Silencing of the transcription factor KLF6 by siRNA leads to cell cycle arrest and sensitizes cells to apoptosis induced by DNA damage

Decreased expression of KLF6 in ectopic endometrial stromal cells contributes to endometriosis progression by targeting CTNNB1

Despite decades of research, endometriosis remains a mysterious gynecological disease with unknown etiology and pathogenesis. Krüppel-like Factor 6 (KLF6), a transcription factor, has a wide expression profile and regulates a variety of biological processes. Here, we investigated the expression and function of KLF6 and its possible regulatory mechanisms in endometriosis. To determine the function of KLF6, knockdown and overexpression experiments were performed in eutopic endometrial stromal cells (EU-ESCs) and ectopic endometrial stromal cells (EC-ESCs), respectively. Cell viability, apoptosis, migration, invasion, and angiogenesis assays were conducted in ESCs. ChIP-sequencing and mRNA-sequencing were performed to investigate the functional mechanism of KLF6 in regulating ESCs. We found that KLF6 was highly expressed in eutopic endometrium of endometriosis patients, compared with ectopic endometrium. Similarly, the same was true in EU-ESCs, which was compared with EC-ESCs. Overexpression of KLF6 significantly suppressed EC-ESC proliferation, migration and invasion and induced cell apoptosis, while knockdown of KLF6 resulted in the opposite effects on EU-ESCs. Overexpression of KLF6 significantly inhibited EC-ESC angiogenesis. Mechanistically, the results of ChIP sequencing and mRNA sequencing revealed that CTNNB1 may be a transcriptional target regulated by KLF6. Reintroduction of KLF6 reversed the effects of KLF6 knockdown on EU-ESCs. KLF6 inhibited the proliferation, migration and angiogenesis of EC-ESCs by inhibiting the expression of CTNNB1. Our findings provided a new perspective on the role of KLF6 in endometriosis progression and inspire potential targeted therapeutic strategies.

Downregulation of krüppel-like factor 6 expression modulates extravillous trophoblast cell behavior by increasing reactive oxygen species

INTRODUCTION

Placental extravillous trophoblasts play a crucial role in the establishment of a healthy pregnancy. Reactive oxygen species (ROS) may contribute to their differentiation and function as mediators in signaling processes or might cause oxidative stress resulting in trophoblast dysfunction. The krüppel-like transcription factor 6 (KLF6) regulates many genes involved in essential cell processes where ROS are also involved. However, whether KLF6 regulates ROS levels has not been previously investigated.

MATERIALS AND METHODS

KLF6 was silenced by siRNAs in HTR8-SV/neo cells, an extravillous trophoblast model. Total and mitochondrial ROS levels, as well as mitochondrial membrane potential and apoptosis were analyzed by flow cytometry. The expression of genes and proteins of interest were analyzed by qRT-PCR and Western blot, respectively. Cell response to oxidative stress, proliferation, viability, morphology, and migration were evaluated.

RESULTS

KLF6 downregulation led to an increase in ROS and NOX4 mRNA levels, accompanied by reduced cell proliferation and increased p21 protein expression. Catalase activity, 2-Cys peroxiredoxin protein levels, Nrf2 cytoplasmic localization and hemoxygenase 1 expression, as well as mitochondrial membrane potential and cell apoptosis were not altered suggesting that ROS increase is not associated with cellular damage. Instead, KLF6 silencing induced cytoskeleton modifications and increased cell migration in a ROS-dependent manner.

DISCUSSION

Present data reveal a novel role of KLF6 on ROS balance and signaling demonstrating that KLF6 downregulation induces an increase in ROS levels that contribute to extravillous trophoblast cell migration.

lncRNA OR3A4 Promotes the Proliferation and Metastasis of Ovarian Cancer Through KLF6 Pathway

