Nuclear translocation of Xenopus laevis paxillin

Paxillin has been recognized as a focal adhesion adapter protein that participates in the integrin-mediated signaling. An earlier study [Ogawa et al. Biochim. Biophys. Acta 1519 (2001) 235] found that frog paxillin was expressed in the kidney epithelial cell line A6 and localized in the nucleus. Here, in this study, we have found that the expression of frog paxillin is up-regulated in the S phase of cell cycle. The protein became phosphorylated on tyrosine when the cells were grown on vitronectin; the tyrosine phosphorylation was not detectable when the cells were cultured on fibronectin, laminin or poly-D-lysine. On the other hand, MAP kinase was revealed to phosphorylate frog paxillin on serine. Both phosphorylation events, namely on tyrosine and serine, were essential for the nuclear translocation of this protein. Our results suggest that the integrin-mediated signaling pathway and the MAP kinase pathway meet at paxillin.