Molecular function and biological importance of CNNM family Mg2+ transporters.

Cyclin M (CNNM) family proteins are evolutionarily conserved Mg2+ transporters. They extrude Mg2+ from cells and maintain intracellular Mg2+ levels within the normal range. Moreover, they play an important role in Mg2+ (re)absorption in the intestine and kidney by mediating the directional transport of Mg2+ across epithelial tissue from the tubular lumen to the body inside. Mg2+ efflux is suppressed by the direct binding with phosphatase of regenerating liver (PRL), and the formation of the complex is dynamically regulated by cysteine phosphorylation of PRL. The dysfunction of CNNM family proteins is responsible for inherited hypomagnesemia, as well as various intractable diseases, such as cancer and hypertension. Through multiple functional analyses of CNNM family proteins, the biomedical significance of the proper regulation of Mg2+ levels has been elucidated.