Krüppel-like factor 4 (KLF4) suppresses neuroblastoma cell growth and determines non-tumorigenic lineage differentiation

MYCN Amplifications and Metabolic Rewiring in Neuroblastoma

Cancer is a disease caused by (epi)genomic and gene expression abnormalities and characterized by metabolic phenotypes that are substantially different from the normal phenotypes of the tissues of origin. Metabolic reprogramming is one of the key features of tumors, including those established in the human nervous system. In this work, we emphasize a well-known cancerous genomic alteration: the amplification of MYCN and its downstream effects in neuroblastoma phenotype evolution. Herein, we extend our previous computational biology investigations by conducting an integrative workflow applied to published genomics datasets and comprehensively assess the impact of MYCN amplification in the upregulation of metabolism-related transcription factor (TF)-encoding genes in neuroblastoma cells. The results obtained first emphasized overexpressed TFs, and subsequently those committed in metabolic cellular processes, as validated by gene ontology analyses (GOs) and literature curation. Several genes encoding for those TFs were investigated at the mechanistic and regulatory levels by conducting further omics-based computational biology assessments applied on published ChIP-seq datasets retrieved from MYCN-amplified- and MYCN-enforced-overexpression within in vivo systems of study. Hence, we approached the mechanistic interrelationship between amplified MYCN and overexpression of metabolism-related TFs in neuroblastoma and showed that many are direct targets of MYCN in an amplification-inducible fashion. These results illuminate how MYCN executes its regulatory underpinnings on metabolic processes in neuroblastoma.

Differences and Similarities between Colorectal Cancer Cells and Colorectal Cancer Stem Cells: Molecular Insights and Implications

Malignant tumors are formed by diverse groups of cancer cells. Cancer stem cells (CSCs) are a subpopulation of heterogeneous cells identified in tumors that have the ability to self-renew and differentiate. Colorectal cancer (CRC), the third most frequent malignant tumor, is progressively being supported by evidence suggesting that CSCs are crucial in cancer development. We aim to identify molecular differences between CRC cells and CRC CSCs, as well as the effects of those differences on cell behavior in terms of migration, EMT, pluripotency, morphology, cell cycle/control, and epigenetic characteristics. The HT-29 cell line (human colorectal adenocarcinoma) and HT-29 CSCs (HT-29 CD133+/CD44+ cells) were cultured for 72 h. The levels of E-cadherin, KLF4, p53, p21, p16, cyclin D2, HDAC9, and P300 protein expression were determined using immunohistochemistry staining. The migration of cells was assessed by employing the scratch assay technique. Additionally, the scanning electron microscopy method was used to examine the morphological features of the cells, and their peripheral/central elemental ratios were compared with the help of EDS. Furthermore, a Muse cell cycle kit was utilized to determine the cell cycle analysis. The HT-29 CSC group exhibited high levels of expression for E-cadherin, p53, p21, p16, cyclin D2, HDAC9, and P300, whereas KLF4 was found to be high in the HT-29. The two groups did not exhibit any statistically significant differences in the percentages of cell cycle phases. The identification of specific CSC characteristics will allow for earlier cancer detection and the development of more effective precision oncology options.

New insights into KLFs and SOXs in cancer pathogenesis, stemness, and therapy

Despite the development of cancer therapies, the success of most treatments has been impeded by drug resistance. The crucial role of tumor cell plasticity has emerged recently in cancer progression, cancer stemness and eventually drug resistance. Cell plasticity drives tumor cells to reversibly convert their cell identity, analogous to differentiation and dedifferentiation, to adapt to drug treatment. This phenotypical switch is driven by alteration of the transcriptome. Several pluripotent factors from the KLF and SOX families are closely associated with cancer pathogenesis and have been revealed to regulate tumor cell plasticity. In this review, we particularly summarize recent studies about KLF4, KLF5 and SOX factors in cancer development and evolution, focusing on their roles in cancer initiation, invasion, tumor hierarchy and heterogeneity, and lineage plasticity. In addition, we discuss the various regulation of these transcription factors and related cutting-edge drug development approaches that could be used to drug "undruggable" transcription factors, such as PROTAC and PPI targeting, for targeted cancer therapy. Advanced knowledge could pave the way for the development of novel drugs that target transcriptional regulation and could improve the outcome of cancer therapy.

