Insulin-like growth factor 1 regulates the location, stability, and transcriptional activity of β-catenin

The insulin-like growth factor (IGF) type 1 receptor is required for growth, transformation, and protection from apoptosis. IGFs can enhance cell migration, which is known to be influenced via regulation of the E-cadherin/β-catenin complex. We sought to investigate whether IGF-1 modulated the interaction between E-cadherin and β-catenin in human colorectal cancer cells. We used the C10 cell line, which we established and have previously shown to lack adenomatous polyposis coli, E-cadherin, or β-catenin mutations. We found that IGF-1 stimulation enhanced tyrosine phosphorylation of two proteins, β-catenin and insulin-receptor substrate 1, which formed a complex with E-cadherin. Tyrosine phosphorylation of β-catenin was accompanied by rapid (<1 min) dissociation from E-cadherin at the plasma membrane, followed by relocation to the cellular cytoplasm. IGF-1 also enhanced the stability of β-catenin protein. Despite this, we observed no enhancement of transcriptional activity in complex with T-cell factor 4 (Tcf-4) in human embryonic kidney 293 cells treated with IGF-1 or insulin alone. IGF-1 did, however, enhance transcriptional activity in combination with lithium chloride, an inhibitor of glycogen synthase kinase 3β, which also stabilizes β-catenin. In conclusion, we have shown that IGF-1 causes tyrosine phosphorylation and stabilization of β-catenin. These effects may contribute to transformation, cell migration, and a propensity for metastasis in vivo.