SIX1 is overexpressed in endometrial carcinoma and promotes the malignant behavior of cancer cells through ERK and AKT signaling

Targeting sine oculis homeoprotein 1 (SIX1): A review of oncogenic roles and potential natural product therapeutics

Sine oculis homeoprotein 1 (SIX1), a prominent representative of the homeodomain transcription factors within the SIX family, has attracted significant interest owing to its role in tumorigenesis, cancer progression, and prognostic assessments. Initially recognized for its pivotal role in embryonic development, SIX1 has emerged as a resurgent factor across a diverse set of mammalian cancers. Over the past two decades, numerous investigations have emphasized SIX1's dual significance as a developmental regulator and central player in oncogenic processes. A mounting body of evidence links SIX1 to the initiation of diverse cancers, encompassing enhanced cellular metabolism and advancement. This review provides an overview of the multifaceted roles of SIX1 in both normal development and oncogenic processes, emphasizing its importance as a possible therapeutic target and prognostic marker. Additionally, this review discusses the natural product agents that inhibit various pro-oncogenic mechanisms associated with SIX1.

Endometrial Stem Cells: Orchestrating Dynamic Regeneration of Endometrium and Their Implications in Diverse Endometrial Disorders

The human endometrium, a vital component of the uterus, undergoes dynamic changes during the menstrual cycle to create a receptive environment for embryo implantation. Its remarkable regenerative capacity can be attributed to the presence of tissue-resident stem cell populations within the endometrium. Despite variations in characteristics among different subtypes, endometrial stem cells exhibit notably robust self-renewal capacity and the ability to differentiate into multiple lineages. This review offers a comprehensive insight into the current literature and recent advancements regarding the roles of various endometrial stem cell types during dynamic regeneration of the endometrium during the menstrual cycle. In addition, emerging evidence suggests that dysfunction or depletion of endometrial stem cells may play critical roles in the development and progression of various endometrial disorders, such as endometriosis, uterine fibroids, adenomyosis, infertility, and endometrial cancer. Therefore, we also highlight potential roles of endometrial stem cells in the development and progression of these endometrial diseases, including their ability to accumulate genetic mutations and express genes associated with endometrial diseases. Understanding the dynamic properties of the endometrium and the roles of endometrial stem cells in various endometrial disorders will shed light on potential therapeutic strategies for managing these conditions and improving women's fertility outcomes.

Manzamine-A Alters In Vitro Calvarial Osteoblast Function

Manzamine-A is a marine-derived alkaloid which has anti-viral and anti-proliferative properties and is currently being investigated for its efficacy in the treatment of certain viruses (malaria, herpes, HIV-1) and cancers (breast, cervical, colorectal). Manzamine-A has been found to exert effects via modulation of SIX1 gene expression, a gene critical to craniofacial development via the WNT, NOTCH, and PI3K/AKT pathways. To date little work has focused on Manzamine-A and how its use may affect bone. We hypothesize that Manzamine-A, through SIX1, alters bone cell activity. Here, we assessed the effects of Manzamine-A on cells that are responsible for the generation of bone, pre-osteoblasts and osteoblasts. PCR, qrtPCR, MTS cell viability, Caspase 3/7, and functional assays were used to test the effects of Manzamine-A on these cells. Our data suggests Six1 is highly expressed in osteoblasts and their progenitors. Further, osteoblast progenitors and osteoblasts exhibit great sensitivity to Manzamine-A treatment exhibited by a significant decrease in cell viability, increase in cellular apoptosis, and decrease in alkaline phosphatase activity. In silico binding experiment showed that manzamine A potential as an inhibitor of cell proliferation and survival proteins, i.e., Iκb, JAK2, AKT, PKC, FAK, and Bcl-2. Overall, our data suggests Manzamine-A may have great effects on bone health overall and may disrupt skeletal development, homeostasis, and repair.

