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

Klf4 and Klf5 differentially inhibit mesoderm and endoderm differentiation in embryonic stem cells

Krüppel-like factors (Klf) 4 and 5 are two closely related members of the Klf family, known to play key roles in cell cycle regulation, somatic cell reprogramming and pluripotency. Here we focus on the functional divergence between Klf4 and Klf5 in the inhibition of mouse embryonic stem (ES) cell differentiation. Using microarrays and chromatin immunoprecipitation coupled to ultra-high-throughput DNA sequencing, we show that Klf4 negatively regulates the expression of endodermal markers in the undifferentiated ES cells, including transcription factors involved in the commitment of pluripotent stem cells to endoderm differentiation. Knockdown of Klf4 enhances differentiation towards visceral and definitive endoderm. In contrast, Klf5 negatively regulates the expression of mesodermal markers, some of which control commitment to the mesoderm lineage, and knockdown of Klf5 specifically enhances differentiation towards mesoderm. We conclude that Klf4 and Klf5 differentially inhibit mesoderm and endoderm differentiation in murine ES cells.

KLF5 regulates the integrity and oncogenicity of intestinal stem cells

The intestinal epithelium maintains homeostasis by a self-renewal process involving resident stem cells, including Lgr5(+) crypt-base columnar cells, but core mechanisms and their contributions to intestinal cancer are not fully defined. In this study, we examined a hypothesized role for KLF5, a zinc-finger transcription factor that is critical to maintain the integrity of embryonic and induced pluripotent stem cells, in intestinal stem-cell integrity and cancer in the mouse. Klf5 was indispensable for the integrity and oncogenic transformation of intestinal stem cells. In mice, inducible deletion of Klf5 in Lgr5(+) stem cells suppressed their proliferation and survival in a manner associated with nuclear localization of β-catenin (Catnb), generating abnormal apoptotic cells in intestinal crypts. Moreover, production of lethal adenomas and carcinomas by specific expression of an oncogenic mutant of β-catenin in Lgr5(+) stem cells was suppressed completely by Klf5 deletion in the same cells. Given that activation of the Wnt/β-catenin pathway is the most frequently altered pathway in human colorectal cancer, our results argue that KLF5 acts as a fundamental core regulator of intestinal oncogenesis at the stem-cell level, and they suggest KLF5 targeting as a rational strategy to eradicate stem-like cells in colorectal cancer.

Epigallocatechin-3-gallate regulates the expression of Kruppel-like factor 4 through myocyte enhancer factor 2A

Epigallocatechin-3-gallate (EGCG), a powerful antioxidant and free ion scavenger found in green tea, exhibits inhibitory effects on different stages of tumorigenesis. Within gastric cancer cells, the transcription factor Kruppel-like factor 4 (KLF4) is downregulated, and it is possible that EGCG exerts its anti-tumorigenic function through modulation of KLF4 expression. In order to examine the effects of EGCG on KLF4 in a gastric tumor model, we treated the gastric cancer cell line NCI-N87 with EGCG. We found that EGCG treatment results in increased expression of KLF4 and alters expression of the KLF4 target genes p21, CDK4, and cyclin D1. EGCG inhibits the growth of NCI-N87 cells in a time- and dose-dependent manner through arresting the cell cycle in the G0/G1 phase. Furthermore, terminal deoxynucleotidyl transferase dUTP nick end labeling assay and 4',6-diamidino-2-phenylindole staining revealed that EGCG is able to promote apoptosis of NCI-N87 cells. The suppressive effects of EGCG on cell growth and cell cycle protein expression are eliminated by decreasing KLF4 mRNA using siRNA and are magnified by overexpressing KLF4. Using KLF4 reporter constructs, we verified that the elevated expression induced by EGCG was mediated by increasing levels of activated MEF2A, which bound to the promoter region of KLF4. Taken together, this is the first time that EGCG is reported to increase the expression of KLF4, suggesting a novel mechanisms in gastric cancer treatment.

Chorioamnionitis-induced fetal gut injury is mediated by direct gut exposure of inflammatory mediators or by lung inflammation

Intra-amniotic exposure to proinflammatory agonists causes chorioamnionitis and fetal gut inflammation. Fetal gut inflammation is associated with mucosal injury and impaired gut development. We tested whether this detrimental inflammatory response of the fetal gut results from a direct local (gut derived) or an indirect inflammatory response mediated by the chorioamnion/skin or lung, since these organs are also in direct contact with the amniotic fluid. The gastrointestinal tract was isolated from the respiratory tract and the amnion/skin epithelia by fetal surgery in time-mated ewes. Lipopolysaccharide (LPS) or saline (controls) was selectively infused in the gastrointestinal tract, trachea, or amniotic compartment at 2 or 6 days before preterm delivery at 124 days gestation (term 150 days). Gastrointestinal and intratracheal LPS exposure caused distinct inflammatory responses in the fetal gut. Inflammatory responses could be distinguished by the influx of leukocytes (MPO(+), CD3(+), and FoxP3(+) cells), tumor necrosis factor-α, and interferon-γ expression and differential upregulation of mRNA levels for Toll-like receptor 1, 2, 4, and 6. Fetal gut inflammation after direct intestinal LPS exposure resulted in severe loss of the tight junctional protein zonula occludens protein 1 (ZO-1) and increased mitosis of intestinal epithelial cells. Inflammation of the fetal gut after selective LPS instillation in the lungs caused only mild disruption of ZO-1, loss in epithelial cell integrity, and impaired epithelial differentiation. LPS exposure of the amnion/skin epithelia did not result in gut inflammation or morphological, structural, and functional changes. Our results indicate that the detrimental consequences of chorioamnionitis on fetal gut development are the combined result of local gut and lung-mediated inflammatory responses.

Inducible intestine-specific deletion of Krüppel-like factor 5 is characterized by a regenerative response in adult mouse colon

Krüppel-like factor 5 (KLF5) is a pro-proliferative transcriptional regulator primarily expressed in the intestinal crypt epithelial cells. Constitutive intestine-specific deletion of Klf5 is neonatal lethal suggesting a crucial role for KLF5 in intestinal development and homeostasis. We have previously shown Klf5 to play an active role regulating intestinal tumorigenesis. Here we examine the effect of inducible intestine-specific deletion of Klf5 in adult mice. Klf5 is lost from the intestine beginning at day 3 after the start of a 5-day treatment with the inducer tamoxifen. Although the mice have no significant weight loss or lethality, the colonic tissue shows signs of epithelial distress starting at day 3 following induction. Accompanying the morphological changes is a significant loss of proliferative crypt epithelial cells as revealed by BrdU or Ki67 staining at days 3 and 5 after start of tamoxifen. We also observed a loss of goblet cells from the colon and Paneth cells from the small intestine upon induced deletion of Klf5. In addition, loss of Klf5 from the colonic epithelium is accompanied by a regenerative response that coincides with an expansion in the zone of Sox9 expression along the crypt axis. At day 11, both proliferation and Sox9 expression return to baseline levels. Microarray and quantitative PCR analyses reveal an up-regulation of several regeneration-associated genes (Reg1A, Reg3G and Reg3B) and down-regulation of many Klf5 targets (Ki-67, cyclin B, Cdc2 and cyclin D1). Sox9 and Reg1A protein levels are also increased upon Klf5 loss. Lentiviral-mediated knockdown of KLF5 and exogenous expression of KLF5 in colorectal cancer cell lines confirm that Sox9 expression is negatively regulated by KLF5. Furthermore, ChIP assays reveal a direct association of KLF5 with both the Sox9 and Reg1A promoters. We have shown that disruption of epithelial homeostasis due to Klf5 loss from the adult colon is followed by a regenerative response led by Sox9 and the Reg family of proteins. Our study demonstrates that adult mouse colonic tissue undergoes acute physiological changes to accommodate the loss of Klf5 withstanding epithelial damage further signifying importance of Klf5 in colonic homeostasis.

