Trp1 has been proposed as a component of the storeoperated Ca 2؉ 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 Ca 2؉ signaling. Importantly, thapsigargin stimulated Ca 2؉ influx, but not internal Ca 2؉ release, and inositol 1,4,5-triphosphate (IP 3 )-stimulated I soc were also attenuated. Furthermore, both anti-Trp1 and anti-caveolin-1 antibodies co-immunoprecipitated hTrp1, caveolin-1, G␣ q/11 , and IP 3 receptortype 3 (IP 3 R3). These results demonstrate that caveolar microdomains provide a scaffold for (i) assembly of key Ca 2؉ 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 IP 3 R3. This finding is potentially important in elucidating the physiological function of Trp.

The trp gene family has been proposed to encode the store-operated Ca 2؉ influx (SOC) channel(s

Agonist-induced Ca 2؉ entry via store-operated Ca 2؉ (SOC) channels is suggested to regulate a wide variety of cellular functions, including salivary gland fluid secretion. However, the molecular components of these channels and their physiological function(s) are largely unknown. Here we report that attenuation of SOC current underlies salivary gland dysfunction in mice lacking transient receptor potential 1 (TRPC1). Neurotransmitter-regulated salivary gland fluid secretion in TRPC1-deficient TRPC1(؊/؊) mice was severely decreased (by 70%). Further, agonist-and thapsigargin-stimulated SOC channel activity was significantly reduced in salivary gland acinar cells isolated from TRPC1(؊/؊) mice. Deletion of TRPC1 also eliminated sustained Ca 2؉ -dependent potassium channel activity, which depends on Ca 2؉ entry and is required for fluid secretion. Expression of key proteins involved in fluid secretion and Ca 2؉ signaling, including STIM1 and other TRPC channels, was not altered. Together, these data demonstrate that reduced SOC entry accounts for the severe loss of salivary gland fluid secretion in TRPC1(؊/؊) mice. Thus, TRPC1 is a critical component of the SOC channel in salivary gland acinar cells and is essential for neurotransmitter-regulation of fluid secretion. transient receptor potential ͉ canonical ͉ Ca 2ϩ entry ͉ acinar cells ͉ muscarinic receptor

Individuals with Parkinson's disease (PD) experience a progressive decline in motor function as a result of selective loss of dopaminergic (DA) neurons in the substantia nigra. The mechanism(s) underlying the loss of DA neurons is not known. Here, we show that a neurotoxin that causes a disease that mimics PD upon administration to mice, because it induces the selective loss of DA neurons in the substantia nigra, alters Ca 2+ homeostasis and induces ER stress. In a human neuroblastoma cell line, we found that endogenous store-operated Ca 2+ entry (SOCE), which is critical for maintaining ER Ca 2+ levels, is dependent on transient receptor potential channel 1 (TRPC1) activity. Neurotoxin treatment decreased TRPC1 expression, TRPC1 interaction with the SOCE modulator stromal interaction molecule 1 (STIM1), and Ca 2+ entry into the cells. Overexpression of functional TRPC1 protected against neurotoxin-induced loss of SOCE, the associated decrease in ER Ca 2+ levels, and the resultant unfolded protein response (UPR). In contrast, silencing of TRPC1 or STIM1 increased the UPR. Furthermore, Ca 2+ entry via TRPC1 activated the AKT pathway, which has a known role in neuroprotection. Consistent with these in vitro data, Trpc1 -/-mice had an increased UPR and a reduced number of DA neurons. Brain lysates of patients with PD also showed an increased UPR and decreased TRPC1 levels. Importantly, overexpression of TRPC1 in mice restored AKT/mTOR signaling and increased DA neuron survival following neurotoxin administration. Overall, these results suggest that TRPC1 is involved in regulating Ca 2+ homeostasis and inhibiting the UPR and thus contributes to neuronal survival.