FOXK2 transcription factor suppresses ERα-positive breast cancer cell growth through down-regulating the stability of ERα via mechanism involving BRCA1/BARD1

FOXK2 amplification promotes breast cancer development and chemoresistance

Oncogene activation through DNA amplification or overexpression is a crucial driver of cancer initiation and progression. The FOXK2 gene, located on chromosome 17q25, encodes a transcription factor with a forkhead DNA-binding domain. Analysis of genomic datasets reveals that FOXK2 is frequently amplified and overexpressed in breast cancer, correlating with poor patient survival. Knockdown of FOXK2 significantly inhibited breast cancer cell proliferation, migration, anchorage-independent growth, and delayed tumor growth in a xenograft mouse model. Additionally, inhibiting FOXK2 sensitized breast cancer cells to chemotherapy. Co-overexpression of FOXK2 and mutant PI3KCA transformed non-tumorigenic MCF-10A cells, suggesting a role for FOXK2 in PI3KCA-driven tumorigenesis. CCNE2, PDK1, and ESR1 were identified as transcriptional targets of FOXK2 in MCF-7 cells. Small-molecule inhibitors of CCNE2/CDK2 (dinaciclib) and PDK1 (dichloroacetate) exhibited synergistic anti-tumor effects with PI3KCA inhibitor (alpelisib) in vitro. Inhibition of FOXK2 by dinaciclib synergistically enhanced the anti-tumor effects of alpelisib in a xenograft mouse model. Collectively, these findings highlight the oncogenic function of FOXK2 and suggest that FOXK2 and its downstream genes represent potential therapeutic targets in breast cancer.

KLF11 promotes the proliferation of breast cancer cells by inhibiting p53-MDM2 signaling

Abnormal Krüppel-like factor 11 (KLF11) expression is frequently found in tumor tissues and is associated with cancer prognosis, but its biological functions and corresponding mechanisms remain elusive. Here, we demonstrated that KLF11 functions as an oncoprotein to promote tumor proliferation in breast cancer cells. Mechanistically, at the transcription level, KLF11 decreased TP53 mRNA expression. Notably, KLF11 also interacted with and stabilized MDM2 through inhibiting MDM2 ubiquitination and subsequent degradation. This increase in MDM2 in turn accelerated the ubiquitin-mediated proteolysis of p53, leading to the reduced expression of p53 and its target genes, including CDKN1A, BAX, and NOXA1. Accordingly, data from animals further confirmed that KLF11 significantly upregulated the growth of breast cancer cells and was inversely correlated with p53 expression. Taken together, our findings reveal a novel mechanism for breast cancer progression in which the function of the tumor suppressor p53 is dramatically weakened.

Phosphorylation of FOXK2 at Thr13 and Ser30 by PDK2 sustains glycolysis through a positive feedback manner in ovarian cancer

Ovarian cancer is one of the most common gynecological malignant tumors with insidious onset, strong invasiveness, and poor prognosis. Metabolic alteration, particularly aerobic glycolysis, which is tightly regulated by transcription factors, is associated with the malignant behavior of OC. We screened FOXK2 in this study as a key transcription factor that regulates glycolysis in OC. FOXK2 is overly expressed in OC, and poor prognosis is predicted by overexpression. FOXK2 promotes OC cell proliferation both in vitro and in vivo and cell migration in vitro. Further studies showed that PDK2 directly binds to the forkhead-associated (FHA) domain of FOXK2 to phosphorylate FOXK2 at Thr13 and Ser30, thereby enhancing the transcriptional activity of FOXK2. FOXK2 transcriptionally regulates the expression of PDK2, thus forming positive feedback to sustain glycolysis in OC cells.

Emerging roles of FOXK2 in cancers and metabolic disorders

FOXK2, a member of the Forkhead box K (FOXK) transcription factor family, is widely expressed in various tissues and organs throughout the body. FOXK2 plays crucial roles in cell proliferation, differentiation, autophagy, de novo nucleotide biosynthesis, DNA damage response, and aerobic glycolysis. Although FOXK2 is recognized as an oncogene in colorectal cancer and hepatocellular carcinoma, it acts as a tumor suppressor in breast cancer, cervical cancer, and non-small cell lung cancer (NSCLC). This review provides an overview of the recent progress in understanding the regulatory mechanisms of FOXK2 and its downstream targets, highlights the significant impact of FOXK2 dysregulation on cancer etiology, and discusses the potential of targeting FOXK2 for cancer treatment.

O-GlcNAcylation of FOXK1 orchestrates the E2F pathway and promotes oncogenesis

Gene transcription is a highly regulated process, and deregulation of transcription factors activity underlies numerous pathologies including cancer. Albeit near four decades of studies have established that the E2F pathway is a core transcriptional network that govern cell division in multi-cellular organisms1,2, the molecular mechanisms that underlie the functions of E2F transcription factors remain incompletely understood. FOXK1 and FOXK2 transcription factors have recently emerged as important regulators of cell metabolism, autophagy and cell differentiation3-6. While both FOXK1 and FOXK2 interact with the histone H2AK119ub deubiquitinase BAP1 and possess many overlapping functions in normal biology, their specific functions as well as deregulation of their transcriptional activity in cancer is less clear and sometimes contradictory7-13. Here, we show that elevated expression of FOXK1, but not FOXK2, in primary normal cells promotes transcription of E2F target genes associated with increased proliferation and delayed entry into cellular senescence. FOXK1 expressing cells are highly prone to cellular transformation revealing important oncogenic properties of FOXK1 in tumor initiation. High expression of FOXK1 in patient tumors is also highly correlated with E2F gene expression. Mechanistically, we demonstrate that FOXK1, but not FOXK2, is specifically modified by O-GlcNAcylation. FOXK1 O-GlcNAcylation is modulated during the cell cycle with the highest levels occurring during the time of E2F pathway activation at G1/S. Moreover, loss of FOXK1 O-GlcNAcylation impairs FOXK1 ability to promote cell proliferation, cellular transformation and tumor growth. Mechanistically, expression of FOXK1 O-GlcNAcylation-defective mutants results in reduced recruitment of BAP1 to gene regulatory regions. This event is associated with a concomitant increase in the levels of histone H2AK119ub and a decrease in the levels of H3K4me1, resulting in a transcriptional repressive chromatin environment. Our results define an essential role of O-GlcNAcylation in modulating the functions of FOXK1 in controlling the cell cycle of normal and cancer cells through orchestration of the E2F pathway.

FOXK2 amplification and overexpression promotes breast cancer development and chemoresistance

Activation of oncogenes through DNA amplification/overexpression plays an important role in cancer initiation and progression. Chromosome 17 has many cancer-associated genetic anomalies. This cytogenetic anomaly is strongly associated with poor prognosis of breast cancer. FOXK2 gene is located on 17q25 and encodes a transcriptional factor with a forkhead DNA binding domain. By integrative analysis of public genomic datasets of breast cancers, we found that FOXK2 is frequently amplified and overexpressed in breast cancers. FOXK2 overexpression in breast cancer patients is associated with poor overall survival. FOXK2 knockdown significantly inhibits cell proliferation, invasion and metastasis, and anchorage-independent growth, as well as causes G0/G1 cell cycle arrest in breast cancer cells. Moreover, inhibition of FOXK2 expression sensitizes breast cancer cells to frontline anti-tumor chemotherapies. More importantly, co-overexpression of FOXK2 and PI3KCA with oncogenic mutations (E545K or H1047R) induces cellular transformation in non-tumorigenic MCF10A cells, suggesting that FOXK2 is an oncogene in breast cancer and is involved in PI3KCA-driven tumorigenesis. Our study identified CCNE2, PDK1, and Estrogen receptor alpha (ESR1) as direct transcriptional targets of FOXK2 in MCF-7 cells. Blocking CCNE2- and PDK1-mediated signaling by using small molecule inhibitors has synergistic anti-tumor effects in breast cancer cells. Furthermore, FOXK2 inhibition by gene knockdown or inhibitors for its transcriptional targets (CCNE2 and PDK1) in combination with PI3KCA inhibitor, Alpelisib, showed synergistic anti-tumor effects on breast cancer cells with PI3KCA oncogenic mutations. In summary, we provide compelling evidence that FOXK2 plays an oncogenic role in breast tumorigenesis and targeting FOXK2-mediated pathways may be a potential therapeutic strategy in breast cancer.

