The interplay of sex steroid hormones and microRNAs in endometrial cancer: current understanding and future directions

As tumor-causing factors, several miRNAs have been identified as potential biomarkers and regulators of EC ( Figure 2 ). miRNAs such as miR-130, miR-200a, miR-429, miR-107 5p, miR-21, miR-125b, miR-101, miR-27a-5p, miR-576-5p, miR-210-3p, miR-1903p, miR-18a-5p, miR-103, miR 215, miR-27a, miR-34a-5p, miR-146-5p, miR-423, and miR-302 have been shown to play different roles in promoting or suppressing EC progression by targeting various genes and signaling pathways ( 83 – 87 , 90 , 91 , 95 , 97 , 101 , 103 , 124 , 138 , 200 ). These findings provide potential targets for diagnosis, prognosis, and therapeutic interventions in EC. miRNAs have been determined to impact the initiation and advancement of EC substantially. The expression of KLF2 in endometrial cancer cells is promoted by miR-15b-3p, while miR-210 negatively regulates NIFX expression. MiR-940 and miR-494-3p are overexpressed in EC tissues and cell lines, with MRVI1 and PTEN being identified as potential targets, respectively ( 114 , 121 , 122 , 161 ). These miRNAs promote the proliferation, migration, and invasion of EC cells. miRNAs also play a crucial role in regulating EC associated with lymph node metastasis. Downregulation of miRNA-184 is linked to lymph node involvement in low-risk EC patients ( 201 ). Overexpression of miR-501 can increase the activation of the AKT/mTOR pathway, leading to higher pelvic lymph node metastasis and reduced overall survival ( 106 ). Profiling the miRNA expression in EEC metastatic loci from lymph nodes could aid in identifying novel diagnostic markers and therapeutic targets ( 202 ). miR-204-5p is a tumor-suppressor miRNA associated with lymph node metastasis in EC, highlighting the importance of the lymph node status in determining adjuvant treatment ( 168 ). Finally, the expression of miR-15a-5p in EC is also correlated with lymph node metastasis, TNM stage, and mortality, and it was significantly reduced in EC patients who experienced recurrence or metastasis ( 203 ).

In vitro exposure of human endometrial stromal cells to estradiol increased the expression of miR-181b and let-7e while decreasing the expression of miR-27b ( 4 ). In EEC cell lines, estrogen treatment improved miR-200c and promoted miR-196a-5p expression, which targeted FOXO1 and increased cell viability ( 8 , 204 ). On the other hand, progesterone inhibited cell-cycle and cell-viability in EC by regulating NEAT1/miR-146b-5p axis via Wnt/β-catenin signaling. It also induces miR-145/miR-143 to inhibit EC by targeting cyclin D2 and promoting miR-133a to increase endometrial cell proliferation ( 176 , 177 ). It is also found that endometrial expression of miR-30b, miR-125b, miR-424, and miR-451 was lower in women with high blood progesterone levels compared to those with low blood progesterone levels ( 4 ). Moreover, miR-195 functioned as a tumor suppressor that targeted GPER1 to inhibit EC through PI3K/AKT signaling ( 131 ).

