Regulation of the Epithelial Mg2+ Channel TRPM6 by Estrogen and the Associated Repressor Protein of Estrogen Receptor Activity (REA)

The maintenance of the Mg2+ balance of the body is essential for neuromuscular excitability, protein synthesis, nucleic acid stability, and numerous enzymatic systems. The Transient Receptor Potential Melastatin 6 (TRPM6) functions as the gatekeeper of transepithelial Mg2+ transport. However, the molecular regulation of TRPM6 channel activity remains elusive. Here, we identified the repressor of estrogen receptor activity ( REA) as an interacting protein of TRPM6 that binds to the 6(th), 7(th), and 8(th) beta-sheets in its alpha-kinase domain. Importantly, REA and TRPM6 are coexpressed in renal Mg2+-transporting distal convoluted tubules (DCT). We demonstrated that REA significantly inhibits TRPM6, but not its closest homologue TRPM7, channel activity. This inhibition occurs in a phosphorylation-dependent manner, since REA has no effect on the TRPM6 phosphotransferase-deficient mutant (K1804R), while it still binds to this mutant. Moreover, activation of protein kinase C by phorbol 12-myristate 13-acetate-PMA potentiated the inhibitory effect of REA on TRPM6 channel activity. Finally, we showed that the interaction between REA and TRPM6 is a dynamic process, as short-term 17 beta-estradiol treatment disassociates the binding between these proteins. In agreement with this, 17 beta-estradiol treatment significantly stimulates the TRPM6-mediated current in HEK293 cells. These results suggest a rapid pathway for the effect of estrogen on Mg2+ homeostasis in addition to its transcriptional effect. Together, these data indicate that REA operates as a negative feedback modulator of TRPM6 in the regulation of active Mg2+ (re) absorption and provides new insight into the molecular mechanism of renal transepithelial Mg2+ transport.