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

Abstract

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.

Keywords: Akt; estrogen receptor-α36; gastric cancer; glucose-regulated protein 94.

Figure 1

Immunohistochemical staining of gastric cancer tissues. (A) Glucose-regulated protein 94 and (B) estrogen receptor-α36 were highly expressed in the cytoplasm of gastric carcinoma cells (magnification, ×400).

Figure 2

17β-estradiol (E2) treatment increases the protein expression levels of glucose-regulated protein (GRP)94, estrogen receptor (ER)-α36 and Ser473-Akt. SGC7901 human gastric adenocarcinoma cells were treated with 10⁻¹² M E2 for 24 h. The addition of an equal volume of alcohol served as a control. The protein levels of GRP94, ER-α36 and Ser473-Akt were measured by western blotting, which was then quantitatively analyzed. (A) Western blotting and (B) quantitative analysis. The levels of GRP94, ER-α36 and total Akt were normalized to β-actin levels, and the levels of Ser473-Akt were normalized against total Akt levels. The data are presented as the mean ± SD of three independent experiments. ^**P<0.01, vs. the control.

Figure 3

Western blot analysis of glucose-regulated protein (GRP)94, estrogen receptor (ER)-α36 and Ser473-Akt expression levels in SGC7901 gastric cancer cells. In SGC7901-Low36 (7901-Low36) cells (with knockdown of ER-α36 expression) the expression levels of GRP94 and Ser473-Akt were reduced, compared with SGC7901-control (SGC7901) cells transfected with an empty expression vector. The expression levels of GRP94, ER-α36 and Ser473-Akt were measured by western blotting, which was then quantitatively analyzed. (A) Western blotting and (B) quantitative analysis. The levels of GRP94, ER-α36 and total Akt were normalized against β-actin levels, and the levels of Ser473-Akt were normalized against total Akt levels. The data are expressed as the mean ± SD from three independent experiments. ^**P<0.01, vs. SGC7901.