Regulation and roles of FOXK2 in cancer

Forkhead box K2 (FOXK2) is a member of the forkhead box transcription factor family that contains an evolutionarily conserved winged-helix DNA-binding domain. Recently, an increasing number of studies have demonstrated that FOXK2 plays an important role in the transcriptional regulation of cancer. Here, we provide an overview of the mechanisms underlying the regulation of FOXK2 expression and function and discuss the roles of FOXK2 in tumor pathogenesis. Additionally, we evaluated the prognostic value of FOXK2 expression in patients with various cancers. This review presents an overview of the different roles of FOXK2 in tumorigenesis and will help inform the design of experimental studies involving FOXK2. Ultimately, the information presented here will help enhance the therapeutic potential of FOXK2 as a cancer target.

Genomic Aberrations Generate Fusion Gene FOXK2::TP63 and Activate NFKB1 in Cutaneous T-Cell Lymphoma

Cutaneous T-cell lymphoma (CTCL) is a severe lymphoid malignancy with a worse prognosis lacking curative treatment regimens. Several gene mutations and deregulated pathways, including NFkB signaling, have been implicated in its pathogenesis. Accordingly, CTCL cell line HUT-78 reportedly contains mutated NFKB2, which is constitutively activated via partial gene deletion, also demonstrating that genomic rearrangements cause driving mutations in this malignancy. Here, along with HUT-78, we analyzed CTCL cell line HH to identify additional aberrations underlying gene deregulation. Karyotyping and genomic profiling of HH showed several rearrangements worthy of detailed investigation. Corresponding to the established karyotype, RNA-seq data and PCR analysis confirmed the presence of t(3;17)(q28;q25), generating a novel fusion gene, FOXK2::TP63. Furthermore, chromosomal rearrangement t(1;4)(p32;q25) was connected to amplification at 4q24–26, affecting aberrant NFKB1 overexpression thereat. Transcription factor binding-site analysis and knockdown experiments demonstrated that IRF4 contributed to NFKB1 expression. Within the same amplicon, we identified amplification and overexpression of NFkB signaling activator CAMK2D (4q26) and p53-inhibitor UBE2D3 (4q24). Genomic profiling data for HUT-78 detailed a deletion at 10q25 underlying reported NFKB2 activation. Moreover, amplifications of ID1 (20q11) and IKZF2 (2q34) in this cell line drove overexpression of these NK cell differentiation factors and possibly thus formed corresponding lineage characteristics. Target gene analysis for NFKB1 via siRNA-mediated knockdown in HH revealed activation of TP63, MIR155, and NOTCH pathway component RBPJ. Finally, treatment of HH with NFkB inhibitor demonstrated a role for NFkB in supporting proliferation, while usage of inhibitor DAPT showed significant survival effects via the NOTCH pathway. Collectively, our data suggest that NFkB and/or NOTCH inhibitors may represent reasonable treatment options for subsets of CTCL patients.

The Function of FoxK Transcription Factors in Diseases

Forkhead box (FOX) transcription factors play a crucial role in the regulation of many diseases, being an evolutionarily conserved superfamily of transcription factors. In recent years, FoxK1/2, members of its family, has been the subject of research. Even though FoxK1 and FoxK2 have some functional overlap, increasing evidence indicates that the regulatory functions of FoxK1 and FoxK2 are not the same in various physiological and disease states. It is important to understand the biological function and mechanism of FoxK1/2 for better understanding pathogenesis of diseases, predicting prognosis, and finding new therapeutic targets. There is, however, a lack of comprehensive and systematic analysis of the similarities and differences of FoxK1/2 roles in disease, prompting us to perform a literature review.

Identification, characterization and functional analysis of gonadal long noncoding RNAs in a protogynous hermaphroditic teleost fish, the ricefield eel (Monopterus albus)

Background

An increasing number of long noncoding RNAs (lncRNAs) have been found to play important roles in sex differentiation and gonad development by regulating gene expression at the epigenetic, transcriptional and posttranscriptional levels. The ricefield eel, Monopterus albus, is a protogynous hermaphroditic fish that undergoes a sequential sex change from female to male. However, the roles of lncRNA in the sex change is unclear.

Results

Herein, we performed RNA sequencing to analyse lncRNA expression patterns in five different stages of M. albus development to investigate the roles of lncRNAs in the sex change process. A total of 12,746 lncRNAs (1503 known lncRNAs and 11,243 new lncRNAs) and 2901 differentially expressed lncRNAs (DE-lncRNAs) were identified in the gonads. The target genes of the DE-lncRNAs included foxo1, foxm1, smad3, foxr1, camk4, ar and tgfb3, which were mainly enriched in signalling pathways related to gonadal development, such as the insulin signalling pathway, MAPK signalling pathway, and calcium signalling pathway. We selected 5 highly expressed DE-lncRNAs (LOC109952131, LOC109953466, LOC109954337, LOC109954360 and LOC109958454) for full length amplification and expression pattern verification. They were all expressed at higher levels in ovaries and intersex gonads than in testes, and exhibited specific time-dependent expression in ovarian tissue incubated with follicle-stimulating hormone (FSH) and human chorionic gonadotropin (hCG). The results of quantitative real-time PCR (qRT-PCR) analysis and a dual-luciferase assay showed that znf207, as the gene targeted by LOC109958454, was expressed in multiple tissues and gonadal developmental stages of M. albus, and its expression was also inhibited by the hormones FSH and hCG.

Conclusions

These results provide new insights into the role of lncRNAs in gonad development, especially regarding natural sex changes in fish, which will be useful for enhancing our understanding of sequential hermaphroditism and sex changes in the ricefield eel (M. albus) and other teleosts.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08679-2.

Biogenesis, functions, and clinical implications of circular RNAs in non-small cell lung cancer

Lung cancer (LC) is the leading cause of cancer-related deaths worldwide, with high morbidity and mortality. Non-small cell lung cancer (NSCLC) is a major pathological type of LC and accounts for more than 80% of all cases. Circular RNAs (circRNAs) are a large class of non-coding RNAs (ncRNAs) with covalently closed-loop structures, a high abundance, and tissue-specific expression patterns. They participate in various pathophysiological processes by regulating complex gene networks involved in proliferation, apoptosis, migration, and epithelial-to-mesenchymal transition (EMT), as well as metastasis. A growing number of studies have revealed that the dysregulation of circRNAs contributes to many aspects of cancer progression, such as its occurrence, metastasis, and recurrence, suggesting their great potential as efficient and specific biomarkers in the diagnosis, prognosis, and therapeutic targeting of NSCLC. In this review, we systematically elucidate the characteristics, biogenesis, and functions of circRNAs and focus on their molecular mechanisms in NSCLC progression. Moreover, we highlight their clinical implications in NSCLC treatment.