Aim: Ovarian cancer is a collaborative malignant tumor of the female reproductive system in clinical research. Some clinical studies have shown that OR3A4, which is a cancer-causing lncRNA, plays a major role in promoting the occurrence and development of a variety of tumors. And we also expressed the view that it expressed in ovarian tissue. However, the function of OR3A4 in ovarian cancer remains unclear. Methods and Results: To further verify the function of lncRNA OR3A4 in ovarian cancer, we established the xenograft model in the zebra fish. In this study, cells transformed with OR3A4 shRNA plasmids were transplanted into the zebra fish, and the cell proliferation and migration ability were significantly reduced compared to the empty vector. While knocking out OR3A4, we further downregulated its expression by siRNA of KLF6. Our study found that the knocked out OR3A4 resulted in a decrease in cell proliferation and migration level, which can be found in the downregulated expression of KLF6. We also verify the relationship between OR3A4 and circulating tumor cells in the zebra fish xenograft model, the results indicate that lncRNA OR3A4 may be involved in the resistance of ovarian cancer to complain. Conclusion: lncRNA OR3A4 promotes the proliferation and metastasis of ovarian cancer through the KLF6 pathway.

The KLF6 Super Enhancer Modulates Cell Proliferation via MiR-1301 in Human Hepatoma Cells

BACKGROUND

Recent studies have attempted to elucidate the function of super enhancers by means of microRNAs. Although the functional outcomes of miR-1301 have become clearer, the pathways that regulate the expressions of miR-1301 remain unclear.

OBJECTIVE

The objective of this paper was to consider the pathway regulating expression of miR- 1301 and miR-1301 signaling pathways with the inhibition of cell proliferation.

METHODS

In this study, we prepared the cell clones that the KLF6 super enhancer was deleted by means of the CRISPR/Cas9 system-mediated genetic engineering. Changes in miR-1301 expression after the deletion of the KLF6 super enhancer were evaluated by RT-PCR analysis, and the signal pathway of miR-1301 with inhibition of the cell proliferation was examined using RNA interference technology.

RESULTS

The results showed that miR-1301 expression was significantly increased after the deletion of the KLF6 super enhancer. Over-expression of miR-1301 induced by deletion of the KLF6 super enhancer also regulated the expression of p21 and p53 in human hepatoma cells. functional modeling of findings using siRNA specific to miR-1301 showed that expression level changes had direct biological effects on cellular proliferation in Human hepatoma cells. Furthermore, cellular proliferation assay was shown to be directly associated with miR-1301 levels.

CONCLUSION

As a result, it was demonstrated that the over-expression of miR-1301 induced by the disruption of the KLF6 super enhancer leads to a significant inhibition of proliferation in HepG2 cells. Moreover, it was demonstrated that the KLF6 super enhancer regulates the cell-proliferative effects which are mediated, at least in part, by the induction of p21and p53 in a p53-dependent manner. Our results provide the functional significance of miR-1301 in understanding the transcriptional regulation mechanism of the KLF6 super enhancer.

Two Sides of the Same Coin: The Roles of KLF6 in Physiology and Pathophysiology

The Krüppel-like factors (KLFs) family of proteins control several key biological processes that include proliferation, differentiation, metabolism, apoptosis and inflammation. Dysregulation of KLF functions have been shown to disrupt cellular homeostasis and contribute to disease development. KLF6 is a relevant example; a range of functional and expression assays suggested that the dysregulation of KLF6 contributes to the onset of cancer, inflammation-associated diseases as well as cardiovascular diseases. KLF6 expression is either suppressed or elevated depending on the disease, and this is largely due to alternative splicing events producing KLF6 isoforms with specialised functions. Hence, the aim of this review is to discuss the known aspects of KLF6 biology that covers the gene and protein architecture, gene regulation, post-translational modifications and functions of KLF6 in health and diseases. We put special emphasis on the equivocal roles of its full-length and spliced variants. We also deliberate on the therapeutic strategies of KLF6 and its associated signalling pathways. Finally, we provide compelling basic and clinical questions to enhance the knowledge and research on elucidating the roles of KLF6 in physiological and pathophysiological processes.

The Klf6-related super enhancer regulates Klf6-SV2 expression mediated proliferation in human hepatoma (HepG2) cells

Background

The Klf6 gene, which belongs to Krüppel-like family of C2H2 zinc finger transcription factors, is greatly related to tumorigenesis via a high rate of somatic mutation in the carcinomas of prostate, liver, colon, stomach, lung, neck, pituitary, and nervous system: Furthermore, the pathways regulating the expressions of Klf6 splice variants termed Klf6-SV1, -SV2, and -SV3 remain obscure although their functional outcomes have been clear. In this study, the functional roles of Klf6 variants in the inhibition of cell proliferation induced by the disruption of Klf6-related super enhancer in human hepatoma (HepG2) cells were evaluated.

