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.
We have discovered that a protein called FicD may be used to inhibit another important protein, called BiP(GRP78). BiP is an essential chaperone protein in the endoplasmic reticulum that helps to maintain homeostasis in healthy cells. It is a key player for the unfolded protein response and we speculate the regulation of BiP by FicD is essential for maintaining homeostasis. We plan to study how FicD turns BiP 'off' and discover how another enzyme turns BiP 'on', so that we can understand that basic machinery used by this signaling system. These studies will have great impact in determining how this system is corrupted in cells with disrupted protein homeostasis (proteostasis), such as cancer, diabetes, protein processing disorders and aging.