Induction of KLF4 in basal keratinocytes blocks the proliferation-differentiation switch and initiates squamous epithelial dysplasia

Klf4 deficiency exacerbates myocardial ischemia/reperfusion injury in mice via enhancing ROCK1/DRP1 pathway-dependent mitochondrial fission

RATIONAL

Excessive mitochondrial fission is considered key process involved in myocardial ischemia/reperfusion (I/R) injury. However, the upstream mechanism remains largely unclear. Decreased level of Kruppel Like Factor 4 (KLF4) has been implicated in the pathogenesis of mitochondrial dysfunction and heart's adaption to stress. However, the role of Klf4 in I/R process is not fully elucidated. This study aims to investigate how Klf4 regulates mitochondrial dynamics and further clarify its underlying mechanism during cardiac I/R injury.

METHODS

Loss-of-function and gain-of-function strategies were applied to investigate the role of Klf4 in cardiac I/R injury via genetic ablation or intra-myocardial adenovirus injection. Mitochondrial dynamics was analyzed by confocal microscopy in vitro and transmission electron microscopy in vivo. Chromatin immunoprecipitation and luciferase reporter assay were performed to explore the underlying mechanisms.

RESULTS

KLF4 was downregulated in I/R heart. Cardiac-specific Klf4 knockout significantly exacerbated cardiac dysfunction in I/R mice. Mechanistically, Klf4 deficiency aggravated mitochondrial apoptosis, reduced ATP generation and boosted ROS overproduction via enhancing DRP1-dependent mitochondrial fission. ROCK1 was identified as a kinase regulating DRP1 activity at Ser616. Klf4 deficiency upregulated the expression of ROCK1 at transcriptional level, thus increasing S616-DRP1-mediated mitochondrial fission during I/R. Finally, reconstitution of Klf4 inhibited mitochondrial fission, restored mitochondrial function and alleviated I/R injury.

CONCLUSION

Our study provides the first evidence that Klf4 deficiency exacerbates myocardial I/R injury through regulating ROCK1 expression at transcriptional level to induce DRP1-mediated mitochondrial fission. Targeting mitochondrial dynamics by restoring Klf4 might be potentially cardio-protective strategies attenuating I/R injury.

The prognostic role of combining Krüppel-like factor 4 score and grade of inflammation in a Norwegian cohort of oral tongue squamous cell carcinomas

Krüppel-like factor 4 (KLF4) is a zinc-finger transcription factor involved in inflammation, cancer development, and progression. However, the relationship between KLF4, inflammation, and prognosis in oral cancer is not fully understood. KLF4 expression levels were examined in a multicenter cohort of 128 oral squamous cell carcinoma (OSCC) specimens from the tongue (OTSCC) using immunohistochemistry. In two external KLF4 mRNA datasets (The Cancer Genome Atlas/The Genotype-Tissue Expression Portal), lower KLF4 mRNA expression was found in OSCC and head and neck squamous cell carcinomas (HNSCC) than in control oral epithelium. These data indicate that down-regulation of KLF4 mRNA is linked to OSCC/HNSCC progression. Using Cox-multivariate analysis, a significantly favorable 5-year disease-specific survival rate was observed for a subgroup of patients with a combination of high levels of KLF4 expression and inflammation. OSCC cell lines exposed to IFN-γ showed a significant upregulation of nuclear KLF4 expression, indicating a link between inflammation and KLF4 expression in OSCC. Overall, the current data suggest a functional link between KLF4 and inflammation. The combination of high KLF4 nuclear expression and marked/moderate stromal inflammation might be useful as a favorable prognostic marker for a subgroup of OTSCC patients.

Prognostic significance of KLF4 in solid tumours: an updated meta-analysis

Background

Kruppel-like factor 4 (KLF4) is a zinc finger-containing transcription factor predominantly expressed in terminally differentiated epithelial tissues. Many studies have shown that KLF4 has various mechanisms in different tumours; however, the prognostic role of KLF4 remains unclear.

Methods and results

We searched the relevant literature that evaluated the prognostic value of KLF4 in different cancers, and the original survival data were obtained from the text, tables or Kaplan–Meier curves for both comparative groups. Thirty studies were included in this meta-analysis, and a total of 10 malignant tumours were involved. The expression of KLF4 was not associated with the prognosis for overall survival (hazard ratio(HR)0.86, 95% confidence interval (CI): 0.65–1.13, P = 0.28), disease-free survival/recurrence-free survival/metastasis-free survival (HR 0.87, 95% CI: 0.52–1.44, P = 0.58) or disease-specific survival (HR 1.13, 95% CI: 0.44–2.87, P = 0.8).

Conclusion

This study showed that the expression of KLF4 was not related to the prognosis of the tumours that were included in the study.

Transcription factors Krüppel-like factor 4 and paired box 5 regulate the expression of the Grainyhead-like genes

Genes from the Grainyhead-like (GRHL) family code for transcription factors necessary for the development and maintenance of various epithelia. These genes are also very important in the development of many types of cancer. However, little is known about the regulation of expression of GRHL genes. Previously, there were no systematic analyses of the promoters of GRHL genes or transcription factors that bind to these promoters. Here we report that the Krüppel-like factor 4 (KLF4) and the paired box 5 factor (PAX5) bind to the regulatory regions of the GRHL genes and regulate their expression. Ectopic expression of KLF4 or PAX5 alters the expression of GRHL genes. In KLF4-overexpressing HEK293 cells, the expression of GRHL1 and GRHL3 genes was upregulated by 32% and 60%, respectively, whereas the mRNA level of GRHL2 gene was lowered by 28% when compared to the respective controls. The levels of GRHL1 and GRHL3 expression were decreased by 30% or 33% in PAX5-overexpressing HEK293 cells. The presence of minor frequency allele of single nucleotide polymorphism rs115898376 in the promoter of the GRHL1 gene affected the binding of KLF4 to this site. The evidence presented here suggests an important role of KLF4 and PAX5 in the regulation of expression of GRHL1-3 genes.

PIK3CA and CCM mutations fuel cavernomas through a cancer-like mechanism

Vascular malformations are thought to be monogenic disorders that result in dysregulated growth of blood vessels. In the brain, cerebral cavernous malformations (CCMs) arise owing to inactivation of the endothelial CCM protein complex, which is required to dampen the activity of the kinase MEKK31-4. Environmental factors can explain differences in the natural history of CCMs between individuals5, but why single CCMs often exhibit sudden, rapid growth, culminating in strokes or seizures, is unknown. Here we show that growth of CCMs requires increased signalling through the phosphatidylinositol-3-kinase (PI3K)-mTOR pathway as well as loss of function of the CCM complex. We identify somatic gain-of-function mutations in PIK3CA and loss-of-function mutations in the CCM complex in the same cells in a majority of human CCMs. Using mouse models, we show that growth of CCMs requires both PI3K gain of function and CCM loss of function in endothelial cells, and that both CCM loss of function and increased expression of the transcription factor KLF4 (a downstream effector of MEKK3) augment mTOR signalling in endothelial cells. Consistent with these findings, the mTORC1 inhibitor rapamycin effectively blocks the formation of CCMs in mouse models. We establish a three-hit mechanism analogous to cancer, in which aggressive vascular malformations arise through the loss of vascular 'suppressor genes' that constrain vessel growth and gain of a vascular 'oncogene' that stimulates excess vessel growth. These findings suggest that aggressive CCMs could be treated using clinically approved mTORC1 inhibitors.

Molecular genetics of meningiomas

Comprehensive genomic studies of meningioma have offered important insights about the molecular mechanisms underlying this common brain tumor. The use of next-generation sequencing techniques has identified driver mutations in approximately 80% of benign sporadic lesions, as well as epigenetic, regulatory, and copy number events that are associated with formation and disease progression. The events described to date fall into five mutually exclusive molecular subgroups that correlate with tumor location and embryological origin. Importantly, these subgroups also carry implications for clinical management, as they are predictive of histologic subtype and the likelihood of progression. Further work is necessary to understand the molecular mechanisms by which identified mutations drive tumorigenesis as well as the genomic pathways that transform benign lesions into malignancies. Progress made during the past decade has opened the door to potential molecular therapies as well as integration of meningioma genotyping data into clinical management decisions. Several pharmacologic trials are currently underway that leverage recent genomic findings to target established oncogenic pathways in refractory tumors. With the combined efforts of physicians and basic science investigators, the clinical management of meningioma will continue to make important strides in the coming years.

