Aging and the Krüppel-like factors

The mammalian Krüppel-like factors (KLFs) are a family of zinc-finger containing transcription factors with diverse patterns of expression and a wide array of cellular functions. While their roles in mammalian physiology are well known, there is a growing appreciation for their roles in modulating the fundamental progression of aging. Here we review the current knowledge of Krüppel-like factors with a focus on their roles in processes regulating aging and age-associated diseases.

Associations of five polymorphisms in the CD44 gene with cancer susceptibility in Asians

CD44 polymorphisms have been previously associated with cancer risk. However, the results between independent studies were inconsistent. Here, a meta-analysis was performed to systematically evaluate associations between CD44 polymorphisms and cancer susceptibility. A comprehensive literature search conducted in PubMed, Embase, and Web of Science databases through August 10, 2016 yielded 11 eligible publications consisting of 5,788 cancer patients and 5,852 controls. Overall, odds ratios (OR) calculated with 95% confidence intervals (CI) identified a significant association between CD44 polymorphism rs13347 and cancer susceptibility under all genetic models. Additionally, the minor allele of polymorphism rs11821102 was associated with a decreased susceptibility to cancer in allele contrast, dominant, and heterozygous models, while no significant association was identified for polymorphisms rs10836347, rs713330, or rs1425802. Subgroup analysis by ethnicity revealed rs13347 was significantly associated with cancer susceptibility for Chinese but not for Indians. Linkage disequilibrium (LD) between different polymorphisms varied across diverse ethnic populations. In conclusion, the results indicate that CD44 polymorphism rs13347 acts as a risk factor for cancer, especially in Chinese, while the minor allele of polymorphism rs11821102 may be associated with a decreased susceptibility to cancer. Nevertheless, further studies on a larger population covering different ethnicities are warranted.

A novel double-targeted nondrug delivery system for targeting cancer stem cells

Instead of killing cancer stem cells (CSCs), the conventional chemotherapy used for cancer treatment promotes the enrichment of CSCs, which are responsible for tumor growth, metastasis, and recurrence. However, most therapeutic agents are only able to kill a small proportion of CSCs by targeting one or two cell surface markers or dysregulated CSC pathways, which are usually shared with normal stem cells (NSCs). In this study, we developed a novel nondrug delivery system for the dual targeting of CSCs by conjugating hyaluronic acid (HA) and grafting the doublecortin-like kinase 1 (DCLK1) monoclonal antibody to the surface of poly(ethylene glycol) (PEG)–poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles (NPs), which can specifically target CD44 receptors and the DCLK1 surface marker – the latter was shown to possess the capacity to distinguish between CSCSs and NSCs. The size and morphology of these NPs were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). This was followed by studies of NP encapsulation efficiency and in vitro drug release properties. Then, the cytotoxicity of the NPs was tested via Cell Counting Kit-8 assay. Finally, the 4T1 CSCs were obtained from the alginate-based platform, which we developed as an in vitro tumor model. Tumor-bearing nude mice were used as in vivo models to systematically detect the ability of NPs to target CSCs. Our results showed that the DCLK1–HA–PEG–PLGA NPs exhibited a targeting effect toward CSCs both in vitro and in vivo. These findings have important implications for the rational design of drug delivery systems that target CSCs with high efficacy.

Effect of Kruppel-like factor 4 on Notch pathway in hepatic stellate cells

The relationship between Kruppel-like factor 4 (KLF4) and the Notch pathway was determined to investigate the effect of KLF4 on the activation of hepatic stellate cells and underlying mechanisms. Fifty SPF BALB/c mice were randomly divided into two groups. A liver fibrosis model was established in 25 mice as the experimental group, and the remaining 25 mice served as controls. On the day 0, 7, 14, and 35, liver tissues were removed for immunofluorescent detection. The Notch pathway inhibitor DAPT was added to the primary original hepatic stellate cells, and KLF4 and Notch-associated factor expression was detected by qRT-PCR. Additionally, the hepatic stellate cell line LX-2 was used to establish control and experimental groups, and was cultured in vitro. LX-2 cells in the experimental groups were treated with DAPT and the Notch activator transforming growth factor-beta 1 separately, whereas those in the control group were given isotonic culture medium. After 48 h, KLF4 expression was examined by Western blotting. After transient transfection of LX-2 cells to increase KLF4, the expression of Notch factor was examined. Immunofluorescence analysis showed that, with the aggravation of liver fibrosis, the absorbance (A) values of KLF4 were decreased (day 0: 980.73±153.19; day 7: 1087.99±230.23; day 14: 390.95±93.56; day 35: 245.99±87.34). The expression of Notch pathway- related factors (Notch-1, Notch-2, and Jagged-1) in the hepatic stellate cell membrane was negatively correlated to KLF4 expression. With the increase of KLF4 expression, Notch-2 (0.73±0.13) and Jagged-1 (0.43±0.12) expression decreased, whereas Notch-1 level was not detectable. When the Notch pathway was inhibited, KLF4 levels generally increased (18.12±1.31). Our results indicate that KLF4 expression is negatively correlated to the Notch pathway in hepatic stellate cells, which may provide a reference for the treatment of hepatic fibrosis.

ESE3 Inhibits Pancreatic Cancer Metastasis by Upregulating E-Cadherin

The ETS family transcription factor ESE3 is a crucial element in differentiation and development programs for many epithelial tissues. Here we report its role as a tumor suppressor in pancreatic cancer. We observed drastically lower ESE3 expression in pancreatic ductal adenocarcinomas (PDAC) compared with adjacent normal pancreatic tissue. Reduced expression of ESE3 in PDAC correlated closely with an increase in lymph node metastasis and vessel invasion and a decrease in relapse-free and overall survival in patients. In functional experiments, downregulating the expression of ESE3 promoted PDAC cell motility and invasiveness along with metastasis in an orthotopic mouse model. Mechanistic studies in PDAC cell lines, the orthotopic mouse model, and human PDAC specimens demonstrated that ESE3 inhibited PDAC metastasis by directly upregulating E-cadherin expression at the level of its transcription. Collectively, our results establish ESE3 as a negative regulator of PDAC progression and metastasis by enforcing E-cadherin upregulation. Cancer Res; 77(4); 874-85. ©2016 AACR.

Cancer Stem Cells Therapeutic Target Database: The First Comprehensive Database for Therapeutic Targets of Cancer Stem Cells

Cancer stem cells (CSCs) are a subpopulation of tumor cells that have strong self-renewal capabilities and may contribute to the failure of conventional cancer therapies. Hence, therapeutics homing in on CSCs represent a novel and promising approach that may eradicate malignant tumors. However, the lack of information on validated targets of CSCs has greatly hindered the development of CSC-directed therapeutics. Herein, we describe the Cancer Stem Cells Therapeutic Target Database (CSCTT), the first online database to provide a rich bioinformatics resource for the display, search, and analysis of structure, function, and related annotation for therapeutic targets of cancer stem cells. CSCTT contains 135 proteins that are potential targets of CSCs, with validated experimental evidence manually curated from existing literatures. Proteins are carefully annotated with a detailed description of protein families, biological process, related diseases, and experimental evidences. In addition, CSCTT has compiled 213 documented therapeutic methods for cancer stem cells, including 118 small molecules and 20 biotherapy methods. The CSCTT may serve as a useful platform for the development of CSC-directed therapeutics against various malignant tumors. The CSCTT database is freely available to the public at http://www.csctt.org/. Stem Cells Translational Medicine 2017;6:331-334.

