Only properly folded proteins are secreted with maintenance of the plasma membrane structure and ER folding capacity being under ER homeostatic control. Misfolded proteins accumulate in the lumen of the ER due to high protein folding demand on the ER. The ER is responsible for the folding and then delivery of proteins via the secretory pathway to a functional site.
Prolonged adverse conditions results in the death of the cell by the autophagic process.
Autophagy is also induced by the formation and collection of misfolded proteins in the endoplasmic reticulum (ER) which causes ER-stress within the cell. The process of autophagy is a cell survival mechanism that occurs when the cell is under stress, via external environmental pressures, including the lack of nutrients, or via the internal microenvironment of the cell, including the replacement of old and defective organelles such as mitochondria. Thus it is unclear whether the process protects or causes diseases such as cancer and neurodegenerative disorders. This process generates ATP, which may delay cell death if the cell is under nutrient depleted conditions leading to the survival of the cell. This then fuses with nearby lysosomes, giving rise to an autolysosome, where the intracellular components are degraded by hydrolytic enzymes. During the formation of the autophagosome structure, organelles such as mitochondria, parts of the ER and Golgi apparatus are engulfed by the autophagosome with the final closure of the double membrane structure occurring next. The formation of the autophagosome double membrane structure within the cytoplasm is thought to be formed from pre-existing membranes within the cell, although it is unknown whether the Golgi apparatus, endoplasmic reticulum (ER) or mitochondria are used preferentially to form the autophagosome structure. Cytoplasm, misfolded protein aggregates, dysfunctional mitochondria and stressed endoplasmic reticulum (ER) are engulfed by the formation of a double membrane forming an autophagosome. The mechanism of organelle autophagy in cells undergoing macro-autophagy (from here on termed autophagy) is poorly understood. The term autophagy, (Type II Apoptosis) is derived from the Greek roots “auto” (self) and “phagy” (eat) and was first coined by De Duve in 1967 to epitomise this type of cell death.
0 kommentar(er)