The preventive and therapeutic effects of AAV1-KLF4-shRNA in cigarette smoke-induced pulmonary hypertension

We found previously that KLF4 expression was up-regulated in cultured rat and human pulmonary artery smooth muscle cells (PASMCs) exposed to cigarette smoke (CS) extract and in pulmonary artery from rats with pulmonary hypertension induced by CS. Here, we aim to investigate whether CS-induced pulmonary hypertension (PH) is prevented and ameliorated by targeted pulmonary vascular gene knockdown of KLF4 via adeno-associated virus 1 (AAV1)-KLF4-shRNA in vivo in rat model. The preventive and therapeutic effects were observed according to the different time-point of AAV1-KLF4-shRNA intratracheal administration. We tested haemodynamic measurements of systemic and pulmonary circulations and observed the degree of pulmonary vascular remodelling. In the preventive experiment, KLF4 expression and some pulmonary circulation hemodynamic measurements such as right ventricular systolic pressure (RVSP), mean right ventricular pressure (mRVP), peak RV pressure rate of rise (dP/dt max) and right ventricle (RV) contractility index were increased significantly in the CS-induced PH model. While in the prevention group (AAV1-KLF4-shRNA group), RVSP, mRVP, dP/dt max and RV contractility index which are associated with systolic function of right ventricle decreased and the degree of pulmonary vascular remodelling relieved. In the therapeutic experiment, we observed a similar trend. Our findings emphasize the feasibility of sustained pulmonary vascular KLF4 gene knockdown using intratracheal delivery of AAV1 in an animal model of cigarette smoke-induced PH and determined gene transfer of KLF4-shRNA could prevent and ameliorate the progression of PH.

New insight into the significance of KLF4 PARylation in genome stability, carcinogenesis, and therapy

KLF4 plays a critical role in determining cell fate responding to various stresses or oncogenic signaling. Here, we demonstrated that KLF4 is tightly regulated by poly(ADP-ribosyl)ation (PARylation). We revealed the subcellular compartmentation for KLF4 is orchestrated by PARP1-mediated PARylation. We identified that PARylation of KLF4 is critical to govern KLF4 transcriptional activity through recruiting KLF4 from soluble nucleus to the chromatin. We mapped molecular motifs on KLF4 and PARP1 that facilitate their interaction and unveiled the pivotal role of the PBZ domain YYR motif (Y430, Y451 and R452) on KLF4 in enabling PARP1-mediated PARylation of KLF4. Disruption of KLF4 PARylation results in failure in DNA damage response. Depletion of KLF4 by RNA interference or interference with PARP1 function by KLF4YYR/AAA (a PARylation-deficient mutant) significantly sensitizes breast cancer cells to PARP inhibitors. We further demonstrated the role of KLF4 in modulating homologous recombination through regulating BRCA1 transcription. Our work points to the synergism between KLF4 and PARP1 in tumorigenesis and cancer therapy, which provides a potential new therapeutic strategy for killing BRCA1-proficient triple-negative breast cancer cells.

Latest Advances for the Sleeping Beauty Transposon System: 23 Years of Insomnia but Prettier than Ever: Refinement and Recent Innovations of the Sleeping Beauty Transposon System Enabling Novel, Nonviral Genetic Engineering Applications

The Sleeping Beauty transposon system is a nonviral DNA transfer tool capable of efficiently mediating transposition-based, stable integration of DNA sequences of choice into eukaryotic genomes. Continuous refinements of the system, including the emergence of hyperactive transposase mutants and novel approaches in vectorology, greatly improve upon transposition efficiency rivaling viral-vector-based methods for stable gene insertion. Current developments, such as reversible transgenesis and proof-of-concept RNA-guided transposition, further expand on possible applications in the future. In addition, innate advantages such as lack of preferential integration into genes reduce insertional mutagenesis-related safety concerns while comparably low manufacturing costs enable widespread implementation. Accordingly, the system is recognized as a powerful and versatile tool for genetic engineering and is playing a central role in an ever-expanding number of gene and cell therapy clinical trials with the potential to become a key technology to meet the growing demand for advanced therapy medicinal products.

Nanomedicine-Based Approaches for mRNA Delivery

Messenger RNA (mRNA) has immense potential for developing a wide range of therapies, including immunotherapy and protein replacement. As mRNA presents no risk of integration into the host genome and does not require nuclear entry for transfection, which allows protein production even in nondividing cells, mRNA-based approaches can be envisioned as safe and practical therapeutic strategies. Nevertheless, mRNA presents unfavorable characteristics, such as large size, immunogenicity, limited cellular uptake, and sensitivity to enzymatic degradation, which hinder its use as a therapeutic agent. While mRNA stability and immunogenicity have been ameliorated by direct modifications on the mRNA structure, further improvements in mRNA delivery are still needed for promoting its activity in biological settings. In this regard, nanomedicine has shown the ability for spatiotemporally controlling the function of a myriad of bioactive agents in vivo. Direct engineering of nanomedicine structures for loading, protecting, and releasing mRNA and navigating in biological environments can then be applied for promoting mRNA translation toward the development of effective treatments. Here, we review recent approaches aimed at enhancing mRNA function and its delivery through nanomedicines, with particular emphasis on their applications and eventual clinical translation.

Cancer Stem Cell Subpopulations Are Present Within Metastatic Head and Neck Cutaneous Squamous Cell Carcinoma

Cancer stem cells (CSCs) have been identified in many cancer types including primary head and neck cutaneous squamous cell carcinoma (HNcSCC). This study aimed to identify and characterize CSCs in metastatic HNcSCC (mHNcSCC). Immunohistochemical staining performed on mHNcSCC samples from 15 patients demonstrated expression of the induced pluripotent stem cell (iPSC) markers OCT4, SOX2, NANOG, KLF4, and c-MYC in all 15 samples. In situ hybridization and RT-qPCR performed on four of these mHNcSCC tissue samples confirmed transcript expression of all five iPSC markers. Immunofluorescence staining performed on three of these mHNcSCC samples demonstrated expression of c-MYC on cells within the tumor nests (TNs) and the peri-tumoral stroma (PTS) that also expressed KLF4. OCT4 was expressed on the SOX2+/NANOG+/KLF4+ cells within the TNs, and the SOX2+/NANOG+/KLF4+ cells within the PTS. RT-qPCR demonstrated transcript expression of all five iPSC markers in all three mHNcSCC-derived primary cell lines, except for SOX2 in one cell line. Western blotting showed the presence of SOX2, KLF4, and c-MYC but not OCT4 and NANOG in the three mHNcSCC-derived primary cell lines. All three cell lines formed tumorspheres, at the first passage. We demonstrated an OCT4+/NANOG+/SOX2+/KLF4+/c-MYC+ CSC subpopulation and an OCT4+/NANOG-/SOX2+/KLF4+/c-MYC+ subpopulation within the TNs, and an OCT4+/NANOG+/SOX2+/KLF4+/c-MYC+ subpopulation within the PTS of mHNcSCC.

Reactivation of super-enhancers by KLF4 in human Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinoma (HNSCC) is a disease of significant morbidity and mortality and rarely diagnosed in early stages. Despite extensive genetic and genomic characterization, targeted therapeutics and diagnostic markers of HNSCC are lacking due to the inherent heterogeneity and complexity of the disease. Herein, we have generated the global histone mark based epigenomic and transcriptomic cartogram of SCC25, a representative cell type of mesenchymal HNSCC and its normal oral keratinocyte counterpart. Examination of genomic regions marked by differential chromatin states and associated with misregulated gene expression led us to identify SCC25 enriched regulatory sequences and transcription factors (TF) motifs. These findings were further strengthened by ATAC-seq based open chromatin and TF footprint analysis which unearthed Krüppel-like Factor 4 (KLF4) as a potential key regulator of the SCC25 cistrome. We reaffirm the results obtained from in silico and chromatin studies in SCC25 by ChIP-seq of KLF4 and identify ΔNp63 as a co-oncogenic driver of the cancer-specific gene expression milieu. Taken together, our results lead us to propose a model where elevated KLF4 levels sustains the oncogenic state of HNSCC by reactivating repressed chromatin domains at key downstream genes, often by targeting super-enhancers.

