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 PKCα by lysophosphatidic acid (LPA), which is known to induce signal transduction cascades in many cell types via binding to specific cell-surface receptors. Under conditions by which LPA activates PKCα, there is significant stimulation of the acrosome reaction, which is inhibited by PKC inhibitors. Protein kinase Cα belongs to the Ca2 -dependent classical PKC family of isoforms, and indeed we show that its activation depends upon the presence of Ca2 in the incubation medium. Protein kinase Cα is a known regulator of phospholipase D (PLD). We investigated the possible regulatory relationships between PKCα and PLD1. Using specific antibodies against PLD1, we demonstrate for the first time its presence in bovine sperm. Furthermore, PLD1 coimmunoprecipitates with PKCα and the PKCα-PLD1 complex decomposes after treatment of the cells with LPA or 12-O-tetradecanoyl phorbol-13-acetate, resulting in the translocation of PKCα to the plasma membrane and translocation of PLD1 to the particulate fraction. A possible bilateral regulation of PKCα and PLD1 activation during the sperm acrosome reaction is suggested.
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