Induction of Intracellular Calcium Concentration by Environmental Benzo(a)pyrene Involves a β2-Adrenergic Receptor/Adenylyl Cyclase/Epac-1/Inositol 1,4,5-Trisphosphate Pathway in Endothelial Cells

Polycyclic aromatic hydrocarbons (PAHs) such as benzo(a)pyrene (B(a)P) are widely distributed environmental contaminants, known as potent ligands of the aryl hydrocarbon receptor (AhR). These chemicals trigger an early and transient increase of intracellular calcium concentration ([Ca2+]i), required for AhR-related effects of PAHs. The mechanisms involved in this calcium mobilization were investigated in the present study. We demonstrated that B(a)P-mediated [Ca2+]i induction was prevented in endothelial HMEC-1 cells by counteracting β2-adrenoreceptor (β2ADR) activity using pharmacological antagonists, anti-β2ADR antibodies, or siRNA-mediated knockdown of β2ADR expression; by contrast, it was strongly potentiated by β2ADR overexpression in human kidney HEK293 cells. B(a)P was shown, moreover, to directly bind to β2ADR, as assessed by in vitro binding assays and molecular modeling. Pharmacological inhibition and/or siRNA-mediated silencing of various signaling actors acting downstream of β2ADR in a sequential manner, such as G protein, adenylyl cyclase, Epac-1 protein, and inositol 1,4,5-trisphosphate (IP3)/IP3 receptor, were next demonstrated to prevent B(a)P-induced calcium signal. Inhibition or knockdown of these signaling elements, as well as the use of chemical β-blockers, were finally shown to counteract B(a)P-mediated induction of cytochrome P-450 1B1, a prototypical AhR target gene. Taken together, our results show that B(a)P binds directly to β2ADR and consequently utilizes β2ADR machinery to mobilize [Ca2+]i, through activation of a G protein/adenylyl cyclase/cAMP/Epac-1/IP3 pathway. This β2ADR-dependent signaling pathway activated by PAHs may likely be crucial for PAH-mediated up-regulation of AhR target genes, thus suggesting a contribution of β2ADR to the health-threatening effects of these environmental pollutants. Background: Calcium signal induced by the environmental polycyclic aromatic hydrocarbon (PAH) benzo(a)pyrene (B(a)P) contributes to its aryl hydrocarbon receptor (AhR)-related toxic effects. Results: β2-Adrenoreceptor (β2ADR) mediates B(a)P-induced calcium signal through a G protein/adenylyl cyclase/cAMP/Epac-1/inositol 1,4,5-trisphosphate pathway. Conclusion: An important crosstalk between β2ADR and AhR pathways can be activated by PAHs. Significance: β2ADR is potentially involved in deleterious effects of PAHs.