Sensitization of human hepatic stellate cells to tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis by leflunomide

Endoplasmic reticulum stress-induced hepatic stellate cell apoptosis through calcium-mediated JNK/P38 MAPK and Calpain/Caspase-12 pathways

Recent reports considered that it was the disturbance of calcium homeostasis and the accumulation of misfolded proteins in the endoplasmic reticulum (ER) that activated hepatic stellate cells (HSCs) apoptosis and promoted fibrosis resolution. However, the signal-transducing events that are activated by ER stress after HSCs activation were incompletely understood. In this study, we induced ER stress with thapsigargin (TG), and determined the activation of calpain and the cleavage of caspase by analyzing the protein levels and the correspondingly increased intracellular calcium levels and the induction of the proapoptotic transcription factor CHOP. Moreover, the phosphorylation of JNK and p38 MAPK were followed by the activation of the executioner caspases, caspase-3. As expected, preventing an increase in intracellular calcium levels using intracellular calcium chelators, EGTA, and BAPTA/AM, could substantially inhibit the phosphorylation of JNK and p38 MAPK, abolish the activation of calpains, namely caspase-12, caspase-9, and caspase-3, and provide significant protection for TG-treated activated HSCs. Interestingly, pretreatment with p38 MAPK inhibitor SB202190, JNK inhibitor SP600125, the pan-caspase inhibitor z-VAD-FMK, or calpain inhibitors calpeptin, significantly reduced the cell apoptosis and the cleavage of caspase-12 and caspase-3. However, pretreatment with z-VAD-FMK failed to reduce the activation of calpain. Additionally, pretreatment with SB202190 and SP600125 also decreased the expression of CHOP. Importantly, PDGF-induced collagen Col1α1 and α-smooth muscle actin (α-SMA), markers for the perpetuation phase of HSCs activation, were inhibited in TG-treated activated HSCs. These findings showed that the Calpain/Caspase-12 activation induced by ER stress and the JNK/p38 MAPK phosphorylation induced by the increase of intracellular calcium concentration releasing from ER are the novel signaling pathway underlying the molecular mechanism of fibrosis recovery.

Inhibition of the mitochondrial pyrimidine biosynthesis enzyme dihydroorotate dehydrogenase by doxorubicin and brequinar sensitizes cancer cells to TRAIL-induced apoptosis

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising agent in selectively killing tumor cells. However, TRAIL monotherapy has not been successful as many cancer cells are resistant to TRAIL. Chemotherapeutic agents, such as doxorubicin have been shown to act synergistically with TRAIL, but the exact mechanisms of actions are poorly understood. In this study, we performed high-throughput small interfering RNA screening and genome-wide gene expression profiling on doxorubicin-treated U1690 cells to explore novel mechanisms underlying doxorubicin-TRAIL synergy. The screening and expression profiling results were integrated and dihydroorotate dehydrogenase (DHODH) was identified as a potential candidate. DHODH is the rate-limiting enzyme in the pyrimidine synthesis pathway, and its expression was downregulated by doxorubicin. We demonstrated that silencing of DHODH or inhibition of DHODH activity by brequinar dramatically increased the sensitivity of U1690 cells to TRAIL-induced apoptosis both in 2D and 3D cultures, and was accompanied by downregulation of c-FLIPL as well as by mitochondrial depolarization. In addition, uridine, an end product of the pyrimidine synthesis pathway was able to rescue the sensitization effects initiated by both brequinar and doxorubicin. Furthermore, several other cancer cell lines, LNCaP, MCF-7 and HT-29 were also shown to be sensitized to TRAIL by brequinar. Taken together, our findings have identified a novel protein target and its inhibitor, brequinar, as a potential agent in TRAIL-based combinatorial cancer therapy and highlighted for the first time the importance of mitochondrial DHODH enzyme and pyrimidine pathway in mediating TRAIL sensitization in cancer cells.