Calreticulin Expression Controls Cellular Redox, Stemness, and Radiosensitivity to Function as a Novel Adjuvant for Radiotherapy in Neuroblastoma

Radiotherapy (RT) is currently only used in children with high-risk neuroblastoma (NB) due to concerns of long-term side effects as well as lack of effective adjuvant. Calreticulin (CALR) has served distinct physiological roles in cancer malignancies; nonetheless, impact of radiation on chaperones and molecular roles they play remains largely unknown. In present study, we systemically analyzed correlation between CALR and NB cells of different malignancies to investigate potential role of CALR in mediating radioresistance of NB. Our data revealed that more malignant NB cells are correlated to lower CALR expression, greater radioresistance, and elevated stemness as indicated by colony- and neurospheroid-forming abilities and vice versa. Of note, manipulating CALR expression in NB cells of varying endogenous CALR expression manifested changes in not only stemness but also radioresistant properties of those NB cells. Further, CALR overexpression resulted in greatly enhanced ROS and led to increased secretion of proinflammatory cytokines. Importantly, growth of NB tumors was significantly hampered by CALR overexpression and was synergistically ablated when RT was also administered. Collectively, our current study unraveled a new notion of utilizing CALR expression in malignant NB to diminish cancer stemness and mitigate radioresistance to achieve favorable therapeutic outcome for NB.

Reciprocal interplays between MicroRNAs and pluripotency transcription factors in dictating stemness features in human cancers

The interplay between microRNAs (miRNAs) and pluripotency transcription factors (TFs) orchestrates the acquisition of cancer stem cell (CSC) features during the course of malignant transformation, rendering them essential cancer cell dependencies and therapeutic vulnerabilities. In this review, we discuss emerging themes in tumor heterogeneity, including the clonal evolution and the CSC models and their implications in resistance to cancer therapies, and then provide thorough coverage on the roles played by key TFs in maintaining normal and malignant stem cell pluripotency and plasticity. In addition, we discuss the reciprocal interactions between miRNAs and MYC, OCT4, NANOG, SOX2, and KLF4 pluripotency TFs and their contributions to tumorigenesis. We provide our view on the potential to interfere with key miRNA-TF networks through the use of RNA-based therapeutics as single agents or in combination with other therapeutic strategies, to abrogate the CSC state and render tumor cells more responsive to standard and targeted therapies.

C1q/TNF-Related Protein 9 Attenuates Atherosclerosis by Inhibiting Hyperglycemia-Induced Endothelial Cell Senescence Through the AMPKα/KLF4 Signaling Pathway

Hyperglycemia-induced endothelial cell senescence has been widely reported to be involved in the pathogenesis of type 2 diabetes mellitus‒accelerated atherosclerosis. Thus, understanding the underlying mechanisms and identifying potential therapeutic targets for endothelial cell senescence are valuable for attenuating atherosclerosis progression. C1q/tumor necrosis factor-related protein 9 (CTRP9), an emerging potential cardiokine, exerts a significant protective effect with respect to atherosclerosis, particularly in endothelial cells. However, the exact mechanism by which CTRP9 prevents endothelial cells from hyperglycemia-induced senescence remains unclear. This study aimed to investigate the effects of CTRP9 on hyperglycemia-induced endothelial cell senescence and atherosclerotic plaque formation in diabetic apolipoprotein E knockout (ApoE KO) mice. Human umbilical vein endothelial cells (HUVECs) were cultured in normal glucose (5.5 mM) and high glucose (40 mM) with or without recombinant human CTRP9 protein (3 μg/ml) for 48 h. Purified lentiviruses overexpressing CTRP9 (Lv-CTRP9) and control vectors containing green fluorescent protein (Lv-GFP) were injected via the tail vein into streptozotocin-induced diabetic ApoE KO mice. Results revealed that exposure of HUVECs to HG significantly increased the expression of Krüppel-like factor 4 (KLF4) and cyclin-dependent kinase inhibitor p21 (p21) and decreased that of telomerase reverse transcriptase (TERT). Treatment with recombinant human CTRP9 protein protected HUVECs from HG-induced premature senescence and dysfunction. CTRP9 promoted the phosphorylation of AMP-activated kinase (AMPK), attenuated the expression of KLF4 and p21 induced by HG, and increased the expression of TERT in HUVECs. Furthermore, in the background of AMPKα knockdown or KLF4 activation, the protective effects of CTRP9 were abolished. In-vivo experiments showed that the overexpression of CTRP9 inhibited vascular senescence and reduced atherosclerotic plaque formation in ApoE KO mice with diabetes. In conclusion, we demonstrate that KLF4 upregulation plays a crucial role in HG-induced endothelial senescence. This anti-atherosclerotic effect of CTRP9 may be partly attributed to the inhibition of HG-induced endothelial senescence through an AMPKα/KLF4-dependent mechanism, suggesting that CTRP9 could benefit further therapeutic approaches for type 2 diabetes mellitus‒accelerated atherosclerosis.

