Transient Receptor Potential Canonical 1 (TRPC1) Channels as Regulators of Sphingolipid and VEGF Receptor Expression: IMPLICATIONS FOR THYROID CANCER CELL MIGRATION AND PROLIFERATION

Background: The identity of calcium channels in the thyroid is undefined. Results: TRPC1 functions as a major regulator of S1P and VEGF receptors via a calcium-dependent mechanism. This is important for cell migration. Conclusion: We have defined a novel physiological role for the TRPC1 channel. Significance: This study explains how TRPC1 regulates receptor expression and migration in thyroid cancer cells. The identity of calcium channels in the thyroid is unclear. In human follicular thyroid ML-1 cancer cells, sphingolipid sphingosine 1-phosphate (S1P), through S1P receptors 1 and 3 (S1P(1)/S1P(3)), and VEGF receptor 2 (VEGFR2) stimulates migration. We show that human thyroid cells express several forms of transient receptor potential canonical (TRPC) channels, including TRPC1. In TRPC1 knockdown (TRPC1-KD) ML-1 cells, the basal and S1P-evoked invasion and migration was attenuated. Furthermore, the expression of S1P(3) and VEGFR2 was significantly down-regulated. Transfecting wild-type ML-1 cells with a nonconducting TRPC1 mutant decreased S1P(3) and VEGFR2 expression. In TRPC1-KD cells, receptor-operated calcium entry was decreased. To investigate whether the decreased receptor expression was due to attenuated calcium entry, cells were incubated with the calcium chelator BAPTA-AM (1,2-bis(o-aminophenoxy)ethane-N,N,N,N-tetraacetic acid). In these cells, and in cells where calmodulin and calmodulin-dependent kinase were blocked pharmacologically, S1P(3) and VEGFR2 expression was decreased. In TRPC1-KD cells, both hypoxia-inducible factor 1 expression and the secretion and activity of MMP2 and MMP9 were attenuated, and proliferation was decreased in TRPC1-KD cells. This was due to a prolonged G(1) phase of the cell cycle, a significant increase in the expression of the cyclin-dependent kinase inhibitors p21 and p27, and a decrease in the expression of cyclin D2, cyclin D3, and CDK6. Transfecting TRPC1 to TRPC1-KD cells rescued receptor expression, migration, and proliferation. Thus, the expression of S1P(3) and VEGFR2 is mediated by a calcium-dependent mechanism. TRPC1 has a crucial role in this process. This regulation is important for the invasion, migration, and proliferation of thyroid cancer cells.