Casein kinase-mediated phosphorylation of serine 839 is necessary for basolateral localization of the Ca

© 2014, Springer-Verlag Berlin Heidelberg. Transient receptor potential melastatin-like 4 (TRPM4) is a Ca<sup>2+</sup>-activated non-selective cation channel expressed in a wide range of human tissues. TRPM4 participates in a variety of physiological processes such as T cell activation, myogenic vasoconstriction, and allergic reactions. TRPM4 Ca<sup>2+</sup> sensitivity is enhanced by calmodulin (CaM) and phosphathydilinositol 4, 5-bisphosphate (PI(4,5)P<inf>2</inf>) binding, as well as, under certain conditions, PKC activation. However, information as to the mechanisms of modulation of this channel remains unknown, including direct identification of phosphorylation sites on TRPM4 and their role in channel features. Here, we use mass-spectrometric-based proteomic approaches (immunoprecipitation and tandem mass spectrometry) to unambiguously identify S839 as a phosphorylation site present on human TRPM4 expressed in a human cell line. Site-directed mutagenesis employing a serine to ala