Noggin inhibits bone formation induced by proteasome inhibitors. Histologic sections of cultured murine neonatal calvarial bones treated with (a) media alone, (b) noggin (2 μg/ml), (c) epoxomicin (20 nM), (d) epoxomicin (20 nM) and noggin (2 μg/ml), (e) rhBMP-2 (100 ng/ml), (f) rhBMP-2 (100 ng/ml) and noggin (2 μg/ml), (g) aFGF (50 ng/ml), (h) aFGF (50 ng/ml) and noggin (2 μg/ml).