RACK1 Inhibits TRPM6 Activity via Phosphorylation of the Fused α-Kinase Domain

Cao, Gang; Thebault, Stéphanie; Wijst, Jenny van der; Kemp, Annemiete van der; Lasonder, Edwin; Bindels, René J. M.; Hoenderop, Joost G. J.

doi:10.1016/j.cub.2007.12.058

Cited by 64 publications

(64 citation statements)

References 36 publications

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“…Several experiments were conducted to explain the molecular mechanism behind the insensitivity of the TRPM6 variants to insulin. The role of the kinase activity present in TRPM6 was excluded by showing that the phosphotransferase-deficient mutant TRPM6(K 1804 R) was still stimulated by insulin (17). Cross-species sequence alignment of TRPM6 suggested the presence of two potential phosphorylation sites, TRPM6(T 1391 ) and TRPM6 (S 1583 ), in the vicinity of the SNPs.…”

Section: Discussionmentioning

confidence: 99%

Loss of insulin-induced activation of TRPM6 magnesium channels results in impaired glucose tolerance during pregnancy

Nair

Hocher

Verkaart

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

126

137

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Hypomagnesemia affects insulin resistance and is a risk factor for diabetes mellitus type 2 (DM2) and gestational diabetes mellitus (GDM). Two single nucleotide polymorphisms (SNPs) in the epithelial magnesium channel TRPM6 (V 1393 I, K 1584 E) were predicted to confer susceptibility for DM2. Here, we show using patch clamp analysis and total internal reflection fluorescence microscopy, that insulin stimulates TRPM6 activity via a phosphoinositide 3-kinase and Rac1-mediated elevation of cell surface expression of TRPM6. Interestingly, insulin failed to activate the genetic variants TRPM6 (V 1393 I) and TRPM6(K 1584 E), which is likely due to the inability of the insulin signaling pathway to phosphorylate TRPM6(T 1391 ) and TRPM6(S 1583 ). Moreover, by measuring total glycosylated hemoglobin (TGH) in 997 pregnant women as a measure of glucose control, we demonstrate that TRPM6(V 1393 I) and TRPM6(K 1584 E) are associated with higher TGH and confer a higher likelihood of developing GDM. The impaired response of TRPM6(V 1393 I) and TRPM6(K 1584 E) to insulin represents a unique molecular pathway leading to GDM where the defect is located in TRPM6. G estational diabetes mellitus (GDM) is a condition in which women without previously diagnosed diabetes exhibit high blood glucose levels during pregnancy. Babies born to mothers with GDM are typically at increased risk of large for gestational age (LGA), low blood sugar, and jaundice (1). Women with GDM are at a higher risk for preeclampsia and Caesarean section (1) as well as developing diabetes mellitus type 2 (DM2) later in life (2). GDM affects 3-10% of pregnancies, depending on the population studied. No specific cause has been identified, but it is believed that in particular sex hormones (i.e., estrogen, progesterone, prolactin) produced during pregnancy increases a woman's resistance to insulin, resulting in impaired glucose tolerance (1, 3). Moreover, pregnant women are prone to lose magnesium (Mg 2+ ). Bardicef et al. (4) demonstrated that pregnancy itself is a condition of intracellular Mg 2+ depletion. This depletion was more pronounced in women affected by GDM. The elevation in female hormones as well as Mg 2+ deficiency during pregnancy impairs insulin sensitivity and these disturbances may even act synergistically.There is growing evidence suggesting that Mg 2+ deficiency is a significant risk factor for the development of insulin resistance and subsequently hypertension and DM2 (5-8), but the underlying molecular mechanism is unknown. The first evidence suggesting a direct connection between Mg 2+ deficiency and the occurrence of metabolic diseases came from the identification of a monogenic disease primarily characterized by significant hypomagnesemia that was caused by a mutation in a mitochondrial tRNA (9). Moreover, in a recent genome-wide association (GWA) study, it was demonstrated that certain SNPs nominally associated with hypomagnesemia also correlate with fasting glucose levels, again supporting the hypothesis of a direct link between Mg 2+ a...

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Section: Discussionmentioning

confidence: 99%

Loss of insulin-induced activation of TRPM6 magnesium channels results in impaired glucose tolerance during pregnancy

Nair

Hocher

Verkaart

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

126

137

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“…The lower abundant product bands of different sizes might be due to binding of so far unknown proteins to the bigger truncation mutants or degradation products. To explore the REA binding site in the TRPM6 ␣-kinase domain, the tertiary structure of this domain was modeled by SWISS-MODEL based on the homology between TRPM6 and TRPM7 ␣-kinase domains (15,31). Because of the significant homology between the TRPM6 and TRPM7 ␣-kinase domains (84%), these two domains share a well-conserved secondary structure.…”

Section: Rea Associates With Trpm6-tomentioning

confidence: 99%

“…Remarkably, TRPM6 contains a C-terminal ␣-kinase domain, of which the regulatory role on channel activity remains elusive (12)(13)(14). It has been shown that RACK1 can interact with this domain and inhibit channel activity in a phosphorylation-dependent manner (15). A recent study demonstrated that the ATP binding motif in the ␣-kinase domain is required for modulation of TRPM6 channel activity by intracellular ATP (16).…”

mentioning

confidence: 99%

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

Cao

Wijst

Kemp

et al. 2009

Journal of Biological Chemistry

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-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␤-estradiol treatment disassociates the binding between these proteins. In agreement with this, 17␤-estradiol treatment significantly stimulates the TRPM6-mediated current in HEK293 cells. These results suggest a rapid pathway for the effect of estrogen on Mg 2؉ 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 Mg 2؉ (re)absorption and provides new insight into the molecular mechanism of renal transepithelial Mg 2؉ transport.