Long Non-Coding RNA in Gastric Cancer: Mechanisms and Clinical Implications for Drug Resistance

Gastric cancer (GC) is the third leading cause of cancer-related deaths worldwide, with high recurrence and mortality rate. Chemotherapy, including 5-fluorouracil (5-FU), adriamycin (ADR), vincristine (VCR), paclitaxel (PTX), and platinum drugs, remains one of the fundamental methods of GC treatment and has efficiently improved patients’ prognosis. However, most patients eventually develop resistance to chemotherapeutic agents, leading to the failure of clinical treatment and patients’ death. Recent studies suggest that long non-coding RNAs (lncRNAs) are involved in the drug resistance of GC by modulating the expression of drug resistance-related genes via sponging microRNAs (miRNAs). Moreover, lncRNAs also play crucial roles in GC drug resistance via a variety of mechanisms, such as the regulation of the oncogenic signaling pathways, inhibition of apoptosis, induction of autophagy, modulation of cancer stem cells (CSCs), and promotion of the epithelial-to-mesenchymal transition (EMT) process. Some of lncRNAs exhibit great potential as diagnostic and prognostic biomarkers, as well as therapeutic targets for GC patients. Therefore, understanding the role of lncRNAs and their mechanisms in GC drug resistance may provide us with novel insights for developing strategies for individual diagnosis and therapy. In this review, we summarize the recent findings on the mechanisms underlying GC drug resistance regulated by lncRNAs. We also discuss the potential clinical applications of lncRNAs as biomarkers and therapeutic targets in GC.

The regulation of PBXs and their emerging role in cancer

Pre‐B‐cell leukaemia transcription factor (PBX) proteins are a subfamily of evolutionarily conserved, atypical homeodomain transcription factors that belong to the superfamily of three amino acid loop extension (TALE) homeodomain proteins. Members of the PBX family play crucial roles in regulating multiple pathophysiological processes, such as the development of organs, congenital cardiac defects and carcinogenesis. The dysregulation of PBXs has been shown to be closely associated with many diseases, particularly cancer. However, the detailed mechanisms of PBX dysregulation in cancer progression are still inconclusive. In this review, we summarize the recent advances in the structures, functions and regulatory mechanisms of PBXs, and discuss their underlying mechanisms in cancer progression. We also highlight the great potential of PBXs as biomarkers for the early diagnosis and prognostic evaluation of cancer as well as their therapeutic applications. The information reviewed here may expand researchers’ understanding of PBXs and could strengthen the clinical implication of PBXs in cancer treatment.

FOXK2 promotes the proliferation of papillary thyroid cancer cell by down-regulating autophagy

Papillary thyroid cancer (PTC) is the most common endocrine system tumor. FOXK2 is involved in the development of different types of cancers, however, its function has not been investigated in papillary thyroid cancer. In the present study, we demonstrated that FOXK2 expression was up-regulated in papillary thyroid carcinoma tissues compared with matched normal tissues. Importantly, we found that FOXK2 expression was significantly associated with the tumor size, T stage, and TNM stage. Furthermore, stable knockdown of FOXK2 markedly inhibited PTC cell proliferation, significantly increased the ratio of LC3-II/LC3-I, and reduced p62 expression, whereas overexpression of FOXK2 showed opposite effects. In FOXK2 knockdown cell lines, mCherry-GFP-LC3 immunofluorescence demonstrated increased punctate aggregates of mCherry-GFP-LC3, and transmission electron microscopy revealed increased numbers of autophagosomes. Autophagy-related protein ULK1, VPS34, and FOXO3 were markedly up-regulated by FOXK2 knockdown and down-regulated by FOXK2 overexpression. Finally, autophagy inhibitor 3-MA attenuated autophagy activation and rescued the inhibition of cell proliferation caused by FOXK2 knockdown, suggesting that FOXK2 silencing inhibits cell proliferation through up-regulating autophagy. These findings revealed an important role of FOXK2 in PTC progression and suggested that FOXK2 might be a potential new target for the diagnosis and treatment of PTC.

Mechanisms of Action And Clinical Implications of MicroRNAs in the Drug Resistance of Gastric Cancer

Gastric cancer (GC) is one of the most common malignant tumors of digestive systems worldwide, with high recurrence and mortality. Chemotherapy is still the standard treatment option for GC and can effectively improve the survival and life quality of GC patients. However, with the emergence of drug resistance, the clinical application of chemotherapeutic agents has been seriously restricted in GC patients. Although the mechanisms of drug resistance have been broadly investigated, they are still largely unknown. MicroRNAs (miRNAs) are a large group of small non-coding RNAs (ncRNAs) widely involved in the occurrence and progression of many cancer types, including GC. An increasing amount of evidence suggests that miRNAs may play crucial roles in the development of drug resistance by regulating some drug resistance-related proteins as well as gene expression. Some also exhibit great potential as novel biomarkers for predicting drug response to chemotherapy and therapeutic targets for GC patients. In this review, we systematically summarize recent advances in miRNAs and focus on their molecular mechanisms in the development of drug resistance in GC progression. We also highlight the potential of drug resistance-related miRNAs as biomarkers and therapeutic targets for GC patients.

ELF5 inhibits the proliferation and invasion of breast cancer cells by regulating CD24

E74-like factor five (ELF5) is a basic transcription factor that plays a key role in breast tissue and gland development. However, the molecular mechanism of ELF5 in breast cancer cells has not been elucidated. In this study, we examined the effect of ELF5 on the human breast cancer cell lines MCF-7 and T47D and confirmed that ELF5 can inhibit cell proliferation, migration and invasion. In further research, the relationship between ELF5 and CD24 was characterized in breast cancer cells. We found that CD24 was a target gene of ELF5 through chromatin immunoprecipitation (ChIP) -Sequence assays, and proved that ELF5 could bind to the ETS cis-element on the proximal promoter of the CD24 gene and regulate the expression of CD24. Moreover, overexpression of ELF5 in MCF-7 cells significantly increased both the mRNA and protein levels of CD24, while knockdown of CD24 expression restored cell proliferation, migration and invasion through adaptive ELF5 expression in MCF-7 cells. Therefore, these data suggest that ELF5 inhibits migration and invasion of breast cancer cells by regulating CD24 expression, which make provides a molecular mechanism for ELF5 to inhibit breast cancer from a new perspective and provides further theoretical support for the treatment and prevention of breast cancer.

FBXL10 promotes ERRα protein stability and proliferation of breast cancer cells by enhancing the mono-ubiquitylation of ERRα

The underlying mechanism of orphan nuclear receptor estrogen-related receptor α (ERRα) in breast cancer was investigated by identifying its interaction partners using mass spectrometry. F-box and leucine-rich repeat protein 10 (FBXL10), which modulates various physiological processes, may interact with ERRα in breast cancer. Here, we investigated the interaction between FBXL10 and ERRα, and their protein expression and correlation in breast cancer. Mechanical studies revealed that FBXL10 stabilized ERRα protein levels by reducing its poly-ubiquitylation and promoting its mono-ubiquitylation. The reporter gene assay and examination of ERRα target genes validated the increased transcriptional activity of ERRα due to its increased protein levels by FBXL10. FBXL10 also increased ERRα enrichment at the promoter region of its target genes. Functionally, FBXL10 facilitated the ERRα/peroxisome proliferator-activated receptor gamma coactivator 1 β (PGC1β)-mediated proliferation and tumorigenesis of breast cancer cells in vitro and in vivo. Our results uncovered a molecular mechanism linking the mono-ubiquitylation and protein stability of ERRα to functional interaction with FBXL10. Moreover, a novel regulatory axis of FBXL10 and ERRα regulating the proliferation and tumorigenesis of breast cancer cells was established.

