Cyclin D1/cdk4, estrogen receptors α and β, in N-methyl-N'-nitro-N-nitrosoguanidine-induced rat gastric carcinogenesis: immunohistochemical study

In Utero Exposure to 3,3',4,4', 5-Pentachlorobiphenyl Dose-Dependently Induces N-butyl-4-(hydroxybutyl) Nitrosamine in Rats With Urinary Bladder Carcinoma

Polychlorinated biphenyls (PCBs) are fat-soluble environmental pollutants that can accumulate in adipose tissue or be secreted in milk. N-butyl-4-(hydroxy butyl) (BBN), a rat bladder carcinogen, recruits the host metabolism to yield its ultimate carcinogenic form via CYP1s. Since estrogen receptors (ERs) mediate biological responses important for the growth of bladder carcinoma, we investigated PCNA, Cyclin D1, ERs, CYP1s, and AhR expression in BBN rat bladder carcinomas with prenatal PCB exposure. Female SD rats were treated with 7.5 μg, 250 ng, and 2.5 ng of 3,3',4,4',5-pentachlorobiphenyl (PCB126)/kg or vehicle on days 13 to 19 post-pregnancy. Six-week-old male offspring were treated with 0.05% BBN for 10 weeks before being anesthetized and the urinary bladder wall incised to expose the bladder carcinomas. N-butyl-4-(hydroxybutyl) bladder carcinoma incidence increased with prenatal PCB exposure dose-dependently. In bladder carcinoma, PCB126 exposure significantly increased PCNA, D1, ERα, CYPIA1, CYP1B1, and AhR expression dose-dependently, and increased ERα expression was particularly prominent. However, the expression of ERβ was low, independent of the volume of PCB126 given, indicating similarity to the Vehicle group. We conclude that prenatal PCB126 exposure in rats can induce PCB126 to dose-dependently metabolize BBN via CYP1A1, and contribute to bladder carcinogenesis with upregulation of ERα expression.

Expression of factors and key components associated with the PI3K signaling pathway in colon cancer

The pathophysiology of colorectal cancer (CRC) has not been fully elucidated. The dysregulation of the phosphatidylinositol 3-kinase (PI3K) signaling pathway frequently contributes to the tumorigenesis and progression of human cancer. The aim of the present study was to explore the expression and clinical significance of a number of associated factors and key components of the PI3K signaling pathway, including phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit α (p110α), phosphorylated protein kinase B (p-Akt) Ser473, p-mammalian target of rapamycin (mTOR) Ser2448, cyclin D1, cyclin dependent kinase (CDK)4, RELA proto-oncogene, nuclear factor-κβ subunit (p65), Ras and extracellular signal-regulated kinase (ERK)1/2 in human CRC. The expression of target proteins was detected using immunohistochemistry (IHC) in 65 CRC cases and 15 colonic adenoma cases. The association between the expression of target proteins and clinical pathological parameters was analyzed using a χ² test. IHC results revealed that the expression of all target proteins was significantly increased in CRC tissues compared with in colonic adenoma tissues (P<0.05). No significant associations were observed between the expression of p110α, p-Akt Ser473, p-mTOR Ser2448 and sex, age, differentiation, lymph node metastasis or Tumor-Node-Metastasis staging (P>0.05). Cyclin D1, CDK4 and Ras were revealed to be expressed significantly higher in poorly differentiated CRC compared with moderately differentiated CRC (P<0.05). Expression of p65 and ERK1/2 were significantly increased in cancer tissues with lymph node metastasis compared with cancer tissues without lymph node metastasis (P<0.05). These results suggest that the target proteins may all participate in the tumorigenesis of CRC. Furthermore, cyclin D1, CDK4, Ras, p65 and ERK1/2 may be important in the progression of CRC. The results of the present study may provide novel predictive factors and therapeutic targets for CRC.

