The function of the endoplasmic reticulum is to fold and secret transmembrane proteins. Proteins in cells provide a variety of functions; such as speeding up chemical reactions through enzymes, protecting the cell against disease through antibodies, and coordinating organism activities with hormones. Proteins are obviously crucial to cells.
However, recent research shows that although proteins are supposed to help cells run efficiently, in some cases, under stress, proteins can cause cell suicide, or apoptosis. Apoptosis is part of the natural cycle of a cell, but in this case, proteins are truncating the cell’s normal cycle, which can even be disease-inducing.
When environmental conditions or genetic factors around the ER go awry, a cellular stress reaction called the Unfolded Protein Response (UPR) either triggers or deactivates DR5, Death Receptor 5 Protein, which can lead to cell suicide. The two main factors which control the UPR are IRE1A and PERK. By activating XBP1, which drives expression of cell-survival genes, IRE1A promotes cell survival. PERK actives CHOP, which in turn activates DR5.
The ER activates UPR in order to alleviate cell stress and return the ER to homeostasis, but this instead can lead to apoptosis.
ER stress is central to many diseases, including neurodegeneration, type II diabetes, cancer, atherosclerosis, and liver disease. This finding is so important because now that scientists have found that IRE1A and PERK are the causes of this response, they can better study the phenomenon.
The idea that an organelle can be stressed is very interesting. I usually think of organelles as having clean structures and clean results, but this story shows that the ER can be overstressed through changing conditions and its actions will reflect this stress.
Another interesting part of this article is that when the ER activates UPR, this will either activate or deactivate the DR5, the cause of cell suicide. In science, we usually think of things as reliable and consistent, but this response to the ER can either save the kill or destroy the cell.
Finally, Cancer is a diseased caused by the over-multiplication of cells. If cell stress leads to cell suicide, then maybe scientists can use their new found understanding of the proteins involved in UPR to figure out a way to destroy cancerous cells.