Downregulation of the KLF4 transcription factor inhibits the proliferation and migration of canine mammary tumor cells

MicroRNA-mediated Krüppel-like factor 4 upregulation induces alternatively activated macrophage-associated marker and chemokine transcription in 4,4'-methylene diphenyl diisocyanate exposed macrophages

1. Occupational exposure to 4,4'-methylene diphenyl diisocyanate (MDI) is associated with occupational asthma (OA) development. Alveolar macrophage-induced recruitment of immune cells to the lung microenvironment plays an important role during asthma pathogenesis. Previous studies identified that MDI/MDI-glutathione (GSH)-exposure downregulates endogenous hsa-miR-206-3p/hsa-miR-381-3p. Our prior report shows that alternatively activated (M2) macrophage-associated markers/chemokines are induced by MDI/MDI-GSH-mediated Krüppel-Like Factor 4 (KLF4) upregulation in macrophages and stimulates immune cell chemotaxis. However, the underlying molecular mechanism(s) by which MDI/MDI-GSH upregulates KLF4 remain unclear.

2. Following MDI-GSH exposure, microRNA(miR)-inhibitors/mimics or plasmid transfection, endogenous hsa-miR-206-3p/hsa-miR-381-3p, KLF4, or M2 macrophage-associated markers (CD206, TGM2), and chemokines (CCL17, CCL22, CCL24) were measured by either RT-qPCR, western blot, or luciferase assay.

3. MDI-GSH exposure downregulates hsa-miR-206-3p/hsa-miR-381-3p by 1.46- to 9.75-fold whereas upregulates KLF4 by 1.68- to 1.99-fold, respectively. In silico analysis predicts binding between hsa-miR-206-3p/hsa-miR-381-3p and KLF4. Gain- and loss-of-function, luciferase reporter assays and RNA-induced silencing complex-immunoprecipitation (RISC-IP) studies confirm the posttranscriptional regulatory roles of hsa-miR-206-3p/hsa-miR-381-3p and KLF4 in macrophages. Furthermore, hsa-miR-206-3p/hsa-miR-381-3p regulate the expression of M2 macrophage-associated markers and chemokines via KLF4.

4. In conclusion, hsa-miR-206-3p/hsa-miR-381-3p play a major role in regulation of MDI/MDI-GSH-induced M2 macrophage-associated markers and chemokines by targeting the KLF4 transcript, and KLF4-mediated regulation in macrophages.

Cardiac lipid metabolism, mitochondrial function, and heart failure

A fine balance between uptake, storage, and the use of high energy fuels, like lipids, is crucial in the homeostasis of different metabolic tissues. Nowhere is this balance more important and more precarious than in the heart. This highly energy-demanding muscle normally oxidizes almost all the available substrates to generate energy, with fatty acids being the preferred source under physiological conditions. In patients with cardiomyopathies and heart failure, changes in the main energetic substrate are observed; these hearts often prefer to utilize glucose rather than oxidizing fatty acids. An imbalance between uptake and oxidation of fatty acid can result in cellular lipid accumulation and cytotoxicity. In this review, we will focus on the sources and uptake pathways used to direct fatty acids to cardiomyocytes. We will then discuss the intracellular machinery used to either store or oxidize these lipids and explain how disruptions in homeostasis can lead to mitochondrial dysfunction and heart failure. Moreover, we will also discuss the role of cholesterol accumulation in cardiomyocytes. Our discussion will attempt to weave in vitro experiments and in vivo data from mice and humans and use several human diseases to illustrate metabolism gone haywire as a cause of or accomplice to cardiac dysfunction.