Antiproliferative effects of the CDK6 inhibitor PD0332991 and its effect on signaling networks in gastric cancer cells

PD0332991 (palbociclib/Ibrance^®) is a cyclin-dependent kinase (CDK)4/6 inhibitor that has recently been approved for the treatment of estrogen receptor-positive advanced breast cancer. The present study investigated the antiproliferative effects of PD0332991 on gastric cancer (GC) cells and the underlying molecular mechanisms. The activity of PD0332991 was tested in several GC cell lines, including AGS, KATO-III, NCI-N87 and HS746T. Growth inhibitory activity of PD0332991, alone or in combination with fluorouracil (5-FU), was measured by MTT assay. The effects of PD0332991 on cell cycle progression were analyzed by flow cytometry and western blotting. Protein pathway array and Ingenuity Pathway Analysis were used to identify signaling pathways that may mediate the antiproliferative effects of PD0332991. PD0332991 inhibited proliferation in a dose-dependent manner and enhanced the activity of 5-FU in all GC cell lines tested. Cells treated with PD0332991 exhibited cell cycle arrest in G₁ phase of the cell cycle, whereas the number of cells in G₂/M phase was decreased. PD0332991 also inhibited CDK6-specific phosphorylation of retinoblastoma on Ser780, reduced the expression of cyclin D1, and induced expression of p53 and p27. Furthermore, 31 proteins were identified, the expression of which was significantly altered following treatment with PD0332991 in at least three cell lines. Pathway analysis indicated that the altered proteins were frequently associated with cell death, cell cycle and the molecular mechanism of cancer. The results of the present study indicated that PD0332991 may inhibit cell proliferation via modulation of the cell cycle, and may affect numerous oncogenic signaling pathways. Therefore, PD0332991 may be considered effective for the treatment of GC.

Preventive effect of Actinidia valvata Dunn extract on N-methyl-N'-nitro-N-nitrosoguanidine-induced gastrointestinal cancer in rats

PURPOSE

This study was conducted to assess the preventive effect of Actinidia valvata Dunn (AVD) extract on an animal model of gastrointestinal carcinogenesis on the basis of changes in tumor incidence, cell proliferation, and apoptosis.

MATERIALS AND METHODS

Seventy-five male Wistar rats were divided into five different treatment groups with 15 rats in each group. Group I was given normal feed, whereas Groups II to IV were treated with 10% sodium chloride in the first six weeks and 100 ug/mL of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in drinking water for 24 weeks. Group II was then given normal feed, whereas Group III was given AVD extract (0.24 g/kg/day) for 12 weeks. Group IV was given AVD extract from the first week to the 36th week, whereas Group V was treated with AVD extract alone for 36 weeks. All rats were sacrificed at the end of the 36-week experiment and assessed for the presence of gastrointestinal tumors. The occurrence of cancer was evaluated by histology. Bax, Bcl-2, Caspase-3, and cyclinD1 were determined by immunohistochemical staining and Western blotting.

RESULTS

The incidences of gastric cancer were 0% in Group I, 73.3% in Group II, 33.3% in Group III, 26.7% in Group IV, and 0% in Group V. Bcl-2 and cyclinD1 expression was decreased in AVD extract treated groups, whereas Bax and Caspase-3 expression was increased. Comparison with group II revealed significant differences (p<0.01).

CONCLUSIONS

AVD extract exhibits an obvious preventive effect on gastrointestinal carcinogenesis induced by MNNG in rats through the regulation of cell proliferation and apoptosis.

Effects of 17β-estradiol and tamoxifen on gastric cancer cell proliferation and apoptosis and ER-α36 expression

