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

Sexual dimorphism during integrative endocrine and immune responses to ionizing radiation in mice

Exposure to cosmic ionizing radiation is an innate risk of the spaceflight environment that can cause DNA damage and altered cellular function. In astronauts, longitudinal monitoring of physiological systems and interactions between these systems are important to consider for mitigation strategies. In addition, assessments of sex-specific biological responses in the unique environment of spaceflight are vital to support future exploration missions that include both females and males. Here we assessed sex-specific, multi-system immune and endocrine responses to simulated cosmic radiation. For this, 24-week-old, male and female C57Bl/6J mice were exposed to simplified five-ion, space-relevant galactic cosmic ray (GCRsim) radiation at 15 and 50 cGy, to simulate predicted radiation exposures that would be experienced during lunar and Martian missions, respectively. Blood and adrenal tissues were collected at 3- and 14-days post-irradiation for analysis of immune and endocrine biosignatures and pathways. Sexually dimorphic adrenal gland weights and morphology, differential total RNA expression with corresponding gene ontology, and unique immune phenotypes were altered by GCRsim. In brief, this study offers new insights into sexually dimorphic immune and endocrine kinetics following simulated cosmic radiation exposure and highlights the necessity for personalized translational approaches for astronauts during exploration missions.

The role of KLF transcription factor in the regulation of cancer progression

Kruppel-like factors (KLFs) are a family of zinc finger transcription factors that have been found to play an essential role in the development of various human tissues, including epithelial, teeth, and nerves. In addition to regulating normal physiological processes, KLFs have been implicated in promoting the onset of several cancers, such as gastric cancer, lung cancer, breast cancer, liver cancer, and colon cancer. To inhibit cancer progression, various existing medicines have been used to modulate the expression of KLFs, and anti-microRNA treatments have also emerged as a potential strategy for many cancers. Investigating the possibility of targeting KLFs in cancer therapy is urgently needed, as the roles of KLFs in cancer have not received enough attention in recent years. This review summarizes the factors that regulate KLF expression and function at both the transcriptional and posttranscriptional levels, which could aid in understanding the mechanisms of KLFs in cancer progression. We hope that this review will contribute to the development of more effective anti-cancer medicines targeting KLFs in the future.

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.

Novel alternative splicing variants of Klf4 display different capacities for self-renewal and pluripotency in mouse embryonic stem cells

Embryonic stem (ES) cells are unique in their ability to self-renew indefinitely while maintaining pluripotency. Krüppel-like factor (Klf) 4 is an important member of the Klf family that is known to play a key role in pluripotency and somatic cell reprogramming. However, the identification and functional comparison of Klf4 splicing isoforms in mouse ESCs (mESCs) remains to be elucidated. Here, we identified three novel alternative splicing variants of Klf4 in mESCs-mKlf4-108, mKlf4-375 and mKlf4-1482-that are distinct from the previously known mKlf4-1449. mKlf4-1449 and mKlf4-1482 may stimulate the growth of ESCs, while mKlf4-108 can only promote the growth of ESCs in LIF^low/serum conditions. In addition, both mKlf4-1449 and mKlf4-1482 can inhibit the differentiation of mESCs. However, the ability of mKlf4-1482 to promote self-renewal and inhibit differentiation is not as strong as that of mKlf4-1449. In contrast, both mKlf4-108 and mKlf4-375 may have the ability to induce endodermal differentiation. Taken together, we have identified for the first time the existence of alternative splicing variants of mKlf4 and have revealed their different roles, which provide new insights into the contribution of Klf4 to the self-renewal and pluripotency of mouse ESCs.