High expression of SIX1 is an independent predictor of poor prognosis in endometrial cancer

Objective: The overexpression of transcription factor Sine oculis homeobox 1 (SIX1) is discovered in various malignant tumors and has been known to be closely associated with tumorigenesis, progression and prognosis. This study aims to determine the role of SIX1 in endometrial cancer (EC). Methods: In this study, we analyzed the SIX1 expression profile and the correlation with the corresponding clinical characteristics of EC samples from the Cancer Genome Atlas (TCGA), Gene Expression Omnibus (GEO) and Clinical Proteomic Tumor Analysis Consortium (CPTAC) databases. Wilcoxon signed-rank test was applied to analyze the difference between tumor group and control group. The potential biological processes or signaling pathways related to SIX1 activity in EC was also assessed. Results: The results showed that SIX1 was overexpressed in EC tissues compared to normal tissues (P=2.029e-15, P=6.25e-6). The SIX1 level was correlated with tumor grade (P=2.91e-4), peritoneal cytology (P=0.005), and the subsequent tumor surgery (P=1.169e-4). SIX1 expression was negatively associated with overall survival rate (P=4.241e-4, P=0.000241) and served as an independent factor that affected EC overall survival rate (P=0.005063), similar to other factors such as age, Figo stage, and tumor (T) stage. SIX1 participates in cancer pathogenesis through gene regulation that involves PI3K/AKT/MTOR signaling, mitotic spindle, G2M checkpoint, E2F targets, NOTCH signaling, glycolysis, cholesterol homeostasis, DNA repair and early estrogen response. Conclusions: Our data demonstrate that SIX1 is overexpressed in EC and associated with adverse clinicopathological outcomes, which can function as an independent factor for EC prognosis.

Six1 Promotes Epithelial-Mesenchymal Transition in Bronchial Epithelial Cells via the TGFβ1/Smad Signalling Pathway

INTRODUCTION

The homeodomain transcription factor sine oculis homeobox homolog 1 (Six1) plays a crucial role in embryogenesis and is not expressed in normal adult tissue but is expressed in many pathological processes, including airway remodelling in asthma. The current study aimed to reveal the effects of Six1 in regulating the airway remodelling and its possible mechanism.

METHODS

A mouse model of ovalbumin-induced asthma-associated airway wall remodelling and a bronchial epithelial cell (16HBE) model of transforming growth factor β1 (TGFβ1)-induced epithelial-mesenchymal transition (EMT) were used to investigate the role of Six1. Then, 16HBE cells were transformed with Six1 expression vectors and treated with a TGFβ1 pathway inhibitor to determine the role of Six1 in EMT. The effect of Six1 and its possible mechanism were assessed by immunohistochemistry, RT-PCR, and Western blot.

RESULTS

Six1 expression was elevated in the lungs in an OVA mouse model of allergic asthma and in 16HBE cells treated with TGFβ1. Six1 overexpression promoted an EMT-like phenotype with a decreased protein expression of E-cadherin and increased protein expression of α-smooth muscle actin (α-SMA) as well as fibronectin in 16HBE cells; these effects appeared to promote TGFβ1 and phospho-Smad2 (pSmad2) production, which are the main products of the TGFβ1/Smad signalling pathway, which could be reduced by a TGFβ1 inhibitor.

CONCLUSION

These data reveal that Six1 and TGFβ1 are potentially a part of an autocrine feedback loop that induces EMT, and these factors can be reduced by blocking the TGFβ1/Smad signalling pathway. As such, these factors may represent a promising novel therapeutic target for airway remodelling in asthma.

SPOCK1/SIX1axis promotes breast cancer progression by activating AKT/mTOR signaling

SPOCK1 is highly expressed in many types of cancer and has been recognized as a promoter of cancer progression. Its regulatory mechanism in breast cancer (BC) remains unclear. This study aimed to explore the precise function of SPOCK1 in BC progression and to identify the mechanism by which SPOCK1 is involved in cell proliferation and epithelial-mesenchymal transition (EMT). Immunohistochemistry (IHC) experiments and database analysis showed that high expression of SPOCK1 was positively associated with histological grade, lymph node metastasis (LN) and poor clinical prognosis in BC. A series of in vitro and in vivo assays elucidated that altering the SPOCK1 level led to distinct changes in BC cell proliferation and metastasis. Investigations of potential mechanisms revealed that SPOCK1 interacted with SIX1 to enhance cell proliferation, cell cycle progression and EMT by activating the AKT/mTOR pathway, whereas inhibition of the AKT/mTOR pathway or depletion of SIX1 reversed the effects of SPOCK1 overexpression. Furthermore, SPOCK1 and SIX1 were highly expressed in BC and might indicate poor prognoses. Altogether, the SPOCK1/SIX1 axis promoted BC progression by activating the AKT/mTOR pathway to accelerate cell proliferation and promote metastasis in BC, so the SPOCK1/SIX1 axis might be a promising clinical therapeutic target for preventing BC progression.