Mechanisms involved in selecting and maintaining neuroblastoma cancer stem cell populations, and perspectives for therapeutic targeting

Pediatric neuroblastomas (NBs) are heterogeneous, aggressive, therapy-resistant embryonal tumours that originate from cells of neural crest (NC) origin and in particular neuroblasts committed to the sympathoadrenal progenitor cell lineage. Therapeutic resistance, post-therapeutic relapse and subsequent metastatic NB progression are driven primarily by cancer stem cell (CSC)-like subpopulations, which through their self-renewing capacity, intermittent and slow cell cycles, drug-resistant and reversibly adaptive plastic phenotypes, represent the most important obstacle to improving therapeutic outcomes in unfavourable NBs. In this review, dedicated to NB CSCs and the prospects for their therapeutic eradication, we initiate with brief descriptions of the unique transient vertebrate embryonic NC structure and salient molecular protagonists involved NC induction, specification, epithelial to mesenchymal transition and migratory behaviour, in order to familiarise the reader with the embryonic cellular and molecular origins and background to NB. We follow this by introducing NB and the potential NC-derived stem/progenitor cell origins of NBs, before providing a comprehensive review of the salient molecules, signalling pathways, mechanisms, tumour microenvironmental and therapeutic conditions involved in promoting, selecting and maintaining NB CSC subpopulations, and that underpin their therapy-resistant, self-renewing metastatic behaviour. Finally, we review potential therapeutic strategies and future prospects for targeting and eradication of these bastions of NB therapeutic resistance, post-therapeutic relapse and metastatic progression.

Pluripotent Stem Cells: Cancer Study, Therapy, and Vaccination

INTRODUCTION

Pluripotent stem cells (PSCs) are promising tools for modern regenerative medicine applications because of their stemness properties, which include unlimited self-renewal and the ability to differentiate into all cell types in the body. Evidence suggests that a rare population of cells within a tumor, termed cancer stem cells (CSCs), exhibit stemness and phenotypic plasticity properties that are primarily responsible for resistance to chemotherapy, radiotherapy, metastasis, cancer development, and tumor relapse. Different therapeutic approaches that target CSCs have been developed for tumor eradication.

RESULTS AND DISCUSSION

In this review, we first provide an overview of different viewpoints about the origin of CSCs. Particular attention has been paid to views believe that CSCs are probably appeared through dysregulation of very small embryonic-like stem cells (VSELs) which reside in various tissues as the main candidate for tissue-specific stem cells. The expression of pluripotency markers in these two types of cells can strengthen the validity of this theory. In this regard, we discuss the common properties of CSCs and PSCs, and highlight the potential of PSCs in cancer studies, therapeutic applications, as well as educating the immune system against CSCs.

CONCLUSION

In conclusion, the resemblance of CSCs to PSCs can provide an appropriate source of CSC-specific antigens through cultivation of PSCs which brings to light promising ideas for prophylactic and therapeutic cancer vaccine development.

Deoxycholic Acid Upregulates the Reprogramming Factors KFL4 and OCT4 Through the IL-6/STAT3 Pathway in Esophageal Adenocarcinoma Cells

Cancer stem cells, a special subgroup of cancer cells, have self-renewal capabilities and multidirectional potential, which may be reprogrammed from the dedifferentiation of cancer cells, contributing to the failure of clinical treatments. Esophageal adenocarcinoma grows in an inflammatory environment stimulated by deoxycholic acid, an important component of gastroesophageal reflux content, contributing to the transformation of esophageal squamous epithelium to the precancerous lesions of esophageal adenocarcinoma, that is, Barrett esophagus. In the present study, deoxycholic acid was used to investigate whether it could induce the expression of reprogramming factors Krüppel-like factor, OCT4, and Nanog; the transformation to cancer stem cells in esophageal adenocarcinoma; and the involvement of the interleukin-6/signal transduction and activation of transcription 3 inflammatory signaling pathway. OE33 cells were treated with deoxycholic acid (250 μM) for 0 hour, 3 hours, 6 hours, and 12 hours before evaluating the messenger RNA expression of Krüppel-like factor, OCT4, Nanog, interleukin-6, and Bcl-xL by reverse transcription-quantitative polymerase chain reaction. Interleukin-6 protein was detected by enzyme linked immunosorbent assay, while signal transduction and activation of transcription 3, phosphorylated signal transduction and activation of transcription 3, Krüppel-like factor, and OCT4 were detected by Western blot. Signal transduction and activation of transcription 3 small interfering RNA and human recombinant interleukin-6 were used to treat OE33 cells and to detect their effects on Krüppel-like factor, OCT4, Nanog, CD44, hypoxia-inducible factor 1-α, and Bcl-xL expression. Results showed that deoxycholic acid promotes the expression of reprogramming factors Krüppel-like factor and OCT4, which are regulated by the interleukin-6/signal transduction and activation of transcription 3 signaling pathway. Deoxycholic acid has a malignancy-inducing effect on the transformation of esophageal adenocarcinoma stem cells, improving the antiapoptotic ability of tumors, and increasing the malignancy of esophageal adenocarcinoma. Deactivating the regulatory signaling pathway of interleukin-6/signal transduction and activation of transcription 3 and neutralizing deoxycholic acid may be novel targets for improving the clinical efficacy of esophageal adenocarcinoma therapy.

