Loss of Krüppel-like factor 4 expression contributes to Sp1 overexpression and human gastric cancer development and progression

Significant biological role of sp1 transactivation in multiple myeloma

PURPOSE

The transcription factor specificity protein 1 (Sp1) controls number of cellular processes by regulating the expression of critical cell cycle, differentiation, and apoptosis-related genes containing proximal GC/GT-rich promoter elements. We here provide experimental and clinical evidence that Sp1 plays an important regulatory role in multiple myeloma (MM) cell growth and survival.

EXPERIMENTAL DESIGN

We have investigated the functional Sp1 activity in MM cells using a plasmid with Firefly luciferase reporter gene driven by Sp1-responsive promoter. We have also used both siRNA- and short hairpin RNA-mediated Sp1 knockdown to investigate the growth and survival effects of Sp1 on MM cells and further investigated the anti-MM activity of terameprocol (TMP), a small molecule that specifically competes with Sp1-DNA binding in vitro and in vivo.

RESULTS

We have confirmed high Sp1 activity in MM cells that is further induced by adhesion to bone marrow stromal cells (BMSC). Sp1 knockdown decreases MM cell proliferation and induces apoptosis. Sp1-DNA binding inhibition by TMP inhibits MM cell growth both in vitro and in vivo, inducing caspase-9-dependent apoptosis and overcoming the protective effects of BMSCs.

CONCLUSIONS

Our results show Sp1 as an important transcription factor in myeloma that can be therapeutically targeted for clinical application by TMP.

MicroRNA-335 acts as a metastasis suppressor in gastric cancer by targeting Bcl-w and specificity protein 1

Aberrant expression of miR-335 has been frequently reported in cancer studies, suggesting that there is a close correlation between miR-335 and cancer during its development, progression, metastasis and prognosis. The expression of miR-335 in gastric cancer and its effects are not known. Relative expression of miR-335 in 4 gastric cancer cell lines and in 70 gastric cancer tissues was confirmed by real-time quantitative reverse transcriptase-PCR compared with controls. Transwell cell migration and Matrigel invasion assay in vitro and metastasis formation assay in vivo were used to examine the effects of miR-335 expression on gastric cancer cell invasion and metastasis. The effect of miR-335 expression on gastric cancer cell proliferation was estimated by the 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay. Luciferase reporter assay and western blot were used to examine the potential target genes and related pathways. Gene silencing with small-interfering RNA was used to examine the effects of target genes on gastric cancer cell invasion. miR-335 was dramatically downregulated in gastric cancer cell lines than in the normal gastric cell line GES-1. Low expression of miR-335 was significantly associated with lymph-node metastasis, poor pT stage, poor pN stage and invasion of lymphatic vessels. Overexpression of miR-335 suppressed gastric cancer cell invasion and metastasis in vitro and in vivo, but has no significant effects on cell proliferation. Furthermore, miR-335 might suppress gastric cancer invasion and metastasis by targeting Bcl-w and specificity protein 1 (SP1). Taken together, our results provide evidence that miR-335 might function as a metastasis suppressor in gastric cancer by targeting SP1 directly and indirectly through the Bcl-w-induced phosphoinositide 3-kinase-Akt-Sp1 pathway. miR-335 showing altered expression at different stages of gastric cancer could be a target for gastric cancer therapies and could be further developed as a potential prognostic factor.

Expression and Function of Kruppel Like-Factors (KLF) in Carcinogenesis

Krüppel-like factor (KLF) family members share a three C2H2 zinc finger DNA binding domain, and are involved in cell proliferation and differentiation control in normal as in pathological situations. Studies over the past several years support a significant role for this family of transcription factors in carcinogenesis. KLFs can both activate and repress genes that participate in cell-cycle regulation. Among them, many up-regulated genes are inhibitors of proliferation, whereas genes that promote cell proliferation are repressed. However, several studies do present KLFs as positive regulator of cell proliferation. KLFs can be deregulated in multiple cancers either by loss of heterozygosity (LOH), somatic mutation or transcriptional silencing by promoter hypermethylation. Accordingly, KLF expression was shown to mediate growth inhibition when ectopically expressed in multiple cancer-derived cell lines through the inhibition of a number of key oncogenic signaling pathways, and to revert the tumorogenic phenotype in vivo. Taken together, these observations suggest that KLFs act as tumor suppressor. However, in some occasion, KLFs could act as tumor promoters, depending on “cellular context”. Thus, this review will discuss the roles and the functions of KLF family members in carcinogenesis, with a special focus on cancers from epithelial origin.