KLF4 transcription factor in tumorigenesis

Krüppel-like transcriptional factor is important in maintaining cellular functions. Deletion of Krüppel-like transcriptional factor usually causes abnormal embryonic development and even embryonic death. KLF4 is a prominent member of this family, and embryonic deletion of KLF4 leads to alterations in skin permeability and postnatal death. In addition to its important role in embryo development, it also plays a critical role in inflammation and malignancy. It has been investigated that KLF4 has a regulatory role in a variety of cancers, including lung, breast, prostate, colorectal, pancreatic, hepatocellular, ovarian, esophageal, bladder and brain cancer. However, the role of KLF4 in tumorigenesis is complex, which may link to its unique structure with both transcriptional activation and transcriptional repression domains, and to the regulation of its upstream and downstream signaling molecules. In this review, we will summarize the structural and functional aspects of KLF4, with a focus on KLF4 as a clinical biomarker and therapeutic target in different types of tumors.

Krüppel-like factors in tumors: Key regulators and therapeutic avenues

Krüppel-like factors (KLFs) are a group of DNA-binding transcriptional regulators with multiple essential functions in various cellular processes, including proliferation, migration, inflammation, and angiogenesis. The aberrant expression of KLFs is often found in tumor tissues and is essential for tumor development. At the molecular level, KLFs regulate multiple signaling pathways and mediate crosstalk among them. Some KLFs may also be molecular switches for specific biological signals, driving their transition from tumor suppressors to promoters. At the histological level, the abnormal expression of KLFs is closely associated with tumor cell stemness, proliferation, apoptosis, and alterations in the tumor microenvironment. Notably, the role of each KLF in tumors varies according to tumor type and different stages of tumor development rather than being invariant. In this review, we focus on the advances in the molecular biology of KLFs, particularly the regulations of several classical signaling pathways by these factors, and the critical role of KLFs in tumor development. We also highlight their strong potential as molecular targets in tumor therapy and suggest potential directions for clinical translational research.

KCa3.1 inhibition-induced activation of the JNK/c-Jun signaling pathway enhances IL-10 expression in peripherally-induced regulatory T cells

The K_Ca3.1 inhibition up-regulates IL-10 expression in regulatory T (T_reg) cells in the recovery phase of inflammatory bowel disease (IBD) model mice; however, the underlying signaling pathway remains unclear. We investigated the involvement of AP-1 (Fos/Jun) and NF-κB in the expression of IL-10 and its transcription factors (TFs) in in vitro-induced mouse splenic T_reg cells. The pharmacological inhibition of JNK reversed K_Ca3.1 inhibition-induced increases in the expression of IL-10 and its TFs. The inhibition of K_Ca3.1 increased phosphorylated JNK and c-Jun levels. Therefore, the JNK/c-Jun signaling pathway may contribute to the K_Ca3.1 inhibition-induced up-regulation of IL-10 in peripherally-induced T_reg cells.

KLF4 inhibition by Kenpaullone induces cytotoxicity and chemo sensitization in B-NHL cell lines via YY1 independent

Krüppel-like factor 4 (KLF4) is a member of the KLF transcription factor family containing zinc-fingers, and is involved in the regulation of apoptosis, proliferation and differentiation of B cells and B-cell malignancies. KLF4 can act like an oncogene, we shown that KLF4 overexpression correlated with poor prognostic and chemoresistance in B-NHL. In addition, we shown that KLF4 is regulated by YY1. In this study, we demonstrate that chemical inhibition of KLF4 by Kenpaullone, results in suppression of proliferation, cell survival, downregulation of Bcl-2 and increases apoptosis in B-NHL cell lines through YY1 independent pathway. Combination of Kenpaullone and Doxorubicin, increased apoptosis. The co-expressions of KLF4/YY1 or KLF4/Bcl-2 in NHL was analyzed using Oncomine Database, exhibiting a positive correlation of expression. The present findings suggest that the chemical inhibition of KLF4 by Kenpaullone treatment could be a potential therapeutic alternatively in KLF4⁺ lymphomas.

