GIP and osteosarcoma: Exposing three human osteosarcoma cell lines expressing GIPRs (TE-85, MG-63, and Saos-2) to GIP resulted in the release of bone formation marker P1NP (Pacheco-Pantoja et al., 2011), in which the expression of Col-1 in Saos-2 cells increased (Bollag et al., 2000).