GAMETE BIOLOGY AND GAMETOGENESIS - C
Wednesday, August 4, 2004
10:30 AM–12:30 PM
(706) PHOSPHATIDYLINOSITOL 4-KINASE AND PHOSPHATIDYLINOSITOL 3-KINASE FUNCTION IN SPERM CAPACITATION AND THE ACROSOME REACTION.
Etkovitz, Nir1, Robinstein, Sara1, Breitbart, Haim1, 1 Bar-Ilan University, Ramat-Gan, Israel
ABSTRACT- Mammalian sperm capacitation and the acrosome reaction(AR) require remodeling of actin filaments in which actin polymerization occurs during capacitation and F-actin breakdown prior to the AR. Phosphoinositides signaling is believed to play an important role in cytoskeletal reorganization, but it is not clear whether lipids which can diffuse along the membrane can mediate the actin assembly required for capacitation and the AR. We recently demonstrate a role for phospholipase D(PLD) in the induction of actin polymerization during mammalian sperm capacitation. Here we demonstrated for the first time that phosphatidylinositol 4-kinase (PI4K) but not phosphatidylinositol 3-kinase(PI3K) is associated with PLD-dependent actin polymerization in bovine sperm capacitation. However, when actin polymerization is induced after short time of incubation with epidermal-growth-factor(EGF) or dibutiryl-cAMP(dbcAMP) which activates protein kinase A(PKA) or in protein kinase C(PKC) inhibited cells, it was found that PI3K is involved as well. F-actin formation induced by activating PKC, was found to be associated with PI4K but not with PI3K activity. These data are based on using the inhibitors wortmannin and LY294002, which inhibit PI3K at very low concentrations(10nM or 10M, respectively) whereas at much higher concentrations(10.M or 100M, respectively) PI4K is inhibited as well. It is concluded that PKA dependent polymerization is associated with PI3K and PI4K activities, however in PKC dependent polymerization PI4K but not PI3K is involved. It is suggested that the PKA/PKC relative activities during capacitation determine the need for PI3K activity. When PKA activity is relatively high, PLC/PKC activities are low, and PI3K mediates actin polymerization. However, when the activity ratio PKA/PKC is lower, there is no need for PI3K activity for F-actin formation. The two PI-kinases are associated with the AR induced by the Ca2+
KEY WORDS: Acrosome Reaction, Phosphatidylinositol kinases, Capacitation, Actin Polymerization