Cancer stem cell subpopulations in moderately differentiated head and neck cutaneous squamous cell carcinoma

Cancer stem cells (CSC), the putative origin of cancer, account for local recurrence and metastasis. We aimed to identify and characterize CSCs within moderately differentiated head and neck cutaneous squamous cell carcinoma (MDHNCSCC).

Formalin-fixed paraffin-embedded MDHNCSCC sections of ten patients underwent 3,3-diaminobenzidine (DAB) immunohistochemical (IHC) staining for induced pluripotent stem cell (iPSC) markers OCT4, NANOG, SOX2, KLF4 and c-MYC. Localization of these markers was investigated using immunofluorescence (IF) IHC staining of three of these MDHNCSCC samples. mRNA expression of these iPSC markers in the MDHNCSCC tissue samples was determined by colorimetric in-situ hybridization (CISH, n = 6), and reverse-transcription quantitative polymerase chain reaction (RT-qPCR, n = 4). RT-qPCR was also performed on four MDHNCSCC-derived primary cell lines.

DAB IHC staining demonstrated expression of all five iPSC markers within all ten MDHNCSCC tissues samples. CISH and RT-qPCR confirmed mRNA expression of all five iPSC markers within all MDHNCSCC tissues samples examined. RT-PCR demonstrated mRNA transcripts of all five iPSC markers in all four MDHNCSCC-derived primary cell lines.

IF IHC staining showed co-expression of OCT4 with SOX2 and KLF4 throughout the tumor nests (TNs) and peri-tumoral stroma (PTS). There was an OCT4⁺/NANOG⁺ subpopulation within the TNs, and an OCT4⁺/NANOG⁻ subpopulation and an OCT4⁺/NANOG⁺ subpopulation within the PTS. All iPSC markers were expressed by the endothelium of microvessels within the PTS.

Our findings suggest the presence of an OCT4⁺/NANOG⁺/SOX2⁺/KLF4⁺/c-MYC⁺ CSC subpopulation within the TNs, PTS and endothelium of microvessels within the PTS; and an OCT4⁺/NANOG⁻/SOX2⁺/KLF4⁺/c-MYC⁺ subpopulation exclusively within the PTS in MDHNCSCC. These CSC subpopulations could be a potential novel therapeutic target for treatment of MDHNCSCC.

Identification of candidate biomarkers correlated with the diagnosis and prognosis of cervical cancer via integrated bioinformatics analysis

Background: Cervical carcinoma is one of the most common malignant gynecological tumors and is associated with high rates of morbidity and mortality. Early diagnosis and early treatment can reduce the mortality rate of cervical cancer. However, there is still no specific biomarkers for the diagnosis and detection of cervical cancer prognosis. Therefore, it is greatly urgent in searching biomarkers correlated with the diagnosis and prognosis of cervical cancer.

Results: The mRNA and microRNA expression profile datasets (GSE7803, GSE9750, GSE63514, and GSE30656) were downloaded from the Gene Expression Omnibus database (GEO). The three microarray datasets were integrated to one via integrated bioinformatics. Differentially expressed genes (DEGs) and microRNAs (DEMs) were obtained by R software. The protein–protein interaction (PPI) networks of the DEGs were performed from the STRING database and further visualized by Cytoscape software. A total of 83 DEGs and 14 DEMs were screened from the microarray expression profile datasets. The miRNAs validated to be associated with cervical cancer were obtained using HMDD online website and the target genes of DEMs were identified using the miRWalk2.0 online database. ESR1, PPP1R3C, NSG1, and TMPRSS11D were the gene targets of hsa-miR-21; the targets of hsa-miR-16 were GYS2, ENDOU, and KLF4. These targets were all downregulated in cervical cancer. Finally, we verified the expression of those targets in cervical tissues from TCGA and GTEx databases and analyzed their relationship with survival of cervical cancer patients. In the end, the expression of key genes in cervical cancer tissues was verified via experiment method, we found KLF4 and ESR1 were downregulated in tumor tissues.

Conclusion: This study indicates that KLF4 and ESR1 are downregulated by the upregulated miR21 and miRNA16 in cervical cancer, respectively, using bioinformatics analysis, and the lower expression of KLF4 and ESR1 is closely related to the poor prognosis. They might be of clinical significance for the diagnosis and prognosis of cervical cancer, and provide effective targets for the treatment of cervical cancer.

Polo-Like Kinase 1 phosphorylates and stabilizes KLF4 to promote tumorigenesis in nasopharyngeal carcinoma

Rationale: Advanced nasopharyngeal carcinoma (NPC) is an aggressive disease with no targeted therapies and poor outcomes. New innovative targets are urgently needed. KLF4 has been extensively studied in the context of tumors, and current data suggest that it can act as either a tissue-specific tumor-inhibiting or a tumor-promoting gene. Here, we found that KLF4 played as a tumor-promoting gene in NPC, and could be mediated by PLK1. Methods: Tissue immunohistochemistry (IHC) assay was performed to identify the role of KLF4 in NPC. Global gene expression experiments were performed to explore the molecular mechanisms underlying KLF4-dependent tumorigenesis. Small-molecule kinase inhibitor screening was performed to identify potential upstream kinases of KLF4. The pharmacologic activity of polo-like kinase inhibitor volasertib (BI6727) in vitro and in vivo was determined. Result: Our investigation showed that high expression of KLF4 was correlated with poor prognosis in NPC. Moreover, genome-wide profiling revealed that KLF4 directly activated oncogenic programmes, including gene sets associated with KRAS, VEGF, and MYC signalling. We further found that inhibition of polo-like kinase 1 could downregulate the expression of KLF4 and that PLK1 directly phosphorylated KLF4 at Ser234. Notably, phosphorylation of KLF4 by PLK1 caused the recruitment and binding of the E3 ligase TRAF6, which resulted in KLF4 K32 K63-linked ubiquitination and stabilization. Moreover, KLF4 could enhance TRAF6 expression at the transcriptional level, thus initiating a KLF4-TRAF6 feed-forward loop. Treatment with the PLK1 inhibitor volasertib (BI6727) significantly inhibited tumor growth in nude mice. Conclusion: Our study unveiled a new PLK1-TRAF6-KLF4 feed-forward loop. The resulting increase in KLF4 ubiquitination leads to stabilization and upregulation of KLF4, which leads to tumorigenesis in NPC. These results expand our understanding of the role of KLF4 in NPC and validate PLK1 inhibitors as potential therapeutic agents for NPC, especially cancer patients with KLF4 overexpression.

Monomethyltransferase SET8 facilitates hepatocellular carcinoma growth by enhancing aerobic glycolysis

Hepatocellular carcinoma (HCC) is one of the most aggressive cancers worldwide. Despite such a public health importance, efficient therapeutic agents are still lacking for this malignancy. Most tumor cells use aerobic glycolysis to sustain anabolic growth, including HCC, and the preference of glycolysis often leads to a close association with poorer clinical outcomes. The histone methyltransferase SET8 plays crucial roles in controlling cell-cycle progression, transcription regulation, and tumorigenesis. However, it remains largely undefined whether SET8 affects the glucose metabolism in HCC. Here, we report that upregulation of SET8 is positively correlated with a poor survival rate in HCC patients. Both in vitro and in vivo studies revealed that SET8 deficiency conferred an impaired glucose metabolism phenotype and thus inhibited the progression of HCC tumors. By contrast, SET8 overexpression aggravated the glycolytic alterations and tumor progression. Mechanistically, SET8 directly binds to and inactivates KLF4, resulting in suppression of its downstream SIRT4. We also provided further evidence that mutations in SET8 failed to restrain the transactivation of SIRT4 by KLF4. Our data collectively uncover a novel mechanism of SET8 in mediating glycolytic metabolism in HCC cells and may provide a basis for targeting SET8 as a therapeutic strategy in HCC.

