The role of progesterone and the progesterone receptor in human reproduction and cancer

Endometrial Progesterone and Estrogen Receptors in Relation to Hormonal Levels in Women with Unexplained Recurrent Miscarriage

OBJECTIVE

 Recurrent miscarriage has been linked to hormonal disturbance due to dysregulation of its receptors rather than to the availability of the hormone. We aimed to investigate endometrial expression of progesterone and estrogen receptors in relation to serum and endometrial hormonal levels in unexplained recurrent miscarriage.

METHODS

 The present case control study included 20 cases with unexplained recurrent miscarriage and 20 parous women as controls. Ovulation was confirmed using an ovulation kit and 10 to 12 days after detecting the urinary luteinizing hormone surge, all women were subjected to a blood sample and to an endometrial biopsy. Progesterone and estrogen levels were measured in serum and in endometrial tissue and receptor concentrations were in the endometrial sample.

RESULTS

 Women with recurrent miscarriage showed significantly lower concentration of receptors in both the cytoplasm and the nucleus of endometrial tissue compared with controls. The nuclear/cytoplasm ratio of progesterone receptor was significantly higher in cases compared with controls, implicating that recurrent miscarriage is probably linked to nongenomic activity of the hormone; this was also significant for estrogen receptor. Serum progesterone and estrogen hormonal levels were comparable between groups while both hormones were significantly reduced in the endometrium of recurrent miscarriage cases. Receptors significantly correlated with endometrial hormonal level but not to serum level.

CONCLUSION

 Recurrent miscarriage might be linked to reduced endometrial progesterone and estrogen receptors and appears to be more related to nongenomic activity of progesterone. Endometrial receptors expression correlates to tissue hormonal level rather than to serum hormonal level.

The role of progesterone and the progesterone receptor in cancer: progress in the last 5 years

INTRODUCTION

Patients with various advanced cancers devoid of nuclear progesterone receptors (nPR) have demonstrated increased quality and length of life when treated with the PR modulator mifepristone, which likely works by interacting with membrane PRs (mPR).

AREAS COVERED

Two immunomodulatory proteins are discussed that seem to play a role in cancers that proliferate whether the malignant tumor is positive or negative for the nPR. These two proteins are the progesterone receptor membrane component-1 (PGRMC-1) and the progesterone-induced blocking factor (PIBF). Both PGRMC-1 and the parent form of PIBF foster increased tumor aggressiveness, whereas splice variants of the 90 kDa form of PIBF inhibit immune response against cancer cells.

EXPERT OPINION

The marked clinical improvement following 200-300 mg of mifepristone is likely related to blocking PIBF. In the low dosage used, mifepristone likely acts as an agonist for PGRMC-1 protein. Mifepristone may be less effective for cancers positive for the nPR because the nPR may be protective and blocking it may have detrimental effects. Based on this hypothetical model, the development of other potential treatment options to provide even greater efficacy for treating cancer are discussed.

A Hypothetical Model Suggesting Some Possible Ways That the Progesterone Receptor May Be Involved in Cancer Proliferation

Cancer and the fetal-placental semi-allograft share certain characteristics, e.g., rapid proliferation, the capacity to invade normal tissue, and, related to the presence of antigens foreign to the host, the need to evade immune surveillance. Many present-day methods to treat cancer use drugs that can block a key molecule that is important for one or more of these characteristics and thus reduce side effects. The ideal molecule would be one that is essential for both the survival of the fetus and malignant tumor, but not needed for normal cells. There is a potential suitable candidate, the progesterone induced blocking factor (PIBF). The parent 90 kilodalton (kDa) form seems to be required for cell-cycle regulation, required by both the fetal-placental unit and malignant tumors. The parent form may be converted to splice variants that help both the fetus and tumors escape immune surveillance, especially in the fetal and tumor microenvironment. Evidence suggests that membrane progesterone receptors are involved in PIBF production, and indeed there has been anecdotal evidence that progesterone receptor antagonists, e.g., mifepristone, can significantly improve longevity and quality of life, with few side effects.

