KLF6 inhibits estrogen receptor-mediated cell growth in breast cancer via a c-Src-mediated pathway

Long non-coding RNA ZFAS1 regulates cell proliferation and invasion in cervical cancer via the miR-190a-3p/KLF6 axis

Long non-coding RNA (lncRNA) ZFAS1 (zinc finger antisense 1) was demonstrated to play critical roles in various cancer progression. However, the functions of ZFAS in cervical cancers (CC) are unclear. Human CC cell lines were used for in vitro experiments. RT-qPCR (Real Time Quantitative PCR) was performed to detect the expression of ZFAS1, microRNA-190a-3p (miR-190a-3p) and Kruppel-like factor 6 (KLF6). Cell proliferation, invasion and migration assays were used to investigate biological behaviors of CC cells related to CC progression. The relationship of KLF6 to ZFAS1 and miR-190a-3p was analyzed by circRIP and luciferase reporter assay. In addition, in vivo experiment was carried out to explore the function of ZFAS1 in tumor growth of CC. The expression levels of ZFAS1 and KLF6 were both significantly elevated, while the expression of miR-190a-3p was inhibited in CC tumor tissues. In addition, ZFAS1 influenced CC tumor growth through miR-190a-3p. KLF6 was a target of miR-190a-3p and inhibited miR-190a-3p-induced CC tumor growth. Furthermore, KLF6 was negatively regulated by miR-190a-3p, but positively regulated by ZFAS1. Overexpression of ZFAS1 and inhibition of miR-190a-3p significantly increased the expression levels of KLF6. Finally, in vitro assays demonstrated that inhibition of ZFAS1 reduced CC tumor growth and the expression levels of KLF6, but increased the expression levels of miR-190a-3p. ZFAS1 could regulate CC pathogenesis via regulating the miR-190a-3p/KLF6 axis, which might be considered as new CC therapeutic targets.

Krüppel-Like Factor 6 Downregulation Is Connected with a Poor Prognosis and Tumor Growth in Non-Small-Cell Lung Cancer

PURPOSE

Research in this article was performed to explore the biological role and clinical significance of Krüppel-like transcription factor 6 (KLF6) in non-small-cell lung cancer (NSCLC).

METHODS

KLF6 expression in NSCLC cell lines was analyzed using reverse transcription PCR and Western blot. The expressed KLF6 protein was examined in 50 surgical NSCLC tissues using immunohistochemistry. Statistical analyses were employed for clinical association examinations. CCK8 assay and Annexin V/PI analysis were used to execute cell proliferation and apoptosis in KLF6-overexpression cell lines and the control groups. Cleaved caspase-3 expression was also detected in KLF6-overexpression cells and NSCLC tissues. KLF6 expression correlation with cleaved caspase-3 was also examined.

RESULTS

It was discovered that downregulation of KLF6 was seen in human NSCLC cell lines. Low KLF6 expression in NSCLC tissues was correlated with poor patient prognosis (P < 0.005); patients with less KLF6 expression possessed a lower cumulative 5-year survival rate. Multivariate analysis showed KLF6 expression as an independent prognostic indicator for NSCLC individuals. Expression levels of KLF6 were associated with NSCLC tumor size (P = 0.041). Overexpression of KLF6 inhibited cell proliferation and stimulated A549 and H322 cell line apoptosis. Cleaved caspase-3 protein had higher expression levels in KLF6-overexpressed cells than in the control group. The KLF6 expression levels were positively related to the cleaved caspase-3 protein expression in NSCLC tissues (r = 0.689, P = 0.001).

CONCLUSIONS

The results indicate that downregulation of KLF6 is a significant NSCLC progression marker. KLF6 prevents cell growth and promotes cell apoptosis, possibly caspase-3 activations.

