SPP1 and hepatocellular carcinoma: In comparison with untreated cells, recombinant human osteopontin (rhOPN) up-regulated CXCR4, SDF-1α, and MMP-2 expression about 5-, 4-, and 6-fold on the protein levels through binding to integrin αvβ3 and CD44v6 in hepatocellular carcinoma cells (SMMC7721 and HepG2).