activation of poly(ADP-ribose) polymerase-1 (PARP-1) in an intact cell can be regulated by protein kinase C (PKC) mediated phosphorylation and (2) to examine the consequence of this regulatory mechanism in the context of cell death induced by the genotoxic agent. In cells stimulated by the PKC activating phorbol esters, DNA breakage was unaffected, PARP-1 was phosphorylated, 1-methyl-3-nitro-1-nitrosoguanidine-induced PARP activation and cell necrosis were suppressed, with all these effects attenuated by the PKC inhibitors GF109203X or Gö6976. Inhibition of cellular PARP activity by PKC-mediated phosphorylation may provide a plausible mechanism for the previously observed cytoprotective effects of PKC activators.