1- Introduction

2- Unfolded protein response signaling pathway

3- ER stress regulates autophagy and mitochondrial and lysosomal dysfunction in cancer

4- ER stress-mediated oxidative stress and inflammatory responses in cancer

5- Conclusion

References

Abstract

The endoplasmic reticulum (ER) acts as a moving organelle with many important cellular functions. As the ER lacks sufficient nutrients under pathological conditions leading to uncontrolled protein synthesis, aggregation of unfolded/misfolded proteins in the ER lumen causes the unfolded protein response (UPR) to be activated. Chronic ER stress produces endogenous or exogenous damage to cells and activates UPR, which leads to impaired intracellular calcium and redox homeostasis. The UPR is capable of recognizing the accumulation of unfolded proteins in the ER. The protein response enhances the ability of the ER to fold proteins and causes apoptosis when the function of the ER fails to return to normal. In different malignancies, ER stress can effectively induce the occurrence of autophagy in cells because malignant tumor cells need to re-use their organelles to maintain growth. Autophagy simultaneously counteracts ER stress-induced ER expansion and has the effect of enhancing cell viability and non-apoptotic death. Oxidative stress also affects mitochondrial function of important proteins through protein overload. Mitochondrial reactive oxygen species (ROS) are produced by calcium-enhanced ER release. The accumulation of toxic substances in ER and mitochondria in mitochondria destroys basic organelle function. It is known that sustained ER stress can also trigger an inflammatory response through the UPR pathway. Inflammatory response is thought to be associated with tumor development. This review discusses the emerging links between UPR responses and autophagy, oxidative stress, and inflammatory response signals in ER stress, as well as the potential development of targeting this multifaceted signaling pathway in various cancers.

Introduction

The endoplasmic reticulum (ER) is an organelle that forms a large membrane-like structure in its cytoplasm. The membranous structure of ER has a series of functions such as folding of newly synthesized proteins, maintenance of calcium homeostasis and phospholipid synthesis, and regulation of intracellular signaling pathways [1–3]. The structure of ER can be divided into a nuclear envelope domain, which is integrated in rough ER, and an ER domain for the synthesis of ribosomes. It also contains membranes, Golgi, vacuoles, mitochondria, peroxisomes, late endosomes and lysosomes, which act to promote lipid transfer to the membrane for calcium signal transmission [4]. ER is primarily used to transport and integrate proteins (secreted and membrane proteins, respectively), helping them to fold and transport (extracellular or cell membranes), lipid biosynthesis and maintenance of calcium homeostasis. In protein translation, ER is also a site that modifies N-linked glycosylation and is closely related to cellular signaling pathways [5–7]. For example, advanced ER stress hepatocytes have the function of reducing drug toxicity; the secreted proteins are synthesized in large amounts by abundant ER in other cells, and detoxification is exerted; sarcoplasmic reticulum as another special form of ER is more intramuscular cells in Exercise contraction and relaxation play a role [8]. Once the homeostasis is destroyed, the protein cannot be properly folded, including lack of molecular chaperone or cellular energy, as well as Ca2+ deficiency, redox environmental damage, protein variation and disulfide bond reduction [9]. Eukaryotic cells respond rapidly to ER dysfunction through a series of adaptive pathways called ER stress. And activate the unfolded protein reaction (UPR) [10,11].