A MicroRNA/Ubiquitin Ligase Feedback Loop Regulates Slug-Mediated Invasion in Breast Cancer

FBXO31-mediated ubiquitination of OGT maintains O-GlcNAcylation homeostasis to restrain endometrial malignancy

Protein O-GlcNAcylation is a post-translational modification coupled to cellular metabolic plasticity. Aberrant O-GlcNAcylation has been observed in many cancers including endometrial cancer (EC), a common malignancy in women. However, clinical characterization of dysregulated O-GlcNAcylation homeostasis in EC and interrogating its molecular mechanism remain incomplete. Here we report that O-GlcNAcylation level is positively correlated with EC histologic grade in a Chinese cohort containing 219 tumors, validated in The Cancer Genome Atlas dataset. Increasing O-GlcNAcylation in patient-derived endometrial epithelial organoids promotes proliferation and stem-like cell properties, whereas decreasing O-GlcNAcylation limits the growth of endometrial cancer organoids. CRISPR screen and biochemical characterization reveal that tumor suppressor F-box only protein 31 (FBXO31) regulates O-GlcNAcylation homeostasis in EC by ubiquitinating the O-GlcNAc transferase OGT. Downregulation of O-GlcNAcylation impedes EC tumor formation in mouse models. Collectively, our study highlights O-GlcNAcylation as a useful stratification marker and a therapeutic vulnerability for the advanced, poorly differentiated EC cases.

The ubiquitin-proteasome system in breast cancer

Ubiquitin-proteasome system (UPS) is a selective proteolytic system that is associated with the expression or function of target proteins and participates in various physiological and pathological processes of breast cancer. Inhibitors targeting the 26S proteasome in combination with other drugs have shown promising therapeutic effects in the clinical treatment of breast cancer. Moreover, several inhibitors/stimulators targeting other UPS components are also effective in preclinical studies, but have not yet been applied in the clinical treatment of breast cancer. Therefore, it is vital to comprehensively understand the functions of ubiquitination in breast cancer and to identify potential tumor promoters or tumor suppressors among UPS family members, with the aim of developing more effective and specific inhibitors/stimulators targeting specific components of this system.

Differential co-expression network analysis with DCoNA reveals isomiR targeting aberrations in prostate cancer

MOTIVATION

One of the standard methods of high-throughput RNA sequencing analysis is differential expression. However, it does not detect changes in molecular regulation. In contrast to the standard differential expression analysis, differential co-expression one aims to detect pairs or clusters whose mutual expression changes between two conditions.

RESULTS

We developed Differential Co-expression Network Analysis (DCoNA)-an open-source statistical tool that allows one to identify pair interactions, which correlation significantly changes between two conditions. Comparing DCoNA with the state-of-the-art analog, we showed that DCoNA is a faster, more accurate and less memory-consuming tool. We applied DCoNA to prostate mRNA/miRNA-seq data collected from The Cancer Genome Atlas (TCGA) and compared predicted regulatory interactions of miRNA isoforms (isomiRs) and their target mRNAs between normal and cancer samples. As a result, almost all highly expressed isomiRs lost negative correlation with their targets in prostate cancer samples compared to ones without the pathology. One exception to this trend was the canonical isomiR of hsa-miR-93-5p acquiring cancer-specific targets. Further analysis showed that cancer aggressiveness simultaneously increased with the expression level of this isomiR in both TCGA primary tumor samples and 153 blood plasma samples of P. Hertsen Moscow Oncology Research Institute patients' cohort analyzed by miRNA microarrays.

AVAILABILITY AND IMPLEMENTATION

Source code and documentation of DCoNA are available at https://github.com/zhiyanov/DCoNA.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Tumor suppressor DEAR1 regulates mammary epithelial cell fate and predicts early onset and metastasis in triple negative breast cancer

