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Breast cancer is a hormone-dependent disease in which estrogen signaling targeting drugs fail in about 10 % due to resistance. Strong evidences highlighted the mitogen role of progesterone, its ligands, and the corresponding progesterone receptor (PR) isoforms in mammary carcinoma. Several PR antagonists have been synthesized; however, some of them are non-selective and led to side or toxic effects. Herein, we evaluated the anti-tumor activity of a commercially available PR modulator, ulipristal acetate (UPA), and a new selective and passive PR antagonist "APR19" in a novel preclinical approach based on patient-derived breast tumor (HBCx-34) xenografted in nude mice. As opposed to P4 that slightly reduces tumor volume, UPA and APR19 treatment for 42 days led to a significant 30 % reduction in tumor weight, accompanied by a significant 40 % retardation in tumor growth upon UPA exposure while a 1.5-fold increase in necrotic areas was observed in APR19-treated tumors. Interestingly, PR expression was upregulated by a 2.5-fold factor in UPA-treated tumors while APR19 significantly reduced expression of both PR and estrogen receptor α, indicating a potential distinct molecular mechanism among PR antagonists. Cell proliferation was clearly reduced in UPA group compared to vehicle conditions, as revealed by the significant reduction in Ki-67, Cyclin D1, and proliferating cell nuclear antigen (PCNA) expression. Likewise, an increase in activated, cleaved poly(ADP-ribose) polymerase (PARP) expression was also demonstrated upon UPA exposure. Collectively, our findings provide direct in vivo evidence for anti-progestin-mediated control of human breast cancer growth, given their anti-proliferative and pro-apoptotic activities, supporting a potential role in breast cancer therapy.

Mature Sertoli cells (SC) are critical mediators of androgen regulation of spermatogenesis, via the androgen receptor (AR) signaling. Available immortalized SC lines loose AR expression or androgen responsiveness, hampering the study of endogenous AR regulation in SC. We have established and characterized a novel clonal mouse immortalized SC line, ST38c. These cells express some SC specific genes (sox9, wt1, tjp1, clu, abp, inhbb), but not fshr, yet more importantly, maintain substantial expression of endogenous AR as determined by PCR, immunocytochemistry, testosterone binding assays and Western blots. Microarrays allowed identification of some (146) but not all (rhox5, spinlw1), androgen-dependent, SC expressed target genes. Quantitative Real-Time PCR validated regulation of five up-regulated and two down-regulated genes. We show that AR undergoes androgen-dependent transcriptional activation as well as agonist-dependent posttranslational stabilization in ST38c cells. This cell line constitutes a useful experimental tool for future investigations on the molecular and cellular mechanisms of androgen receptor signaling in SC function.

Steroid hormone receptors are ligand-stimulated transcription factors that modulate gene transcription by recruiting coregulators to gene promoters. Subcellular localization and dynamic movements of transcription factors have been shown to be one of the major means of regulating their transcriptional activity. In the present report we describe the subcellular localization and the dynamics of intracellular trafficking of steroid receptor coactivator 1 (SRC-1). After its synthesis in the cytoplasm, SRC-1 is imported into the nucleus, where it activates transcription and is subsequently exported back to the cytoplasm. In both the nucleus and cytoplasm, SRC-1 is localized in speckles. The characterization of SRC-1 nuclear localization sequence reveals that it is a classic bipartite signal localized in the N-terminal region of the protein, between amino acids 18 and 36. This sequence is highly conserved within the other members of the p160 family. Additionally, SRC-1 nuclear export is inhibited by leptomycin B. The region involved in its nuclear export is localized between amino acids 990 and 1038. It is an unusually large domain differing from the classic leucine-rich NES sequences. Thus SRC-1 nuclear export involves either an alternate type of NES or is dependent on the interaction of SRC-1 with a protein, which is exported through the crm1/exportin pathway. Overall, the intracellular trafficking of SRC-1 might be a mechanism to regulate the termination of hormone action, the interaction with other signaling pathways in the cytoplasm and its degradation.