Involvement of DHX9/YB-1 complex induced alternative splicing of Krüppel-like factor 5 mRNA in phenotypic transformation of vascular smooth muscle cells

Phenotypic transformation of vascular smooth muscle cells is a key phenomenon in the development of aortic dissection disease. However, the molecular mechanisms underlying this phenomenon have not been fully understood. We used β-BAPN combined with ANG II treatment to establish a disease model of acute aortic dissection (AAD) in mice. We first examined the gene expression profile of aortic tissue in mice with AAD using a gene chip, followed by confirmation of DExH-box helicase 9 (DHX9) expression using RT-PCR, Western blot, and immunofluorescence analysis. We further developed vascular smooth muscle cell-specific DHX9 conditional knockout mice and conducted differential and functional analysis of gene expression and alternative splicing in mouse vascular smooth muscle cells. Finally, we examined the involvement of DHX9 in Krüppel-like factor 5 (KLF5) mRNA alternative splicing. Our study reported a significant decrease in the expression of DHX9 in the vascular smooth muscle cells (VSMCs) of mice with AAD. The smooth muscle cell-specific knockout of DHX9 exacerbated the development of AAD and altered the transcriptional level expression of many smooth muscle cell phenotype-related genes. Finally, we reported that DHX9 may induce alternative splicing of KLF5 mRNA by bridging YB-1. These results together suggested a new pathogenic mechanism underlying the development of AAD, and future research of this mechanism may help identify effective therapeutic intervention for AAD.

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.

Krüppel-Like Factor 4 Enhances Sensitivity of Cisplatin to Esophageal Squamous Cell Carcinoma (ESCC) Cells

Background

The aim of this study was to elucidate the role of Krüppel-Like factor 4 (KLF4) in cisplatin resistance in esophageal squamous cell carcinoma (ESCC) cells, which may eventually help to improve the treatment efficacy.

Material/Methods

Human esophageal squamous cell carcinoma (ESCC) cell line CaEs-17, TE-1, EC109, KYSE510, KYSE140, KYSE70, and KYSE30 were selected to detect their sensitivity to cisplatin. 5-Azacytidine-2′-deoxycytidine (5′-Aza-CdR) treatment and methylation-specific PCR (MS-PCR) were used to detect the methylation status for KLF4. Cell viability, apoptosis, and cell cycle were measured using methyl thiazolyl tetrazolium (MTT) assay, Annexin V affinity assay, and flow cytometry, respectively.

Results

The sensitivity to cisplatin was different in the seven ESCC cell lines, with TE-1 having the lowest sensitivity and KYSE140 having the highest sensitivity. Interestingly, the level of KLF4 was relatively low in TE-1 cells; while it was high in KYSE140 cells. These results suggested that KLF4 may be involved in cisplatin resistance. The promoter region was mostly unmethylated in KYSE140 cells; while it was hypermethylated in TE-1 cells. After treatment with demethylation reagent 5-Aza-CdR, cisplatin sensitivities were significantly increased after upregulation of KLF4, as the IC50 values were significantly decreased in the TE-1 cell treated with 5-Aza-CdR. Furthermore, upregulation of KLF4 induced cell apoptosis and cell cycle arrest at S phase.

Conclusions

KLF4 enhances the sensitivity of cisplatin to ESCC cells through apoptosis induction and cell cycle arrest. Our data provided a novel insight to the mechanism of cisplatin resistance; overexpression of KLF4 may be a potential therapeutic strategy for cisplatin resistance in human ESCC.

Krüppel-like factor 4 (KLF4): What we currently know

Krüppel-like factor 4 (KLF4) is an evolutionarily conserved zinc finger-containing transcription factor that regulates diverse cellular processes such as cell growth, proliferation, and differentiation. Since its discovery in 1996, KLF4 has been gaining a lot of attention, particularly after it was shown in 2006 as one of four factors involved in the induction of pluripotent stem cells (iPSCs). Here we review the current knowledge about the different functions and roles of KLF4 in various tissue and organ systems.

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.