Triple negative breast cancer (TNBC) is a disease of poor prognosis, with the majority classified as the basal-like subtype associated with epithelial-mesenchymal transition and metastasis. Because basal breast cancers originate from proliferative luminal progenitor-like cells upon dysregulation of proper luminal differentiation, genes regulating luminal-basal transition are critical to elucidate novel therapeutic targets to improve TNBC outcomes. Herein we demonstrate that the tumor suppressor DEAR1/TRIM62 is a critical regulator of luminal cell fate. DEAR1 loss in human mammary epithelial cells results in significantly enhanced mammosphere formation that is accelerated in the presence of TGF-β/SMAD3 signaling. Mammospheres formed following DEAR1 loss are enriched for ALDH1A1 and CK5 expression, EpCAM^-/CD49f⁺ and CD44^high/24^low basal-like epithelial cells, indicating that DEAR1 regulates stem/progenitor cell properties and luminal-basal progenitor transition. We show that DEAR1 maintains luminal differentiation as a novel ubiquitin ligase for SNAI2/SLUG, a master regulator driving stemness and generation of basal-like progenitor populations. We also identify a significant inverse correlation between DEAR1 and SNAI2 expression in a 103 TNBC case cohort and show that low DEAR1 expression significantly correlates with young age of onset and shorter time to metastasis, suggesting DEAR1 could serve as a biomarker to stratify early onset TNBCs for targeted stem cell therapies.

Loss of miR-936 leads to acquisition of androgen-independent metastatic phenotype in prostate cancer

Prostate cancer (PCa) progresses from a hormone-sensitive, androgen-dependent to a hormone-refractory, androgen-independent metastatic phenotype. Among the many genes implicated, ANXA2, a calcium-dependent phospholipid binding protein, has been found to have a critical role in the progression of PCa into more invasive metastatic phenotype. However, the molecular mechanisms underlying the absence of ANXA2 in early PCa and its recurrence in advanced stage are yet unknown. Moreover, recent studies have observed the deregulation of microRNAs (miRNAs) are involved in the development and progression of PCa. In this study, we found the down-regulation of miR-936 in metastatic PCa wherein its target ANXA2 was overexpressed. Subsequently, it has been shown that the downregulation of miRNA biogenesis by siRNA treatment in ANXA2-null LNCaP cells could induce the expression of ANXA2, indicating the miRNA mediated regulation of ANXA2 expression. Additionally, we demonstrate that miR-936 regulates ANXA2 expression by direct interaction at coding as well as 3'UTR region of ANXA2 mRNA by luciferase reporter assay. Furthermore, the overexpression of miR-936 suppresses the cell proliferation, cell cycle progression, cell migration, and invasion abilities of metastatic PCa PC-3 cells in vitro and tumor forming ability in vivo. These results indicate that miR-936 have tumor suppressor properties by regulating the over expression of ANXA2 in hormone-independent metastatic PCa. Moreover, our results suggest that this tumor suppressor miR-936 could be developed as a targeted therapeutic molecule for metastatic PCa control and to improve the prognosis in PCa patients.

F-box protein FBXO41 suppresses breast cancer growth by inducing autophagic cell death through facilitating proteasomal degradation of oncogene SKP2

F-box proteins form SCF (Cullin1, SKP1 and F-box-protein) ubiquitin ligase complexes to ubiquitinate cellular proteins. They play key role in several biological processes, including cell cycle progression, cellular signaling, stress response and cell death pathways. Therefore, deregulation of F-box proteins is closely associated with cancer progression. However, the role of most of the F-box proteins, including FBXO41, in cancer progression remains elusive. Here, we unravel the role of FBXO41 in cancer progression. We show that FBXO41 suppresses cancer cell proliferation and tumor growth by inducing autophagic cell death through an alternative pathway. Results revealed that FBXO41-mediated autophagic cell death induction is dependent on accumulation of cell cycle checkpoint protein p21. We found that FBXO41 increases the expression levels of p21 at the post-translational level by promoting the proteasomal degradation of SKP2, an oncogenic F-box protein. Mechanistically, FBXO41 along with p21 disrupts the inhibitory BCL2 (anti-apoptotic protein)-Beclin1 (autophagy initiating factor) complex of autophagy induction to release Beclin1, thereby inducing autophagy. Overall, the present study establishes a new FBXO41-SKP2-p21 axis for induction of autophagic cell death to prevent cancer growth, which could be explored to develop promising cancer therapeutics.

F-box protein FBXO41 plays vital role in arsenic trioxide-mediated autophagic death of cancer cells

Arsenic trioxide (ATO), a potent anti-neoplastic drug, is known to prevent cancer cell growth through induction of autophagic cell death. However, importance of cellular factors in ATO-mediated autophagic cell death is poorly understood. In this study, using biochemical and immunofluorescence techniques, we show that F-box protein FBXO41 plays a critical role in anti-proliferative activity of ATO. Our study reveals the importance of FBXO41 in induction of autophagic death of cancer cells by ATO. Further, we show that the autophagic cell death induced by FBXO41 is distinct and independent of apoptosis and necrosis, showing that FBXO41 may play vital role in inducing autophagic death of apoptosis resistant cancer cells. Overall, our study elucidates the importance of FBXO41 in ATO induced autophagic cell death to prevent cancer progression, which could be explored to develop promising cancer therapeutic strategy.

