The integrin-binding motif RGDS induces protein tyrosine phosphorylation without activation in Bufo arenarum (amphibia) oocytes

MOUGUELAR, V. S.,; CABADA, M.O.; COUX, G.

REPRODUCTION

BIOSCIENTIFICA LTD

Lugar: Bristol; Año: 2011 vol. 141 p. 581 - 593

1470-1626

Integrins are cell adhesion molecules that are thought to be involved in sperm–oocyte interaction. Nevertheless, their function inmammalian fertilization is still controversial, as different species behave differently. In amphibians, their role is mainly supported byXenopus laevis studies, where RGDS peptide induces oocyte activation. We recently provided evidence suggesting the presence andinvolvement of integrins in the interaction of the oocyte plasma membrane (PM) with sperm in the amphibian Bufo arenarum. In order tounderstand the role of integrin homologs in oocytes and their possible contribution to egg activation mechanisms, we examined thepresence of integrin subunits and the effect of RGDS peptide on oocytes and during fertilization. Western blot studies detected integrinsubunits a5, aV and b1 in oocytes. In sperm, we could detect only the aV integrin subunit. We found that RGDS peptide was unable toelicit egg activation or MAPK dephosphorylation, but can induce reversible inhibition of fertilization. A similar partial inhibition wasproduced by an anti-b1 integrin antibody. Using an anti-phosphotyrosine antibody we found major changes in phosphotyrosinecontainingproteins in egg extracts minutes after fertilization. Cytosol and PMs isolated from oocytes and fertilized eggs showedadditional fertilization-induced phosphorylated proteins. Some of these were also present in cytosol and PMs from RGDS-treated oocytes(partially mimicking fertilization). These findings suggest that B. arenarum fertilization involves integrins (e.g. b1 subunit) as adhesionproteins. Our data support the view that RGDS-binding receptors may function as signaling receptors in B. arenarum oocytes, butintegrin engagement by RGDS is not sufficient for oocyte activation.