MAYORGA Luis Segundo
congresos y reuniones científicas
A dual role for Rab3a in the acrosome reaction of human sperm.
BUSTOS, MA; BRANHAM, M.T; MAYORGA, L.S.; TOMES C.N.
Congreso; SAIB XLV; 2009
The sperm is endowed with a single secretory granule thatundergoes a special type of regulated exocytosis (the acrosomereaction, AR). The AR relies on the same fusion machinery astypical exocytotic cells (i.e. SNAREs and Rabs). Rab3A is aGTPase that cycles between a GDP-bound (inactive) state thatlocalizes at the cytosol and a GTP-bound (active) state that isattached to membranes. The role of Rab3A is controversial becausein some models it stimulates exocytosis whereas in others behavesas an inhibitor. In human sperm, recombinant, prenylated Rab3Ainduces the AR in intact as well as SLO-permeabilized cells when isGTPgS-loaded. Different AR inducers like Ca and 8-pCPT-2?-OMe-cAMP (8pCPT, Epac-selective cAMP analogue) augment thelevels of GTP-bound Rab3A. Here, we report that Rab3Adistributed in the same proportion between cytosol and membranesin resting sperm. There was an enhanced binding of Rab3A tomembranes after stimulating with A23187 or 8pCPT; but not withN6-Benzoyl-cAMP (a PKA-selective analogue), consistent withprevious observations that Epac, but not PKA, exhibits a role in theAR. Interestingly, recombinant, prenylated and loaded withGTPgS, but not GTP, Rab3A exhibited an inhibitory role during thelate stages of the AR. In summary, Rab3A seems to have a dual roledepending on the stage it is added, this could explain the differencesamong models.