PRL and breast cancer: In order to assess whether PRL-induced tyrosyl phosphorylation of PAK1 has a physiological effect on breast cancer metastasis, TMX2-28 stably overexpressing GFP, myc-PAK1 WT, or myc-PAK1 Y3F were inoculated in mouse mammary fat pads and mice were treated with PRL for 8 weeks.