KLF4-mediated upregulation of CD9 and CD81 suppresses hepatocellular carcinoma development via JNK signaling

Tetraspanins CD9 and CD81 frequently serve as the surface markers of exosomes, which are involved in intercellular communication during tumor progression. KLF4 is a well-known tumor suppressor in various cancers. This study aims to investigate the relationship between KLF4 and CD9/CD81 in hepatocellular carcinoma (HCC). The results showed that CD9 and CD81 were transcriptionally activated by KLF4 in HCC cell lines. Decreased expressions of CD9 and CD81 were found in most HCC tumor tissues and predicted advanced stages. Furthermore, KLF4 expression was positively associated with CD9 and CD81 expression in HCC specimens. Functionally, overexpression of CD9 and CD81 inhibited HCC cell proliferation in vitro and in vivo and silencing CD9 and CD81 displayed opposite phenotypes. Mechanistically, we found that JNK signaling pathway may be involved in the growth suppression mediated by CD9 and CD81. In addition, increased expression of KLF4, CD9 or CD81 had no obvious impact on exosome secretion from HCC cells. Collectively, we identified CD9 and CD81 as new transcriptional targets of KLF4 and the dysregulated KLF4-CD9/CD81-JNK signaling contributes to HCC development. Our findings will provide new promising targets against this disease.

The Rise of Molecules Able To Regenerate the Central Nervous System

Injury to the adult central nervous system (CNS) usually leads to permanent deficits of cognitive, sensory, and/or motor functions. The failure of axonal regeneration in the damaged CNS limits functional recovery. The lack of information concerning the biological mechanism of axonal regeneration and its complexity has delayed the process of drug discovery for many years compared to other drug classes. Starting in the early 2000s, the ability of many molecules to stimulate axonal regrowth was evaluated through automated screening techniques; many hits and some new mechanisms involved in axonal regeneration were identified. In this Perspective, we discuss the rise of the CNS regenerative drugs, the main biological techniques used to test these drug candidates, some of the most important screens performed so far, and the main challenges following the identification of a drug that is able to induce axonal regeneration in vivo.

KLF4 functions as an oncogene in promoting cancer stem cell-like characteristics in osteosarcoma cells

Despite more effective chemotherapy combined with limb-salvage surgery for the osteosarcoma treatment, survival rates for osteosarcoma patients have stagnated over the past three decades due to the poor prognosis. Osteosarcoma cancer stem cells (OSCs) are responsible for the growth and metastasis of osteosarcoma. The existence of OSCs offers a theoretical explanation for therapeutic failures including tumor recurrence, metastasis, and drug resistance. Understanding the pathways that regulate properties of OSCs may shed light on mechanisms that lead to osteosarcoma and suggest better modes of treatment. In this study, we showed that the expression level of Kruppel-like factor 4 (KLF4) is highly associated with human osteosarcoma cancer stemness. KLF4-overexpressed osteosarcoma cells displayed characteristics of OSCs: increased sphere-forming potential, enhanced levels of stemness-associated genes, great chemoresistance to adriamycin and CDDP, as well as more metastasis potential. Inversely, KLF4 knockdown could reduce colony formation in vitro and inhibit tumorigenesis in vivo, supporting an oncogenic role for KLF4 in osteosarcoma pathogenesis. Furthermore, KLF4 was shown to activate the p38 MAPK signaling pathway to promote cancer stemness. Altogether, our studies uncover an essential role for KLF4 in regulation of OSCs and identify KLF4-p38 MAPK axis as a potential therapeutic target for osteosarcoma treatment.

Context-dependent functions of KLF4 in cancers: Could alternative splicing isoforms be the key?

Krüppel-like factor 4 (KLF4) is an important transcription factor that is expressed in a variety of tissues and regulates many critical physiologic and cellular processes, including cell proliferation, differentiation, stem cell reprogramming, maintenance of genomic stability, and normal tissue homeostasis. KLF4 has both tumor suppressive and oncogenic functions in gastrointestinal and other cancers. These functions are thought to be context dependent, but how KLF4 exerts these differential functions and the molecular mechanisms behind them remain poorly understood. Recent studies have shown that the KLF4 gene undergoes alternative splicing, and the protein products of certain transcripts antagonize wild-type KLF4 function, suggesting an additional layer of regulation of KLF4 function. Therefore, detailed study of KLF4 alternative splicing may not only provide new insights into the complexity of KLF4 functions but also lead to rational targeting of KLF4 for cancer prevention and therapy.