Ovarian hormones, such as progesterone and estrogen, play a crucial role in regulating the endometrium and its monthly cycle. These hormones are responsible for the endometrium’s monthly proliferation, differentiation, and shedding and are the source of EC ( 45 ). The presence of Estrogen Receptor (ER) and Progesterone Receptor (PR) is linked to clinicopathological variables and can affect the prognosis of patients with EC. Steroid receptors ER and PR, activated by estrogen and progesterone, respectively, are critical in developing endometrioid-type EC ( 46 , 47 ). These hormones are a key factor in EC occurrence and development, with 75-90% of EC incidents being dependent on estrogen ( 11 ). Estrogen exposure can result in endometrial hyperplasia and EC, while prolonged use of estrogens is associated with type 1 endometrioid malignancies ( 48 ). On the other hand, progesterone acts as an antagonist, inhibiting cell division, downregulating ER, and promoting cell differentiation ( 49 ). Overexposure to estrogen is a high-risk factor for EC, particularly for women undergoing estrogen-only hormonal therapy, using tamoxifen as an adjunct therapy, dealing with obesity, or suffering from PCOS. On the other hand, the progesterone receptor is a favorable prognostic marker for multiple solid tumors, but its expression is reduced in malignant tumors ( 50 ). The relationship between unopposed estrogen and EC is unclear, and progesterone can be used as a targeted therapy ( 51 ). Progesterone is used for treating young endometrial cancer patients, and the long non-coding RNA HOTAIR is a potential predictor for progesterone response. The expression of HOTAIR is regulated by LSD1, and inhibiting LSD1 can induce apoptosis ( 52 ). The use of oral contraceptives (OCs) and progestin-only contraceptives (POCs) has been linked to an increased risk of cancer ( 53 , 54 ). The loss of estrogen and progesterone receptors is associated with a higher rate of an advanced stage of endometrial cancer and increased expression of certain genes ( 55 , 56 ). An imbalanced hormone state can arise from variations in the manifestation of genes and enzymes involved in the signaling of steroid hormones. Ovarian hormones regulate gene transcription by binding to DNA and initiating signaling pathways. It has been found that estrogen and progesterone are significant predictors of EC and that ER and PR are involved in genomic processes in cancer cells ( 57 ). Altered expression of hormone-regulated genes has been linked to a role for PAX2 in fine-tuning the interplay between ER alpha and PR ( 57 , 58 ). Inhibiting ERRα/TGF-β can suppress in vitro invasion of EC cells, and ER signaling increases the expression of the oncogene PIWIL1 in ER-positive endometrial cancer cells ( 59 , 60 ). Tumor suppressor genes such as CACNA2D3 are associated with EC and can exert a tumor-suppressive effect in vitro ( 3 , 61 ). A novel signature of five genes has been developed to improve risk assessment and provide potential targets for EC therapies ( 11 ). Work is also being done to develop biomarkers for endometriosis, including the examination of PDCD4 and its regulation by progesterone ( 62 ). ER-positive endometrioid endometrial cancer (EEC) exhibits the highest rate of alterations in PTEN, while ARID1A is a common mutation in ER-negative EEC ( 63 , 64 ). DNA methylation and hydroxymethylation also regulate gene expression and are associated with steroid receptors, enzymes involved in estrogen synthesis, and TET proteins that mediate hydroxymethylation ( 65 ). The role of steroid hormones in EC mediated by insulin have also been investigated and findings showed the increased expression and phosphorylation of Akt, MAPK, and ERK in EC cells ( 66 ). Other factors include the regulation of transcription factors by cell adhesion, biomarkers in blood for hormone quantification, and intra-tumoral heterogeneity ( 67 , 68 ). The immune system component NLRP3 inflammasome and the gene BCL11A have also been linked to EC progression, ERR, USP14, and estrogen ( 69 – 71 ). Additionally, the expression of the hormone receptors can also be used to predict lymph node involvement. A study found that high expression of ER has been associated with poor prognosis in endometrial tumors, and patients with ER/PR loss have deeper myometrial infiltration and higher rates of pelvic lymph node metastasis ( 72 ). One study found that decreased expression of combined ER/PR (estrogen receptor/progesterone receptor) was associated with a poorer outcome in endometrial cancer patients, but hormone receptor status alone did not significantly improve mortality prediction ( 73 ). Variation in Hormone replacement therapy (HRT) type and the BMI status of the women is associated with an increased risk of EC ( 74 ). Obesity is a well-known risk factor for EC, but the mechanisms of obesity-related carcinogenesis are not well-defined and may vary based on the presence of Lynch syndrome ( 75 ). Hormonal therapy is considered best for low-grade disease and hormone receptor positivity, and it is better tolerated than chemotherapy ( 76 ). Another study found that oral estradiol plus vaginal progesterone therapy affected endometrial thickness, biopsy pathology, and cancer incidence in post-menopausal women ( 77 ). A study on the relationship of menopausal hormone therapy and EC found that patients with hormone therapy had lower BMIs, less diabetes, and fewer recurrences, but age and tumor stage had a bigger impact on overall survival ( 78 ). Prognostic factors such as the expression of ER, PR, and HER2 are also being assessed to improve patient outcomes ( 79 ). The cutoff values for the positivity of ER/PR in endometrial cancer are still being debated, and the expression of these receptors and other proteins are evaluated to determine their impact on EC prognosis ( 80 ). The recurrence of EC is one of the major problem in its diagnosis and treatment. Researchers explored the role of sex hormones and insulin/insulin-like growth factor axis signaling in endometrial cancer recurrence. It was found that circulating estradiol and tumor tissue phosphorylated IGR1R/IR were associated with a higher risk of recurrence ( 12 ). A recurrence prediction model was created to anticipate the likelihood of endometrial cancer reoccurrence in stage I-II patients after surgical treatment. The final prediction model incorporated factors such as age, adjuvant treatment, histologic type, and expression levels of Ki67, ER, PR, and WFDC2 and showed adequate discrimination power ( 81 ).

