Loss of progesterone receptor may lead to an invasive phenotype in human endometrial cancer

Epithelial to Mesenchymal Transition and Cell Biology of Molecular Regulation in Endometrial Carcinogenesis

Endometrial carcinogenesis is involved in several signaling pathways and it comprises multiple steps. The four major signaling pathways-PI3K/AKT, Ras/Raf/MEK/ERK, WNT/β-catenin, and vascular endothelial growth factor (VEGF)-are involved in tumor cell metabolism, growth, proliferation, survival, and angiogenesis. The genetic mutation and germline mitochondrial DNA mutations also impair cell proliferation, anti-apoptosis signaling, and epithelial⁻mesenchymal transition by several transcription factors, leading to endometrial carcinogenesis and distant metastasis. The PI3K/AKT pathway activates the ransforming growth factor beta (TGF-β)-mediated endothelial-to-mesenchymal transition (EMT) and it interacts with downstream signals to upregulate EMT-associated factors. Estrogen and progesterone signaling in EMT also play key roles in the prognosis of endometrial carcinogenesis. In this review article, we summarize the current clinical and basic research efforts regarding the detailed molecular regulation in endometrial carcinogenesis, especially in EMT, to provide novel targets for further anti-carcinogenesis treatment.

Prostaglandin E2 receptor EP1 in healthy and diseased human endometrium

Prostaglandin E2 (PGE2) is well described to be associated with both endometrial functions and disorders. The primary aim of this study was to explore the underlying mechanisms that affect the growth and function of endometrial epithelium and stroma by assessing the staining intensity of PGE2 receptors (EP) in healthy endometrium across the menstrual cycle and in pathological endometrium, such as ovarian endometriosis and endometrial cancer. We retrospectively analyzed the EPs staining intensity in human nonpregnant endometrium throughout the menstrual cycle by immunohistochemistry and further focused on EP1 (n = 42). The variation of EP1 was compared among healthy endometrium, ovarian endometriosis (n = 14), and endometrial cancer (n = 140) crosswise. EP1 presented cyclical changes with increased intensity in both epithelium and stroma during the proliferative phase. EP1 staining in the epithelium was increased in endometriotic tissue compared to healthy endometrium and tumor tissue, while in the stroma, the staining in the tumor was lower than that in both normal tissue and endometriosis. No significant differences in EP1 intensity were detected for histological, stage, grading, metastatic and recurrent subtypes in endometrial cancer. EP1 was also correlated with neither progression-free survival nor overall survival of patients with cancer. EP1 staining in progesterone receptor B (PRB)-positive tumor was stronger compared to PRB-negative tumor. EP1 may play a role in human endometrial physiology and pathology. Further studies on the effect of EP1 on human endometrium are needed.

Association between Morphological Patterns of Myometrial Invasion and Cancer Stem Cell Markers in Endometrial Endometrioid Carcinoma

In endometrial endometrioid adenocarcinoma (EEC), the depth of myometrial invasion (MI) is an important parameter for determining whether additional treatment is warranted. The present study investigated the association between MI patterns, cancer stem cell (CSC) phenotypes, and their clinicopathological significance in EEC. A total of 73 cases of EEC with MI were examined in this study. Haematoxylin and eosin-stained tissue specimens were analysed for MI pattern, which was categorised as infiltrating; expansile; adenomyosis (AM)-like; or microcystic, elongated, and fragmented (MELF)-type. The expression of CSC markers such as cluster of differentiation (CD)44, CD133, and Nanog1, as well as oestrogen receptor (ER) and progesterone receptor (PR) was examined by immunohistochemistry. Clinicopathological features including age, DOI, MI pattern, LVI, lymph node (LN) metastasis, disease progression, and survival outcome were recorded. Most examined cases (45/73) were International Federation of Gynecology and Obstetrics (FIGO) stage I. MI showed infiltrating (49.3%), AM-like (26.3%), MELF (15.1%), and expansile (9.6%) patterns. Tumours with the infiltrating pattern were associated with high FIGO grade (P = 0.002), reduced ER and PR, and CD44 expression (P = 0.014, 0.026, and 0.030, respectively); those with a MELF pattern showed LN metastasis (P < 0.001), lymphovascular invasion (P = 0.011), and reduced ER, CD44, and CD133 expression (P = 0.036, 0.006, and 0.016, respectively). EEC with infiltrating/MELF patterns of MI is associated with worse prognosis. These results suggest that CSC expression profiles are an unfavourable indicator of EEC.