Emerging roles of Myc in stem cell biology and novel tumor therapies

The pathophysiological roles and the therapeutic potentials of Myc family are reviewed in this article. The physiological functions and molecular machineries in stem cells, including embryonic stem (ES) cells and induced pluripotent stem (iPS) cells, are clearly described. The c-Myc/Max complex inhibits the ectopic differentiation of both types of artificial stem cells. Whereas c-Myc plays a fundamental role as a "double-edged sword" promoting both iPS cells generation and malignant transformation, L-Myc contributes to the nuclear reprogramming with the significant down-regulation of differentiation-associated genetic expression. Furthermore, given the therapeutic resistance of neuroendocrine tumors such as small-cell lung cancer and neuroblastoma, the roles of N-Myc in difficult-to-treat tumors are discussed. N-Myc and p53 exhibit the co-localization in the nucleus and alter p53-dependent transcriptional responses which are necessary for DNA repair, anti-apoptosis, and lipid metabolic reprogramming. NCYM protein stabilizes N-Myc, resulting in the stimulation of Oct4 expression, while Oct4 induces both N-Myc and NCYM via direct transcriptional activation of N-Myc, [corrected] thereby leading to the enhanced metastatic potential. Importantly enough, accumulating evidence strongly suggests that c-Myc can be a promising therapeutic target molecule among Myc family in terms of the biological characteristics of cancer stem-like cells (CSCs). The presence of CSCs leads to the intra-tumoral heterogeneity, which is mainly responsible for the therapeutic resistance. Mechanistically, it has been shown that Myc-induced epigenetic reprogramming enhances the CSC phenotypes. In this review article, the author describes two major therapeutic strategies of CSCs by targeting c-Myc; Firstly, Myc-dependent metabolic reprogramming is closely related to CD44 variant-dependent redox stress regulation in CSCs. It has been shown that c-Myc increases NADPH production via enhanced glutaminolysis with a finely-regulated mechanism. Secondly, the dormancy of CSCs due to FBW7-depedent c-Myc degradation pathway is also responsible for the therapeutic resistance to the conventional anti-tumor agents, the action points of which are largely dependent on the operation of the cell cycle. That is why the loss-of-functional mutations of FBW7 gene are expected to trigger "awakening" of dormant CSCs in the niche with c-Myc up-regulation. Collectively, although the further research is warranted to develop the effective anti-tumor therapeutic strategy targeting Myc family, we cancer researchers should always catch up with the current advances in the complex functions of Myc family in highly-malignant and heterogeneous tumor cells to realize the precision medicine.

Graphene Oxide-Silver Nanoparticles Nanocomposite Stimulates Differentiation in Human Neuroblastoma Cancer Cells (SH-SY5Y)

Recently, graphene and graphene related nanocomposite receive much attention due to high surface-to-volume ratio, and unique physiochemical and biological properties. The combination of metallic nanoparticles with graphene-based materials offers a promising method to fabricate novel graphene-silver hybrid nanomaterials with unique functions in biomedical nanotechnology, and nanomedicine. Therefore, this study was designed to prepare graphene oxide (GO) silver nanoparticles (AgNPs) nanocomposite (GO-AgNPs) containing two different nanomaterials in single platform with distinctive properties using luciferin as reducing agents. In addition, we investigated the effect of GO-AgNPs on differentiation in SH-SY5Y cells. The synthesized GO-AgNPs were characterized by ultraviolet-visible absorption spectroscopy (UV-vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The differentiation was confirmed by series of cellular and biochemical assays. The AgNPs were distributed uniformly on the surface of graphene oxide with an average size of 25 nm. As prepared GO-AgNPOs induces differentiation by increasing the expression of neuronal differentiation markers and decreasing the expression of stem cell markers. The results indicated that the redox biology involved the expression of various signaling molecules, which play an important role in differentiation. This study suggests that GO-AgNP nanocomposite could stimulate differentiation of SH-SY5Y cells. Furthermore, understanding the mechanisms of differentiation of neuroblastoma cells could provide new strategies for cancer and stem cell therapies. Therefore, these studies suggest that GO-AgNPs could target specific chemotherapy-resistant cells within a tumor.

Klf4 reduces stemness phenotype, triggers mesenchymal-epithelial transition (MET)-like molecular changes, and prevents tumor progression in nasopharygeal carcinoma

The reprogramming factor Krüppel-like factor 4 (Klf4), one of the Yamanaka's reprogramming factors, plays an essential role in reprogramming somatic cells into induced pluripotent stem cells (iPSCs). Klf4 is dysregulated and displays divergent functions in multiple malignancies, but the biological roles of Klf4 in nasopharyngeal carcinoma (NPC) remain unknown. The present study revealed that Klf4 downregulation in a cohort of human NPC biopsies is significantly associated with invasive and metastatic phenotypes of NPC. Our results showed exogenous expression of Klf4 significantly inhibited cell proliferation, decreased stemness, triggered mesenchymal-epithelial transition (MET)-like molecular changes, and suppressed migration and invasion of NPC cells, whereas depletion of endogeneous Klf4 by RNAi reversed the aforementioned biological behaviors and characheristics. Klf4 silencing significantly enhanced the metastatic ability of NPC cells in vivo. In addition, CHIP assay confirmed that E-cadherin is a transcriptional target of Klf4 in NPC cells. Additional studies demonstrated that Klf4-induced MET-like cellular marker alterations, and reduced motility and invasion of NPC cells were mediated by E-cadherin. This study revealed the clinical correlation between Klf4 expression and epithelial-mesenchymal transition (EMT) biomarkers (including its target gene E-cadherin) in a cohort of NPC biopsies. Taken together, our findings suggest, for what we believe is the first time, that Klf4 functions as a tumor suppressor in NPC to decrease stemness phenotype, inhibit EMT and prevent tumor progression, suggesting that restoring Klf4 function may provide therapeutic benefits in NPC.