High mobility group box-1 promotes the proliferation and migration of hepatic stellate cells via TLR4-dependent signal pathways of PI3K/Akt and JNK

Background

The migration of hepatic stellate cells (HSCs) is essential to the hepatic fibrotic response, and recently High-mobility group box 1 (HMGB1) has been shown up-regulated during liver fibrosis. Nevertheless, whether HMGB1 can modulate the proliferation and migration of HSCs is poorly understood, as well as the involved intracellular signaling. In this study, we examined the effect of HMGB1 on proliferation, migration, pro-fibrotic function of HSCs and investigated whether toll-like family of receptor 4 (TLR4) dependent signal pathway is involved in the intracellular signaling regulation.

Methodology/Principal Findings

Modified transwell chamber system to mimic the space of Disse was used to evaluate the migration of human primary HSCs, and the protein expressions of related signal factors were evaluated by western blot. Cell proliferation was analyzed by MTT assay, the pro-fibrotic functions of HSCs by qRT-PCR and ELISA respectively. Recombinant human HMGB1 could significantly promote migration of HSCs under both haptotactic and chemotactic stimulation, especially the latter. Human TLR4 neutralizing antibody could markedly inhibit HMGB1-induced migration of HSCs. HMGB1 could enhance the phosphorylation of JNK and PI3K/Akt, and TLR4 neutralizing antibody inhibited HMGB1-enhanced phosphorylation of JNK and PI3K/Akt and activation of NF-κB. JNK inhibitor (SP600125) and PI3K inhibitor (LY 294002) significantly inhibited HMGB1-induced proliferation and migration of HSCs, and also reduced HMGB1-enhanced related collagen expressions and pro-fibrotic cytokines production.

Conclusions/Significance

HMGB1 could significantly enhance migration of HSCs in vitro, and TLR4-dependent JNK and PI3K/Akt signal pathways are involved in the HMGB1-induced proliferation, migration and pro-fibrotic effects of HSCs, which indicates HMGB1 might be an effective target to treat liver fibrosis.

Expression of survivin in activated hepatic stellate cells and effect of transfection of antisense oligonucleotide targeting the survivin gene on apoptosis of HSC-T6 cells

AIM: To investigate the expression of survivin in activated hepatic stellate cell (HSC) and the effect of transfection of antisense oligonucleotide (ASODN) targeting the survivin gene on apoptosis of HSC-T6 cells.

METHODS: The experiment set the control group which not added liposome and oligonucleotide (ODN), liposome group which only added liposome, sense oligonucleotide (SODN) group (1 000 nmol/L) and 400, 800, 1 000 nmol/L ASODN group. The expression of survivin protein in activated HSC, hepatic carcinoma cells, and normal liver cells was detected by immunofluorescence. ASODN targeting the survivin gene was transfected into HSC-T6 cells with LipofectamineTM 2000, and transfection efficiency was detected by fluorescence microscopy. Forty-eight hours after transfection, the changes in survivin mRNA and protein expression were assessed by RT-PCR and Western blot, respectively, and cell apoptosis was measured by PI staining and flow cytometry.

RESULTS: The positive rate of survivin expression in activated HSC was significantly higher than that in normal liver cells (66.07% ± 8.55% vs 9.74% ± 2.68%, P < 0.05). The positive rate of survivin expression was highest in hepatic carcinoma cells among the three groups of cells (69.41% ± 9.10%). Strong green fluorescence was observed by fluorescence microscopy in cells transfected with different concentrations of ASODN, and the transfection efficiency reached 80%. Compared with blank control cells and cells transfected with empty lipofectamineTM 2000 or control oligonucleotide, the expression levels of survivin mRNA (0.94 ± 0.03, 0.95 ± 0.04 and 0.92 ± 0.04 vs 0.64 ± 0.02, 0.54 ± 0.02 and 0.26 ± 0.01) and protein (0.84 ± 0.02, 0.82 ± 0.03 and 0.81 ± 0.02 vs 0.53 ± 0.02, 0.38 ± 0.01 and 0.20 ± 0.01) were significantly decreased (all P < 0.01), and the apoptosis rate (19.00% ± 0.53%, 29.80% ± 1.54% and 48.70% ± 2.00%, respectively) significantly increased (all P < 0.01) in cells transfected with different concentrations of ASODN.

CONCLUSION: Survivin is highly expressed in activated HSC-T6 cells. Down-regulation of survivin expression by transfection of ASODN targeting the survivin gene can induce apoptosis of HSC-T6 cells.