Bile salts inhibit growth and induce apoptosis of human esophageal cancer cell line

Continuous taurocholic acid exposure promotes esophageal squamous cell carcinoma progression due to reduced cell loss resulting from enhanced vascular development

BACKGROUND

Refluxogenic effects of smoking and alcohol abuse may be related to the risk of esophageal squamous cell carcinoma (ESCC). The present study attempts to clarify the effects of continuous taurocholic acid (TCA) exposure, which is neither mutagenic nor genotoxic, on ESCC progression.

METHODS

A squamous carcinoma cell line (ESCC-DR) was established from a tumor induced in a rat model of gastroduodenal reflux. ESCC-DR cells were incubated with 2 mM TCA for ≥2 months. The effects of continuous TCA exposure were evaluated in vitro on cell morphology, growth, and invasion and in vivo on xenograft tumor growth in nude mice. Moreover, the mean level of secreted transforming growth factor (TGF)-β1 and vascular endothelial growth factor (VEGF) proteins in cell culture supernatants and mRNA synthesis of TGF-β1 and VEGF-A of ESCC cells were measured. The angiogenic potential was further examined by a migration assay using human umbilical vein endothelial cells (HUVECs).

RESULTS

Continuous TCA exposure induced marked formation of filopodia in vitro. Expression levels of angiogenic factors were significantly higher in the cells treated with TCA than in control cells. Tumor xenografts derived from cells pre-exposed to TCA were larger and more vascularized than those derived from control cells. In addition, TCA exposure increased HUVEC migration.

CONCLUSION

Continuous TCA exposure enhanced ESCC progression due to reduced cell loss in vivo. Cell loss was inhibited by TCA-induced vascular endothelial cell migration, which was mediated by TGF-β1 and VEGF-A released from ESCC cells.

Investigating the pathogenic role of PADI4 in oesophageal cancer

PADI4 post-translationally converts peptidylarginine to citrulline. PADI4 can disrupt the apoptotic process via the citrullination of histone H3 in the promoter of p53-target genes. The current study focused on PADI4 expression in various subtypes of oesophageal carcinoma (EC) by immunohistochemistry, western blotting and real time PCR. The study also investigated the effect of bile acid deoxycholate (DCA) on PADI4 expression in Eca-109 cells that originated from EC. Apoptosis and DCA-induced toxicity were analyzed by TUNEL, MTT assay and flow cytometry. Additionally, the present study investigated the correlation between single nucleotide polymorphism (SNP) in PADI4 gene and EC risk in Chinese population using Illumina GoldenGate assay. Compared with paraneoplastic tissues, the transcriptional and translational levels of PADI4 were significantly elevated in oesophageal squamous cell carcinoma (ESCC, n=9) and oesophageal adenocarcinoma (EAC, n=5) tissues. Immunolabeling detected expression of PADI4 in ESCC tissues (98.56%, n=139), EAC samples (87.5%, n=16) and oesophageal small cell undifferentiated carcinoma (91.7%, n=12) but not in normal tissues (0%, n=16). Furthermore, PADI4 levels is positively correlated with the pathological classification of ESCC (p=0.009). PADI4 expression levels were consistent with the number of apoptotic cells in the induced Eca-109 cells. rs10437048 [OR= 0.012831; 95% CI, 0.001746~0.094278; p=1.556×10^-12] were significantly associated with decreased risk of EC, whereas rs41265997 [OR=12.7; 95% CI, 0.857077~33.207214; p=3.896×10^-8] were significantly associated with increased risk of EC. rs41265997 in exon 3 of PADI4 gene is non-synonymous and converts ACG to ATG resulting in a threonine /methionine conversion at position 274 of the protein. Haplotypes GC that carries the variant alleles for rs2501796 and rs2477134 was significantly associated with increased risk of EC (frequency=0.085, p=0.0256, OR=2.7). The results suggest that PADI4 expression is related to the tumorigenic process of EC and the DCA-induced apoptosis. The PADI4 gene may be a valid EC susceptibility gene.