A colon cancer-derived mutant of Krüppel-like factor 5 (KLF5) is resistant to degradation by glycogen synthase kinase 3β (GSK3β) and the E3 ubiquitin ligase F-box and WD repeat domain-containing 7α (FBW7α)

Krüppel-like factor 5 (KLF5) is a zinc finger transcription factor that is highly expressed in the crypt epithelial cells of the intestine and plays a critical role in regulating proliferation of both normal intestinal epithelial cells and colorectal cancer cells. Stability of the KLF5 is mediated by proteasomal degradation via phosphorylation by glycogen synthase kinase 3β (GSK3β) and recognition by F-box and WD repeat domain-containing 7 (FBW7) of a phosphodegron sequence surrounding serine 303 in KLF5. A genomic analysis of colorectal cancer tissues identified a somatic mutation (P301S) in KLF5 within the phosphodegron sequence. We hypothesized that due to its close proximity to the phosphodegron sequence, the P301S mutation may affect signaling that is involved in proper KLF5 degradation. We demonstrated that the P301S KLF5 mutant has a longer half-life than wild type (WT) KLF5. Furthermore, P301S KLF5 has a higher transcriptional activity than WT KLF5 as demonstrated by luciferase assays using cyclin D1 and CDC2 promoter constructs. In contrast to WT KLF5, P301S KLF5 does not physically interact with FBW7α. Concomitantly, the P301S KLF5 mutant displays reduced levels of phosphorylation at serine 303 in comparison with WT KLF5. These results of our study indicate that amino acid residue 301 of KLF5 is critical for proper recognition of the phosphodegron sequence by FBW7α and that the P301S mutation inhibits this recognition, leading to a degradation-resistant protein with elevated levels and enhanced transcriptional activity. These findings raise a potentially oncogenic role for the P301S KLF5 mutant in colorectal cancer.

Restoring KLF5 in esophageal squamous cell cancer cells activates the JNK pathway leading to apoptosis and reduced cell survival

Esophageal cancer is the eighth most common cancer in the world and has an extremely dismal prognosis, with a 5-year survival of less than 20%. Current treatment options are limited, and thus identifying new molecular targets and pathways is critical to derive novel therapies. Worldwide, more than 90% of esophageal cancers are esophageal squamous cell cancer (ESCC). Previously, we identified that Krüppel-like factor 5 (KLF5), a key transcriptional regulator normally expressed in esophageal squamous epithelial cells, is lost in human ESCC. To examine the effects of restoring KLF5 in ESCC, we transduced the human ESCC cell lines TE7 and TE15, both of which lack KLF5 expression, with retrovirus to express KLF5 upon doxycycline induction. When KLF5 was induced, ESCC cells demonstrated increased apoptosis and decreased viability, with up-regulation of the proapoptotic factor BAX. Interestingly, c-Jun N-terminal kinase (JNK) signaling, an important upstream mediator of proapoptotic pathways including BAX, was also activated following KLF5 induction. KLF5 activation of JNK signaling was mediated by KLF5 transactivation of two key upstream regulators of the JNK pathway, ASK1 and MKK4, and inhibition of JNK blocked apoptosis and normalized cell survival following KLF5 induction. Thus, restoring KLF5 in ESCC cells promotes apoptosis and decreases cell survival in a JNK-dependent manner, providing a potential therapeutic target for human ESCC.

Loss of miR-10a activates lpo and collaborates with activated Wnt signaling in inducing intestinal neoplasia in female mice

miRNAs are small regulatory RNAs that, due to their considerable potential to target a wide range of mRNAs, are implicated in essentially all biological process, including cancer. miR-10a is particularly interesting considering its conserved location in the Hox cluster of developmental regulators. A role for this microRNA has been described in developmental regulation as well as for various cancers. However, previous miR-10a studies are exclusively based on transient knockdowns of this miRNA and to extensively study miR-10a loss we have generated a miR-10a knock out mouse. Here we show that, in the Apc^min mouse model of intestinal neoplasia, female miR-10a deficient mice develop significantly more adenomas than miR-10^+/+ and male controls. We further found that Lpo is extensively upregulated in the intestinal epithelium of mice deprived of miR-10a. Using in vitro assays, we demonstrate that the primary miR-10a target KLF4 can upregulate transcription of Lpo, whereas siRNA knockdown of KLF4 reduces LPO levels in HCT-116 cells. Furthermore, Klf4 is upregulated in the intestines of miR-10a knockout mice. Lpo has previously been shown to have the capacity to oxidize estrogens into potent depurinating mutagens, creating an instable genomic environment that can cause initiation of cancer. Therefore, we postulate that Lpo upregulation in the intestinal epithelium of miR-10a deficient mice together with the predominant abundance of estrogens in female animals mainly accounts for the sex-related cancer phenotype we observed. This suggests that miR-10a could be used as a potent diagnostic marker for discovering groups of women that are at high risk of developing colorectal carcinoma, which today is one of the leading causes of cancer-related deaths.

Posttranscriptional regulation by microRNA molecules constitutes an important mechanism for gene regulation and numerous studies have demonstrated a correlation between deregulated microRNA levels and diseases, such as cancer. However, genetics studies linking individual microRNAs to the etiology of cancer remain scarce. Here, we provide causal evidence for the involvement of the conserved microRNA miR-10a in the development of intestinal adenomas in the face of activated Wnt signaling. Interestingly, we find that loss of miR-10a mediates an increase in intestinal adenomas in female mice only and delineate the pathway to involve aberrant upregulation of the miR-10a target Klf4 and subsequent transcriptional activation of the Lpo gene encoding the antibacterial protein Lactoperoxidase. Lpo, in turn, has previously been demonstrated to oxidize estrogens into DNA-damaging mutagens.

Klf5 controls bone marrow homing of stem cells and progenitors through Rab5-mediated β1/β2-integrin trafficking

Kruppel-like factor 5 (Klf5) regulates pluripotent stem cell self-renewal but its role in somatic stem cells is unknown. Here we show that Klf5 deficient haematopoietic stem cells and progenitors (HSC/P) fail to engraft after transplantation. This HSC/P defect is associated with impaired bone marrow homing and lodging and decreased retention in bone marrow, and with decreased adhesion to fibronectin and expression of membrane-bound β1/β2-integrins. In vivo inducible gain-of-function of Klf5 in HSCs increases HSC/P adhesion. The expression of Rab5 family members, mediators of β1/β2-integrin recycling in the early endosome, is decreased in Klf5^Δ/Δ HSC/Ps. Klf5 binds directly to the promoter of Rab5a/b and overexpression of Rab5b rescues the expression of activated β1/β2-integrins, adhesion and bone marrow homing of Klf5^Δ/Δ HSC/Ps. Altogether, these data indicate that Klf5 is indispensable for adhesion, homing, lodging and retention of HSC/Ps in the bone marrow through Rab5-dependent post-translational regulation of β1/β2 integrins.

Integrative genomic and functional profiling of the pancreatic cancer genome

Background

Pancreatic cancer is a deadly disease with a five-year survival of less than 5%. A better understanding of the underlying biology may suggest novel therapeutic targets. Recent surveys of the pancreatic cancer genome have uncovered numerous new alterations; yet systematic functional characterization of candidate cancer genes has lagged behind. To address this challenge, here we have devised a highly-parallel RNA interference-based functional screen to evaluate many genomically-nominated candidate pancreatic cancer genes simultaneously.

Results

For 185 candidate pancreatic cancer genes, selected from recurrently altered genomic loci, we performed a pooled shRNA library screen of cell growth/viability across 10 different cell lines. Knockdown-associated effects on cell growth were assessed by enrichment or depletion of shRNA hairpins, by hybridization to barcode microarrays. A novel analytical approach (COrrelated Phenotypes for On-Target Effects; COPOTE) was used to discern probable on-target knockdown, based on identifying different shRNAs targeting the same gene and displaying concordant phenotypes across cell lines. Knockdown data were integrated with genomic architecture and gene-expression profiles, and selected findings validated using individual shRNAs and/or independent siRNAs. The pooled shRNA library design delivered reproducible data. In all, COPOTE analysis identified 52 probable on-target gene-knockdowns. Knockdown of known oncogenes (KRAS, MYC, SMURF1 and CCNE1) and a tumor suppressor (CDKN2A) showed the expected contrasting effects on cell growth. In addition, the screen corroborated purported roles of PLEKHG2 and MED29 as 19q13 amplicon drivers. Most notably, the analysis also revealed novel possible oncogenic functions of nucleoporin NUP153 (ostensibly by modulating TGFβ signaling) and Kruppel-like transcription factor KLF5 in pancreatic cancer.

Conclusions

By integrating physical and functional genomic data, we were able to simultaneously evaluate many candidate pancreatic cancer genes. Our findings uncover new facets of pancreatic cancer biology, with possible therapeutic implications. More broadly, our study provides a general strategy for the efficient characterization of candidate genes emerging from cancer genome studies.