Identification of EMT-Related Gene Signatures to Predict the Prognosis of Patients With Endometrial Cancer

Background

Endometrial cancer (EC) is one of the most common gynecological cancers. Epithelial–mesenchymal transition (EMT) is believed to be significantly associated with the malignant progression of tumors. However, there is no relevant study on the relationship between EMT-related gene (ERG) signatures and the prognosis of EC patients.

Methods

We extracted the mRNA expression profiles of 543 tumor and 23 normal tissues from The Cancer Genome Atlas database. Then, we selected differentially expressed ERGs (DEERGs) among these mRNAs. Next, univariate and multivariate Cox regression analyses were performed to select the ERGs with predictive ability for the prognosis of EC patients. In addition, risk score models were constructed based on the selected genes to predict patients’ overall survival (OS), progression-free survival (PFS), and disease-free survival (DFS). Finally, nomograms were constructed to estimate the OS and PFS of EC patients, and pan-cancer analysis was performed to further analyze the functions of a certain gene.

Results

Six OS-, ten PFS-, and five DFS-related ERGs were obtained. By constructing the prognostic risk score model, we found that the OS, PFS, and DFS of the high-risk group were notably poorer. Last, we found that AQP5 appeared in all three gene signatures, and through pan-cancer analysis, it was also found to play an important role in immunity in lower grade glioma (LGG), which may contribute to the poor prognosis of LGG patients.

Conclusions

We constructed ERG signatures to predict the prognosis of EC patients using bioinformatics methods. Our findings provide a thorough understanding of the effect of EMT in patients with EC and provide new targets and ideas for individualized treatment, which has important clinical significance.

MicroRNA-155-3p promotes glioma progression and temozolomide resistance by targeting Six1

The prognosis of glioma is generally poor and is the cause of primary malignancy in the brain. The role of microRNAs has been implicated in tumour inhibition or activation. In several cancers, the Six1 signalling pathway has been found to be aberrant and also relates to the formation of tumours. We analysed the database for expression profiles and clinical specimens of various grades of glioma to assess microRNA-155-3p (miR-155-3p) expression. The role of miR-155-3p in glioblastoma, cell cycle, proliferation, apoptosis and resistance to temozolomide was assessed in vitro through flow cytometry and cell proliferation assays. Bioinformatics analyses, and assays using luciferase reporter, and immunoblotting revealed that miR-155-3p targets Six1 and that the relationship between glioma and healthy brain tissues was significantly inverse. In rescue experiments, overexpressed Six1 revoked the changes in cell cycle distribution, proliferation and resistance to temozolomide estimated by apoptosis induced by overexpressed miR-155-3p. MiR-155-3p inhibition reduced glioma cell growth and proliferation in the brain of a mouse model and increased the survival of mice with gliomas. Thus, miR-155-3p modulates Six1 expression and facilitates the progression of glioblastoma and resistance to temozolomide and may act as a novel diagnostic biomarker and a target for glioma treatment.