Krüppel-like factors 4 and 5: unity in diversity

Krüppel-like factors (Klf) 4 and 5 belong to a family of zinc finger-containing transcription factors that share homology with the Drosophila gene Krüppel. They regulate proliferation and differentiation of a wide variety of cells and have been linked to tumorigenesis. Their most striking role so far has turned out to be their ability to reprogram/ maintain embryonic stem cell fate. In this review, the data available in the field regarding their role in proliferation and differentiation and their coupling to carcinogenesis are summarized. The emphasis is on their context dependence and how they might be able to regulate diverse transcriptional outputs from the genome.

Sp1 upregulates survivin expression in adenocarcinoma of lung cell line A549

Survivin has been implicated in tumor genesis, progression, and resistance to anticancer agents. However, the precise regulatory mechanism for survivin expression is not thoroughly defined. In this study, we showed that Sp1 was co-overexpressed with survivin in adenocarcinoma of lung cells A549, but not in differentiated human bronchial epithelial cells 4F0439 or small airway epithelial cells 3F1584. Subsequently, transfection experiments demonstrated that the inhibition of Sp1 signaling suppressed survivin expression in A549 cells, whereas Sp1 overexpression increased the level of survivin protein as well as its mRNA. We also found that Sp1 could decrease capase-9 activity, which is shown to be suppressed by survivin during apoptosis inhibition. Finally, Luciferase activity and ChIP assays revealed that Sp1 activated survivin promoter by direct interaction with it. Taken together, our data suggest Sp1 plays a potent role in the upregulation of survivin expression in lung cancer cells at the transcriptional level.

Interleukin-10 genotypes of the -1087 single nucleotide polymorphism influence sp1 expression in periodontitis lesions

BACKGROUND

Interleukin (IL)-10 is an important cytokine in immune regulation, and the -1087 IL-10 single nucleotide polymorphism (SNP) is associated with chronic periodontitis. The binding of the transcription factor Sp1 to the -1087 position in the IL-10 promoter upregulates IL-10 gene expression, especially in patients with the GG genotype. A correlation between the -1087 GG genotype and high IL-10 and Sp1 gene expressions was found.

METHODS

Twenty-five individuals with severe generalized chronic periodontitis were genotyped for the -1087 IL-10 gene polymorphism. SV40 promoter factor 1/specificity protein 1 (Sp1) and IL-10 mRNA were analyzed using a real-time polymerase chain reaction. The amount of Sp1-positive cells and Sp1-positive B cells, as well as the amount of Sp1 protein, in periodontitis lesions were assessed using immunohistochemistry and an in situ proximity ligation assay.

RESULTS

The mRNA expression of Sp1 and IL-10 in patients with the GG genotype was four times higher than that in patients with the AA genotype. Proportions of Sp1-positive cells overall and Sp1-positive B cells were larger in patients with the GG genotype than in patients with the AA genotype.

CONCLUSION

The transcription factor Sp1 was present in large amounts in periodontitis lesions, and the local expression of Sp1 was related to the -1087 IL-10 SNP.

Mammalian Krüppel-like factors in health and diseases

The Krüppel-like factor (KLF) family of transcription factors regulates diverse biological processes that include proliferation, differentiation, growth, development, survival, and responses to external stress. Seventeen mammalian KLFs have been identified, and numerous studies have been published that describe their basic biology and contribution to human diseases. KLF proteins have received much attention because of their involvement in the development and homeostasis of numerous organ systems. KLFs are critical regulators of physiological systems that include the cardiovascular, digestive, respiratory, hematological, and immune systems and are involved in disorders such as obesity, cardiovascular disease, cancer, and inflammatory conditions. Furthermore, KLFs play an important role in reprogramming somatic cells into induced pluripotent stem (iPS) cells and maintaining the pluripotent state of embryonic stem cells. As research on KLF proteins progresses, additional KLF functions and associations with disease are likely to be discovered. Here, we review the current knowledge of KLF proteins and describe common attributes of their biochemical and physiological functions and their pathophysiological roles.

Altered intestinal epithelial homeostasis in mice with intestine-specific deletion of the Krüppel-like factor 4 gene

The zinc finger transcription factor, Krüppel-like factor 4 (KLF4), is expressed in the post-mitotic, differentiated epithelial cells lining the intestinal tract and exhibits a tumor suppressive effect on intestinal tumorigenesis. Here we report a role for KLF4 in maintaining homeostasis of intestinal epithelial cells. Mice with conditional ablation of the Klf4 gene from the intestinal epithelium were viable. However, both the rates of proliferation and migration of epithelial cells were increased in the small intestine of mutant mice. In addition, the brush-border alkaline phosphatase was reduced as was expression of ephrine-B1 in the small intestine, resulting in mispositioning of Paneth cells to the upper crypt region. In the colon of mutant mice, there was a reduction of the differentiation marker, carbonic anhydrase-1, and failure of differentiation of goblet cells. Mechanistically, deletion of Klf4 from the intestine resulted in activation of genes in the Wnt pathway and reduction in expression of genes encoding regulators of differentiation. Taken together, these data provide new insights into the function of KLF4 in regulating postnatal proliferation, migration, differentiation, and positioning of intestinal epithelial cells and demonstrate an essential role for KLF4 in maintaining normal intestinal epithelial homeostasis in vivo.

