Constitutive activity of the human TRPML2 channel induces cell degeneration.
The mucolipin (TRPML) ion channel proteins represent a distinct subfamily of channel proteins within the transient receptor potential (TRP) superfamily of cation channels. Mucolipin 1, 2, and 3 (TRPML1, -2, and -3, respectively) are channel proteins that share high sequence homology with each other and homology in the transmembrane domain with other TRPs. Mutations in the TRPML1 protein are implicated in mucolipidosis type IV, whereas mutations in TRPML3 are found in the varitint-waddler mouse. The properties of the wild type TRPML2 channel are not well known. Here we show functional expression of the wild type human TRPML2 channel (h-TRPML2). The channel is functional at the plasma membrane and characterized by a significant inward rectification similar to other constitutively active TRPML mutant isoforms. The h-TRPML2 channel displays nonselective cation permeability, which is Ca(2+)-permeable and inhibited by low extracytosolic pH but not Ca(2+) regulated. In addition, constitutively active h-TRPML2 leads to cell death by causing Ca(2+) overload. Furthermore, we demonstrate by functional mutation analysis that h-TRPML2 shares similar characteristics and structural similarities with other TRPML channels that regulate the channel in a similar manner. Hence, in addition to overall structure, all three TRPML channels also share common modes of regulation.
Lev
Shaya
S
Department of Medical Neurobiology and the Kühne Minerva Center for Studies of Visual Transduction, Faculty of Medicine of the Hebrew University, Jerusalem, Israel.
Zeevi
David A
DA
Frumkin
Ayala
A
Offen-Glasner
Vered
V
Bach
Gideon
G
Minke
Baruch
B
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002412:Cations / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004330:Drosophila; D015870:Gene Expression / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000166:cytology; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D018408:Patch-Clamp Techniques; D053499:Plasma Membrane Calcium-Transporting ATPases / Q000378:metabolism; D017354:Point Mutation; D014162:Transfection; D050051:Transient Receptor Potential Channels / Q000235:genetics* / Q000378:metabolism*
D002412:Cations; C510642:MCOLN3 protein, human; C510641:Mcoln2 protein, human; D050051:Transient Receptor Potential Channels; D053499:Plasma Membrane Calcium-Transporting ATPases; D002118:Calcium