Messenger RNA Delivery for Tissue Engineering and Regenerative Medicine Applications

The ability to control cellular processes and precisely direct cellular reprogramming has revolutionized regenerative medicine. Recent advances in in vitro transcribed (IVT) mRNA technology with chemical modifications have led to development of methods that control spatiotemporal gene expression. Additionally, there is a current thrust toward the development of safe, integration-free approaches to gene therapy for translational purposes. In this review, we describe strategies of synthetic IVT mRNA modifications and nonviral technologies for intracellular delivery. We provide insights into the current tissue engineering approaches that use a hydrogel scaffold with genetic material. Furthermore, we discuss the transformative potential of novel mRNA formulations that when embedded in hydrogels can trigger controlled genetic manipulation to regenerate tissues and organs in vitro and in vivo. The role of mRNA delivery in vascularization, cytoprotection, and Cas9-mediated xenotransplantation is additionally highlighted. Harmonizing mRNA delivery vehicle interactions with polymeric scaffolds can be used to present genetic cues that lead to precise command over cellular reprogramming, differentiation, and secretome activity of stem cells-an ultimate goal for tissue engineering.

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.

A SIRT1-centered circuitry regulates breast cancer stemness and metastasis

Cancer stem cell (CSC)-dictated intratumor heterogeneity accounts for the majority of drug-resistance and distant metastases of breast cancers. Here, we identify a SIRT1-PRRX1-KLF4-ALDH1 circuitry, which couples CSCs, chemo-resistance, metastasis and aging. Pro-longevity protein SIRT1 deacetylates and stabilizes the epithelial-to-mesenchymal-transition (EMT) inducer PRRX1, which inhibits the transcription of core stemness factor KLF4. Loss of SIRT1 destabilizes PRRX1, disinhibits KLF4, and activates the transcription of ALDH1, which induces and functionally marks CSCs, resulting in chemo-resistance and metastatic relapse. Clinically, the level of PRRX1 is positively linked to SIRT1, whereas KLF4 is reversely correlated. Importantly, KLF4 inhibitor Kenpaullone sensitizes breast cancer cells and xenograft tumors to Paclitaxel and improves therapeutic effects. Our findings delineate a SIRT1-centered circuitry that regulates CSC origination, and targeting this pathway might be a promising therapeutic strategy.

Ablation of NTPDase2+ cells inhibits the formation of filiform papillae in tongue tip

BACKGROUND

Lingual epithelia in the tongue tip are among the most rapidly regenerating tissues, but the mechanism of cell genesis in this tissue is still unknown. Previous study has suggested the existence of multiple stem cell pools in lingual epithelia and papillae. Like K14+ and Sox2+ cells, NTPDase2+ cells have characteristics of stem cells.

METHODS

We employed a system using doxycycline to conditionally ablate NTPDase2+ cells in lingual epithelia and papillae by regulated expression of the diphtheria toxin A (DTA) gene. Transgenic lines, which expressed the rtTA gene in NTPDase2+ cells, were produced by pronuclear injection of zygotes from C57BL/6 mice using the BAC clone RP23-47P18. The NTPDase2-rtTA transgenic mice were crossed with the TetO-DTA transgenic animals. The double transgenic mice were treated with doxycycline. Doxycycline (Dox) was diluted in 5% sucrose in water to a final concentration of 0.3-0.5 mg/mL and supplied as drinking water.

RESULTS

After 15 days of Dox induction, the expression of NTPDase2, Sox2 and K14 was ablated from lingual epithelia. DTA expression in NTPDase2+ cells did not inhibit the turnover of GNAT3+ or PLCβ2+ cells in taste buds, nor the expression of S100β beneath lingual epithelia and papillae. After 35 days ablation of NTPDase2+ cells, the basic structure of lingual epithelia and papillae remained intact. However, the ratio of cell to total tissue area was decreased in lingual epithelia and circumvallate (CV) papillae. DTA expression also inhibited the regeneration of filiform papillae on the dorsal surface of the tongue tip.

CONCLUSIONS

These studies provide important insights into the understanding of dynamic equilibrium among the multiple stem cell populations present in the lingual epithelia and papillae.

Role of Krüppel-like factor 4 in cigarette smoke-induced pulmonary vascular remodeling

Pulmonary hypertension (PH) is characterized by excessive proliferation of pulmonary artery smooth muscle cells (PASMCs), leading to dysregulated vascular remodeling. Cigarette smoke (CS) is a common risk factor causing PH, and our previous study showed that CS extract (CSE) stimulated abnormal PASMC proliferation. However, the molecular mechanism remains unclear. In systemic circulation, vascular remodeling in some diseases is associated with upregulation of Krüppel-like factor 4 (KLF4), which stimulates the proliferation of vascular smooth muscle cells. We therefore hypothesized that upregulation of KLF4 may play a role in pulmonary vascular remodeling and the development of PH. Our results showed that KLF4 expression was increased significantly in remodeled pulmonary arteries from the rat smoking model of pulmonary vascular remodeling, compared with controls. In human PASMCs in vitro, KLF4 knockdown by gene silencing decreased proliferation and migration significantly. At the same time, it inhibited the CSE-induced increase of AKT phosphorylation. These results indicate that KLF4 contributes to CS-induced pulmonary vascular remodeling, and that KLF4 gene knockdown may be a useful therapeutic intervention for PH.

KLF4α stimulates breast cancer cell proliferation by acting as a KLF4 antagonist

Krüppel-like factor 4 (KLF4), a transcription factor involved in both tumor suppression and oncogenesis in various human tumors, is subject to alternative splicing that produces KLF4α. KLF4α is primarily expressed in the cytoplasm because it lacks exon 3 of KLF4, which contains the nuclear localization signal. The role of KLF4 in breast cancer remains unclear and nothing is known yet about the expression and function of the isoform KLF4α. Here, we show that KLF4α is expressed in normal and tumoral tissue of the breast and provide evidence that the KLF4α/KLF4(full-length) (FL) ratio is increased in tumors compared to corresponding normal tissue. Forced increase of the KLF4α/KLF4(FL) ratio in the metastatic breast cancer cell line MDA-MB-231 decreases the levels of E-Cadherin, p21Cip1, and p27Kip1, three known KLF4(FL) target genes, and stimulates cell proliferation. We suggest that cytoplasmic KLF4α binds to KLF4(FL) and retains it in the cytoplasm thereby antagonizing the gene regulatory activities of KLF4(FL) in the nucleus. Our results establish KLF4α as a KLF4 isoform that opposes the function of KLF4(FL) and as an important factor in the complex and unresolved role of KLF4(FL) in breast carcinogenesis.

A miRNA signature for an environmental heterocyclic amine defined by a multi-organ carcinogenicity bioassay in the rat

Heterocyclic amines (HCAs) produced during high-temperature cooking have been studied extensively in terms of their genotoxic/genetic effects, but recent work has implicated epigenetic mechanisms involving non-coding RNAs. Colon tumors induced in the rat by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) have altered microRNA (miRNA) signatures linked to dysregulated pluripotency factors, such as c-Myc and Krüppel-like factor 4 (KLF4). We tested the hypothesis that dysregulated miRNAs from PhIP-induced colon tumors would provide a "PhIP signature" for use in other target organs obtained from a 1-year carcinogenicity bioassay in the rat. Downstream targets that were corroborated in the rat were then investigated in human cancer datasets. The results confirmed that multiple let-7 family members were downregulated in PhIP-induced skin, colon, lung, small intestine, and Zymbal's gland tumors, and were associated with c-myc and Hmga2 upregulation. PhIP signature miRNAs with the profile mir-21high/mir-126low/mir-29clow/mir-215low/mir-145low were linked to reduced Klf4 levels in rat tumors, and in human pan-cancer and colorectal cancer. It remains to be determined whether this PhIP signature has predictive value, given that more than 20 different genotoxic HCAs are present in the human diet, plus other agents that likely induce or repress many of the same miRNAs. Future studies should define more precisely the miRNA signatures of other HCAs, and their possible value for human risk assessment.

Restoration of KLF4 Inhibits Invasion and Metastases of Lung Adenocarcinoma through Suppressing MMP2

Background: KLF4 is a zin-finger transcription factor that plays roles in differentiation, development, and proliferation. Recent studies show that KLF4 is involved in tumorigenesis and somatic cells reprogramming. Metastasis is the primary cause of death in patients with lung cancer, and its biological mechanisms are poorly understood.

Goals: In this study, we aim to explore the expression pattern and biological function of KLF4 in lung adenocarcinoma.