E3 Ubiquitin Ligases in Breast Cancer Metastasis: A Systematic Review of Pathogenic Functions and Clinical Implications

Female breast cancer has become the most commonly occurring cancer worldwide. Although it has a good prognosis under early diagnosis and appropriate treatment, breast cancer metastasis drastically causes mortality. The process of metastasis, which includes cell epithelial–mesenchymal transition, invasion, migration, and colonization, is a multistep cascade of molecular events directed by gene mutations and altered protein expressions. Ubiquitin modification of proteins plays a common role in most of the biological processes. E3 ubiquitin ligase, the key regulator of protein ubiquitination, determines the fate of ubiquitinated proteins. E3 ubiquitin ligases target a broad spectrum of substrates. The aberrant functions of many E3 ubiquitin ligases can affect the biological behavior of cancer cells, including breast cancer metastasis. In this review, we provide an overview of these ligases, summarize the metastatic processes in which E3s are involved, and comprehensively describe the roles of E3 ubiquitin ligases. Furthermore, we classified E3 ubiquitin ligases based on their structure and analyzed them with the survival of breast cancer patients. Finally, we consider how our knowledge can be used for E3s’ potency in the therapeutic intervention or prognostic assessment of metastatic breast cancer.

Feedback-regulated transcriptional repression of FBXO31 by c-Myc triggers ovarian cancer tumorigenesis

FBXO31, a member of F-box protein family, has been shown to play an important role in preventing tumorigenesis by preserving genomic stability during cell proliferations as well as upon genotoxic stresses. Inactivation of FBXO31 due to loss of heterozygosity is associated with various cancers, including ovarian cancer, one of the deadliest forms of gynecological cancers. However, the role and regulation of FBXO31 in ovarian cancer remained elusive. Here, using biochemical and molecular biology techniques, we show that c-Myc suppresses the mRNA levels of FBXO31 in ovarian cancer cell lines and mouse model. Chromatin immunoprecipitation experiment showed that c-Myc is recruited to the promoter region of FBXO31 and prevents FBXO31 mRNA synthesis. In contrast, FBXO31 maintains the c-Myc expression at an optimum through proteasome pathway. FBXO31 interacts with and facilitates the polyubiquitination of c-Myc through the SCF complex and thereby inhibits ovarian cancer growth both in vitro and in vivo. Moreover, FBXO31-mediated proteasomal degradation of c-Myc is unique. Unlike other negative regulators, FBXO31 recognizes c-Myc in phosphorylation independent manner to direct its degradation. Further, expression levels analysis revealed that c-Myc and FBXO31 share a converse correlation of expression in ovarian cancer cell lines and patient samples. We observed an increase in the expression levels of c-Myc with a concomitant decrease in the levels of FBXO31 in higher grades of ovarian cancer patient samples. In conclusion, our study demonstrated that oncogene c-Myc impairs the tumor-suppressive functions of FBXO31 to promote ovarian cancer progression, and therefore c-Myc-FBXO31 axis can be explored to develop better cancer therapy. This article is protected by copyright. All rights reserved.

Systematic analysis of the expression and prognosis relevance of FBXO family reveals the significance of FBXO1 in human breast cancer

Background

Breast cancer (BC) remains a prevalent and common form of cancer with high heterogeneity. Making efforts to explore novel molecular biomarkers and serve as potential disease indicators, which is essential to effectively enhance the prognosis and individualized treatment of BC. FBXO proteins act as the core component of E3 ubiquitin ligase, which play essential regulators roles in multiple cellular processes. Recently, research has indicated that FBXOs also play significant roles in cancer development. However, the molecular functions of these family members in BC have not been fully elucidated.

Methods

In this research, we investigated the expression data, survival relevance and mutation situation of 10 FBXO members (FBXO1, 2, 5, 6, 16, 17, 22, 28, 31 and 45) in patients with BC from the Oncomine, GEPIA, HPA, Kaplan–Meier Plotter, UALCAN and cBioPortal databases. The high transcriptional levels of FBXO1 in different subtypes of BC were verified by immunohistochemical staining and the specific mutations of FBXO1 were obtained from COSMIC database. Top 10 genes with the highest correlation to FBXO1 were identified through cBioPortal and COXPRESdb tools. Additionally, functional enrichment analysis, PPI network and survival relevance of FBXO1 and co-expressed genes in BC were obtained from DAVID, STRING, UCSC Xena, GEPIA, bc-GenExMiner and Kaplan–Meier Plotter databases. FBXO1 siRNAs were transfected into MCF-7 and MDA-MB-231 cell lines. Expression of FBXO1 in BC cell lines was detected by western-blot and RT-qPCR. Cell proliferation was detected by using CCK-8 kit and colony formation assay. Cell migration was detected by wound‐healing and transwell migration assay.