Hsa-mir-27a genetic variant contributes to gastric cancer susceptibility through affecting miR-27a and target gene expression

Aberrant microRNA (miRNA) expression is presently proposed to correlate with various human cancers and common single-nucleotide polymorphisms (SNP) at miRNA genes can influence the maturation of miRNAs or miRNA-mediated transcriptional regulation. However, whether miRNAs SNP alter gastric cancer susceptibility is still unclear. Here we investigated the possible role of a common A/G polymorphism (rs895819) within hsa-mir-27a in the development or progression of gastric cancer, and assessed the effect of rs895819 on the expression of miR-27a and its target gene Zinc finger and BTB domain containing 10 (ZBTB10). In the present case-control study, we found that subjects with the variant genotypes (AG + GG) showed a significantly increased risk of gastric cancer relative to AA carriers (adjusted odds ratio = 1.48, 95% confidence interval 1.06-2.05; P = 0.019). The elevated risk was especially evident in older subjects (age >58 years), men, nonsmokers and rural subjects. A significant association of hsa-mir-27a variant genotypes with lymph node metastasis was also observed. Further functional analyses indicated that variant genotypes might be responsible for elevated miR-27a levels and reduced ZBTB10 mRNA. Moreover, an inverse correlation was found between ZBTB10 and miR-27a levels. In conclusion, we were the first to show that a common polymorphism (rs895819) in hsa-mir-27a, by modulating miR-27a and ZBTB10 levels, acted as an important factor of the gastric cancer susceptibility.

Expression of the tumor suppressor Krüppel-like factor 4 as a prognostic predictor for colon cancer

BACKGROUND

The zinc finger transcription factor Krüppel-like factor 4 (KLF4) regulates numerous physiologic processes, including proliferation, differentiation, and development. Studies also showed that KLF4 is involved in tumorigenesis and somatic cell reprogramming. Here, we aimed to assess whether KLF4 is a prognostic indicator for colon cancer.

METHODS

Levels of KLF4 were measured by immunohistochemical analysis of a tissue microarray containing 367 independent colon cancer sections. Univariate data analysis was done in addition to construction of multivariate models with several clinicopathologic factors to evaluate KLF4 as an independent predictor of survival and cancer recurrence (disease-free survival).

RESULTS

Colon cancer tissues had significantly overall lower KLF4 levels compared with noncancer tissues (P < 0.0001). Using logistic regression, a trend was noted for decreased odds of KLF4 expression in higher stages of tumors. In univariate and multivariate analyses, KLF4 was a significant predictor of survival and recurrence.

CONCLUSIONS

KLF4 expression is significantly downregulated in colon cancer, and loss of KLF4 is an independent predictor of survival and recurrence.

IMPACT

These findings suggest that KLF4 may serve as a prognostic biomarker for colon cancer.

Occurrence and significance of the nuclear transcription factor Krüppel-like factor 4 (KLF4) in the vessel wall

Practically all mammalian cells including human can switch, according to micro- or macroenvironmental conditions, from states of cellular quiescence to inflammatory activation and vice versa. Along with recent knowledge, cellular quiescence is not a passive, but a highly active state with broad engagement of the cell synthetic and secretory machinery. Inflammatory activation is a beneficial process in cases of infection; however, if its control fails, it may degrade into autoimmune diseases or cancer growth. Control over cellular quiescence is exerted predominantly by a set of zinc-finger transcription proteins, referred to as Krüppel-like factors (KLFs). This review article offers recent information concerning activities of Krüppel-like factor 4 in the vascular wall.

Profiling and comparing transcription factors activated in non-metastatic and metastatic nasopharyngeal carcinoma cells

Transcription factors (TFs) are modulators of gene expression that are critically important in the establishment and progression of human cancers. In the current study, the activity profiles of TFs in a normal nasopharyngeal epithelial cell line and in nasopharyngeal carcinoma (NPC) cell lines were studied using oligonucleotide array-based TF assays. Compared to the normal epithelial cell line NP69, nine TFs in the non-metastatic NPC cell line (6-10B) and eight TFs in a metastatic NPC cell line (5-8F) were upregulated. Among upregulated TFs, Sp1, AP2, and ATF/CREB families exhibited relatively high activities in NPC cell lines. Transcription levels of Sp1, ATF-1, ATF-2, AP2alpha, AP2gamma, and CREB1 were higher in 5-8F cells than in 6-10B cells. In addition, higher expression of the Sp1 target genes MMP-9 and VEGF was observed in 5-8F cells. Sp1 silencing reduced VEGF and MMP-9 expression. Inhibition of Sp1 expression and activity in 5-8F cells by mithramycin resulted in downregulated expression and secretion of MMP-9 and VEGF, concomitant with inhibition of cell migration and invasion. These results suggest that dynamic changes in TF activities occur in NPC cells and that these changes may play important roles in regulating the expression of genes associated with the development and progression of NPC.

