Progesterone receptor isoform ratios influence the transcriptional activity of progestins via the progesterone receptor

Effects of melatonin implants on uterine inflammation and ovarian progesterone receptor expression in female cats: A histopathological and molecular analysis

This study aimed to evaluate the histopathological and molecular effects of subcutaneous melatonin implants on the reproductive organs of female cats. Twenty cats were randomly divided into two groups: a control group (Cont), which underwent ovariohysterectomy without prior treatment, and a melatonin-treated group (Mel), which received 18 mg melatonin implants subcutaneously in the interscapular region before ovariohysterectomy. Histopathological and immunohistochemical analyses of uterine tissues were performed, along with quantitative RT-PCR and Western blot to assess inflammatory markers and progesterone receptor expression. Histopathological findings revealed normal uterine structures in most control cats, with mild inflammation observed in a few cases. In contrast, melatonin-treated cats exhibited varying degrees of uterine inflammation, ranging from mild to severe. Immunohistochemical analysis showed elevated IL-1β expression in the treated group compared to controls. Molecular analysis revealed significant upregulation of IL-6, TNF-α, NF-kB, IFN-γ, ICAM-1, and iNOS in uterine tissues of the treated group (p < 0.05). Western blot analysis confirmed increased IL-6, TNF-α, NF-kB, IFN-γ, and PGR protein expression in melatonin-treated cats, supporting inflammatory and hormonal alterations. Additionally, increased mRNA expression of progesterone receptor isoforms PR-A and PR-B was detected in ovarian tissues of melatonin-treated cats (p < 0.05). The results indicate that while melatonin implants effectively suppress estrus in female cats, they may induce uterine inflammation and alter the hormonal and immune profiles of reproductive tissues. These findings highlight the need for further investigation into the long-term safety and mechanisms of melatonin's effects on reproductive health.

Structural proteomics defines a sequential priming mechanism for the progesterone receptor

The progesterone receptor (PR) is a steroid-responsive nuclear receptor with two isoforms: PR-A and PR-B. Disruption of PR-A:PR-B signaling is associated with breast cancer through interactions with oncogenic co-regulatory proteins (CoRs). However, molecular details of isoform-specific PR-CoR interactions remain poorly understood. Using structural mass spectrometry, we investigate the sequential binding mechanism of purified full-length PR and intact CoRs, steroid receptor coactivator 3 (SRC3) and p300, as complexes on target DNA. Our findings reveal selective CoR NR-box binding by PR and unique interaction surfaces between PR and CoRs during complex assembly, providing a structural basis for CoR sequential binding on PR. Antagonist-bound PR showed persistent CoR interactions, challenging the classical model of nuclear receptor activation and repression. Collectively, we offer a peptide-level perspective on the organization of the PR transcriptional complex and infer the mechanisms behind the interactions of these proteins, both in active and inactive conformations.

Structural proteomics defines a sequential priming mechanism for the progesterone receptor

The progesterone receptor (PR) is a steroid-responsive nuclear receptor with two isoforms: PR-A and PR-B. Disruption of PR-A:PR-B signaling is associated with breast cancer through interactions with oncogenic co-regulatory proteins (CoRs). However, molecular details of isoform-specific PR-CoR interactions remain poorly understood. Using structural mass spectrometry, we investigate the sequential binding mechanism of purified full-length PR and intact CoRs, steroid receptor coactivator 3 (SRC3) and p300, as complexes on target DNA. Our findings reveal selective CoR NR-box binding by PR and unique interaction surfaces between PR and CoRs during complex assembly, providing a structural basis for CoR sequential binding on PR. Antagonist-bound PR showed persistent CoR interactions, challenging the classical model of nuclear receptor activation and repression. Collectively, we offer a peptide-level perspective on the organization of the PR transcriptional complex and infer the mechanisms behind the interactions of these proteins, both in active and inactive conformations.

Progestins and breast cancer hallmarks: The role of the ERK1/2 and JNK pathways in estrogen receptor positive breast cancer cells

Progestins used in hormonal contraceptives and menopausal hormone therapy (MHT) have been linked to increased breast cancer risk. Whether the association holds for all progestins is unclear and the underlying mechanisms remain poorly understood. We directly compared the effects of four progestins (medroxyprogesterone acetate (MPA), norethisterone acetate (NET-A), levonorgestrel (LNG) and drospirenone (DRSP)) to each other and the natural progestogen progesterone (P4) on selected cancer hallmarks. To provide mechanistic insight into these effects, we assessed the role of the progesterone receptor (PR), and the extracellular signal-related kinase (ERK1/2) and c-Jun N terminal (JNK) signaling pathways. We showed that the increased proliferation of the luminal T47D breast cancer cell line by P4 and all progestins, albeit to different extents, was inhibited by PR knockdown and inhibition of both the ERK1/2 and JNK pathways. While knockdown of the PR also blocked the upregulation of MKI67 and CCND1 mRNA expression by selected progestogens, only a role for the ERK1/2 pathway could be established in these effects. Similarly, only a role for the ERK1/2 pathway could be confirmed for progestogen-induced colony formation, whereas both the ERK1/2 and JNK pathways were required for cell migration in response to the three older progestins implicated in the etiology of breast cancer, MPA, NET-A and LNG. Together our results show that all the progestins elicit their effects on cell proliferation via a mechanism requiring the PR, ERK1/2 and JNK pathways. While the ERK1/2 and JNK pathways are also required for increased cell migration by the older progestins, only a role for the ERK1/2 pathway could be established in their effects on colony formation. Notably, the cytoplasmic PR was not needed for activation of the ERK1/2 pathway by the progestogens. Given that DRSP showed significantly lower proliferation than MPA and NET-A, and that it had no effect on breast cancer cell migration and colony formation, hormonal formulations containing the newer generation progestin DRSP may provide a better benefit/risk profile towards breast cancer than those containing the older generation progestins.