SPP1 and hepatocellular carcinoma: However, in an in vitro culture system using adjustable matrix stiffness, OPN expression was significantly upregulated in HCC cells with increased matrix stiffness, accompanied by phosphorylation of GSK-3β and expression of nuclear β-catenin, and analysis of integrin β1 knockdown further suggested that high matrix stiffness upregulated OPN expression in HCC cells by activating integrin β1/GSK-3β/β-catenin signaling pathway (You et al., 2015).