Spatiotemporal endometrial transcriptome analysis revealed the luminal epithelium as key player during initial maternal recognition of pregnancy in the mare

During the period of maternal recognition of pregnancy (MRP) in the mare, the embryo needs to signal its presence to the endometrium to prevent regression of the corpus luteum and prepare for establishment of pregnancy. This is achieved by mechanical stimuli and release of various signaling molecules by the equine embryo while migrating through the uterus. We hypothesized that embryo's signals induce changes in the endometrial gene expression in a highly cell type-specific manner. A spatiotemporal transcriptomics approach was applied combining laser capture microdissection and low-input-RNA sequencing of luminal and glandular epithelium (LE, GE), and stroma of biopsy samples collected from days 10-13 of pregnancy and the estrous cycle. Two comparisons were performed, samples derived from pregnancies with conceptuses ≥ 8 mm in diameter (comparison 1) and conceptuses ≤ 8 mm (comparison 2) versus samples from cyclic controls. The majority of gene expression changes was identified in LE and much lower numbers of differentially expressed genes (DEGs) in GE and stroma. While 1253 DEGs were found for LE in comparison 1, only 248 were found in comparison 2. Data mining mainly focused on DEGs in LE and revealed regulation of genes related to prostaglandin transport, metabolism, and signaling, as well as transcription factor families that could be involved in MRP. In comparison to other mammalian species, differences in regulation of genes involved in epithelial barrier formation and conceptus attachment and implantation reflected the unique features of equine reproduction at the time of MRP at the molecular level.

Long noncoding RNA ZBED3-AS1 restrains breast cancer progression by targeting the microRNA-513a-5p/KLF6 axis

Breast cancer (BC) is the most commonly occurring malignancy in women. This study aimed to investigate the functions of the long noncoding RNA ZBED3‐AS1 (ZBED3‐AS1) in BC and its molecular mechanisms. qRT‐PCR was conducted to access the expression of ZBED3‐AS1, microRNA‐513a‐5p (miR‐513a‐5p), and Kruppel like factor 6 (KLF6) in BC. Additionally, BC cell viability and proliferative capacity were measured by MTT and 5‐Ethynyl‐20‐deoxyuridine (EdU) assays. A transwell assay was used for evaluating BC cell migration and invasion. The interactions among ZBED3‐AS1, miR‐513a‐5p, and KLF6 in BC were confirmed by dual‐luciferase reporter assay. Furthermore, feedback approaches were performed to determine whether ZBED3‐AS1 influences BC cell behaviors by regulating the miR‐513a‐5p/KLF6 axis. The murine xenograft model was established to assess the effect of ZBED3‐AS1 on tumor growth. The expression of ZBED3‐AS1 and KLF6 was reduced, while miR‐513a‐5p expression was elevated in BC. ZBED3‐AS1 elevation attenuated the malignant behaviors of BC cells, including viability, proliferative capacity, migration, and invasion. Mechanical experiments revealed that ZBED3‐AS1 targeted miR‐513a‐5p, and miR‐513a‐5p targeted KLF6 in BC. Feedback approaches validated that miR‐513a‐5p overexpression or KLF6 depletion reversed the inhibitory effects of ZBED3‐AS1 upregulation on viability, proliferative capacity, migration, and invasion of BC cells. Furthermore, ZBED3‐AS1 elevation attenuated the tumor growth in the murine xenograft model. ZBED3‐AS1 hindered the malignant development of BC cells by regulating the miR‐513a‐5p/KLF6 axis, providing a novel therapeutic target in BC.

LncRNA LUCAT1/miR-181a-5p axis promotes proliferation and invasion of breast cancer via targeting KLF6 and KLF15

BACKGROUND

Long non-coding RNAs (lncRNAs) are novel regulatory molecules in breast cancer development. LncRNA LUCAT1 is a potential tumor promoter in human cancers. In this study, we aimed to explore the role of LUCAT1 in human breast cancer tissues and cells.

METHODS

A total of 31 breast cancer patients who underwent tumor resection, but without chemo- or radiotherapy or acute lung/heart/kidney diseases, provided tumor and adjacent normal tissues. Bioinformatic analysis, qRT-PCR, and luciferase reporter assay were carried out during the study.

RESULTS

qRT-PCR analysis indicated that, compared with the adjacent tissues and MCF-10A normal breast epithelial cells, LUCAT1 was markedly up-regulated in the breast cancer tissues and five BC cell lines, including MDA-MB-231, MDA-MB-468, MDA-MB-435, SKBR3, and MCF-7. The knockdown of LUCAT1, through the transfection of small interfering RNA (siRNA) specific to LUCAT1, resulted in inhibition of proliferation in breast cancer cells. The expression levels of miR-181a-5p were decreased in the breast cancer tissues and five BC cell lines. Bioinformatic analysis and luciferase reporter assay suggested the interaction between miR-181a-5p and LUCAT1. In addition, the effects of LUCAT1 on promoting cell proliferation were attenuated by overexpression of miR-181a-5p through the transfection of miR-181a-5p mimic. Moreover, bioinformatics and luciferase reporter assay confirmed that miR-181a-5p targeted the 3'-UTR region of KLF6 and KLF15 mRNA, which were two tumor suppressor genes. LUCAT1/miR-181a-5p axis regulated the expression of KLF6 and KLF15 both in vitro and in vivo.