Targeting cancer stem cell pathways for cancer therapy

Since cancer stem cells (CSCs) were first identified in leukemia in 1994, they have been considered promising therapeutic targets for cancer therapy. These cells have self-renewal capacity and differentiation potential and contribute to multiple tumor malignancies, such as recurrence, metastasis, heterogeneity, multidrug resistance, and radiation resistance. The biological activities of CSCs are regulated by several pluripotent transcription factors, such as OCT4, Sox2, Nanog, KLF4, and MYC. In addition, many intracellular signaling pathways, such as Wnt, NF-κB (nuclear factor-κB), Notch, Hedgehog, JAK-STAT (Janus kinase/signal transducers and activators of transcription), PI3K/AKT/mTOR (phosphoinositide 3-kinase/AKT/mammalian target of rapamycin), TGF (transforming growth factor)/SMAD, and PPAR (peroxisome proliferator-activated receptor), as well as extracellular factors, such as vascular niches, hypoxia, tumor-associated macrophages, cancer-associated fibroblasts, cancer-associated mesenchymal stem cells, extracellular matrix, and exosomes, have been shown to be very important regulators of CSCs. Molecules, vaccines, antibodies, and CAR-T (chimeric antigen receptor T cell) cells have been developed to specifically target CSCs, and some of these factors are already undergoing clinical trials. This review summarizes the characterization and identification of CSCs, depicts major factors and pathways that regulate CSC development, and discusses potential targeted therapy for CSCs.

KLF4 inhibition promotes the expansion of keratinocyte precursors from adult human skin and of embryonic-stem-cell-derived keratinocytes

Expanded autologous skin keratinocytes are currently used in cutaneous cell therapy, and embryonic-stem-cell-derived keratinocytes could become a complementary alternative. Regardless of keratinocyte provenance, for efficient therapy it is necessary to preserve immature keratinocyte precursors during cell expansion and graft processing. Here, we show that stable and transient downregulation of the transcription factor Krüppel-like factor 4 (KLF4) in keratinocyte precursors from adult skin, using anti-KLF4 RNA interference or kenpaullone, promotes keratinocyte immaturity and keratinocyte self-renewal in vitro, and enhances the capacity for epidermal regeneration in mice. Both stable and transient KLF4 downregulation had no impact on the genomic integrity of adult keratinocytes. Moreover, transient KLF4 downregulation in human-embryonic-stem-cell-derived keratinocytes increased the efficiency of skin-orientated differentiation and of keratinocyte immaturity, and was associated with improved generation of epidermis. As a regulator of the cell fate of keratinocyte precursors, KLF4 could be used for promoting the ex vivo expansion and maintenance of functional immature keratinocyte precursors.

Identification of GSK3β inhibitor kenpaullone as a temozolomide enhancer against glioblastoma

Cancer stem cells are associated with chemoresistance and rapid recurrence of malignant tumors, including glioblastoma (GBM). Although temozolomide (TMZ) is the most effective drug treatment for GBM, GBM cells acquire resistance and become refractory to TMZ during treatment. Therefore, glioma stem cell (GSC)-targeted therapy and TMZ-enhancing therapy may be effective approaches to improve GBM prognosis. Many drugs that suppress the signaling pathways that maintain GSC or enhance the effects of TMZ have been reported. However, there are no established therapies beyond TMZ treatment currently in use. In this study, we screened drug libraries composed of 1,301 existing drugs using cell viability assays to evaluate effects on GSCs, which led to selection of kenpaullone, a kinase inhibitor, as a TMZ enhancer targeting GSCs. Kenpaullone efficiently suppressed activity of glycogen synthase kinase (GSK) 3β. Combination therapy with kenpaullone and TMZ suppressed stem cell phenotype and viability of both GSCs and glioma cell lines. Combination therapy in mouse models significantly prolonged survival time compared with TMZ monotherapy. Taken together, kenpaullone is a promising drug for treatment of GBM by targeting GSCs and overcoming chemoresistance to TMZ.