Chromatin composition alterations and the critical role of MeCP2 for epigenetic silencing of progesterone receptor-B gene in endometrial cancers

OBJECTIVE

To understand the epigenetic mechanism underlying the PR-B gene silencing in endometrial cancer (EC) cells, we compared the chromatin composition between transcriptionally active and silenced PR-B genes in EC cell lines and cancer tissues.

METHODS

Chromatin Immunoprecipitation (ChIP) assay was performed to measure MBD occupancy and histone acetylation/methylation in transcriptionally active and silenced PR-B genes. PR-B-positive/-negative, as well as epigenetic inhibitor-treated/-untreated EC cells were used as study models. Real-time polymerase chain reaction (PCR) and Western blot analysis were applied to measure the mRNA and protein levels of PR-B, MBD, and histones.

RESULTS

A close association among PR-B methylation, MBD binding and PR-B gene silencing was observed. Treatment with epigenetic inhibitors led to dynamic changes in the PR-B chromatin composition and gene expression. Increased H3/H4 acetylation and H3-K4 methylation, and decreased H3-K9 methylation were found to be associated with re-activation of silenced PR-B genes. MeCP2 knockdown resulted in a decreased MeCP2 binding to PR-B genes and an increased PR-B expression. ChIP analysis of MeCP2 binding to PR-B genes in the PR-B-positive/-negative EC samples confirmed the significant role of MeCP2 in PR-B silencing.

CONCLUSION

PR-B gene expression is regulated by a concerted action of epigenetic factors including DNA methylation, MBD binding, and histone modifications. MeCP2 occupancy of PR-B genes plays a critical role in PR-B gene silencing. These findings enriched our knowledge of the epigenetic regulation of PR-B expression in EC, and suggested that the epigenetic re-activation of PR-B could be explored as a potential strategy to sensitize the PR-B-negative endometrial cancers to progestational therapy.

The EMT signaling pathways in endometrial carcinoma

Endometrial cancer (EC) is the most common gynecologic malignancy of the female genital tract and the fourth most common neoplasia in women. In EC, myometrial invasion is considered one of the most important prognostic factors. For this process to occur, epithelial tumor cells need to undergo an epithelial to mesenchymal transition (EMT), either transiently or stably, and to differing degrees. This process has been extensively described in other types of cancer but has been poorly studied in EC. In this review, several features of EMT and the main molecular pathways responsible for triggering this process are investigated in relation to EC. The most common hallmarks of EMT have been found in EC, either at the level of E-cadherin loss or at the induction of its repressors, as well as other molecular alterations consistent with the mesenchymal phenotype-like L1CAM and BMI-1 up-regulation. Pathways including progesterone receptor, TGFβ, ETV5 and microRNAs are deeply related to the EMT process in EC.

Progesterone inhibits epithelial-to-mesenchymal transition in endometrial cancer

BACKGROUND

Every year approximately 74,000 women die of endometrial cancer, mainly due to recurrent or metastatic disease. The presence of tumor infiltrating lymphocytes (TILs) as well as progesterone receptor (PR) positivity has been correlated with improved prognosis. This study describes two mechanisms by which progesterone inhibits metastatic spread of endometrial cancer: by stimulating T-cell infiltration and by inhibiting epithelial-to-mesenchymal cell transition (EMT).

