PRLRs contain intracellular phosphorylated tyrosine residues that are able to bind and activate STATs, demonstrated by the co-immunoprecipitation of rat Stat5 and Prlrs mutated to have a single intracellular tyrosine (Pezet et al. 1997). Prlr mutants with a single tyrosine residue at positions 599, 498 or 492 (reported according to their position in the mature peptide as 580, 479 or 473 in Pezet et al. 1997) were all able to activate Stat5; Y599 gave a much stronger response. Short forms of PRLR lacking these tyrosines did not bind STAT5. The equivalent human tyrosine residues are Y509 and Y611; Y492 is not conserved in humans.
Activation of STAT1 and STAT3 by PRLR has been reported (Da Silva et al. 1996) but the interaction has been suggested to be indirect and possibly mediated by JAK2.