Results

We found that FBXO2, FBXO6, FBXO16 and FBXO17 were potential favorable prognostic factors for BC. FBXO1, FBXO5, FBXO22, FBXO28, FBXO31 and FBXO45 may be the independent poor prognostic factors for BC. All of them were correlated to clinicopathological staging. Moreover, knockdown of FBXO1 in MCF7 and MDA-MB-231 cell lines resulted in decreased cell proliferation and migration in vitro. We identified that FBXO1 was an excellent molecular biomarker and therapeutic target for different molecular typing of BC.

Conclusion

This study implies that FBXO1, FBXO2, FBXO5, FBXO6, FBXO16, FBXO17, FBXO22, FBXO28, FBXO31 and FBXO45 genes are potential clinical targets and prognostic biomarkers for patients with different molecular typing of BC. In addition, the overexpression of FBXO1 is always found in breast cancer and predicts disadvantageous prognosis, implicating it could as an appealing therapeutic target for breast cancer patients.

Ginkgoic acid impedes gastric cancer cell proliferation, migration and EMT through inhibiting the SUMOylation of IGF-1R

The imbalance of SUMOylation is related to different cancers, including gastric cancer (GC). Ginkgolic acid (GA) inhibits the growth and invasion of many cancer cells, and it has been reported to restrain SUMOylation. However, the role of GA in GC and whether it functions through SUMOylation remains to be clarified. Our research revealed that GA (15:1) inhibited cell proliferation, migration, epithelial-mesenchymal transition (EMT) and overall protein SUMOylation in BGC823 and HGC27 cells. In addition, knockdown of SUMO1 (small ubiquitin-like modifier) instead of SUMO2/3 played a similar role to GA in cell behaviors. Besides, nuclear IGF-1R (insulin-like growth factor 1 receptor) expression was markedly upregulated in GC cells compared to normal gastric epithelial cells. GA prevented IGF-1R from binding to SUMO1, thereby suppressing its nuclear accumulation. Further research found that IGF-1R directly bound to SNAI2 (snail family zinc finger 2) promoter. The interference of IGF-1R downregulated the mRNA and protein levels of SNAI2, while the overexpression of SUMO1, IGF-1R and UBC9 (SUMO-conjugating enzyme) played the opposite role. Furthermore, the co-transfection of SUMO1, UBC9 and IGF-1R vectors or the overexpression of SNAI2 reversed the inhibitory effects of GA on cell proliferation, migration and EMT. Finally, GA impeded the growth of GC xenografts and decreased the expression of nuclear IGF-1R and SNAI2 in vivo. In conclusion, these findings demonstrated that GA hindered the progression of GC by inhibiting the SUMOylation of IGF-1R. Thus, GA might be a promising therapeutic for GC.

F-box protein FBXO31 modulates apoptosis and epithelial-mesenchymal transition of cervical cancer via inactivation of the PI3K/AKT-mediated MDM2/p53 axis

AIMS

Cervical cancer (CC) is one of the most common malignant tumours in the world and a serious threat to women's health. The dysregulation of protein degradation mediated by F-box proteins is involved in tumorigenesis, and F-box protein FBXO31 has been reported to play an important role in various human cancers. However, the role of FBXO31 in CC remains unclear. This study aimed to investigate the function and underlying regulatory mechanism of FBXO31 in CC.

MAIN METHODS

In this study, quantitative real-time polymerase chain reaction (qRT-PCR) and western blot were used to measure target gene expression; the Cell Counting Kit-8, cell death ELISA, Transwell invasion assay, wound-healing assay and western blot were applied to assess cell viability, apoptosis, invasion, migration and epithelial-mesenchymal transition (EMT), respectively.