Burrowing through the Heterogeneity: Review of Mouse Models of PTCL-NOS

Currently, there are 19 different peripheral T-cell lymphoma (PTCL) entities recognized by the World Health Organization; however, ~70% of PTCL diagnoses fall within one of three subtypes [i.e., peripheral T-cell lymphoma not otherwise specified (PTCL-NOS), anaplastic large-cell lymphoma, and angioimmunoblastic T-cell lymphoma]. PTCL-NOS is a grouping of extra-thymic neoplasms that represent a challenging and heterogeneous subset of non-Hodgkin’s lymphomas. Research into peripheral T-cell lymphomas has been cumbersome as the lack of defining cytogenetic, histological, and molecular features has stymied diagnosis and treatment of these diseases. Similarly, the lacks of genetically manipulated murine models that faithfully recapitulate disease characteristics were absent prior to the turn of the century. Herein, we review the literature concerning existing mouse models for PTLC-NOS, while paying particular attention to the etiology of this heterogeneous disease.

The role of CD44 in glioblastoma multiforme

A transmembrane molecule with several isoforms, CD44 is overexpressed in many tumors and promotes tumor formation through interactions with the tumor microenvironment. CD44 has been implicated in malignant processes including cell motility, tumor growth, and angiogenesis. The role of CD44 has been examined in many cancer types. This paper provides, to our knowledge, the first focused review of the role of CD44 in glioblastoma multiforme (GBM), the most common and fatal of primary brain cancers. We summarize research that describes how CD44 promotes GBM aggressiveness by increasing tumor cell invasion, proliferation and resistance to standard chemoradiation therapy. Effects of CD44 inhibition in GBM are also explored. Clinical trials investigating CD44 targeting in CD44-positive solid tumors are underway, and the evidence presented here suggests that CD44 inhibition in GBM may be a promising therapy.

Krüppel-like factor 4 is a novel prognostic predictor for urothelial carcinoma of bladder and it regulates TWIST1-mediated epithelial-mesenchymal transition

BACKGROUND

Krüppel-like factor 4 (KLF4) exerts tumor suppressive or oncogenic functions in a cell-type-dependent manner, but its prognostic role in urothelial carcinoma of bladder (UCB) remains unclear. We aimed to determine how KLF4 regulates epithelial-mesenchymal transition (EMT) and predicts patient survival in UCB.

PATIENTS AND METHODS

The roles of KLF4 and other EMT regulators in cancer progression were studied in UCB specimens of 398 patients, UCB cell lines. The results were validated by open-access The Cancer Genome Atlas dataset.

RESULTS

Over a median follow-up of 46.5 months, tissue microarray demonstrated that strong KLF4 expression was associated with higher risk toward metastasis and death (P<0.001). KLF4 expression positively correlated with TWIST1 and vimentin, and inversely correlated with E-cadherin expression. Metastasis-free survival was poorest in KLF4/TWIST1 coexpression group, followed by KLF4 or TWIST1 expression-alone group, and no-expression group (P<0.001). Multivariate analysis substantiated that KLF4/TWIST1 coexpression independently predicted overall mortality and metastasis risk with hazard ratios of 2.43 (95% CI: 1.65-3.64) and 7.54 (CI: 4.03-12.10). The Cancer Genome Atlas dataset of bladder cancer also revealed a trend toward decreased overall survival in the high KLF4 expression group as compared to the low KLF4 group. In vitro, KLF4 is accompanied with decreased E-cadherin and β-catenin expressions, increased vimentin and fibronectin expressions, and enhanced migration/invasion. KLF4 knockdown suppressed TWIST1 expression and inhibited EMT, migration and invasion, whereas enforced KLF4 overexpression activated TWIST1 expression and restored EMT and metastatic phenotype. Furthermore, TWIST1 knockdown abolished KLF4-faciliated EMT and metastatic feature without affecting KLF4 expression.

CONCLUSIONS

KLF4 promotes TWIST1-mediated EMT and may represent a novel prognostic predictor in UCB.

The Novel KLF4/MSI2 Signaling Pathway Regulates Growth and Metastasis of Pancreatic Cancer

PURPOSE

Musashi 2 (MSI2) is reported to be a potential oncoprotein in cases of leukemia and several solid tumors. However, its expression, function, and regulation in pancreatic ductal adenocarcinoma (PDAC) cases have yet to be demonstrated. Therefore, in the current study, we investigated the clinical significance and biologic effects of MSI2 expression in PDAC cases and sought to delineate the clinical significance of the newly identified Krüppel-like factor 4 (KLF4)/MSI2 regulatory pathway.

EXPERIMENTAL DESIGN

MSI2 expression and its association with multiple clinicopathologic characteristics in human PDAC specimens were analyzed immunohistochemically. The biological functions of MSI2 regarding PDAC cell growth, migration, invasion, and metastasis were studied using gain- and loss-of-function assays both in vitro and in vivo Regulation of MSI2 expression by KLF4 was examined in several cancer cell lines, and the underlying mechanisms were studied using molecular biologic methods.

RESULTS

MSI2 expression was markedly increased in both PDAC cell lines and human PDAC specimens, and high MSI2 expression was associated with poor prognosis for PDAC. Forced MSI2 expression promoted PDAC proliferation, migration, and invasion in vitro and growth and metastasis in vivo, whereas knockdown of MSI2 expression did the opposite. Transcriptional inhibition of MSI2 expression by KLF4 occurred in multiple PDAC cell lines as well as mouse models of PDAC.

CONCLUSIONS

Lost expression of KLF4, a transcriptional repressor of MSI2 results in overexpression of MSI2 in PDACs, which may be a biomarker for accurate prognosis. A dysregulated KLF4/MSI2 signaling pathway promotes PDAC progression and metastasis. Clin Cancer Res; 23(3); 687-96. ©2016 AACR.

Post-Transcriptional Regulation of KLF4 by High-Risk Human Papillomaviruses Is Necessary for the Differentiation-Dependent Viral Life Cycle

Human papillomaviruses (HPVs) are epithelial tropic viruses that link their productive life cycles to the differentiation of infected host keratinocytes. A subset of the over 200 HPV types, referred to as high-risk, are the causative agents of most anogenital malignancies. HPVs infect cells in the basal layer, but restrict viral genome amplification, late gene expression, and capsid assembly to highly differentiated cells that are active in the cell cycle. In this study, we demonstrate that HPV proteins regulate the expression and activities of a critical cellular transcription factor, KLF4, through post-transcriptional and post-translational mechanisms. Our studies show that KLF4 regulates differentiation as well as cell cycle progression, and binds to sequences in the upstream regulatory region (URR) to regulate viral transcription in cooperation with Blimp1. KLF4 levels are increased in HPV-positive cells through a post-transcriptional mechanism involving E7-mediated suppression of cellular miR-145, as well as at the post-translational level by E6–directed inhibition of its sumoylation and phosphorylation. The alterations in KLF4 levels and functions results in activation and suppression of a subset of KLF4 target genes, including TCHHL1, VIM, ACTN1, and POT1, that is distinct from that seen in normal keratinocytes. Knockdown of KLF4 with shRNAs in cells that maintain HPV episomes blocked genome amplification and abolished late gene expression upon differentiation. While KLF4 is indispensable for the proliferation and differentiation of normal keratinocytes, it is necessary only for differentiation-associated functions of HPV-positive keratinocytes. Increases in KLF4 levels alone do not appear to be sufficient to explain the effects on proliferation and differentiation of HPV-positive cells indicating that additional modifications are important. KLF4 has also been shown to be a critical regulator of lytic Epstein Barr virus (EBV) replication underscoring the importance of this cellular transcription factor in the life cycles of multiple human cancer viruses.

Viruses that induce persistent infections often alter the expression and activities of cellular transcription factors to regulate their productive life cycles. Human papillomaviruses (HPVs) are epithelial tropic viruses that link their productive life cycles to the differentiation of infected host keratinocytes. Our studies show that KLF-4, originally characterized as a pluripotency factor, binds HPV-31 promoters activating viral transcription as well as modulates host cell differentiation and cell cycle progression. KLF4 levels and activity are enhanced in HPV-positive cells by E6 and E7 mediated post-transcriptional and post-translational mechanisms resulting in altered target gene expression and biological functions from that seen in normal keratinocytes. Importantly, silencing KLF4 hinders viral genome amplification and late gene expression. Along with its recently identified role in Epstein Barr Virus reactivation during differentiation, our studies demonstrate the importance of KLF4 in the life cycles of multiple human cancer viruses.