Immune disorder in endometrial cancer: Immunosuppressive microenvironment, mechanisms of immune evasion and immunotherapy

Immunotherapy is an emerging clinical approach that has gained traction over the past decade as a novel treatment option for lung cancer and melanoma. Notably, researchers have made marked improvements in the treatment of endometrial cancer (EC), and potential immune responses have been identified in patients with EC, thereby offering the possibility of exploring immunotherapy for EC. Nevertheless, various needs remain unmet, and immunotherapy applications in EC have yielded limited success, as only a minority of patients exhibited a clinical response. Therefore, further understanding of immune dysfunction associated with EC is still required. The present review describes recent findings regarding the immunosuppressive microenvironment of EC, with emphasis on immune evasion mechanisms and immunotherapy in EC.

The role of progesterone and the progesterone receptor in cancer

There is an abundance of accumulating data strongly suggesting there is a key role for the progesterone receptor in the molecular events effecting the growth or containment of a variety of cancers. This knowledge should lead to novel new strategies to combat various cancers, including drugs classified as progesterone receptor modulators or monoclonal antibodies against some of the key proteins needed for cancer proliferation by suppressing immune surveillance. Areas covered: The role of the classic nuclear receptor and molecular events needed for proliferation are reviewed including cancers of the breast, endometrium, prostate, thyroid, and leiomyomas and leiomyosarcoma. The potential role of non-genomic membrane progesterone receptors is reviewed. The prognostic role of the presence of progesterone receptors is also discussed. Over 1000 research publications were read after conducting a PubMed search. Expert commentary: Discussion is made about a unique immunomodulatory protein called the progesterone induced blocking factor (PIBF). The role of this protein, that is unique to rapidly growing cells, may hold a key to how the cancer cells escape immune surveillance. Thus, techniques to suppress the intracytoplasmic isoforms of PIBF may play a significant role in the fight against all cancers, not just the ones with the classic nuclear progesterone receptors.

The rapid immunosuppression in phytohemagglutinin-activated human T cells is inhibited by the proliferative Ca(2+) influx induced by progesterone and analogs

Progesterone, an endogenous immunomodulator, suppresses human T-cell activation during pregnancy. A sustained Ca(2 +) influx is an important signal for T-cell proliferation after crosslinking of T-cell receptor/CD3 complexes by anti-CD3 antibodies or phytohemagglutinin (PHA). Progesterone targets cell membrane sites inducing rapid responses including elevated intracellular free calcium concentration ([Ca(2+)]i) and suppressed T-cell PHA-activated proliferation. Interestingly, both PHA and progesterone induce [Ca(2+)]i elevation, but it remains unclear whether the PHA-induced Ca(2+) influx is affected by progesterone leading to T-cell immunosuppression. Primary T-cells were isolated from human peripheral blood and the quench effect on intracellular fura-2 fluorescence of Mn(2+) was used to explore the responses to Ca(2+) influx with cell proliferation being determined by MTT assay. PHA-stimulated Ca(2+) influx was dose-dependently suppressed by progesterone and its agonist R5020, which correlated with PHA-activated T-cell proliferation inhibition. A similar dose-dependent suppression effect on cellular Ca(2+) influx and proliferation occurred with the TRPC channel inhibitor BTP2 and selective TRPC3 channel inhibitor Pyr3. In addition, two progesterone analogs, Org OD 02-0 and 20α-hydroxyprogesterone (20α-OHP), also produced dose-dependent suppression of Ca(2+) influx, but had no effect on proliferation. Finally, inhibition of PHA-activated T-cell proliferation by progesterone is further suppressed by 20α-OHP, but not by Org OD 02-0. Overall, progesterone and R5020 are able to rapidly decrease PHA-stimulated sustained Ca(2+) influx, probably via blockade of TRPC3 channels, which suppresses T-cell proliferation. Taken together, the roles of progesterone and its analogs regarding the rapid response Ca(2+) influx need to be further explored in relation to cytokine secretion and proliferation in activated T-cells.