Deficiency of Kruppel-like factor KLF4 in mammary tumor cells inhibits tumor growth and pulmonary metastasis and is accompanied by compromised recruitment of myeloid-derived suppressor cells

Increasing evidence indicates that myeloid-derived suppressor cells (MDSCs) negatively regulate immune responses during tumor progression, inflammation and infection. However, the underlying molecular mechanisms of their development and mobilization remain to be fully delineated. Kruppel-like factor KLF4 is a transcription factor that has an oncogenic function in breast cancer development, but its function in tumor microenvironment, a critical component for tumorigenesis, has not been examined. By using a spontaneously metastatic 4T1 breast cancer mouse model and an immunodeficient NOD/SCID mouse model, we demonstrated that KLF4 knockdown delayed tumor development and inhibited pulmonary metastasis, which accompanied by decreased accumulation of MDSCs in bone marrow, spleens and primary tumors. Mechanistically, we found that KLF4 knockdown resulted in a significant decrease of circulating GM-CSF, an important cytokine for MDSC biology. Consistently, recombinant GM-CSF restored the frequency of MDSCs in purified bone marrow cells incubated with conditioned medium from KLF4 deficient cells. In addition, we identified CXCL5 as a critical mediator to enhance the expression and function of GM-CSF. Reduced CXCL5 expression by KLF4 knockdown in primary tumors and breast cancer cells was correlated with a decreased GM-CSF expression in our mouse models. Finally, we found that CXCL5/CXCR2 axis facilitated MDSC migration and that anti-GM-CSF antibodies neutralized CXCL5-induced accumulation of MDSCs. Taken together, our data suggest that KLF4 modulates maintenance of MDSCs in bone marrow by inducing GM-CSF production via CXCL5 and regulates recruitment of MDSCs into the primary tumors through the CXCL5/CXCR2 axis, both of which contribute to KLF4-mediated mammary tumor development.

Regulation of hypoxia-inducible factor 1α (HIF-1α) by lysophosphatidic acid is dependent on interplay between p53 and Krüppel-like factor 5

Hypoxia-inducible factor 1α (HIF-1α) and p53 are pivotal regulators of tumor growth. Lysophosphatidic acid (LPA) is a lipid mediator that functions as a mitogen by acting through LPA receptors. We have shown previously that LPA stimulates HIF-1α expression in colon cancer cells. To determine the mechanism of HIF-1α induction by LPA, we compared the effect of LPA on HIF-1α in several colon cancer cell lines. LPA transcriptionally induced HIF-1α in colon cancer cells. HIF-1α induction was observed in cells expressing WT p53, where LPA decreased p53 expression. However, LPA failed to induce HIF-1α when the p53 gene was mutated. A decrease in p53 expression was dependent on induction of p53-specific E3 ubiquitin ligase Mdm2 by LPA. Krüppel-like factor 5 (KLF5) is an effector of LPA-induced proliferation of colon cancer cells. Because HIF-1α was necessary for LPA-induced growth of colon cancer cells, we determined the relationship between KLF5 and HIF-1α by a loss-of-function approach. Silencing of KLF5 inhibited LPA-induced HIF-1α induction, suggesting that KLF5 is an upstream regulator of HIF-1α. KLF5 and p53 binding to the Hif1α promoter was assessed by ChIP assay. LPA increased the occupancy of the Hif1α promoter by KLF5, while decreasing p53 binding. Transfection of HCT116 cells with KLF5 or p53 attenuated the binding of the other transcription factor. These results identify KLF5 as a transactivator of HIF-1α and show that LPA regulates HIF-1α by dynamically modulating its interaction with KLF5 and p53.

Different expression patterns and functions of acetylated and unacetylated Klf5 in the proliferation and differentiation of prostatic epithelial cells

KLF5 is a basic transcription factor that regulates multiple biological processes. While it was identified as a putative tumor suppressor in prostate cancer, likely due to its function as an effector of TGF-β in the inhibition of cell proliferation, KLF5 is unacetylated and promotes cell proliferation in the absence of TGF-β. In this study, we evaluated the expression and function of KLF5 in prostatic epithelial homeostasis and tumorigenesis using mouse prostates and human prostate epithelial cells in 3-D culture. Histological and molecular analyses demonstrated that unacetylated-Klf5 was expressed in basal or undifferentiated cells, whereas acetylated-Klf5 was expressed primarily in luminal and/or differentiated cells. Androgen depletion via castration increased both the level of Klf5 expression and the number of Klf5-positive cells in the remaining prostate. Functionally, knockdown of KLF5 in the human RWPE-1 prostate cell line decreased the number of spheres formed in 3-D culture. In addition, knockout of Klf5 in prostate epithelial cells, mediated by probasin promoter-driven Cre expression, did not cause neoplasia but promoted cell proliferation and induced hyperplasia when one Klf5 allele was knocked out. Knockout of both Klf5 alleles however, caused apoptosis rather than cell proliferation in the epithelium. In castrated mice, knockout of Klf5 resulted in more severe shrinkage of the prostate. These results suggest that KLF5 plays a role in the proliferation and differentiation of prostatic epithelial cells, yet loss of KLF5 alone is insufficient to induce malignant transformation in epithelial cells.

Regulatable in vivo biotinylation expression system in mouse embryonic stem cells

Embryonic stem (ES) cells have several unique attributes, the two most important of which are they can differentiate into all cell types in the body and they can proliferate indefinitely. To study the regulation of these phenomena, we developed a regulatable in vivo biotinylation expression system in mouse ES cells. The E. coli biotin ligase gene BirA, whose protein product can biotinylate a 15-aa peptide sequence, called the AviTag, was cloned downstream of an IRES. The primary vector containing the doxycycline controlled transactivator gene tTA and IRES-BirA was knocked into the ROSA26 locus by homologous recombination. The secondary vector containing the AviTag tagged hKlf4 gene was exchanged into the ROSA26 locus using Cre recombinase. Western blot analysis showed that the doxycycline induced BirA protein can biotinylate the doxycycline induced AviTag tagged hKlf4 protein. The induction of hKlf4 repressed cell growth in the presence or absence of LIF. Chromatin immunoprecipitation assays using streptavidin beads showed that the AviTag tagged hKlf4 protein could enrich the Nanog enhancer. Our results suggested that the regulatable biotinylation system is promising for the gene function studies in mouse ES cells.

Dysregulated expression of FOXM1 isoforms drives progression of pancreatic cancer

The transcription factor Forkhead box M1 (FOXM1) plays important roles in oncogenesis. However, the expression statuses of FOXM1 isoforms and their impact on and molecular basis in oncogenesis are unknown. We sought to determine the identities of FOXM1 isoforms in and the impact of their expression on pancreatic cancer development and progression using human tissues, cell lines, and animal models. Overexpression of FOXM1 mRNA and protein was pronounced in human pancreatic tumors and cancer cell lines. We identified five FOXM1 isoforms present in pancreatic cancer: FOXM1a, FOXM1b, and FOXM1c along with two isoforms tentatively designated as FOXM1b1 and FOXM1b2 because they were closely related to FOXM1b. Interestingly, FOXM1c was predominantly expressed in pancreatic tumors and cancer cell lines, whereas FOXM1a expression was generally undetectable in them. Functional analysis revealed that FOXM1b, FOXM1b1, FOXM1b2, and FOXM1c, but not FOXM1a, promoted pancreatic tumor growth and metastasis. Consistently, FOXM1b, FOXM1b1, FOXM1b2, and FOXM1c activated transcription of their typical downstream genes. Also, Sp1 mechanistically activated the FOXM1 promoter, whereas Krüppel-like factor 4 (KLF4) repressed its activity. Finally, we identified an Sp1- and KLF4-binding site in the FOXM1 promoter and showed that both Sp1 and KLF4 protein bound directly to it. Deletion mutation of this binding site significantly attenuated the transcriptional regulation of the FOXM1 promoter positively by Sp1 and negatively by KLF4. We showed that overexpression of specific FOXM1 isoforms critically regulates pancreatic cancer development and progression by enhancing tumor cell invasion and metastasis. Our findings strongly suggest that targeting specific FOXM1 isoforms effectively attenuates pancreatic cancer development and progression.