Oncogenic microRNA-27a is a target for anticancer agent methyl 2-cyano-3,11-dioxo-18beta-olean-1,12-dien-30-oate in colon cancer cells

Methyl 2-cyano-3,11-dioxo-18beta-olean-1,12-dien-30-oate (CDODA-Me) is a synthetic derivative of glycyrrhetinic acid, a triterpenoid phytochemical found in licorice extracts. CDODA-Me inhibited growth of RKO and SW480 colon cancer cells and this was accompanied by decreased expression of Sp1, Sp3 and Sp4 protein and mRNA and several Sp-dependent genes including survivin, vascular endothelial growth factor (VEGF), and VEGF receptor 1 (VEGFR1 or Flt-1). CDODA-Me also induced apoptosis, arrested RKO and SW480 cells at G(2)/M, and inhibited tumor growth in athymic nude mice bearing RKO cells as xenografts. CDODA-Me decreased expression of microRNA-27a (miR-27a), and this was accompanied by increased expression of 2 miR-27a-regulated mRNAs, namely ZBTB10 (an Sp repressor) and Myt-1 which catalyzes phosphorylation of cdc2 to inhibit progression of cells through G(2)/M. Both CDODA-Me and antisense miR-27a induced comparable responses in RKO and SW480 cells, suggesting that the potent anticarcinogenic activity of CDODA-Me is due to repression of oncogenic miR-27a.

Putative tumor-suppressive function of Kruppel-like factor 4 in primary lung carcinoma

PURPOSE

Krüppel-like factor 4 (KLF4) is a zinc-finger protein that plays important roles in stem cells and the development of gastric cancers. However, the role of KLF4 in primary lung cancer is unknown. The purpose of this study is to determine possible roles of KLF4 in lung cancer.

EXPERIMENTAL DESIGN

The KLF4 expression in primary lung cancer tissues and case-matched normal lung tissues were determined by protein and mRNA analyses. The effects of KLF4 on cell proliferation, clonogenic formation, and cell cycle progression were determined in cultured lung cancer cells or bronchial epithelial cells after enforced KLF4 overexpression or small interfering RNA knockdown. The in vivo antitumor activity of KLF4 was evaluated by using stably transfected lung cancer cells and by adenovector-mediated gene delivery. The effect of KLF4 in regulating p21 and cyclin D1 was also evaluated.

RESULTS

KLF4 protein and mRNA levels were dramatically decreased in most primary lung tumors compared with in case-matched normal lung tissues. Enforced expression of KLF4 resulted in marked inhibition of cell growth and clonogenic formation. The tumor-suppressive effect of KLF4 was associated with its role in up-regulating p21 and down-regulating cyclin D1, leading to cell cycle arrest at the G(1)-S checkpoint. Knockdown of KLF4 promoted cell growth in immortalized human bronchial epithelial cells. The enforced expression of KLF4 gene to lung cancer cells by ex vivo transfection or adenovector-mediated gene transfer suppressed tumor growth in vivo.

CONCLUSIONS

Our results suggest that KLF4 plays an important role in suppressing the growth of lung carcinoma.

Critical role and regulation of transcription factor FoxM1 in human gastric cancer angiogenesis and progression

The mammalian forkhead box (Fox) transcription factor FoxM1b is implicated in tumorigenesis. However, the presence of expression and role of FoxM1b in gastric cancer remain unknown. Therefore, we investigated FoxM1b expression in 86 cases of primary gastric cancer and 57 normal gastric tissue specimens. We further investigated the underlying mechanisms of altered FoxM1b expression in and the effect of this altered expression on gastric cancer growth and metastasis using in vitro and animal models of gastric cancer. We found weak expression of FoxM1b protein in the mucous neck region of gastric mucosa, whereas we observed strong staining for FoxM1b in tumor cell nuclei in various gastric tumors and lymph node metastases. A Cox proportional hazards model revealed that FoxM1b expression was an independent prognostic factor in multivariate analysis (P < 0.001). Experimentally, overexpression of FoxM1b by gene transfer significantly promoted the growth and metastasis of gastric cancer cells in orthotopic mouse models, whereas knockdown of FoxM1b expression by small interfering RNA did the opposite. Promotion of gastric tumorigenesis by FoxM1b directly and significantly correlated with transactivation of vascular endothelial growth factor expression and elevation of angiogenesis. Given the importance of FoxM1b to regulation of the expression of genes key to cancer biology overall, dysregulated expression and activation of FoxM1b may play important roles in gastric cancer development and progression.