The present study aimed to investigate the effects of 17β-estradiol and tamoxifen, an agonist and inhibitor of the estrogen receptor (ER), respectively, on the proliferation and apoptosis of gastric cancer cells, as well as the messenger (m)RNA expression levels of ER-α36. Nested reverse transcription-polymerase chain reaction (RT-PCR) confirmed that ER-α36 was expressed in the BGC823, MKN45 and SGC7901 human gastric cancer cell lines. Subsequently, the BGC823 cell line was stimulated with various concentrations of 17β-estradiol or tamoxifen for 24 or 48 h, and the proliferation, apoptosis and mRNA expression levels of ER-α36 were determined by water-soluble tetrazolium (WST)-1 assay, flow cytometry and RT-quantitative PCR, respectively. The activity of BGC823 cells was significantly increased following treatment with 10⁻¹² mol/l 17β-estradiol for 24 h (P=0.013), as compared with the control, and reached a peak at 48 h (P=0.002). Notably, the activity of BGC823 cells was decreased with increasing concentrations of 17β-estradiol, although it remained higher compared with that of the control. In the tamoxifen-treated groups, the cell activity decreased as the drug concentration increased. The apoptosis rate was markedly reduced in the 17β-estradiol group after 24 h (10⁻¹² mol/l, P=0.013; 10⁻¹¹ mol/l, P=0.023; and 10⁻¹⁰ mol/l, P=0.017) and after 48 h (10⁻¹² mol/l, P=0.002; 10⁻¹¹ mol/l, P=0.011; and 10⁻¹⁰ mol/l, P=0.033), whereas the rate of apoptosis increased as the tamoxifen concentration increased (24 h: 5×10⁻⁶ mol/l, P=0.002; and 10⁻⁵ mol/l, P=0.001; and 48 h: 5×10⁻⁶ mol/l, P=0.014 and 10⁻⁵ mol/l, P=0.0021), as compared with the control group. The mRNA expression levels of ER-α36 were significantly increased after 24 h of treatment with 10⁻¹² mol/l (P=0.024), 10⁻¹¹ mol/l (P=0.0113) and 10⁻¹⁰ mol/l (P=0.0037) 17β-estradiol compared with the control group when the concentration of 17β-estradiol was low, and the same was observed after 48 h of treatment 10⁻¹² mol/l (P=0.0164), 10⁻¹¹ mol/l (P=0.0342) and 10⁻¹⁰ mol/l (P=0.0198) 17β-estradiol. The mRNA expression levels of ER-α36 were significantly decreased with increasing concentrations of tamoxifen after 24 h (5×10⁻⁶ mol/l, P=0.0233; and 10⁻⁵ mol/l, P=0.007) and after 48 h (5×10⁻⁶ mol/l, P=0.001; and 10⁻⁵ mol/l, P=0.0153). In addition, the ability of tamoxifen to inhibit the growth of gastric cancer cells was concentration-dependent. The results of the present study suggested that gastric cancer cells were sensitive to the effects of 17β-estradiol and tamoxifen, and that tamoxifen is able to induce gastric cancer cell apoptosis. The expression levels of ER-α36 were upregulated, and the growth of gastric cancer cells was increased, following treatment with 17β-estradiol, thus suggesting that gastric cancer tumors are stimulated by estrogen.

Reproductive factors, hormone use and gastric cancer risk: The Singapore Chinese Health Study

Gastric cancer incidence varies greatly worldwide, but is consistently twice as high in men than in women. The hormone-related factors hypothesized to be associated with lower risk of gastric cancer in women have not been fully explored in populations with a high background risk of gastric cancer. The Singapore Chinese Health Study (SCHS) is a prospective cohort study in which 34,022 of the participants enrolled between 1993 and 1998 were women between 45 and 74 years of age. Information on reproductive histories, hormone replacement therapy (HRT) and oral contraceptive (OC) use was collected through in-person interviews at baseline. As of December 31, 2013, 269 incident gastric cancer cases were identified. Multivariable-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated to evaluate gastric cancer risk associations. Older age at natural menopause (≥55 versus <45 years: HR = 0.50, 95% CI: 0.25-0.99), type of menopause (other versus natural: HR = 0.48, 95% CI: 0.27-0.87) and greater years of menstrual cycling (fourth versus first quartile: HR = 0.67, 95% CI: 0.46-0.96) were associated with a decreased risk of gastric cancer. Ever use of OCs and HRT was also associated with reduced risk of gastric cancer; the multivariable-adjusted HRs (95% CIs) were 0.40 (0.17-0.90) for use of HRT >3 years and 0.67 (0.47-0.94) for ever use of OCs, compared with never use. Reproductive factors associated with a longer window of fertility and the use of exogenous hormones were shown to reduce gastric cancer development in a cohort of Chinese women with a high background risk of gastric cancer.

Increased cyclin T1 expression as a favorable prognostic factor in treating gastric adenocarcinoma

The expression of cyclin A, B1, D1 and E in gastric adenocarcinoma is known to be associated with clinical outcome. However, few studies have investigated the role of cyclin T1 and cyclin-dependent kinase 9 (CDK9) in gastric adenocarcinoma. Therefore, this study assessed the clinical significance of cyclin T1 and CDK9 expression in gastric adenocarcinoma. A total of 39 gastric adenocarcinoma patients received either radical total or distal gastrectomy in this study. Surgical tissue slides were stained with CDK9 and cyclin T1 antibodies, and immunohistochemistry scores and disease-free survival (DFS) rates were analyzed. Among the 19 patients with tumor-recurrent or distant metastasis, 16 were recorded as exhibiting low expression of cyclin T1. The remaining three patients exhibited high expression of the antibody. The results of patients with a higher T stage, N stage and tumor grade were less favorable. For patients with adenocarcinoma, the percentage of tissue slides stained with cyclin T1 was significantly higher than for those with normal stomach epithelia. The DFS rates of patients with low expression of cyclin T1 were significantly associated with poorer DFS rates. In conclusion, high expression of cyclin T1 is a favorable prognostic factor in treating patients with stomach adenocarcinoma.

