Descripción: The present study focused on interactions between signaling pathways activated by progestins and by type I and II receptor tyrosine kinases (RTKs) in mammary tumors. An experimental model in which the synthetic progestin medroxyprogesterone acetate (MPA) induced mammary adenocarcinomas in Balb/c mice was used. MPA-stimulated proliferation, both in vivo and in vitro, of progestin-dependent tumors induced up-regulation of ErbB-2 protein levels and tyrosine phosphorylation of this receptor. Combinations of antisense oligodeoxynueleotides (ASODNs) directed to ErbB-2 mRNA with ASODNs directed to the insulin-like growth factor-I receptor (IGF-IR) were used to study the effect of the simultaneous block of these receptors on the MPA-induced proliferation of epithelial cells from the progestin-dependent C4HD line. Neither synergistic nor additive effects on the inhibition of MPA-induced proliferation of C4HD cells were observed as a result of the combination of these ASODNs. Suppression of IGF-IR expression by ASODNs resulted in complete abrogation of MPA-induced phosphorylation of ErbB-2 in C4HD cells, whereas blockage of ErbB-2 did not affect IGF-IR phosphorylation. These results show the existence of a hierarchical interaction between IGF-IR and ErbB-2, by means of which IGF-IR directs ErbB-2 phosphorylation. We demonstrated, for the first time, that this hierarchical interaction involves physical association of both receptors, resulting in the formation of a heteromeric complex. Furthermore, confocal laser microscopy experiments demonstrated that MPA was able to induce co-localization of ErbB-2 and IGF-IR. This hetero-oligomer was also found in MCF-7 human breast cancer cells in which association of IGF-IR and ErbB-2 was induced by heregulin and IGF-I.

Descripción: Interactions between steroid hormone receptors and signal transducer and activator of transcription (Stat)-mediated signaling pathways have already been described. In the present study, we explored the capacity of progestins to modulate Stat3 transcriptional activation in an experimental model of hormonal carcinogenesis in which the synthetic progestin medroxyprogesterone acetate (MPA) induced mammary adenocarcinomas in BALB/c mice and in the human breast cancer cell line T47D. We found that C4HD epithelial cells, from the MPA-induced mammary tumor model, expressed Stat3 and that MPA treatment of C4HD cells up-regulated Stat3 protein expression. In addition, MPA induced rapid, nongenomic Stat3, Jak1, and Jak2 tyrosine phosphorylation in C4HD and T47D cells. MPA treatment of C4HD cells also resulted in rapid c-Src tyrosine phosphorylation. These effects were completely abolished by the progestin antagonist RU486. Abrogation of Jak1 and Jak2 activity by transient transaction of C4HD cells with dominant negative (DN) Jak1 or DN Jak2 vectors, or inhibition of Src activity by preincubation of cells with the Src family kinase inhibitor PP2, blocked the capacity of MPA to induce Stat3 phosphorylation. Treatment of C4HD cells with MPA induced Stat3 binding to DNA. In addition, MPA promoted strong Stat3 transcriptional activation in C4HD and T47D 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, Stat3-C. While expression of Stat3Y705-F mutant had an inhibitory effect on MPA-induced growth of C4HD cells, transfection with the constitutively activated Stat3-C vector 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-F expression vector significantly inhibited these cells' ability to form tumors in syngeneic mice. Our results have for the first time demonstrated that progestins are able to induce Stat3 transcriptional activation, which is in turn an obligatory requirement for progestin stimulation of both in vitro and in vivo breast cancer growth. Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Descripción: Uterine decidualization is characterized by stromal cell proliferation and differentiation, which are controlled by ovarian hormones estradiol and progesterone. Here we report that the proliferative response of UIII rat uterine stromal cells to a short treatment with progestins requires active progesterone receptor (PR) and estrogen receptor β (ERβ) as well as a rapid and transient activation of Erk1-2 and Akt signaling. The optimal R5020 concentration for the proliferative response as well as for activation of the signaling cascades was between 10 and 100 pM. UIII cells are negative for ERα and have low levels of ERβ and PR located mainly in the cytoplasm. Upon progestin treatment PR translocated to the cell nucleus where it colocalized with activated Erk1-2. Neither progestins nor estradiol transactivated the corresponding transfected reporter genes, suggesting that endogenous PR and ERβ are transcriptionally incompetent. A fraction of endogenous PR and ERβ form a complex as demonstrated by coimmunoprecipitation. Taken together, our results suggest that the proliferative response of uterine stromal cells to picomolar concentrations of progestins does not require direct transcriptional effects and is mediated by activation of the Erk1-2 and Akt signaling pathways via cross talk between PR and ERβ. Copyright © 2005 by The Endocrine Society.