miR-489-3p/SIX1 Axis Regulates Melanoma Proliferation and Glycolytic Potential

Sine oculis homeobox 1 (SIX1), a key transcription factor for regulating aerobic glycolysis, participates in the occurrence of various cancer types. However, the role of SIX1 in melanoma and the upstream regulating mechanisms of SIX1 remain to be further investigated. MicroRNAs (miRNAs) have emerged as key regulators in tumorigenesis and progression. Here, we show that miR-489-3p suppresses SIX1 expression by directly targeting its 3′ untranslated region (3′ UTR) in melanoma cells. miR-489-3p suppressed melanoma cell proliferation, migration, and invasion through inhibition of SIX1. Mechanistically, by targeting SIX1, miR-489-3p dampens glycolysis, with decreased glucose uptake, lactate production, ATP generation, and extracellular acidification rate (ECAR), as well as an increased oxygen consumption rate (OCR). Importantly, glycolysis regulated by the miR-489-3p/SIX1 axis is critical for its regulation of melanoma growth and metastasis both in vitro and in vivo. In melanoma patients, miR-489-3p expression is negatively correlated with SIX1 expression. In addition, patients who had increased glucose uptake in tumors and with metastasis assessed by positron emission tomography (PET) scans showed decreased miR-489-3p expression and increased expression of SIX1. Collectively, our study demonstrates the importance of the miR-489-3p/SIX1 axis in melanoma, which can be a potential and a promising therapeutic target in melanoma.

SIX1 Regulates Aberrant Endometrial Epithelial Cell Differentiation and Cancer Latency Following Developmental Estrogenic Chemical Exposure

Early-life exposure to estrogenic chemicals can increase cancer risk, likely by disrupting normal patterns of cellular differentiation. Female mice exposed neonatally to the synthetic estrogen diethylstilbestrol (DES) develop metaplastic and neoplastic uterine changes as adults. Abnormal endometrial glands express the oncofetal protein sine oculis homeobox 1 (SIX1) and contain cells with basal [cytokeratin (CK)14⁺/18^-] and poorly differentiated features (CK14⁺/18⁺), strongly associating SIX1 with aberrant differentiation and cancer. Here, we tested whether SIX1 expression is necessary for abnormal endometrial differentiation and DES-induced carcinogenesis by using Pgr-cre to generate conditional knockout mice lacking uterine Six1 (Six1 ^d/d). Interestingly, corn oil (CO) vehicle-treated Six1 ^d/d mice develop focal endometrial glandular dysplasia and features of carcinoma in situ as compared with CO wild-type Six1 (Six1 ^+/+) mice. Furthermore, Six1 ^d/d mice neonatally exposed to DES had a 42% higher incidence of endometrial cancer relative to DES Six1 ^+/+ mice. Although DES Six1 ^d/d mice had >10-fold fewer CK14⁺/18^- basal cells within the uterine horns as compared with DES Six1 ^+/+ mice, the appearance of CK14⁺/18⁺ cells remained a feature of neoplastic lesions. These findings suggest that SIX1 is required for normal endometrial epithelial differentiation, CK14⁺/18⁺ cells act as a cancer progenitor population, and SIX1 delays DES-induced endometrial carcinogenesis by promoting basal differentiation of CK14⁺/18⁺ cells. In human endometrial biopsies, 35% of malignancies showed CK14⁺/18⁺ expression, which positively correlated with tumor stage and grade and was not present in normal endometrium. IMPLICATIONS: Aberrant epithelial differentiation is a key feature in both the DES mouse model of endometrial cancer and human endometrial cancer. The association of CK14⁺/18⁺ cells with human endometrial cancer provides a novel cancer biomarker and could lead to new therapeutic strategies.

MicroRNA-23a inhibits endometrial cancer cell development by targeting SIX1

The present study focused on exploring the inhibitory mechanism of microRNA (miR)-23a in endometrial cancer. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used to investigate miR-23a expression in endometrial tissues and endometrial cancer cells. A colony formation assay using crystal violet staining was performed to compare cell proliferation, while wound-healing and Transwell assays were performed to compare cell migration and invasion. Subsequently, bioinformatics and a luciferase reporter gene assay were used to investigate the effect of miR-23a on sine oculis homeobox homolog 1 (SIX1) expression, and the biological function of SIX1 was analyzed. Additionally, a nude mouse tumorigenicity assay was performed to test the inhibitory effect of miR-23a and Taxol® therapy in endometrial cancer. Finally, immunohistochemistry and RT-qPCR were used to explore the association between miR-23a and SIX1 expression in endometrial cancer tissues. miR-23a was underexpressed in endometrial cancer tissues compared with in para-carcinoma tissues, and the overexpression of miR-23a inhibited proliferation and invasion of endometrial cancer cells. Furthermore, SIX1 was demonstrated to be a downstream target of miR-23a, and miR-23a reduced SIX1 expression. Additionally, SIX1 inversely promoted cell proliferation, migration and invasion. In addition, the effects of reduced cell proliferation and increased cell invasion following miR-23a overexpression could be reversed by adding SIX1 to in vitro culture. Furthermore, the inhibitory effect of miR-23a and Taxol therapy, which reduced SIX1 expression in endometrial cancer, was demonstrated in vivo. Finally, a negative association between miR-23a and SIX1 expression was demonstrated in endometrial cancer tissues. The results of the present study revealed that miR-23a may inhibit endometrial cancer development by targeting SIX1.