KEY FINDINGS

FBXO31 was expressed at a low level in 37 pairs of CC tissues and three types of CC cell lines. Overexpression of FBXO31 inhibited cell viability, invasion, migration, EMT and induced apoptosis in SiHa cells. FBXO31 promoted p53 activity through suppression of murine double minute 2 (MDM2) expression. Overexpression of MDM2 ameliorated the inhibitory effect of FBXO31 on SiHa cells, while the MDM2/p53 axis-specific inhibitor Nutlin-3a facilitated this inhibitory effect. Further, we confirmed that FBXO31 inactivated MDM2/p53 axis dependence on the phospholipid inositol 3-kinase (PI3K)/protein kinase B (AKT) signalling pathway.

SIGNIFICANCE

Collectively, our results reveal that FBXO31 down-regulates CC progression by blocking the PI3K/AKT-mediated MDM2/p53 axis, suggesting that FBXO31 may serve as a promising therapeutic target for CC treatment.

Slug and E-Cadherin: Stealth Accomplices?

During physiological epithelial-mesenchymal transition (EMT), which is important for embryogenesis and wound healing, epithelial cells activate a program to remodel their structure and achieve a mesenchymal fate. In cancer cells, EMT confers increased invasiveness and tumor-initiating capacity, which contribute to metastasis and resistance to therapeutics. However, cellular plasticity that navigates between epithelial and mesenchymal states and maintenance of a hybrid or partial E/M phenotype appears to be even more important for cancer progression. Besides other core EMT transcription factors, the well-characterized Snail-family proteins Snail (SNAI1) and Slug (SNAI2) play important roles in both physiological and pathological EMT. Often mentioned in unison, they do, however, differ in their functions in many scenarios. Indeed, Slug expression does not always correlate with complete EMT or loss of E-cadherin (CDH1). For example, Slug plays important roles in mammary epithelial cell progenitor cell lineage commitment and differentiation, DNA damage responses, hematopoietic stem cell self-renewal, and in pathologies such as pulmonary fibrosis and atherosclerosis. In this Perspective, we highlight Slug functions in mammary epithelial cells and breast cancer as a “non-EMT factor” in basal epithelial cells and stem cells with focus reports that demonstrate co-expression of Slug and E-cadherin. We speculate that Slug and E-cadherin may cooperate in normal mammary gland and breast cancer/stem cells and advocate for functional assessment of such Slug⁺/E-cadherin^low/+ (SNAI2⁺/CDH1^low/+) “basal-like epithelial” cells. Thus, Slug may be regarded as less of an EMT factor than driver of the basal epithelial cell phenotype.

Potential miRNAs for miRNA-Based Therapeutics in Breast Cancer

MicroRNAs (miRNAs) are small non-coding RNAs that can post-transcriptionally regulate the genes involved in critical cellular processes. The aberrant expressions of oncogenic or tumor suppressor miRNAs have been associated with cancer progression and malignancies. This resulted in the dysregulation of signaling pathways involved in cell proliferation, apoptosis and survival, metastasis, cancer recurrence and chemoresistance. In this review, we will first (i) provide an overview of the miRNA biogenesis pathways, and in vitro and in vivo models for research, (ii) summarize the most recent findings on the roles of microRNAs (miRNAs) that could potentially be used for miRNA-based therapy in the treatment of breast cancer and (iii) discuss the various therapeutic applications.

MiR-652 serves as a prognostic biomarker in gastric cancer and promotes tumor proliferation, migration, and invasion via targeting RORA

PURPOSE

MicroRNAs (miRNAs) have been reported to be involved in tumorigenesis. The aim of this study was to investigate the functional role and prognostic value of miR-652 in gastric cancer (GC).

METHODS

Quantitative real-time polymerase chain reaction (qRT-PCR) was used to determine the expression levels of miR-652 in human GC tissue samples and GC cell lines. The Kaplan-Meier survival curves and Cox regression analysis were performed to measure the prognostic value of miR-652 in GC. The tumor cell proliferation capacity was estimated by MTT assay, and cell migration and invasion were assessed by Transwell assays. The luciferase reporter assay was performed to confirm the target gene of miR-652.

RESULTS

MiR-652 was significantly elevated in GC tissues and cell lines (all P< 0.001). And the expression level of miR-652 was significantly associated with TNM stage and lymph node metastasis (all P< 0.05). GC patients with high expression of miR-652 had a shorter overall survival rate than those with low miR-652 expression (log-rank P< 0.001). The miR-652 and TNM stage were proven to be independent prognostic predictors for the GC patients. Overexpressing miR-652 could enhance cell proliferation, migration and invasion (all P< 0.01). RORA was proved to be the target gene of miR-652.

