PKA can phosphorylate serines S167 or S171 on the intracellular domain of PDPN, whereas CDK5 preferentially phosphorylates S171. However, phosphorylation of both intracellular serines on PDPN is required to inhibit PDPN mediated cell migration. Thus, PKA and CDK5 may phosphorylate PDPN S167 and S171, respectively, in order to decrease cell motility.