Involvement of FLIP in 2-methoxyestradiol-induced tumor regression in transgenic adenocarcinoma of mouse prostate model

PURPOSE

The purpose of this study is to investigate whether Fas-associated death domain interleukin-1 converting enzyme like inhibitory protein (FLIP) inhibition is a therapeutic target associated with 2-methoxyestradiol (2-ME2)-mediated tumor regression.

EXPERIMENTAL DESIGN

Expression and levels of FLIP were analyzed using (a) real-time PCR and immunoblot analysis in androgen-independent PC-3 cells treated with the newly formulated 2-ME2 and (b) immunohistochemistry in different Gleason pattern human prostate tumors. Transient transfections and chromatin immunoprecipitation (ChIP) assays were used to identify the transcription factors that regulate FLIP. Involvement of FLIP in 2-ME2-induced tumor regression was evaluated in transgenic adenocarcinoma mouse prostate (TRAMP) mice.

RESULTS

High Gleason pattern (5+5) human prostate tumors exhibit significant increase in FLIP compared with low Gleason pattern 3+3 (P=or<0.04). 2-ME2 reduced the levels and promoter activity of FLIP (P=0.001) in PC-3 cells. Transient expression assays show sequences between -503/+242 being sufficient for 2-ME2-induced inhibition of FLIP promoter activity. Cotransfection experiments show that overexpression of Sp1 activated, whereas Sp3 inhibited, Sp1 transactivation of FLIP promoter activity (P=0.0001). 2-ME2 treatment reduced binding of Sp1 to the FLIP promoter as evidenced by ChIP. Further, levels of FLIP associated with Fas or FADD decreased, whereas cleavage of caspase-8, levels of Bid, and apoptosis increased in response to 2-ME2 treatment in PC-3 cells. Administration of 2-ME2 regressed established prostate tumors in TRAMP mice that were associated with reduced expression of FLIP and Sp1.

CONCLUSION

Targeting Sp1-mediated FLIP signaling pathway may provide a novel approach for prostate cancer management.

Mouse embryonic fibroblasts null for the Krüppel-like factor 4 gene are genetically unstable

Krüppel-like factor 4 (KLF4) is a zinc-finger transcription factor with tumor suppressive activity in colorectal cancer. Here, we investigated whether KLF4 is involved in maintaining genetic stability in mouse embryonic fibroblasts (MEFs) isolated from mice wild type (+/+), heterozygous (+/-), or homozygous (-/-) for the Klf4 alleles. Compared to Klf4(+/+) and Klf4(+/-) MEFs, Klf4(-/-) MEFs had both a higher level of apoptosis and rate of proliferation. Quantification of chromosome numbers showed that Klf4(-/-) MEFs were aneuploid. A higher number of Klf4(-/-) MEFs exhibited gamma-H2AX foci and had higher amounts of gamma-H2AX compared to controls. Cytogenetic analysis demonstrated the presence of numerous chromosome aberrations including dicentric chromosomes, chromatid breaks, and double minute chromosomes in Klf4(-/-) cells but in few, if any, Klf4(+/+) or Klf4(+/-) MEFs. Approximately 25% of Klf4(-/-) MEFs exhibited centrosome amplification in contrast to the less than 5% of Klf4(+/+) or Klf4(+/-) MEFs. Finally, only Klf4(-/-) MEFs were capable of anchorage-independent growth. Taken together, these findings demonstrate that MEFs null for the Klf4 alleles are genetically unstable, as evidenced by the presence of aneuploidy, chromosome aberration and centrosome amplification. The results support a crucial role for KLF4 in maintaining genetic stability and as a tumor suppressor.

Non-classical genomic estrogen receptor (ER)/specificity protein and ER/activating protein-1 signaling pathways

17beta-estradiol binds to the estrogen receptor (ER) to activate gene expression or repression and this involves both genomic (nuclear) and non-genomic (extranuclear) pathways. Genomic pathways include the classical interactions of ligand-bound ER dimers with estrogen-responsive elements in target gene promoters. ER-dependent activation of gene expression also involves DNA-bound ER that subsequently interacts with other DNA-bound transcriptions factors and direct ER-transcription factor (protein-protein) interactions where ER does not bind promoter DNA. Ligand-induced activation of ER/specificity protein (Sp) and ER/activating protein-1 [(AP-1); consisting of jun/fos] complexes are important pathways for modulating expression of a large number of genes. This review summarizes some of the characteristics of ER/Sp- and ER/AP-1-mediated transactivation, which are dependent on ligand structure, cell context, ER-subtype (ERalpha and ERbeta), and Sp protein (SP1, SP3, and SP4) and demonstrates that this non-classical genomic pathway is also functional in vivo.

Selection strategy of transgenic vectors in research of gastrointestinal tumors

Along with the development of life science, the use of transgenic vectors is becoming more and more popular. Besides cloning and expressing target genes, this technology plays an important role in gene diagnosis, gene therapy and new drug development. In this article, we give an overview of transgenic vectors on their classification, characteristics, advantages, disadvantages and applications in the research of gastrointestinal tumors.

