KLF6, a candidate tumor suppressor gene mutated in prostate cancer

FOXP3 up-regulates p21 expression by site-specific inhibition of histone deacetylase 2/histone deacetylase 4 association to the locus

p21 loss has been implicated in conferring oncogenic activity to known tumor suppressor gene KLF4 and cancer drug tamoxifen. Regulators of p21, therefore, play critical roles in tumorigenesis. Here, we report that X-linked tumor suppressor FOXP3 is essential for p21 expression in normal epithelia and that lack of FOXP3 is associated with p21 down-regulation in breast cancer samples. A specific FOXP3 binding site in the intron 1 is essential for p21 induction by FOXP3. FOXP3 specifically inhibited binding of histone deacetylase 2 (HDAC2) and HDAC4 to the site and increased local histone H3 acetylation. Short hairpin RNA silencing of either HDAC2 or HDAC4 is sufficient to induce p21 expression. Our data provides a novel mechanism for transcription activation by FOXP3 and a genetic mechanism for lack of p21 in a large proportion of breast cancer.

Functional role of the KLF6 tumour suppressor gene in gastric cancer

Gastric cancer is the second most common cancer and a leading cause of cancer-related death worldwide. The Kruppel-like factor 6 (KLF6) tumour suppressor gene had been previously shown to be inactivated in a number of human cancers through loss of heterozygosity (LOH), somatic mutation, decreased expression and increased alternative splicing into a dominant negative oncogenic splice variant, KLF6-SV1. In the present study, 37 gastric cancer samples were analysed for the presence of loss of heterozygosity (LOH) of the KLF6 locus and somatic mutation. In total, 18 of 34 (53%) of the gastric cancer samples analysed demonstrated KLF6 locus specific loss. Four missense mutations, such as T179I, R198G, R71Q and S180L, were detected. Interestingly, two of these mutations R71Q and S180L have been identified independently by several groups in various malignancies including prostate, colorectal and gastric cancers. In addition, decreased wild-type KLF6 (wtKLF6) expression was associated with loss of the KLF6 locus and was present in 48% of primary gastric tumour samples analysed. Functional studies confirmed that wtKLF6 suppressed proliferation of gastric cancer cells via transcriptional regulation of the cyclin-dependent kinase inhibitor p21 and the oncogene c-myc. Functional characterisation of the common tumour-derived mutants demonstrated that the mutant proteins fail to suppress proliferation and function as dominant negative regulators of wtKLF6 function. Furthermore, stable overexpression of the R71Q and S180L tumour-derived mutants in the gastric cancer cell line, Hs746T, resulted in an increased tumourigenicity in vivo. Combined, these findings suggest an important role for the KLF6 tumour suppressor gene in gastric cancer development and progression and identify several highly cancer-relevant signalling pathways regulated by the KLF6 tumour suppressor gene.

The molecular programme of tumour reversion: the steps beyond malignant transformation

How cells become malignant has preoccupied scientists for over a century. However, the converse question is also valid: are tumour cells capable of reverting from their malignant state? Askanazy's studies in 1907 indicated that teratoma cells could differentiate into normal somatic tissues and current evidence indicates that some tumour cells have acquired the molecular circuitry that results in the negation of chromosomal instability, translocations, oncogene activation and loss of tumour suppressor genes. Studying these extremely rare events of tumour reversion and deciphering these pathways, which involve SIAH1, presenilin 1, TSAP6 and translationally controlled tumour protein (TCTP), could lead to new avenues in cancer treatment.

The role of KLF6 and its splice variants in cancer therapy

The Krüppel-like zinc finger transcription factor (KLF6) gene encodes a family of proteins generated through alternative splicing involved in the regulation of cancer development and progression. Alternative splicing of the KLF6 gene results in the production of at least four alternatively spliced isoforms, two of which are extensively discussed in this review. The full length form of the KLF6 gene is a tumor suppressor gene that is frequently inactivated by loss of heterozygozity (LOH), somatic mutation, and/or decreased expression in human cancer. While the exact mechanisms underlying KLF6's tumor suppressor roles are not completely known, a number of highly relevant, overlapping pathways have been described: transactivation of p21 in a p53-independent manner, reduction of cyclin D1/cdk4 complexes via interaction with cyclin D1, inhibition of c-Jun proto-oncoprotein activities, decreased VEGF expression, and induction of apoptosis. Kruppel-like factor 6 splice variant 1 (KLF6-SV1) is an oncogenic splice variant of the KLF6 tumor suppressor gene that is specifically overexpressed in a number of human cancers. Increased KLF6-SV1 expression is associated with poor prognosis in prostate, lung, and ovarian cancer. Furthermore, KLF6-SV1 has been shown to be biologically active, antagonizing the tumor suppressor function of KLF6 and promoting tumor growth and dissemination in both ovarian and prostate cancer models. In addition, a common germline polymorphism in the KLF6 gene associated with increased prostate cancer risk in a large multi-institutional study of 3411 men results in increased expression of KLF6-SV1. Furthermore, recent studies have demonstrated that targeted reduction of KLF6-SV1 results in the induction of spontaneous apoptosis in cell culture, synergizes with chemotherapeutic agents like cisplatin, and results in significant tumor regression in vivo. Combined, these data make the KLF6 gene family a compelling therapeutic target for both the treatment of localized as well as metastatic cancer.