Identification of genes and genetic networks associated with BAG3‑dependent cell proliferation and cell survival in human cervical cancer HeLa cells

Bcl‑2‑associated athanogene (BAG) 3, is a member of the BAG protein family and a known co‑chaperone of heat shock protein (HSP) 70. BAG3 serves a role in regulating a variety of cellular functions, including cell growth, proliferation and cell death including apoptosis. BAG3 is a stress‑inducible protein, however the constitutive expression level of BAG3 is increased in cancer cells compared with healthy cells. Recent proteomics technology combined with bioinformatics has revealed that BAG3 participates in an interactome with a number of proteins other than its typical partner HSP70. The functional types represented in the interactome included nucleic acid binding proteins and transcription factors, as well as chaperones, which indicated that overexpression of BAG3 may contribute to proliferation and cell survival through the alteration of gene transcription. While an increasing number of studies have addressed the function of BAG3 as a co‑chaperone protein, BAG3‑dependent alteration of gene transcription has not been studied extensively. The present study established two BAG3 knockout human cervical cancer HeLa cell clones and addressed the role of BAG3 in cell proliferation and survival through gene transcription, using DNA microarray‑based transcriptome analysis and bioinformatics. The present study also identified two genetic networks associated with 'cellular growth and proliferation' and 'cell death and survival', which are dysregulated in the absence of BAG3, and may therefore be linked to BAG3 overexpression in cancer. These findings provide a molecular basis for understanding of BAG3‑dependent cell proliferation and survival from the aspect of alteration of gene expression.

Krüppel-like factor 4 expression in solid tumor prognosis: A meta-analysis

BACKGROUND

Accumulating studies have demonstrated that Krüppel-like factor 4 (KLF4) can act as a tumor suppressor or oncogene in the carcinogenesis of diverse cancers. The prognostic value of KLF4 in various human solid cancers remains controversial. Thus, the present meta-analysis was conducted to evaluate the prognostic value of KLF4 in solid tumors.

METHODS

Eligible literature was retrieved by searching the PubMed, Embase, and Cochrane Library. Combined hazard ratios (HRs) for overall survival (OS) and disease-free survival (DFS) were assessed using fixed-effects and random-effects models. Meta-regression and subgroup analyses were performed to identify the source of heterogeneity. In addition, publication bias was assessed using Begg's funnel plot and Egger's regression asymmetry test.

RESULTS

The 22 eligible studies finally enrolled a total of 2988 patients to assess the prognostic value of KLF4 in solid tumors. Low KLF4 expression was clearly related to worse OS (HR = 1.71, 95% confidence interval [CI] = 1.30-2.24, P < 0.001) and DFS (HR = 1.74, 95% CI = 1.34-2.26, P < 0.001), indicating that low KLF4 expression could be an independent prognostic factor for poor survival in solid cancers.

CONCLUSION

KLF4 might be a potential marker to predict prognosis in solid cancer patients.

Association of multiple genetic variants with breast cancer susceptibility in the Han Chinese population

We selected 13 tag single nucleotide polymorphisms (tSNPs) to investigate whether they were associated with breast cancer risk in the Chinese Han population. Upon statistical analyses of clinical data from 551 patients and 577 controls, we found that six of the 13 SNPs were associated with breast cancer; namely, rs4973768(Odds ratio (OR) = 1.30, 95% confidence interval (CI) =1.01-1.67), rs981782(OR =1.30, 95% CI=1.01-1.66), rs1432679(OR =0.84, 95% CI=0.70-0.99), rs10759243(OR=1.30, 95%CI=1.09-1.55), rs10822013(OR =1.18, 95% CI=1.00-1.39) and rs704010(OR =1.63, 95% CI=1.04-2.56). When stratified based on breast cancer subtype, our analyses revealed that three SNPs (rs981782, rs10759243 and rs704010) correlated with ER+ breast cancer, while another three (rs4973768, rs1432679 and rs10822013) correlated with ER- breast cancer. We obtained similar results while investigating the correlation of SNPs with PR status or clinical stage. Our results suggest that associations identified between SNPs and breast cancer through genome-wide association studies (GWAS) may not always be generalizable across races.