Wnt Signaling in Cancer Stem Cell Biology

Aberrant regulation of Wnt signaling is a common theme seen across many tumor types. Decades of research have unraveled the epigenetic and genetic alterations that result in elevated Wnt pathway activity. More recently, it has become apparent that Wnt signaling levels identify stem-like tumor cells that are responsible for fueling tumor growth. As therapeutic targeting of these tumor stem cells is an intense area of investigation, a concise understanding on how Wnt activity relates to cancer stem cell traits is needed. This review attempts at summarizing the intricacies between Wnt signaling and cancer stem cell biology with a special emphasis on colorectal cancer.

Auraptene Attenuates Malignant Properties of Esophageal Stem-Like Cancer Cells

The high incidence of esophageal squamous cell carcinoma has been reported in selected ethnic populations including North of Iran. Low survival rate of esophageal carcinoma is partially due to the presence of stem-like cancer cells with chemotherapy resistance. In the current study, we aimed to determine the effects of auraptene, an interesting dietary coumarin with various biological activities, on malignant properties of stem-like esophageal squamous cell carcinoma, in terms of sensitivity to anticancer drugs and expression of specific markers. To do so, the half maximal inhibitory concentration values of auraptene, cisplatin, paclitaxel, and 5-fluorouracil were determined on esophageal carcinoma cells (KYSE30 cell line). After administrating combinatorial treatments, including nontoxic concentrations of auraptene + cisplatin, paclitaxel, or 5-fluorouracil, sensitivity of cells to chemical drugs and also induced apoptosis were assessed. In addition, quantitative real-time polymerase chain reaction was used to study changes in the expression of tumor suppressor proteins 53 and 21 ( P53 and P21), cluster of differentiation 44 ( CD44), and B cell-specific Moloney murine leukemia virus integration site 1 ( BMI-1) upon treatments. Results of thiazolyl blue assay revealed that auraptene significantly ( P < .05) increased toxicity of cisplatin, paclitaxel, and 5-fluorouracil in KYSE30 cells, specifically 72 hours after treatment. Conducting an apoptosis assay using flow cytometry also confirmed the synergic effects of auraptene. Results of quantitative real-time polymerase chain reaction revealed significant ( P < .05) upregulation of P53 and P21 upon combinatorial treatments and also downregulation of CD44 and BMI-1 after auraptene administration. Current study provided evidence, for the first time, that auraptene attenuates the properties of esophageal stem-like cancer cells through enhancing sensitivity to chemical agents and reducing the expression of CD44 and BMI-1 markers.

Neurotrophin signaling in cancer stem cells

Cancer stem cells (CSCs), are thought to be at the origin of tumor development and resistance to therapies. Thus, a better understanding of the molecular mechanisms involved in the control of CSC stemness is essential to the design of more effective therapies for cancer patients. Cancer cell stemness and the subsequent expansion of CSCs are regulated by micro-environmental signals including neurotrophins. Over the years, the roles of neurotrophins in tumor development have been well established and regularly reviewed. Especially, nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are reported to stimulate tumor cell proliferation, survival, migration and/or invasion, and favors tumor angiogenesis. More recently, neurotrophins have been reported to regulate CSCs. This review briefly presents neurotrophins and their receptors, summarizes their roles in different cancers, and discusses the emerging evidence of neurotrophins-induced enrichment of CSCs as well as the involved signaling pathways.

Carcinoma Cell Hyaluronan as a "Portable" Cancerized Prometastatic Microenvironment

Hyaluronan (HA) is a structurally simple polysaccharide, but its ability to act as a template for organizing pericellular matrices and its regulated synthesis and degradation are key to initiating repair responses. Importantly, these HA functions are usurped by tumor cells to facilitate progression and metastasis. Recent advances have identified the functional complexities associated with the synthesis and degradation of HA-rich matrices. Three enzymes synthesize large HA polymers while multiple hyaluronidases or tissue free radicals degrade these into smaller bioactive fragments. A family of extracellular and cell-associated HA-binding proteins/receptors translates the bioinformation encrypted in this complex polymer mixture to activate signaling networks required for cell survival, proliferation, and migration in an actively remodeling microenvironment. Changes in HA metabolism within both the peritumor stroma and parenchyma are linked to tumor initiation, progression, and poor clinical outcome. We review evidence that metastatic tumor cells must acquire the capability to autonomously synthesize, assemble, and process their own "portable" HA-rich microenvironments to survive in the circulation, metastasize to ectopic sites, and escape therapeutic intervention. Strategies to disrupt the HA machinery of primary tumor and circulating tumor cells may enhance the effectiveness of current conventional and targeted therapies. Cancer Res; 76(9); 2507-12. ©2016 AACR.

Oncogenic roles and drug target of CXCR4/CXCL12 axis in lung cancer and cancer stem cell

Although the great progress has been made in diagnosis and therapeutic in lung cancer, it induces the most cancer death worldwide in both males and females. Chemokines, which have chemotactic abilities, contain up to 50 family members. By binding to G protein-coupled receptors (GPCR), holding seven-transmembrane domain, they function in immune cell trafficking and regulation of cell proliferation, differentiation, activation, and migration, homing under both physiologic and pathologic conditions. The alpha-chemokine receptor CXCR4 for the alpha-chemokine stromal cell-derived-factor-1 (SDF-1) is most widely expressed by tumors. In addition to human tissues of the bone marrow, liver, adrenal glands, and brain, the CXC chemokine SDF-1 or CXCL12 is also highly expressed in lung cancer tissues and is associated with lung metastasis. Lung cancer cells have the capabilities to utilize and manipulate the CXCL12/CXCR system to benefit growth and distant spread. CXCL12/CXCR4 axis is a major culprit for lung cancer and has a crucial role in lung cancer initiation and progression by activating cancer stem cell. This review provides an evaluation of CXCL12/CXCR4 as the potential therapeutic target for lung cancers; it also focuses on the synergistic effects of inhibition of CXCL12/CXCR4 axis and immunotherapy as well as chemotherapy. Together, CXCL12/CXCR4 axis can be a potential therapeutic target for lung cancers and has additive effects with immunotherapy.

Drug Delivery Using Nanoparticles for Cancer Stem-Like Cell Targeting

The theory of cancer stem-like cell (or cancer stem cell, CSC) has been established to explain how tumor heterogeneity arises and contributes to tumor progression in diverse cancer types. CSCs are believed to drive tumor growth and elicit resistance to conventional therapeutics. Therefore, CSCs are becoming novel target in both medical researches and clinical studies. Emerging evidences showed that nanoparticles effectively inhibit many types of CSCs by targeting various specific markers (aldehyde dehydrogenases, CD44, CD90, and CD133) and signaling pathways (Notch, Hedgehog, and TGF-β), which are critically involved in CSC function and maintenance. In this review, we briefly summarize the current status of CSC research and review a number of state-of-the-art nanomedicine approaches targeting CSC. In addition, we discuss emerging therapeutic strategies using epigenetic drugs to eliminate CSCs and inhibit cancer cell reprogramming.

