RUNX2 and plasma cell myeloma: We showed that in the co-culture studies, a marker of OB differentiation Runx2 gene expression, was inhibited by the presence of 5TGM1 myeloma cells and that this effect could be reversed by co-treatment of cultures with a blocking antibody for Sostdc1, indicating that the levels of Sostdc1 generated in co-cultures are biologically active.