Klf4 inhibits tumor growth and metastasis by targeting microRNA-31 in human hepatocellular carcinoma

MicroRNAs (miRNAs or miRs) are short, endogenous non-coding RNA molecules, demonstrating abnormal expression in cancer initiation and progression. In this study, we profiled 18 differentially regulated miRNAs, including miRNA-31, using miRNA array. Kruppel (or Krüppel)-like factor 4 (Klf4) is a transcription factor and putative tumor suppressor. Both were found to be significantly downregulated in liver cancer tissues and cells. However, little is known about the correlation between Klf4 and miRNA-31 in hepatocellular carcinoma (HCC). The mRNA expression of Klf4 was decreased and inversely associated with the clinical stage, T classification and hepatitis B in patients with HCC, while the expression of miR-31 was lower (r=0.326, P=0.018). Using cell counting kit 8 (CCK8) and Transwell migration assays, we found that Klf4 and miR-31 inhibited the proliferation and metastasis of liver cancer cells. Moreover, we demonstrated that Klf4 directly binds to the promoter of miR-31 and activates its transcription. In vitro experiments confirmed that Klf4 regulated miR-31 and thereby inhibited HCC cell growth and metastasis. Taken together, our findings indicate that Klf4 directly regulates miR-31 in HCC. Thus, miR-31 may serve as a potential diagnostic marker and therapeutic target in HCC.

Kruppel-like factor 4 (KLF-4) inhibits the epithelial-to-mesenchymal transition and proliferation of human endometrial carcinoma cells

Kruppel-like factors (KLFs) are a group of transcriptional regulators, being tumor-suppressive in various types of cancers, but not clear in human endometrial carcinoma (EC). We investigated the KLF-4 expression in both mRNA and protein levels in 29 EC specimens with RT-qPCR and Western blotting methods, and then to determine its promotion to Epithelial-to-mesenchymal transition (EMT) and proliferation of EC Ishikawa cells, via analyzing EMT-associated markers and via CCK-8 and colony forming assay. We found the downregulation of KLF-4 in the 29 EC specimens, correlating with the EC malignance. Moreover, we confirmed reduced levels of EMT and cell proliferation of Ishikawa cells post-KLF-4 overexpression. In conclusion, the significantly reduced KLF-4 correlated with the EC malignance. And the overexpressed KLF-4 promoted the EMT and proliferation of EC cells in vitro. The present study recognized the tumor suppressive role of KLF-4 in EC.

p21 and CK2 interaction-mediated HDAC2 phosphorylation modulates KLF4 acetylation to regulate bladder cancer cell proliferation

Krüppel-like factor 4 (KLF4) is a transcription factor involved in both tumor suppression and oncogenesis as a transcriptional activator or repressor in a context-dependent manner. KLF4 acts as a regulator of p53 depending on p21 status in breast cancer. However, the mechanisms underlying the distinct role of KLF4 remain poorly understood. Here, we revealed that p21 depletion converted KLF4 from a cell cycle inhibitor to a promoter of bladder cancer cell proliferation. Additionally, KLF4 was acetylated in a p21-dependent manner to inhibit bladder cancer cell growth as a tumor suppressor. However, deacetylated KLF4 functioned as an oncogene promoting bladder cancer cell proliferation. Mechanistically, p21 and CK2 interaction, but not CK2 alone, enhanced HDAC2 phosphorylation and restricted KLF4 deacetylation and subsequent tumor promotion. Furthermore, we observed that KLF4 was acetylated by CBP/p300 and that overexpression of CBP resulted in KLF4 acetylation and tumor suppression even in p21-depleted bladder cancer cells. Moreover, we discovered that Notch-1 knockdown-induced KLF4 is acetylated form of KLF4, which may mediate Notch-1 function in bladder cancer cell proliferation. Our data demonstrate that KLF4 acts as a tumor suppressor or oncogene to activate or repress target gene transcription depending on its acetylation status, which is regulated by p21 and CK2 interaction-mediated HDAC2 phosphorylation. Targeting KLF4 at the post-transcriptional levels may provide novel insight for bladder cancer therapy.