Curcumin Induces Apoptosis of Colorectal Cancer Stem Cells by Coupling with CD44 Marker

This study investigated the effect of curcumin on colorectal cancer stem cells (CCSCs) and its possible mechanism. Comparison of the metabolic profiles of human adenomatous polyp (N = 61) and colorectal cancer (CRC) (N = 57) tissue found statistically significant differences (p < 0.05) in their composition of adenosine monophosphate (AMP), adenine, 5'-methythioadenosine, 3-hydroxybutyric acid, prostaglandin E2, threonine, and glutamine. Our cell culture model study found that curcumin treatment (50 μM for 48 h) did indeed increase apoptosis of CRC cells as well as of CCSCs, but at a significant level only in CD44(+) cells. Further metabolic profile studies of the CRC, CD44(+), and CD44(-) cells indicated that curcumin treatment increased glyceraldehyde and hydroxypropionic acid in CD44(-) cells but decreased glutamine content in both curcumin-treated CRC and CD44(+) cells. Based on our comparison of the metabolic profiles of human tissues and cancer cells, we suggest that curcumin might couple with CD44 and that curcumin-CD44(+) coupling at the cell membrane might have some blocking effect on the transport of glutamine into the cells, thus decreasing the glutamine content in the CD44(+) cells and inducing apoptosis.

KLF4 Is Essential for Induction of Cellular Identity Change and Acinar-to-Ductal Reprogramming during Early Pancreatic Carcinogenesis

Understanding the molecular mechanisms of tumor initiation has significant impact on early cancer detection and intervention. To define the role of KLF4 in pancreatic ductal adenocarcinoma (PDA) initiation, we used molecular biological analyses and mouse models of klf4 gain- and loss-of-function and mutant Kras. KLF4 is upregulated in and required for acinar-to-ductal metaplasia. Klf4 ablation drastically attenuates the formation of pancreatic intraepithelial neoplasia induced by mutant Kras(G12D), whereas upregulation of KLF4 does the opposite. Mutant KRAS and cellular injuries induce KLF4 expression, and ectopic expression of KLF4 in acinar cells reduces acinar lineage- and induces ductal lineage-related marker expression. These results demonstrate that KLF4 induces ductal identity in PanIN initiation and may be a potential target for prevention of PDA initiation.

KLF4-Mediated Suppression of CD44 Signaling Negatively Impacts Pancreatic Cancer Stemness and Metastasis

KLF4 and CD44 regulate cancer cell stemness, but their precise functions and roles in metastatic progression are not well understood. In this study, we used both inducible and genetic engineering approaches to assess whether the activities of these two factors intersect in pancreatic cancer. We found that genetic ablation of Klf4 in pancreatic cancer cells isolated from Klf4(flox/flox) mice drastically increased CD44 expression and promoted the acquisition of stem-like properties, whereas tetracycline-inducible expression of KLF4 suppressed these properties in vitro and in vivo Further mechanistic investigation revealed that KLF4 bound to the CD44 promoter to negatively regulate transcription and also the expression of the CD44 variant. Moreover, in human pancreatic ductal adenocarcinoma (PDAC) tissues, the expression patterns of KLF4 and CD44 were mutually exclusive, and this inverse relationship was particularly striking in human metastatic pancreatic tumors and in autochthonous mouse models of PDAC. Taken together, our findings demonstrate that KLF4 acts as a tumor suppressor in PDAC cells that restricts metastatic behaviors through direct negative regulation of CD44, providing support for the clinical investigation of therapeutic approaches focusing on targeted KLF4 activation in advanced tumors. Cancer Res; 76(8); 2419-31. ©2016 AACR.

Relationship between KLF4 and primary hepatocellular carcinoma

Kruppel-like factors (KLFs) are a family of transcription factors with zinc finger structure, which play a key role in cell proliferation, apoptosis, differentiation and embryonic development. KLF4 is an important member of the KLF family, and it is highly expressed in primary hepatocellular carcinoma tissues. However, the mechanism of KLF4 in primary hepatocellular carcinoma remains to be explored. This paper reviews the biological function of KLF4 in primary hepatocellular carcinoma.

The role of pluripotency factors to drive stemness in gastrointestinal cancer

A better molecular understanding of gastrointestinal cancers arising either from the stomach, the pancreas, the intestine, or the liver has led to the identification of a variety of potential new molecular therapeutic targets. However, in most cases surgery remains the only curative option. The intratumoral cellular heterogeneity of cancer stem cells, bulk tumor cells, and stromal cells further limits straightforward targeting approaches. Accumulating evidence reveals an intimate link between embryonic development, stem cells, and cancer formation. In line, a growing number of oncofetal proteins are found to play common roles within these processes. Cancer stem cells share features with true stem cells by having the capacity to self-renew in a de-differentiated state, to generate heterogeneous types of differentiated progeny, and to give rise to the bulk tumor. Further, various studies identified genes in cancer stem cells, which were previously shown to regulate the pluripotency circuitry, particularly the so-called "Yamanaka-Factors" (OCT4, KLF4, SOX2, and c-MYC). However, the true stemness potential of cancer stem cells and the role and expression pattern of such pluripotency genes in various tumor cell types remain to be explored. Here, we summarize recent findings and discuss the potential mechanisms involved, and link them to clinical significance with a particular focus on gastrointestinal cancers.

Molecular Biomarkers of Pancreatic Intraepithelial Neoplasia and Their Implications in Early Diagnosis and Therapeutic Intervention of Pancreatic Cancer

Lack of early detection and effective interventions is a major reason for the poor prognosis and dismal survival rates for pancreatic cancer. Pancreatic intraepithelial neoplasia (PanIN) is the most common precursor of invasive pancreatic ductal adenocarcinoma (PDAC). Each stage in the progression from PanIN to PDAC is well characterized by multiple significant genetic alterations affecting signaling pathways. Understanding the biological behavior and molecular alterations in the progression from PanIN to PDAC is crucial to the identification of noninvasive biomarkers for early detection and diagnosis and the development of preventive and therapeutic strategies for control of pancreatic cancer progression. This review focuses on molecular biomarkers of PanIN and their important roles in early detection and treatment of pancreatic cancer.

Deregulated KLF4 Expression in Myeloid Leukemias Alters Cell Proliferation and Differentiation through MicroRNA and Gene Targets

Acute myeloid leukemia (AML) is characterized by increased proliferation and blocked differentiation of hematopoietic progenitors mediated, in part, by altered myeloid transcription factor expression. Decreased Krüppel-like factor 4 (KLF4) expression has been observed in AML, but how decreased KLF4 contributes to AML pathogenesis is largely unknown. We demonstrate decreased KLF4 expression in AML patient samples with various cytogenetic aberrations, confirm that KLF4 overexpression promotes myeloid differentiation and inhibits cell proliferation in AML cell lines, and identify new targets of KLF4. We have demonstrated that microRNA 150 (miR-150) expression is decreased in AML and that reintroducing miR-150 expression induces myeloid differentiation and inhibits proliferation of AML cells. We show that KLF family DNA binding sites are necessary for miR-150 promoter activity and that KLF2 or KLF4 overexpression induces miR-150 expression. miR-150 silencing, alone or in combination with silencing of CDKN1A, a well-described KLF4 target, did not fully reverse KLF4-mediated effects. Gene expression profiling and validation identified putative KLF4-regulated genes, including decreased MYC and downstream MYC-regulated gene expression in KLF4-overexpressing cells. Our findings indicate that decreased KLF4 expression mediates antileukemic effects through regulation of gene and microRNA networks, containing miR-150, CDKN1A, and MYC, and provide mechanistic support for therapeutic strategies increasing KLF4 expression.