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“…The C terminus of the TRPM subfamily harbors a coiled-coil region, which is involved in channel tetramerization and is critical for channel activation (7, 8, 14 -16). The members TRPM6 and TRPM7 contain a unique ␣-kinase domain at the far end of the C terminus, which regulates channel activity by a variety of molecular mechanisms (17,18).From the subfamily of TRPV channels, TRPV1-4 play a role in sensory signaling, whereas the Ca 2ϩ -selective and highly homologous TRPV5 and TRPV6 channels are crucial players in Ca 2ϩ homeostasis. Like the other members of this TRPV subfamily the C terminus of TRPV5 is relatively short as compared with the N terminus.…”

mentioning

confidence: 99%

mentioning

confidence: 99%

Role of the Transient Receptor Potential Vanilloid 5 (TRPV5) Protein N Terminus in Channel Activity, Tetramerization, and Trafficking

Groot

Hagen

Verkaart

et al. 2011

Journal of Biological Chemistry

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The epithelial Ca 2؉ channel transient receptor potential vanilloid 5 (TRPV5) constitutes the apical entry site for active Ca 2؉ reabsorption in the kidney. The TRPV5 channel is a member of the TRP family of cation channels, which are composed of four subunits together forming a central pore. Regulation of channel activity is tightly controlled by the intracellular N and C termini. The TRPV5 C terminus regulates channel activity by various mechanisms, but knowledge regarding the role of the N terminus remains scarce. To study the role of the N terminus in TRPV5 regulation, we generated different N-terminal deletion constructs. We found that deletion of the first 32 residues did not affect TRPV5-mediated 45 Ca 2؉ uptake, whereas deletion up to residue 34 and 75 abolished channel function. Immunocytochemistry demonstrated that these mutant channels were retained in the endoplasmic reticulum and in contrast to wildtype TRPV5 did not reach the Golgi apparatus, explaining the lack of complex glycosylation of the mutants. A limited amount of mutant channels escaped the endoplasmic reticulum and reached the plasma membrane, as shown by cell surface biotinylation. These channels did not internalize, explaining the reduced but significant amount of these mutant channels at the plasma membrane. Wild-type TRPV5 channels, despite significant plasma membrane internalization, showed higher plasma membrane levels compared with the mutant channels. The assembly into tetramers was not affected by the N-terminal deletions. Thus, the N-terminal residues 34 -75 are critical in the formation of a functional TRPV5 channel because the deletion mutants were present at the plasma membrane as tetramers, but lacked channel activity.The epithelial Ca 2ϩ channel TRPV5, 3 the gatekeeper of active Ca 2ϩ reabsorption in the kidney, is a member of the TRP superfamily. TRP channels are involved in many different biological processes ranging from sensory physiology, contributing to taste, olfaction, and vision to muscle proliferation and Ca 2ϩ and Mg 2ϩ homeostasis of the body (1, 2). Based on their sequence and structural homology, the mammalian TRP channel superfamily is divided into six subfamilies: TRPA (ankyrin), TRPC (canonical), TRPM (melastatin), TRPP (polycystin), TRPML (mucolipin), and TRPV (vanilloid). All TRP proteins have a common topology, including six transmembrane segments flanked by large cytoplasmic N-and C-terminal domains. They are suggested to assemble into tetramers, the hydrophobic loop between transmembrane 5 and 6 forming a putative core domain, ultimately leading to the formation of a cation-selective channel (1, 3).Despite this common topology, the structure and function of the cytosolic N-and C-terminal domains between the different TRP subfamilies are quite diverse (4). The N terminus of the TRPM subfamily holds four TRPM homology regions, which are essential for proper functioning of these channels (5-8).Highly conserved ankyrin repeats are present in the N termini of TRPC, TRPV, and TRPA channels. Ankyrin repeats a...

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RACK1 Inhibits TRPM6 Activity via Phosphorylation of the Fused α-Kinase Domain

Abstract: We propose a unique mode of TRPM6 regulation in which the Mg(2+) influx is controlled by RACK1 through its interaction with the alpha-kinase and the phosphorylation state of the threonine(1851) residue.

Cited by 64 publications

References 36 publications

Loss of insulin-induced activation of TRPM6 magnesium channels results in impaired glucose tolerance during pregnancy

Loss of insulin-induced activation of TRPM6 magnesium channels results in impaired glucose tolerance during pregnancy

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

Role of the Transient Receptor Potential Vanilloid 5 (TRPV5) Protein N Terminus in Channel Activity, Tetramerization, and Trafficking

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