STRESS INDUCTION OF GLUCOSE REGULATED PROTEIN GRP78/BiP

描述(申请人提供)：未折叠蛋白反应(UPR)触发多个途径，使细胞对以内质网(ER)为目标的应激条件做出反应。内质网是合成和修饰分泌和膜蛋白的细胞器，也是细胞内主要的钙储存室。葡萄糖调节蛋白GRP78，也被称为免疫球蛋白结合蛋白，由于其在蛋白质折叠和组装、靶向错误折叠的蛋白质降解、内质网钙结合和控制跨膜内质网应激传感器的激活中的作用，是内质网功能的中央调节因子。编码GRP78(GRP78)基因的激活被广泛用于内质网应激的监测，并导致了几个独特的信号通路的发现，通过这些通路，这个关键细胞器中的压力被传递到细胞核，启动UPR。此外，由于GRP78的抗凋亡特性，GRP78的应激诱导代表了UPR中一个重要的促生存成分。作为ER功能的主要调节者，GRP78在调节细胞内稳态、癌细胞死亡和侵袭性生长之间的平衡以及调节对化疗药物的敏感性方面具有独特的优势。在过去的资助期间，我们发现组蛋白脱乙酰酶(HDAC)抑制剂是GRP78转录的新诱导剂，并与内质网应激诱导剂协同作用，导致GRP78表达上调。由于HDAC抑制剂目前被开发为一类很有前途的新型抗癌药物，我们发现了一个受这些化合物影响的新的UPR靶点。目前该方案的中心假设是GRP78的转录受染色质的乙酰化和与GRP78启动子结合的转录因子的调控，GRP78表达的变化影响肿瘤的发展及其对HDAC抑制剂治疗干预的反应。通过基因打靶，我们创造了新的小鼠模型，其中GRP78在特定组织中的表达减少或被敲除，这将使我们能够直接测试GRP78在癌症发病机制中的作用。我们有三个具体目标。在目标1中，我们将确定HDAC抑制剂激活GRP78转录的机制。在目标2中，我们将确定目前正在临床试验中的HDAC抑制剂对GRP78的增强诱导是否通过抑制细胞凋亡来增强癌细胞的耐药性。在目标3中，我们将确定是否减少或有条件地敲除GRP78将导致抑制癌症的进展和转移。如果我们的假设是正确的，它将确立GRP78作为癌症进展和对HDAC抑制剂治疗的耐药性的预后标志物。此外，靶向抑制GRP78可用于阻止肿瘤进展和克服对HDAC抑制剂治疗的耐药性。

DESCRIPTION (provided by applicant): The unfolded protein response (UPR) triggers multiple pathways to allow cells to respond to stress conditions that target the endoplasmic reticulum (ER). The ER is a cellular organelle where secretory and membrane proteins are synthesized and modified and is also a major intracellular calcium storage compartment. The glucose regulated protein GRP78, also referred to as the immunoglobulin binding protein, BiP, is a central regulator for ER function due to its role in protein folding and assembly, targeting misfolded protein for degradation, ER calcium binding and controlling the activation of transmembrane ER stress sensors. The activation of the gene encoding GRP78 (Grp78) is widely used as a monitor for ER stress and has led to the discoveries of several unique signaling pathways whereby stress in this critical organelle is transmitted to the nucleus to initiate the UPR. Further, due to its anti-apoptotic property, stress induction of GRP78 represents an important pro-survival component of the UPR. As a master regulator of ER function, GRP78 is uniquely poised to have a major role in regulating cellular homeostasis and the balance between cancer cell death and aggressive growth, as well as modulating the sensitivity to chemotherapeutic agents. During the past grant period, we discovered that histone deacetylase (HDAC) inhibitors are novel inducers of Grp78 transcription and act synergistically with ER stress inducers resulting in upregulation of GRP78. Since HDAC inhibitors are currently being exploited as a promising new class of anti-cancer agents, we have discovered a novel UPR target affected by these compounds. The central hypothesis of the current proposal is that Grp78 transcription is regulated by the acetylation of chromatin and transcription factors binding to the Grp78 promoter, and that changes in GRP78 expression influence the development of tumors and their responses to therapeutic intervention by HDAC inhibitors. Through genetic targeting, we have created novel mouse models where GRP78 expression is reduced or can be knocked out in specific tissues and this will allow us to test directly the role of GRP78 in the pathogenesis of cancer. We have three specific aims. In Aim 1, we will determine the mechanisms whereby HDAC inhibitors activate Grp78 transcription. In Aim 2, we will determine whether enhanced-induction of GRP78 by HDAC inhibitors currently being tested in clinical trials confers drug resistance in cancer cells through inhibition of apoptosis. In Aim 3, we will determine whether reduction or conditional knockout of GRP78 will lead to suppression of cancer progression and metastasis. If our hypothesis is correct, it will establish GRP78 as a prognostic marker for cancer progression and resistance against HDAC inhibitor therapy. Further, targeted inhibition of GRP78 could be used to halt tumor progression and overcome resistance to HDAC inhibitor therapy.