Cross-talk between Progesterone Receptor and Signal Transducer and Activator of Transcription 3 (STAT3) in breast cancer

PROIETTI CJ ; SCHILLACI R ; ROSEMBLIT C ; SALATINO M ; CARNEVALE R ; PECCI A ; KORNBLIHTT AR ; CHARREAU EH ; ELIZALDE PV

Seefeld

Simposio; 16th International Symposium of the Journal of Steroid Biochemistry & Molecular Biology; 2004

The presence of interactions between steroid hormone receptors and signal transducers and activators of transcription (Stats)-mediated signaling pathways has already been described. In the present work, we assessed progestins ability to modulate Stat3 transcriptional activation in an experimental model of hormonal carcinogenesis in the which the synthetic progestin medroxyprogesterone acetate (MPA) induced mammary adenocarcinomas in female Balb/c mice. Our findings demonstrated that primary cultures of C4HD epithelial celIs, from the MPA-induced mammary tumor model, expressed Stat3 at protein level and that MPA treatment of C4HD cells for 48-h upregulated Stat3 protein expression. In addition, MPA was able to induce Stat3 tyrosine phosphorylation after 5-10 min stimulation. Electrophoretic mobility shift assays (EMSA) showed that MPA treatment of C4HD cells for 15 min induced Stat3 binding to DNA using as labeled probe either the sis-inducible element (SIE) of the human c-fos promoter or the interleukin-6-inducible high affinity Stat3-responsive site within the rat alpha(2)-macroglobulin promoter. The progestin antagonist RU486 completely abolished MPA-induced Stat3 binding to DNA indicating that MPA effect is mediated by the classic PR. Transient transfections of C4HD cells with a luciferase reporter gene containing four copies of the m67 high-affinity Stat 3 binding site gene, demonstrated that MPA promoted a significant increase in luciferase activity, which was inhibited by RU486. These results provide the first demonstration that progestins, acting through the classic PR are able to induce transcriptional activation of Stat3 in mammary tumor cells.