Djalila Mekahli, Geert Bultynck, Jan B. Parys, Humbert De Smedt, and Ludwig Missiaen
Laboratory of Molecular and Cellular Signaling, Department of Molecular Cell Biology,
K.U.Leuven Campus Gasthuisberg O&N I, Herestraat 49, 3000 Leuven, Belgium

Correspondence: Ludwig.Missiaen@med.kuleuven.be

The endoplasmic reticulum (ER) as an intracellular Ca²+ store not only sets up cytosolic Ca²+ signals but, among other functions, also assembles and folds newly synthesized proteins. Alterations in ER homeostasis, including severe Ca²+ depletion, are an upstream event in the pathophysiology of many diseases. On the one hand, an insufficient release of activator Ca²+ may no longer sustain essential cell functions. On the other hand, loss of luminal Ca²+ causes ER stress and activates an unfolded protein response, which, depending on the duration and severity of the stress, can reestablish normal ER function or lead to cell death. We will review these various diseases by mainly focusing on the mechanisms that cause ER Ca²+ depletion.