Osteopontin (SPP1) is a member of the small integrin-binding ligand N-linked glycoprotein (SIBLING) family of proteins (Bellahcène et al. 2008). It is a highly phosphorylated sialoprotein and prominent component of the mineralized extracellular matrices of bones and teeth. It binds multiple integrins including alphaVbeta3, alphaVbeta1 and alphaVbeta5 (Liaw et al. 1995) alpha9beta1 (Smith et al. 1996, Yokosaki et al. 1999), alpha4beta1 (Bayliss et al. 1998) and the receptor CD44 (Weber et al. 1996, Katagiri et al. 1999). The SPP1–CD44 interaction may be important for colorectal cancer progression (Rao et al. 2013).