GRP78在雌激素膜通路介导的胃癌细胞生长调控中的机制

It has been established that up-regulated expression of 78-kDa glucose-regulated protein (GRP78)，an endoplasmic reticulum chaperone, may contribute to the proliferation of gastric cancer, but its mechanism is still unclear. Our previous studies have found that treatment gastric cancer SGC7901 cells with 17β-Estradiol (E2) increased the expression levels of both GRP78 and estrogen receptor-α36 (ER-α36) , a novel variant of ER-α, which has been cloned and showed to mediate membrane-initiated estrogen signaling and was highly expressed in human gastric cancer tissues. In established gastric cancer cells with knocked-down levels of ER-α36 expression (SGC-L36), the levels of GRP78 expression were declined, accompanying with decreased expression of Cyclin D1. Unlike the overexpression of ER-α36 (in established gastric cancer cells with overexpressed levels of ER-α36 (SGC-H36)), the levels of GRP78 and Cyclin D1 expression increased. In addition, in comparison with paired normal tissues, GRP78 was highly expressed in tumor specimens from gastric cancer patients, and its expression was positively correlated with tumor size, depth of invasion of gastric cancer and expression of ER-α36. These suggested that GRP78 plays a pivotal role in development and progression of gastric cancer through estrogen-ER-α36 signaling pathway. On the whole, in this research, we will reveal the signal transduction pathway and the underlying mechanism of GRP78 mediated by ER-α36 signaling pathway, contribute to the cell growth (proliferation and apoptosis) of gastric cancer, using gastric cancer cell lines expressing low and high levels of (ER-α36, ER-α66 (classical ER-α) and GRP78), nude mice models and human gastric cancer tissues with clinical features. And we believe that this research will provide a theoretical and experimental basis for development of a new target in gastric cancer diagnosis and treatment.

GRP78被认为是促胃癌细胞增殖、存活的重要分子，但迄今为止，GRP78参与胃癌发生发展的机制尚不清楚。申请者基于雌激素膜通路（ER-α36）与胃癌生长有关的前期研究发现：给予17β-雌二醇，可促进胃癌细胞表达GRP78和ER-α36；ER-α36基因沉默的胃癌细胞中，GRP78和生长关键分子CyclinD1蛋白的表达下降，反之亦然。人胃癌组织中GRP78的表达明显高于癌旁及正常组织，且与肿瘤大小、浸润深度和雌激素膜信号（ER-α36）的表达等相关。据此，申请者推测：雌激素可能通过启动ER-α36相关的膜通路影响GRP78的表达，从而调控胃癌细胞生长(增殖和凋亡)。本项目拟建立细胞、裸鼠模型及人体胃癌样本，深入探讨GRP78在雌激素-ER-α36膜信号通路调控胃癌细胞生长（增殖和凋亡）中的作用及其机制，为设计干预胃癌的新策略提供理论和实验依据。

本项目确定了人体胃癌组织中GRP78的表达与定位，并发现GRP78的高表达与浸润深度、淋巴结转移相关和ER-α36的表达有关。构建了高表达ER-α36、低表达ER-α36和高表达GRP78的重组胃癌细胞株。研究发现高表达GRP78促进胃癌细胞生长。GRP78的表达受雌激素-ER-α36信号通路调控，经Akt/GSK-3β途径影响胃癌细胞生长。雌激素可通过Akt/GSK-3β途径，拮抗衣霉素所诱导的内质网应激对胃癌细胞生长和侵袭的抑制。低浓度雌激素可通过GRP78-ER-α36信号通路，经Akt途径促进胃癌干细胞增殖。裸鼠移植瘤实验发现，相对于低表达ER-α36的重组细胞组，高表达ER-α36组细胞的GRP78表达更高，且具有更强的生长及侵袭能力。初级胆汁酸（胆酸和鹅脱氧胆酸）可上调ER-α36和EGFR表达及ERK磷酸化，促进胃癌细胞生长。本项从分子、细胞、人体及动物实验多层面研究证实了GRP78参与雌激素-ER-α36信号通路介导的胃癌（干）细胞生长与侵袭的理论推断，其结果在解释胃癌流行病学证据显示的胃癌发病男性明显多于女性、雌激素在胃癌的发生过程中扮演重要作用等的机制研究方面取得重要进展，该项研究成果将可能对胃癌的诊断与治疗产生重大影响。