Results

As a result, the disruption of Klf6-related super enhancer not only induced the upregulation of Klf6-SV2 but also led to a significant reduction of proliferation in HepG2 cells. In addition, the disruption of Klf6-related super enhancer led to the induction of p21 and Bax genes mediated by the upregulation of Klf6-SV2.

Conclusion

In conclusion, it was demonstrated that Klf6-related super enhancer modulates cell proliferation via the regulation of Klf6-SV2 expression in human hepatoma (HepG2) cells. The results provide the functional significance of Klf6-related super enhancer in understanding the transcriptional regulation mechanism of Klf6.

Krüppel-Like Factor 6 Is Required for Oxidative and Oncogene-Induced Cellular Senescence

Krüppel-like factor 6 (KLF6) is a transcription factor involved in the regulation of several cellular processes. Regarding its role in tumorigenesis, KLF6 is considered a tumor suppressor. Numerous reports demonstrate its frequent genomic loss or down-regulation, implying a functional inactivation in a broad range of human cancers. Previous work from our laboratory showed that the down-regulation of KLF6 expression in normal fibroblasts leads to cellular transformation, while its ectopic expression interferes with the oncogenic transformation triggered by activated Ras through a cell cycle arrest. We hypothesize that the growth suppressor activity of KLF6 may involve the induction of cellular senescence thereby helping to prevent the proliferation of cells at risk of neoplastic transformation. Here, we explored the association of KLF6 up-regulation in two different cellular senescence scenarios. We found that KLF6 silencing bypasses both oxidative and oncogene-induced senescence. In this context, KLF6 expression per se was capable to trigger cellular senescence in both normal and tumoral contexts. As such, the findings presented in this report provide insights into a potential mechanism by which KLF6 may play a suppressing role of uncontrolled or damaged cell proliferation.

miR-106b-responsive gene landscape identifies regulation of Kruppel-like factor family

MicroRNA dysregulation is a common feature of cancer and due to the promiscuity of microRNA binding this can result in a wide array of genes whose expression is altered. miR-106b is an oncomiR overexpressed in cholangiocarcinoma and its upregulation in this and other cancers often leads to repression of anti-tumorigenic targets. The goal of this study was to identify the miR-106b-regulated gene landscape in cholangiocarcinoma cells using a genome-wide, unbiased mRNA analysis. Through RNA-Seq we found 112 mRNAs significantly repressed by miR-106b. The majority of these genes contain the specific miR-106b seed-binding site. We have validated 11 genes from this set at the mRNA level and demonstrated regulation by miR-106b of 7 proteins. Combined analysis of our miR-106b-regulated mRNA data set plus published reports indicate that miR-106b binding is anchored by G:C pairing in and near the seed. Novel targets Kruppel-like factor 2 (KLF2) and KLF6 were verified both at the mRNA and at the protein level. Further investigation showed regulation of four other KLF family members by miR-106b. We have discovered coordinated repression of multiple members of the KLF family by miR-106b that may play a role in cholangiocarcinoma tumor biology.

Ah Receptor Pathway Intricacies; Signaling Through Diverse Protein Partners and DNA-Motifs

The Ah receptor is a transcription factor that modulates gene expression via interactions with multiple protein partners; these are reviewed, including the novel NC-XRE pathway involving KLF6.

Luna, a Drosophila KLF6/KLF7, is maternally required for synchronized nuclear and centrosome cycles in the preblastoderm embryo

Krüppel like factors (KLFs) are conserved transcription factors that have been implicated in many developmental processes including differentiation, organ patterning, or regulation of stem cell pluripotency. We report the generation and analysis of loss-of-function mutants of Drosophila Klf6/7, the luna gene. We demonstrate that luna mutants are associated with very early embryonic defects prior to cellularization at the syncytial stage and cause DNA separation defects during the rapid mitotic cycles resulting in un-coupled DNA and centrosome cycles. These defects manifest themselves, both in animals that are maternally homozygous and heterozygous mutant. Surprisingly, luna is only required during the syncytial stages and not later in development, suggesting that the DNA segregation defect is linked to centrosomes, since centrosomes are dispensable for later cell divisions.