The Janus-faced roles of Krüppel-like factor 4 in oral squamous cell carcinoma cells

Krüppel-like factor 4 (KLF4) is a zinc-finger transcription factor that regulates many essential processes, including development and cell differentiation, proliferation, and apoptosis. Along with these roles in normal cells and tissues, KLF4 has important tumor suppressive and oncogenic functions in some malignancies. However, the roles of KLF4 in oral squamous cell carcinoma remain unclear. This study investigated the epigenetic alterations and possible roles of KLF4 in oral cancer carcinogenesis. Notably, KLF4 expression was significantly decreased in human oral cancer tissues compared with healthy controls, and KLF4 promoter hypermethylation contributed to the suppression of KLF4 expression. KLF4 expression was associated with tumor grade. Its expression was much lower in poorly differentiated oral cancers than in well-differentiated cancer cells. KLF4 exerted its antitumor activity in vitro and/or in vivo by inhibiting cell proliferation, cell cycle progression, cell colony formation and by inducing apoptosis. In addition, KLF4 over-expression promoted oral cancer cell migration and invasion in vitro. Knockdown of KLF4 promoted oral cancer cells growth and colony formation, and simultaneously inhibited cell migration and invasion. Mechanistic studies revealed that MMP-9 might contribute to KLF4-mediated cell migration and invasion. These results provide evidence that KLF4 might play Janus-faced roles in oral cancer carcinogenesis, acting both as a tumor suppressor and as an oncogene.

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

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

The Krüppel-like factors in female reproductive system pathologies

Female reproductive tract pathologies arise largely from dysregulation of estrogen and progesterone receptor signaling, leading to aberrant cell proliferation, survival, and differentiation. The signaling pathways orchestrated by these nuclear receptors are complex, require the participation of many nuclear proteins serving as key binding partners or targets, and involve a range of paracrine and autocrine regulatory circuits. The members of the Krüppel-like factor (KLF) family of transcription factors are ubiquitously expressed in reproductive tissues and have been increasingly implicated as critical co-regulators and integrators of steroid hormone actions. Herein, we explore the involvement of KLF family members in uterine pathology, describe their currently known molecular mechanisms, and discuss their potential as targets for therapeutic intervention.

Role of Krüppel-like factors in cancer stem cells

Cancer stem cells (CSCs), or cancer cells with stem cell properties, are a rare population of tumor bulk and are recognized to be responsible for cancer recurrence, drug resistance, and metastasis. However, the molecular mechanisms of how to regulate the differentiation and self-renewing of CSCs are poorly understood. Krüppel-like factors (KLFs) are essential DNA-binding transcriptional regulators with diverse functions in various cellular processes, including differentiation, proliferation, inflammation, migration, and pluripotency. Recent progress has highlighted the significance of KLFs in tumor progression and CSCs. The regulatory functions of KLFs in the development of cancer and CSCs have become a burgeoning area of intense research. In this review, we summarize the current understanding and progress of the transcriptional regulation of KLFs in CSCs and discuss the functional implications of targeting CSCs by KLFs for cancer therapeutics.

Expression of KLF4 is a predictive marker for survival in pediatric Burkitt lymphoma

Krüppel-like factor 4 (KLF4) is expressed in a variety of tissues with diverse physiological functions and activities. KLF4 can also function as a tumor suppressor or an oncogene, depending on the cellular context. Its role in hematological malignancies is controversial. This study examined the expression levels of KLF4 by immunohistochemistry in 73 pediatric non-Hodgkin lymphomas (NHLs) in a tissue microarray and also on several B-NHL cell lines. Elevated levels of KLF4 expression were detected in 66% of lymphoma cases and were more frequent in the Burkitt lymphoma (p = 0.05) subtype. There was a significant predictive power for outcome with low KLF4 expression, predicting a favorable overall survival compared to high levels. Multivariate analyses confirmed the association of KLF4 expression with unfavorable overall survival (p < 0.005). These findings were consistent with analyses in existing NHL microarray datasets. The present findings revealed that KLF4 is overexpressed in Burkitt pediatric lymphoma and is a potential biomarker for inferior overall survival.

Krüppel-like factors in cancer

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