Tyrosine phosphorylation of Crk-associated substrate lymphocyte-type is a critical element in TCR- and beta 1...

Crk-associated substrate (Cas) lymphocyte-type (Cas-L) is a 105-kDa cytoplasmic protein consisting of Src homology-3 domain and multiple YXXP motifs (substrate domain). Our previous studies showed that Cas-L is tyrosine-phosphorylated following the ligation of TCR and beta 1 integrins in T lymphocytes. Here we show that Cas-L is involved in T cell motility following the ligation of TCR and beta 1 integrin. Peripheral T lymphocytes showed a marked increase of migration on fibronectin (FN) after the ligation of TCR. In contrast, the migrating Jurkat cells, in which Cas-L was marginally expressed, were less than one-tenth in number on the same condition. Transfection of wild-type Cas-L into Jurkat cells resulted in restoring CD3 plus FN-induced cell migration. Furthermore, following the ligation of beta 1 integrin alone, the Cas-L transfectants significantly migrated better than the vector control. Mutational analysis of Cas-L revealed that the substrate domain is required for both FN- and CD3-induced tyrosine phosphorylation of Cas-L and cell migration caused by FN alone and CD3 plus FN. In contrast, the Src homology-3 domain is required only for the FN-induced tyrosine phosphorylation of Cas-L and cell migration, but not for CD3-induced tyrosine phosphorylation or CD3 plus FN-induced cell migration. These data strongly suggest that Cas-L is a key molecule in T cell migration induced by the ligation of CD3 and beta 1 integrins and that tyrosine phosphorylation of Cas-L is essential for T cell migration.