Cell attachment activity of the 44 kilodalton bone phosphoprotein is not restricted to bone cells

Proteins that promote cell migration, attachment and spreading are considered to play an important role in the regulation of cell function. Recently, a 44 kilodalton bone phosphoprotein (44K BPP) was shown to enhance the attachment of gingival fibroblasts and osteoblasts in vitro. The potential importance of this attachment protein in the regulation of mineralized tissue homeostasis prompted us to evaluate its ability to promote the attachment and migration of several other cell types. All the fibroblast cell lines and non-transformed calvaria cell lines assayed exhibited enhanced attachment and spreading in response to 44K BPP. Rat osteosarcoma cells (ROS 17/2.8) expressing osteoblast-like features, exhibited enhanced attachment in response to 44K BPP, while non-osteoblast-like cells (ROS 25/1) obtained from the same osteosarcoma did not. Two epithelial cell lines, CCL4 and A431, demonstrated enhanced attachment when exposed to fibronectin or laminin, but not 44K BPP. Another epithelial-like cell line, HT 1080, derived from a fibrosarcoma, showed enhanced attachment in the presence of all three attachment proteins. Fibronectin, but not 44K BPP, promoted the chemotactic migration of fibroblasts. These studies indicate that the role of 44K BPP attachment protein in the regulation of cell behavior is not restricted to bone cells.