Phospholipids involved in the signal transduction cascade leading to acrosomal exocytosis

BELMONTE SILVIA, SUHAIMAN LAILA, LOPEZ CECILIA, PELLETÁN LEONARDO, MAYORGA LUIS

Rosario, Sante Fé, Argentina

Congreso; XLII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular. SAIB.; 2006

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular. SAIB.

PHOSPHOLIPIDS INVOLVED IN THE SIGNAL TRANSDUCTION CASCADE LEADING TO ACROSOMAL EXOCYTOSIS Belmonte Silvia, Suhaiman Laila, López Cecilia, Pelletán Leonardo, Mayorga Luis. Laboratorio de Biología Celular y Molecular, IHEM- CONICET, Fac. Ccias Médicas, U.N. de Cuyo Mendoza The acrosome is an exocytic granule that overlies the spermatozoan nucleus. The acrosome reaction (AR) is a tightly regulated calcium-dependent exocytic event leading to a massive fusion between the outer acrosomal and the plasma membrane. We have developed a model of SLO-permeabilized spermatozoa capable of undergoing AR upon stimulation. By using this approach, we have characterized a sequence of events occurring downstream the calcium influx through SOC channels. Phorbol esters (PMA), activators of PKC, promote AR in intact sperm. Here, we demonstrate that PMA and diacylglicerol (DAG, the physiological PKC activator) also triggers exocytosis in permeabilized sperm. The effect was not abrogated by chelating the extracellular calcium, suggesting that these compounds are interacting with factors acting downstream the increase of cytoplasmic calcium. PMA and DAG-induced AR was blocked by PKC (cheleritrine) and PLD inhibitors (butan 1-ol, anti-PLD antibodies) suggesting that PKC is upstream in the exocytic signaling cascade. The fact that phosphatidylinositol 4,5-biphosphate (PIP2) was able to recover exocytosis after inhibitors treatment, remarks its essential role in exocytosis. Our results suggest that DAG, phosphatidic acid and PIP2 are part of the signaling cascade activated downstream the opening of SOC channels.    Keywords: acrosome reaction, PMA, PIP2, sperm