Involvement of Intracellular Ca2+-and PI3K-Dependent ERK Activation in TCDD-Induced Inhibition of Cell Proliferation in SK-N-SH Human Neuronal Cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin(TCDD) has previously shown to induce neurotoxicity through intracellular $Ca^{2+}$ increase in rat neurons. In this study we investigated the role and signaling pathway of intracellular $Ca^{2+}$ in TCDD-induced inhibition of neuronal cell proliferation in SK-N-SH human neuronal cells. We found that TCDD(10nM) rapidly increased the level of intracellular $Ca^{2+}$, which was completely blocked by the extracellular $Ca^{2+}$ chelation with EGTA (1 mM) or by pretreatment of the cells with the non-selective cation channel blocker. flufenamic acid (200 ${\mu}M$). However, pretreatment of the cells with dantrolene (25 ${\mu}M$) and TMB-8(10 ${\mu}M$), intracellular $Ca^{2+}$-release blockers, or a voltage-sensitive $Ca^{2+}$ channel blocker, varapamil (100 ${\mu}M$), failed to block the TCDD-induced $Ca^{2+}$ increase in the cells. In addition, TCDD induced a rapid and transient activation of phatidvlinositol 3-kinase (PI3K) and extracellular signal-regulated kinase 1/2(ERK1/2), which was ingnificantly blocked by the pretreatment with BAPTA, an intracellular $Ca^{2+}$ chelator, and LY294002, a PI3K inhibitor. Furthermore, inhibitors of PI3K, ERK, or an intracellular $Ca^{2+}$ chelator further potentiated the anti-proliferative effect of TCDD in the cells. Collectively, the results suggest that intracellular $Ca^{2+}$ and PI3K-dependent activation of ERK 1/2 may be involved in the TCDD-induced inhibition of cell proliferation in SK-N-SH human neuronal cells.