Membrane protein CNNM4–dependent Mg2+ efflux suppresses tumor progression
Yosuke Funato, … , Kazuya Kikuchi, Hiroaki Miki
Yosuke Funato, … , Kazuya Kikuchi, Hiroaki Miki
Published October 27, 2014
Citation Information: J Clin Invest. 2014;124(12):5398-5410. https://doi.org/10.1172/JCI76614.
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Research Article Oncology

Membrane protein CNNM4–dependent Mg2+ efflux suppresses tumor progression

Abstract

Intracellular Mg2+ levels are strictly regulated; however, the biological importance of intracellular Mg2+ levels and the pathways that regulate them remain poorly understood. Here, we determined that intracellular Mg2+ is important in regulating both energy metabolism and tumor progression. We determined that CNNM4, a membrane protein that stimulates Mg2+ efflux, binds phosphatase of regenerating liver (PRL), which is frequently overexpressed in malignant human cancers. Biochemical analyses of cultured cells revealed that PRL prevents CNNM4-dependent Mg2+ efflux and that regulation of intracellular Mg2+ levels by PRL and CNNM4 is linked to energy metabolism and AMPK/mTOR signaling. Indeed, treatment with the clinically available mTOR inhibitor rapamycin suppressed the growth of cancer cells in which PRL was overexpressed. In ApcΔ14/+ mice, which spontaneously form benign polyps in the intestine, deletion of Cnnm4 promoted malignant progression of intestinal polyps to adenocarcinomas. IHC analyses of tissues from patients with colon cancer demonstrated an inverse relationship between CNNM4 expression and colon cancer malignancy. Together, these results indicate that CNNM4-dependent Mg2+ efflux suppresses tumor progression by regulating energy metabolism.

Authors

Yosuke Funato, Daisuke Yamazaki, Shin Mizukami, Lisa Du, Kazuya Kikuchi, Hiroaki Miki

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Figure 8

Genetic ablation of CNNM4 promotes cancer malignancy.

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Genetic ablation of CNNM4 promotes cancer malignancy. (A) Macroscopic vi...
(A) Macroscopic views of the resected intestines of ApcΔ14/+ Cnnm4+/+ and ApcΔ14/+ Cnnm4–/– mice at 7 months of age. Polyps are indicated by arrows. Scale bar: 5 mm. (B) The size of each polyp was measured, and the size distributions of each mouse are shown (14 ApcΔ14/+ Cnnm4+/+ mice and 17 ApcΔ14/+ Cnnm4–/– mice). Black bars indicate the mean ± SEM. *P < 0.05 by 2-tailed Student’s t test. (C) Magnesium levels in the polyps were measured (≥3 per mouse), and the average levels for each mouse are shown (8 ApcΔ14/+ Cnnm4+/+ mice and 12 ApcΔ14/+ Cnnm4–/– mice). Black bars indicate the mean ± SEM. **P < 0.01 by 2-tailed Student’s t test. (D and E) Sections of the intestinal polyps were subjected to H&E staining, and the representative results are shown in D. Dotted lines indicate the boundaries between the epithelial layer and the smooth muscle layer, and arrows indicate adenocarcinomas that extended into the smooth muscle layer. Scale bar: 300 μm. The proportion of adenocarcinomas to total polyps was quantified for each mouse and is shown in E (7 mice for each genotype). Black bars indicate the mean ± SEM. ***P < 0.001 by 2-tailed Student’s t test. (F) Serial sections of the intestinal polyps from ApcΔ14/+ Cnnm4–/– mice were subjected to H&E (left) or immunofluorescence staining with anti–β-catenin (green), anti–α-SMA (red), and DAPI (blue) (right). Scale bars: 50 μm.