p44/42 MAPK activation is necessary for receptor activator of nuclear factor-kappaB ligand induction by high extracellular calcium

Although extracellular calcium (Ca(2+)(o)) has been suggested to modulate bone remodeling, the exact mechanism is unclear. This study was performed to explore the signaling pathways of high Ca(2+)(o) that are responsible for controlling the expression of receptor activator of NF-kappaB ligand (RANKL) in mouse osteoblastic cells. As previously reported, high Ca(2+)(o) increased RANKL expression. However, the G protein-coupled Ca(2+)(o)-sensing receptor (CaSR) was not detected in the primary cultured mouse osteoblastic cell. The inhibition of the pertussis-sensitive G protein, phospholipase C, protein kinase C, intracellular calcium mobilization, p38 MAPK, or phosphoinositide 3-kinase did not block RANKL induction caused by high Ca(2+)(o). In contrast, the inhibition of p44/42 MAPK pathway reduced the RANKL expression induced by high Ca(2+)(o). Moreover, high Ca(2+)(o) activated p44/42 MAPK and MEK1/2. These results suggest that RANKL induction by high Ca(2+)(o) might not be mediated by CaSR and its putative downstream signaling pathways, but the pathway employing p44/42 MAPK is involved in the high Ca(2+)(o)-induced RANKL expression in mouse osteoblastic cells.