The model for PRL-induced PRLR activation suggests that JAK2 phosphorylates PRLR on specific tyrosine residues. Consistent with this, JAK2 and PRLR are phosphorylated in response to activating ligand (Lebrun et al. 1994) and PRLR tyrosine phosphorylation is required for subsequent Stat signaling (Pezet et al. 1997). Though this evidence is consistent with a role for JAK2, it has not been formally demonstrated that JAK2 is the kinase responsible for PRLR tyrosine phosphorylation.