A Sphingosine-1–Phosphate-Activated Calcium Channel Controlling Vascular Smooth Muscle Cell Motility

Abstract

Abstract-In a screen of potential lipid regulators of transient receptor potential (TRP) channels, we identified sphingosine-1-phosphate (S1P) as an activator of TRPC5. We explored the relevance to vascular biology because S1P is a key cardiovascular signaling molecule. TRPC5 is expressed in smooth muscle cells of human vein along with TRPC1, which forms a complex with TRPC5. Importantly, S1P also activates the TRPC5-TRPC1 heteromultimeric channel. Because TRPC channels are linked to neuronal growth cone extension, we considered a related concept for smooth muscle. We find S1P stimulates smooth muscle cell motility, and that this is inhibited by E3-targeted anti-TRPC5 antibody. Ion permeation involving TRPC5 is crucial because S1P-evoked motility is also suppressed by the channel blocker 2-aminoethoxydiphenyl borate or a TRPC5 ion-pore mutant. S1P acts on TRPC5 via two mechanisms, one extracellular and one intracellular, consistent with its bipolar signaling functions. The extracellular effect appears to have a primary role in S1P-evoked cell motility. The data suggest S1P sensing by TRPC5 calcium channel is a mechanism contributing to vascular smooth muscle adaptation. Key Words: vascular smooth muscle Ⅲ vein Ⅲ sphingosine-1-phosphate Ⅲ transient receptor potential Ⅲ calcium channel S phingosine-1-phosphate (S1P) has emerged as a major endogenous signaling phospholipid with diverse roles in yeast, plants, and mammals. 1 Proposed functions include the regulation of cell proliferation, migration, programmed death, and pathological processes including cancer, asthma, inflammation, and trauma. There has been particular interest in the role of S1P in the cardiovascular system, where it accumulates in atherosclerotic lesions and plays a role in ischemic preconditioning of the heart. 2-5 S1P is derived from the phosphorylation of sphingosine catalyzed by sphingosine kinase, sphingosine being from ceramide and ceramide from sphingomyelin, a constituent lipid of signaling microdomains of plasma membrane lipid rafts and caveolae. 3 S1P is detected in serum at almost 1 mol/L, although protein binding impacts on the available concentration and local concentrations may vary substantially. 6 S1P is quite unusual among signaling molecules in having separate intracellular and extracellular effects. 1,4,7,8 It affects vascular smooth muscle cell migration, 9,10 evokes contraction of rat mesenteric artery, 11 and slows pacemaker activity of the sino-atrial node of the heart. 12 The underlying mechanisms are only partially worked out, but vascular smooth muscle cells respond to S1P with transient followed by sustained elevation of the cytosolic Ca 2ϩ concentration, 10,11,13,14 whereas cardiac myocytes show activation of potassium current and S1P-evoked "Ca 2ϩ deregulation," depending on extracellular Ca 2ϩ . 12,15 Despite positive effects on Ca 2ϩ signaling, the molecular basis of a Ca 2ϩ channel stimulated by S1P is unknown. L-type voltage-gated Ca 2ϩ channels are inhibited by S1P. 12 The Drosophila transient receptor potential ...

Transient Receptor Potential Canonical 1 (TRPC1) Channels as Regulators of Sphingolipid and VEGF Receptor Expression

“…9. Furthermore, in smooth muscle cells, S1P-induced migration is dependent on activation of TRPC5 (40). In light of our observation and the significance of S1P in enhancing the migration of several cancer cells, it would thus be of interest to more closely investigate the relationships between S1P and TRPC-dependent calcium entry also in other cancer cells.…”

“…Furthermore, S1P enhanced calcium entry through stretch-activated TRPC1 channels in skeletal muscle cells (39). In vascular smooth muscles cells, S1P activates TRPC5 via a receptor-mediated mechanism (40).…”

Selective Gαi Subunits as Novel Direct Activators of Transient Receptor Potential Canonical (TRPC)4 and TRPC5 Channels

“…Receptors coupled to G␣ i2 primarily activate TRPC4 and receptors coupled to G␣ i3 primarily activate TRPC5 to mediate the receptor-stimulated monovalent cation current and the Ca 2ϩ influx. Several studies have reported modulation of TRPC4 and TRPC5 activity by GTP␥S-activated PTX-sensitive G-proteins and G i/o -coupled receptors (6,8,25). Activation of TRPC4 by muscarinic receptor stimulation of GI smooth muscle was inhibited by PTX and was shown to be critical in evoking and regulating GI tract motility (21).…”

“…Several studies have also suggested that PTX-sensitive G-proteins play an important role in the activation process of TRPC4 and TRPC5 by GPCR (6,8,25). In our previous study, we showed that G␣ i2 activates TRPC4␤ and that PTX inhibits the activation of TRPC4␤ by stimulation of M2 muscarinic receptors (25).…”

Imbalance and dysfunction of transient receptor potential channels contribute to the pathogenesis of hypertension

“…TRPC3 has been shown to be involved in the agonist-induced depolarization and vasoconstriction of arterial SMCs, and suppression of TRPC3 expression was found to significantly decrease the depolarization and constriction of intact cerebral arteries in response to UTP [37]. Xu et al [38] found that sphingolipids and TRP channels are functionally linked in VSMCs and that the sphingolipids' metabolite, sphingosine-1-phosphate, activates TRPC5, thus controlling VSMC motility. TRPC6 has been suggested to have a major role in the regulation of myogenic tone [39].…”