Csk defines the ability of integrin-mediated cell adhesion and migration in human colon cancer cells: implication for a potential role in cancer metastasis.
ABSTRACT Progression of human colon cancer is often associated with elevated expression and activity of the Src family tyrosine kinase (SFK). SFK is ordinarily in equilibrium between inactive and primed states by a balance of negative regulatory kinase Csk and its counteracting tyrosine phosphatase(s), both of which act on the regulatory C-terminal tyrosine of SFK. To evaluate the contribution of the regulatory system of SFK in cancer progression, we here modulated the equilibrium status of SFK by introducing wild-type or dominant-negative Csk in human epithelial colon cancer cells, HCT15 and HT29. Overexpression of wild-type Csk induced decreased SFK activation, increased cell-cell contacts mediated by E-cadherin, decreased the number of focal contacts and decreased cell adhesion/migration and in vitro invasiveness. Conversely, expression of a dominant-negative Csk resulted in elevated SFK activation, enhanced phosphorylation of FAK and paxilllin, enhanced cell scattering, an increased number of focal contacts, dramatic rearrangement of actin cytoskeleton and increased cell adhesion/migration and in vitro invasiveness. In these scattered cells, however, localization, expression and phosphorylation of either E-cadherin or beta-catenin were not significantly affected, suggesting that the E-cadherin-mediated cell-cell contact is indirectly regulated by SFK. Furthermore, all these events occurred absolutely dependent on integrin-mediated cell adhesion. These findings demonstrate that Csk defines the ability of integrin-SFK-mediated cell adhesion signaling that influences the metastatic potential of cancer cells.
Article: FAK/src-family dependent activation of the Ste20-like kinase SLK is required for microtubule-dependent focal adhesion turnover and cell migration.[show abstract] [hide abstract]
ABSTRACT: Cell migration involves a multitude of signals that converge on cytoskeletal reorganization, essential for development, immune responses and tissue repair. Using knockdown and dominant negative approaches, we show that the microtubule-associated Ste20-like kinase SLK is required for focal adhesion turnover and cell migration downstream of the FAK/c-src complex. Our results show that SLK co-localizes with paxillin, Rac1 and the microtubules at the leading edge of migrating cells and is activated by scratch wounding. SLK activation is dependent on FAK/c-src/MAPK signaling, whereas SLK recruitment to the leading edge is src-dependent but FAK independent. Our results show that SLK represents a novel focal adhesion disassembly signal.PLoS ONE 02/2008; 3(4):e1868. · 4.09 Impact Factor
Article: COOH-terminal Src kinase-mediated c-Jun phosphorylation promotes c-Jun degradation and inhibits cell transformation.[show abstract] [hide abstract]
ABSTRACT: The oncoprotein c-Jun is a component of the activator protein-1 transcription factor complex, which is involved in cellular proliferation, transformation, and death. The stabilization of c-Jun is critically important for its function. The phosphorylation of c-Jun by c-Jun NH(2)-terminal kinase 1 and extracellular signal-regulated protein kinases reduces c-Jun ubiquitination resulting in increased stabilization of c-Jun. In this report, we showed that COOH-terminal Src kinase (CSK) binds with and phosphorylates c-Jun at Y26 and Y170. Phosphorylation of c-Jun by CSK, in opposition to c-Jun NH(2)-terminal kinase 1 and extracellular signal-regulated protein kinases, promoted c-Jun degradation and reduced stability. By promoting c-Jun degradation, CSK helps to maintain a low steady-state level of c-Jun, thereby inhibiting activator protein-1 activity and cell transformation caused by c-Jun. These results indicated that this function of CSK controls cell proliferation under normal growth conditions and may have implications for CSK loss of function in carcinogenesis.Cancer Research 07/2006; 66(11):5729-36. · 7.86 Impact Factor