RGN (Regucalcin) belongs to the SMP-30/CGR1 family. This protein is Ca (2+)-binding protein that does not contain EF-hand motif of Ca (2+)-binding domain. RGN plays a pivotal role in the keep of intracellular Ca2+ homeostasis due to activating Ca2+ pump enzymes in the plasma membrane (basolateral membrane), microsomes (endoplasmic reticulum) and mitochondria of many cells.