Protein Kinase A and Phosphatidyl-Inositol-3-Kinase Activities during Sperm Capacitation Protect the Sperm from Undergoing Spontaneous Acrosome Reaction

In order to fertilize the egg, the spermatozoon should undergo a process called acrosome exocytosis or acrosome reaction (AR), a process which can take place only after a series of biochemical changes collectively called capacitation that the sperm undergo in the female reproductive tract. Polymerization of G-actin to F-actin which occurs during sperm capacitation prevents the occurrence of spontaneous-AR (sAR), which decreases fertilization rate. We present for the first time the involvement of PKA in preventing sAR. PKA mediates PLD activation, a known factor involved in mechanism that prevents sAR. We previously demonstrated that Calmodulin-kinase II (CaMKII) and phospholipase-D (PLD) prevents spontaneous acrosome reaction in two distinct pathways, however under physiological conditions both should be active in order to prevent sAR. When the PLD pathway is blocked, the occurrence of sAR can be artificially reversed by inhibition of protein - phosphatase 1 (PP1), this effect is mediated by phosphatidyl-inositol-3-kinase (PI3K). In conclusion, PKA and PI3K are involved in actin polymerization which prevents the occurrence of sAR in sperm capacitation.