Aberrant Splicing of Estrogen Receptor, HER2, and CD44 Genes in Breast Cancer

Breast cancer (BC) is the most common cause of cancer-related death among women under the age of 50 years. Established biomarkers, such as hormone receptors (estrogen receptor [ER]/progesterone receptor) and human epidermal growth factor receptor 2 (HER2), play significant roles in the selection of patients for endocrine and trastuzumab therapies. However, the initial treatment response is often followed by tumor relapse with intrinsic resistance to the first-line therapy, so it has been expected to identify novel molecular markers to improve the survival and quality of life of patients. Alternative splicing of pre-messenger RNAs is a ubiquitous and flexible mechanism for the control of gene expression in mammalian cells. It provides cells with the opportunity to create protein isoforms with different, even opposing, functions from a single genomic locus. Aberrant alternative splicing is very common in cancer where emerging tumor cells take advantage of this flexibility to produce proteins that promote cell growth and survival. While a number of splicing alterations have been reported in human cancers, we focus on aberrant splicing of ER, HER2, and CD44 genes from the viewpoint of BC development. ERα36, a splice variant from the ER1 locus, governs nongenomic membrane signaling pathways triggered by estrogen and confers 4-hydroxytamoxifen resistance in BC therapy. The alternative spliced isoform of HER2 lacking exon 20 (Δ16HER2) has been reported in human BC; this isoform is associated with transforming ability than the wild-type HER2 and recapitulates the phenotypes of endocrine therapy-resistant BC. Although both CD44 splice isoforms (CD44s, CD44v) play essential roles in BC development, CD44v is more associated with those with favorable prognosis, such as luminal A subtype, while CD44s is linked to those with poor prognosis, such as HER2 or basal cell subtypes that are often metastatic. Hence, the detection of splice variants from these loci will provide keys to understand the pathogenesis, predict the prognosis, and choose specific therapies for BC.

p-21 activated kinase 4 (PAK4) maintains stem cell-like phenotypes in pancreatic cancer cells through activation of STAT3 signaling

Pancreatic cancer (PC) remains a highly lethal malignancy due to its unusual chemoresistance and high aggressiveness. A subpopulation of pancreatic tumor cells, known as cancer stem cells (CSCs), is considered responsible not only for tumor-maintenance, but also for its widespread metastasis and therapeutic failure. Here we investigated the role of p-21 activated kinase 4 (PAK4) in driving PC stemness properties. Our data demonstrate that triple-positive (CD24⁺/CD44⁺/EpCAM⁺) subpopulation of pancreatic CSCs exhibits greater level of PAK4 as compared to triple-negative (CD24⁻/CD44⁻/EpCAM⁻) cells. Moreover, PAK4 silencing in PC cells leads to diminished fraction of CD24, CD44, and EpCAM positive cells. Furthermore, we show that PAK4-silenced PC cells exhibit decreased sphere-forming ability and increased chemo-sensitivity to gemcitabine toxicity. PAK4 expression is also associated with enhanced levels of stemness-associated transcription factors (Oct4/Nanog/Sox2 and KLF4). Furthermore, our data show decreased nuclear accumulation and transcriptional activity of STAT3 in PAK4-silenced PC cells and restitution of its activity leads to restoration of stem cell phenotypes. Together, our findings deliver first experimental evidence for the involvement of PAK4 in PC stemness and support its clinical utility as a novel therapeutic target in PC.

Expression of cancer stem cell markers and their correlation with pathogenesis in vascular tumors

Vascular tumor, which belongs to a kind of complicated lesion in soft tissue tumor, is derived from mesenchymal tissue. Although many studies have been focused on the pathogenesis of vascular tumors in human, the specific mechanism of the vascular tumors was currently unclear. Previous studies have reported an association of cancer stem cells with the development of tumor in many solid tumors. Thus the purpose of this study was to explore whether different expression level of cancer stem cell markers including CD29, CD44, CD133, nestin and ALDH1 in vascular tumor may help to elucidate the possible pathogenesis of vascular tumor. In present study, tissues of 9 cases of hemangioma, 22 cases of hemangiosarcoma, 3 cases of Kaposi's sarcoma, and 5 cases of hemangioendothelioma were immunostained for CD29, CD44, CD133, nestin and ALDH1. Of the 39 vascular tumor cases included in the current study, CD29, CD133 and nestin were positive in most vascular tumor cases. Although CD44 and ALDH1 were observed in vascular tumor cases, the percentage of cells staining for the two markers was less than 2% in all cases of vascular tumor. Capillary hemangiomas exhibited significantly higher expression rate of CD29 and nestin compared with malignant vascular tumors and hemangioendotheliomas (P<0.05, Fisher's exact test), while CD44, CD133 and ALDH1 exhibited no statistically significant difference between these two groups. Pearson correlation analysis exhibited that CD29 expression and nestin expression in vascular tumor were no statistically significant relationship (C=0.288, P=0.063>0.05). Our findings confirmed that the five cancer stem cells markers, including CD29, CD44, CD133, nestin and ALDH1, exhibited different expression levels in vascular tumors and demonstrated that immunohistochemical analysis for cancer stem cells markers may provide useful information for studying the pathogenesis of vascular tumors.

Aberrant RNA splicing in cancer; expression changes and driver mutations of splicing factor genes

Alternative splicing is a widespread process contributing to structural transcript variation and proteome diversity. In cancer, the splicing process is commonly disrupted, resulting in both functional and non-functional end-products. Cancer-specific splicing events are known to contribute to disease progression; however, the dysregulated splicing patterns found on a genome-wide scale have until recently been less well-studied. In this review, we provide an overview of aberrant RNA splicing and its regulation in cancer. We then focus on the executors of the splicing process. Based on a comprehensive catalog of splicing factor encoding genes and analyses of available gene expression and somatic mutation data, we identify cancer-associated patterns of dysregulation. Splicing factor genes are shown to be significantly differentially expressed between cancer and corresponding normal samples, and to have reduced inter-individual expression variation in cancer. Furthermore, we identify enrichment of predicted cancer-critical genes among the splicing factors. In addition to previously described oncogenic splicing factor genes, we propose 24 novel cancer-critical splicing factors predicted from somatic mutations.

MicroRNA Signaling Pathway Network in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is considered to be the most lethal and aggressive malignancy with high mortality and poor prognosis. Their responses to current multimodal therapeutic regimens are limited. It is urgently needed to identify the molecular mechanism underlying pancreatic oncogenesis. Twelve core signaling cascades have been established critical in PDAC tumorigenesis by governing a wide variety of cellular processes. MicroRNAs (miRNAs) are aberrantly expressed in different types of tumors and play pivotal roles as post-transcriptional regulators of gene expression. Here, we will describe how miRNAs regulate different signaling pathways that contribute to pancreatic oncogenesis and progression.

Identification of a non-coding KLF4 transcript generated from intron retention and downregulated in human hepatocellular carcinoma

The Krüppel-like factor 4 (KLF4) gene is related to various biological processes including stem cell reprogramming and tumorigenesis. In this study, we identified and characterized a non-coding transcript of KLF4, which was designated KLF4‑003, in human liver tissue samples. KLF4‑003 was identified in a number of cell lines by reverse transcription PCR and DNA sequencing. Its expression levels were determined in 54 pairs of human hepatocellular carcinoma (HCC) tissues and a number of HCC cell lines by real-time PCR (RT-PCR). Methylation status of KLF4‑003 CpG islands was determined by bisulfite sequencing. The regulatory effect of KLF4‑003 CpG islands hypermethylation in Hep3B cells was then validated by the 5-aza-dC demethylation treatment, followed by RT-PCR analysis. Receiver operating characteristic (ROC) curve was created to evaluate the diagnostic value for differentiating between HCC cancer and benign diseases. The association study between KLF4‑003 expression level and clinical traits of HCC patients was performed with SPSS. We found that KLF4‑003 was downregulated in 46 out of 54 HCC samples compared with their adjunct normal tissues. The reduced KLF4‑003 expression was significantly associated with HCC recurrence (P=0.045) in the follow-up of 31 HCC patients. Significant differences were detected between the methylation status of HCC specimens and their adjacent normal controls. Demethylation treatment significantly rescued the expression of KLF4‑003 in Hep3B cells. Such observation indicated that the CpG island hypermethylation was at least partially responsible for the downregulation of KLF4‑003 in HCC. The area under ROC curve for the prediction of HCC reached 0.803 (95% CI=0.719-0.886, P<0.001). Our results suggested that the expression of KLF4‑003 was epigenetically regulated by methylation status of a KLF4‑003 CpG island in HCC. The differential expression of KLF4‑003 might play an important role in HCC development and might serve as a potential biomarker for the diagnosis of HCC.