CONCLUSIONS

Our data indicate that LUCAT1/miR-181a-5p axis can serve as a novel therapeutic target in breast cancer.

The Clinical Relevance and Function of Krüppel-Like Factor 16 in Breast Cancer

Background

Krüppel-like factor 16 (KLF16), a member of the KLF family, is involved in metabolism and regulation of the endocrine system and has emerging roles in tumor progression. However, the expression of KLF16 and its role in breast cancer are elusive.

Methods

We investigated the expression and prognostic value of KLFs in breast cancer using data acquired from the TCGA BRCA dataset and the Kaplan–Meier plotter dataset. The protein levels of KLF16 in breast specimens were detected by immunohistochemistry (IHC). KLF16 silencing using shRNAs was performed to explore the effects of KLF16 on breast cancer cell growth, migration, and invasion. The expression of EMT markers in cells manipulated for KLF16 expression was assessed by Western blotting.

Results

Using publicly available dataset and specimens from breast cancer patients, we found that the expression levels of KLF16 were significantly higher in tumor tissues and that high levels of KLF16 were associated with poor prognosis in breast cancer patients. Moreover, KLF16 expression levels had relation to several clinicopathological parameters of breast cancer, including the molecular subtype and histological grade. Importantly, knockdown of KLF16 dramatically suppressed cell proliferation both in vitro and in vivo. Also, KLF16 deletion impaired migration, and invasion in breast cancer cells, and suppressed epithelial–mesenchymal transition (EMT).

Conclusion

Our results suggest that KLF16 has important oncogenic functions in breast cancer and that the expression levels of KLF16 are associated with prognosis in breast cancer patients. Our findings also suggest that KLF16 is involved in proliferation, migration, and invasion in breast cancer cells. Thus, KLF16 might be a promising prognostic marker and a therapeutic target for breast cancer.

Krüppel-like factors in breast cancer: Function, regulation and clinical relevance

Breast cancer has accounted for the leading cause of cancer-related mortality among women worldwide. Although the progress in its diagnosis and treatment has come at a remarkable pace during the past several decades, there are still a wide array of problems regarding its progression, metastasis and treatment resistance that have not yet been fully clarified. Recently, an increasing number of studies have revealed that some members of Krüppel-like factors(KLFs) are significantly associated with cell proliferation, apoptosis, metastasis, cancer stem cell regulation and prognostic and predictive value for patients in breast cancer, indicating their promising prognostic and predictive potential for breast cancer survival and outcome. In this review, we will summarize our current knowledge of the functions, regulations and clinical relevance of KLFs in breast cancer.

Aberrant alternative splicing in breast cancer

Alternative splicing is critical for human gene expression regulation, which plays a determined role in expanding the diversity of functional proteins. Importantly, alternative splicing is a hallmark of cancer and a potential target for cancer therapeutics. Based on the statistical data, breast cancer is one of the top leading causes of cancer-related deaths in women worldwide. Strikingly, alternative splicing is closely associated with breast cancer development. Here, we seek to provide a general review of the relationship between alternative splicing and breast cancer. We introduce the process of alternative splicing and its regulatory role in cancers. In addition, we highlight the functions of aberrant alternative splicing and mutations of splicing factors in breast cancer progression. Moreover, we discuss the role of alternative splicing in cancer drug resistance and the potential of being targets for cancer therapeutics.