Helicobacter pylori promotes the expression of Krüppel-like factor 5, a mediator of carcinogenesis, in vitro and in vivo

Helicobacter pylori is the strongest known risk factor for the development of gastric adenocarcinoma. H. pylori expresses a repertoire of virulence factors that increase gastric cancer risk, including the cag pathogenicity island and the vacuolating cytotoxin (VacA). One host element that promotes carcinogenesis within the gastrointestinal tract is Krüppel-like factor 5 (KLF5), a transcription factor that mediates key cellular functions. To define the role of KLF5 within the context of H. pylori-induced inflammation and injury, human gastric epithelial cells were co-cultured with the wild-type cag⁺ H. pylori strain 60190. KLF5 expression was significantly upregulated following co-culture with H. pylori, but increased expression was independent of the cag island or VacA. To translate these findings into an in vivo model, C57BL/6 mice were challenged with the wild-type rodent-adapted cag⁺ H. pylori strain PMSS1 or a PMSS1 cagE⁻ isogenic mutant. Similar to findings in vitro, KLF5 staining was significantly enhanced in gastric epithelium of H. pylori-infected compared to uninfected mice and this was independent of the cag island. Flow cytometry revealed that the majority of KLF5⁺ cells also stained positively for the stem cell marker, Lrig1, and KLF5⁺/Lrig1⁺ cells were significantly increased in H. pylori-infected versus uninfected tissue. To extend these results into the natural niche of this pathogen, levels of KLF5 expression were assessed in human gastric biopsies isolated from patients with or without premalignant lesions. Levels of KLF5 expression increased in parallel with advancing stages of neoplastic progression, being significantly elevated in gastritis, intestinal metaplasia, and dysplasia compared to normal gastric tissue. These results indicate that H. pylori induces expression of KLF5 in gastric epithelial cells in vitro and in vivo, and that the degree of KLF5 expression parallels the severity of premalignant lesions in human gastric carcinogenesis.

p53 mutation alters the effect of the esophageal tumor suppressor KLF5 on keratinocyte proliferation

Krüppel-like factor 5 (KLF5) is a key transcriptional regulator that is typically pro-proliferative in non-transformed epithelial cells but inhibits proliferation in transformed epithelial cells. However, the underlying mechanisms for this context-dependent function are not known. KLF5 is epigenetically silenced and exhibits a tumor suppressive function in esophageal squamous cell cancer (ESCC). Since p53 mutation is the most common genetic alteration in ESCC, as in other human epithelial cancers, we hypothesized that the context-dependent functions of KLF5 in cell proliferation were dependent on p53 status. In fact, in non-transformed human primary esophageal keratinocytes, when p53 was wild-type, KLF5 was pro-proliferative; however, KLF5 became anti-proliferative when p53 was mutated. KLF5 loss in human primary keratinocytes harboring p53 mutation accelerated the cell cycle and decreased expression of p21Waf1/Cip1; similar effects were also seen in ESCC cells with established p53 mutations. Further, p21Waf1/Cip1 was directly and differentially bound and regulated by KLF5 in the presence or absence of mutant p53, and suppression of p21Waf1/Cip1 reversed the antiproliferative effects of KLF5 in the presence of p53 mutation. Thus, KLF5 is a critical brake on an aberrant cell cycle, with important tumor suppressive functions in esophageal squamous cell and potentially other epithelial cancers.

Critical role of Klf5 in regulating gene expression during post-eyelid opening maturation of mouse corneas

BACKGROUND

Klf5 plays an important role in maturation and maintenance of the mouse ocular surface. Here, we quantify WT and Klf5-conditional null (Klf5CN) corneal gene expression, identify Klf5-target genes and compare them with the previously identified Klf4-target genes to understand the molecular basis for non-redundant functions of Klf4 and Klf5 in the cornea.

METHODOLOGY/PRINCIPAL FINDINGS

Postnatal day-11 (PN11) and PN56 WT and Klf5CN corneal transcriptomes were quantified by microarrays to compare gene expression in maturing WT corneas, identify Klf5-target genes, and compare corneal Klf4- and Klf5-target genes. Whole-mount corneal immunofluorescent staining was employed to examine CD45+ cell influx and neovascularization. Effect of Klf5 on expression of desmosomal components was studied by immunofluorescent staining and transient co-transfection assays. Expression of 714 and 753 genes was increased, and 299 and 210 genes decreased in PN11 and PN56 Klf5CN corneas, respectively, with 366 concordant increases and 72 concordant decreases. PN56 Klf5CN corneas shared 241 increases and 98 decreases with those previously described in Klf4CN corneas. Xenobiotic metabolism related pathways were enriched among genes decreased in Klf5CN corneas. Expression of angiogenesis and immune response-related genes was elevated, consistent with neovascularization and CD45+ cell influx in Klf5CN corneas. Expression of 1574 genes was increased and 1915 genes decreased in WT PN56 compared with PN11 corneas. Expression of ECM-associated genes decreased, while that of solute carrier family members increased in WT PN56 compared with PN11 corneas. Dsg1a, Dsg1b and Dsp were down-regulated in Klf5CN corneas and their corresponding promoter activities were stimulated by Klf5 in transient co-transfection assays.

CONCLUSIONS/SIGNIFICANCE

Differences between PN11 and PN56 corneal Klf5-target genes reveal dynamic changes in functions of Klf5 during corneal maturation. Klf5 contributes to corneal epithelial homeostasis by regulating the expression of desmosomal components. Klf4- and Klf5-target genes are largely distinct, consistent with their non-redundant roles in the mouse cornea.

Dysregulated Krüppel-like factor 4 and vitamin D receptor signaling contribute to progression of hepatocellular carcinoma

BACKGROUND & AIMS

Krüppel-like factor 4 (KLF4) is a transcription factor and putative tumor suppressor. However, little is known about its effects in hepatocellular carcinogenesis. We investigated the clinical significance, biologic effects, and mechanisms of dysregulated KLF4 signaling.

METHODS

We performed microarray analysis of hepatocellular carcinoma (HCC) tissues. We used molecular biology analyses and animal models to evaluate activation and function of KLF4-vitamin D receptor (VDR) pathway.

RESULTS

Expression of KLF4 protein was decreased or lost in primary HCC samples, in particular, lymph node metastases, compared with normal liver tissues. Loss of KLF4 from primary tumors was significantly associated with reduced survival time and was identified as a prognostic marker. Most human HCC cell lines had losses or substantial decreases in levels of KLF4. Exogenous expression of KLF4 in HCC cells upregulated expression of mesenchymal-epithelial transition (MET) and inhibited their migration, invasion, and proliferation in vitro. When these cells were injected into mice, tumors grew more slowly and metastasis was inhibited, compared with HCC cells that did not express KLF4. VDR is a direct transcriptional target of KLF4; we identified 2 sites in the VDR promoter that bound specifically to KLF4. Increased expression of VDR sensitized tumor cells to the inhibitory effects of vitamin D.

CONCLUSIONS

KLF4 binds to the promoter of VDR to regulate its expression; levels of KLF4 are reduced and levels of VDR are increased in HCC cell lines and primary tumor samples. Expression of KLF4 in HCC cells sensitizes them to the anti-proliferative effects of VD3. This pathway might be manipulated to prevent or treat liver cancer.

Krüppel-like factor 4, a tumor suppressor in hepatocellular carcinoma cells reverts epithelial mesenchymal transition by suppressing slug expression

Krüppel-like factor 4 (KLF4) is a zinc-finger transcription factor that plays an important role in differentiation and pathogenesis. KLF4 has been suggested to act as an oncogene or tumor suppressor in different tumor types. However, the role of KLF4 in hepatocellular carcinoma (HCC) remains unclear. Here, we demonstrate that forced expression of Klf4 in murine HCC cell lines reduced anchorage-independent growth in soft agar as well as cell migration and invasion activities in vitro. Ectopic Klf4 expression impaired subcutaneous tumor growth and lung colonization in vivo. By contrast, Klf4 knockdown enhanced HCC cell migration. Interestingly, ectopic expression of Klf4 changed the morphology of murine HCC cells to a more epithelial phenotype. Associated with this, we found that expression of Slug, a critical epithelial mesenchymal transition (EMT)-related transcription factor, was significantly down-regulated in Klf4-expressing cells. Chromatin immunoprecipitation (ChIP) and luciferase reporter assays showed that Klf4 is able to bind and repress the activity of the Slug promoter. Furthermore, ectopic Slug expression partially reverts the Klf4-mediated phenotypes. Consistent with a role as a tumor suppressor in HCC, analysis of the public microarray databases from Oncomine revealed reduced KLF4 expression in human HCC tissues in comparison with normal liver tissues in 3 out of 4 data sets. By quantitative reverse transcription-polymerase chain reaction (qRT-PCR), we found reduced KLF4 mRNA in 50% of HCC tissues. Importantly, an inverse correlation between the expression of KLF4 and SLUG was found in HCC tissues. Our data suggest that KLF4 acts as a tumor suppressor in HCC cells, in part by suppressing SLUG transcription.