Krüppel-like factors in mammalian stem cells and development

Krüppel-like factors (KLFs) are a family of zinc-finger transcription factors that are found in many species. Recent studies have shown that KLFs play a fundamental role in regulating diverse biological processes such as cell proliferation, differentiation, development and regeneration. Of note, several KLFs are also crucial for maintaining pluripotency and, hence, have been linked to reprogramming and regenerative medicine approaches. Here, we review the crucial functions of KLFs in mammalian embryogenesis, stem cell biology and regeneration, as revealed by studies of animal models. We also highlight how KLFs have been implicated in human diseases and outline potential avenues for future research.

DNA-Methyltransferase 1 Induces Dedifferentiation of Pancreatic Cancer Cells through Silencing of Krüppel-Like Factor 4 Expression

Purpose: The dismal prognosis of pancreatic cancer has been linked to poor tumor differentiation. However, molecular basis of pancreatic cancer differentiation and potential therapeutic value of the underlying molecules remain unknown. We investigated the mechanistic underexpression of Krüppel-like factor 4 (KLF4) in pancreatic cancer and defined a novel epigenetic pathway of its activation for pancreatic cancer differentiation and treatment.Experimental Design: Expressions of KLF4 and DNMT1 in pancreatic cancer tissues were determined by IHC and the genetic and epigenetic alterations of KLF4 in and KLF4's impact on differentiation of pancreatic cancer were examined using molecular biology techniques. The function of dietary 3,3'-diindolylmethane (DIM) on miR-152/DNMT1/KLF4 signaling in pancreatic cancer was evaluated using both cell culture and animal models.Results: Overexpression of DNMT1 and promoter hypermethylation contributed to decreased KLF4 expression in and associated with poor differentiation of pancreatic cancer. Manipulation of KLF4 expression significantly affected differentiation marker expressions in pancreatic cancer cells. DIM treatment significantly induced miR-152 expression, which blocked DNMT1 protein expression and its binding to KLF4 promoter region, and consequently reduced promoter DNA methylation and activated KLF4 expression in pancreatic cancer cells. In addition, DIM treatment caused significant inhibition of cell growth in vitro and tumorigenesis in animal models of pancreatic cancer.Conclusions: This is the first demonstration that dysregulated KLF4 expression associates with poor differentiation of pancreatic cancer. Epigenetic activation of miR-152/DNMT1/KLF4 signaling pathway by dietary DIM causes differentiation and significant growth inhibition of pancreatic cancer cells, highlighting its translational implications for pancreatic and other cancers. Clin Cancer Res; 23(18); 5585-97. ©2017 AACR.

The Transcription Regulator Krüppel-Like Factor 4 and Its Dual Roles of Oncogene in Glioblastoma and Tumor Suppressor in Neuroblastoma

The Krüppel-like factor 4 (KLF4) gene is located on chromosome 9q31. All of the currently known 17 KLF transcription regulators that have similarity with members of the specificity protein family are distinctly characterized by the Cys₂/His₂ zinc finger motifs at their carboxyl terminals for preferential binding to the GC/GT box or the CACCC element of the gene promoter and enhancer regions. KLF4 is a transcriptional regulator of cell proliferation, differentiation, apoptosis, migration, and invasion, emphasizing its importance in diagnosis and prognosis of particular tumors. KLF4 has been implicated in tumor progression as well as in tumor suppression, depending on tumor types and contexts. Different studies so far strongly suggest that KLF4 acts as an oncogene in glioblastoma, which is the most malignant and prevalent brain tumor in human adult. It is now well established that the presence of glioblastoma stem cells (GSCs) in glioblastoma causes therapy resistance and progressive growth of the tumor. Because KLF4 is one of the key stemness factors in GSCs, it is likely that KLF4 contributes significantly to the survival of GSCs and the recurrence of glioblastoma. On the other hand, recent studies show that KLF4 can act as a tumor suppressor in human malignant neuroblastoma, which is a deadly tumor mostly in children, by inhibiting the cell cycle and activating the cell differentiation and death pathways. Our increasing understanding of the molecular mechanisms of the contrasting roles of KLF4 in glioblastoma and neuroblastoma is useful for superior diagnosis, therapy, and prognosis of these tumors of the nervous system.

Krüppel-like Factor 4 Blocks Hepatocellular Carcinoma Dedifferentiation and Progression through Activation of Hepatocyte Nuclear Factor-6

PURPOSE

Tumor differentiation is a behavioral index for hepatocellular carcinoma (HCC) and a prognostic factor for patients with HCC who undergo orthotopic liver transplantation (OLT). However, the molecular basis for HCC differentiation and prognostic value of the underlying molecules that regulate HCC differentiation are unclear. In this study, we defined a potential driver pathway for HCC differentiation and prognostication.