Comparative Transcriptome Profiling of mRNA and lncRNA of Ovaries in High and Low Egg Production Performance in Domestic Pigeons (Columba livia)

Egg production performance is one of the most important economic traits in pigeon industry. However, little is known regarding how egg production performance is regulated by long non-coding RNAs (lncRNAs) in pigeons. To evaluate the lncRNAs and mRNAs in ovaries associated with egg production performance in domestic pigeons, high-throughput RNA sequencing of ovaries between high and low egg production performance groups were performed and analyzed in this study. A total of 34,346 mRNAs and 24,601 lncRNAs were identified, including 14,525 known lncRNAs and 10,076 novel lncRNAs, of which 811 mRNAs and 148 lncRNAs (P < 0.05) were significantly differentially expressed (DE) between the groups of high and low egg production performance. GO and KEGG annotation analysis indicated that the target genes of DE lncRNAs and DE mRNAs were related to cell differentiation, ATP binding and methylation. Moreover, we found that FOXK2, a target gene of lncRNA MSTRG.7894.4, was involved in regulating estrogen receptors. Our study provided a catalog of lncRNAs and mRNAs associated with egg production performance, and they deserve further study to deepen the understanding of biological processes in the ovaries of pigeons.

Acetylation of ELF5 suppresses breast cancer progression by promoting its degradation and targeting CCND1

E74-like ETS transcription factor 5 (ELF5) is involved in a wide spectrum of biological processes, e.g., mammogenesis and tumor progression. We have identified a list of p300-interacting proteins in human breast cancer cells. Among these, ELF5 was found to interact with p300 via acetylation, and the potential acetylation sites were identified as K130, K134, K143, K197, K228, and K245. Furthermore, an ELF5-specific deacetylase, SIRT6, was also identified. Acetylation of ELF5 promoted its ubiquitination and degradation, but was also essential for its antiproliferative effect against breast cancer, as overexpression of wild-type ELF5 and sustained acetylation-mimicking ELF5 mutant could inhibit the expression of its target gene CCND1. Taken together, the results demonstrated a novel regulation of ELF5 as well as shedding light on its important role in modulation of breast cancer progression.

TIMELESS inhibits breast cancer cell invasion and metastasis by down-regulating the expression of MMP9

Breast cancer is the first killer leading to female death, and tumor metastasis is one of the important factors leading to the death of patients, but the specific mechanism of breast cancer metastasis is not very clear at present. Our study showed that overexpression of TIMELESS could significantly inhibit the invasion and metastasis of breast cancer cells ZR-75-30 and the assembly of F-actin protein. On the contrary, knockdown of TIMELESS promoted the invasion and metastasis of breast cancer cells. Further study revealed that TIMELESS overexpression decreased the mRNA and protein levels of MMP9. Furthermore, TIMELESS could interact with p65, leading to repress the association of p65 and its acetyltransferase CBP and down-regulating the acetylation level of p65, which inhibited the activation of NF-κB signal pathway. In conclusion, our research showed that TIMELESS may repress the invasion and metastasis of breast cancer cells via inhibiting the acetylation of p65, inhibiting the activation of NF-κB, thus down-regulating the expression of MMP9, and then inhibiting the invasion and metastasis of breast cancer cells.

Identification of ZG16B as a prognostic biomarker in breast cancer

Zymogen granule protein 16B (ZG16B) has been identified in various cancers, while so far the association between ZG16B and breast cancer hasn’t been explored. Our aim is to confirm whether it can serve as a prognostic biomarker in breast cancer. In this study, Oncomine, Cancer Cell Line Encyclopedia (CCLE), Ualcan, and STRING database analyses were conducted to detect the expression level of ZG16B in breast cancer with different types. Kaplan–Meier plotter was used to analyze the prognosis of patients with high or low expression of ZG16B. We found that ZG16B was significantly upregulated in breast cancer. Moreover, ZG16B was closely associated with foregone biomarkers and crucial factors in breast cancer. In the survival analysis, high expression of ZG16B represents a favorable prognosis in patients. Our work demonstrates the latent capacity of ZG16B to be a biomarker for prognosis of breast cancer.

FOXK2 downregulation suppresses EMT in hepatocellular carcinoma

Forkhead box K2 (FOXK2) was first identified as an NFAT-like interleukin-binding factor. FOXK2 has been reported to act as either oncogene or tumor suppressor. However, functional and regulating mechanisms of FOXK2 in epithelial–mesenchymal transition (EMT) in hepatocellular carcinoma (HCC) remain unclear. An FOXK2-specific siRNA was employed to decrease the endogenous expression of FOXK2. MTT assay, colony formation and transwell assay were used to evaluate proliferation, migration and invasion of Hep3B and HCCLM3 cells, respectively. The protein expression associated with EMT and Akt signaling pathways was evaluated using western blot. FOXK2 downregulation could inhibit cell proliferation and colony formation and suppress migration and invasion in Hep3B and HCCLM3 cells. The expression of E-cadherin was significantly upregulated, and the expression of snail and p-Akt was significantly downregulated in siFOXK2-transfected cells compared with control cells. SF1670 induced the expression of p-Akt and snail and suppressed the expression of E-cadherin in Hep3B and HCCLM3 cells. SF1670 promoted the invasion and colony formation of Hep3B and HCCLM3 cells. SF1670 partly inhibited the effect of FOXK2 suppression on Hep3B and HCCLM3 cells. In conclusion, this study revealed that FOXK2 downregulation suppressed the EMT in HCC partly through inhibition of the Akt signaling pathway.

PBX1 is a valuable prognostic biomarker for patients with breast cancer

Pre-B-cell leukemia transcription factor (PBX) proteins have important roles in the development of numerous organs. To date, four members of the PBX family have been identified to be involved in human cancer but little is known about their expression patterns and precise functions in breast cancer (BC) progression. The aim of the present study was to determine whether they have the potential to be prognostic biomarkers in patients with BC. The expression patterns of PBXs were evaluated using Oncomine, Cancer Cell Line Encyclopedia and Gene expression-based Outcome for Breast cancer Online algorithm analyses. The prognostic value of PBX1 was determined by Kaplan-Meier plotter analysis. It was observed that, among all PBX family members, only PBX1 was significantly upregulated in BC vs. normal tissues. Meta-analysis in the Oncomine database revealed that PBX1 was significantly upregulated in invasive breast carcinoma stroma, ductal breast carcinoma, invasive lobular breast carcinoma, invasive mixed breast carcinoma and male breast carcinoma compared with normal tissues. In addition, PBX1 was significantly correlated with forkhead box protein A1. Subtype analysis indicated that PBX1 overexpression was associated with luminal-like and hormone receptor-sensitive subtypes. In the survival analysis, a high expression level of PBX1 was associated with poor prognosis of patients with estrogen receptor (ER)-positive, luminal A and luminal B subtypes of BC. The results of the present study indicate that PBX1 may serve as a specific biomarker and essential prognostic factor for ER-positive, luminal A and luminal B subtypes of BC.