Krüppel-like factor 9 inhibits glioma cell proliferation and tumorigenicity via downregulation of miR-21

Krüppel-like factors (KLFs) are zinc finger-containing transcription factors that play key roles in the regulation of differentiation and development as well as biological processes central to the development of malignancies. Increasing evidence indicates that Krüppel-like factor 9 (KLF9) plays a critical role in regulating tumorigenesis. However, the biological role and molecular mechanism of KLF9 in glioma progression remain unclear. Herein, we found that KLF9 expression was strongly reduced in gliomas. Reduced KLF9 expression promoted glioma cell proliferation. Importantly, re-constitution of KLF9 expression inhibited glioma cell proliferation and tumor growth in vivo. Furthermore, we determined that KLF9 interacted with the miR-21 promoter, leading to suppression of miR-21 expression and cell cycle arrest. Taken together, our findings indicate a novel mechanism for KLF function in tumorigenesis and may also suggest new targets for clinical intervention in human cancer.

Single-cell RNA sequencing identifies extracellular matrix gene expression by pancreatic circulating tumor cells

Circulating tumor cells (CTCs) are shed from primary tumors into the bloodstream, mediating the hematogenous spread of cancer to distant organs. To define their composition, we compared genome-wide expression profiles of CTCs with matched primary tumors in a mouse model of pancreatic cancer, isolating individual CTCs using epitope-independent microfluidic capture, followed by single-cell RNA sequencing. CTCs clustered separately from primary tumors and tumor-derived cell lines, showing low-proliferative signatures, enrichment for the stem-cell-associated gene Aldh1a2, biphenotypic expression of epithelial and mesenchymal markers, and expression of Igfbp5, a gene transcript enriched at the epithelial-stromal interface. Mouse as well as human pancreatic CTCs exhibit a very high expression of stromal-derived extracellular matrix (ECM) proteins, including SPARC, whose knockdown in cancer cells suppresses cell migration and invasiveness. The aberrant expression by CTCs of stromal ECM genes points to their contribution of microenvironmental signals for the spread of cancer to distant organs.

Single-cell RNA sequencing identifies extracellular matrix gene expression by pancreatic circulating tumor cells

Circulating tumor cells (CTCs) are shed from primary tumors into the bloodstream, mediating the hematogenous spread of cancer to distant organs. To define their composition, we compared genome-wide expression profiles of CTCs with matched primary tumors in a mouse model of pancreatic cancer, isolating individual CTCs using epitope-independent microfluidic capture, followed by single-cell RNA sequencing. CTCs clustered separately from primary tumors and tumor-derived cell lines, showing low-proliferative signatures, enrichment for the stem-cell-associated gene Aldh1a2, biphenotypic expression of epithelial and mesenchymal markers, and expression of Igfbp5, a gene transcript enriched at the epithelial-stromal interface. Mouse as well as human pancreatic CTCs exhibit a very high expression of stromal-derived extracellular matrix (ECM) proteins, including SPARC, whose knockdown in cancer cells suppresses cell migration and invasiveness. The aberrant expression by CTCs of stromal ECM genes points to their contribution of microenvironmental signals for the spread of cancer to distant organs.

Regulation of EMT by KLF4 in gastrointestinal cancer

Gastrointestinal (GI) cancer is characterized by its aggressiveness, but the underlying mechanism is not fully understood. Studies reveal that epithelial to mesenchymal transition (EMT), which is regulated by a series of transcription factors and signaling pathways, is strongly associated with GI cancer cell proliferation, invasion and metastasis. Importantly, EMT is a product of crosstalk between signaling pathways. Krüppel-like factor 4 (KLF4), a zinc finger-type transcription factor, is decreased or lost in most GI cancers. By transcriptionally regulating its downstream target genes, KLF4 plays important roles of GI cancer tumorigenesis, proliferation and differentiation. In this review, we focus on the mechanism of KLF4 in GI cancer EMT, and demonstrate that through crosstalk with TGF-β, Notch, and Wnt signaling pathways, KLF4 negatively regulates EMT of GI cancers. Finally, we indicate the challenging new frontiers for KLF4 which contributes to better understanding of the mechanism of GI cancer aggressiveness.

XMD8-92 inhibits pancreatic tumor xenograft growth via a DCLK1-dependent mechanism

XMD8-92 is a kinase inhibitor with anti-cancer activity against lung and cervical cancers, but its effect on pancreatic ductal adenocarcinoma (PDAC) remains unknown. Doublecortin-like kinase1 (DCLK1) is upregulated in various cancers including PDAC. In this study, we showed that XMD8-92 inhibits AsPC-1 cancer cell proliferation and tumor xenograft growth. XMD8-92 treated tumors demonstrated significant downregulation of DCLK1 and several of its downstream targets (including c-MYC, KRAS, NOTCH1, ZEB1, ZEB2, SNAIL, SLUG, OCT4, SOX2, NANOG, KLF4, LIN28, VEGFR1, and VEGFR2) via upregulation of tumor suppressor miRNAs let-7a, miR-144, miR-200a-c, and miR-143/145; it did not however affect BMK1 downstream genes p21 and p53. These data taken together suggest that XMD8-92 treatment results in inhibition of DCLK1 and downstream oncogenic pathways (EMT, pluripotency, angiogenesis and anti-apoptotic), and is a promising chemotherapeutic agent against PDAC.

The early manifestation, tumor-specific occurrence and prognostic significance of TGFBR2 aberrant splicing in oral carcinoma

Alternative splicing is an important mechanism that can disrupt cell cycle control resulting in tumorigenesis. Although many alterations of Transforming Growth Factor Beta (TGFβ) signaling are reported in cancers, the role of splice aberrations in destabilizing this signaling is the least understood mechanism. In this study, we compared TGFBR2 alternative splicing events in potentially malignant oral disorders (PMDs) and oral squamous cell carcinoma (OSCC) samples with those in normal samples. Interestingly, there were five alternatively spliced forms of TGFBR2 with a deficient kinase domain in OSCCs. The TGFBR2 aberrant splicing was tumor-specific, suggesting that selective splicing out of TGFBR2 kinase domain could be a mechanism misused by cancer cells for evading TGFβ signaling-mediated anti-tumor activities. Moreover, these aberrant transcripts were present in PMDs as well, suggesting an early occurrence of these events during oral carcinogenesis and offering the possibility of early diagnosis of malignancy. Furthermore, OSCC patients who harbored these aberrantly spliced transcripts exhibited poor disease free survival (p=0.028) and poor overall survival (p=0.013). Thus, assessing the presence of these TGFBR2 transcripts can serve as a prognostic marker for oral cancer.

FOXM1 and its oncogenic signaling in pancreatic cancer pathogenesis

Pancreatic cancer is a devastating disease with an overall 5-year survival rate less than 5%. Multiple signaling pathways are implicated in the pathogenesis of pancreatic cancer, such as Wnt/β-catenin, Notch, Hedgehog, hypoxia-inducible factor, signal transducer and activator of transcription, specificity proteins/Krüppel-like factors, and Forkhead box (FOX). Recently, increasing evidence has demonstrated that the transcription factor FOXM1 plays important roles in the initiation, progression, and metastasis of a variety of human tumors, including pancreatic cancer. In this review, we focus on the current understanding of the molecular pathogenesis of pancreatic cancer with a special focus on the function and regulation of FOXM1 and rationale for FOXM1 as a novel molecular target for pancreatic cancer prevention and treatment.