Lowly methylated region analysis identifies EBF1 as a potential epigenetic modifier in breast cancer

Breast cancer (BC) encompasses heterogeneous pathologies with different subtypes exhibiting distinct molecular changes, including those related to DNA methylation. However, the role of these changes in mediating BC heterogeneity is poorly understood. Lowly methylated regions (LMRs), non-CpG island loci that usually contain transcription factor (TF) binding sites, have been suggested to act as regulatory elements that define cellular identity. In this study, we aimed to identify the key subtype-specific TFs that may lead to LMR generation and shape the BC methylome and transcription program. We initially used whole-genome bisulfite sequencing (WGBS) data available at The Cancer Genome Atlas (TCGA) portal to identify subtype-specific LMRs. Differentially methylated regions (DMRs) within the BC PAM50 subtype-specific LMRs were selected by comparing tumors and normal tissues in a larger TCGA cohort assessed by HumanMethylation450 BeadChip (450K) arrays and TF enrichment analyses were performed. To assess the impact of LMRs on gene expression, TCGA RNA sequencing data were downloaded and Pearson correlations between methylation levels of loci presenting subtype-specific TF motifs and expression of the nearest genes were calculated. WGBS methylome data revealed a large number of LMRs for each of the BC subtypes. Analysis of these LMRs in the 450K datasets available for a larger sample set identified 7,765, 5,657, and 19 differentially methylated positions (DMPs) between normal adjacent tissues and tumor tissues from basal, luminal, and HER2-enriched subtypes, respectively. Unsupervised clustering showed that the discriminatory power of the top DMPs was remarkably strong for basal BC. Interestingly, in this particular subtype, we found 4,409 differentially hypomethylated positions grouped into 1,185 DMRs with a strong enrichment for the early B-cell factor 1 (EBF1) motifs. The methylation levels of the DMRs containing EBF1 motifs showed a strong negative correlation with the expression of 719 nearby genes, including BTS2 and CD74, two oncogenes known to be specific for basal BC subtype and for poor outcome. This study identifies LMRs specific to the three main BC subtypes and reveals EBF1 as a potentially important regulator of BC subtype-specific methylation and gene expression program.

A summary of relationships between alternative splicing and breast cancer

Alternative splicing (AS) is the process of combinatorial rearrangement of parts of exons, and/or parts of introns into mature RNA to result in a multitude of transcripts. AS is a biological process through which organisms produce as many protein variants as possible by a limited genetic resource. It plays an important role in growth and development of the organisms. Over the past few years, alternative splicing has been discovered to be critical for genesis and development of malignant tumors, including breast cancer. If the relationships between AS and breast cancer can be discussed more deeply, it will be helpful for better diagnosis, judging prognosis and intervening with breast cancer. In this paper, the relationships between AS and breast cancer are elaborated from different angles, in hope that this summary is beneficial for readers to understand the roles of AS and breast cancer.

Kruppel-like factor 6 suppresses growth and invasion of hepatocellular carcinoma cells in vitro and in vivo

Kruppel-like factor 6 (KLF6) as a novel tumor suppressive gene participates in multiple biological behaviors and plays an important role in regulating tumor cell growth and invasion. However, the functions of KLF6 in hepatocellular carcinoma (HCC) remain poorly understood. The expression level of KLF6 was examined by immunohistochemical assay in human HCC tissues, and KLF6-overexpressed HCC cells (SMCC-7721 and HepG2) were used for evaluating cell proliferation and invasion by MTT and Transwell assays. A subcutaneous HCC tumor model was established for assessing tumor growth in vivo. Our results showed that the expression of KLF6 was significantly downregulated in HCC tissues compared with the adjacent non-cancerous tissues (50.0% vs. 72.0%, P = 0.034) and negatively associated with the lymph-vascular space invasion (LVSI) in HCC patients (P = 0.003). Furthermore, overexpression of KLF6 reduced cell proliferation and weakened the cell invasive potential followed with the decreased expression of PCNA and MMP-9 in HCC cells. The in vivo experiment indicated that KLF6 overexpression suppressed the xenograft tumor growth. Therefore, our findings show that KLF6 suppresses growth and invasion of HCC cells in vitro and in vivo, suggesting a tumor suppressive function in HCC and provides the potential therapeutic target for the treatment of HCC.

Ah Receptor Pathway Intricacies; Signaling Through Diverse Protein Partners and DNA-Motifs

The Ah receptor is a transcription factor that modulates gene expression via interactions with multiple protein partners; these are reviewed, including the novel NC-XRE pathway involving KLF6.