CONCLUSION

MiR-652 functions as an oncogene in GC and promotes tumor progression via targeting RORA. MiR-652 might be a novel predictive marker for the poor prognosis of GC patients.

Ubiquitin‑proteasomes are the dominant mediators of the regulatory effect of microRNA‑1 on cardiac remodeling after myocardial infarction

Patients with ischemic hearts who have refused coronary vascular reconstruction may exhibit dynamic myocardial remodeling and cardiac dysfunction. In the present study, the role of miRNA-1 and its association with the ubiquitin-proteasome system (UPS) in regulating myocardial remodeling was investigated. A myocardial infarction (MI) model was constructed and the hearts were treated with miRNA-1 antagomir, miRNA-1 lentiviral vectors and the UPS proteasome blocker bortezomib. The expression levels of miRNA-1 were evaluated using reverse transcription PCR and the abundance of the ubiquitin-proteasome protein and caspase-3 were evaluated via western blot analysis. Furthermore, the collagen volume fraction was calculated using Masson's trichrome staining, and the apoptosis index was detected via terminal deoxynucleotidyl transferase dUTP-biotin nick end labeling staining. Transforming growth factor (TGF)-β expression was assessed via immunohistochemical staining. Echocardiographic characteristics and myocardial infarct size were analyzed. miRNA-1 expression levels were found to be increased following MI. miRNA-1 antagomir administration clearly inhibited miRNA-1 expression, whereas the miRNA-1 lentiviral vector exerted the opposite effect. The levels of 19s proteasome, 20S proteasome and ubiquitin ligase E3 were decreased in the miRNA-1 antagomir group, but were significantly increased in the miRNA-1 lentiviral group; however, only 20S proteasome expression was decreased in the bortezomib group. Collagen hyperplasia and TGF-β expression were decreased in both the miRNA-1 antagomir and bortezomib groups, although the effects of the miRNA-1 antagomir were more noticeable. The miRNA-1 antagomir and the UPS proteasome blocker both alleviated the ultrastructural impairments, demonstrated by a decreased left ventricular (LV) end-diastolic diameter and LV mass, but the miRNA-1 antagomir was also able to increase LV ejection fraction and LV fractional shortening. miRNA-1 regulated UPS-associated mRNA expression and affected the majority of the UPS components in the myocardium, thereby leading to increased myocardial cell apoptosis, myocardial fibrosis and remodeling. The miRNA-1 antagomir exerted a more prominent cardioprotective effect compared with the UPS proteasome blocker bortezomib.

F-box protein FBXO16 functions as a tumor suppressor by attenuating nuclear β-catenin function

Aberrant activation of β‐catenin has been implicated in a variety of human diseases, including cancer. In spite of significant progress, the regulation of active Wnt/β‐catenin‐signaling pathways is still poorly understood. In this study, we show that F‐box protein 16 (FBXO16) is a putative tumor suppressor. It is a component of the SCF (SKP1‐Cullin1‐F‐box protein) complex, which targets the nuclear β‐catenin protein to facilitate proteasomal degradation through the 26S proteasome. FBXO16 interacts physically with the C‐terminal domain of β‐catenin and promotes its lysine 48‐linked polyubiquitination. In addition, it inhibits epithelial‐to‐mesenchymal transition (EMT) by attenuating the level of β‐catenin. Therefore, depletion of FBXO16 leads to increased levels of β‐catenin, which then promotes cell invasion, tumor growth, and EMT of cancer cells. Furthermore, FBXO16 and β‐catenin share an inverse correlation of cellular expression in clinical breast cancer patient samples. In summary, we propose that FBXO16 functions as a putative tumor suppressor by forming an SCF^FBXO16 complex that targets nuclear β‐catenin in a unique manner for ubiquitination and subsequent proteasomal degradation to prevent malignancy. This work suggests a novel therapeutic strategy against human cancers related to aberrant β‐catenin activation. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Estrogen receptor-α-miR-1271-SNAI2 feedback loop regulates transforming growth factor-β-induced breast cancer progression

BACKGROUND

Breast cancer is the most common cancer among women worldwide, and approximately 70% of breast cancers are hormone receptor-positive and express estrogen receptor-α (ERα) or/and progesterone receptor. ERα has been identified to promote the growth of primary breast cancer, however, it can also antagonize signaling pathways that lead to epithelial-mesenchymal transition (EMT), including transforming growth factor-β (TGF-β) signaling. miRNA alteration or dysfunction is involved in cancer development and progression. Although miR-1271 has identified as a tumor suppressor in various cancers, the role of miR-1271 in breast cancer is still limited.

