ZFYVE16 and osteoporosis: Endosome-associated FYVE-domain protein (endofin), previously implicated in regulating membrane trafficking, also recruits protein phosphatase 1 catalytic subunit (PP1c) to exert a negative regulative effect on BMP signaling by dephosphorylating the BMP type I receptor.304 A single point mutation of endofin (F872A) disrupts endofin–PP1c interaction and sensitizes BMP signaling to increase osteogenesis in vitro and in vivo.304 Casein kinase II (CK2) phosphorylates the ALK3 receptor to block its activity, reducing BMP2’s osteogenic effects on osteoblasts in patients with osteoporosis.305