Cell-Autonomous (Cell-Intrinsic) Stress Responses

In this chapter, the role of cell-intrinsic stress responses is examined which include autophagic processes, the oxidative stress response, the heat shock response, the unfolded proteins response, and the DNA damage response. Autophagy (macroautophagy, microautophagy, and chaperone-mediated autophagy) is a self-digestive process in response to environmental stress to eukaryotic cells, by which cytoplasmic components are delivered to the lysosome for recycling and degradation. The oxidative stress response is directed against any oxidative stress and is mediated by antioxidative defense systems including antioxidant enzymes such as superoxide dismutase, detoxifying enzymes such as glutathione peroxidase, and energy-dependent efflux pumps. The heat shock response is induced upon exposure of cells to any stress condition and characterized by emission of heat shock proteins which operate as DAMPs to maintain and restore homeostasis. The unfolded protein response is induced by any stress of the endoplasmic reticulum that is perceived by three sensor molecules. Under remediable endoplasmic reticulum stress conditions, the sensors trigger signalling pathways to resolve this stress. However, in severe irremediable endoplasmic reticulum stress, the unfolded protein response may lead to pro-inflammatory and pro-apoptotic responses resulting in regulated cell death. Finally, the DNA damage response is induced by any DNA damage that occurs in a variety of exogenous and endogenous conditions. When successful, this stress response leads to DNA repair and is associated with the emission of various DAMPs which contribute to restoration of homeostasis. When unsuccessful, the DNA damage response, like the unsuccessful unfolded protein response, can result in regulated cell death, either in form of apoptosis or necrosis. Together, the ultimate goal of all the stress responses is to maintain cellular homeostasis and ensure cell integrity. When they fail, the incidence of regulated cell death is frequently observed.