Methods: We determined KLF4 in lung adenocarcinoma tissue and cell lines, using immunohistochemistry and western blotting. And we further analyzed the correlation between KLF4 expression and clinicopathologic parameters. We restored KLF4 expression and studied its effect on lung adenocarcinoma cells in vivo and in vitro. Luciferase assay was used to study impact of KLF4 on activity of MMP2 promoter.

Results: KLF4 is dramatically down-regulated in lung adenocarcinoma tissue and cell lines. Promoter methylation contributes to the down-regulation of KLF4. Down-regulation of KLF4 in lung adenocarcinoma tissue is significantly associated with reduced survival time. Restoration of KLF4 inhibits migration and invasion of lung adenocarcinoma cells in vitro. Metastases to lungs significantly decrease in mice intravenously injected with tumor cells overexpressing KLF4. KLF4 inhibits invasion and metastasis via suppressing MMP2 promoter activity.

Conclusion: The ability of KLF4 to inhibit migration, invasion, and metastasis of lung tumor cells indicates a potential role of KLF4 as therapeutic target in lung adenocarcinoma. KLF4 might be utilized as a favorable biomarker for prognosis of lung adenocarcinoma patients.

Morusin inhibits cell proliferation and tumor growth by down-regulating c-Myc in human gastric cancer

Morusin is a pure extract from the root bark of Morus australis (Moraceae). In recent years, morusin has been reported to exhibit anti-tumor biological activity in some types of human cancers through different mechanisms. Here, we attempted to investigate the inhibitory effect and mechanism of morusin on gastric cancer. Morusin markedly inhibited gastric cancer cell proliferation by down-regulating CDKs and Cyclins, such as CDK2, CDK4, Cyclin D1 and Cyclin E1. Additionally, morusin suppressed tumor growth in vitro and in vivo. Up-regulation of CDKs and Cyclins in gastric cancer cells was induced by c-Myc binding at the E-Box regions of CDKs and the Cyclin promoter. In addition, compared with the control group, the morusin-treated group showed reduced expression of c-Myc and c-Myc protein binding at the E-Box regions. Based on these results, we overexpressed c-Myc in gastric cancer cells and found that overexpressing c-Myc rescued morusin-induced inhibition of cell proliferation and tumor growth. These results suggest that morusin inhibits cell proliferation and tumor growth by down-regulating c-Myc in human gastric cancer.

KLF4 Plays an Essential Role in Corneal Epithelial Homeostasis by Promoting Epithelial Cell Fate and Suppressing Epithelial-Mesenchymal Transition

Purpose

The purpose of this study was to test the hypothesis that KLF4 promotes corneal epithelial (CE) cell fate by suppressing the epithelial–mesenchymal transition (EMT), using spatiotemporally regulated CE-specific ablation of Klf4 in Klf4^Δ/ΔCE (Klf4^LoxP/LoxP/Krt12^rtTA/rtTA/Tet-O-Cre) mice.

Methods

CE-specific ablation of Klf4 was achieved by feeding Klf4^Δ/ΔCE mice with doxycycline chow. The wild-type (WT; normal chow-fed littermates) and the Klf4^Δ/ΔCE histology was compared by hematoxylin and eosin–stained sections; EMT marker expression was quantified by quantitative PCR, immunoblots, and immunofluorescent staining; and wound healing rate was measured by CE debridement using Algerbrush. KLF4 and EMT markers were quantified in human corneal limbal epithelial (HCLE) cells undergoing TGF-β1–induced EMT by quantitative PCR, immunoblots, and immunofluorescent staining.

Results

The epithelial markers E-cadherin, Krt12, claudin-3, and claudin-4 were down-regulated, whereas the mesenchymal markers vimentin, β-catenin, survivin, and cyclin-D1 and the EMT transcription factors Snail, Slug, Twist1, Twist2, Zeb1, and Zeb2 were up-regulated in the Klf4^Δ/ΔCE corneas. The Klf4^Δ/ΔCE cells migrated faster, filling 93% of the debrided area within 16 hours compared with 61% in the WT. After 7 days of wounding, the Klf4^Δ/ΔCE cells that filled the gap failed to regain epithelial characteristics, as they displayed abnormal stratification; down-regulation of E-cadherin and Krt12; up-regulation of β-catenin, survivin, and cyclin-D1; and a 2.5-fold increase in the number of proliferative Ki67⁺ cells. WT CE cells at the migrating edge and the HCLE cells undergoing TGF-β1–induced EMT displayed significant down-regulation of KLF4.

Conclusions

Collectively, these results reveal that KLF4 plays an essential role in CE homeostasis by promoting epithelial cell fate and suppressing EMT.

Transdifferentiation and reprogramming: Overview of the processes, their similarities and differences

Reprogramming, or generation of induced pluripotent stem (iPS) cells (functionally similar to embryonic stem cells or ES cells) by the use of transcription factors (typically: Oct3/4, Sox2, c-Myc, Klf4) called "Yamanaka factors" (OSKM), has revolutionized regenerative medicine. However, factors used to induce stemness are also overexpressed in cancer. Both, ES cells and iPS cells cause teratoma formation when injected to tissues. This raises a safety concern for therapies based on iPS derivates. Transdifferentiation (lineage reprogramming, or -conversion), is a process in which one mature, specialized cell type changes into another without entering a pluripotent state. This process involves an ectopic expression of transcription factors and/or other stimuli. Unlike in the case of reprogramming, tissues obtained by this method do not carry the risk of subsequent teratomagenesis.

Impairment of DYRK2 augments stem-like traits by promoting KLF4 expression in breast cancer

Whereas accumulating studies have supported the cancer stem cell theory, a specific therapy targeting a cancer stem cell subpopulation has not been established. Here, we show that dual-specificity tyrosine phosphorylation-kinase 2 (DYRK2) is a novel negative regulator for formation of breast cancer stem cells. Downregulation of DYRK2 promotes cancer stem-like traits in vitro, tumourigenesis in vivo and the proportion of the cancer stem cell population in human breast cancer tissues. We found that Krupple-like factor 4 (KLF4) serves as a key mediator of DYRK2's control over the cancer stem phenotype. Reduced DYRK2 expression increases KLF4 expression, which induces cancer stem-like properties. We identified androgen receptor (AR) as a transcription factor binding to the KLF4 promoter region; this process is dependent on DYRK2 kinase activity. Our findings delineate a mechanism of cancer stem cell regulation by the DYRK2-AR-KLF4 axis in breast cancer. Targeting of this pathway may be a promising strategy against breast cancer stem cells.

Expression of Krüppel-like factor 4 in breast cancer tissues and its effects on the proliferation of breast cancer MDA-MB-231 cells

The aim of the present study was to detect the expression of Krüppel-like factor 4 (KLF4) in breast cancer tissues and to evaluate the effect on the proliferation of breast cancer MDA-MB-231 cells. The expression of KLF4 protein in 239 breast cancer tissues and 40 paracancerous tissues were detected by an immunohistochemical assay, and its correlation with clinical pathological parameters was analyzed. A eukaryotic expression vector, pcDNA3.1-KLF4, was constructed by transient transfection of breast cancer MDA-MB-231 cells with liposomes (experimental group). The untransfected cells and those transfected with empty plasmid pcDNA3.1 were used as the blank and negative control groups, respectively. The expression of the KLF4 gene and protein in the three groups were detected by reverse transcription polymerase chain reaction and western blotting, respectively. Furthermore, the cell proliferative capacity was detected by an MTT assay. The positive expression rate of KLF4 protein in breast cancer tissues (39.0%, 93/239) was significantly lower than that of paracancerous tissues (77.5%, 31/40) (P<0.05). In addition, KLF4 protein expression in breast cancer tissues was correlated with pathological type, histological grade and lymphatic metastasis (P<0.05). KLF4 mRNA and protein were both expressed by the experimental group, but not by the two control groups. Meanwhile, the proliferative capacity of the experimental group was also significantly decreased. A significant decrease in the positive expression rate of KLF4 protein in breast cancer tissues was correlated with several clinical pathological parameters. In addition, transfection of the KLF4 gene inhibited the proliferation of breast cancer cells, suggesting that this gene is important in the onset and progression of this type of cancer.