Biphasic ER-α36-mediated estrogen signaling regulates growth of gastric cancer cells

To examine the expression patterns of ER-α36 and Cyclin D1 in human gastric cancer tissues and to investigate the effects of ER-α36-mediated estrogen signaling on the growth of gastric cancer cells, 117 samples of formalin-fixed and paraffin-embedded gastric cancer tumor tissues and 40 fresh gastric cancer tumor tissues were analyzed with immunohistochemistry assay and western blot analysis. ER-α36 expression was well correlated with gender (male:female ratio 2.88:1, P=0.01), invasion to serosa (P=0.01) as well as Cyclin D1 expression (P<0.01). The effects of different concentrations of estrogen on the growth of different gastric cancer cells and normal gastric cells as well as gastric cancer SGC7901 cells with different levels of ER-α36 expression were examined. SGC7901 cells with high levels of ER-α36 expression exhibited estrogen hypersensitivity, high growth rate and high levels of Cyclin D1 expression while SGC7901 cells with knocked-down levels of ER-α36 expression were insensitive to estrogen stimulation, grew slowly and expressed less Cyclin D1. Our results indicate that ER-α36 mediates biphasic estrogen signaling in the growth of gastric cancer cells.

Vascular endothelial growth factor mRNA levels as a biomarker for short-term N-butyl-N-(4-hydroxybutyl) nitrosamine-induced rat bladder carcinogenesis bioassay

Generically, carcinogenic effects of chemicals in bladder carcinogenesis are judged by induction of papillary or nodular (PN) hyperplasia in rats given N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) for 4 weeks and the test chemical for 22-28 weeks. However, upregulation of vascular endothelial growth factor (VEGF) begins early in rat BBN bladder carcinogenesis. To establish a short-term rat bladder carcinogenic bioassay, we analyzed the correlations between VEGF, VEGF mRNA and bladder lesions inductions at 10 and 26 weeks after BBN treatment. Six-week-old male Wistar (slc) rats were given 0.05% BBN for 4, 10 or 26 weeks. To avoid individual rat bias, the bladders were investigated by partial cystectomy at 10 weeks and total cystectomy at 26 weeks. After induction, PN hyperplasia and carcinoma in rats increased with the length of BBN treatment and immunohistochemical VEGF expression also increased following carcinogenesis, but the immunoreactivity of individual lesions was quite variable. Moreover, induction of PN hyperplasia at 10 weeks' BBN treatment was not significantly correlated with that at 26 weeks' treatment; thus, it was not possible to predict the carcinogenic effect due to the induction of PN hyperplasia at 26 weeks' BBN treatment by that at 10 weeks' treatment. However, VEGF mRNA levels of rat bladders at 10 weeks' BBN treatment revealed a strong significant correlation with the incidence of bladder lesions at 26 weeks' treatment. Here, we suggest that quantitative VEGF mRNA levels are a good biomarker for a short-term BBN-induced bioassay for rat bladder carcinogenesis.

The involvement of Helicobacter pylori thioredoxin-1 in gastric carcinogenesis

Helicobacter pylori infection is related to the development of gastric diseases. Various virulence factors are responsible for the pathogenic mechanisms of H. pylori infection. Our previous studies using two-dimensional gel electrophoresis showed that H. pylori thioredoxin-1 (Trx1) is overexpressed in gastric carcinomas. Here, we examined whether H. pylori Trx1 is a novel virulence factor associated with gastric tumorigenesis. We found that Trx1 expression in H. pylori isolated from gastric cancer tissues was significantly higher than that from tissues exhibiting gastritis. In the gastric epithelial cell line GES-1, infection of H. pylori with high Trx1 expression significantly induced cell apoptosis, decreased the expression of cyclin D1 and upregulated p21. However, in the gastric cancer cell line BGC823, high Trx1 expression in H. pylori significantly increased cell proliferation, and upregulated cyclin D1. The effects on cell lines were confirmed using the H. pylori Trx1-knockout mutant strain. Our observations indicate that high Trx1 expression in H. pylori is associated with gastric carcinogenesis. In H. pylori, Trx1 likely participates in the pathogenesis of gastric cancer and H. pylori expressing high levels of Trx1 would be expected to be highly pathogenic in gastric diseases in China.