Forkhead box K2 promotes human colorectal cancer metastasis by upregulating ZEB1 and EGFR

Background: Metastasis is the major reason for high recurrence rates and poor survival among patients with colorectal cancer (CRC). However, the underlying molecular mechanism of CRC metastasis is unclear. This study aimed to investigate the role of forkhead box K2 (FOXK2), one of the most markedly increased FOX genes in CRC, and the mechanism by which it is deregulated in CRC metastasis. Methods: FOXK2 levels were analyzed in two independent human CRC cohorts (cohort I, n = 363; cohort II, n = 390). In vitro Transwell assays and in vivo lung and liver metastasis models were used to examine CRC cell migration, invasion and metastasis. Chromatin immunoprecipitation and luciferase reporter assays were used to measure the binding of transcription factors to the promoters of FOXK2, zinc finger E-box binding homeobox 1 (ZEB1) and epidermal growth factor receptor (EGFR). Cetuximab was utilized to treat FOXK2-mediated metastatic CRC. Results: FOXK2 was significantly upregulated in human CRC tissues, was correlated with more aggressive features and indicated a poor prognosis. FOXK2 overexpression promoted CRC migration, invasion and metastasis, while FOXK2 downregulation had the opposite effects. ZEB1 and EGFR were determined to be direct transcriptional targets of FOXK2 and were essential for FOXK2-mediated CRC metastasis. Moreover, activation of EGFR signaling by EGF enhanced FOXK2 expression via the extracellular regulated protein kinase (ERK) and nuclear factor (NF)-κB pathways. The EGFR monoclonal antibody cetuximab significantly inhibited FOXK2-promoted CRC metastasis. In clinical CRC tissues, FOXK2 expression was positively correlated with the expression of p65, ZEB1 and EGFR. CRC patients who coexpressed p65/FOXK2, FOXK2/ZEB1 and FOXK2/EGFR had poorer prognosis. Conclusions: FOXK2 serves as a prognostic biomarker in CRC. Cetuximab can block the EGF-NF-κB-FOXK2-EGFR feedback loop and suppress CRC metastasis.

FOXK transcription factors: Regulation and critical role in cancer

Growing evidence suggests that alterations of gene expression including expression and activities of transcription factors are closely associated with carcinogenesis. Forkhead Box Class K (FOXK) proteins, FOXK1 and FOXK2, are a family of evolutionarily conserved transcriptional factors, which have recently been recognized as key transcriptional regulators involved in many types of cancer. Members of the FOXK family mediate a wide spectrum of biological processes, including cell proliferation, differentiation, apoptosis, autophagy, cell cycle progression, DNA damage and tumorigenesis. Therefore, the deregulation of FOXKs can affect the cell fate and they promote tumorigenesis as well as cancer progression. The mechanisms of FOXKs regulation including post-translational modifications (PTMs), microRNAs (miRNAs) and protein-protein interactions are well demonstrated. However, the detailed mechanisms of FOXKs activation and deregulation in cancer progression are still inconclusive. In this review, we summarize the regulatory mechanisms of FOXKs expression and activity, and their role in the development and progression of cancer. We have discussed whether FOXKs act as tumor suppressors/oncoproteins in tumor cells and their therapeutic applications in malignant diseases are also discussed. This review may assist in designing experimental studies involving FOXKs and it would strength the therapeutic potential of FOXKs as targets for cancers.

FOXK2 Transcription Factor and Its Emerging Roles in Cancer

Forkhead box (FOX) transcription factors compose a large family of regulators of key biological processes within a cell. FOXK2 is a member of FOX family, whose biological functions remain relatively unexplored, despite its description in the early nineties. More recently, growing evidence has been pointing towards a role of FOXK2 in cancer, which is likely to be context-dependent and tumour-specific. Here, we provide an overview of important aspects concerning the mechanisms of regulation of FOXK2 expression and function, as well as its complex interactions at the chromatin level, which orchestrate how it differentially regulates the expression of gene targets in pathophysiology. Particularly, we explore the emerging functions of FOXK2 as a regulator of a broad range of cancer features, such as cell proliferation and survival, DNA damage, metabolism, migration, invasion and metastasis. Finally, we discuss the prognostic value of assessing FOXK2 expression in cancer patients and how it can be potentially targeted for future anticancer interventions.

Circlular RNA BARD1 (Hsa_circ_0001098) overexpression in breast cancer cells with TCDD treatment could promote cell apoptosis via miR-3942/BARD1 axis

Breast cancer threatened the health of millions of people around the world. Here we explored the influence of TCDD on the expression of circRNA_BARD1 (circ_0001098) in breast cancer and studied the potential molecular mechanism of circRNA_BARD1. The data from GSE76608 was applied to analyze differentially expressed circRNAs and mRNAs. The expressions of circRNA_BARD1, BARD1, miR-3942-3p, miR-4760-3p and apoptosis-related protein p53 were detected by qRT-PCR or western blot. Circinteractome, TargetScan, CIRCNET and dual luciferase reporter assay were employed to uncover the target relationship between circRNA_BARD1/BARD1 and miR-3942-3p/miR-4760-3p. Flow cytometric analysis was used to reveal cell cycle and cell apoptosis. Immunofluorescence was applied to determinate γ-H2AX level. Xenograft assay and in vivo 3-D imaging was implemented to further verify the conclusions in vitro. CircRNA_BARD1 (circ_0001098) was up-regulated in breast cancer with the treatment of TCDD and the up-regulation of circRNA_BARD1 could restrain cell proliferation, block cell cycle and promote cell apoptosis. Moreover, the target relationship between circRNA_BARD1/BARD1 and miR-3942-3p was confirmed. In addition, miR-3942-3p overexpression promoted the disease progression and BARD1 up-regulation inhibited the disease progression in the breast cancer. Similarly, circRNA_BARD1 overexpression induced by TCDD suppressed the growth and metastasis of tumor in vivo. In conclusion, TCDD induced circ_0001098 overexpression and then suppressed breast cancer tumorigenesis via miR-3942-3p/BARD1 axis. The finding of TCDD-circRNA-miRNA-mRNA axis might bring a new perspective for cure strategy of breast cancer.

Pyrroline-5-carboxylate reductase 1 promotes cell proliferation via inhibiting apoptosis in human malignant melanoma

Introduction

Human malignant melanoma (MM) is a highly malignant tumor of cutaneous melanocytes with a fast progression. We investigated the cellular effects of pyrroline-5- carboxylate reductase 1 (PYCR1) in the MM cell lines, A375 and M14.

Methods

Cell Counting Kit-8 assay, transwell assay, and flow cytometry analysis were performed to evaluate the proliferation, migration and apoptosis of MM cell lines, respectively. To gain more insight into the role of PYCR1 in tumor growth, we analyzed the AKT phosphorylation level in PYCR1-specific siRNA (siPYCR1) and negative control (NC) cells.

Results

Biochemical analysis revealed a clear increase in PYCR1 expression in human MM samples, and its high expression predicted a poor prognosis. Silencing of PYCR1 suppressed the proliferation and migration of A375 and M14 cells. The percentage of apoptosis in cells transfected with siPYCR1 significantly increased in comparison to that of cells transfected with negative control siRNA (NC). The enhanced apoptosis in PYCR1 knockdown cells was consistent with an increased level of markers of apoptosis. siPYCR1 inhibited AKT phosphorylation, as well as the expression of its downstream protein, P70, suggesting that PYCR1 promoted cell growth of the MM cell lines A375 and M14 through stimulation of the AKT pathway. Moreover, forkhead box K2 and regulatory associated protein of MTOR complex 1 shared a similar expression pattern to that of PYCR1 and were significantly downregulated in PYCR1 knockdown cells.