MicroRNA-362 Inhibits Cell Proliferation and Invasion by Directly Targeting SIX1 in Colorectal Cancer

PURPOSE

Colorectal cancer (CRC) is the third most common cancer in China and poses high morbidity and mortality. In recent years, increasing evidence has indicated that microRNAs played important functions in the occurrence and development of tumors. The purpose of this study was to identify the biological mechanisms of miR-362 in CRC.

MATERIALS AND METHODS

Quantitative real-time PCR was carried out to assess the expression of miR-362 and SIX1. The Kaplan-Meier method was employed to evaluate the 5-year overall survival of CRC patients. The proliferative and invasive abilities of CRC cells were assessed by MTT and transwell assays.

RESULTS

miR-362 was significantly decreased in CRC tissues and cell lines, compared to the normal tissues and normal cells. A significant connection was confirmed between the overall survival of 53 CRC patients and low expression of miR-362. Downregulation of miR-362 inhibited the proliferation and invasion through binding to the 3'-UTR of SIX1 mRNA in CRC. Additionally, we discovered that SIX1 was a direct target gene of miR-362 and that the expression of miR-362 had a negative connection with SIX1 expression in CRC. SIX1 could reverse partial functions in the proliferation and invasion in CRC cells.

CONCLUSION

miR-362 may be a prognostic marker in CRC and suppress CRC cell proliferation and invasion in part through targeting the 3'-UTR of SIX1 mRNA. The newly identified miR-362/SIX1 axis provides insight into the progression of CRC.

Regulation of cancer stem cell properties by SIX1, a member of the PAX-SIX-EYA-DACH network

The PAX-SIX-EYA-DACH network (PSEDN) is a central developmental transcriptional regulatory network from Drosophila to humans. The PSEDN is comprised of four conserved protein families; including paired box (PAX), sine oculis (SIX), eyes absent (EYA), and dachshund (DACH). Aberrant expression of PSEDN members, particularly SIX1, has been observed in multiple human cancers, where SIX1 expression correlates with increased aggressiveness and poor prognosis. In conjunction with its transcriptional activator EYA, the SIX1 transcription factor increases cancer stem cell (CSC) numbers and induces epithelial-mesenchymal transition (EMT). SIX1 promotes multiple hallmarks and enabling characteristics of cancer via regulation of cell proliferation, senescence, apoptosis, genome stability, and energy metabolism. SIX1 also influences the tumor microenvironment, enhancing recruitment of tumor-associated macrophages and stimulating angiogenesis, to promote tumor development and progression. EYA proteins are multifunctional, possessing a transcriptional activation domain and tyrosine phosphatase activity, that each contributes to cancer stem cell properties. DACH proteins function as tumor suppressors in solid cancers, opposing the actions of SIX-EYA and reducing CSC prevalence. Multiple mechanisms can lead to increased SIX1 expression, including loss of SIX1-targeting tumor suppressor microRNAs (miRs), whose expression correlates inversely with SIX1 expression in cancer patient samples. In this review, we discuss the major mechanisms by which SIX1 confers CSC and EMT features and other important cancer cell characteristics. The roles of EYA and DACH in CSCs and cancer progression are briefly highlighted. Finally, we summarize the clinical significance of SIX1 in cancer to emphasize the potential therapeutic benefits of effective strategies to disrupt PSEDN protein interactions and functions.