HER2 and uPAR cooperativity contribute to metastatic phenotype of HER2-positive breast cancer

Human epidermal growth factor receptor type 2 (HER2)-positive breast carcinoma is highly aggressive and mostly metastatic in nature though curable/manageable in part by molecular targeted therapy. Recent evidence suggests a subtype of cells within HER2-positive breast tumors that concomitantly expresses the urokinase plasminogen activator receptor (uPAR) with inherent stem cell/mesenchymal-like properties promoting tumor cell motility and a metastatic phenotype. This HER-positive/uPAR-positive subtype may be partially responsible for the failure of HER2-targeted treatment strategies. Herein we discuss and substantiate the cumulative preclinical and clinical evidence on HER2-uPAR cooperativity in terms of gene co-amplification and/or mRNA/protein co-overexpression. We then propose a regulatory signaling model that we hypothesize to maintain upregulation and cooperativity between HER2 and uPAR in aggressive breast cancer. An improved understanding of the HER2/uPAR interaction in breast cancer will provide critical biomolecular information that may help better predict disease course and response to therapy.

Identification of miRNAs that specifically target tumor suppressive KLF6-FL rather than oncogenic KLF6-SV1 isoform

The Krüppel like factor 6 (KLF6) gene encodes multiple protein isoforms derived from alternative mRNA splicing, most of which are intimately involved in hepatocarcinogenesis and tumor progression. Recent bioinformatics analysis shows that alternative mRNA splicing of the KLF6 gene produces around 16 alternatively spliced variants with divergent or even opposing functions. Intriguingly, the full-length KLF6 (KLF6-FL) is a tumor suppressor gene frequently inactivated in liver cancer, whereas KLF6 splice variant 1 (KLF6-SV1) is an oncogenic isoform with antagonistic function against KLF6-FL. Compelling evidence indicates that miRNA, the small endogenous non-coding RNA (ncRNA), acts as a vital player in modulating a variety of cellular biological processes through targeting different mRNA regions of protein-coding genes. To identify the potential miRNAs specifically targeting KLF6-FL, we utilized bioinformatics analysis in combination with the luciferase reporter assays and screened out two miRNAs, namely miR-210 and miR-1301, specifically targeted the tumor suppressive KLF6-FL rather than the oncogenic KLF6-SV1. Our in vitro experiments demonstrated that stable expression of KLF6-FL inhibited cell proliferation, migration and angiogenesis while overexpression of miR-1301 promoted cell migration and angiogenesis. Further experiments demonstrated that miR-1301 was highly expressed in liver cancer cell lines as well as clinical specimens and we also identified the potential methylation and histone acetylation for miR-1301 gene. To sum up, our findings unveiled a novel molecular mechanism that specific miRNAs promoted tumorigenesis by targeting the tumor suppressive isoform KLF6-FL rather than its oncogenic isoform KLF6-SV1.

Mutations and Krüppel-like factor 6 (KLF6) expression levels in breast cancer

The transcription factor KLF6 gene has been identified as a tumor suppressor because of its inactivation in several types of cancers by different mechanisms. However, there are no data in the literature investigating the KLF6 mutation rate and expression levels in breast cancer. Therefore, the present study was conducted in order to investigate whether genetic alterations of KLF6 in association with the KLF6 mRNA expression levels may play a role in breast carcinogenesis. For this purpose, we analyzed alterations of the KLF6 gene by direct sequencing and the mRNA levels by reverse transcription-PCR (RT-PCR). In addition to four different non-coding alterations, one missense and two silent alterations were identified in the coding sequence. Reduced KLF6 expression was observed in 41 (83.67 %) of the 49 breast cancer tumors. These findings suggest that the mutation profile of the KLF6 gene in breast tumors is similar to other cancer types. However, these mutations do not exert any effect on the gene expression rate. Downregulation of KLF6 during the progression of breast cancer is independent of the mutations and occurs by a different mechanism.

Krüppel-like factor 6 in the progression and prognosis of malignant melanoma

Objectives:

The aims of this study were to investigate the incidence of Krüppel-like factor 6 (KLF6) protein staining in patients with cutaneous malignant melanoma and examine its potential relevance to clinicopathological characteristics and tumour cell proliferation.

Methods:

Clinicopathological data from patients with cutaneous malignant melanoma were analysed retrospectively. Presence of KLF6 and the antigen Ki-67 in malignant melanoma and healthy tissue samples from each patient was detected by immunohistochemistry. The proliferation index was calculated on the basis of Ki-67 expression. The relationship between KLF6 and clinicopathological characteristics was also analysed.

