Price B D, Mannheim-Rodman L A, Calderwood S K
Joint Center for Radiation Therapy, Dana-Farber Cancer Institute, Boston, Massachusetts 02115.
J Cell Physiol. 1992 Sep;152(3):545-52. doi: 10.1002/jcp.1041520314.
The glucose regulated proteins (GRPs) are major structural components of the endoplasmic reticulum (ER) and are involved in the import, folding, and processing of ER proteins. Expression of the glucose regulated proteins (GRP78 and GRP94) is greatly increased after cells are exposed to stress agents (including A23187 and tunicamycin) which inhibit ER function. Here, we demonstrate that three novel inhibitors of ER function, thapsigargin (which inhibits the ER Ca(2+)-ATPase), brefeldin A (an inhibitor of vesicle transport between the ER and Golgi) and AIF4-, (which inhibits trimeric G-proteins), can increase the expression of both GRP78 and 94. The common characteristic shared by activators of GRP expression is that they disrupt some function of the ER. The increased levels of GRPs may be a response to the accumulation of aberrant proteins in the ER or they may be increased in response to structural/functional damage to the ER. The increased accumulation of GRP78 mRNA after exposure of cells to either thapsigargin, brefeldin A, AIF4-, A23187, or tunicamycin can be blocked by pre-incubation in cycloheximide. In contrast, accumulation of GRPs after exposure to hypoxia was independent of cycloheximide. In addition, the protein kinase inhibitor genistein blocked the thapsigargin induced accumulation of GRP78 mRNA, whereas the protein phosphatase inhibitor okadaic acid caused increased accumulation of GRP78 mRNA. The data indicates that there are at least 2 mechanisms for induced expression of GRPs, one of which involves a phosphorylation step and requires new protein synthesis (e.g., thapsigargin, A23187) and one which is independent of both these steps (hypoxia).
葡萄糖调节蛋白（GRPs）是内质网（ER）的主要结构成分，参与内质网蛋白质的导入、折叠和加工。细胞暴露于抑制内质网功能的应激剂（包括A23187和衣霉素）后，葡萄糖调节蛋白（GRP78和GRP94）的表达会大幅增加。在此，我们证明了三种新型内质网功能抑制剂：毒胡萝卜素（抑制内质网Ca(2 +)-ATP酶）、布雷菲德菌素A（内质网与高尔基体之间囊泡运输的抑制剂）和AIF4-（抑制三聚体G蛋白），均可增加GRP78和GRP94的表达。GRP表达激活剂的共同特征是它们破坏了内质网的某些功能。GRPs水平的升高可能是对内质网中异常蛋白质积累的一种反应，或者可能是对内质网结构/功能损伤的反应。细胞暴露于毒胡萝卜素、布雷菲德菌素A、AIF4-、A23187或衣霉素后，GRP78 mRNA的积累增加可通过预先用放线菌酮孵育来阻断。相比之下，暴露于缺氧环境后GRPs的积累与放线菌酮无关。此外，蛋白激酶抑制剂染料木黄酮可阻断毒胡萝卜素诱导的GRP78 mRNA积累，而蛋白磷酸酶抑制剂冈田酸则导致GRP78 mRNA积累增加。数据表明，GRPs诱导表达至少有两种机制，其中一种涉及磷酸化步骤且需要新的蛋白质合成（如毒胡萝卜素、A23187），另一种则与这两个步骤无关（缺氧）。
