MARCKS protein participates in acrosomal exocitosis in human sperm

RODRIGUEZ PEÑA, MARCELO JAVIER; MAYORGA, LUIS SEGUNDO; MICHAUT, MARCELA ALEJANDRA

Rosario, Santa Fe, Argentina

Congreso; Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB); 2006

Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB)

Although PKC has been proposed as a key component of the acrosomal exocytosis, the targets for its phosphorylation activity are unknown. MARCKS is a prominent substrate of PKC in many cell types; nevertheless the presence of MARCKS in sperm, as a possible PKC substrate has not been investigated. Using a specific antibody against MARCKS, Western blot analysis reveled the presence of MARCKS in human sperm. Furthermore, immunocytochemistry assays showed that MARCKS localized at the acrosomal region in human sperm. This localization prompted us to investigate if MARCKS might participate in acrosomal exocytosis. To test this hypothesis, we expressed MARCKS effector domain (ED) as a GST- fusion protein. Then, using the Streptolysin O-permeabilized sperm model, we investigated the effect of GST-MARCKS ED on the acrosome exocytosis stimulated by a PKC activator, phorbol 12-myristate, 13-acetate (PMA). GST-MARCKS ED inhibited specifically acrosomal exocytosis stimulated by PMA in a concentration-dependent manner. In addition, GST-MARCKS ED also inhibited the acrosomal exocytosis stimulated by calcium and Rab3A -two well known activators of this secretion process. These results show that MARCKS is expressed in human sperm and suggest that MARCKS might be an important component in acrosomal exocytosis signal transduction pathways in human sperm.