Homeostasis of the endoplasmic reticulum (ER) is essential for normal cellular functions. reporter and ChIP assays we dissected the Ufm1 promoter and found that Ufm1 was a potential target of Xbp-1 one of NBP35 crucial transcription factors in UPR. We further examined the effect of Xbp-1 deficiency on the expression of the Ufm1 components. Interestingly the expression of Ufm1 Uba5 RCAD/Ufl1 and C53/LZAP in wild-type mouse embryonic fibroblasts (MEFs) was significantly induced by inhibition of vesicle trafficking but the induction was negated by Xbp-1 deficiency. Finally we found that knockdown of the Ufm1 system in U2OS cells brought on UPR and amplification of the ER network. Taken together our study provided critical insight into the regulatory mechanism of the Ufm1 system and established a direct link between this novel Ubl system and the ER network. Introduction The endoplasmic reticulum (ER) is an organelle that Silicristin plays essential functions in lipid biosynthesis protein folding and calcium homeostasis. By adjusting the protein-folding capacity cells maintain homeostatic control of protein influx and secretion thereby ensuring the quality of cell-surface and secreted proteins. Perturbation of the ER homeostasis prospects to ER stress and activation of the Unfolded Protein Response (UPR) [1] [2]. Generally the UPR includes four effector responses. First protein Silicristin synthesis and translocation into the ER is usually attenuated thereby reducing protein weight in the ER. Second expression of chaperone proteins and other proteins that handle unfolded proteins is usually elevated to increase the protein-folding capacity. Third the capacity of ER-associated degradation (ERAD) is usually enhanced to obvious unfolded proteins. Finally if a homeostasis cannot be re-established cells undergo apoptosis. At the molecular level three apical transmission transducers have been recognized including protein kinase RNA-like ER kinase (PERK) inositol-requiring protein-1 (IRE1) and activating transcription factor 6 (ATF6) [3]. IRE1 is usually a type I transmembrane protein that has a stress-sensing lumen domain name and a cytoplasmic portion made up of Silicristin both a Ser/Thr kinase domain name and an endonuclease domain name [4] [5]. Accumulation of unfolded proteins in the ER triggers IRE1’s endonuclease activity that produces a precise cleavage of an intron from X-box-binding protein 1 (Xbp-1) mRNA to generate a potent transcriptional transactivator Xbp-1s [6]-[8]. Xbp-1s subsequently translocates into the nucleus and induces expression of the genes such as chaperones and ERAD components [7] [9]. Much like IRE1 PERK is also a type I transmembrane protein that has a stress-sensing lumen domain name and a cytoplasmic kinase domain name [10]. Upon the ER stress active PERK Silicristin phosphorylates the α-subunit of eukaryotic translation initiation factor-2 (eIF2α) at ser51 which leads to attenuation of translation initiation and global reduction of protein synthesis [11]. The third transducer is usually a bZIP family transcription factor ATF6 that is normally tethered to ER membranes. Under ER stress ATF6 is usually released from your ER and translocates to the Golgi where it is cleaved by proteases (site 1 and site 2 proteases) [12]-[14]. The cytoplasmic portion of ATF6 is usually released and techniques into the nucleus to activate expression of genes that are associated with protein folding and ERAD [15] [16]. Together these cellular signaling pathways alleviate the ER stress and restore the ER homeostasis. Ubiquitin (Ub) and Ubiquitin-like (Ubl) protein modifiers play crucial roles in many cellular processes such as gene expression transmission transduction and cell cycle progression [17]. Human Ubiquitin-fold modifier 1 (Ufm1) is usually a newly recognized Ubl with 85 amino acid residues [18]. Despite a very limited sequence identity (16%) with Ub human Ufm1 displays a solution structure of ubiquitin fold with specific α-linens and an α-helix [19]. However the surface electrostatic potential of human Ufm1 is usually markedly different from those of Ub and NEDD8 and a cluster of the acidic residues in the α1 surface of Ub and NEDD8 are not present in Ufm1 [19]. Ufm1 is usually synthesized as a precursor and is processed by cysteine proteases UfSP1 and UfSP2 at the C-terminus to expose the conserved Gly83 residue [20]. Processed Ufm1 is usually activated by Uba5 the Ufm1 activating enzyme to form Ufm1-Uba5 thioester complex [18]. Activated Silicristin Ufm1 is usually then transferred to the catalytic cysteine of Ufc1 the Ufm1 conjugating enzyme [18]. With the help of E3s Ufm1 is usually presumed to modify its protein targets..