Decreased Kruppel-like factor 4 (KLF4) expression may correlate with poor survival in gastric adenocarcinoma

Kruppel-like factors (KLFs) play either anti- or pro-proliferation roles in different human cancers. Here, we investigated the expression of KLF4 in gastric cancers and its correlation with clinicopathological parameters and overall survival. KLF4 expression was measured in 118 surgical specimens by immunohistochemical microarray assay. No association of cytoplasmic KLF4 expression with gender, TNM status, stage, survival, and pathological type was found. Using Kaplan-Meier analysis, significantly higher overall survival rate was observed in patients with high cytoplasmic KLF4 expression compared to low cytoplasmic KLF4 expression. Univariate analysis revealed that cytoplasmic KLF4 expression, grade, histological type, lymph node metastasis, and stages were correlated to longer overall survival. Our results suggest that KLF4 may play an anti-oncogenic role in gastric tumorigenesis.

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.

MicroRNA-137 represses Klf4 and Tbx3 during differentiation of mouse embryonic stem cells

MicroRNA-137 (miR-137) has been shown to play an important role in the differentiation of neural stem cells. Embryonic stem (ES) cells have the potential to differentiate into different cell types including neurons; however, the contribution of miR-137 in the maintenance and differentiation of ES cells remains unknown. Here, we show that miR-137 is mainly expressed in ES cells at the mitotic phase of the cell cycle and highly upregulated during differentiation. We identify that ES cell transcription factors, Klf4 and Tbx3, are downstream targets of miR-137, and we show that endogenous miR-137 represses the 3' untranslated regions of Klf4 and Tbx3. Transfection of ES cells with mature miR-137 RNA duplexes led to a significant reduction in cell proliferation and the expression of Klf4, Tbx3, and other self-renewal genes. Furthermore, we demonstrate that increased miR-137 expression accelerates differentiation of ES cells in vitro. Loss of miR-137 during ES cell differentiation significantly impeded neuronal gene expression and morphogenesis. Taken together, our results suggest that miR-137 regulates ES cell proliferation and differentiation by repressing the expression of downstream targets, including Klf4 and Tbx3.

DCLK1 regulates pluripotency and angiogenic factors via microRNA-dependent mechanisms in pancreatic cancer

Stem cell pluripotency, angiogenesis and epithelial-mesenchymal transition (EMT) have been shown to be significantly upregulated in pancreatic ductal adenocarcinoma (PDAC) and many other aggressive cancers. The dysregulation of these processes is believed to play key roles in tumor initiation, progression, and metastasis, and is contributory to PDAC being the fourth leading cause of cancer-related deaths in the US. The tumor suppressor miRNA miR-145 downregulates critical pluripotency factors and oncogenes and results in repressed metastatic potential in PDAC. Additionally, the miR-200 family regulates several angiogenic factors which have been linked to metastasis in many solid tumors. We have previously demonstrated that downregulation of DCLK1 can upregulate critical miRNAs in both in vitro and in vivo cancer models and results in downregulation of c-MYC, KRAS, NOTCH1 and EMT-related transcription factors. A recent report has also shown that Dclk1 can distinguish between normal and tumor stem cells in Apc (min/+) mice and that ablation of Dclk1(+) cells resulted in regression of intestinal polyps without affecting homeostasis. Here we demonstrate that the knockdown of DCLK1 using poly(lactide-co-glycolide)-encapsulated-DCLK1-siRNA results in AsPC1 tumor growth arrest. Examination of xenograft tumors revealed, (a) increased miR-145 which results in decreased pluripotency maintenance factors OCT4, SOX2, NANOG, KLF4 as well as KRAS and RREB1; (b) increased let-7a which results in decreased pluripotency factor LIN28B; and (c) increased miR-200 which results in decreased VEGFR1, VEGFR2 and EMT-related transcription factors ZEB1, ZEB2, SNAIL and SLUG. Specificity of DCLK1 post-transcriptional regulation of the downstream targets of miR-145, miR-200 and let-7a was accomplished utilizing a luciferase-based reporter assay. We conclude that DCLK1 plays a significant master regulatory role in pancreatic tumorigenesis through the regulation of multiple tumor suppressor miRNAs and their downstream pro-tumorigenic pathways. This novel concept of targeting DCLK1 alone has several advantages over targeting single pathway or miRNA-based therapies for PDAC.

Deficiency of Kruppel-like factor KLF4 in mammary tumor cells inhibits tumor growth and pulmonary metastasis and is accompanied by compromised recruitment of myeloid-derived suppressor cells

Increasing evidence indicates that myeloid-derived suppressor cells (MDSCs) negatively regulate immune responses during tumor progression, inflammation and infection. However, the underlying molecular mechanisms of their development and mobilization remain to be fully delineated. Kruppel-like factor KLF4 is a transcription factor that has an oncogenic function in breast cancer development, but its function in tumor microenvironment, a critical component for tumorigenesis, has not been examined. By using a spontaneously metastatic 4T1 breast cancer mouse model and an immunodeficient NOD/SCID mouse model, we demonstrated that KLF4 knockdown delayed tumor development and inhibited pulmonary metastasis, which accompanied by decreased accumulation of MDSCs in bone marrow, spleens and primary tumors. Mechanistically, we found that KLF4 knockdown resulted in a significant decrease of circulating GM-CSF, an important cytokine for MDSC biology. Consistently, recombinant GM-CSF restored the frequency of MDSCs in purified bone marrow cells incubated with conditioned medium from KLF4 deficient cells. In addition, we identified CXCL5 as a critical mediator to enhance the expression and function of GM-CSF. Reduced CXCL5 expression by KLF4 knockdown in primary tumors and breast cancer cells was correlated with a decreased GM-CSF expression in our mouse models. Finally, we found that CXCL5/CXCR2 axis facilitated MDSC migration and that anti-GM-CSF antibodies neutralized CXCL5-induced accumulation of MDSCs. Taken together, our data suggest that KLF4 modulates maintenance of MDSCs in bone marrow by inducing GM-CSF production via CXCL5 and regulates recruitment of MDSCs into the primary tumors through the CXCL5/CXCR2 axis, both of which contribute to KLF4-mediated mammary tumor development.

Attenuation of krüppel-like factor 4 facilitates carcinogenesis by inducing g1/s phase arrest in clear cell renal cell carcinoma

Krüppel-like factor 4 (KLF4) is a transcription factor with diverse functions in various cancer types; however, the function of KLF4 in clear cell renal cell carcinoma (ccRCC) carcinogenesis remains unknown. In this study, we initially examined KLF4 expression by using a cohort of surgically removed ccRCC specimens and cell lines. Results indicated that the transcription and translation of KLF4 were lower in ccRCC tissues than in patient-matched normal tissues. Furthermore, the KLF4 expression was significantly downregulated in the five ccRCC cell lines at protein and mRNA levels compared with that in normal renal proximal tubular epithelial cell lines (HKC). KLF4 downregulation was significantly correlated with tumor stage and tumor diameter. Promoter hypermethylation may contribute to its low expression. In addition, in vitro studies indicated that the KLF4 overexpression significantly inhibited proliferation in human ccRCC cell lines 786-O and ACHN. Moreover, the KLF4 overexpression arrested the cell cycle progress at the G1/S phase transition by upregulating p21^WAF1/CIP1 expression and downregulating cyclin D1 expression, KLF4 knockdown in HKC cells did the opposite. In vivo studies confirmed the anti-proliferative effect of KLF4. Our results suggested that KLF4 had an important function in suppressing the growth of ccRCC.