In human T cells mifepristone antagonizes glucocorticoid non-genomic rapid responses in terms of Na(+)/H(+)-exchange 1 activity, but not ezrin/radixin/moesin phosphorylation

Glucocorticoids (GCs) and progesterone have been employed as immunosuppressive agents during pregnancy for many years. Intracellular acidification by GCs is due to a rapid non-genomic inhibition of membrane Na(+)/H(+)-exchange 1 (NHE1) activity and is followed by immunosuppression of PHA-stimulated proliferation. NHE1 is tethered to the cortical actin cytoskeleton through ezrin/radixin/moesin (ERM) proteins within lipid rafts; these regulate cell shape, migration and resistance to apoptosis. We explored whether mifepristone (RU486), an antagonist of GCs in T cells, is able to completely block rapid non-genomic responses, namely NHE1 activity and the phosphorylation C-terminal residues of ERM proteins at threonine (cp-ERM). GCs stimulate a rapid non-genomic cp-ERM response in cells within 5min. RU486 antagonized the GC-induced rapid decrease in NHE1 activity, and arrested PHA-stimulated T cells at G0/G1 phase but had no effect on the rapid increase in cp-ERM, which persisted for 24h. However, the cp-ERM response was blocked by staurosporine in both resting and GC stimulated cells. The results of RU486 antagonized the GC induced rapid decrease in NHE1 ion transport activity, but not the increase cp-ERM. This suggests that RU486 in T cells exerts its antagonistic effects at NHE1 containing plasma membrane sites and not where cp-ERM links lipid rafts to cortical cytoskeletons.

Evidence that exposure to progesterone alone is a sufficient stimulus to cause a precipitous rise in the immunomodulatory protein the progesterone induced blocking factor (PIBF)

PURPOSE

To determine if exposure to progesterone alone is sufficient to increase the production of the immunomodulatory protein known as the progesterone induced blocking factor (PIBF). Also to determine what method of progesterone delivery or form of P best stimulates PIBF secretion.

METHODS

Serum samples from patients with infertility and paid volunteers were evaluated for both PIBF and progesterone at various times during the follicular phase and the luteal phase in both natural cycles and cycles involving embryo transfer after endogenous and exogenous progesterone exposure and after various synthetic progestins. PIBF was measured by a non-commercial research ELISA assay. Comparisons were made of serum PIBF before and after exposure to progesterone, 17-hydroxyprogesterone, and oral contraceptives. PIBF was also measured before and after transfer of embryos.

RESULTS

Progesterone alone without exposure to the fetal allogeneic stimulus was able to produce a marked increase in serum PIBF. Neither a synthetic progestin (19-nortestosterone derivative) nor 17-hydroxyprogesterone caused an increase in PIBF. Some PIBF is generally detected even in the follicular phase.

CONCLUSIONS

A previous concept considered that an allogeneic stimulus, e.g., from the fetal semi-allograft, was necessary to induce de novo progesterone receptors in gamma delta T cells, which, in turn, when exposed to a high concentration of progesterone, would secrete high levels of PIBF. These data show that exposure to an allogeneic stimulus is not needed to cause a marked rise in PIBF, merely progesterone alone is sufficient.

Non-genomic rapid responses via progesterone in human peripheral T cells are not indirectly mimicked by sphingosine 1-phosphate

Progesterone is an endogenous immunomodulator that suppresses T cell activation during pregnancy. Progesterone has been shown to induce rapid responses that cause intracellular calcium ([Ca(2+)]i) elevation and acidification followed by inhibition of phytohemagglutinin (PHA)-stimulated proliferation. These rapid responses involve T cell plasma membrane sites, but the mechanisms remain unclear. Three new membrane progesterone receptors (mPRα/mPRβ/mPRγ) have been identified as expressed in T cells. These proteins have been identified as G-protein-coupled receptors. Recently, mPRs have been classified as progestin and adipoQ receptors (PAQRs). Furthermore, they have been suggested to be alkaline ceramidases, possibly involved in mediating sphingolipid signaling. Alkaline ceramidases are capable of converting ceramide to sphingosine, which might then be further phosphorylated sphingosine via sphingosine kinase to sphingosine 1-phosphate (S1P). This pathway could result in progesterone acting indirectly via S1P on membrane sphingosine 1-phosphate receptors (S1PRs) in T cells to induce rapid responses. Therefore, our aim was to investigate whether progesterone rapid responses occur indirectly in T cells via S1P. We found that S1P induces [Ca(2+)]i elevation however there was no change in intracellular pH. This is different from the situation with progesterone: S1P alone does not suppress PHA-stimulated cell proliferation and does not act synergistically with progesterone on the inhibition of PHA-induced cell proliferation. In contrast, S1P at 1μM is able to antagonize the proliferation inhibitory effect of progesterone. Thus the rapid responses that are induced by progesterone in human peripheral T cells probably do not involve indirect signaling via S1P and S1PRs.