title: Gain-of-function mutation in TRPML3 causes the mouse Varitint-Waddler phenotype.
abstract: 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 alpha-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.
authors.affiliation: Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
authors.forename: Hyun Jin
authors.initials: HJ
authors.lastname: Kim
authors.forename: Qin
authors.initials: Q
authors.lastname: Li
authors.forename: Sandra
authors.initials: S
authors.lastname: Tjon-Kon-Sang
authors.forename: Insuk
authors.initials: I
authors.lastname: So
authors.forename: Kirill
authors.initials: K
authors.lastname: Kiselyov
authors.forename: Shmuel
authors.initials: S
authors.lastname: Muallem
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D016923:Cell Death / Q000235:genetics; D002460:Cell Line; D006031:Glycosylation; D006801:Humans; D017136:Ion Transport / Q000235:genetics; D051379:Mice; D009081:Mucolipidoses / Q000235:genetics / Q000378:metabolism*; D020125:Mutation, Missense; D010641:Phenotype; D011499:Protein Processing, Post-Translational / Q000235:genetics; D017433:Protein Structure, Secondary / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D012964:Sodium / Q000378:metabolism*; D050051:Transient Receptor Potential Channels / Q000235:genetics / Q000378:metabolism*
chemical_list: C510642:MCOLN3 protein, human; D050051:Transient Receptor Potential Channels; D012964:Sodium