Core-binding factor β interacts with Runx2 and is required for skeletal development

Abstract

Core-binding factor (CBF, also called polyomavirus enhancer binding protein 2 (PEBP2B)) is associated with an inversion of chromosome 16 and is associated with acute myeloid leukemia in humans1. CBF forms a heterodimer with RUNX1 (runt-related transcription factor 1), which has a DNA binding domain homologous to the pair-rule protein runt in Drosophila melanogaster. Both RUNX1 and CBF are essential for hematopoiesis2, 3, 4, 5, 6. Haploinsufficiency of another runt-related protein, RUNX2 (also called CBFA1), causes cleidocranial dysplasia in humans7 and is essential in skeletal development by regulating osteoblast differentiation and chondrocyte maturation8, 9, 10, 11, 12, 13, 14, 15. Mice deficient in Cbfb (Cbfb-/-) die at midgestation4, 5, 6, so the function of Cbf in skeletal development has yet to be ascertained. To investigate this issue, we rescued hematopoiesis of Cbfb-/- mice by introducing Cbfb using the Gata1 promoter. The rescued Cbfb-/- mice recapitulated fetal liver hematopoiesis in erythroid and megakaryocytic lineages and survived until birth, but showed severely delayed bone formation. Although mesenchymal cells differentiated into immature osteoblasts, intramembranous bones were poorly formed. The maturation of chondrocytes into hypertrophic cells was markedly delayed, and no endochondral bones were formed. Electrophoretic mobility shift assays and reporter assays showed that Cbf was necessary for the efficient DNA binding of Runx2 and for Runx2-dependent transcriptional activation. These findings indicate that Cbf is required for the function of Runx2 in skeletal development.