MEK/ERK signaling is a critical mediator for integrin-induced cell scattering in highly metastatic hepatocellular carcinoma cells

The human hepatocellular carcinoma (HCC)-derived cell line KYN-2 is thought to provide a good model for studying the molecular basis of invasion and metastasis of human HCC, because it often shows cell scattering in vitro and intrahepatic metastasis in vivo. We previously found that integrin-mediated extracellular signals inactivated E-cadherin in KYN-2, and caused loss of cell-cell contact with gain of cell motility, which is considered to be a critical step in the process of cancer cell invasion and metastasis. To further understand molecular mechanisms involved in biological aggressiveness of HCC, we investigated intracellular signaling involved in integrin-mediated scattering of KYN-2 cells. Cultured KYN-2 cells formed trabecular aggregates in suspension, but when adhering to integrin-stimulating substrata, they scattered according to phosphorylation of extracellular signal-regulated kinase (ERK). Upon treatment with ERK kinase (MEK) inhibitor PD98059, adhered KYN-2 cell scattering was inhibited, tight cell-to-cell contact was recovered, and both E-cadherin and actin filaments accumulated in the area of intercellular contact zone. In contrast, constitutively active MEK1-transfected KYN-2 cells showed reduced E-cadherin and actin filaments in the intercellular contact zone, showing a flattened phenotype with broad lamellipodia. Enforced signaling of MEK-ERK pathway in KYN-2 cells suppressed cadherin-mediated homotypic adhesion and increased the potential of cell motility. An antibody-based protein microarray analysis revealed that the cytoplasmic protein c-Cbl was significantly downregulated in MEK1-transfected KYN-2 cells, suggesting that c-Cbl might be a candidate downstream mediator of integrin/MEK/ERK-mediated cell scattering. In conclusion, cell scattering of the highly metastatic cell line KYN-2 is regulated through the integrin-MEK-ERK signaling cascade, suggesting that this molecular pathway may be critical in intrahepatic metastasis of human HCC.