Krüppel-like factor 6 rendered rat Schwann cell more sensitive to apoptosis via upregulating FAS expression

Krüppel-like factor 6 (KLF6) is a tumor suppressor gene and play a role in the regulation of cell proliferation and apoptosis. After the peripheral nerve injury (PNI), the microenvironment created by surrounding Schwann cells (SCs) is a critical determinant of its regenerative potential. In this study, we examined the effects of KLF6 on SCs responses during PNI. Both KLF6 mRNA and protein expression levels were upregulated in the injured sciatic nerve, and immunofluorescence results showed that many KLF6-positive cells simultaneously expressed the SC markers S-100 and p75NTR. The apoptosis inducers TNFα and cisplatin upregulated KLF6 expression in primary cultured SCs and the SC line RSC96. Although KLF6 overexpression exacerbated cisplatin- and TNFα-induced apoptosis, expression levels of the apoptosis regulators Bcl2 and Bax were not significantly affected in either KLF6-overexpressing or KLF6-depleted RSC96 cells. Realtime PCR arrays and qRT-PCR demonstrated that KLF6 overexpression upregulated four pro-apoptotic genes, FAS, TNF, TNFSF12, and PYCARD, and inhibited expression of the anti-apoptotic IL10 gene expression. Further analysis revealed that FAS protein expression was positively correlated with KLF6 expression in SCs. These data suggest that KLF6 upregulation may render SCs more vulnerable to apoptosis after injury via upregulating FAS expression.

Expression and Function of Kruppel Like-Factors (KLF) in Carcinogenesis

Krüppel-like factor (KLF) family members share a three C2H2 zinc finger DNA binding domain, and are involved in cell proliferation and differentiation control in normal as in pathological situations. Studies over the past several years support a significant role for this family of transcription factors in carcinogenesis. KLFs can both activate and repress genes that participate in cell-cycle regulation. Among them, many up-regulated genes are inhibitors of proliferation, whereas genes that promote cell proliferation are repressed. However, several studies do present KLFs as positive regulator of cell proliferation. KLFs can be deregulated in multiple cancers either by loss of heterozygosity (LOH), somatic mutation or transcriptional silencing by promoter hypermethylation. Accordingly, KLF expression was shown to mediate growth inhibition when ectopically expressed in multiple cancer-derived cell lines through the inhibition of a number of key oncogenic signaling pathways, and to revert the tumorogenic phenotype in vivo. Taken together, these observations suggest that KLFs act as tumor suppressor. However, in some occasion, KLFs could act as tumor promoters, depending on “cellular context”. Thus, this review will discuss the roles and the functions of KLF family members in carcinogenesis, with a special focus on cancers from epithelial origin.

Biology of Krüppel-like factor 6 transcriptional regulator in cell life and death

An essential role for the Krüppel-like transcription factor family has been determined in the regulation of remarkable processes including cell proliferation, differentiation, signal transduction, oncogenesis, and cell death. A member of this group, Krüppel-like factor 6 (KLF6), identified on the basis of its ability to regulate a group of genes belonging to the carcinoembryonic antigen gene family, has been involved in human carcinogenesis. Early studies proposed a tumor suppressor function for KLF6 because of its ability to reduce cell proliferation through several biochemical mechanisms including regulation of cell cycle components, oncogene products, and apoptosis. Mutations within the klf6 gene, decreased expression and/or loss-of-heterozygosity were associated with the development of different human malignancies, and, hence, further supporting the tumor suppressor function of KLF6. This view has been challenged by other studies in distinct types of human cancers describing infrequent genetic alterations of klf6 gene or even enhanced expression in some tumors. The scenario about KLF6 function became still more complex as the description of oncogenic KLF6 splice variant 1 (SV1) with dominant negative activity against the wild type KLF6 (wtKLF6) protein. Additionally, increased evidence is suggesting that KLF6 is a bonafide target of several signaling cascades, which ultimate regulatory effect on this protein could drive decisions of cell life and death, facing the dilemma about how wtKLF6 could be involved in both processes. These apparently conflicting situations, emerged by apparently opposite effects mediated by wtKLF6, may be related, at least in part, to the biological cross-talk with the c-Jun oncoprotein. Depending on the stimulus received by the cell, wtKLF6 interaction with c-Jun determines different cell outcomes such as proliferation control or apoptosis. Thus, KLF6 responsiveness represents a kind of cell warning signal on receiving different stimuli, including oncogenic activation and microbial infections, orchestrating the implementation of proliferation and apoptotic programs.

