VIPR1 and osteosarcoma: Although the expression of VPAC1 and VPAC2 has been proven in a mesenchymal derived osteoblastic cell line [54] as well as in rat osteosarcoma UMR-106 cells [23] and the involvement of VPAC1 receptor in mechanical induction of osteoblast differentiation has also been demonstrated [46], this function seems tissue specific.