Results:

KLF6 was detected more frequently in normal healthy skin tissue compared with cutaneous malignant melanoma lesions ( n = 40). There was a negative correlation between the presence of KLF6 and the proliferation index. The presence of KLF6 was also significantly correlated with tumour diameter, lymph node metastasis, tumour–node–metastasis stage and 3-year survival rate.

Conclusions:

KLF6 protein is downregulated in human cutaneous malignant melanoma lesions compared with healthy skin tissue. KLF6 may be involved in tumour progression and may be a tumour suppressor and prognostic marker for cutaneous malignant melanoma.

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.

PSG gene expression is up-regulated by lysine acetylation involving histone and nonhistone proteins

Background

Lysine acetylation is an important post-translational modification that plays a central role in eukaryotic transcriptional activation by modifying chromatin and transcription-related factors. Human pregnancy-specific glycoproteins (PSG) are the major secreted placental proteins expressed by the syncytiotrophoblast at the end of pregnancy and represent early markers of cytotrophoblast differentiation. Low PSG levels are associated with complicated pregnancies, thus highlighting the importance of studying the mechanisms that control their expression. Despite several transcription factors having been implicated as key regulators of PSG gene family expression; the role of protein acetylation has not been explored.

Methodology/Principal Findings

Here, we explored the role of acetylation on PSG gene expression in the human placental-derived JEG-3 cell line. Pharmacological inhibition of histone deacetylases (HDACs) up-regulated PSG protein and mRNA expression levels, and augmented the amount of acetylated histone H3 associated with PSG 5′regulatory regions. Moreover, PSG5 promoter activation mediated by Sp1 and KLF6, via the core promoter element motif (CPE, −147/−140), was markedly enhanced in the presence of the HDAC inhibitor trichostatin A (TSA). This effect correlated with an increase in Sp1 acetylation and KLF6 nuclear localization as revealed by immunoprecipitation and subcellular fractionation assays. The co-activators PCAF, p300, and CBP enhanced Sp1-dependent PSG5 promoter activation through their histone acetylase (HAT) function. Instead, p300 and CBP acetyltransferase domain was dispensable for sustaining co-activation of PSG5 promoter by KLF6.

Conclusions/Significance

Results are consistent with a regulatory role of lysine acetylation on PSG expression through a relaxed chromatin state and an increase in the transcriptional activity of Sp1 and KLF6 following an augmented Sp1 acetylation and KLF6 nuclear localization.

Krüppel-like factor 6 expression changes during trophoblast syncytialization and transactivates ßhCG and PSG placental genes

Background

Krüppel-like factor-6 (KLF6) is a widely expressed member of the Sp1/KLF family of transcriptional regulators involved in differentiation, cell cycle control and proliferation in several cell systems. Even though the highest expression level of KLF6 has been detected in human and mice placenta, its function in trophoblast physiology is still unknown.

Methodology/Principal Findings

Herein, we explored KLF6 expression and sub-cellular distribution in human trophoblast cells differentiating into the syncytial pathway, and its role in the regulation of genes associated with placental development and pregnancy maintenance. Confocal immunofluorescence microscopy demonstrated that KLF6 is expressed throughout human cytotrophoblast differentiation showing no evident modifications in its nuclear and cytoplasmic localization pattern. KLF6 transcript and protein peaked early during the syncytialization process as determined by qRT-PCR and western blot assays. Overexpression of KLF6 in trophoblast-derived JEG-3 cells showed a preferential nuclear signal correlating with enhanced expression of human β-chorionic gonadotropin (βhCG) and pregnancy-specific glycoprotein (PSG) genes. Moreover, KLF6 transactivated βhCG5, PSG5 and PSG3 gene promoters. Deletion of KLF6 Zn-finger DNA binding domain or mutation of the consensus KLF6 binding site abolished transactivation of the PSG5 promoter.

Conclusions/Significance

Results are consistent with KLF6 playing a role as transcriptional regulator of relevant genes for placental differentiation and physiology such as βhCG and PSG, in agreement with an early and transient increase of KLF6 expression during trophoblast syncytialization.

