Calcium signaling and endoplasmic reticulum stress.

Cellular homeostasis is essential for healthy functioning of cells and tissues as well as proper organ development and maintenance. A disruption in cellular homeostasis triggers stress responses including the unfolded protein response (UPR), an endoplasmic reticulum (ER) stress coping response. There is increasing evidence that Ca signaling plays a pivotal role in stress responses, as Ca is involved many cellular activities. The ER is the main Ca storage organelle and the source of Ca for intracellular signaling. The ER is equipped with a variety of stress sensors and contains many Ca handling proteins that support a role for Ca in stress sensing and in coordinating strategies required to cope with cellular stress. Maintenance of ER Ca homeostasis is therefore vital in sustaining cellular functions especially during times of cellular stress. Here we focus on selected aspects of ER Ca homeostasis, its links to ER stress, and activation of the ER stress coping response.