High-throughput screening strategies for targeted identification of therapeutic compounds in colorectal cancer

Recent advancements in understanding the role of both genetics and molecular pathways in the formation and progression of colorectal cancer have allowed the identification of factors that may be targeted for drug discovery. During the past decade, various approaches have been developed to target specific steps or components of these pathways in order to prevent the development and progression of colorectal cancer and to treat this disease. The innovation and optimization of high-throughput screening methods, as well as the recent emphasis from the NIH on translational sciences, have enabled rapid progress in drug discovery in many fields, including colorectal cancer. Here we present a summary of the recent efforts of targeted high-throughput drug discovery directed at pathways affected in colorectal cancer.

Krüppel-like factor 5 protects against murine colitis and activates JAK-STAT signaling in vivo

Inflammatory bowel disease (IBD), which is characterized by chronic or recurring inflammation of the gastrointestinal tract, affects 1.4 million persons in the United States alone. KLF5, a Krüppel-like factor (KLF) family member, is expressed within the epithelia of the gastrointestinal tract and has been implicated in rapid cell proliferation, migration, and remodeling in a number of tissues. Given these functions, we hypothesized that constitutive Klf5 expression would protect against the development of colitis in vivo. To examine the role of KLF5 in vivo, we used the Villin promoter to target Klf5 to the entire horizontal axis of the small intestine and colon. Villin-Klf5 transgenic mice were born at normal Mendelian ratios and appeared grossly normal to at least 1 year of age. Surprisingly, there were no significant changes in cell proliferation or in the differentiation of any of the intestinal lineages within the duodenum, jejunum, ileum, and colon of Villin-Klf5 mice, compared to littermate controls. However, when Villin-Klf5 mice were treated with dextran sodium sulfate (DSS) to induce colitis, they developed less colonic injury and significantly reduced disease activity scores than littermate controls. The mechanism for this decreased injury may come via JAK-STAT signaling, the activation of which was increased in colonic mucosa of DSS treated Villin-Klf5 mice compared to controls. Thus, KLF5 and its downstream mediators may provide therapeutic targets and disease markers for IBD or other diseases characterized by injury and disruption of intestinal epithelia.

Regulation of KLF4 turnover reveals an unexpected tissue-specific role of pVHL in tumorigenesis

The transcription factor Krüppel-like factor 4 (KLF4) is an important regulator of cell-fate decision, including cell-cycle regulation, apoptosis, and stem cell renewal, and plays an ambivalent role in tumorigenesis as a tissue-specific tumor suppressor or oncogene. Here, we report that the Von Hippel-Lindau gene product, pVHL, physically interacts with KLF4 and regulates its rapid turnover observed in both differentiated and stem cells. We provide mechanistic insights into KLF4 degradation and show that pVHL depletion in colorectal cancer cells leads to cell-cycle arrest concomitant with increased transcription of the KLF4-dependent p21 gene. Finally, immunohistochemical staining revealed elevated pVHL and reduced KLF4 levels in colon cancer tissues. We therefore propose that unexpectedly pVHL, via the degradation of KLF4, is a facilitating factor in colorectal tumorigenesis.

Novel insight into KLF4 proteolytic regulation in estrogen receptor signaling and breast carcinogenesis

Krüppel-like factor 4 (KLF4), a zinc finger-containing transcriptional factor, is a pivotal regulator of cellular fate. KLF4 has attracted considerable attention for its opposing effect in carcinogenesis as tumor suppressor (e.g. colorectal cancer) or oncoprotein (e.g. breast cancer), depending on tissue context, with the underlying mechanism remaining largely unknown. Here we report that KLF4 mediates estrogen signaling in breast cancer formation. Accumulation of KLF4 by inhibiting its turnover triggers estrogen-induced transactivation. We identified Von Hippel-Lindau, pVHL, as the protein that governs KLF4 turnover in breast cancer cells and demonstrated that estrogen-induced down-regulation of pVHL facilitates accumulation of KLF4. We provide mechanistic insights into KLF4 steady-state degradation as well as its elevation in the presence of estrogen and show that elevated levels of pVHL or depletion of KLF4 attenuates the estrogen-induced transactivation and cell growth. Finally, immunohistochemical staining revealed reduced concentration of pVHL and accumulation of KLF4 in breast cancer tissues. We thus propose that suppression of pVHL in response to estrogen signaling results in elevation of KLF4, which mediates estrogen-induced mitogenic effect.

Disruption of Klf4 in villin-positive gastric progenitor cells promotes formation and progression of tumors of the antrum in mice

BACKGROUND & AIMS

Krüppel-like factor 4 (Klf4) is a putative gastric tumor suppressor gene. Rare, villin-positive progenitor cells in the gastric antrum have multilineage potential. We investigated the function of Klf4 in these cells and in gastric carcinogenesis.

METHODS

We created mice with disruption of Klf4 in villin-positive antral mucosa cells (Villin-Cre(+);Klf4(fl/fl) mice). Villin-Cre(+);Klf4(fl/fl) and control mice were given drinking water with or without 240 ppm N-methyl-N-nitrosourea at 5 weeks of age and thereafter on alternating weeks for a total of 10 weeks. Gastric mucosa samples were collected at 35, 50, or 80 weeks of age from mice that were and were not given N-methyl-N-nitrosourea, and analyzed by histopathologic and molecular analyses. Findings were compared with those from human gastric tumor specimens.

RESULTS

Preneoplasia formed progressively in the antrum in 35- to 80-week-old Villin-Cre(+);Klf4(fl/fl) mice. Gastric tumors developed in 29% of 80-week-old Villin-Cre(+);Klf4(fl/fl) mice, which were located exclusively in the lesser curvature of the antrum. N-methyl-N-nitrosourea accelerated tumor formation, and tumors developed significantly more frequently in Villin-Cre(+);Klf4(fl/fl) mice than in control mice, at 35 and 50 weeks of age. Mouse and human gastric tumors had reduced expression of Krüppel-like factor 4 and increased expression of FoxM1 compared with healthy gastric tissue. Expression of Krüppel-like factor 4 suppressed transcription of FoxM1.

CONCLUSIONS

Inactivation of Klf4 in villin-positive gastric progenitor cells induces transformation of the gastric mucosa and tumorigenesis in the antrum in mice. Villin-Cre(+);Klf4(fl/fl) have greater susceptibility to chemical-induced gastric carcinogenesis and increased rates of gastric tumor progression than control mice.

Altered expression of Krüppel-like factor 4 and β-catenin in human gastric cancer

The effects of the interaction between KLF4 and β-catenin may be significant in human carcinogenesis and tumor development. This study aimed to determine whether the expression of KLF4 and β-catenin in gastric cancer tissues is associated with clinicopathological characteristics. Western blot analysis and immunohistochemistry were performed to detect KLF4 and β-catenin expression in tumor and corresponding non-cancerous tissues from 49 patients. The data revealed that KLF4 expression was significantly reduced in gastric cancer tissues compared with normal tissues. By contrast, the expression of the β-catenin protein was significantly increased in all tumor tissues, but was not expressed in distant normal mucosae. The altered expression of the KLF4 and β-catenin proteins was associated with advanced tumor stage and gastric cancer. In addition, the expression of the KLF4 and β-catenin proteins was inversely associated in moderately differentiated human gastric cancers. This study showed that β-catenin expression is significantly increased and KLF4 protein expression is markedly decreased in gastric cancer tissues, thus showing that the expression of KLF4 is inversely correlated with that of β-catenin in gastric cancer. The altered expression of the two proteins is associated with advanced tumor stage in gastric cancer.

