Regulation of c-jun and jun-B by progestins in T-47D human breast cancer cells

Progesterone receptors, their isoforms and progesterone regulated transcription

This review discusses mechanisms by which progesterone receptors (PR) regulate transcription. We examine available data in different species and tissues regarding: (1) regulation of PR levels; and (2) expression profiling of progestin-regulated genes by total PRs, or their PRA and PRB isoforms. (3) We address current views about the composition of progesterone response elements, and postulate that PR monomers acting through "half-site" elements are common, entailing cooperativity with neighboring DNA-bound transcription factors. (4) We summarize transcription data for multiple progestin-regulated promoters as directed by total PR, or PRA vs. PRB. We conclude that current models and methods used to study PR function are problematical, and recommend that future work employ cells and receptors appropriate to the species, focusing on analyses of the effects of endogenous receptors targeting endogenous genes in native chromatin.

Activation of progestin receptors in female reproductive behavior: Interactions with neurotransmitters

The steroid hormone, progesterone (P), modulates neuroendocrine functions in the central nervous system resulting in alterations in physiology and reproductive behavior in female mammals. A wide body of evidence indicates that these neural effects of P are predominantly mediated via their intracellular progestin receptors (PRs) functioning as "ligand-dependent" transcription factors in the steroid-sensitive neurons regulating genes and genomic networks. In addition to P, intracellular PRs can be activated by neurotransmitters, growth factors and cyclic nucleotides in a ligand-independent manner via crosstalk and convergence of pathways. Furthermore, recent studies indicate that rapid signaling events associated with membrane PRs and/or extra-nuclear, cytoplasmic PRs converge with classical PR activated pathways in neuroendocrine regulation of female reproductive behavior. The molecular mechanisms, by which multiple signaling pathways converge on PRs to modulate PR-dependent female reproductive behavior, are discussed in this review.

Progestins in the menopause in healthy women and breast cancer patients

At present, more than 200 progestin compounds are synthetized, but their biological effects are different: this is function of their structure, receptor affinity, metabolic transformations, the target tissues considered, dose. The action of progestins in breast cancer is controversial; some studies indicate an increase in breast cancer incidence, others show no differences, and yet others indicate a decrease. Many studies agree that treatment with progestins plus estrogens at a low dose and during a limited period (less than 5 years) can have beneficial effects in peri- and post-menopausal women. It was demonstrated that various progestins (e.g. nomegestrol acetate, medrogestone, promegestone), as well as tibolone and its metabolites, can block the enzymes involved in estradiol bioformation (sulfatase, 17beta-hydroxysteroid dehydrogenase) in breast cancer. Progesterone is converted into various metabolic products: in normal breast tissue the transformation is mainly to 4-ene derivatives, whereas in the tumor tissue 5alpha-pregane derivatives are predominant. Aromatase activity is the last step in the formation of estrogens by the conversion of androgens. In recent studies it was shown that 20alpha-dihydroprogesterone, a metabolite found mainly in normal breast tissue and having anti-proliferative properties, can act as an anti-aromatase agent. The data suggest the possible utilization of this compound in breast cancer prevention. In conclusion, in order to clarify and better understand the response of progestins in breast cancer (incidence and mortality), as well as in hormone replacement therapy or in endocrine dysfunction, new clinical trials are necessary using other progestins in function of the dose and period of treatment.

Progestins and breast cancer

In the last years there has been an extraordinary development in the synthesis of new progestins. These compounds are classified, in agreement with their structure, in various groups which include progesterone, retroprogesterones, 17alpha-hydroxyprogesterones, 19-norprogesterones, 17alpha-hydroxyprogesterone derivatives, androstane and estrane derivatives. The action of progestins is a function of many factors: its structure, affinity to the progesterone receptor or to other steroid receptors, the target tissue considered, the biological response, the experimental conditions, dose, and metabolic transformation. The information on the action of progestins in breast cancer patients is very limited. Positive response with the progestins: medroxyprogesterone acetate and megestrol acetate was obtained in post-menopausal patients with advanced breast cancer. However, extensive information on the effect of progestins was obtained in in vitro studies using hormone-dependent and hormone-independent human mammary cancer cell lines. It was demonstrated that in the hormone-dependent breast cancer cells, various progestins (nomegestrol acetate, tibolone, medrogestone, promegestone) are potent sulfatase inhibitory agents. The progestins can also involve the inhibition of mRNA of this enzyme. In another series of studies it was also demonstrated that various progestins are very active in inhibiting the 17beta-hydroxysteroid dehydrogenase for the conversion of estrone to estradiol. More recently it was observed that the progestins promegestone or medrogestone stimulate the sulfotransferase for the formation of estrogen sulfates. Consequently, the blockage in the formation of estradiol via sulfatase, or the stimulatory effect on sulfotransferase activity, by progestins can open interesting and new possibilities in clinical applications in breast cancer.