Proteostasis, AMPylation and the Unfolded Protein repsonse (UPR)

 描述（由申请人提供）：通常破坏多种细胞过程以促进癌细胞增殖，其中之一是内质网（ER）中发生的未折叠蛋白反应（UPR）。在正常细胞中，由于肿瘤环境中常见的各种原因（例如葡萄糖水平改变，氧化还原状态，钙水平和化学应激源），不正确折叠或糖基化的蛋白质偶尔会在ER中积累。细胞激活UPR以防止未折叠蛋白质的积累，这最终导致蛋白质毒性和细胞死亡。重要的是，BiP（内质网中的一种必需伴侣蛋白）的表达增加是多种癌症中这种生存机制的关键因素。我们最近发现了一种新的BiP调节形式，即通过蛋白质FicD进行的AMP化。我们观察到FicD在正常生长条件下在BiP的ATP结合位点附近的苏氨酸上添加了一个腺苷酸（AMP）分子。这种修饰在多种ER应力诱导条件下迅速消失。我们假设这种可逆的修饰抑制了一部分细胞BiP的伴侣蛋白活性，并且这种抑制被缓解以增加ER应激期间活性伴侣蛋白的量并促进细胞存活。我们的计划是表征FicD介导的AMPylation对BiP的影响，并确定脱AMPylating酶是否是可行的抑制靶标。我们想了解这个信号系统中涉及的基本机制和机制。这些研究将对理解该系统如何在蛋白质稳态（proteostasis）被破坏的细胞中被破坏产生重大影响，例如癌症、糖尿病、蛋白质加工障碍和衰老。

 DESCRIPTION (provided by applicant): A variety of cellular processes are commonly subverted to encourage the proliferation of cancer cells, one of which is the unfolded protein response (UPR) that occurs in the endoplasmic reticulum (ER). In normal cells, improperly folded or glycosylated proteins will occasionally accumulate in the ER due to a variety of causes that are common in the tumor milieu (examples include altered glucose levels, redox state, calcium levels, and chemical stressors). The cell activates the UPR to prevent accumulation of unfolded proteins, which eventually leads to proteotoxicity and cell death. Importantly, heightened expression of BiP, an essential chaperone protein in the Endoplasmic Reticulum, is a critical factor for this survival mechanism in a variety of cancers. We have recently discovered a new form of BiP regulation, AMPylation by the protein FicD. We observe that FicD adds an adenosine monophosphate (AMP) molecule to a threonine near the ATP binding site of BiP during normal growth conditions. This modification rapidly disappears under multiple ER stress-inducing conditions. We hypothesize that this reversible modification inhibits the chaperone activity of a portion of cellular BiP, and this inhibition is relieved to increase the amount of acive chaperone during ER stress and promote cell survival. Our plan is to characterize the effect of FicD-mediated AMPylation on BiP and determine if the deAMPylating enzyme is a viable inhibition target. We want to understand the basic machinery and mechanisms involved in this signaling system. These studies will have great impact on the understanding of how this system is corrupted in cells with disrupted protein homeostasis (proteostasis), such as cancer, diabetes, prtein processing disorders and aging.