Figure 4. Schematic representation of PTHrP-induced osteoclast formation. PTHrP induces RANKL expression in PDL cells by a mechanism independent of the cAMP/PKA signaling pathway. PKC contributes to induction of RANKL mRNA induced by PTHrP in PDL cells as well as regulation of osteoclast precursor cell number. PGE₂ induces RANKL expression in PDL cells via the cAMP/PKA signaling pathway.