Endometrial cancer (EC), a malignancy in the inner lining of the uterus, is a major contributor to deaths among gynecological malignancies. EC is characterized by abnormal cell growth, uncontrolled cell proliferation, excessive activation of signaling pathways, and microRNA (miRNA) activity ( 1 ). The progression and malignant transformation of EC are linked to central cellular processes such as epithelial-to-mesenchymal transition (EMT) and invasion ( 2 ). However, the pathogenesis of EC is complex and multi-factorial, and not fully understood. Studies have explored the influence of various factors in EC, such as estrogen receptor alpha (ER-α) activation of the MAPK signaling pathway ( 3 ) and the molecular responses in the endometrium to hormonal stimuli ( 4 ). Despite the growing use of molecular techniques in the study of gynecologic malignancies, the underlying molecular mechanisms and pathology remain elusive ( 5 ). There are concerns regarding the current guidelines pertaining to the diagnosis, prognosis, and treatment of EC, which are deemed inadequate ( 6 ). This highlights the need to explore innovative therapeutic strategies for this common female malignancy. The role of non-coding RNAs (ncRNAs), such as miRNAs and long non-coding RNAs (lncRNA), in cancer diagnosis, prognosis, and therapy selection is gaining recognition in the scientific community. These ncRNAs play a key role in regulating cellular metabolism and transforming cells into cancer cells ( 7 ). Recent studies have identified miRNAs as potential therapeutic targets for EC ( 8 ). This review focuses on the role of miRNAs in diagnosing and treating EC, a type of cancer that primarily affects younger and post-menopausal women and is a major health concern. To highlight the most recent advances and gaps in this research area, articles since 2018 are included. This review examines various targets and pathways that may contribute to the development of EC by regulating miRNAs.

A number of miRNAs have been discovered to control the production of estrogen and progesterone receptors in endometrial cells ( Figure 3 ). For example, miR-107-5p, which promotes tumor proliferation and invasion by targeting ERα, and miR-194-3p and miR-196a, which regulate the expression of PR-A and PR-B proteins ( 4 , 85 ). Additionally, miR-181c affects estrogen-dependent EC cell growth by targeting PTEN, and miR-92a increases stromal endometrial cell proliferation and progesterone resistance ( 4 , 123 ). However, the exact mechanisms by which miRNAs regulate ER in the endometrium are not yet fully understood ( 4 ). Although, in Figure 4 , the possible mechanism by which sex steroid hormones can cause/suppress EC is depicted. Sex steroid hormones dependent up-regulated and down-regulated miRNAs in Endometrial Cancer. The markings 1, 14 and 28 in the bottom of endometrium, depicts the days of menstrual cycle. Interaction of miRNAs with sex steroid hormones in the regulation of Endometrial Cancer.

The regulation of sex steroid hormones by miRNAs or vice versa holds great promise for the future of EC research. The study of these interactions has the potential to uncover new mechanisms involved in the development and progression of EC, as well as provide new targets for therapeutic intervention. One area of future research could be to understand further the specific miRNAs involved in regulating sex steroid hormones in EC. This could be accomplished through large-scale sequencing studies or microarray analysis to identify miRNAs differentially expressed in EC compared to normal tissue. Additionally, functional studies could assess the effects of inhibiting or overexpressing specific miRNAs on hormone levels and EC cell proliferation. Another area of focus could be investigating the effects of miRNA-mediated regulation of hormones in EC under various conditions, such as in response to different treatments or stages of the disease. This information would be valuable in understanding the changing nature of miRNA control over hormones in EC and its potential as a therapeutic target. In conclusion, regulating sex steroid hormones by miRNAs is a highly promising area of research with numerous potential avenues for future exploration. As the field advances, we can expect a better understanding of the underlying mechanisms of EC and the development of new, more effective treatments for EC patients.

MicroRNAs or miRNAs or miRs are non-coding RNA molecules that play a crucial role in gene regulation, impacting cellular functions and associated with various pathological conditions, including EC. Their altered expression levels have been linked to prognostic factors and significantly impact tumorigenesis and progression in EC ( 31 , 32 ). miRNAs have the potential to serve as non-invasive biomarkers for EC diagnosis by distinguishing between different conditions, such as endometrial hyperplasia ( 33 , 34 ). They can regulate tumor suppressor genes and predict future EC development based on the patient’s immune microenvironment and insulin status ( 35 , 36 ). miRNAs impact cell proliferation, differentiation, and apoptosis, and a higher accuracy miRNA signature can be obtained using miRNA clusters, serum type, and larger sample sizes ( 4 , 37 – 39 ). miRNAs can also act as oncogenes or tumor suppressors ( 40 ). The specific molecular characterization of miRNAs, involved in the regulation of the MAPK signaling pathway, has been shown to discriminate endometrioid endometrial carcinoma (EEC) from serous endometrial carcinoma (SEC) ( 41 ). An analysis of miRNA arrays revealed 20 miRNAs that differed significantly between patients with endometrial hyperplasia (EH) and those with simple hyperplasia/complex hyperplasia-non-atypical (SH/CH-nonA) ( 42 ). These findings highlight the important role of miRNAs in the regulation of gene expression and the pathophysiology of EC.