Retinoic acid receptor α mediates all-trans-retinoic acid-induced Klf4 gene expression by regulating Klf4 promoter activity in vascular smooth muscle cells

The transcription factor Krüppel-like factor 4 (KLF4) plays a critical role in vascular smooth muscle cell (VSMC) differentiation induced by all-trans-retinoic acid (ATRA). Although it has been demonstrated that ATRA stimulation augments both KLF4 protein and mRNA levels in VSMCs, the molecular mechanisms by which ATRA regulates Klf4 transcription are unknown. In this study, we examined the roles of ATRA-selective nuclear retinoic acid receptors (RARs) in the transcriptional regulation of Klf4. The introduction of small interfering RNA and an RAR antagonist demonstrated that RARα, but not RARβ or RARγ, mediated ATRA-induced Klf4 expression. A luciferase assay for the Klf4 promoter showed that three GC boxes in the proximal Klf4 promoter were indispensible for ATRA-induced Klf4 transcription and that RARα enhanced Klf4 promoter activity in a GC box-dependent manner. Furthermore, chromatin immunoprecipitation and oligonucleotide pulldown assays demonstrated that the transcription factors KLF4, Sp1, and YB1 directly bound to the GC boxes of the proximal Klf4 promoter. Upon RARα agonist stimulation, RARα was recruited to the Klf4 promoter through its interaction with KLF4, Sp1, and YB1 to form a transcriptional activation complex on the three GC boxes of the Klf4 promoter. These results suggest that RARα serves as an essential co-activator for ATRA signaling and that the recruitment of RARα to the KLF4-Sp1-YB1 complex, which leads to Klf4 expression in VSMCs, is independent of a retinoic acid response element.

Krüppel-like factor 4 regulates membranous and endochondral ossification

Krüppel-like factor 4 (KLF4/GKLF/EZF) is a zinc finger type of transcription factor highly expressed in the skin, intestine, testis, lung and bone. The role played by Klf4 has been studied extensively in normal epithelial development and maintenance; however, its role in bone cells is unknown. Previous reports showed that Klf4 is expressed in the developing flat bones but its expression diminishes postnatally. We now show that in the developing long bones, Klf4 is expressed in the perichondrium, trabecular osteoblasts and prehypertrophic chondrocytes. In contrast, osteoblasts lining at the surface of the bone collar showed extremely low levels of Klf4 expression. To investigate the possible roles played by Klf4 during skeletal development, we generated transgenic mice expressing Klf4 under mouse type I collagen regulatory sequence. Transgenic mice exhibited severe skeletal deformities and died soon after birth. Transgenic mice showed delayed formation of the calvarial bones; and over-expressing Klf4 in primary mouse calvarial osteoblasts in culture resulted in strong repression of mineralization indicating that this regulation of Klf4 is through an osteoblast-autonomous effect. Surprisingly, long bones of the transgenic mice exhibited delayed marrow cavity formation. Even at E18.5, the presumptive marrow space was occupied by cartilage anlage and invasion of the vascular endothelial cells and osteoclasts were seldom observed. Instead of entering the cartilage anlage, osteoclasts accumulated at the periosteum in the transgenic mice. Significantly, osteocalcin, which is known to chemotact osteoclasts, was up-regulated at the perichindrium as early as E14.5 in the mutants. In vitro studies showed that this induction of osteocalcin by Klf4 was regulated at its transcriptional level. Our results demonstrate that Klf4 regulates normal skeletal development through coordinating the differentiation and migration of osteoblasts, chondrocytes, vascular endothelial cells and osteoclasts.

MicroRNA-449a overexpression, reduced NOTCH1 signals and scarce goblet cells characterize the small intestine of celiac patients

MiRNAs play a relevant role in regulating gene expression in a variety of physiological and pathological conditions including autoimmune disorders. MiRNAs are also important in the differentiation and function of the mouse intestinal epithelium. Our study was aimed to look for miRNA-based modulation of gene expression in celiac small intestine, and particularly for genes involved in cell intestinal differentiation/proliferation mechanisms. A cohort of 40 children (20 with active CD, 9 on a gluten-free diet (GFD), and 11 controls), were recruited at the Paediatrics Department (University of Naples Federico II). The expression of 365 human miRNAs was quantified by TaqMan low-density arrays. We used bioinformatics to predict putative target genes of miRNAs and to select biological pathways. The presence of NOTCH1, HES1, KLF4, MUC-2, Ki67 and beta-catenin proteins in the small intestine of CD and control children was tested by immunohistochemistry. The expression of about 20% of the miRNAs tested differed between CD and control children. We found that high miR-449a levels targeted and reduced both NOTCH1 and KLF4 in HEK-293 cells. NOTCH1, KLF4 signals and the number of goblet cells were lower in small intestine of children with active CD and in those on a GFD than in controls, whereas more nuclear beta-catenin staining, as a sign of the WNT pathway activation, and more Ki67 staining, as sign of proliferation, were present in crypts from CD patients than in controls.

In conclusion we first demonstrate a miRNA mediated gene regulation in small intestine of CD patients. We also highlighted a reduced NOTCH1 pathway in our patients, irrespective of whether the disease was active or not. We suggest that NOTCH pathway could be constitutively altered in the celiac small intestine and could drive the increased proliferation and the decreased differentiation of intestinal cells towards the secretory goblet cell lineage.

Comprehensive analysis of clinical significance of stem-cell related factors in renal cell cancer

Background

C-MYC, LIN28, OCT4, KLF4, NANOG and SOX2 are stem cell related factors. We detected whether these factors express in renal cell carcinoma (RCC) tissues to study their correlations with the clinical and pathological characteristics.

Methods

The expressions of c-MYC, LIN28, SOX2, KLF4, OCT4 and NANOG in 30 RCC patients and 5 non-RCC patients were detected with quantitative real-time reverse transcription-PCR (qRT-PCR). The data were analyzed with Wilcoxon signed rank sum test and x² test.

Results

In RCC group, c-MYC expression was significantly higher in RCC tissues compared with normal tissues (P < 0.05). The expression levels of OCT4, KLF4, NANOG and SOX2 were significantly lower in RCC tissues compared with normal tissues (P < 0.05). LIN28 expression level was not significant. No difference was observed when it comes to clinical and pathological characteristics such as gender, age, tumor size, cTNM classification and differentiation status (P > 0.05). Also the expression levels of all above factors were not significantly changed in non-RCC group (P > 0.05).

Conclusions

The present analysis strongly suggests that altered expression of several stem cell related factors may play different roles in RCC. C-MYC may function as an oncogene and OCT4, KLF4, NANOG and SOX2 as tumor suppressors.

Krüppel-like factor 5 is important for maintenance of crypt architecture and barrier function in mouse intestine

BACKGROUND & AIMS

Krüppel-like factor 5 (KLF5) is transcription factor that is expressed by dividing epithelial cells of the intestinal epithelium. KLF5 promotes proliferation in vitro and in vivo and is induced by mitogens and various stress stimuli. To study the role of KLF5 in intestinal epithelial homeostasis, we examined the phenotype of mice with conditional deletion of Klf5 in the gut.

METHODS

Mice were generated with intestinal-specific deletion of Klf5 (Vil-Cre;Klf5fl/fl). Morphologic changes in the small intestine and colon were examined by immunohistochemistry, immunoblotting, and real-time polymerase chain reaction.

RESULTS

Klf5 mutant mice were born at a normal Mendelian ratio but had high mortality compared with controls. Complete deletion of Klf5 from the intestinal mucosa resulted in neonatal lethality that corresponded with an absence of epithelial proliferation. Variegated intestinal-specific deletion of Klf5 in adult mice resulted in morphologic changes that included a regenerative phenotype, impaired barrier function, and inflammation. Adult mutant mice exhibited defects in epithelial differentiation and migration. These changes were associated with reduced expression of Caudal type homeobox (Cdx) 1, Cdx2, and Eph and ephrin signaling proteins. Concomitantly, Wnt signaling to β-catenin was reduced. Proliferation in regenerative crypts was associated with increased expression of the progenitor cell marker Sox9.

CONCLUSIONS

Deletion of Klf5 in the gut epithelium of mice demonstrated that KLF5 maintains epithelial proliferation, differentiation, and cell positioning along the crypt radial axis. Morphologic changes that occur with deletion of Klf5 are associated with disruption of canonical Wnt signaling and increased expression of Sox9.

Krüppel-like factor 4 (KLF4) directly regulates proliferation in thymocyte development and IL-17 expression during Th17 differentiation

Krüppel-like factor 4 (KLF4), a transcription factor, plays a key role in the pluripotency of stem cells. We sought to determine the function of KLF4 in T-cell development and differentiation by using T-cell-specific Klf4-knockout (KO) mice. We found that KLF4 was highly expressed in thymocytes and mature T cells and was rapidly down-regulated in mature T cells after activation. In Klf4-KO mice, we observed a modest reduction of thymocytes (27%) due to the reduced proliferation of double-negative (DN) thymocytes. We demonstrated that a direct repression of Cdkn1b by KLF4 was a cause of decreased DN proliferation. During in vitro T-cell differentiation, we observed significant reduction of IL-17-expressing CD4(+) T cells (Th17; 24%) but not in other types of Th differentiation. The reduction of Th17 cells resulted in a significant attenuation of the severity (35%) of experimental autoimmune encephalomyelitis in vivo in Klf4-KO mice as compared with the Klf4 wild-type littermates. Finally, we demonstrated that KLF4 directly binds to the promoter of Il17a and positively regulates its expression. In summary, these findings identify KLF4 as a critical regulator in T-cell development and Th17 differentiation.

