A Novel Link between Fic (Filamentation Induced by cAMP)-mediated Adenylylation/AMPylation and the Unfolded Protein Response

• Published in: The Journal of biological chemistry 2015-03, Vol.290 (13), p.8482-8499
• Main Authors: Sanyal, Anwesha, Chen, Andy J., Nakayasu, Ernesto S., Lazar, Cheri S., Zbornik, Erica A., Worby, Carolyn A., Koller, Antonius, Mattoo, Seema
• Format: Article
• Language: English
• Subjects: Activating Transcription Factor 6 - metabolism; Adenylylation; AMP; AMPylation; Apoptosis; BiP; Carrier Proteins - physiology; Cell Survival; eIF-2 Kinase - metabolism; Endoplasmic Reticulum - metabolism; Filamentation Induced by cAMP; Glycosylation; Heat-Shock Proteins - metabolism; HEK293 Cells; HeLa Cells; Humans; Hydrophobic and Hydrophilic Interactions; HYPE/FicD; MCF-7 Cells; Membrane Proteins - physiology; Nucleotidyltransferases - physiology; Post-translational Modification; Protein Processing, Post-Translational; Protein Structure, Tertiary; Protein Transport; Signal Transduction; Signaling; Unfolded Protein Response; Unfolded Protein Response (UPR); Up-Regulation
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M114.618348

The maintenance of endoplasmic reticulum (ER) homeostasis is a critical aspect of determining cell fate and requires a properly functioning unfolded protein response (UPR). We have discovered a previously unknown role of a post-translational modification termed adenylylation/AMPylation in regulating signal transduction events during UPR induction. A family of enzymes, defined by the presence of a Fic (filamentation induced by cAMP) domain, catalyzes this adenylylation reaction. The human genome encodes a single Fic protein, called HYPE (Huntingtin yeast interacting protein E), with adenylyltransferase activity but unknown physiological target(s). Here, we demonstrate that HYPE localizes to the lumen of the endoplasmic reticulum via its hydrophobic N terminus and adenylylates the ER molecular chaperone, BiP, at Ser-365 and Thr-366. BiP functions as a sentinel for protein misfolding and maintains ER homeostasis. We found that adenylylation enhances BiP's ATPase activity, which is required for refolding misfolded proteins while coping with ER stress. Accordingly, HYPE expression levels increase upon stress. Furthermore, siRNA-mediated knockdown of HYPE prevents the induction of an unfolded protein response. Thus, we identify HYPE as a new UPR regulator and provide the first functional data for Fic-mediated adenylylation in mammalian signaling. Background: Adenylylation/AMPylation by Fic proteins alters cellular signaling. HYPE, the sole human Fic protein, is an adenylyltransferase. Results: BiP is identified as a substrate for HYPE. HYPE adenylylates BiP and is required for UPR induction. Conclusion: HYPE regulates ER homeostasis. Significance: Adenylylation/AMPylation is a new mode of UPR regulation. This is the first demonstration of a physiological role for human HYPE.