Impaired basolateral sorting of pro-EGF causes isolated recessive renal hypomagnesemia
Wouter M. Tiel Groenestege, … , Nine V. Knoers, René J. Bindels
Wouter M. Tiel Groenestege, … , Nine V. Knoers, René J. Bindels
Published August 1, 2007
Citation Information: J Clin Invest. 2007;117(8):2260-2267. https://doi.org/10.1172/JCI31680.
View: Text | PDF
Research Article Article has an altmetric score of 8

Impaired basolateral sorting of pro-EGF causes isolated recessive renal hypomagnesemia

Abstract

Primary hypomagnesemia constitutes a rare heterogeneous group of disorders characterized by renal or intestinal magnesium (Mg2+) wasting resulting in generally shared symptoms of Mg2+ depletion, such as tetany and generalized convulsions, and often including associated disturbances in calcium excretion. However, most of the genes involved in the physiology of Mg2+ handling are unknown. Through the discovery of a mutation in the EGF gene in isolated autosomal recessive renal hypomagnesemia, we have, for what we believe is the first time, identified a magnesiotropic hormone crucial for total body Mg2+ balance. The mutation leads to impaired basolateral sorting of pro-EGF. As a consequence, the renal EGFR is inadequately stimulated, resulting in insufficient activation of the epithelial Mg2+ channel TRPM6 (transient receptor potential cation channel, subfamily M, member 6) and thereby Mg2+ loss. Furthermore, we show that colorectal cancer patients treated with cetuximab, an antagonist of the EGFR, develop hypomagnesemia, emphasizing the significance of EGF in maintaining Mg2+ balance.

Authors

Wouter M. Tiel Groenestege, Stéphanie Thébault, Jenny van der Wijst, Dennis van den Berg, Rob Janssen, Sabine Tejpar, Lambertus P. van den Heuvel, Eric van Cutsem, Joost G. Hoenderop, Nine V. Knoers, René J. Bindels

×

Figure 3

Electrophysiological analysis of pro-EGF and pro-EGF–P1070L on TRPM6 channel activity.

Options: View larger image (or click on image) Download as PowerPoint
Electrophysiological analysis of pro-EGF and pro-EGF–P1070L on TRPM6 cha...
(A) Average time course of outward (at +80 mV) current densities from HEK293 cells transfected with TRPM6 in control conditions (open circles) and after EGF treatment (30 minutes, 10 nM, filled circles) in comparison with mock-transfected cells without EGF treatment (triangles) and after EGF stimulation (filled triangles). n = 17–20. (B) Dose-response curve of EGF-induced current in TRPM6-transfected HEK293 cells indicating half maximal effective concentration of 1.7 nM. n = 11–14. (C) Histogram presenting the current densities at +80 mV of TRPM6-transfected cells (200 seconds after establishment of the whole-cell configuration) treated with mock (mock), pro-EGF (EGF WT) or pro-EGF–P1070L (EGF-P1070L) supernatant. All treatments were performed for 30 minutes at 37°C. White bars indicate experimental conditions in which HEK293 cells were transfected with mock DNA whereas black bars indicate HEK293 cells transfected with TRPM6. Asterisk indicates significance in comparison with nontreated TRPM6-transfected cells. P = 0.024; n = 6. (D) Supernatants of mock-, pro-EGF–, or pro-EGF–P1070L–transfected HEK293 cells were analyzed by ELISA. Asterisk indicates mock and pro-EGF–P1070L supernatant were significantly different from EGF supernatant. P = 0.006; n = 4. (E) Histogram summarizing the current density (pA/pF) at +80 mV (200 seconds after break-in) of HEK293 cells treated with the apical or basolateral supernatant of MDCK cells stably transfected with either wild-type pro-EGF, pro-EGF–P1070L, or mock DNA (30 minutes, 37°C). White bars indicate experimental conditions in which HEK293 cells were transfected with mock DNA whereas black bars indicate HEK293 cells transfected with TRPM6. Crosses indicate significance in comparison with the mock treatment at the apical side (wild-type pro-EGF apical, P = 0.0001, n = 6; pro-EGF–P1070L apical, P = 0.029, n = 6), and pound symbol represents significance in comparison with the mock treatment at the basolateral side (wild-type pro-EGF basolateral P = 0.031, n = 6). (F) Schematic model illustrating how pro-EGF–P1070L mutation results in IRH. The pro-EGF–P1070L mutation leads to impaired basolateral sorting of pro-EGF, resulting in abrogated stimulation of the EGFR localized at the basolateral membrane. Activation of the EGFR in DCT by EGF is necessary to prevent renal Mg2+ wasting by stimulation of the epithelial Mg2+ channel TRPM6.