IRS1 and hepatocellular carcinoma: To verify that Irs1 expression was indeed regulated by β-catenin in the liver, cells from the rat hepatoma cell line H4IIE, which is known to express the active form of β-catenin, were transfected with siβ-catenin, which resulted in an ∼80% reduction of the β-catenin mRNA expression level (Fig. 8a).