Expression of 17β-hydroxysteroid dehydrogenase type 1 in gastric cancer

There are several findings suggesting the protective role of estrogens in gastric carcinogenesis. Extragonadal 17β-estradiol (E2) may be formed during estrone (E1) reduction to E2 by 17-β-hydroxysteroid dehydrogenase type 1 (HSD17B1). Therefore, we studied the HSD17B1 transcript and protein levels in primary nontumoral and tumoral gastric tissue from the same 21 patients with gastric cancer (GC). We also assessed the effect of 5-Aza-2'-deoxycytidine (5-dAzaC), on the methylation status of HSD17B1 and its expression and conversion of E1 to E2 in HGC-27 and EPG 85-257 GC cells. We identified the presence of HSD17B1 transcript and protein in HGC-27 and EPG 85-257 GC cells as well as in primary nontumoral and tumoral tissues from patients with GC. Moreover, we found that 5-dAzaC significantly up-regulated the HSD17B1 transcript and protein levels, which is associated with increased conversion of E1 to E2 in HGC-27 and EPG 85-257 GC cells. The changes in HSD17B1 expression in both HGC-27 and EPG 85-257 cells were accompanied by 5-dAzaC induced DNA demethylation in the 5' flanking region. Our results demonstrated that HSD17B1 expression and its ability to convert the weak estrogen E1 to the more potent E2 can be associated with DNA methylation in the 5' flanking region in GC cells.

ER-α36-mediated gastric cancer cell proliferation via the c-Src pathway

Previously, a novel variant of estrogen receptor (ER)-α, ER-α36, was identified and cloned and reported to mainly mediate non-genomic estrogen signaling. More recently, we identified that ER-α36 is important for the invasion and lymph node metastasis of human gastric cancer. In the present study, the c-Src signaling pathway was demonstrated to be involved in the non-genomic estrogen signaling mediated by ER-α36 in SGC7901 gastric cancer cells. SGC7901 cells were subjected to the siRNA-mediated knockdown of ER-α36 (PLKO.1-PURO-SP6-ER-α36-L) or transfected with an ER-α36 upregulated expression plasmid (PLJM1-ER-α36-H) and treated with 17β-estradiol (E2β) and PP2, a c-Src protein inhibitor. The expression of ER-α36 and c-src/p-c-Src and cyclin D1 was examined by western blot analysis, and tumor cell growth was analyzed by cell proliferation and nude mouse xenograft assays. The ER variant, ER-α36, was shown to enhance gastric cancer cell proliferation through activation of the membrane-initiated c-Src signaling pathways, indicating that ER-α36 is important for the regulation of proliferation in gastric cancer. In addition, ER-α36 was shown to directly interact with c-Src by immunoprecipitation. The results of the present study indicate that the use of ER-α36 may be a targeted therapeutic approach in gastric cancer.

Relationship between expression of SOCS2 and STAT3 and biologic behaviors of gastric carcinoma

AIM: To investigate the relationship between expression of suppressor of cytokine signaling 2 (SOCS2) and signal transducer and activator of transcription 3 (STAT3) and biological behaviors of gastric carcinoma.

METHODS: The expression of SOCS2 and STAT3 in 55 cases of gastric carcinoma and 55 cases of normal gastric tissue was detected by immunohistochemistry. The correlation of SOCS2 and STAT3 expression with tumor differentiation grade, lymph node metastasis, depth of invasion, clinical stage and patients' gender and age was analyzed.

RESULTS: The positive rate of SOCS2 expression in gastric carcinoma was significantly lower than that in normal gastric tissues (25.5% vs 91.1%, P < 0.05). SOCS2 expression in gastric carcinoma was significantly associated with tumor differentiation grade, lymph node metastasis and clinical stage (all P < 0.05). The positive rate of STAT3 expression in gastric carcinoma was significantly higher than that in normal gastric tissue (72.7% vs 18.2%, P < 0.05). STAT3 expression in gastric carcinoma was significantly associated with tumor differentiation grade, lymph node metastasis, depth of invasion, and clinical stage (all P < 0.05). There was a significant negative relation between the expression of SOCS2 and that of STAT3 in gastric carcinoma (r = -0.486, P < 0.01).

CONCLUSION: SOCS2 is lowly expressed in gastric carcinoma, while STAT3 is highly expressed in gastric carcinoma. Interaction between SOCS2 and STAT3 may contribute to gastric carcinogenesis.