EXPERIMENTAL DESIGN

The regulation and function of Krüppel-like factor 4 (KLF4) and hepatocyte nuclear factor-6 (HNF-6) in HCC differentiation was evaluated using human tissues, molecular and cell biology, and animal models, and its prognostic significance was determined according to its impact on patient survival.

RESULTS

There was a direct relationship between the expression levels of KLF4 and HNF6 in HCC. Reduced KLF4 or HNF6 expression correlated with high HCC grade. Poorly differentiated HCC cells had lower expression of KLF4 or HNF6 and differentiation-associated markers than did well-differentiated cells. Elevated KLF4 of HNF6 expression induced differentiation of poorly differentiated hepatoma cells. Mechanistically, KLF4 trans-activated HNF-6 expression. Restored HNF-6 expression upregulated expression of differentiation-associated markers and inhibited HCC cell migration and invasion, whereas HNF-6 knockdown did the opposite. Loss of KLF4 expression in primary HCC correlated with reduced overall survival and shortened relapse-free survival durations after OLT. Combination of KLF4 expression and the Milan criteria improved prognostication for HCC after OLT.

CONCLUSIONS

The dysregulated KLF4/HNF-6 pathway drives dedifferentition and progression of HCC, and KLF4 is a biomarker for accurate prognostication of patients with HCC treated by OLT when integrated with the Milan Criteria.

A distinct gene expression signature characterizes human neuroblastoma cancer stem cells

Neuroblastoma, a malignancy of multipotent embryonic neural crest cells, is the most common extracranial solid cancer in childhood and most common cancer in infancy. Cellular phenotype has been shown to be an important determinant of the malignant potential in human neuroblastoma cells and tumors. Whereas neuroblastic (N-type) are moderately malignant and nonneuronal (S-type) cells are nonmalignant, I-type stem cells are highly tumorigenic, irrespective of N-myc amplification status. In the present study, we sought to determine which genes were overexpressed in the I-type cells which might characterize and maintain the stem cell state and/or malignancy of human neuroblastoma cancer stem cells. We used a microarray platform to compare the steady-state expression levels of mRNAs from 13 human neuroblastoma cell lines representing the three cellular phenotypes. Using qRT-PCR and Western blot analyses, we identified seven genes whose expression is consistently elevated exclusively in neuroblastoma cancer stem cells: CD133, KIT, NOTCH1, GPRC5C, PIGF2, TRKB, and LNGFR. Moreover, we show that the genes are phenotype specific, as differentiation of I-type BE(2)-C cells to either an N- or S-type morphology results in significantly reduced mRNA expression. Finally, we show that NOTCH1 plays an important role in maintaining the stem cell phenotype. The identification and characterization of these genes, elevated in highly malignant neuroblastoma stem cells, could provide the basis for developing novel therapies for treatment of this lethal childhood cancer.

Functional interplay between MYCN, NCYM, and OCT4 promotes aggressiveness of human neuroblastomas

Neuroblastoma is a pediatric solid tumor that originates from embryonic neural crest cells. The MYCN gene locus is frequently amplified in unfavorable neuroblastomas, and the gene product promotes the progression of neuroblastomas. However, the molecular mechanisms by which MYCN amplification contributes to stem cell-like states of neuroblastoma remain elusive. In this study, we show that MYCN and its cis-antisense gene, NCYM, form a positive feedback loop with OCT4, a core regulatory gene maintaining a multipotent state of neural stem cells. We previously reported that NCYM is co-amplified with the MYCN gene in primary human neuroblastomas and that the gene product promotes aggressiveness of neuroblastoma by stabilization of MYCN. In 36 MYCN-amplified primary human neuroblastomas, OCT4 mRNA expression was associated with unfavorable prognosis and was correlated with that of NCYM. The OCT4 protein induced both NCYM and MYCN in human neuroblastoma cells, whereas NCYM stabilized MYCN to induce OCT4 and stem cell-related genes, including NANOG, SOX2, and LIN28. In sharp contrast to MYCN, enforced expression of c-MYC did not enhance OCT4 expression in human neuroblastoma cells. All-trans retinoic acid treatment reduced MYCN, NCYM, and OCT4 expression, accompanied by the decreased amount of OCT4 recruited onto the intron 1 region of MYCN. Knockdown of NCYM or OCT4 inhibited formation of spheres of neuroblastoma cells and promoted asymmetric cell division in MYCN-amplified human neuroblastoma cells. These results suggest that the functional interplay between MYCN, NCYM, and OCT4 contributes to aggressiveness of MYCN-amplified human neuroblastomas.

