The endoplasmic reticulum is a focal point for co-ordination of cellular activity

Bootman, Martin; Petersen, Ole H. and Verkhratsky, Alexei (2002). The endoplasmic reticulum is a focal point for co-ordination of cellular activity. Cell Calcium, 32(5-6) pp. 231–234.

DOI: https://doi.org/10.1016/S0143-4160(02)00200-2

Abstract

The endoplasmic reticulum (ER) is an extensive organelle network formed by cisternae and microtubules, which stretches from the nuclear envelope to the cell surface in all eukaryotic cells. For many years, the ER was accepted as an intracellular “skeleton” and the place of protein synthesis. Recent discoveries have contributed to a growing appreciation for the role of the ER in co-ordinating extracellular and intracellular signals with long-term adaptive responses. Firstly, the ER was identified as a source for fast physiological signalling as a dynamic Ca²⁺ reservoir, which can be activated as a consequence of both electrical and chemical and cell stimulation. As such, the ER plays a crucial role in the propagation of cytosolic Ca²⁺ waves and and it can also function as an intracellular Ca²⁺ tunnel, allowing movement of ions through its lumen. Secondly, the classical work of Palade demonstrated that the ER serves as a common transport route by which secretory proteins are delivered to their destination. Further developments in this area have shown that the ER acts as a specialised environment for post-translational processing and targeting of many other types of proteins. Numerous chaperones resident within the ER lumen form various conformational intermediates, which determine the trafficking of proteins to the place of their final abode. Finally, it has become clear, that not only does the ER provide a place for protein folding and transport, but it also actively co-ordinates this process with the cellular status and physiological activity. This co-ordination is achieved by several signalling pathways originating from within the ER, thus coupling processes in the ER with those in the nucleus, which regulate gene expression. Consequently, the ER network can be regarded as a multi-functional organelle able to sense, convey, integrate and generate signalling events that are profoundly important for cellular physiology.

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