The Krüppel-like factor 6 genotype is associated with gastric cancer in a Chinese population

Association of the IVS1 -27G/A polymorphism of Krüppel-like factor 6 (KLF6) with gastric cancer was examined in a Chinese population comprising 300 gastric cancer patients and 300 healthy controls. Single-nucleotide polymorphism analysis was performed by amplifying intron 1 of KLF6 and sequencing the products. The KLF6 genotype IVS1 -27AA was significantly less frequent in gastric cancer patients than in controls and significantly less frequent in patients with advanced (stage III/IV) gastric cancer than in those with early (stage I/II) cancer. Stratification by location, Lauren's classification and histological differentiation revealed no significant differences in genotype distribution. Thus, in this Chinese population the KLF6 IVS1 -27AA genotype was associated with a decreased risk of gastric cancer and with cancer stage. Further study is required to clarify the mechanisms involved and, potentially, to facilitate the design of effective clinical trials.

Human phosphatidylethanolamine-binding protein 4 promotes transactivation of estrogen receptor alpha (ERalpha) in human cancer cells by inhibiting proteasome-dependent ERalpha degradation via association with Src

We identified human phosphatidylethanolamine-binding protein 4 (hPEBP4) as a human-derived novel member of the phosphatidylethanolamine-binding protein family, which is involved in apoptosis resistance of tumor cells. Because of its preferential expression in estrogen-related cancers, we wondered whether hPEBP4 plays a role in estrogen-induced cancer cell growth. Here, we demonstrated that hPEBP4 inhibited the 17beta-estradiol (E(2))-induced, proteasome-dependent estrogen receptor alpha (ERalpha) degradation to increase the protein level of ERalpha. Silencing of hPEBP4 inhibited the recruitment of ERalpha to the promoter of the ERalpha target gene pS2 in MCF-7 breast cancer cells after E(2) treatment. E(2)-induced, ERalpha-mediated transcription via the estrogen-response element, as well as the cellular proliferation, was significantly suppressed in hPEBP4-silenced MCF-7 cells. We found that Src, whose association with ERalpha facilitates the ERalpha binding to components of proteolytic machinery, could associate with hPEBP4 and that overexpression of hPEBP4 prevented the E(2)-induced interaction between ERalpha and Src. ERalpha overexpression, proteasome inhibitor, or Src inhibitor could reverse the suppression of ERalpha-mediated transactivation by hPEBP4 silencing. The inhibition of the proteasome degradation and the promotion of transactivation of ERalpha by hPEBP4 via the Src pathway were further confirmed in HeLa cells. Finally, we found that the promoting effects of hPEBP4 on ERalpha-mediated transactivation and estrogen-induced proliferation of cancer cells did not depend on its regulation of Akt and ERK activity. Our data suggest that hPEBP4 inhibits proteasome-dependent ERalpha degradation through the Src pathway, thus enhancing ERalpha-mediated transactivation and promoting the proliferation of cancer cells in response to estrogen.

Nuclear expression of KLF6 tumor suppressor factor is highly associated with overexpression of ERBB2 oncoprotein in ductal breast carcinomas

Background

Krüppel-like factor 6 (KLF6) is an evolutionarily conserved and ubiquitously expressed protein that belongs to the mammalian Sp1/KLF family of transcriptional regulators. Though KLF6 is a transcription factor and harbors a nuclear localization signal it is not systematically located in the nucleus but it was detected in the cytoplasm of several tissues and cell lines. Hence, it is still not fully settled whether the tumor suppressor function of KLF6 is directly associated with its ability to regulate target genes.

Methodology/Principal Findings

In this study we analyzed KLF6 expression and sub-cellular distribution by immunohistochemistry in several normal and tumor tissues in a microarray format representing fifteen human organs. Results indicate that while both nuclear and cytoplasmic distribution of KLF6 is detected in normal breast tissues, breast carcinomas express KLF6 mainly detected in the cytoplasm. Expression of KLF6 was further analyzed in breast cancer tissues overexpressing ERBB2 oncoprotein, which is associated with poor disease prognosis and patient's survival. The analysis of 48 ductal carcinomas revealed a significant population expressing KLF6 predominantly in the nuclear compartment (X²p = 0.005; Fisher p = 0.003). Moreover, this expression pattern correlates directly with early stage and small ductal breast tumors and linked to metastatic events in lymph nodes.

Conclusions/Significance

Data are consistent with a preferential localization of KLF6 in the nuclear compartment of early stage and small HER2-ERBB2 overexpressing ductal breast tumor cells, also presenting lymph node metastatic events. Thus, KLF6 tumor suppressor could represent a new molecular marker candidate for tumor prognosis and/or a potential target for therapy strategies.