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The PDZ‐scaffold protein INAD abolishes apparent store‐dependent regulation of the light‐activated cation channel TRP
Author(s) -
Harteneck Christian,
Kuchta Sabiranjo,
Huber Armin,
Paulsen Reinhard,
Schultz Günter
Publication year - 2002
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fj.02-0192fje
Subject(s) - visual phototransduction , transient receptor potential channel , microbiology and biotechnology , pdz domain , scaffold protein , phospholipase c , phospholipase , transduction (biophysics) , depolarization , protein kinase c , protein kinase a , biology , signal transduction , chemistry , calcium signaling , phosphorylation , biophysics , biochemistry , receptor , retinal , enzyme
ABSTRACT In fly photoreceptor cells, light initiates a G protein‐coupled phospholipase Cβ‐dependent signaling cascade that results in the depolarization of the cell membrane, which is mediated by the cation channels TRP and TRPL. Together with phospholipase Cβ and an eye‐specific protein kinase C, TRP is tethered to the scaffolding protein INAD, which forms a multimolecular signaling complex. Divergent data from expressed TRP and studies from photoreceptor cells have brought up a controversy whether or not a capacitative calcium entry (CCE) mechanism is involved in the Drosophila phototransduction pathway. Our initial characterization of TRP from photoreceptors of Calliphora vicina supported the hypothesis of a CCE mechanism, as heterologously expressed TRP was stimulated after application of thapsigargin. The situation changed when the PDZ domain protein INAD was coexpressed with TRP. In cells coexpressing TRP and INAD, no calcium entry was detectable on application of store depletion protocols. Suppression of CCE by INAD was not observed when the described interaction was disrupted by mutations in TRP and INAD. Our data show that apparent activation of TRP by CCE is abolished by INAD. Within the complex, the proteins necessary for phototransduction mutually influence their activities. The results support the hypothesis of a store‐independent activation of TRP.