METHODOLOGY AND PRINCIPAL FINDINGS

Paraffin sections from patients with (n = 9) or without (n = 9) progressive endometrial cancer (recurrent or metastatic disease) were assessed for the presence of CD4+ (helper), CD8+ (cytotoxic) and Foxp3+ (regulatory) T-lymphocytes and PR expression. Progressive disease was observed to be associated with significant loss of TILs and loss of PR expression. Frozen tumor samples, used for genome-wide expression analysis, showed significant regulation of pathways involved in immunesurveillance, EMT and metastasis. For a number of genes, such as CXCL14, DKK1, DKK4, PEG10 and WIF1, quantitive RT-PCR was performed to verify up- or downregulation in progressive disease. To corroborate the role of progesterone in regulating invasion, Ishikawa (IK) endometrial cancer cell lines stably transfected with PRA (IKPRA), PRB (IKPRB) and PRA+PRB (IKPRAB) were cultured in presence/absence of progesterone (MPA) and used for genome-wide expression analysis, Boyden- and wound healing migration assays, and IHC for known EMT markers. IKPRB and IKPRAB cell lines showed MPA induced inhibition of migration and loss of the mesenchymal marker vimentin at the invasive front of the wound healing assay. Furthermore, pathway analysis of significantly MPA regulated genes showed significant down regulation of important pathways involved in EMT, immunesuppression and metastasis: such as IL6-, TGF-β and Wnt/β-catenin signaling.

CONCLUSION

Intact progesterone signaling in non-progressive endometrial cancer seems to be an important factor stimulating immunosurveilance and inhibiting transition from an epithelial to a more mesenchymal, more invasive phenotype.

Role of progesterone in endometrial cancer

Progesterone is a key hormone in the endometrium that opposes estrogen-driven growth. Insufficient progesterone will result in unopposed estrogen action that could lead to the development of endometrial hyperplasia and adenocarcinoma. Although these endometrial neoplasias can regress in response to progestin treatment, this does not occur in all instances. To understand this resistance to progesterone and to improve on existing hormonal therapies, it is imperative that the molecular mechanisms of progesterone action through its receptor be deciphered in endometrial cancer. This review highlights what is known thus far regarding the efficacy of progestin therapy in the clinic and the role of progesterone in endometrial cancer cell behavior and gene regulation.

Progesterone receptor action in leiomyoma and endometrial cancer

Progesterone is a key hormone in the regulation of uterine function. In the normal physiological context, progesterone is primarily involved in remodeling of the endometrium and maintaining a quiescent myometrium. When pathologies of the uterus develop, specifically, endometrial cancer and uterine leiomyoma, response to progesterone is usually altered. Progesterone acts through mainly two isoforms of the progesterone receptor (PR), PRA and PRB which have been reported to exhibit different transcriptional activities. Studies examining the expression and function of the PRs in the normal endometrium and myometrium as well as in endometrial cancer and uterine leiomyoma are summarized here. The clinical use of progestins and the transcriptional activity of the PR on genes specific to endometrial cancer and leiomyoma are described. An increased understanding of the differential expression of PRs and response to progesterone in these two diseases is critical in order to develop more efficient and targeted therapies.

Differences in invasive capacity of endometrial cancer cell lines expressing different progesterone receptor isotypes: possible involvement of cadherins

OBJECTIVE

Loss of expression of progesterone receptors (PR) in endometrial cancer is related to a more invasive and metastatic phenotype. In this study we aim to investigate whether selective loss of PRA or PRB affects the invasive capacity of endometrial cancer cells.

METHODS

cDNA microarrays were performed to compare gene expression profiles of a set of endometrial cancer sub-cell lines expressing PRA and/or PRB. In vitro invasion assays were performed to assess whether differences in gene expression between the lines were reflected by their invasive behavior.

RESULTS

It was observed that cell lines that express only PRA express higher levels of cadherins, and show a lower level of invasion compared to cell lines that express PRB. When cadherin function was inhibited in exclusively PRA-expressing cell lines, an increase of in vitro invasion was observed. In support of these findings, it was observed that in higher grade and more invasive endometrial cancer, expression of E-cadherin decreased.

CONCLUSIONS

These results indicate that relative loss of PRA during progression of endometrial cancer can have a negative impact on cadherin expression, which may lead to development of a more metastatic phenotype.

