Downregulation of estrogen receptor-α36 expression attenuates metastasis of hepatocellular carcinoma cells

This study aimed to examine the role of estrogen receptor (ER)-α36 in the metastasis of hepatocellular carcinoma (HCC) and in the epithelial-mesenchymal transition (EMT). HCC HepG2 and Huh7 cells with the knocked-down level of ER-α36 expression were established. Cell growth and migration of the HepG2 and Huh7 cell variants were studied using MTS, transwell, and wound-healing assays, and the metastatic abilities of HepG2 cell variants were examined using a tail-vein injection model in nude mice. Levels of EMT markers, Src phosphorylation in HepG2 and Huh7 cell variants, and tumors formed by HepG2 cell variants in the nude mice were examined using Western blot and immunohistochemistry. We found that the growth and metastatic abilities of HepG2 and Huh7 cells with the knocked-down level of ER-α36 expression (HepG2/Si36 and Huh7/Si36) were significantly reduced, with increased levels of cytokeratin and E-Cadherin expression, and decreased levels of Vimentin, Snail, Slug and the Src phosphorylation, compared to the HCC cells transfected with an empty vector (HepG2/Vector and Huh7/Vector). We also found ER-α36 knockdown suppressed the lung metastasis of HepG2 cells with the involvement of EMT and the Src pathway in vivo. The Src inhibitor PP2 suppressed the growth and migration of HepG2/Vector and Huh7/Vector cells with decreased Vimentin, Snail, and Slug and increased cytokeratin and E-Cadherin expressions, but failed to induce the migration and the EMT markers in HepG2/Si36 and Huh7/Si36 cells. ER-α36 is involved in the metastasis of HCC cells through the regulation of EMT and the Src signaling pathway.

Estrogen receptor-α36 is involved in diallyl sulfide-induced inhibition of malignant growth of HepG2 and Huh7 hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) is a highly malignant disease that currently lacks effective treatment. Epidemiological studies have suggested the preventive role of raw garlic intake in different tumors, such as HCC. Although diallyl sulfide (DAS), the main component of garlic extracts, has been reported to inhibit the growth of HCC cells, the underlying mechanism remains elusive. This study aimed to investigate the inhibitory effect of DAS on the growth of HepG2 and Huh7 hepatocellular carcinoma cells and its underlying mechanism. HepG2 and Huh7 cells were treated with DAS and nude mice were intrahepatically injected with human HCC HepG2 cells and maintained with or without DAS administration for 28 days. MTS and clonogenic assays revealed that DAS inhibited the growth and clonogenicity of HepG2 and Huh7 hepatocellular carcinoma cells. Furthermore, DAS inhibited the growth of xenograft tumors accompanied by a decreased rate of pathological karyomitosis as observed by H&E staining. The expression levels of estrogen receptor-α36 (ER-α36) and epidermal growth factor receptor (EGFR) in HepG2 and Huh7 cells and in xenograft tumors derived from HepG2 cells after DAS treatment were detected by immunohistochemistry and western blotting. We found that DAS disrupted the positive regulatory loop between ER-α36 and EGFR, and decreased the phosphorylation of AKT at Ser 473 both in vivo and in vitro. DAS also induced cell apoptosis, as evidenced by Hoechst and TUNEL staining. Western blotting revealed activation of caspase3, increased BAX and decreased Bcl-2 expression. However, the ER-α36 expression knockdown attenuated DAS-induced ERK and AKT phosphorylation in HCC cells. DAS was also able to inhibit ER-α36-mediated activation of the MAPK/ERK signaling induced by estrogen. Thus, our results indicate that ER-α36 signaling is involved in DAS-induced inhibition of HCC cell growth both in vitro and in vivo.

Estrogen receptor-α36-mediated rapid estrogen signaling regulates 78 kDa glucose-regulated protein expression in gastric carcinoma cells

To determine whether estrogen receptor-α36 (ER-α36) -mediated rapid estrogen signaling is associated with 78 kDa glucose-regulated protein (GRP78) expression in gastric cancer, 86 samples of gastric tumor tissue with corresponding normal and tumor-adjacent tissues were used to examine expression patterns of GRP78 and ER-α36. Immunohistochemistry demonstrated that 55/86 (63.95%) patients with gastric carcinoma, and western blot analysis revealed that GRP78 was upregulated in 15/20 (75%) of tumor specimens. GRP78 expression was positively associated with ER-α36 expression, the male sex and lymph node metastasis (P<0.05). Estrogen treatment increased GRP78 and ER-α36 expression, as well as GSK-3β phosphorylation in established gastric cancer SGC-7901 cells. The steady-state level of GRP78 protein expression and the level of phosphorylated GSK-3β at Ser9 were decreased in SGC-7901 cells with ER-α36 knockdown. Forced expression of ER-α36 in SGC-7901 cells, however, led to an increase in GRP78 expression and GSK-3β phosphorylation. It may therefore be concluded that ER-α36-mediated rapid estrogen signaling positively regulates GRP78 expression, presumably via the GSK-3β pathway, which may be associated with gastric carcinogenesis.

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.

Involvement of the Akt signaling pathway in ER-α36/GRP94-mediated signaling in gastric cancer

Glucose-regulated protein 94 (GRP94) has been implicated in the promotion of tumor proliferation and metastasis. Previous studies have found that GRP94 is involved in the malignant growth of gastric carcinoma cells through estrogen receptor-α36 (ER-α36)-mediated estrogen signaling, but the underlying mechanism remains unclear. In the present study, we examined the expression levels of GRP94 and ER-α36 in tumor specimens from gastric cancer patients by immunohistochemistry, and found that both GRP94 and ER-α36 were highly expressed in the cytoplasms of gastric carcinoma cells. Furthermore, treatment with 17β-estradiol at a concentration of 10⁻¹² M for 24 h increased the expression levels of GRP94 and ER-α36, and the phosphorylation levels of Akt at the Ser473 site (Ser473-Akt). In established SGC7901 gastric cancer cells with knockdown of ER-α36 expression, the levels of GRP94 and Ser473-Akt expression were significantly reduced. Thus, the Akt signaling pathway is a potentially important signaling pathway in ER-α36-GRP94-mediated gastric carcinogenesis.