Src regulates phorbol 12-myristate 13-acetate-activated PKC-induced migration via Cas/Crk/Rac1 signaling pathway in glioblastoma cells

In this study, we demonstrate that phorbol 12-myristate 13-acetate (PMA)-activated protein kinase C (PKC) induced migration in A172 glioblastoma cells via Src. PMA treatment induced tyrosine phosphorylation of Crk-associated substrate (Cas) and formation of a complex with Crk, followed by Rac1 activation, a downstream effector of Cas/Crk complex. These effects were blocked by a tyrosine kinase inhibitor (PP2) or Src small interfering RNA (siRNA), indicating that Src was involved in the PMA-induced activation of Cas/Crk/Rac1 signaling pathway. An immunohistochemical study showed that after PMA treatment, Cas, Crk and Rac1 translocated into lamellipodia. Tyrosine phosphorylated Cas was also detected at the periphery of the cells, where focal complexes were prominent. These results indicated that signaling of Cas, Crk and Rac1 might be involved in PMA-induced cytoskeletal reorganization. Translocation of Rac1 to the cell membrane is known to be dependent on phosphorylation of tyrosine-221 residue of Crk. We demonstrated that PMA induced phosphorylation of Crk, and this phosphorylation was blocked by PP2 or Src siRNA. These results indicated that Src might regulate the subcellular localization of Rac1 through phosphorylation of Crk. We propose that PMA-induced migration was dependent on activation of PKC/Src/Cas/Crk/Rac1 signaling pathway via modulating cytoskeletal reorganization during glioblastoma cell migration.