title: EGF increases TRPM6 activity and surface expression.
abstract: Recent identification of a mutation in the EGF gene that causes isolated recessive hypomagnesemia led to the finding that EGF increases the activity of the epithelial magnesium (Mg2+) channel transient receptor potential M6 (TRPM6). To investigate the molecular mechanism mediating this effect, we performed whole-cell patch-clamp recordings of TRPM6 expressed in human embryonic kidney 293 (HEK293) cells. Stimulation of the EGF receptor increased current through TRPM6 but not TRPM7. The carboxy-terminal alpha-kinase domain of TRPM6 did not participate in the EGF receptor-mediated increase in channel activity. This activation relied on both the Src family of tyrosine kinases and the downstream effector Rac1. Activation of Rac1 increased the mobility of TRPM6, assessed by fluorescence recovery after photobleaching, and a constitutively active mutant of Rac1 mimicked the stimulatory effect of EGF on TRPM6 mobility and activity. Ultimately, TRPM6 activation resulted from increased cell surface abundance. In contrast, dominant negative Rac1 decreased TRPM6 mobility, abrogated current development, and prevented the EGF-mediated increase in channel activity. In summary, EGF-mediated stimulation of TRPM6 occurs via signaling through Src kinases and Rac1, thereby redistributing endomembrane TRPM6 to the plasma membrane. These results describe a regulatory mechanism for transepithelial Mg2+ transport and consequently whole-body Mg2+ homeostasis.
authors.affiliation: Department of Physiology, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, Nijmegen, Netherlands.
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Thebault
authors.forename: R Todd
authors.initials: RT
authors.lastname: Alexander
authors.forename: Wouter M
authors.initials: WM
authors.lastname: Tiel Groenestege
authors.forename: Joost G
authors.initials: JG
authors.lastname: Hoenderop
authors.forename: René J
authors.initials: RJ
authors.lastname: Bindels
mesh_terms: D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D004815:Epidermal Growth Factor / Q000378:metabolism*; D066246:ErbB Receptors / Q000502:physiology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000502:physiology; D006801:Humans; D008274:Magnesium / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D015398:Signal Transduction; D050053:TRPM Cation Channels / Q000032:analysis / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000502:physiology; D019061:src-Family Kinases / Q000502:physiology
chemical_list: D050053:TRPM Cation Channels; C459082:TRPM6 protein, human; D004815:Epidermal Growth Factor; D019869:Phosphatidylinositol 3-Kinases; D066246:ErbB Receptors; D019061:src-Family Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D020830:rac1 GTP-Binding Protein; D008274:Magnesium; D002118:Calcium