Effects of a bone lysine-rich 18 kDa protein on osteoblast-like MC3T3-E1 cells

A lysine-rich 18 kDa protein was isolated from bovine bone and examined for its effects on osteoblast-like MC3T3-E1 cells. This protein is homologous to a heparin-binding protein in brain and uterus. This protein enhanced cell attachment independent of the Arg-Gly-Asp cell-binding sequence and stimulated proliferation during the growth phase. Addition of this protein to cell cultures on days 11, 12, and 13 after confluency resulted in a 1.6-2.0-fold increase in the alkaline phosphatase activity and little increase in the DNA content. These findings suggest that the 18 kDa protein may be functional in promoting the proliferation and differentiation of osteoblasts.