RGDS INDUCES PROTEIN TYROSINE PHOSPHORYLATION WITHOUT ACTIVATION IN BUFO ARENARUM (AMPHIBIA) OOCYTES

COUX, GABRIELA; MOUGUELAR, VALERIA

Los Cocos

Simposio; The First South American Spring Symposium in Signal Transduction and Molecular Medicine; 2010

SISTAM

Integrins are cell adhesion molecules that are thought to be involved in sperm-oocyte interaction. In order to understand the role of integrin homologs in Bufo arenarum oocytes and their possible contribution to egg activation mechanisms, we examined the presence of integrin subunits and the effect of RGDS peptide on oocytes and during fertilization. Western-blot studies detected integrin subunits a5 and b1 in oocytes but not in sperm. We found that RGDS peptide was unable to elicit egg activation or mitogen-activated protein kinase dephosphorylation, but produced reversible inhibition of fertilization. A similar partial inhibition was produced by an anti-b1 integrin antibody. Using an anti-phosphotyrosine antibody we found major changes in phosphotyrosine containing proteins in egg extracts minutes after fertilization. Cytosol and plasma membranes isolated from oocytes and fertilized eggs showed additional fertilization-induced phosphorylated proteins. Some of these were also present in cytosol and plasma membranes from RGDS-treated oocytes (partially mimicking fertilization). These findings suggest that B. arenarum fertilization involves integrins (e.g. b1 subunit) as adhesion proteins. Our data support the view that RGDS binding receptors may function as signaling receptors in B. arenarum oocytes, but integrin engagement by RGDS is not sufficient for oocyte activation.