Oestrogen regulated gene expression in normal and malignant endometrial tissue

OBJECTIVES

The aim of this study was to examine the expression of oestrogen regulated genes in premenopausal and postmenopausal normal and malignant endometrial specimens. The molecular mechanisms and the role of these genes in endometrial carcinogenesis are poorly understood.

METHODS

Normal and malignant endometrial specimens were collected from patients undergoing hysterectomy. Real time TaqMan PCR was used to examine the mRNA expression levels of oestrogen receptor a (ERa) and b (ERb), progesterone receptor (PR), insulin like growth factor 1 (IGF-1) and vascular endothelial growth factor (VEGF).

RESULTS

Expression analysis was carried out on 60 patients. ERa was more predominantly expressed in the endometrial samples than ERb, 28% of the specimens did not express ER. Normal pre and postmenopausal tissue expressed higher levels of ERa, PR and IGF-1 than malignant tissue. ERa and PR expression was significantly higher in the proliferative phase endometrium compared to the secretory phase (P < 0.05). PR mRNA expression was significantly correlated with ERa in all tissue types.

CONCLUSIONS

ERa expression may play an important role in the regulation of PR in normal and malignant endometrium. Further work is needed to establish if IGF-1 plays a role in a subset of endometrial cancers and if isoforms of VEGF play a role in endometrial cancer.

Cervical intraepithelial neoplasia: prognosis by combined LOH analysis of multiple loci

OBJECTIVE

Cervical intraepithelial neoplasias (CIN) show markedly variable clinical behavior. Clinically, it is important to distinguish CIN lesions with different behaviors and identify those likely to persist and progress. The purpose of this study is to explore whether CIN lesions with different clinical behaviors can be stratified by analysis of loss of heterozygosity (LOH) at multiple loci.

METHODS

One hundred sixty-four cases of CIN (54 CIN1, 59 CIN2 and 51 CIN3) were screened for LOH at 12 microsatellite markers including 10 from 3p14, 3p21-22, 6p21 and 11q23. LOH was correlated with clinical follow-up data and high-risk HPV infection.

RESULTS

In a pilot study of 71 cases of CIN, screening of 12 microsatellite markers identified four (D3S1300, D3S1260, D11S35, and D11S528) at which LOH was significantly associated with disease persistence/progression. These four markers were further investigated in a larger cohort, which brought the total number of cases examined to 164. Combined analysis of LOH at the above four loci permitted the identification of 22-47% of CIN lesions depending on the histological grade, which showed disease persistence/progression. LOH at these loci was significantly associated with HPV16 infection. Bioinformatic analysis identified several candidate genes including the fragile histidine triad gene and progesterone receptor gene that may be the target of deletions.

CONCLUSIONS

LOH at D3S1300, D3S1260, D11S35 and D11S528 was significantly associated with cins that showed persistence/progression, and combined LOH analyses at these loci could be used to identify such cases.

Progesterone receptors in endometrial cancer invasion and metastasis: development of a mouse model

Progestagens inhibit growth of endometrial cancer cells in vivo and in vitro, and also are reported to inhibit endometrial cancer cell invasion. The progesterone receptor (PR) isotypes PRA and PRB have different transcriptional activity. There are indications that relative over expression of PRB could lead to development of a more invasive phenotype in endometrial cancer. To study the effect of progestagens and the two PR isotypes on tumor dissemination, in vitro and in vivo models should be applied. The Ishikawa endometrial cancer cell line (clone 3H12) was transfected to stably express a high level of human PRB (hPRB), which resulted in the PRB-1 sub-cell line. Ovariectomized athymic NMRI nu/nu mice were injected intraperitoneally with these PRB-1 cells. After 3, 5 and 10 weeks, the animals were sacrificed. Spread of PRB-1 cells in and outside the peritoneal cavity was studied macroscopically and microscopically, and also by PCR detection. After 10 weeks, the PRB-1 cells had formed extensive tumor mass in the peritoneal cavity. Also, cells could be detected outside the peritoneal cavity, indicating metastatic ability of these cells. The present study describes an in vivo model that can provide a valuable tool in studying the influence of progestagens and the two PR isotypes on endometrial cancer cell invasion and metastasis.