TRPML3 and hearing loss in the varitint-waddler mouse

Atiba-Davies, Margaret; Noben-Trauth, Konrad

doi:10.1016/j.bbadis.2007.01.007

Cited by 22 publications

(18 citation statements)

References 20 publications

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“…Homozygotes for the A419P mutation have a severe phenotype that results in embryonic lethality. A milder phenotype is observed with the ϩ/A419P heterozygote, when the I362T mutation occurs in the same allele as A419P (4,5).…”

mentioning

confidence: 97%

“…Unregulated State-The presence of the A419P and I362T mutations in the same allele results in a milder varitint-waddler phenotype (5). In an attempt to understand this phenotype, we analyzed the function of TRPML3(I362T) and TRPML3(I362T/A419P).…”

Section: Trpml3(i362t) Is Not Active But Trpml3(i362t/a419p) Is Lockmentioning

confidence: 99%

“…Mutations in TRPML1 cause the lysosomal storage disease mucolipidosis type IV (2,3). The A419P mutations in the ␣-helical fifth transmembrane domain of TRPML3 cause the varitint-waddler phenotype, which is characterized by pigmentation defect, hearing loss, circling behavior, and embryonic lethality (4,5). Homozygotes for the A419P mutation have a severe phenotype that results in embryonic lethality.…”

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confidence: 99%

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Gain-of-function Mutation in TRPML3 Causes the Mouse Varitint-Waddler Phenotype

Kim

Tjon-Kon-Sang

et al. 2007

Journal of Biological Chemistry

111

147

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TRPML3 is a member of the TRPML subfamily of the transient receptor potential cation channel superfamily. The TRPML3(A419P) mutation causes a severe form, whereas the TRPML3(I362T/A419P) mutation results in a mild form of the varitint-waddler phenotype. The channel properties of TRPML3 and how the mutations cause each phenotype are not known. In this study, we report the first channel properties of TRPML3 as a strongly inward rectifying cation channel with a novel regulation by extracytosolic Na ؉ . Preincubating the extracytosolic face of TRPML3 in Na ؉ -free medium is required for channel activation, but then the channel slowly inactivates. The A419P mutation locks the channel in an open unregulated state. Similar gain of function was observed with the A419G mutation, which, like A419P, is expected to destabilize the ␣-helical fifth transmembrane domain of TRPML3. The I362T mutation results in an inactive channel, but the channel properties of TRPML3(I362T/A419P) are similar to those of TRPML3(A419P). However, the surface expression and current density of TRPML3(I362T/A419P) are lower than those of TRPML3(A419P). The A419P mutation also affects channel glycosylation and causes massive cell death. These findings show that the varitint-waddler phenotype is due to a gain of function of TRPML3(A419P) that is reduced by the TRPML3(I362T/A419P) mutant, resulting in a milder phenotype.TRPML3 is a putative channel belonging to the TRPML subfamily of the transient receptor potential channels (1). The TRPML subfamily consists of three members. Mutations in TRPML1 cause the lysosomal storage disease mucolipidosis type IV (2, 3). The A419P mutations in the ␣-helical fifth transmembrane domain of TRPML3 cause the varitint-waddler phenotype, which is characterized by pigmentation defect, hearing loss, circling behavior, and embryonic lethality (4, 5). Homozygotes for the A419P mutation have a severe phenotype that results in embryonic lethality. A milder phenotype is observed with the ϩ/A419P heterozygote, when the I362T mutation occurs in the same allele as A419P (4, 5).The channel function of TRPML3 and the effect of the A419P and I362T mutations on channel function are unknown. We report here that TRPML3 functions as an inward rectifying cation channel that is inactivated by extracytosolic cations. The A419P mutation locks the channel in an open state and eliminates regulation of the channel by extracytosolic cations. The I362T mutation inhibits channel activity and reduces the surface expression and current density of the A419P mutant. We conclude that the varitint-waddler phenotype is the result of a gain-of-function mutation in TRPML3. EXPERIMENTAL PROCEDURESPlasmid Construction, Mutagenesis, and Reagents-Human TRPML3 was amplified from human placenta and cloned into the pEGFPC1 and p3XFLAG-CMV-7.1 vectors. Mutations were introduced with the QuikChange kit.Cell Culture, Transfection, and Western Blotting-HEK293 cells were maintained in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum. Cells ...

