Insulin determines TGF-β-induced epithelial-to-mesenchymal transition through FOXO1 cellular translocation

Background and Aims: It remains unknown why TGF-β easily induces epithelial-to-mesenchymal transition (EMT) in vitro, but is rarely detectable in vivo. This study scrutinizes the key role of FOXO1 in the TGF-β-induced EMT in hepatocytes, cholangiocytes and liver cancer cells.

Methods: Expression of FOXO1, EMT phenotype proteins such as SNAIL1 and E-cadherin, as well as phosphorylation of SMAD2/3 were examined by immunohistochemistry in liver tissue of patients. TGF-β-induced EMT and the role of insulin on EMT were investigated in cultured hepatocytes, cholangiocytes, HCC- and cholangiocarcinoma cells.

Results: Immunohistochemical staining shows robust SMAD2/3 phosphorylation in liver cells, including hepatocytes, cholangiocytes and cancer cells. However, the same cells maintain E-cadherin expression and do not express SNAIL1. In cultured hepatocytes, cholangiocytes and liver cancer cells, TGF-β stimulation induces expression of core EMT transcription factors SNAIL1 and SNAIL2, which subsequently leads to loss of E-cadherin expression upregulation of mesenchymal markers such as collagen and vimentin. SNAIL1 and SNAIL2 transcription requires both TGF-β-induced p-SMAD2/3-SMAD4 and FOXO1, which form a complex and bind to the promoters of SNAILs. Notably, insulin concentrations in medium of liver cells rapidly reduce to very low levels within 48h. Mechanistically, adding insulin into the culture medium inhibits TGF-β-induced SNAIL1/2 transcription, subsequent E-cadherin loss and EMT through phosphorylation and nuclear exclusion of FOXO1.

Conclusion: Given a key role of insulin in the regulation of systemic homeostasis, insulin depletion is an impossible mission in mammals. The presence of insulin impedes EMT of liver cells through phosphorylating FOXO1 in mammals.

Publication History

Article published online:
20 January 2025