Chemical and biological analysis of active free and conjugated bile acids in animal bile using HPLC-ELSD and MTT methods

The aim of the present study was to determine the chemical composition and in vitro cytotoxic activity of seven bile samples and bile acids using the high-performance liquid chromatography (HPLC)-evaporative light scattering detector (ELSD) method. Free and conjugated bile acid standards were used to identify and quantify the chemical components of the seven animal bile samples. The MTT assay was used to determine the cytotoxic effect of the animal bile samples and the free and conjugated bile acids on hepatocellular carcinoma MHCC97-L cells. Chemical analysis revealed that the bile samples from the different animals shared little similarity in terms of their composition. A cell viability assay revealed that cattle bile, as well as its major components, DCA, CDCA and TCDCA, exhibited a marked cytotoxic effect on the hepatocellular carcinoma MHCC97-L cells. The bear bile samples that originated from the Asian black bear and the American black bear contained a unique component, TUDCA, which distinguished them from the other animal bile, though their inhibitory action on MHCC97-L cells was not markedly distinct. The present study reveals that cattle bile may be a potential alternative to bear bile for hepatocarcinoma therapy.

Deoxycholate promotes survival of breast cancer cells by reducing the level of pro-apoptotic ceramide

Introduction

At physiologic concentration in serum, the bile acid sodium deoxycholate (DC) induces survival and migration of breast cancer cells. Here we provide evidence of a novel mechanism by which DC reduces apoptosis that is induced by the sphingolipid ceramide in breast cancer cells.

Methods

Murine mammacarcinoma 4T1 cells were used in vitro to determine apoptosis and alteration of sphingolipid metabolism by DC, and in vivo to quantify the effect of DC on metastasis.

Results

We found that DC increased the number of intestinal metastases generated from 4T1 cell tumors grafted into the fat pad. The metastatic nodes contained slowly dividing cancer cells in immediate vicinity of newly formed blood vessels. These cells were positive for CD44, a marker that has been suggested to be expressed on breast cancer stem cells. In culture, a subpopulation (3 ± 1%) of slowly dividing, CD44⁺ cells gave rise to rapidly dividing, CD44^- cells. DC promoted survival of CD44⁺ cells, which was concurrent with reduced levels of activated caspase 3 and ceramide, a sphingolipid inducing apoptosis in 4T1 cells. Z-guggulsterone, an antagonist of the farnesoid-X-receptor, obliterated this anti-apoptotic effect, indicating that DC increased cell survival via farnesoid-X-receptor. DC also increased the gene expression of the vascular endothelial growth factor receptor 2 (Flk-1), suggesting that DC enhanced the initial growth of secondary tumors adjacent to blood vessels. The Flk-1 antagonist SU5416 obliterated the reduction of ceramide and apoptosis by DC, indicating that enhanced cell survival is due to Flk-1-induced reduction in ceramide.

Conclusions

Our findings show, for the first time, that DC is a natural tumor promoter by elevating Flk-1 and decreasing ceramide-mediated apoptosis of breast cancer progenitor cells. Reducing the level or effect of serum DC and elevating ceramide in breast cancer progenitor cells by treatment with Z-guggulsterone and/or vascular endothelial growth factor receptor 2/Flk-1 antagonists may thus be a promising strategy to reduce breast cancer metastasis.

Cytoprotective effects of proteasome beta5 subunit overexpression in lens epithelial cells

PURPOSE

To determine whether the overexpression of the proteasome catalytic beta5 subunit (PSMB5) can induce the expression of the catalytic subunits beta1 and beta2, enhance proteasome activity, and exert a cytoprotective effect in lens epithelial cells.

METHODS

Cells from the human lens epithelial cell line SRA01/04 (LECs) were stably transfected either with a plasmid expressing the proteasome catalytic subunit beta5 or with an empty plasmid. beta-5-expressing LECs and controls were analyzed for the expression of beta1, beta2, beta5, and alpha6 proteasome subunits; chymotrypsin-like (CT-L) and peptidylglutamyl-peptide hydrolase (PGPH) catalytic activities; as well as for the accumulation of carbonylated proteins, rates of cell viability, and apoptosis after oxidative stress.

RESULTS

Stable expression of the beta5 proteasome subunit resulted in increased expression of the catalytic subunits beta1 and beta2, increased CT-L and PGPH proteasome activities, and increased resistance to accumulation of carbonylated proteins and cell death after oxidative stress.

CONCLUSIONS

The proteasome activity can be genetically "upregulated" in lens cells by overexpression of the beta5 catalytic subunit. The resulting increase in proteasome activity leads to a decrease in the accumulation of oxidized proteins and enhanced cell survival following oxidative stress.