Mammalian Krüppel-like factors in health and diseases

The Krüppel-like factor (KLF) family of transcription factors regulates diverse biological processes that include proliferation, differentiation, growth, development, survival, and responses to external stress. Seventeen mammalian KLFs have been identified, and numerous studies have been published that describe their basic biology and contribution to human diseases. KLF proteins have received much attention because of their involvement in the development and homeostasis of numerous organ systems. KLFs are critical regulators of physiological systems that include the cardiovascular, digestive, respiratory, hematological, and immune systems and are involved in disorders such as obesity, cardiovascular disease, cancer, and inflammatory conditions. Furthermore, KLFs play an important role in reprogramming somatic cells into induced pluripotent stem (iPS) cells and maintaining the pluripotent state of embryonic stem cells. As research on KLF proteins progresses, additional KLF functions and associations with disease are likely to be discovered. Here, we review the current knowledge of KLF proteins and describe common attributes of their biochemical and physiological functions and their pathophysiological roles.

ROS receptor tyrosine kinase: a new potential target for anticancer drugs

ROS kinase is one of the last two remaining orphan receptor tyrosine kinases with an as yet unidentified ligand. The normal functions of human ROS kinase in different body tissues have not been fully identified so far. However, the ectopic expression, as well as the production of variable mutant forms of ROS kinase has been reported in a number of cancers, such as glioblastoma multiforme, and non-small cell lung cancer, suggesting a role for ROS kinase in deriving such tumors. It is thought also that c-ROS gene may have a role in some cardiovascular diseases, and the fact that homozygous male mice targeted against c-ROS gene are healthy but infertile, has inspired researchers to think about ROS inhibition as a method for development of new male contraceptives. The recent discovery of new selective and potent inhibitors for ROS kinase, along with the development of new specific diagnostic methods for the detection of ROS fusion proteins, raises the importance of using these selective inhibitors for targeting ROS mutations as a new method for treatment of cancers harboring such genes. This review focuses on the ectopic expression of ROS and its fusion proteins in different cancer types and highlights the importance of targeting these proteins for treatment of substantial cancers. It describes also the recent advances in the field of ROS kinase inhibition, and the potential clinical applications of ROS kinase inhibitors.

Nuclear expression of KLF6 tumor suppressor factor is highly associated with overexpression of ERBB2 oncoprotein in ductal breast carcinomas

Background

Krüppel-like factor 6 (KLF6) is an evolutionarily conserved and ubiquitously expressed protein that belongs to the mammalian Sp1/KLF family of transcriptional regulators. Though KLF6 is a transcription factor and harbors a nuclear localization signal it is not systematically located in the nucleus but it was detected in the cytoplasm of several tissues and cell lines. Hence, it is still not fully settled whether the tumor suppressor function of KLF6 is directly associated with its ability to regulate target genes.

Methodology/Principal Findings

In this study we analyzed KLF6 expression and sub-cellular distribution by immunohistochemistry in several normal and tumor tissues in a microarray format representing fifteen human organs. Results indicate that while both nuclear and cytoplasmic distribution of KLF6 is detected in normal breast tissues, breast carcinomas express KLF6 mainly detected in the cytoplasm. Expression of KLF6 was further analyzed in breast cancer tissues overexpressing ERBB2 oncoprotein, which is associated with poor disease prognosis and patient's survival. The analysis of 48 ductal carcinomas revealed a significant population expressing KLF6 predominantly in the nuclear compartment (X²p = 0.005; Fisher p = 0.003). Moreover, this expression pattern correlates directly with early stage and small ductal breast tumors and linked to metastatic events in lymph nodes.

Conclusions/Significance

Data are consistent with a preferential localization of KLF6 in the nuclear compartment of early stage and small HER2-ERBB2 overexpressing ductal breast tumor cells, also presenting lymph node metastatic events. Thus, KLF6 tumor suppressor could represent a new molecular marker candidate for tumor prognosis and/or a potential target for therapy strategies.