Tp. Lockwich et al., Assembly of Trp1 in a signaling complex associated with caveolin-scaffolding lipid raft domains, J BIOL CHEM, 275(16), 2000, pp. 11934-11942
Trp1 has been proposed as a component of the store-operated Ca2+ entry (SOC
) channel. However, neither the molecular mechanism of SOC nor the role of
Trp in this process is yet understood. We have examined possible molecular
interactions involved in the regulation of SOC and Trp1 and report here for
the first time that Trp1 is assembled in signaling complex associated with
caveolin-scaffolding lipid raft domains. Endogenous hTrp1 and caveolin-1 w
ere present in low density fractions of Triton X-100-extracted human subman
dibular gland cell. membranes. Depletion of plasma membrane cholesterol inc
reased Triton X-100 solubility of Trp1 and inhibited carbachol-stimulated C
a2+ signaling. Importantly, thapsigargn stimulated Ca2+ influx, but not int
ernal Ca2+ release, and inositol 1,4,5-triphosphate (IP3)-stimulated I-soc
were also attenuated. Furthermore, both anti-Trp1 and anti-caveolin-1 antib
odies co-immunoprecipitated hTrp1, caveolin-1, G alpha(q/11), and IP3 recep
tor-type 3 (IP3R3). These results demonstrate that caveolar microdomains pr
ovide a scaffold for (i) assembly of key Ca2+ signaling proteins into a com
plex and (ii) coordination of the molecular interactions leading to the act
ivation of SOC. importantly, we have shown that Trp1 is also localized in t
his microdomain where it interacts with one or more components of this comp
lex, including IP3R3. This finding is potentially important in elucidating
the physiological function of Trp.