RON is a receptor tyrosine kinase involved in epithelial cancer pathogenesis and malignant progression. In colorectal cancer, altered expression and activation of RON contribute to colon epithelial cell transformation with malignant phenotypes. β-arrestin-1 is an adaptor protein originally discovered for its involvement in signal transduction through G-protein-coupled receptor kinases of the seven transmembrane receptor family. We have studied the potential mechanisms by which activated RON regulates β-arrestin-1 activities leading to increased invasiveness. Using β-arrestin-1 inactivated NIH3T3 cells, we found that tumorigenic activities mediated by oncogenic RON variant RONΔ160 were significantly diminished, indicating that β-arrestin-1 is a critical component in RON mediated oncogenic phenotypes. Consistent with these findings, we demonstrated that β-arrestin-1 is highly expressed and constitutively phosphorylated at Ser-12 residue in a panel of RON positive human colorectal cancer cell lines (HT29,HCT116 and SW620), but neither in adenoma-derived cells nor in normal fibroblast cells. Activating RON with its ligand, MSP, induced significant de-phosphorylation of β-arrestin -1 in a time-response manner, suggests that RON stimulates β-arrestin-1 activity. This effect can be completely inhibited by MEK inhibitor PD98095. Silencing β-arrestin-1 expression by specific RNA interfere techniques caused dramatic morphological and phenotypic changes in colorectal cancer cells. More importantly cells became much more sensitive to apoptosis as illustrated by H33258 fluorescence nuclear staining. In conclusion, our data shows that β-arrestin -1 is highly expressed in RON positive colon cancer cells and RON activation by MSP induces de-phosphorylation and activation of β-arrestin-1. Further more, Knock down of β-arrestin-1 led to more apoptosis in cancer cells; Taking together these results suggest RON activation in colon cancer cells may increase malignancy through activation of β-arrestin-1. This research was funded in part by NIH R01 91980.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]