Dysregulated expression of FOXM1 isoforms drives progression of pancreatic cancer

The transcription factor Forkhead box M1 (FOXM1) plays important roles in oncogenesis. However, the expression statuses of FOXM1 isoforms and their impact on and molecular basis in oncogenesis are unknown. We sought to determine the identities of FOXM1 isoforms in and the impact of their expression on pancreatic cancer development and progression using human tissues, cell lines, and animal models. Overexpression of FOXM1 mRNA and protein was pronounced in human pancreatic tumors and cancer cell lines. We identified five FOXM1 isoforms present in pancreatic cancer: FOXM1a, FOXM1b, and FOXM1c along with two isoforms tentatively designated as FOXM1b1 and FOXM1b2 because they were closely related to FOXM1b. Interestingly, FOXM1c was predominantly expressed in pancreatic tumors and cancer cell lines, whereas FOXM1a expression was generally undetectable in them. Functional analysis revealed that FOXM1b, FOXM1b1, FOXM1b2, and FOXM1c, but not FOXM1a, promoted pancreatic tumor growth and metastasis. Consistently, FOXM1b, FOXM1b1, FOXM1b2, and FOXM1c activated transcription of their typical downstream genes. Also, Sp1 mechanistically activated the FOXM1 promoter, whereas Krüppel-like factor 4 (KLF4) repressed its activity. Finally, we identified an Sp1- and KLF4-binding site in the FOXM1 promoter and showed that both Sp1 and KLF4 protein bound directly to it. Deletion mutation of this binding site significantly attenuated the transcriptional regulation of the FOXM1 promoter positively by Sp1 and negatively by KLF4. We showed that overexpression of specific FOXM1 isoforms critically regulates pancreatic cancer development and progression by enhancing tumor cell invasion and metastasis. Our findings strongly suggest that targeting specific FOXM1 isoforms effectively attenuates pancreatic cancer development and progression.

Shaking the family tree: identification of novel and biologically active alternatively spliced isoforms across the KLF family of transcription factors

Alternative splicing represents a unique post-transcriptional mechanism that increases the complexity of the eukaryotic proteome-generating protein isoforms whose functions can be novel, diverse, and/or even antagonistic when compared to its full-length transcript. The KLF family of genes consists of ≥17 members, which are involved in the regulation of numerous critical cellular processes, including differentiation, cell proliferation, growth-related signal transduction, angiogenesis, and apoptosis. Using a strategy based on RT-PCR, selective cloning, and promoter-based assays of cancer-relevant genes, we identify and characterize the existence of multiple biologically active KLF splice forms across the entire family of proteins. We demonstrate biological function for a number of these isoforms. Furthermore, we highlight a possible functional interaction between full-length KLF4 and one of its splice variants in up-regulating cellular proliferation. Taken together, this report identifies for the first time a more complete view of the genomic and proteomic breadth and complexity of the KLF transcription factor family, revealing the existence of highly expressed and biologically active isoforms previously uncharacterized. In essence, knowing that these KLF isoforms exist provides the first step toward understanding the roles of these genes in human health and disease.

Klf4 transcription factor is expressed in the cytoplasm of prostate cancer cells

BACKGROUND

Cancer initiation and progression might be driven by small populations of cells endowed with stem cell-like properties. Here we comparatively addressed the expression of genes encoding putative stemness regulators including c-Myc, Klf4, Nanog, Oct4A and Sox2 genes in benign prostatic hyperplasia (BPH) and prostate cancer (PCA).

METHODS

Fifty-eight PCA and thirty-nine BPH tissues samples were used for gene expression analysis, as evaluated by quantitative real-time polymerase chain reaction (qRT-PCR). The expression of specific Klf4 isoforms was tested by conventional PCR. Klf4 specific antibodies were used for protein detection in a tissue microarray including 404 prostate samples.

RESULTS

Nanog, Oct4A and Sox2 genes were comparably expressed in BPH and PCA samples, whereas c-Myc and Klf4 genes were expressed to significantly higher extents in PCA than in BPH specimens. Immunohistochemical studies revealed that Klf4 protein is detectable in a large majority of epithelial prostatic cells, irrespective of malignant transformation. However, in PCA, a predominantly cytoplasmic location was observed, consistent with the expression of a differentially spliced Klf4α isoform.

CONCLUSION

Klf4 is highly expressed at gene and protein level in BPH and PCA tissues but a cytoplasmic location of the specific gene product is predominantly detectable in malignant cells. Klf4 location might be of critical relevance to steer its functions during oncogenesis.

Dysregulated Krüppel-like factor 4 and vitamin D receptor signaling contribute to progression of hepatocellular carcinoma

BACKGROUND & AIMS

Krüppel-like factor 4 (KLF4) is a transcription factor and putative tumor suppressor. However, little is known about its effects in hepatocellular carcinogenesis. We investigated the clinical significance, biologic effects, and mechanisms of dysregulated KLF4 signaling.

METHODS

We performed microarray analysis of hepatocellular carcinoma (HCC) tissues. We used molecular biology analyses and animal models to evaluate activation and function of KLF4-vitamin D receptor (VDR) pathway.

RESULTS

Expression of KLF4 protein was decreased or lost in primary HCC samples, in particular, lymph node metastases, compared with normal liver tissues. Loss of KLF4 from primary tumors was significantly associated with reduced survival time and was identified as a prognostic marker. Most human HCC cell lines had losses or substantial decreases in levels of KLF4. Exogenous expression of KLF4 in HCC cells upregulated expression of mesenchymal-epithelial transition (MET) and inhibited their migration, invasion, and proliferation in vitro. When these cells were injected into mice, tumors grew more slowly and metastasis was inhibited, compared with HCC cells that did not express KLF4. VDR is a direct transcriptional target of KLF4; we identified 2 sites in the VDR promoter that bound specifically to KLF4. Increased expression of VDR sensitized tumor cells to the inhibitory effects of vitamin D.

CONCLUSIONS

KLF4 binds to the promoter of VDR to regulate its expression; levels of KLF4 are reduced and levels of VDR are increased in HCC cell lines and primary tumor samples. Expression of KLF4 in HCC cells sensitizes them to the anti-proliferative effects of VD3. This pathway might be manipulated to prevent or treat liver cancer.

Expression of Kruppel-like factor KLF4 in mouse hair follicle stem cells contributes to cutaneous wound healing

Background

Kruppel-like factor KLF4 is a transcription factor critical for the establishment of the barrier function of the skin. Its function in stem cell biology has been recently recognized. Previous studies have revealed that hair follicle stem cells contribute to cutaneous wound healing. However, expression of KLF4 in hair follicle stem cells and the importance of such expression in cutaneous wound healing have not been investigated.

Methodology/Principal Findings

Quantitative real time polymerase chain reaction (RT-PCR) analysis showed higher KLF4 expression in hair follicle stem cell-enriched mouse skin keratinocytes than that in control keratinocytes. We generated KLF4 promoter-driven enhanced green fluorescence protein (KLF4/EGFP) transgenic mice and tamoxifen-inducible KLF4 knockout mice by crossing KLF4 promoter-driven Cre recombinase fused with tamoxifen-inducible estrogen receptor (KLF4/CreER™) transgenic mice with KLF4(flox) mice. KLF4/EGFP cells purified from dorsal skin keratinocytes of KLF4/EGFP transgenic mice were co-localized with 5-bromo-2'-deoxyuridine (BrdU)-label retaining cells by flow cytometric analysis and immunohistochemistry. Lineage tracing was performed in the context of cutaneous wound healing, using KLF4/CreER™ and Rosa26RLacZ double transgenic mice, to examine the involvement of KLF4 in wound healing. We found that KLF4 expressing cells were likely derived from bulge stem cells. In addition, KLF4 expressing multipotent cells migrated to the wound and contributed to the wound healing. After knocking out KLF4 by tamoxifen induction of KLF4/CreER™ and KLF4(flox) double transgenic mice, we found that the population of bulge stem cell-enriched population was decreased, which was accompanied by significantly delayed cutaneous wound healing. Consistently, KLF4 knockdown by KLF4-specific small hairpin RNA in human A431 epidermoid carcinoma cells decreased the stem cell population and was accompanied by compromised cell migration.

Conclusions/Significance

KLF4 expression in mouse hair bulge stem cells plays an important role in cutaneous wound healing. These findings may enable future development of KLF4-based therapeutic strategies aimed at accelerating cutaneous wound closure.