Estrogen induces phospholipase A₂ activation through ERK1/2 to mobilize intracellular calcium in MCF-7 cells

The principal secreted estrogen, 17β-estradiol rapidly activates signaling cascades that regulate important physiological processes including ion transport across membranes, cytosolic pH and cell proliferation. These effects have been extensively studied in the MCF-7 estrogen-responsive human breast carcinoma cell line. Here, we demonstrate that a physiological concentration of 17β-estradiol caused a rapid, synchronous and transient increase in intracellular calcium concentration in a confluent monolayer of MCF-7 cells 2-3 min after treatment. This response was abolished when cells were pre-incubated with the phospholipase A₂ (PLA₂) inhibitor quinacrine or with the cyclooxygenase inhibitor indomethacin. The translocation of GFP-cPLA₂α to perinuclear membranes occurred 1-2 min after 17β-estradiol treatment; this translocation was concurrent with the transient phosphorylation of cPLA₂α at serine residue 505. The phosphorylation and translocation of cPLA₂ were sensitive to inhibition of the extracellular signal regulated kinase (ERK) signaling cascade and occurred simultaneously with a transient activation of ERK. The phosphorylation of cPLA₂ could be stimulated by membrane impermeable 17β-estradiol conjugated to bovine serum albumen and was blocked by an antagonist of the classical estrogen receptor. Here we show, for the first time, that PLA₂ and the eicosanoid biosynthetic pathway are involved in the 17β-estradiol induced rapid calcium responses of breast cancer cells.