JNK 及 p38 MAPK 磷酸化 paxillin 在 T細胞活化上之角色研究

Abstract

Paxillin is a 68-kD cytoskeletal adaptor protein associated with focal adhesion complex. It is a multidomain adaptor that facilitates signal integration and transduction. Recent studies revealed critical roles for tyrosine and serine phosphorylation of paxillin by FAK, JNK and p38 MAPK, but the consequence of paxillin phosphorylation in T cells remains unknown. In this study, we addressed this issue by overexpressing paxillin mutants with respective phosphorylation sites of FAK, JNK, and p38 MAPK in T cells, and examined the role of paxillin phosphorylation in T cell activation, adhesion, and migration. Contradictory to the reported effect on epithelial cells and neurite, all the paxillin mutants examined did not interfere with integrin-mediated T-cell adhesion. Overexpression of paxillin with mutations at phosphorylation sites of FAK (Y31F/Y118F) in T cells reduced SDF-1alpha--stimulated migration, but did not affect T cell activation, and other parameters of T cell activation remain normal. In contrast, overexpression of paxillin with double mutations at phosphorylation sites of p38 MAPK and JNK (S85A/S178A) in T cells did not alter cell adhesion and migration, but effectively suppressed IL-2 production, the signature of T cell activation. Inhibition by [S85A/S178A]-paxillin could be partly attributed to a selective suppression of NFAT activation. To study the role of paxillin in T cell activation in normal T cells, we further generated [S85A/S178A]-paxillin transgenic mice. Although no significant effect of [S85A/S178A]-paxillin on T cell development was observed, both T cell proliferation and IL-2 production were suppressed in transgenic mice compared to NLC mice. In addition, NFAT translocation was partially interfered by [S85A/S178A]-paxillin transgene. In summary, phosphorylations of paxillin by different kinases play different roles in T cells and non-T cells. How [S85A/S178A]-paxillin modulates T cell activation and NFAT activation will be further investigated.