A bone-derived growth factor isolated from rat calvariae is beta 2 microglobulin.

Rat calvariae are known to secrete a bone-derived growth factor (BDGF) that stimulates bone DNA and collagen synthesis. BDGF was purified from calvarial culture medium with dialysis, gel filtration and HPLC. Amino acid composition of BDGF was compatible with murine beta 2 microglobulin (beta 2 m), and amino terminal sequence analysis revealed identity with mature murine beta 2 m. This was confirmed by Western blot analysis using a polyclonal antibody to beta 2 m. Like BDGF, human beta 2 m stimulated bone DNA, collagen and noncollagen protein synthesis. Thus, BDGF, an autologous regulator of bone formation, is homologous to beta 2 m.