Activation of protein kinase C alpha in the lysophosphatidic acid-induced bovine sperm acrosome reaction and phospholipase D1 regulation

Protein kinase C (PKC) has been implicated in the sperm acrosome reaction. In the present study, we demonstrate induction of the acrosome reaction and activation of sperm PKC alpha by lysophosphatidic acid (LPA), which is kno wn to induce signal transduction cascades in many cell types via binding to specific cell-surface receptors. Under conditions by which LPA activates P KC alpha, there is significant stimulation of the acrosome reaction, which is inhibited by PK inhibitors. Protein kinase Co belongs to the Ca2+-depend ent classical PKC family of isoforms, and indeed we show that its activatio n depends upon the presence of Ca2+ in the incubation medium. Protein kinas e Co is a known regulator of phospholipase D (PLD). We investigated the pos sible regulatory relationships between PKC alpha and PLD1. Using specific a ntibodies against PLD1, we demonstrate for the first time its presence in b ovine sperm. Furthermore, PLD1 coimmunoprecipitates with PKC alpha and the PKC alpha -PLD1 complex decomposes after treatment of the cells with LPA or 12-O-tetradecanoyl phorbol-13-acetate, resulting in the translocation of P KC alpha to the plasma membrane and translocation of PLD1 to the particulat e fraction. A possible bilateral regulation of PKC alpha and PLD1 activatio n during the sperm acrosome reaction is suggested.