The E3 ubiquitin ligase SMAD ubiquitination regulatory factor 2 negatively regulates Krüppel-like factor 5 protein

The zinc finger transcription factor Krüppel-like factor 5 (KLF5) is regulated posttranslationally. We identified SMAD ubiquitination regulatory factor 2 (SMURF2), an E3 ubiquitin ligase, as an interacting protein of KLF5 by yeast two-hybrid screen, coimmunoprecipitation, and indirect immunofluorescence studies. The SMURF2-interacting domains in KLF5 were mapped to its carboxyl terminus, including the PY motif of KLF5 and its zinc finger DNA-binding domain. KLF5 protein levels were reduced significantly upon overexpression of SMURF2 but not catalytically inactive SMURF2-C716A mutant or SMURF1. SMURF2 alone reduced the protein stability of KLF5 as shown by cycloheximide chase assay, indicating that SMURF2 specifically destabilizes KLF5. In contrast, KLF5(1-165), a KLF5 amino-terminal construct that lacks the PY motif and DNA binding domain, was not degraded by SMURF2. The degradation of KLF5 by SMURF2 was blocked by the proteasome inhibitor MG132, and SMURF2 efficiently ubiquitinated both overexpressed and endogenous KLF5. In contrast, knocking down SMURF2 by siRNAs significantly enhanced KLF5 protein levels, reduced ubiquitination of KLF5, and increased the expression of cyclin D1 and PDGF-A, two established KLF5 target genes. In consistence, SMURF2, but not the E3 ligase mutant SMURF2-C716A, significantly inhibited the transcriptional activity of KLF5, as demonstrated by dual luciferase assay using the PDGF-A promoter, and suppressed the ability of KLF5 to stimulate cell proliferation as measured by BrdU incorporation. Hence, SMURF2 is a novel E3 ubiquitin ligase for KLF5 and negatively regulates KLF5 by targeting it for proteasomal degradation.

Cooperative transcriptional activation by Klf4, Meis2, and Pbx1

The Kruppel-like factor Klf4 is implicated in tumorigenesis and maintaining stem cell pluripotency, and Klf4 can both activate and repress gene expression. We show that the Pbx1 and Meis2 homeodomain proteins interact with Klf4 and can be recruited to DNA elements comprising a Klf4 site or GC box, with adjacent Meis and Pbx sites. Meis2d and Pbx1a activate expression of p15(Ink4a) and E-cadherin, dependent on the Meis2d transcriptional activation domain. In HepG2 cells, reducing expression of endogenous Meis2 or Pbx1 decreases p15 gene expression and increases the number of cells entering S phase. Although DNA binding by all three proteins contributes to full cooperative activation, the sequence requirements for binding by Meis2 and Pbx1 are variable. In the E-cadherin promoter, a Pbx-like site is required for full activation, whereas in the p15 promoter, the Klf4 site appears to play the major role. Through a bioinformatics search we identified additional genes with conserved binding sites for Klf4, Meis2, and Pbx1 and show that at least some of these genes can be activated cooperatively by Klf4 and Meis2/Pbx1. We suggest a model in which genes with Klf4 sites can be cooperatively activated by Meis2/Pbx1 and Klf4, dependent primarily on recruitment by Klf4. This provides a mechanism to modulate transcriptional regulation by the multifunctional Klf4 transcription factor.

Loss of transcription factor KLF5 in the context of p53 ablation drives invasive progression of human squamous cell cancer

Squamous cell cancers account for more than half of all human cancers, and esophageal cancer is the sixth leading cause of cancer death worldwide. The majority of esophageal squamous cell carcinomas have identifiable p53 mutations, yet the same p53 mutations are found at comparable frequencies in precancerous dysplasia, indicating that transformation requires additional somatic changes yet to be defined. Here, we show that the zinc finger transcription factor Krüppel-like factor 5 (KLF5) transactivates NOTCH1 in the context of p53 mutation or loss. KLF5 loss limited NOTCH1 activity and was sufficient on its own to transform primary human keratinocytes harboring mutant p53, leading to the formation of invasive tumors. Restoration of NOTCH1 blocked transformation of KLF5-deficient and p53-mutant keratinocytes. Although human dysplastic epithelia accumulated KLF5, KLF5 expression was lost concurrently with NOTCH1 in squamous cell cancers. Taken together, these results define KLF5 loss as a critical event in squamous cell transformation and invasion. Our findings suggest that KLF5 may be a useful diagnostic and therapeutic target in esophageal squamous carcinomas and possibly more generally in other cancers associated with p53 loss of function.

Kruppel-like factor 5 is required for formation and differentiation of the bladder urothelium

Kruppel-like transcription factor 5 (Klf5) was detected in the developing and mature murine bladder urothelium. Herein we report a critical role of KLF5 in the formation and terminal differentiation of the urothelium. The Shh(GfpCre) transgene was used to delete the Klf5(floxed) alleles from bladder epithelial cells causing prenatal hydronephrosis, hydroureter, and vesicoureteric reflux. The bladder urothelium failed to stratify and did not express terminal differentiation markers characteristic of basal, intermediate, and umbrella cells including keratins 20, 14, and 5, and the uroplakins. The effects of Klf5 deletion were unique to the developing bladder epithelium since maturation of the epithelium comprising the bladder neck and urethra was unaffected by the lack of KLF5. mRNA analysis identified reductions in Pparγ, Grhl3, Elf3, and Ovol1expression in Klf5 deficient fetal bladders supporting their participation in a transcriptional network regulating bladder urothelial differentiation. KLF5 regulated expression of the mGrhl3 promoter in transient transfection assays. The absence of urothelial Klf5 altered epithelial-mesenchymal signaling leading to the formation of an ectopic alpha smooth muscle actin positive layer of cells subjacent to the epithelium and a thinner detrusor muscle that was not attributable to disruption of SHH signaling, a known mediator of detrusor morphogenesis. Deletion of Klf5 from the developing bladder urothelium blocked epithelial cell differentiation, impaired bladder morphogenesis and function causing hydroureter and hydronephrosis at birth.

Krüppel-like transcription factors in the nervous system: novel players in neurite outgrowth and axon regeneration

The Krüppel-like family of transcription factors (KLFs) have been widely studied in proliferating cells, though very little is known about their role in post-mitotic cells, such as neurons. We have recently found that the KLFs play a role in regulating intrinsic axon growth ability in retinal ganglion cells (RGCs), a type of central nervous system (CNS) neuron. Previous KLF studies in other cell types suggest that there may be cell-type specific KLF expression patterns, and that their relative expression allows them to compete for binding sites, or to act redundantly to compensate for another's function. With at least 15 of 17 KLF family members expressed in neurons, it will be important for us to determine how this complex family functions to regulate the intricate gene programs of axon growth and regeneration. By further characterizing the mechanisms of the KLF family in the nervous system, we may better understand how they regulate neurite growth and axon regeneration.

Conditional disruption of mouse Klf5 results in defective eyelids with malformed meibomian glands, abnormal cornea and loss of conjunctival goblet cells

Members of the Krüppel-like family of transcription factors regulate diverse developmental processes in various organs. Previously, we have demonstrated the role of Klf4 in the mouse ocular surface. Herein, we determined the role of the structurally related Klf5, using Klf5-conditional null (Klf5CN) mice derived by mating Klf5-LoxP and Le-Cre mice. Klf5 mRNA was detected as early as embryonic day 12 (E12) in the cornea, conjunctiva and eyelids, wherein its expression increased during development. Though the embryonic eye morphogenesis was unaltered in the Klf5CN mice, postnatal maturation was defective, resulting in smaller eyes with swollen eyelids that failed to separate properly. Klf5CN palpebral epidermis was hyperplastic with 7-9 layers of keratinocytes, compared with 2-3 in the wild type (WT). Klf5CN eyelid hair follicles and sebaceous glands were significantly enlarged, and the meibomian glands malformed. Klf5CN lacrimal glands displayed increased vasculature and large number of infiltrating cells. Klf5CN corneas were translucent, thicker with defective epithelial basement membrane and hypercellular stroma. Klf5CN conjunctiva lacked goblet cells, demonstrating that Klf5 is required for conjunctival goblet cell development. The number of Ki67-positive mitotic cells was more than doubled, consistent with the increased number of Klf5CN ocular surface epithelial cells. Co-ablation of Klf4 and Klf5 resulted in a more severe ocular surface phenotype compared with Klf4CN or Klf5CN, demonstrating that Klf4 and Klf5 share few if any, redundant functions. Thus, Klf5CN mice provide a useful model for investigating ocular surface pathologies involving meibomian gland dysfunction, blepharitis, corneal or conjunctival defects.