Intelectin 1 suppresses the growth, invasion and metastasis of neuroblastoma cells through up-regulation of N-myc downstream regulated gene 2

BACKGROUND

Recent studies have revealed the potential roles of intelectin 1 (ITLN1) in tumorigenesis. However, its functions and underlying mechanisms in neuroblastoma (NB), the most common extracranial solid tumor in childhood, still remain largely unknown.

METHODS

Human neuroblastoma cell lines were treated with recombinant ITLN1 protein or stably transfected with ITLN1 expression and short hairpin RNA vectors. Gene expression and signaling pathway were detected by western blot and real-time quantitative RT-PCR. Gene promoter activity and transcription factor binding were detected by luciferase reporter and chromatin immunoprecipitation assays. Growth and aggressiveness of tumor cells were measured by MTT colorimetry, colony formation, scratch assay, matrigel invasion assay, and nude mice model.

RESULTS

Mining of public microarray databases revealed that N-myc downstream regulated gene 2 (NDRG2) was significantly correlated with ITLN1 in NB. Gain- and loss-of-function studies indicated that secretory ITLN1 facilitated the NDRG2 expression, resulting in down-regulation of vascular endothelial growth factor (VEGF) and matrix metalloproteinase 9 (MMP-9), in NB cell lines SH-SY5Y, SK-N-BE(2), and SK-N-SH. Krüppel-like factor 4 (KLF4), a transcription factor crucial for NDRG2 expression, was up-regulated by ITLN1 in NB cells via inactivation of phosphoinositide 3-kinase (PI3K)/AKT signaling. Ectopic expression of ITLN1 suppressed the growth, invasion and metastasis of NB cells in vitro and in vivo. Conversely, knockdown of ITLN1 promoted the growth, invasion, and metastasis of NB cells. In addition, rescue experiments in ITLN1 over-expressed or silenced NB cells showed that restoration of NDRG2 expression prevented the tumor cells from ITLN1-mediated changes in these biological features. In clinical NB tissues, ITLN1 was down-regulated and positively correlated with NDRG2 expression. Patients with high ITLN1 or NDRG2 expression had greater survival probability.

CONCLUSIONS

These findings indicate that ITLN1 functions as a tumor suppressor that affects the growth, invasion and metastasis of NB through up-regulation of NDRG2.

Prediction of potential cancer-risk regions based on transcriptome data: towards a comprehensive view

A novel integrative pipeline is presented for discovery of potential cancer-susceptibility regions (PCSRs) by calculating the number of altered genes at each chromosomal region, using expression microarray datasets of different human cancers (HCs). Our novel approach comprises primarily predicting PCSRs followed by identification of key genes in these regions to obtain potential regions harboring new cancer-associated variants. In addition to finding new cancer causal variants, another advantage in prediction of such risk regions is simultaneous study of different types of genomic variants in line with focusing on specific chromosomal regions. Using this pipeline we extracted numbers of regions with highly altered expression levels in cancer condition. Regulatory networks were also constructed for different types of cancers following the identification of altered mRNA and microRNAs. Interestingly, results showed that GAPDH, LIFR, ZEB2, mir-21, mir-30a, mir-141 and mir-200c, all located at PCSRs, are common altered factors in constructed networks. We found a number of clusters of altered mRNAs and miRNAs on predicted PCSRs (e.g.12p13.31) and their common regulators including KLF4 and SOX10. Large scale prediction of risk regions based on transcriptome data can open a window in comprehensive study of cancer risk factors and the other human diseases.

12-O-tetradecanoylphorbol-13-acetate promotes breast cancer cell motility by increasing S100A14 level in a Kruppel-like transcription factor 4 (KLF4)-dependent manner

The S100 protein family represents the largest subgroup of calcium binding EF-hand type proteins. These proteins have been reported to be involved in a wide range of biological functions that are related to normal cell development and tumorigenesis. S100A14 is a recently identified member of the S100 protein family and differentially expressed in a number of different human malignancies. However, the transcriptional regulation of S100A14 and its role in breast cancer needs to be further investigated. Here, we determined that 12-O-tetradecanoylphorbol-13-acetate (TPA) up-regulated the expression of KLF4 and facilitated its binding directly to two conserved GC-rich DNA segments within the S100A14 promoter, which is essential for the transactivation of KLF4 induced S100A14 expression. Furthermore, stable silencing of KLF4 significantly suppressed breast cancer cell migration induced by TPA. Collectively, these results offer insights into the fact that TPA provokes cell motility through regulating the expression and function of S100A14 in a KLF4-dependent manner.

Krüppel-like factors in cancer

Krüppel-like factors (KLFs) are a family of DNA-binding transcriptional regulators with diverse and essential functions in a multitude of cellular processes, including proliferation, differentiation, migration, inflammation and pluripotency. In this Review, we discuss the roles and regulation of the 17 known KLFs in various cancer-relevant processes. Importantly, the functions of KLFs are context dependent, with some KLFs having different roles in normal cells and cancer, during cancer development and progression and in different cancer types. We also identify key questions for the field that are likely to lead to important new translational research and discoveries in cancer biology.