miRNAs are small RNA molecules that play important roles in development, cell differentiation, and homeostasis. miRNAs are often present in tandem with multiple miRNAs in intergenic and intragenic genomic regions and are transcribed by RNA polymerase II as a single transcript ( Figure 1 ). The RNase III enzyme Dicer processes them in the cytoplasm to produce mature double-stranded miRNAs. The processing of miRNAs can result in multiple sequence variants known as isomiRs. These isomiRs can form stem-loop structures and are cleaved by the RNase III enzymes Drosha and Dicer to generate precursor miRs and mature miRs. The primary precursor miRNA (primiRNA) is then transported from the nucleus to the cytoplasm by Exportin 5 and processed by Dicer to produce mature double-stranded miRNAs ( 43 ). These mature miRNAs are incorporated into the RNA-induced silencing complex (RISC) and target complementary sequences in the 3′ untranslated region (UTR) of mRNAs. By destabilizing target mRNAs, miRNAs reduce protein output and change gene expression ( Figure 1 ) ( 44 ). Mechanism of miRNA biogenesis and their functional implications.

miRNAs are tiny, non-coding RNA molecules that play crucial roles in regulating gene expression, including the regulation of hormones such as estrogen and progesterone. In endometrial cancer, imbalanced sex hormone levels contribute to tumor development and growth, making the study of miRNA-mediated regulation of these hormones a valuable avenue for research. Understanding the dual effect of miRNAs, i.e., the oncogenic and tumor suppressor effects, is warranted in EC. This knowledge can potentially lead to improved diagnosis and treatment options for EC patients.

EC is the most generally diagnosed form of gynecological cancer in developed nations, making up approximately 5% of all cancers in women ( 9 ). EC originates in the endometrium, the inner lining of the uterus. It is most commonly found in post-menopausal women. EC has witnessed a marked surge in recent times, however, the underlying reason behind this trend remains elusive. EC is ranked as the fourth most common cancer in high-income countries and the most prevalent gynecological cancer globally, with 382,069 new cases reported in 2018 ( 10 ). In 2020, there were around 417,000 new cases globally and 97,300 deaths from EC, as per statistics ( 11 ). Although, the exact causes of EC are unknown; lifestyle changes, obesity, infertility, hormone replacement therapy, and diabetes are believed to play a role. Advanced disease increases the likelihood of recurrence, and established risk factors include obesity and high estrogen exposure ( 12 ). EC is divided into type I (endometrioid) and type II (non-endometrioid). Type-I ECs are estrogen-dependent and have a good prognosis, while type II cancers are nonestrogen-dependent and have a more aggressive clinical course with a poor prognosis ( 13 ). However, recent methodologies have challenged this dualistic classification of EC ( 14 ). Further, it is found that Type I tumors have downregulation or mutations of the PTEN gene, while type II tumors have high expression of non-functional tumor proteins ( 7 ). A confluence of several factors is believed to increase the likelihood of EC. Risk factors, such as obesity, diabetes, a family history of cancer, and Hormone Replacement Therapy (HRT), play a significant role in EC ( 15 – 17 ). Lifestyle factors like diet, physical activity, and smoking may also contribute to the development of EC ( 15 , 16 , 18 – 20 ). Additionally, certain medical conditions, such as polycystic ovary syndrome (PCOS), diabetes, and Lynch syndrome, may increase the risk of EC ( 21 ). EC is associated with abnormal production of hormones, inflammation, and hyperinsulinemia ( 22 ). The use of oral contraceptives reduces EC risk by 30-40% ( 23 , 24 ). Coffee consumption, use of antidepressants, and male-origin microchimerism are linked to a reduced risk of EC ( 25 – 27 ), while the correlation between aspirin use and EC is inconclusive ( 28 , 29 ). Smoking is inversely related to endometrial cancer, but the evidence does not support this relationship ( 18 ). The prognosis for early EC is generally good, but 7% of cases recur, and the 3-year survival rate is relatively low ( 30 ). This emphasizes the importance of conducting additional research into the molecular mechanisms of EC (such as miRNAs) for better prognosis and cancer prevention.

LT was responsible for conducting the literature review, collecting and analyzing data, and writing the first draft of the manuscript. ST contributed to the literature search, conceptualization and design of the study, provided critical feedback on the manuscript, and assisted with the editing and finalization of the manuscript. All authors contributed to the article and approved the submitted version.