Osteopontin: A Bone Matrix Protein for Adhesion Assay

Abstract

Skeletal development is a tightly regulated homeostatic process that requires proper functioning of osteoblasts, the bone forming cells, and osteoclasts, the bone resorbing cells. Improper functioning of either of these cell types results in diseases such as osteoporosis, osteogenesis imperfecta as well as Paget's disease. Crucial for the proper maintenance of the skeleton is the bone matrix, which encompasses both organic and inorganic components. Osteopontin (Opn) is an example of a major non-collagenous protein present in bone. Its expression is crucial for bone remodeling since it functions in recruiting osteoclasts for bone resorption and facilitates their adhesion to the bone matrix. Osteopontin is expressed in variety of cells and functions in facilitating signal transduction upon engagement of integrin. Osteopontin binds to the αvß3 (vitronectin receptor) the major integrin expressed on osteoclasts thereby mediating cell adhesion and migration. As a model to study osteopontin-mediated adhesion we have employed commercially available osteopontin and the HEK 293 cells that stably overexpress the vitronectin receptor (Vnr cells). We studied the ability of the Vnr cells to adhere to different extracellular matrices including osteopontin.