Transcriptional Downregulation of miR-4306 serves as a New Therapeutic Target for Triple Negative Breast Cancer

Rationale: Triple-negative breast cancer (TNBC) is characterized by the absence of estrogen receptor alpha (ER-α), human epidermal growth factor receptor 2 (HER2) and progesterone receptor (PR) expression, but the effect of lacking the three factors on TNBC is unclear. Whether loss of the three factors contributes to deregulate genes that participate in the progress of TNBC remains unknown. Methods: We performed microRNA arrays and comprehensive analysis to screen for miRNAs that are transcriptionally regulated by ER-α, HER2 and PR. Functional assays and molecular mechanism studies were used to investigate the role of miR-4306 in TNBC. An orthotopic mouse model of TNBC was used to evaluate the therapeutic potential of a cholesterol-conjugated miR-4306 mimic. Results: We found that miR-4306 is transcriptionally regulated by ER-α, HER2 and PR, and the downregulation of miR-4306 in TNBC is caused by the loss of ER-α, HER2 and PR. Clinically, low miR-4306 expression is strongly associated with lymph node metastasis and poor survival for TNBC. Upregulation of miR-4306 greatly suppresses TNBC cell proliferation, migration and invasion and abrogates angiogenesis and lymphangiogenesis in vitro. According to in vivo models, miR-4306 overexpression considerably inhibits TNBC growth, lung metastasis, angiogenesis and lymph node metastasis. Mechanistic analyses indicate that miR-4306 directly targets SIX1/Cdc42/VEGFA to inactivate the signaling pathways mediated by SIX1/Cdc42/VEGFA. Finally, the orthotopic mouse model of TNBC reveals that miR-4306 mimic can be used for TNBC treatment in combination with cisplatin. Conclusions: Our findings suggest that miR-4306 acts as a tumor suppressor in TNBC and is a potential therapeutic target for TNBC treatment.

Significance of expression of SIX1 and CD147 in gastric adenocarcinoma

AIM

To detect the expression of SIX1 and CD147 and analyze their clinical significance in gastric adenocarcinoma.

METHODS

Seventy-nine cases of gastric adenocarcinoma were collected as an observation group, and 45 normal gastric mucosal samples were collected as a control group. Expression of SIX1 and CD147 in these samples was detected by immunohistochemistry.

RESULTS

Expression of SIX1 and CD147 differed significantly between the two groups. Expression of SIX1 and CD147 was correlated with maximum tumor diameter and tumor infiltration. Expression of SIX1 was correlated with lymph node metastasis, and expression of CD147 was correlated with differentiation. There was a positive correlation between SIX1 and CD147 expression in the observation group. The expression of SIX1 and CD147 was correlated with survival time.

CONCLUSION

Higher expression of SIX1 and CD147 can promote tumor formation and progression in gastric adenocarcinoma. SIX1 and CD147 may have synergistic effects, and they correlate with prognosis in gastric adenocarcinoma.

microRNA-488 inhibits chemoresistance of ovarian cancer cells by targeting Six1 and mitochondrial function

Dysregulation of miR-488 has been implicated in several human cancers. In this study, we aim to explore its expression and biological function in ovarian cancers. We found miR-488 expression was downregulated in ovarian cancer tissues. Using CCK8 and colony formation assay showed that miR-488 inhibited SKOV3 cell proliferation and colony formation, with downregulation of cyclin D1 and cyclin E protein. While miR-488 inhibitor promoted OVCAR3 cell growth and colony formation. Cell viability and Annexin V/PI staining showed that miR-488 downregulated cell survival and increased apoptosis rate when treated with cisplatin and paclitaxel. Further experiments using MitoTracker and JC-1 staining indicated that miR-488 regulated mitochondrial fission/fusion balance and inhibited mitochondrial membrane potential, with p-Drp1, Drp1 and Fis1 downregulation. Luciferase reporter assay showed that Six1 is a target of miR-488. We also found a negative association between Six1 and miR-488 in ovarian cancer tissues. In addition, Six1 overexpression induced mitochondrial fission and increased mitochondrial potential, with upregulation of Drp1 signaling. Six1 depletion showed the opposite effects. Restoration of Six1 in SKOV3 cells rescued decreased p-Drp1 and Drp1 expression induced by miR-488 mimic. Six1 plasmid also reversed the effects of miR-488 on chemoresistance and apoptosis. Taken together, the present study showed that, by targeting Six1, miR-488 inhibits chemoresistance of ovarian cancer cells through regulation of mitochondrial function.