Phospholipids involved int the signal transduction cascade leading to acrosomal exocytosis

BELMONTE, SILVIA A; SUHAIMAN, LAILA; LÓPEZ, CECILIA I; PELLETÁN, LEONARDO E; MAYORGA, LUIS S

Rosario, Argentina

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

SAIB

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 (butan1ol, antiPLD antibodies) suggesting that PKC is upstream in the exocytic signaling cascade. The fact that phosphatidylinositol4,5-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: sperm, acrosome reaction, PMA and PIP2