Krüppel-like factor 9 loss-of-expression in human endometrial carcinoma links altered expression of growth-regulatory genes with aberrant proliferative response to estrogen

Endometrial cancer is the most commonly diagnosed female genital tract malignancy. Krüppel-like factor 9 (KLF9), a member of the evolutionarily conserved Sp family of transcription factors, is expressed in uterine stroma and glandular epithelium, where it affects cellular proliferation, differentiation, and apoptosis. Deregulated expression of a number of Sp proteins has been associated with multiple types of human tumors, but a role for KLF9 in endometrial cancer development and/or progression is unknown. Here, we evaluated KLF9 expression in endometrial tumors and adjacent uninvolved endometrium of women with endometrial carcinoma. KLF9 mRNA and protein levels were lower in endometrial tumors coincident with decreased expression of family member KLF4 and growth-regulators FBJ murine osteosarcoma viral oncogene homolog (FOS) and myelocytomatosis viral oncogene homolog (MYC) and with increased expression of telomerase reverse transcriptase (TERT) and the chromatin-modifying enzymes DNA methyltransferase 1 (DNMT1) and histone deacetylase 3 (HDAC3). Expression of estrogen receptor alpha (ESR1) and the tumor-suppressor phosphatase and tensin homolog deleted in chromosome 10 (PTEN) did not differ between tumor and normal tissue. The functional relevance of attenuated KLF9 expression in endometrial carcinogenesis was further evaluated in the human endometrial carcinoma cell line Ishikawa by siRNA targeting. KLF9 depletion resulted in loss of normal cellular response to the proliferative effects of estrogen concomitant with reductions in KLF4 and MYC and with enhancement of TERT and ESR1 gene expression. Silencing of KLF4 did not mimic the effects of silencing KLF9 in Ishikawa cells. We suggest that KLF9 loss-of-expression accompanying endometrial carcinogenesis may predispose endometrial epithelial cells to mechanisms of escape from estrogen-mediated growth regulation, leading to progression of established neoplasms.

Estrogen regulates tumor growth through a nonclassical pathway that includes the transcription factors ERβ and KLF5

Clinical evidence suggests that antiestrogens inhibit the development of androgen-insensitive prostate cancer. Here, we show that the estrogen receptor β (ERβ) mediates inhibition by the antiestrogen ICI 182,780 (ICI) and its enhancement by estrogen. ERβ associated with gene promoters through the tumor-suppressing transcription factor KLF5 (Krüppel-like zinc finger transcription factor 5). ICI treatment increased the recruitment of the transcription coactivator CBP [CREB (adenosine 3',5'-monophosphate response element-binding protein)-binding protein] to the promoter of FOXO1 through ERβ and KLF5, which enhanced the transcription of FOXO1. The increase in FOXO1 abundance led to anoikis in prostate cancer cells, thereby suppressing tumor growth. In contrast, estrogen induced the formation of complexes containing ERβ, KLF5, and the ubiquitin ligase WWP1 (WW domain containing E3 ubiquitin protein ligase 1), resulting in the ubiquitination and degradation of KLF5. The combined presence of KLF5 and ERβ positively correlated with longer cancer-specific survival in prostate cancer patients. Our results demonstrate that estrogens and antiestrogens affect prostate tumor growth through ERβ-mediated regulation of KLF5.

Regulation of corneal epithelial barrier function by Kruppel-like transcription factor 4

PURPOSE

Previously, the authors showed that Klf4-conditional null (Klf4CN) corneas display epithelial fragility. Here, they investigated the mechanism by which Klf4 regulates corneal epithelial barrier function.

METHODS

Klf4CN mice were generated by breeding Le-Cre with Klf4-LoxP mice. Fluorescein staining was used to test the corneal barrier function. RT-PCR, immunoblots, and immunofluorescence were used to detect the expression of cell junctional proteins. The effect of Klf4 on promoter activities was measured by transient cotransfection assays. Trans-epithelial electrical resistance (TEER) was used to measure the barrier-forming ability of control or anti-KLF4 siRNA-treated cells.

RESULTS

Increased fluorescein staining and decreased tight junction protein Tjp1 expression demonstrated that the Klf4CN corneal epithelial barrier function is defective. Expression of desmosomal components Dsp, Dsg-1a, and Dsg-1b was downregulated in the Klf4CN corneas, and their corresponding promoter activities were upregulated by Klf4 in transient cotransfection assays. Hemidesmosomal α3- and β4-integrin levels were not affected even though there were fewer hemidesmosomes in the Klf4CN corneas. The basement membrane components laminin-α5, -α3, -β3, and -β1-1 were downregulated, suggesting that the disrupted basement membrane is responsible for fewer hemidesmosomes in the Klf4CN cornea. Tight junction proteins OCLN1 and TJP1were downregulated in anti-KLF4 siRNA-treated cells, which failed to develop epithelial barrier function as measured by TEER.

CONCLUSIONS

Klf4 contributes to corneal epithelial barrier function by upregulating the expression of functionally related subsets of cell junctional proteins and basement membrane components.

Krüppel-like factor 5 protects against dextran sulfate sodium-induced colonic injury in mice by promoting epithelial repair

BACKGROUND & AIMS

Krüppel-like factor 5 (KLF5) is a transcription factor that promotes proliferation, is highly expressed in dividing crypt cells of the gastrointestinal epithelium, and is induced by various stress stimuli. We sought to determine the role of KLF5 in colonic inflammation and recovery by studying mice with dextran sulfate sodium (DSS)-induced colitis.

METHODS

Wild-type (WT) and Klf5(+/-) mice were given DSS in the drinking water to induce colitis. For recovery experiments, mice were given normal drinking water for 5 days after DSS administration. The extent of colitis was determined using established clinical and histological scoring systems. Immunohistochemical and immunoblotting analyses were used to examine proliferation, migration, and expression of the epidermal growth factor receptor.

RESULTS

Klf5 expression was increased in colonic tissues of WT mice given DSS; induction of Klf5 was downstream of mitogen-activated protein kinase signaling. In DSS-induced colitis, Klf5(+/-) mice exhibited greater sensitivity to DSS than WT mice, with significantly higher clinical and histological colitis scores. In recovery experiments, Klf5(+/-) mice showed poor recovery, with continued weight loss and higher mortality than WT mice. Klf5(+/-) mice from the recovery period had reduced epithelial proliferation and cell migration at sites of ulceration compared to WT mice; these reductions correlated with reduced expression of epidermal growth factor receptor.

CONCLUSIONS

Epithelial repair is an important aspect of recovery from DSS-induced colitis. The transcription factor KLF5 regulates mucosal healing through its effects on epithelial proliferation and migration.

Epithelial microRNAs regulate gut mucosal immunity via epithelium-T cell crosstalk

Colonic homeostasis entails epithelium-lymphocyte cooperation, yet many participants in this process are unknown. We show here that epithelial microRNAs mediate the mucosa-immune system crosstalk necessary for mounting protective T helper type 2 (T(H)2) responses. Abolishing the induction of microRNA by gut-specific deletion of Dicer1 (Dicer1(Δgut)), which encodes an enzyme involved in microRNA biogenesis, deprived goblet cells of RELMβ, a key T(H)2 antiparasitic cytokine; this predisposed the host to parasite infection. Infection of Dicer1(Δgut) mice with helminths favored a futile T(H)1 response with hallmarks of inflammatory bowel disease. Interleukin 13 (IL-13) induced the microRNA miR-375, which regulates the expression of TSLP, a T(H)2-facilitating epithelial cytokine; this indicated a T(H)2-amplification loop. We found that miR-375 was required for RELMβ expression in vivo; miR-375-deficient mice had significantly less intestinal RELMβ, which possibly explains the greater susceptibility of Dicer1(Δgut) mice to parasites. Our findings indicate that epithelial microRNAs are key regulators of gut homeostasis and mucosal immunity.