Conclusion

PYCR1 promoted tumor progression through the AKT pathway in human MM in vitro. Our results expand the knowledge of PYCR1 functions in solid tumors and provide a potential target for the clinical treatment of human MM.

Checkpoint suppressor 1 suppresses transcriptional activity of ERα and breast cancer cell proliferation via deacetylase SIRT1

Breast cancer is a highly heterogeneous carcinoma in women worldwide, but the underlying mechanisms that account for breast cancer initiation and development have not been fully established. Mounting evidence indicates that Checkpoint suppressor 1 (CHES1) is tightly associated with tumorigenesis and prognosis in many types of cancer. However, the definitive function of CHES1 in breast cancer remains to be explored. Here we showed that CHES1 had a physical interaction with estrogen receptor-α (ERα) and repressed the transactivation of ERα in breast cancer cells. Mechanistically, the interaction between CHES1 and ERα enhanced the recruitment of nicotinamide adenine dinucleotide (NAD+) deacetylase Sirtuin 1 (SIRT1), and it further induced SIRT1-mediated ERα deacetylation and repression on the promoter-binding enrichment of ERα. In addition, we also found that the expression of CHES1 was repressed by estrogen-ERα signaling and the expression level of CHES1 was significantly downregulated in ERα-positive breast cancer. The detailed mechanism was that ERα may directly bind to CHES1 potential promoter via recognizing the conserved estrogen response element (ERE) motif in response to estrogen stimulation. Functionally, CHES1 inhibited ERα-mediated proliferation and tumorigenesis of breast cancer cells in vivo and in vitro. Totally, these results identified a negative cross-regulatory loop between ERα and CHES1 that was required for growth of breast cancer cells, it might uncover novel insight into molecular mechanism of CHES1 involved in breast cancer and provide new avenues for molecular-targeted therapy in hormone-regulated breast cancer.

α-catenin SUMOylation increases IκBα stability and inhibits breast cancer progression

α-catenin has been demonstrated to suppress several different types of cancers. Here we demonstrate that α-catenin is modified by SUMO protein, which covalently binds α-catenin at the carboxy terminus at lysine 870. Substitution of lysine 870 with arginine completely abolishes α-catenin SUMOylation. This modification can be removed by SENP1. However, α-catenin SUMOylation does not affect its stability and subcellular localization. In addition, we observed that the SUMOylation-deficient α-catenin mutant has a reduced interaction with IκBα which prevents subsequent ubiquitination of IκBα, and therefore a reduced suppression of expression of the NF-κB target genes TNF-α, IL-8, VEGF, and uPA. In addition, the α-catenin SUMOylation mutant shows impaired suppression of tumor growth. These results demonstrate that SUMOylation at lysine 870 of α-catenin plays a key role in the suppression of the NF-κB pathway, which inhibits breast cancer tumor growth and migration.

SUMOylation modulates FOXK2-mediated paclitaxel sensitivity in breast cancer cells

The forkhead transcription factor FOXK2 plays a critical role in suppressing tumorigenesis and mediating cytotoxic drug action in breast cancer. However, the mechanism by which the biological function of FOXK2 is regulated remains poorly understood. Here, we investigated the role of SUMOylation in modulating FOXK2-mediated drug sensitivity. We identified SUMOylation consensus motifs within the FOXK2 sequence and constructed two SUMOylation-defective double mutants by converting lysine 527 and 633 to arginines and glutamic acid 529 and 635 to alanines, respectively. We found that both the FOXK2 SUMOylation-deficient (K527/633 R) and (E529/635 A) mutants were ineffective in mediating the cytotoxic function of paclitaxel when compared to the wild-type (WT) FOXK2. When overexpressed, unlike the wild-type (WT) FOXK2, the K527/633 R mutant had little effect on the sensitivity of MCF-7 and MDA-MB-231 cells to paclitaxel, as examined by cell viability and clonogenic assays. Our results also showed that MCF-7 cells overexpressing the K527/633 R mutant form of FOXK2 or the empty expression vector have lower protein and mRNA levels of its tumour suppressive transcriptional target FOXO3 compared to the wild-type FOXK2. Consistently, ChIP assays revealed that unlike wild-type FOXK2, the SUMOylation-defective (K527/633 R) mutant is unable to bind to the FOXO3 promoter, despite expressing comparable levels of protein and having the same subcellular localization as the wild-type FOXK2 in MCF-7 cells. Interestingly, expression of neither the wild-type nor the K527/633 R mutant FOXK2 had any effect on the proliferation and paclitaxel sensitivity of the MCF-7 TaxR paclitaxel-resistant cells. In agreement, both the wild-type and the (K527/633 R) mutant FOXK2 failed to bind to the endogenous FOXO3 promoter in these cells. Collectively, our results suggest that SUMOylation positively regulates FOXK2 transcriptional activity and has a role in mediating the cytotoxic response to paclitaxel through the tumour suppressor FOXO3.

Forkhead box K2 inhibits the proliferation, migration, and invasion of human glioma cells and predicts a favorable prognosis

Purpose

Forkhead box K2 (FOXK2) is a member of the forkhead box family of transcription factors. Recently, researchers discovered that overexpression of FOXK2 inhibits the proliferation and metastasis of breast cancer, non-small cell lung cancer, and colorectal cancer, and is related to the clinical prognosis. However, in hepatocellular carcinoma, FOXK2 results in the opposite phenotypes. Currently, the contribution of FOXK2 to glioma pathogenesis is not clear.

Patients and methods

We evaluated the expression of FOXK2 in 151 glioma patients using immunohistochemistry assays. The associations among the expression of FOXK2, clinicopathological parameters, and the prognosis of glioma patients were statistically analyzed. We downregulated and upregulated the level of FOXK2 in glioma cells by transfections with small interfering RNA and plasmids. Then, we investigated the effects on tumor cell behavior in vitro by Cell Counting Kit-8 assays, colony-formation assay, transwell assay, and the epithelial-to-mesenchymal transition (EMT) biomarker levels.

Results

The clinical data showed that expression of FOXK2 gradually decreased with increasing World Health Organization (WHO) grades and a low level of FOXK2 indicates a poor prognosis. FOXK2 expression is negatively correlated with Ki67 expression and the WHO degree but is not correlated with other clinicopathological parameters, including sex, age, Karnofsky Performance Status, tumor diameter, O-6-methylguanine-DNA methyltransferase, and glutathione S-transferase pi. FOXK2 knockdown enhances glioma cell proliferation, migration, invasion, and EMT process, and, in contrast, FOXK2 overexpression inhibits glioma cell proliferation, migration, invasion, and the EMT process.

Conclusion

Expression of FOXK2 gradually decreases with increasing WHO grades. FOXK2 inhibits tumor proliferation, migration, and invasion. FOXK2 is a critical mediator of the EMT process.