METHODS

The effect of miR-1271 on breast cancer progression was investigated both in vitro and in vivo. The EMT-related protein expression levels and localization were analyzed by western blotting and immunofluorescence, respectively. Chromatin immunoprecipitation and dual-luciferase reporter assays were used to validate the regulation of ERα-miR-1271-SNAI2 feedback loop.

RESULTS

miR-1271 suppresses breast cancer progression and EMT phenotype both in vitro and in vivo by targeting SNAI2. Estrogen reverses TGF-β-induced EMT in a miR-1271 dependent manner. Furthermore, ERα transactivates the miR-1271 expression and is also transcriptionally repressed by SNAI2.

CONCLUSIONS

Our data uncover the ERα-miR-1271-SNAI2 feedback loop and provide a mechanism to explain the TGF-β network in breast cancer progression.

Identification of Key Potential Targets and Pathway for Arsenic Trioxide by Systemic Bioinformatics Analysis in Pancreatic Cancer

Arsenic trioxide is an approved chemotheraputic agent for the treatment of acute promyelocytic leukemia (APL). Recently, numerous studies suggested that arsenic trioxide acts as anti-cancer roles in various human malignancies. However, the molecular mechanisms are not fully elucidated. In this study, we explored the critical targets of arsenic trioxide and their interaction network systematically by searching the publicly available published database like DrugBank (DB) and STRING. Seven direct protein targets (DPTs) and 111 DPT-associated genes were identified. The enrichment analysis of arsenic trioxide associated genes/proteins revealed 10 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Among these pathways, phosphatidylinositol-4,5-bisphosphate-3-kinase -Akt (PI3K-Akt) single pathway and pancreatic cancer pathway are highly correlated with arsenic trioxide and have 5 overlapped targets. Then we investigated the gene alternation of selected critical genes in pancreatic cancer studies using cBio portal. These results indicated that arsenic trioxide could act anti-tumor function through PI3K-Akt single pathway and identified critical genes might be therapeutic targets for pancreatic cancer.

MicroRNA-214 promotes the proliferation, migration and invasion of gastric cancer MKN28 cells by suppressing the expression of Dact2

The present study examined the expression of Dapper, antagonist of β-catenin 2 (Dact2) and microRNA (miR)-214 in gastric cancer at tissue and cellular levels, and to understand their biological roles. A total of 42 gastric cancer patients were enrolled in the present study. Bioinformatics tool was used to predict the miR molecule that potentially regulates Dact2 expression. To measure the expression of miR-214 and Dact2, reverse transcription-quantitative polymerase chain reaction was employed. Mixed gastric adenocarcinoma type MKN28 cells were transfected with negative control (NC), miR-214 mimics or inhibitor. The CCK-8 assay was used to investigate the proliferation of mixed gastric adenocarcinoma type MKN28 cells. To study migration and invasion abilities of mixed gastric adenocarcinoma type MKN28 cells, the Transwell assay was performed. To determine the expression of Dact2 protein, western blotting was conducted and the rescue assay was utilized to study the biological roles of miR-214 and Dact2 in mixed gastric adenocarcinoma type MKN28 cells. To test whether Dact2 is a direct target of miR-214, the dual luciferase reporter assay was performed. Results indicated that the expression of miR-214 was elevated, but expression of Dact2 mRNA was decreased in gastric cancer tissues, which was closely correlated with the invasion, metastasis, occurrence and development of gastric cancer. Notably, miR-214 promoted the proliferation of mixed gastric adenocarcinoma type MKN28 cells in vitro, whereas but Dact2 inhibited the proliferation of these cells. Downregulation of miR-214 expression or upregulation of Dact2 expression inhibited the migration and invasion of mixed gastric adenocarcinoma type MKN28 cells. Furthermore, miR-214 regulated the expression of Dact2 protein and its downstream β-catenin protein in mixed gastric adenocarcinoma type MKN28 cells. Dact2 reversed the effect of miR-214 on the proliferation, migration and invasion of mixed gastric adenocarcinoma type MKN28 cells. In addition, miR-214 directly targeted the 3'-UTR seeding region of Dact2 mRNA to regulate its expression. The present study demonstrated that expression of miR-214 was upregulated in gastric cancer tissues, and positively correlated with lymphatic metastasis and clinical staging. In addition, expression of Dact2 was downregulated in gastric cancer tissues and negatively correlated with lymphatic metastasis and clinical staging. Notably, the present findings suggest that miR-214 promoted the proliferation, migration and invasion of mixed gastric adenocarcinoma type MKN28 cells by suppressing the expression of Dact2.