Kruppel-like factor 4 induces p27Kip1 expression in and suppresses the growth and metastasis of human pancreatic cancer cells

The zinc finger transcription factor Krüppel-like factor 4 (KLF4) has been implicated in both tumor suppression and progression. However, its function in pancreatic cancer has not been well characterized. Here, we show that pancreatic cancer cell lines expressed various levels of KLF4 RNA and protein. Ectopic expression of KLF4 by FG and BxPC-3 pancreatic cancer cells resulted in cell cycle arrest and marked inhibition of cell growth in vitro and attenuation of tumor growth and metastasis in an orthotopic mouse model. Overexpression of KLF4 also led to significant induction of p27(Kip1) expression, at both the RNA and protein levels, in a dose- and time-dependent manner, indicating that KLF4 transcriptionally regulates the expression of p27(Kip1). Chromatin immunoprecipitation assays consistently showed that KLF4 protein physically interacts with the p27(Kip1) promoter. Promoter deletion and point mutation analyses indicated that a region between nucleotides -435 and -60 of the p27(Kip1) promoter and intact of the three KLF4-binding sites within that region were required for the full induction of p27(Kip1) promoter activity by KLF4. Our findings suggest that KLF4 transactivates p27(Kip1) expression and inhibits the growth and metastasis of human pancreatic cancer.

Roles of Krüpel-like factor 4 in normal homeostasis, cancer and stem cells

Krüpel-like factor 4 (KLF4) is a zinc finger-type transcription factor expressed in a variety of tissues, including the epithelium of the intestine and the skin, and it plays an important role in differentiation and cell cycle arrest. Depending on the gene targeted, KLF4 can both activate and repress transcription. Moreover, in certain cellular contexts, KLF4 can function as a tumor suppressor or an oncogene. Finally, KLF4 is important in reprogramming differentiated fibroblasts into inducible pluripotent stem cells, which highly resemble embryonic stem cells. This review summarizes what is known about the diverse functions of KLF4 as well as their molecular mechanisms.

Identification of Pou5f1, Sox2, and Nanog downstream target genes with statistical confidence by applying a novel algorithm to time course microarray and genome-wide chromatin immunoprecipitation data

Background

Target genes of a transcription factor (TF) Pou5f1 (Oct3/4 or Oct4), which is essential for pluripotency maintenance and self-renewal of embryonic stem (ES) cells, have previously been identified based on their response to Pou5f1 manipulation and occurrence of Chromatin-immunoprecipitation (ChIP)-binding sites in promoters. However, many responding genes with binding sites may not be direct targets because response may be mediated by other genes and ChIP-binding site may not be functional in terms of transcription regulation.

Results

To reduce the number of false positives, we propose to separate responding genes into groups according to direction, magnitude, and time of response, and to apply the false discovery rate (FDR) criterion to each group individually. Using this novel algorithm with stringent statistical criteria (FDR < 0.2) to a compendium of published and new microarray data (3, 6, 12, and 24 hr after Pou5f1 suppression) and published ChIP data, we identified 420 tentative target genes (TTGs) for Pou5f1. The majority of TTGs (372) were down-regulated after Pou5f1 suppression, indicating that the Pou5f1 functions as an activator of gene expression when it binds to promoters. Interestingly, many activated genes are potent suppressors of transcription, which include polycomb genes, zinc finger TFs, chromatin remodeling factors, and suppressors of signaling. Similar analysis showed that Sox2 and Nanog also function mostly as transcription activators in cooperation with Pou5f1.

Conclusion

We have identified the most reliable sets of direct target genes for key pluripotency genes – Pou5f1, Sox2, and Nanog, and found that they predominantly function as activators of downstream gene expression. Thus, most genes related to cell differentiation are suppressed indirectly.

Sumoylation of specificity protein 1 augments its degradation by changing the localization and increasing the specificity protein 1 proteolytic process

Although specificity protein 1 (Sp1) accumulation has been found in various tumor strains, its mechanism is still not very clear. Herein, we found that modification of Sp1 by SUMO-1 facilitates Sp1 degradation. Our findings revealed that, although the amounts of Sp1 and Sp1 mutant (K16R) [Sp1(K16R)] mRNA in cells were equal, the protein level of Sp1(K16R) was higher than that of wild-type Sp1. We also proved that this sumoylation site was not the residue at which ubiquitination occurred. Invitro and in vivo pull-down assays revealed that more sumoylated Sp1 was localized in the cytoplasm, and the interaction between SUMO-1-Sp1 and the proteasome subunit rpt6 in HeLa cells was enhanced. In addition, although Sp1 accumulated in the tumorous cervical tissue, it was not prone to sumoylation. Finally, by overexpression of HA (hemagglutinin)-SUMO-1-Sp1-myc, HA-Sp1-myc, and HA-Sp1(K16R), we found that modification of Sp1 by SUMO-1 was important for Sp1 proteolysis. In conclusion, modification of Sp1 by SUMO-1 altered its localization and then increased its interaction with rpt6. This interaction increased the efficiency of Sp1 proteolytic processing and ubiquitination and then resulted in Sp1 degradation. Therefore, sumoylation of Sp1 is attenuated during tumorigenesis in order to increase Sp1 stability.