Sumoylation of TCF21 downregulates the transcriptional activity of estrogen receptor-alpha

Aberrant estrogen receptor-α (ERα) signaling is recognized as a major contributor to the development of breast cancer. However, the molecular mechanism underlying the regulation of ERα in breast cancer is still inconclusive. In this study, we showed that the transcription factor 21 (TCF21) interacted with ERα, and repressed its transcriptional activity in a HDACs-dependent manner. We also showed that TCF21 could be sumoylated by the small ubiquitin-like modifier SUMO1, and this modification could be reversed by SENP1. Sumoylation of TCF21 occurred at lysine residue 24 (K24). Substitution of K24 with arginine resulted in complete abolishment of sumoylation. Sumoylation stabilized TCF21, but did not affect its subcellular localization. Sumoylation of TCF21 also enhanced its interaction with HDAC1/2 without affecting its interaction with ERα. Moreover, sumoylation of TCF21 promoted its repression of ERα transcriptional activity, and increased the recruitment of HDAC1/2 to the pS2 promoter. Consistent with these observations, sumoylation of TCF21 could inhibit the growth of ERα-positive breast cancer cells and decreased the proportion of S-phase cells in the cell cycle. These findings suggested that TCF21 might act as a negative regulator of ERα, and its sumoylation inhibited the transcriptional activity of ERα through promoting the recruitment of HDAC1/2.

FOXK2 suppresses the malignant phenotype and induces apoptosis through inhibition of EGFR in clear-cell renal cell carcinoma

Forkhead box K2 (FOXK2) belongs to the forkhead box transcription factor family. Recent studies have revealed that FOXK2 plays essential roles in cancer cell proliferation and survival. However, the biological function of FOXK2 in renal cell carcinoma remains unexplored. In our study, we demonstrated that FOXK2 mRNA and protein levels were decreased in clear-cell renal cell carcinoma (ccRCC) tissues compared to those in corresponding non-tumor renal tissues, and decreased FOXK2 levels were associated with poor prognosis in ccRCC patients after nephrectomy. FOXK2 suppressed proliferation, migration and invasion capabilities of ccRCC cells and induced cellular apoptosis in vitro. Moreover, we found that FOXK2 overexpression inhibited xenograft tumor growth and promoted apoptosis in vivo. Genome-wide transcriptome profiling using FOXK2 overexpressed 769-P cells revealed that the epidermal growth factor receptor (EGFR) was a potential downstream gene of FOXK2. Overexpression of EGFR is able to rescue the inhibited proliferation capacity and the enhanced apoptosis capacity due to the overexpression of FOXK2 in 769-P cells. Collectively, our results indicate that FOXK2 inhibits the malignant phenotype of ccRCC and acts as a tumor suppressor possibly through the inhibition of EGFR.

U-box ubiquitin ligase PPIL2 suppresses breast cancer invasion and metastasis by altering cell morphology and promoting SNAI1 ubiquitination and degradation

Metastasis is the leading cause of breast cancer fatalities. To develop new therapeutic strategies, the mechanisms underlying breast cancer invasion and metastasis need to be further investigated. Peptidylprolyl isomerase (cyclophilin)-like 2 (PPIL2) is a U-box-type E3 ubiquitin ligase belonging to the cyclophilin family. Proteins within this family are the major cytosolic binding proteins of the immunosuppressant drug cyclosporine A (CsA). Although PPIL2 has been reported to potentially be involved in cell migration, its role in breast cancer is still unclear. Herein, we demonstrate that PPIL2 suppressed metastasis in a breast cancer model by altering cell morphology and suppressing the epithelial–mesenchymal transition (EMT) process. Moreover, elevated PPIL2 inhibited EMT and breast cancer invasion by interacting with the classical EMT transcription factor, SNAI1, to enhance its ubiquitin-dependent degradation. Furthermore, PPIL2 protein level and stability was upregulated after CsA treatment, indicating that PPIL2 might be involved in CsA-mediated repression of EMT in breast cancer. Analysis of tissue samples taken from breast cancer patients showed a significant correlation between the expression of PPIL2 and the degree of cancer invasion and metastasis. In summary, these results would shed light on a potential clinical use of CsA in breast cancer patients.

SYNJ2BP promotes the degradation of PTEN through the lysosome-pathway and enhances breast tumor metastasis via PI3K/AKT/SNAI1 signaling

SYNJ2BP plays an important role in breast cancer metastasis. However, the molecular mechanism associated with the function of SYNJ2BP in metastasis remains unclear. In this study, we investigated the role of SYNJ2BP in tumor metastasis and established the associated underlying mechanism. Over-expression of SYNJ2BP promoted both cell migration and invasion. In contrast, silencing SYNJ2BP caused the suppression of cell migration and invasion. SYNJ2BP increased the levels of phosphorylation for AKT and GSK3β, which could be inhibited by the PI3K inhibitor, LY294002, and the GSK3β inhibitor, LiCl, and regulated the accumulation of SNAI1 in the nucleus and the expression of the SNAI1 target gene, E-cadherin (EMT marker). It is known that the stability of PTEN is regulated by ubiquitination. However, in this study, we additionally demonstrated that SYNJ2BP mediated the degradation of PTEN protein by the lysosome-pathway and induced the activation of PI3K/AKT signaling by promoting the co-localization of PTEN with autophagy-lysosomes and the expression of LC3-II and p62. In vivo study, the overexpression of SYNJ2BP significantly increased the metastasis of 4T1 cells in BALB/c mice. In addition, SYNJ2BP was highly expressed in breast carcinoma (p = 0.0031), but not in normal breast tissue, while analysis of tissue samples taken from SNAI1-positive human breast cancers showed a significant correlation between the expression of SYNJ2BP and that of p-AKT (p < 0.005). Collectively, our data identified a tumor inducer, SYNJ2BP, which could activate the PI3K/AKT/GSK3β/SNAI1 signaling pathway through the lysosome-mediated degradation of PTEN, and promote both EMT and tumor metastasis during the progression of breast cancer.

Members of FOX family could be drug targets of cancers

FOX families play important roles in biological processes, including metabolism, development, differentiation, proliferation, apoptosis, migration, invasion and longevity. Here we are focusing on roles of FOX members in cancers, FOX members and drug resistance, FOX members and stem cells. Finally, FOX members as drug targets of cancer treatment were discussed. Future perspectives of FOXC1 research were described in the end.

CCN5/WISP-2 restores ER-∝ in normal and neoplastic breast cells and sensitizes triple negative breast cancer cells to tamoxifen

CCN5/WISP-2 is an anti-invasive molecule and prevents breast cancer (BC) progression. However, it is not well understood how CCN5 prevents invasive phenotypes of BC cells. CCN5 protein expression is detected in estrogen receptor-α (ER-α) -positive normal breast epithelial cells as well as BC cells, which are weakly invasive and rarely metastasize depending on the functional status of ER-α. A unique molecular relation between CCN5 and ER-α has been established as the components of the same signaling pathway that coordinate some essential signals associated with the proliferation as well as delaying the disease progression from a non-invasive to invasive phenotypes. Given the importance of this connection, we determined the role of CCN5 in regulation of ER-α in different cellular settings and their functional relationship. In a genetically engineered mouse model, induced expression of CCN5 in the mammary ductal epithelial cells by doxycycline promotes ER-α expression. Similarly, CCN5 regulates ER-α expression and activity in normal and neoplastic breast cells, as documented in various in vitro settings such as mouse mammary gland culture, human mammary epithelial cell and different BC cell cultures in the presence or absence of human recombinant CCN5 (hrCCN5) protein. Mechanistically, at least in the BC cells, CCN5 is sufficient to induce ER-α expression at the transcription level via interacting with integrins-α6β1 and suppressing Akt followed by activation of FOXO3a. Moreover, in vitro and in vivo functional assays indicate that CCN5 treatment promotes response to tamoxifen in triple-negative BC (TNBC) cells possibly via restoring ER-α. Collectively, these studies implicates that the combination treatments of CCN5 (via activation of CCN5 or hrCCN5 treatment) and tamoxifen as potential therapies for TNBC.

