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.