FBXO32 suppresses breast cancer tumorigenesis through targeting KLF4 to proteasomal degradation

Krüppel-like factor 4 (KLF4, GKLF) is a zinc-finger transcription factor involved in a large variety of cellular processes, including apoptosis, cell cycle progression, as well as stem cell renewal. KLF4 is critical for cell fate decision and has an ambivalent role in tumorigenesis. Emerging data keep reminding us that KLF4 dysregulation either facilitates or impedes tumor progression, making it important to clarify the regulating network of KLF4. Like most transcription factors, KLF4 has a rather short half-life within the cell and its turnover must be carefully orchestrated by ubiquitination and ubiquitin-proteasome system. To better understand the mechanism of KLF4 ubiquitination, we performed a genome-wide screen of E3 ligase small interfering RNA library based on western blot and identified SCF-FBXO32 to be a new E3 ligase, which is responsible for KLF4 ubiquitination and degradation. The F-box domain is critical for FBXO32-dependent KLF4 ubiquitination and degradation. Furthermore, we demonstrated that FBXO32 physically interacts with the N-terminus (1-60 aa) of KLF4 via its C-terminus (228-355 aa) and directly targets KLF4 for ubiquitination and degradation. We also found out that p38 mitogen-activated protein kinase pathway may be implicated in FBXO32-mediated ubiquitination of KLF4, as p38 kinase inhibitor coincidently abrogates endogenous KLF4 ubiquitination and degradation, as well as FBXO32-dependent exogenous KLF4 ubiquitination and degradation. Finally, FBXO32 inhibits colony formation in vitro and primary tumor initiation and growth in vivo through targeting KLF4 into degradation. Our findings thus further elucidate the tumor-suppressive function of FBXO32 in breast cancer. These results expand our understanding of the posttranslational modification of KLF4 and of its role in breast cancer development and provide a potential target for diagnosis and therapeutic treatment of breast cancer.

KLF4 is regulated by RAS/RAF/MEK/ERK signaling through E2F1 and promotes melanoma cell growth

Melanoma is the most lethal form of skin cancer and treatment of metastatic melanoma remains challenging. BRAF/MEK inhibitors show only temporary benefit due the occurrence of resistance and immunotherapy is effective only in a subset of patients. To improve patient survival, there is a need to better understand molecular mechanisms that drive melanoma growth and operate downstream of the mitogen activated protein kinase (MAPK) signaling. The Krüppel-like factor 4 (KLF4) is a zinc-finger transcription factor that plays a critical role in embryonic development, stemness and cancer, where it can act either as oncogene or tumor suppressor. KLF4 is highly expressed in post-mitotic epidermal cells, but its role in melanoma remains unknown. Here, we address the function of KLF4 in melanoma and its interaction with the MAPK signaling pathway. We find that KLF4 is highly expressed in a subset of human melanomas. Ectopic expression of KLF4 enhances melanoma cell growth by decreasing apoptosis. Conversely, knock-down of KLF4 reduces melanoma cell proliferation and induces cell death. In addition, depletion of KLF4 reduces melanoma xenograft growth in vivo. We find that the RAS/RAF/MEK/ERK signaling positively modulates KLF4 expression through the transcription factor E2F1, which directly binds to KLF4 promoter. Overall, our data demonstrate the pro-tumorigenic role of KLF4 in melanoma and uncover a novel ERK1/2-E2F1-KLF4 axis. These findings identify KLF4 as a possible new molecular target for designing novel therapeutic treatments to control melanoma growth.

Transcriptomic Analysis Shows Decreased Cortical Expression of NR4A1, NR4A2 and RXRB in Schizophrenia and Provides Evidence for Nuclear Receptor Dysregulation

Many genes are differentially expressed in the cortex of people with schizophrenia, implicating factors that control transcription more generally. Hormone nuclear receptors dimerize to coordinate context-dependent changes in gene expression. We hypothesized that members of two families of nuclear receptors (NR4As), and retinoid receptors (RARs and RXRs), are altered in the dorsal lateral prefrontal cortex (DLPFC) of people with schizophrenia. We used next generation sequencing and then qPCR analysis to test for changes in mRNA levels for transcripts encoding nuclear receptors: orphan nuclear receptors (3 in the NR4A, 3 in the RAR, 3 in the RXR families and KLF4) in total RNA extracted from the DLPFC from people with schizophrenia compared to controls (n = 74). We also correlated mRNA levels with demographic factors and with estimates of antipsychotic drug exposure (schizophrenia group only). We tested for correlations between levels of transcription factor family members and levels of genes putatively regulated by these transcription factors. We found significantly down regulated expression of NR4A1 (Nurr 77) and KLF4 mRNAs in people with schizophrenia compared to controls, by both NGS and qPCR (p = or <0.01). We also detected decreases in NR4A2 (Nurr1) and RXRB mRNAs by using qPCR in the larger cohort (p<0.05 and p<0.01, respectively). We detected decreased expression of RARG and NR4A2 mRNAs in females with schizophrenia (p<0.05). The mRNA levels of NR4A1, NR4A2 and NR4A3 were all negative correlated with lifetime estimates of antipsychotic exposure. These novel findings, which may be influenced by antipsychotic drug exposure, implicate the orphan and retinoid nuclear receptors in the cortical pathology found in schizophrenia. Genes down stream of these receptors can be dysregulated as well, but the direction of change is not immediately predictable based on the putative transcription factor changes.

Genetically modified laboratory mice with sebaceous glands abnormalities

Sebaceous glands (SG) are exocrine glands that release their product by holocrine secretion, meaning that the whole cell becomes a secretion following disruption of the membrane. SG may be found in association with a hair follicle, forming the pilosebaceous unit, or as modified SG at different body sites such as the eyelids (Meibomian glands) or the preputial glands. Depending on their location, SG fulfill a number of functions, including protection of the skin and fur, thermoregulation, formation of the tear lipid film, and pheromone-based communication. Accordingly, SG abnormalities are associated with several diseases such as acne, cicatricial alopecia, and dry eye disease. An increasing number of genetically modified laboratory mouse lines develop SG abnormalities, and their study may provide important clues regarding the molecular pathways regulating SG development, physiology, and pathology. Here, we summarize in tabulated form the available mouse lines with SG abnormalities and, focusing on selected examples, discuss the insights they provide into SG biology and pathology. We hope this survey will become a helpful information source for researchers with a primary interest in SG but also as for researchers from unrelated fields that are unexpectedly confronted with a SG phenotype in newly generated mouse lines.

KATapulting toward Pluripotency and Cancer

Development is generally regarded as a unidirectional process that results in the acquisition of specialized cell fates. During this process, cellular identity is precisely defined by signaling cues that tailor the chromatin landscape for cell-specific gene expression programs. Once established, these pathways and cell states are typically resistant to disruption. However, loss of cell identity occurs during tumor initiation and upon injury response. Moreover, terminally differentiated cells can be experimentally provoked to become pluripotent. Chromatin reorganization is key to the establishment of new gene expression signatures and thus new cell identity. Here, we explore an emerging concept that lysine acetyltransferase (KAT) enzymes drive cellular plasticity in the context of somatic cell reprogramming and tumorigenesis.

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.

KLF4 and NANOG are prognostic biomarkers for triple-negative breast cancer

BACKGROUND

Prognosis of breast cancer patients has been reported to depend on the expression of induced pluripotent stem (iPS) cell-inducing factors: KLF4 and NANOG. However, the relationship between KLF4 or NANOG expression in each breast cancer subtype and the life prognosis has not been elucidated.

METHOD

KLF4 and NANOG expression levels were evaluated in 208 patients using a newly developed tissue microarray (TMA). In vitro, siRNA against klf4 (siKLF4) was transfected in TNBC cell line MDA-MB-231, and the expression of KLF4 was inhibited.

RESULTS

Triple-negative breast cancer (TNBC) patients in KLF4 high-expression (upper) group had more favorable overall survival (OS) and disease-free survival (DFS) rates than KLF4 lower group (p = 0.0453 and p = 0.0427). In contrast, patients in the NANOG upper group had significantly poorer prognosis than lower group in TNBC breast cancer subtypes (p < 0.0001). Multivariate analysis showed that KLF4 (p = 0.0313), NANOG (p = 0.0002), and TNM stage (p = 0.0001) are mutually independent prognostic factors. It was also shown that the proliferation and invasion ability of siKLF4-induced TNBC cells were up-regulated significantly.

