How is Ire1 activated?
Ire1 is activated in response to accumulation of misfolded proteins within the endoplasmic reticulum as part of the unfolded protein response (UPR). It is a unique enzyme, possessing both kinase and RNase activity that is required for specific splicing of Xbp1 mRNA leading to UPR activation.
How is Ire1 regulated by BiP?
One model proposes that Ire1 activity is mainly regulated by the ER-resident chaperone BiP (Kar2 in yeast). In this model, BiP inhibits Ire1 activity by binding to it in the absence of stress. During stress, BiP is titrated away by unfolded proteins, leaving Ire1 free to oligomerize and activate.
What causes unfolded protein response?
Multiple perturbations can cause accumulation of unfolded proteins in the endoplasmic reticulum (ER) and activate the unfolded protein response (UPR). These conditions include hypoxia, glucose deprivation, oxidative stress, viral infection, high fat or cholesterol, and mutations in specific proteins.
What are the consequences of unfolded protein response signaling?
This UPR signaling is adaptive and restored the normal function of cells by decreasing protein synthesis, increasing the folding capacity of ER and degradation of misfolded proteins. If the stress condition is overwhelmed, then UPR signaling shifts to apoptotic pathways.
What is the function of thapsigargin?
Thapsigargin is an inhibitor of sarco endoplasmic reticulum Ca2 ATPase (SERCA). It pumps calcium ions from the cytoplasm into the lumen of the endoplasmic reticulum (ER) and thapsigargin. This process will causes an increase in the cytoplasmic calcium levels while also depleting ER stores.
What is Tunicamycin used for?
Tunicamycin is the most common agent used to study the effects of nucleoside antibiotics on the kidney. It is also commonly used in vitro to study the effects of ER stress in various cell types (Bassik and Kampmann, 2011).
Is IRE1 a kinase?
Ire1, an ER-resident transmembrane kinase/RNase, senses the protein folding status inside the ER. When activated, Ire1 oligomerizes and trans-autophosphorylates, activating its RNase and initiating a nonconventional mRNA splicing reaction.
What are ER stressors?
ER stress occurs when the capacity of the ER to fold proteins becomes saturated. ER stress may be caused by factors that impair protein glycosylation or disulfide bond formation, or by overexpression of or mutations in proteins entering the secretory pathway.
Who discovered the unfolded protein response?
One day in October, 1996, somebody called to say that Peter Walter talked in a meeting about his identification of Hac1p as a yeast UPR-specific transcription factor as well as his discovery of Ire1p-dependent HAC1 mRNA splicing.
Which amino acids can be ubiquitinated?
Ubiquitin has seven lysine residues and an N-terminus that serves as points of ubiquitination; they are K6, K11, K27, K29, K33, K48, K63 and M1, respectively. Lysine 48-linked chains were the first identified and are the best-characterised type of ubiquitin chain.
What is the role of Calreticulin?
Function. Calreticulin binds to misfolded proteins and prevents them from being exported from the endoplasmic reticulum to the Golgi apparatus. A similar quality-control molecular chaperone, calnexin, performs the same service for soluble proteins as does calreticulin, however it is a membrane-bound protein.
Does protein folding require energy?
Hydrophobic effect Since it is known that protein folding is a spontaneous reaction, then it must assume a negative Gibbs free energy value.
How is phosphorylation of Ire1 related to molecular weight shift?
We demonstrated that the molecular weight shift of IRE1 was a result of phosphorylation by performing a pulse-chase experiment coupled with digestion of the immunoprecipitated IRE1 using λ protein phosphatase (λPPase; Fig. 1 C ).
What is the role of Ire1 in bone marrow?
The ER stress sensor, IRE1, is critical for B cells. Normal B cell development in the bone marrow requires IRE1 ( Zhang et al., 2005 ). Upon encountering its cognate antigen, a B cell differentiates into a plasma cell, which can produce large quantities of high-affinity antibodies against the antigen.
How does the dual cytosolic domain of Ire1 act in vivo?
We also discovered that the dual cytosolic domains of plant IRE1s act in vivo in a mechanism consistent with IRE1p and hIRE1 and that plant IRE1B not only interacts with IRE1p but also forms typical IRE1 dynamic foci in yeast.
How does the RNase of Ire1 regulate Ridd?
Other than splicing XBP1 mRNA, the RNase of IRE1 can rapidly cleave a subset of mRNAs and so halts the production of proteins that challenge the ER. This mechanism is known as regulated IRE1-dependent decay (RIDD; Hollien and Weissman, 2006 ).