Progestins Induce Transcriptional Activation of Signal Transducer and Activator of Transcription 3 (Stat3) Via Jak and Src-Dependent Mechanism in Breast Cancer Cells

PROIETTI, C.; SALATINO, M.; ROSEMBLIT, C.; CARNEVALE, R.; PECCI, A; KORNBLIHTT, A; MOLINOLO, E.; FRAHM, I; CHARREAU, E; SCHILLACI, R.; ELIZALDE, P.

MOLECULAR AND CELLULAR BIOLOGY

AMER SOC MICROBIOLOGY

Año: 2005 vol. 25 p. 4826 - 4840

0270-7306

Interactions between steroid hormone receptors and signal transducers and activators oftranscription (Stats)-mediated signaling pathways have already been described. In thepresent study, we explored the capacity of progestins to modulate Stat3 transcriptionalactivation in an experimental model of hormonal carcinogenesis in which the syntheticprogestin medroxyprogesterone acetate (MPA) induced mammary adenocarcinomas inBalb/c mice, and in the human breast cancer cell line T47D. We found that C4HDepithelial cells, from the MPA-induced mammary tumor model, expressed Stat3 and thatMPA treatment of C4HD cells up-regulated Stat3 protein expression. In addition, MPAinduced rapid, nongenomic, Stat3, Jak1, and Jak2 tyrosine phosphorylation in C4HD andT47D cells. MPA treatment of C4HD cells also resulted in rapid c-Src tyrosinephosphorylation. These effects were completely abolished by the progestin antagonistRU486. Abrogation of Jak1 and Jak2 activity by transient transfection of C4HD cells withdominant negative (DN) Jak1 or DN Jak2 vectors, or inhibition of Src activity bypreincubation of cells with the Src family kinase inhibitor PP2, blocked MPA capacity toinduce Stat3 phosphorylation. Treatment of C4HD cells with MPA induced Stat3 bindingto DNA. In addition, MPA promoted strong Stat3 transcriptional activation in C4HD andT47D cells, that was inhibited by RU486 and by blockage of Jak1, Jak2 and Src activities.To investigate the correlation between MPA-induced Stat3 activation and cell growth,C4HD cells were transiently transfected with a DN Stat3 expression vector, Stat3Y705-F,or with a constitutively activated Stat3 mutant, Stat3C. While expression of Stat3Y705-Fmutant had an inhibitory effect on MPA-induced growth of C4HD cells, transfection withthe constitutively activated Stat3-Cvector resulted in MPA-independent proliferation.Finally, we addressed the effect of targeting Stat3 in in vivo growth of C4HD breast tumors.Blockage of Stat3 activation by transfection of C4HD cells with the DN Stat3Y705-Fexpression vector significantly inhibited these cells ability to form tumors in syngeneicmice. Our results have for the first time demonstrated that progestins are able to induceStat3 transcriptional activation, which is in turn an obligatory requirement for progestinstimulation of both in vitro and in vivo breast cancer growth.