The SCFFBXO46 ubiquitin ligase complex mediates degradation of the tumor suppressor FBXO31 and thereby prevents premature cellular senescence

The tumor suppressor F-box protein 31 (FBXO31) is indispensable for maintaining genomic stability. Its levels drastically increase following DNA damage, leading to cyclin D1 and MDM2 degradation and G₁ and G₂/M arrest. Prolonged arrest in these phases leads to cellular senescence. Accordingly, FBXO31 needs to be kept at low basal levels in unstressed conditions for normal cell cycle progression during growth and development. However, the molecular mechanism maintaining these basal FBXO31 levels has remained unclear. Here, we identified the F-box family SCF-E3 ubiquitin ligase FBXO46 (SCF^FBXO46) as an important proteasomal regulator of FBXO31 and found that FBXO46 helps maintain basal FBXO31 levels under unstressed conditions and thereby prevents premature senescence. Using molecular docking and mutational studies, we showed that FBXO46 recognizes an RXXR motif located at the FBXO31 C terminus to direct its polyubiquitination and thereby proteasomal degradation. Furthermore, FBXO46 depletion enhanced the basal levels of FBXO31, resulting in senescence induction. In response to genotoxic stress, ATM (ataxia telangiectasia-mutated) Ser/Thr kinase-mediated phosphorylation of FBXO31 at Ser-278 maintained FBXO31 levels. In contrast, activated ATM phosphorylated FBXO46 at Ser-21/Ser-67, leading to its degradation via FBXO31. Thus, ATM-catalyzed phosphorylation after DNA damage governs FBXO31 levels and FBXO46 degradation via a negative feedback loop. Collectively, our findings reveal that FBXO46 is a crucial proteasomal regulator of FBXO31 and thereby prevents senescence in normal growth conditions. They further indicate that FBXO46-mediated regulation of FBXO31 is abrogated following genotoxic stress to promote increased FBXO31 levels for maintenance of genomic stability.

The role of F-box only protein 31 in cancer

F-box only protein 31 (FBXO31), initially identified in 2005, is a novel subunit of the S-phase kinase associated protein 1-Cullin 1-F-box ubiquitin ligase. As with other F-box proteins, FBXO31 may interact with several proteins to promote their ubquitination and subsequent degradation in an F-box-dependent manner. It has been revealed that FBXO31 serves a crucial role in DNA damage response and tumorigenesis. However, the expression and function of FBXO31 varies in different types of human cancer. To the best of our knowledge, the present review is the first to summarize the role of FBXO31 in different types of human cancer and determine its underlying mechanisms, thereby paving the road for the design of FBXO31-targeted anticancer therapies.

Poly r(C) binding protein 1-mediated regulation of microRNA expression underlies post-sevoflurane amelioration of acute lung injury in rats

Acute lung injury (ALI) presents a pervasive health burden due to the high morbidity and mortality associated with it. Volatile anesthetics like sevoflurane has been previously shown to have organ-protective effect, both in the context of normal physiological function in liver, and during LPS-induced ALI. Sevoflurane was shown to exert lung protective effect during LPS-induced ALI by modulating expression level of microRNAs (miRNAs), specifically miR-155. The objective of the current study was to define the underlying mechanism by which sevoflurane alters miRNA expression levels. Lung injury caused by LPS and its amelioration post sevoflurane administration was first confirmed. Expression levels of different miRNA and messenger RNAs (mRNAs) encoding inflammatory cytokines were measured in a rat model of lipopolysaccharide (LPS)-induced ALI, which were subsequently treated with either sevoflurane or vehicle control. Host of miRNAs and messenger RNAs encoding pro-inflammatory cytokines are overexpressed during LPS-induced ALI, which are reversed following sevoflurane administration. Mass spectrometry analysis revealed that the RNA-binding protein, poly r(C) binding protein 1 (PCBP1) expression is induced in ALI and is repressed following sevoflurane treatment. RNA immunoprecipitation experiments revealed that PCBP1 expression dictates the altered miRNA expression and sevoflurane altered miRNA expression by suppressing PCBP1 expression. Our study thus elucidates a unique mechanism of lung protective effect of sevoflurane mediated by suppression of expression of a RNA-binding protein that potentiates expression of pro-inflammatory miRNAs.