CONCLUSION

Our findings suggested that KLF4 and NANOG expression levels were favorable prognostic factors for TNBC patients. KLF4 also had an ability to inhibit the proliferation and invasion of TNBC.

Krüppel-like factor 4: A new potential biomarker of lung cancer

Lung cancer is most prevalent human cancer worldwide. However, no molecular markers are currently available for predicting lung cancer prognosis. Therefore, identifying novel biomarkers may be useful for improving clinical diagnosis and patient stratification. Krüppel-like factor 4 (KLF4) is a transcription factor with opposing roles in different human cancers. Its overexpression in several cancers is correlated with a poor prognosis. However, the expression and role of KLF4 in lung cancer remains to be elucidated. The aim of this study was to determine the profile of KLF4 expression in different types of lung cancer. The KLF4 protein expression level was tested and evaluated by immunohistochemical analysis in 47 lung tumors and normal tissues, and then correlated with clinical characteristics. A differential expression of KLF4 was observed between normal tissue and each of the lung cancer types. A significant decrease in KLF4 expression was observed in non-small-cell lung cancer (NSCLC) compared with that in normal tissue, while significant overexpression was detected in small-cell lung cancer. Furthermore, a higher rate of expression was observed in stage II, III and IV disease compared with stage I disease in NSCLC tissues. KLF4 expression was not found to be associated with age or gender. Our results suggested that the KLF4 protein level may be a potential biomarker in patients with advanced lung cancer.

Cancer Stem Cell Hierarchy in Glioblastoma Multiforme

Glioblastoma multiforme (GBM), an aggressive tumor that typically exhibits treatment failure with high mortality rates, is associated with the presence of cancer stem cells (CSCs) within the tumor. CSCs possess the ability for perpetual self-renewal and proliferation, producing downstream progenitor cells that drive tumor growth. Studies of many cancer types have identified CSCs using specific markers, but it is still unclear as to where in the stem cell hierarchy these markers fall. This is compounded further by the presence of multiple GBM and glioblastoma cancer stem cell subtypes, making investigation and establishment of a universal treatment difficult. This review examines the current knowledge on the CSC markers SALL4, OCT-4, SOX2, STAT3, NANOG, c-Myc, KLF4, CD133, CD44, nestin, and glial fibrillary acidic protein, specifically focusing on their use and validity in GBM research and how they may be utilized for investigations into GBM's cancer biology.

MiR-367 negatively regulates apoptosis induced by adriamycin in osteosarcoma cells by targeting KLF4

Diverse functions of microRNAs have been investigated in tumorigenesis in osteosarcoma (OS), involving the regulation of proliferation, invasion, migration, apoptosis and drug resistance. MiR-367 was found to be an oncogene and increased in OS. However, the function of miR-367 in drug resistance in OS cells is still unknown. In this study, we found that miR-367 was up-regulated in OS tissues and OS cell cultures. Meanwhile, treatment with adriamycin (ADR) induced apoptosis of OS cells with upregulation of miR-367. Notably, KLF4 was demonstrated to be a direct target of miR-367 by gene reporter assay, and miR-367 significantly blocked both mRNA and protein level of KLF4. In addition, overexpression of miR-367 markedly suppressed the increase of KLF4 induced by ADR in OS cells, as well as Bax and cleaved caspase-3, which were significantly reversed by anti-miR-367 transfection. Taken together, our data demonstrates that miR-367 and KLF4 play important roles in OS treatment and ADR resistance, suggesting that miR-367 is a potential biomarker of chemotherapy resistance in OS and also probably a novel therapeutic target against OS.

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miR-367 functions as an oncogene in OS targeting the tumor suppressor KLF4.

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ADR induces apoptosis in OS via miR-367/KLF4/Bax signaling pathway.

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miR-367 enhances the resistance of ADR to OS cells through suppressing KLF4.

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miR-367 could be a potential biomarker of chemotherapy resistance against OS.

Factor-Reduced Human Induced Pluripotent Stem Cells Efficiently Differentiate into Neurons Independent of the Number of Reprogramming Factors

Reprogramming of somatic cells into induced pluripotent stem cells (iPSCs) by overexpression of the transcription factors OCT4, SOX2, KLF4, and c-Myc holds great promise for the development of personalized cell replacement therapies. In an attempt to minimize the risk of chromosomal disruption and to simplify reprogramming, several studies demonstrated that a reduced set of reprogramming factors is sufficient to generate iPSC. We recently showed that a reduction of reprogramming factors in murine cells not only reduces reprogramming efficiency but also may worsen subsequent differentiation. To prove whether this is also true for human cells, we compared the efficiency of neuronal differentiation of iPSC generated from fetal human neural stem cells with either one (OCT4; hiPSC_1F-NSC) or two (OCT4, KLF4; hiPSC_2F-NSC) reprogramming factors with iPSC produced from human fibroblasts using three (hiPSC_3F-FIB) or four reprogramming factors (hiPSC_4F-FIB). After four weeks of coculture with PA6 stromal cells, neuronal differentiation of hiPSC_1F-NSC and hiPSC_2F-NSC was as efficient as iPSC_3F-FIB or iPSC_4F-FIB. We conclude that a reduction of reprogramming factors in human cells does reduce reprogramming efficiency but does not alter subsequent differentiation into neural lineages. This is of importance for the development of future application of iPSC in cell replacement therapies.

Endothelial Transdifferentiation of Tumor Cells Triggered by the Twist1-Jagged1-KLF4 Axis: Relationship between Cancer Stemness and Angiogenesis

Tumor hypoxia is associated with malignant biological phenotype including enhanced angiogenesis and metastasis. Hypoxia increases the expression of vascular endothelial cell growth factor (VEGF), which directly participates in angiogenesis by recruiting endothelial cells into hypoxic area and stimulating their proliferation, for increasing vascular density. Recent research in tumor biology has focused on the model in which tumor-derived endothelial cells arise from tumor stem-like cells, but the detailed mechanism is not clear. Twist1, an important regulator of epithelial-mesenchymal transition (EMT), has been shown to mediate tumor metastasis and induce tumor angiogenesis. Notch signaling has been demonstrated to be an important player in vascular development and tumor angiogenesis. KLF4 (Krüppel-like factor 4) is a factor commonly used for the generation of induced pluripotent stem (iPS) cells. KLF4 also plays an important role in the differentiation of endothelial cells. Although Twist1 is known as a master regulator of mesoderm development, it is unknown whether Twist1 could be involved in endothelial transdifferentiation of tumor-derived cells. This review focuses on the role of Twist1-Jagged1/Notch-KLF4 axis on tumor-derived endothelial transdifferentiation, tumorigenesis, metastasis, and cancer stemness.

Differentiation-Dependent KLF4 Expression Promotes Lytic Epstein-Barr Virus Infection in Epithelial Cells

Epstein-Barr virus (EBV) is a human herpesvirus associated with B-cell and epithelial cell malignancies. EBV lytically infects normal differentiated oral epithelial cells, where it causes a tongue lesion known as oral hairy leukoplakia (OHL) in immunosuppressed patients. However, the cellular mechanism(s) that enable EBV to establish exclusively lytic infection in normal differentiated oral epithelial cells are not currently understood. Here we show that a cellular transcription factor known to promote epithelial cell differentiation, KLF4, induces differentiation-dependent lytic EBV infection by binding to and activating the two EBV immediate-early gene (BZLF1 and BRLF1) promoters. We demonstrate that latently EBV-infected, telomerase-immortalized normal oral keratinocyte (NOKs) cells undergo lytic viral reactivation confined to the more differentiated cell layers in organotypic raft culture. Furthermore, we show that endogenous KLF4 expression is required for efficient lytic viral reactivation in response to phorbol ester and sodium butyrate treatment in several different EBV-infected epithelial cell lines, and that the combination of KLF4 and another differentiation-dependent cellular transcription factor, BLIMP1, is highly synergistic for inducing lytic EBV infection. We confirm that both KLF4 and BLIMP1 are expressed in differentiated, but not undifferentiated, epithelial cells in normal tongue tissue, and show that KLF4 and BLIMP1 are both expressed in a patient-derived OHL lesion. In contrast, KLF4 protein is not detectably expressed in B cells, where EBV normally enters latent infection, although KLF4 over-expression is sufficient to induce lytic EBV reactivation in Burkitt lymphoma cells. Thus, KLF4, together with BLIMP1, plays a critical role in mediating lytic EBV reactivation in epithelial cells.