Expression patterns of SP1 and SP3 during mouse spermatogenesis: SP1 down-regulation correlates with two successive promoter changes and translationally compromised transcripts

Because of their prominent roles in regulation of gene expression, it is important to understand how levels of Krüpple-like transcription factors SP1 and SP3 change in germ cells during spermatogenesis. Using immunological techniques, we found that both factors decreased sharply during meiosis. SP3 declined during the leptotene-to-pachytene transition, whereas SP1 fell somewhat later, as spermatocytes progressed beyond the early pachytene stage. SP3 reappeared for a period in round spermatids. For Sp1, the transition to the pachytene stage is accompanied by loss of the normal, 8.2-kb mRNA and appearance of a prevalent, 8.8-kb variant, which has not been well characterized. We have now shown that this pachytene-specific transcript contains a long, unspliced sequence from the first intron and that this sequence inhibits expression of a reporter, probably because of its many short open-reading frames. A second testis-specific Sp1 transcript in spermatids of 2.4 kb also has been reported previously. Like the 8.8-kb variant, it is compromised translationally. We have confirmed by Northern blotting that the 8.8-, 8.2-, and 2.4-kb variants account for the major testis Sp1 transcripts. Thus, the unexpected decline of SP1 protein in the face of continuing Sp1 transcription is explained, in large part, by poor translation of both novel testis transcripts. As part of this work, we also identified five additional, minor Sp1 cap sites by 5' rapid amplification of cDNA ends, including a trans-spliced RNA originating from the Glcci1 gene.

Thyroid hormone receptors suppress pituitary tumor transforming gene 1 activity in hepatoma

Pituitary tumor transforming gene 1 (PTTG1) is expressed in most tumors. However, whether thyroid hormone (T(3)) and its receptors (TR) regulate PTTG1 in human hepatocellular carcinomas (HCC) remains unclear. Previous cDNA microarrays revealed PTTG1 is down-regulated by T(3)/TR. This study investigated the significance of PTTG1 regulation by T(3) in HCC cells. The PTTG1 mRNA and protein expression were repressed by T(3) in HCC cell lines overexpressing TR. However, after knockdown of TRs expression by RNA interference, PTTG1 repression by T(3) was abolished. Similar results were observed in thyroidectomized rats. To localize the regulatory region in the PTTG1 promoter, serial deletions within the PTTG1 promoter region were constructed. The promoter activity of the PTTG1 gene was repressed (25-51%) by T(3). Additionally, these findings indicate that PTTG1 may be regulated by Sp1. The critical role of the -594 and -520 Sp1 binding sites was confirmed by electrophoretic mobility shift assay. Transfection with Sp1 expression vector enhanced the activity of the PTTG1 promoter fragment reporter. Also, Sp1 was down-regulated in HCC cells and in thyroidectomized rat after T(3) treatment. Additionally, ectopic expression of PTTG1 promotes cell proliferation in Hep3B hepatoma cells. Conversely, knockdown of PTTG1 or Sp1 expression reduced cell proliferation in HepG2 cells. Notably, the expression of PTTG1 and Sp1 was inversely correlated with the expression of TR proteins in HCC. Together, these findings indicate that PTTG1 gene expression is mediated by Sp1 and is indirectly down-regulated by T(3). Finally, overexpression of PTTG1 or SP1 in HCCs is TR-dependent and crucial in the development of HCC.

RECK--a newly discovered inhibitor of metastasis with prognostic significance in multiple forms of cancer

The RECK (reversion-inducing cysteine rich protein with Kazal motifs) protein was initially discovered by its ability to induce reversion in ras-activated fibroblasts. The key action of RECK is to inhibit matrix metalloproteinases (MMPs) involved in breakdown of the extracellular matrix (ECM), and angiogenesis-namely MMP-2, MMP-9 and MTP-1. To this effect, it plays important physiological roles in embryogenesis and vasculogenesis. Additionally, it has a significant effect on tumorigenesis by limiting angiogenesis and invasion of tumours through the ECM. RECK has been studied in the context of a number of human tumours including colorectal, breast, pancreas, gastric, hepatocellular, prostate, and non-small cell lung carcinoma. In many of these tumours, RECK is down-regulated most likely as a result of inhibition at the Sp1 promoter site. MMP-2 and MMP-9 generally show an inverse association with RECK expression, but there are exceptions to this rule. Likewise, a reduction in tumour microvascular density (MVD) and VEGF have also been correlated with increased RECK levels, although more studies are required to define this effect. The predominant finding across all human tumour studies is a significantly improved prognosis (due to decreased invasion and metastasis) in tumours with preserved RECK expression. Although further research is required, RECK is a promising prognostic marker and potential therapeutic agent in multiple cancers.

