Figure 4.

Ectopic PTK6 is active and promotes STAT3 phosphorylation at tyrosine residue 705 in the mouse mammary gland. Immunofluorescence assays were performed on mammary gland serial sections from age-matched nontransgenic (NT) or transgenic (Tg) animals using antibodies specific for active PTK6 (P-Y342) and active STAT3 (P-Y705). PTK6 was not expressed in prepubescent transgenic animals up to 6 weeks of age, and STAT3 phosphorylation was minimal. Upon maturity, PTK6 was expressed and activated in Tg mammary glands, and STAT3 phosphorylation and translocation to the nucleus was observed (12 weeks of age). At 40 weeks of age, ectopic PTK6 remained active and STAT3 displayed activating phosphorylation and nuclear localization in Tg animals, but this phosphorylation was not detected in NT mammary glands. Primary antibody binding was detected with fluorescein isothiocyanate (green) and sections were counterstained with DAPI (blue). The size bar represents 20 μm.