Expression of truncated transient receptor potential protein 1α (Trp1α) -: Evidence that the Trp1 C terminus modulates store-operated Ca2+ entry

Transient receptor potential protein 1 (Trp1) has been proposed as a component of the store-operated Ca2+ entry (SOCE) channel. However, the exact mechanism by which Trp1 is regulated by store depletion is not known. Here, we examined the role of the Trpl C-terminal domain in SOCE by expressing hTrp1 alpha lacking amino acids 664-793 (Delta Trp1 alpha) or full-length hTrp1 alpha in the HSG (human submandibular gland) cell line. Both carbachol (CCh) and thapsigargin (Tg) activated sustained Ca2+ influx in control (nontransfected), Delta Trp1 alpha-, and Trp1 alpha -expressing cells. Sustained [Ca2+](i), following stimulation with either Tg or CCh in Delta Trp1 alpha -expressing cells, was about 1.5-2-fold higher than in Trp1 alpha -expressing cells and 4-fold higher than in control cells. Importantly, (i) basal Ca2+ influx and (ii) Tg- or CCh-stimulated internal Ca2+ release were similar in all the cells. A similar increase in Tg-stimulated Ca2+ influx was seen in cells expressing Delta 2Tr1 alpha, lacking the C-terminal domain amino acid 649-793, which includes the EWKFAR sequence. Further, both inositol 1,4,5-trisphosphate receptor-3 and caveolin-1 were immunoprecipitated with Delta Trp1 alpha and Trp1 alpha. In aggregate, these data suggest that (i) the EWKFAR sequence does not contribute significantly to the Trp1-associated increase in SOCE, and (ii) the Trpl C-terminal region, amino acids 664-793, is involved in the modulation of SOCE.