From the previous introduction, we can know that UPR can promote cell survival, thereby reducing ER stress and restoring homeostasis. However, long-term UPR activation induces apoptosis via the PERK<\/u><\/a>\u2013eIF2\u03b1<\/u><\/a>\u2013ATF4<\/u><\/a>\u2013CHOP <\/u><\/a>pathway. Studies have shown that the CHOP encoded by the gene DDIT3 can induce the expression of pro-apoptotic genes (such as DR5<\/u><\/a>, TRB3<\/u><\/a>, BIM<\/u><\/a>\u00a0and PUMA), and inhibit the expression of BCL2<\/u><\/a>, thereby triggering apoptosis when the ER stress is triggered. In addition, ATF4-CHOP heterodimer also initiates the restoration of mRNA translation, resulting in increased protein synthesis, ATP depletion, oxidative stress and cell death. If the Ddit3 gene is deleted from the cell, ER stress causes less protein aggregation in the endoplasmic reticulum and reduces oxidative stress and apoptosis. If any other UPR gene is deleted, this will not happen instead. In addition, CHOP also activates ER oxidase 1\u03b1 (ERO1\u03b1), an oxidoreductase that mediates the transfer of electrons to molecular oxygen during the formation of disulfide bonds to produce hydrogen peroxide. This reaction increases the ability to generate reactive oxygen species (ROS) from the ER and inositol-1,4,5-triphosphate receptor (IP3R) -mediated Ca2 +<\/sup>\u00a0efflux. Ca2 +<\/sup>\u00a0released from ER is absorbed by mitochondria through the ER membrane associated with mitochondria, thereby promoting mitochondrial ROS production through different mechanisms. The flux of Ca2 +<\/sup>\u00a0between the endoplasmic reticulum and mitochondria may combine the protein folding ATP requirement with the mitochondrial production of ATP. Therefore, endoplasmic reticulum stress causes oxidative stress and impairs mitochondrial function, resulting in cell death in a CHOP-dependent manner.<\/p>\n Cell Growth And Differentiation<\/b><\/strong> Cellular Metabolism<\/b><\/strong><\/p>\n When the researchers discovered that PERK deletion and the mutation of the PERK phosphorylation site of eIF2\u03b1 could cause defects in glucose metabolism, the link between ER stress signals and metabolism was confirmed. ER homeostasis and UPR activation are key to glucose and lipid metabolism. The steady state of blood glucose is strictly controlled by the levels of insulin and glucagon in the blood. ER homeostasis and UPR activation in insulin-secreting beta cells and hepatocytes that respond to insulin and glucagon play an important role in maintaining glucose homeostasis. And related studies have found that each UPR sub-pathway seems to maintain a liposomal homeostasis through different mechanisms.<\/p>\n Protein <\/b><\/strong>S<\/b><\/strong>ecretion<\/b><\/strong> In eukaryotic cells, the endoplasmic reticulum is an organelle involved in protein folding and entering the secretory pathway.\u00a0The destruction of the cellular environment or the increase in protein synthesis often leads to misfolding of proteins in organelles, where misfolded or unfolded proteins accumulate\u2014called endoplasmic reticulum stress, and the accumulated wrong proteins activate adaptive unfolded proteins […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[55],"tags":[62],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.creative-diagnostics.com\/blog\/index.php\/wp-json\/wp\/v2\/posts\/982"}],"collection":[{"href":"https:\/\/www.creative-diagnostics.com\/blog\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.creative-diagnostics.com\/blog\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.creative-diagnostics.com\/blog\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.creative-diagnostics.com\/blog\/index.php\/wp-json\/wp\/v2\/comments?post=982"}],"version-history":[{"count":5,"href":"https:\/\/www.creative-diagnostics.com\/blog\/index.php\/wp-json\/wp\/v2\/posts\/982\/revisions"}],"predecessor-version":[{"id":988,"href":"https:\/\/www.creative-diagnostics.com\/blog\/index.php\/wp-json\/wp\/v2\/posts\/982\/revisions\/988"}],"wp:attachment":[{"href":"https:\/\/www.creative-diagnostics.com\/blog\/index.php\/wp-json\/wp\/v2\/media?parent=982"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.creative-diagnostics.com\/blog\/index.php\/wp-json\/wp\/v2\/categories?post=982"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.creative-diagnostics.com\/blog\/index.php\/wp-json\/wp\/v2\/tags?post=982"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"\"](\"http:\/\/www.creative-diagnostics.com\/blog\/wp-content\/uploads\/2020\/04\/13131414.png\")
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\nCells need a large amount of protein in the process of proliferation and differentiation, which will cause an increase in protein synthesis, which is the main cause of endoplasmic reticulum stress and UPR activation.\u00a0During ER stress, the monitoring mechanism delays the process of ER and cell division.\u00a0It depends on the mitogen-activated protein kinase (MAPK) SLT2, but not on PERK, IRE1\u03b1 and ATF6\u03b1 (UPR sensors).
\nThe discovery of the role of UPR in cell differentiation is demonstrated by the need for the IRE1\u03b1\u2013XBP1 pathway in plasma cell differentiation.\u00a0Since cell differentiation is related to the six-fold expansion of ER, the IRE1\u03b1\u2013XBP1 pathway is required for the expansion of the secretory pathway in cells with large amounts of protein secretion.\u00a0Interestingly, \u00a0the increase of immunoglobulins load is not reason of the activation of the IRE1\u03b1\u2013XBP1 pathway .\u00a0Instead, it is caused by a differentiation-dependent signal from the B cell receptor that upregulates genes encoding components such as secretory pathways and plasma cell transcription factors, such as Mist1.\u00a0Surprisingly, deleting PERK, eIF2\u03b1-P or ATF6\u03b1 did not cause defects in plasma cell differentiation.\u00a0In addition, XBP1 can induce a wide range of secretory pathway genes, as well as increased endoplasmic reticulum and lysosomal protein content, mitochondrial quality and function, ribosome number, and protein synthesis levels.\u00a0Therefore, the IRE1\u03b1\u2013XBP1 pathway significantly promotes the characteristic phenotypes of specialized secretory cells, such as gastric zymogen cells, \u03b2 cells, and intestinal Paneth cells.<\/p>\n
\nER is responsible for post-translational modification, folding and transportation of secreted proteins (such as cytokines and hormones).\u00a0Endoplasmic reticulum stress inhibits the synthesis and secretion of secreted proteins through various mechanisms.\u00a0A well-studied example is insulin.\u00a0In beta cells, proinsulin interacts with many ER proteins to promote their folding and transport. For example, embryo knockout of XBP1 significantly impaired proinsulin processing. Because increased ER pressure and excessive activation of IRE1\u03b1 induced RIDD, which degrades mRNAs20 encoding proinsulin processing enzymes.\u00a0Therefore, during the transcription, translation, and secretion stages, endoplasmic reticulum stress and UPR activation affect insulin levels.\u00a0Similarly, endoplasmic reticulum stress and the UPR pathway also affect other secreted proteins at the level of transcription or translation.\u00a0Because these secreted proteins affect the function of distant organs, endoplasmic reticulum stress not only damages the survival and function of secreted cells, but also affects the entire organism.<\/p>\n","protected":false},"excerpt":{"rendered":"