Cloning and expression of the human transient receptor potential 4 (TRP4) gene: localization and functional expression of human TRP4 and TRP3.
Mammalian homologues of the Drosophila transient receptor potential (TRP) protein have been proposed to function as ion channels, and in some cases as store-operated or capacitative calcium entry channels. However, for each of the mammalian TRP proteins, different laboratories have reported distinct modes of cellular regulation. In the present study we describe the cloning and functional expression of the human form of TRP4 (hTRP4), and compare its activity with another well studied protein, hTRP3. When hTRP4 was transiently expressed in human embryonic kidney (HEK)-293 cells, basal bivalent cation permeability (barium) was increased. Whole-cell patch-clamp studies of hTRP4 expressed in Chinese hamster ovary cells revealed a constitutively active non-selective cation current which probably underlies the increased bivalent cation entry. Barium entry into hTRP4-transfected HEK-293 cells was not further increased by phospholipase C (PLC)-linked receptor activation, by intracellular calcium store depletion with thapsigargin, or by a synthetic diacylglycerol, 1-oleoyl-2-acetyl-sn-glycerol (OAG). In contrast, transient expression of hTRP3 resulted in a bivalent cation influx that was markedly increased by PLC-linked receptor activation and by OAG, but not by thapsigargin. Despite the apparent differences in regulation of these two putative channel proteins, green fluorescent protein fusions of both molecules localized similarly to the plasma-membrane, notably in discrete punctate regions suggestive of specialized signalling complexes. Our findings indicate that while both hTRP4 and hTRP3 can apparently function as cation channels, their putative roles as components of capacitative calcium entry channels are not readily demonstrable by examining their behaviour when exogenously expressed in cells.
McKay
R R
RR
Laboratory of Signal Transduction, National Institute of Environmental Health Sciences-NIH, PO Box 12233, Research Triangle Park, NC 27709, USA.
Szymeczek-Seay
C L
CL
Lievremont
J P
JP
Bird
G S
GS
Zitt
C
C
Jüngling
E
E
Lückhoff
A
A
Putney
J W
JW
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D015220:Calcium Channels / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D002460:Cell Line; D002874:Chromosome Mapping; D002882:Chromosomes, Human, Pair 13; D003001:Cloning, Molecular; D006224:Cricetinae; D017931:DNA Primers; D018076:DNA, Complementary; D006801:Humans; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D011487:Protein Conformation; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050052:TRPC Cation Channels
D015220:Calcium Channels; D017931:DNA Primers; D018076:DNA, Complementary; D050052:TRPC Cation Channels; C104603:TRPC3 cation channel; C489571:TRPC4 ion channel; C096351:transient receptor potential cation channel, subfamily C, member 1