Assembly of Trp1 in a signaling complex associated with caveolin-scaffolding lipid raft domains

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 were present in low density fractions of Triton X-100-extracted human submandibular gland cell. membranes. Depletion of plasma membrane cholesterol increased Triton X-100 solubility of Trp1 and inhibited carbachol-stimulated Ca2+ signaling. Importantly, thapsigargn stimulated Ca2+ influx, but not internal Ca2+ release, and inositol 1,4,5-triphosphate (IP3)-stimulated I-soc were also attenuated. Furthermore, both anti-Trp1 and anti-caveolin-1 antibodies co-immunoprecipitated hTrp1, caveolin-1, G alpha(q/11), and IP3 receptor-type 3 (IP3R3). These results demonstrate that caveolar microdomains provide a scaffold for (i) assembly of key Ca2+ signaling proteins into a complex and (ii) coordination of the molecular interactions leading to the activation of SOC. importantly, we have shown that Trp1 is also localized in this microdomain where it interacts with one or more components of this complex, including IP3R3. This finding is potentially important in elucidating the physiological function of Trp.