Lytic EBV infection of differentiated oral epithelial cells results in the release of infectious viral particles and is required for efficient transmission of EBV from host to host. Lytic infection also causes a tongue lesion known as oral hairy leukoplakia (OHL). However, surprisingly little is known in regard to how EBV gene expression is regulated in epithelial cells. Using a stably EBV- infected, telomerase-immortalized normal oral keratinocyte cell line, we show here that undifferentiated basal epithelial cells support latent EBV infection, while differentiation of epithelial cells promotes lytic reactivation. Furthermore, we demonstrate that the KLF4 cellular transcription factor, which is required for normal epithelial cell differentiation and is expressed in differentiated, but not undifferentiated, normal epithelial cells, induces lytic EBV reactivation by activating transcription from the two EBV immediate-early gene promoters. We also show that the combination of KLF4 and another differentiation-dependent cellular transcription factor, BLIMP1, synergistically activates lytic gene expression in epithelial cells. We confirm that KLF4 and BLIMP1 expression in normal tongue epithelium is confined to differentiated cells, and that KLF4 and BLIMP1 are expressed in a patient-derived OHL tongue lesion. These results suggest that differentiation-dependent expression of KLF4 and BLIMP1 in epithelial cells promotes lytic EBV infection.

Interplay between arginine methylation and ubiquitylation regulates KLF4-mediated genome stability and carcinogenesis

KLF4 is an important regulator of cell-fate decision, including DNA damage response and apoptosis. We identify a novel interplay between protein modifications in regulating KLF4 function. Here we show that arginine methylation of KLF4 by PRMT5 inhibits KLF4 ubiquitylation by VHL and thereby reduces KLF4 turnover, resulting in the elevation of KLF4 protein levels concomitant with increased transcription of KLF4-dependent p21 and reduced expression of KLF4-repressed Bax. Structure-based modelling and simulations provide insight into the molecular mechanisms of KLF4 recognition and catalysis by PRMT5. Following genotoxic stress, disruption of PRMT5-mediated KLF4 methylation leads to abrogation of KLF4 accumulation, which, in turn, attenuates cell cycle arrest. Mutating KLF4 methylation sites suppresses breast tumour initiation and progression, and immunohistochemical stain shows increased levels of both KLF4 and PRMT5 in breast cancer tissues. Taken together, our results point to a critical role for aberrant KLF4 regulation by PRMT5 in genome stability and breast carcinogenesis.

Krüppel-like factor 4 plays an important role in regulating responses to DNA damage, cell-fate decision and apoptosis. Here the authors show that aberrant regulation by methyltransferase PRMT5 results in failure to arrest the cell cycle and genome instability, pointing to a role in carcinogenesis.

Human induced pluripotent stem cells in Parkinson's disease: A novel cell source of cell therapy and disease modeling

Human induced pluripotent stem cells (hiPSCs) and human embryonic stem cells (hESCs) are two novel cell sources for studying neurodegenerative diseases. Dopaminergic neurons derived from hiPSCs/hESCs have been implicated to be very useful in Parkinson's disease (PD) research, including cell replacement therapy, disease modeling and drug screening. Recently, great efforts have been made to improve the application of hiPSCs/hESCs in PD research. Considerable advances have been made in recent years, including advanced reprogramming strategies without the use of viruses or using fewer transcriptional factors, optimized methods for generating highly homogeneous neural progenitors with a larger proportion of mature dopaminergic neurons and better survival and integration after transplantation. Here we outline the progress that has been made in these aspects in recent years, particularly during the last year, and also discuss existing issues that need to be addressed.

Glucocorticoid receptor and Klf4 co-regulate anti-inflammatory genes in keratinocytes

The glucocorticoid (GC) receptor (GR) and Kruppel-like factor Klf4 are transcription factors that play major roles in skin homeostasis. However, whether these transcription factors cooperate in binding genomic regulatory regions in epidermal keratinocytes was not known. Here, we show that in dexamethasone-treated keratinocytes GR and Klf4 are recruited to genomic regions containing adjacent GR and KLF binding motifs to control transcription of the anti-inflammatory genes Tsc22d3 and Zfp36. GR- and Klf4 loss of function experiments showed total GR but partial Klf4 requirement for full gene induction in response to dexamethasone. In wild type keratinocytes induced to differentiate, GR and Klf4 protein expression increased concomitant with Tsc22d3 and Zfp36 up-regulation. In contrast, GR-deficient cells failed to differentiate or fully induce Klf4, Tsc22d3 and Zfp36 correlating with increased expression of the epithelium-specific Trp63, a known transcriptional repressor of Klf4. The identified transcriptional cooperation between GR and Klf4 may determine cell-type specific regulation and have implications for developing therapies for skin diseases.

Kruppel-like factor 4 signals through microRNA-206 to promote tumor initiation and cell survival

Tumor cell heterogeneity poses a major hurdle in the treatment of cancer. Mammary cancer stem-like cells (MaCSCs), or tumor-initiating cells, are highly tumorigenic sub-populations that have the potential to self-renew and to differentiate. These cells are clinically important, as they display therapeutic resistance and may contribute to treatment failure and recurrence, but the signaling axes relevant to the tumorigenic phenotype are poorly defined. The zinc-finger transcription factor Kruppel-like factor 4 (KLF4) is a pluripotency mediator that is enriched in MaCSCs. KLF4 promotes RAS-extracellular signal-regulated kinase pathway activity and tumor cell survival in triple-negative breast cancer (TNBC) cells. In this study, we found that both KLF4 and a downstream effector, microRNA-206 (miR-206), are selectively enriched in the MaCSC fractions of cultured human TNBC cell lines, as well as in the aldehyde dehydrogenase-high MaCSC sub-population of cells derived from xenografted human mammary carcinomas. The suppression of endogenous KLF4 or miR-206 activities abrogated cell survival and in vivo tumor initiation, despite having only subtle effects on MaCSC abundance. Using a combinatorial approach that included in silico as well as loss- and gain-of-function in vitro assays, we identified miR-206-mediated repression of the pro-apoptotic molecules programmed cell death 4 (PDCD4) and connexin 43 (CX43/GJA1). Depletion of either of these two miR-206-regulated transcripts promoted resistance to anoikis, a prominent feature of CSCs, but did not consistently alter MaCSC abundance. Consistent with increased levels of miR-206 in MaCSCs, the expression of both PDCD4 and CX43 was suppressed in these cells relative to control cells. These results identify miR-206 as an effector of KLF4-mediated prosurvival signaling in MaCSCs through repression of PDCD4 and CX43. Consequently, our study suggests that a pluripotency factor exerts prosurvival signaling in MaCSCs, and that antagonism of KLF4-miR-206 signaling may selectively target the MaCSC niche in TNBC.

KLF4-dependent phenotypic modulation of smooth muscle cells has a key role in atherosclerotic plaque pathogenesis

Previous studies investigating the role of smooth muscle cells (SMCs) and macrophages in the pathogenesis of atherosclerosis have provided controversial results owing to the use of unreliable methods for clearly identifying each of these cell types. Here, using Myh11-CreER(T2) ROSA floxed STOP eYFP Apoe(-/-) mice to perform SMC lineage tracing, we find that traditional methods for detecting SMCs based on immunostaining for SMC markers fail to detect >80% of SMC-derived cells within advanced atherosclerotic lesions. These unidentified SMC-derived cells exhibit phenotypes of other cell lineages, including macrophages and mesenchymal stem cells (MSCs). SMC-specific conditional knockout of Krüppel-like factor 4 (Klf4) resulted in reduced numbers of SMC-derived MSC- and macrophage-like cells, a marked reduction in lesion size, and increases in multiple indices of plaque stability, including an increase in fibrous cap thickness as compared to wild-type controls. On the basis of in vivo KLF4 chromatin immunoprecipitation-sequencing (ChIP-seq) analyses and studies of cholesterol-treated cultured SMCs, we identified >800 KLF4 target genes, including many that regulate pro-inflammatory responses of SMCs. Our findings indicate that the contribution of SMCs to atherosclerotic plaques has been greatly underestimated, and that KLF4-dependent transitions in SMC phenotype are critical in lesion pathogenesis.