Sox9 mediated transcriptional activation of FOXK2 is critical for colorectal cancer cells proliferation

FOXK2, which belongs to the fork head DNA binding protein family, has been shown to play a critical role in tumorigenesis. Here, we detected FOXK2 expression and its clinical significance in colorectal cancer, which has not been fully investigated before. Results from public database and our cohort indicated that FOXK2 was transcriptionally activated in colorectal cancer tissues compared to non-cancer tissues. High expression of FOXK2 was significantly correlated with poor survival. In vitro cell experiments suggested that FOXK2 promoted cell proliferation. Furthermore, we found that oncogene SOX9 was responsible for the up-regulation of FOXK2 by directly binding on its promoter. Depletion of FOXK2 attenuated SOX9 induced cell growth. In addition, we observed that the expression of FOXK2 was significantly associated with the expression of SOX9 both in the public database and our colorectal cancer tissues. The patients with SOX9⁺FOXK2⁺ had a poor overall survival (p = 0.0084). In conclusion, our data suggested that SOX9 transcriptionally activated FOXK2 was involved in the pathogenesis of colorectal cancer and might be a novel target for colorectal cancer therapy.

FOXK2 Elicits Massive Transcription Repression and Suppresses the Hypoxic Response and Breast Cancer Carcinogenesis

Although clinically associated with severe developmental defects, the biological function of FOXK2 remains poorly explored. Here we report that FOXK2 interacts with transcription corepressor complexes NCoR/SMRT, SIN3A, NuRD, and REST/CoREST to repress a cohort of genes including HIF1β and EZH2 and to regulate several signaling pathways including the hypoxic response. We show that FOXK2 inhibits the proliferation and invasion of breast cancer cells and suppresses the growth and metastasis of breast cancer. Interestingly, FOXK2 is transactivated by ERα and transrepressed via reciprocal successive feedback by HIF1β/EZH2. Significantly, the expression of FOXK2 is progressively lost during breast cancer progression, and low FOXK2 expression is strongly correlated with higher histologic grades, positive lymph nodes, and ERα^-/PR^-/HER2^- status, all indicators of poor prognosis.

Effects of the lifestyle habits in breast cancer transcriptional regulation

Through research carried out in the last 25 years about the breast cancer etiology, it has been possible to estimate that less than 10 % of patients who are diagnosed with the condition are carriers of some germline or somatic mutation. The clinical reports of breast cancer patients with healthy twins and the development of disease in women without high penetrance mutations detected, warn the participation more factors in the transformation process. The high incidence of mammary adenocarcinoma in the modern woman and the urgent need for new methods of prevention and early detection have demanded more information about the role that environment and lifestyle have on the transformation of mammary gland epithelial cells. Obesity, alcoholism and smoking are factors that have shown a close correlation with the risk of developing breast cancer. And although these conditions affect different cell regulation levels, the study of its effects in the mechanisms of transcriptional and epigenetic regulation is considered critical for a better understanding of the loss of identity of epithelial cells during carcinogenesis of this tissue. The main objective of this review was to establish the importance of changes occurring to transcriptional level in the mammary gland as a consequence of acute or chronic exposure to harmful products such as obesity-causing foods, ethanol and cigarette smoke components. At analyze the main studies related to topic, it has concluded that the understanding of effects caused by the lifestyle factors in performance of the transcriptional mechanisms that determine gene expression of the mammary gland epithelial cells, may help explain the development of this disease in women without genetic propensity and different phenotypic manifestations of this cancer type.

DEC1 regulates breast cancer cell proliferation by stabilizing cyclin E protein and delays the progression of cell cycle S phase

Breast cancer that is accompanied by a high level of cyclin E expression usually exhibits poor prognosis and clinical outcome. Several factors are known to regulate the level of cyclin E during the cell cycle progression. The transcription factor DEC1 (also known as STRA13 and SHARP2) plays an important role in cell proliferation and apoptosis. Nevertheless, the mechanism of its role in cell proliferation is poorly understood. In this study, using the breast cancer cell lines MCF-7 and T47D, we showed that DEC1 could inhibit the cell cycle progression of breast cancer cells independently of its transcriptional activity. The cell cycle-dependent timing of DEC1 overexpression could affect the progression of the cell cycle through regulating the level of cyclin E protein. DEC1 stabilized cyclin E at the protein level by interacting with cyclin E. Overexpression of DEC1 repressed the interaction between cyclin E and its E3 ligase Fbw7α, consequently reducing the level of polyunbiquitinated cyclin E and increased the accumulation of non-ubiquitinated cyclin E. Furthermore, DEC1 also promoted the nuclear accumulation of Cdk2 and the formation of cyclin E/Cdk2 complex, as well as upregulating the activity of the cyclin E/Cdk2 complex, which inhibited the subsequent association of cyclin A with Cdk2. This had the effect of prolonging the S phase and suppressing the growth of breast cancers in a mouse xenograft model. These events probably constitute the essential steps in DEC1-regulated cell proliferation, thus opening up the possibility of a protein-based molecular strategy for eliminating cancer cells that manifest a high-level expression of cyclin E.

Forkhead box K2 modulates epirubicin and paclitaxel sensitivity through FOXO3a in breast cancer

The forkhead transcription factor FOXK2 has recently been implicated in cancer cell proliferation and survival, but a role in cancer chemotherapeutic drug resistance has hitherto not been explored. Here we demonstrate that FOXK2 has a central role in mediating the cytotoxic drug response in breast cancer. Clonogenic and cell viability assays showed that enhanced FOXK2 expression sensitizes MCF-7 breast cancer cells to paclitaxel or epirubicin treatment, whereas FOXK2 depletion by small interfering RNAs (siRNAs) confers drug resistance. Our data also showed that the activation of the tumour suppressor FOXO3a by paclitaxel and epirubicin is mediated through the induction of FOXK2, as depletion of FOXK2 by siRNA limits the induction of FOXO3a by these drugs in MCF-7 cells. Chromatin immunoprecipitation (ChIP) analysis showed that in response to drug treatment, FOXK2 accumulates and binds to the proximal FOXO3a promoter region in MCF-7 cells. Furthermore, we also uncovered that FOXK2 is deregulated and, therefore, can express at high levels in the nucleus of both the paclitaxel and epirubicin drug-resistant MCF-7 cells. Our results showed that ectopically overexpressed FOXK2 accumulates in the nuclei of drug-resistant MCF-7 cells but failed to be recruited to target genes, including FOXO3a. Crucially, we found that FOXO3a is required for the anti-proliferative and epirubicin-induced cytotoxic function of FOXK2 in MCF-7 cells by sulphorhodamine and clonogenic assays. The physiological importance of the regulation of FOXO3a by FOXK2 is further confirmed by the significant correlations between FOXO3a and FOXK2 expression in breast carcinoma patient samples. Further survival analysis also reveals that high nuclear FOXK2 expression significantly associates with poorer clinical outcome, particularly in patients who have received conventional chemotherapy, consistent with our finding that FOXK2 is deregulated in drug-resistant cells. In summary, our results suggest that paclitaxel and epirubicin target the FOXK2 to modulate their cytotoxicity and deregulated FOXK2 confers drug resistance.