The oncogenic microRNA-27a targets genes that regulate specificity protein transcription factors and the G2-M checkpoint in MDA-MB-231 breast cancer cells

There is evidence that specificity proteins (Sp), such as Sp1, Sp3, and Sp4, are overexpressed in tumors and contribute to the proliferative and angiogenic phenotype associated with cancer cells. Sp1, Sp3, and Sp4 are expressed in a panel of estrogen receptor (ER)-positive and ER-negative breast cancer cell lines, and we hypothesized that regulation of their expression may be due to microRNA-27a (miR-27a), which is also expressed in these cell lines and has been reported to regulate the zinc finger ZBTB10 gene, a putative Sp repressor. Transfection of ER-negative MDA-MB-231 breast cancer cells with antisense miR-27a (as-miR-27a) resulted in increased expression of ZBTB10 mRNA and decreased expression of Sp1, Sp3, and Sp4 at the mRNA and protein levels and also decreased activity in cells transfected with constructs containing Sp1 and Sp3 promoter inserts. In addition, these responses were accompanied by decreased expression of Sp-dependent survival and angiogenic genes, including survivin, vascular endothelial growth factor (VEGF), and VEGF receptor 1 (VEGFR1). Moreover, similar results were observed in MDA-MB-231 cells transfected with ZBTB10 expression plasmid. Both as-miR-27a and ZBTB10 overexpression decreased the percentage of MDA-MB-231 cells in S phase of the cell cycle; however, ZBTB10 increased the percentage of cells in G(0)-G(1), whereas as-miR-27a increased the percentage in G(2)-M. This latter response was associated with induction of Myt-1 (another miR-27a target gene), which inhibits G(2)-M through enhanced phosphorylation and inactivation of cdc2. Thus, the oncogenic activity of miR-27a in MDA-MB-231 cells is due, in part, to suppression of ZBTB10 and Myt-1.

The diverse functions of Krüppel-like factors 4 and 5 in epithelial biology and pathobiology

The Krüppel-like factors (KLFs) comprise a family of evolutionarily conserved zinc finger transcription factors that regulate numerous biological processes including proliferation, differentiation, development and apoptosis. KLF4 and KLF5 are two closely related members of this family and are both highly expressed in epithelial tissues. In the intestinal epithelium, KLF4 is expressed in terminally differentiated epithelial cells at the villus borders of the mucosa and inhibits cell growth, while KLF5 is expressed in proliferating epithelial cells at the base of the intestinal crypts and promotes cell growth. KLF4 and KLF5 respond to a myriad of external stress stimuli and are likely involved in restoring cellular homeostasis following exposure to stressors. Confirming their importance in maintaining tissue integrity, KLF4 and KLF5 are both dysregulated in various types of cancer. Here we review the recent advances in defining the physiological and pathobiological roles of KLF4 and KLF5, focusing on their functions in the intestinal epithelium.

Molecular basis of the synergistic antiangiogenic activity of bevacizumab and mithramycin A

The impact of antiangiogenic therapy on the Sp1/vascular endothelial growth factor (VEGF) pathway and that of alteration of Sp1 signaling on the efficacy of antiangiogenic therapy is unclear, yet understanding their interactions has significant clinical implications. Treatment with bevacizumab, a neutralizing antibody against VEGF, suppressed human pancreatic cancer growth in nude mice. Gene expression analyses revealed that this treatment substantially up-regulated the expression of Sp1 and its downstream target genes, including VEGF and epidermal growth factor receptor, in tumor tissues, whereas it did not have this effect on pancreatic cancer cells in culture. Treatment with mithramycin A, an Sp1 inhibitor, suppressed the expression of Sp1 and its downstream target genes in both cell culture and tumors growing in nude mice. Combined treatment with bevacizumab and mithramycin A produced synergistic tumor suppression, which was consistent with suppression of the expression of Sp1 and its downstream target genes. Thus, treatment with bevacizumab may block VEGF function but activate the pathway of its expression via positive feedback. Given the fact that Sp1 is an important regulator of the expression of multiple angiogenic factors, bevacizumab-initiated up-regulation of Sp1 and subsequent overexpression of its downstream target genes may profoundly affect the potential angiogenic phenotype and effectiveness of antiangiogenic strategies for human pancreatic cancer. Therefore, this study is the first to show the significance and clinical implications of alteration of Sp1 signaling in antiangiogenic therapy for pancreatic cancer and other cancers.