Abstract 1981 FicD Sensitizes Cellular Response to Glucose Fluctuations in Mouse Embryonic Fibroblasts

During homeostasis, the endoplasmic reticulum (ER) maintains productive transmembrane and secretory protein folding that is vital for proper cellular function. The ER-resident chaperone, BiP, plays a pivotal role in managing ER stress induced by the accumulation of unfolded proteins. BiP function is regulated by FicD-mediated AMPylation and deAMPylation in response to changes in ER stress. Though AMPylation of BiP is predicted to function as a molecular rheostat for induction of UPR signaling, little is known about the molecular consequences of loss of FicD. In this study, we show that mouse embryonic fibroblasts (MEFs) in the presence and absence of FicD exhibit distinct molecular responses to pharmacologically and metabolically induced ER stress. Using a variety of molecular and omics tools, we observe both pharmacological ER stress inducers and the metabolic stress induced by glucose starvation leads to robust unfolded protein response (UPR) in both cell types, albeit to a different extent. Notably, wildtype MEFs respond to pharmacological ER stress inducers by downregulating BiP AMPylation, whereas they respond to metabolic stress induced by glucose starvation by upregulating the BiP AMPylation. Overall, the deletion of FicD dampens the UPR, alters the cell stress recovery response, presents widespread gene expression changes, and exhibits unconstrained protein secretion. Our findings not only shed light on the multifaceted role of FicD within the ER but also demonstrate that beyond its involvement in ER stress management, FicD influences the cellular response to stress. National Institutes of Health MIRA R35GM134945 Welch Foundation grant I-156 Once Upon a Time Foundation.