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confidence: 97%

Section: Trpml3(i362t) Is Not Active But Trpml3(i362t/a419p) Is Lockmentioning

confidence: 99%

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confidence: 99%

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Gain-of-function Mutation in TRPML3 Causes the Mouse Varitint-Waddler Phenotype

Kim

Tjon-Kon-Sang

et al. 2007

Journal of Biological Chemistry

111

147

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“…The leading MET-channel candidate, the TMC proteins, show an appropriate temporal and spatial distribution that supports their candidacy as hcMET-channels [53]. Care must be taken though as a previous candidate TRPA1 [59,7,21], as well as several other TRP channels show a similar temporal [3] or spatial [4,51,79,86,105,106] expression pattern.…”

Section: What Does It Take To Validate a Potential Hcmet-channel Cmentioning

confidence: 99%

The how and why of identifying the hair cell mechano-electrical transduction channel

Effertz

Scharr

Ricci

2014

Pflugers Arch - Eur J Physiol

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Identification of the auditory hair cell mechano-electrical transduction (hcMET) channel has been a major focus in the hearing research field since the 1980s, when direct mechanical gating of a transduction channel was proposed [23]. To this day, the molecular identity of this channel remains controversial. However, many of the hcMET-channel's properties have been characterized including: pore properties, calcium dependent ion permeability, rectification, and single channel conductance. At this point, elucidating the molecular identity of the hcMET-channel will provide new tools for understanding the mechanotransduction process. This review discusses the significance of identifying the hcMET-channel, the difficulties associated with that task, as well as the establishment of clear criteria for this identification. Finally, we discuss potential candidate channels in light of these criteria.

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“…The subfamily consists of TRPML1, mutations in which cause the lysosomal storage disease mucolipidosis type IV (3), TRPML2 and TRPML3. The A419P mutation in the putative fifth transmembrane domain (TMD) of TRPML3 causes the varitint-waddler phenotype that is characterized by pigmentation defect, hearing loss, circling behavior, and embryonic lethality (4,5).…”

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confidence: 99%

Properties of the TRPML3 Channel Pore and Its Stable Expansion by the Varitint-Waddler-causing Mutation

Kim

Yamaguchi

et al. 2010

Journal of Biological Chemistry

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TRPML3 is a H؉ -regulated Ca 2؉ channel that shuttles between intracellular compartments and the plasma membrane. The A419P mutation causes the varitint-waddler phenotype as a result of gain-of-function (GOF). The mechanism by which A419P leads to GOF is not known. Here, we show that the TRPML3 pore is dynamic when conducting Ca 2؉ to change its conductance and permeability, which appears to be mediated by trapping Ca 2؉ within the pore. The pore properties can be restored by strong depolarization or by conducting Na ؉ through the pore. The A419P mutation results in expanded channel pore with altered permeability that limits modulation of the pore by Ca 2؉. This effect is specific for the A419P mutation and is not reproduced by other GOF mutations, including A419G, H283A, and proline mutations in the fifth transmembrane domain. These findings describe a novel mode of a transient receptor potential channel behavior and suggest that pore expansion by the A419P mutation may contribute to the varitint-waddler phenotype.TRPML3 belongs to the TRPML subfamily of the transient receptor potential (TRP) 3 channels superfamily (1, 2). The subfamily consists of TRPML1, mutations in which cause the lysosomal storage disease mucolipidosis type IV (3), TRPML2 and TRPML3. The A419P mutation in the putative fifth transmembrane domain (TMD) of TRPML3 causes the varitint-waddler phenotype that is characterized by pigmentation defect, hearing loss, circling behavior, and embryonic lethality (4, 5).TRPML3 functions as an inwardly rectifying cation channel (6), with high Ca 2ϩ /K ϩ selectivity (7-10) and shuttles between the plasma membrane and intracellular organelles to regulate membrane trafficking (11,12) We (6) and others (8 -10) have shown that the A419P mutation is a GOF mutation that locks TRPML3 in an open conformation. The mechanism by which the A419P mutation leads to GOF is not known. Although elimination of the inhibition of TRPML3 activity by H ϩ e-cyto plays a role in the GOF (7), the A419P mutation may also affect the pore selectivity and conductance. Because proline introduces a kink or a break in ␣-helical transmembrane spans, and the A419G mutation that may disrupt ␣-helical structures results in a similar GOF in TRPML3 as the A419P (6, 9), it was postulated that the GOF by TRPML3(A419P) is caused by destabilization of the fifth TMD helix of TRPML3 (9, 13). However, it is still unclear how the proline-induced destabilization of the fifth TMD affects the behavior of the TRPML3 pore to lead to the GOF.Very little is known of the properties of the TRPML3 pore. As indicated above, the pore of the wild-type (WT) channel shows high Ca 2ϩ /K ϩ and Ca 2ϩ /Cs ϩ selectivity with similar Na ϩ and Ca 2ϩ conductance at isotonic ion concentrations (7). With limited exceptions, ionic selectivity and conductance are considered constant and defining features of ion channels. The best known examples of ion channels with variable permeability are the ionotropic P2X receptors, which undergo time-dependent slow pore expansion subse...

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TRPML3 and hearing loss in the varitint-waddler mouse

Cited by 22 publications

References 20 publications

Gain-of-function Mutation in TRPML3 Causes the Mouse Varitint-Waddler Phenotype

Gain-of-function Mutation in TRPML3 Causes the Mouse Varitint-Waddler Phenotype

The how and why of identifying the hair cell mechano-electrical transduction channel

Properties of the TRPML3 Channel Pore and Its Stable Expansion by the Varitint-Waddler-causing Mutation

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