Molecular Pathology of the Genitourinary Tract: Prostate and Bladder

The knowledge of cellular mechanisms in tumors of the prostate and bladder has grown exponentially. Molecular technologies have led to the discovery of TMPRSS2 in prostate cancer and the molecular pathways distinguishing low- and high-grade urothelial neoplasms. UroVysion with fluorescence in situ hybridization is already commonplace as an adjunct to cytologic diagnosis of urothelial neoplasms. This trend portends the future in which classification and diagnosis of tumors of the prostate and bladder through morphologic analysis will be supplemented by molecular information correlating with prognosis and targeted therapy. This article outlines tumor molecular pathology of the prostate and bladder encompassing current genomic, epigenomic, and proteonomic findings.

KLF6 and TP53 mutations are a rare event in prostate cancer: distinguishing between Taq polymerase artifacts and true mutations

Krüppel-like factor 6 (KLF6) has been reported to act as a tumor suppressor gene involved in the regulation of the cell cycle by activating p21 in a p53-independent manner. Many studies suggest that KLF6 is inactivated by allelic loss and somatic mutation. However, there is a high variability in the reported frequency of mutations (from 1 to 55%). TP53 also regulates the cell cycle through the activation of p21. In prostate cancer, the reported frequency of TP53 mutations ranges from 3 to 42%. In all these reports, there is a considerable degree of methodological heterogeneity. Our aim was to determine the frequency of KLF6 and TP53 mutations in a well-defined group of prostate tumors with different stages and Gleason grades. The four exons of KLF6 and exons 4-9 of TP53 were studied in 103 cases, including 90 formalin-fixed, paraffin-embedded (FFPE) and 13 frozen samples. All tumors were analyzed through PCR and direct sequencing. All changes found were confirmed by a second independent PCR and sequencing reaction. For KLF6, mutation (E227G) was only detected in one tumor (1%) and for TP53, three different mutations (L130H, H214R, and Y234C) were detected in five tumors (5%). This low mutation index is in keeping with recent papers on the subject. Our study strongly supports the notion that KLF6 and TP53 mutations are not frequent events in prostate cancer. When using FFPE tissues, it is mandatory to perform at least two independent rounds of PCR and sequencing to confirm mutations and exclude Taq polymerase-induced artifacts.

Laminin-332 is a substrate for hepsin, a protease associated with prostate cancer progression

Hepsin, a cell surface protease, is widely reported to be overexpressed in more than 90% of human prostate tumors. Hepsin expression correlates with tumor progression, making it a significant marker and target for prostate cancer. Recently, it was reported that in a prostate cancer mouse model, hepsin up-regulation in tumor tissue promotes progression and metastasis. The underlying mechanisms, however, remain largely uncharacterized. Hepsin transgenic mice displayed reduced laminin-332 (Ln-332) expression in prostate tumors. This is an intriguing cue, since proteolytic processing of extracellular matrix macromolecules, such as Ln-332, is believed to be involved in cancer progression, and Ln-332 expression is lost during human prostate cancer progression. In this study, we provide the first direct evidence that hepsin cleaves Ln-332. Cleavage is specific, since it is both inhibited in a dose-dependent manner by a hepsin inhibitor (Kunitz domain-1) and does not occur when catalytically inactive hepsin is used. By Western blotting and mass spectrometry, we determined that hepsin cleaves the beta3 chain of Ln-332. N-terminal sequencing identified the cleavage site at beta3 Arg(245), in a sequence context (SQLR(245) LQGSCFC) conserved among species and in remarkable agreement with reported consensus target sequences for hepsin activity. In vitro cell migration assays showed that hepsin-cleaved Ln-332 enhanced motility of DU145 prostate cancer cells, which was inhibited by Kunitz domain-1. Further, hepsin-overexpressing LNCaP prostate cancer cells also exhibited increased migration on Ln-332. Direct cleavage of Ln-332 may be one mechanism by which hepsin promotes prostate tumor progression and metastasis, possibly by up-regulating prostate cancer cell motility.

Microsatellite instability and loss of heterozygosity in squamous cell carcinoma of the head and neck

BACKGROUND

Microsatellite instability (MSI) in head and neck squamous cell carcinoma (HNSCC) has been reported with a wide range of frequencies. The aim of our study was to disclose the frequency and basis of MSI in HNSCC and to correlate MSI and findings on loss of heterozygosity (LOH) with the clinical data.

METHODS

We analyzed MSI and LOH in 91 tumors. All tumors presenting instability were analyzed for the expression of mismatch repair genes (MMR) proteins.

RESULTS

Low-level microsatellite instability (MSI-L) was seen in 7.7% of the HNSCC. None of the MSI-L tumors had aberrant MMR protein expression. LOH rates up to 57% were identified for different regions on chromosome 3p. For the marker D10S197, we found a significant correlation between LOH and tumor stage IV.

CONCLUSION

Our results indicate that MMR gene inactivation is rare among primary HNSCC. In contrast, the MSI-L phenotype plays a role in a small subset of tumors. LOH on chromosome arm 3p and 10p12 seems to be involved in tumorigenesis and progression HNSCC, respectively.

KLF6-SV1 overexpression accelerates human and mouse prostate cancer progression and metastasis

Metastatic prostate cancer (PCa) is one of the leading causes of death from cancer in men. The molecular mechanisms underlying the transition from localized tumor to hormone-refractory metastatic PCa remain largely unknown, and their identification is key for predicting prognosis and targeted therapy. Here we demonstrated that increased expression of a splice variant of the Kruppel-like factor 6 (KLF6) tumor suppressor gene, known as KLF6-SV1, in tumors from men after prostatectomy predicted markedly poorer survival and disease recurrence profiles. Analysis of tumor samples revealed that KLF6-SV1 levels were specifically upregulated in hormone-refractory metastatic PCa. In 2 complementary mouse models of metastatic PCa, KLF6-SV1-overexpressing PCa cells were shown by in vivo and ex vivo bioluminescent imaging to metastasize more rapidly and to disseminate to lymph nodes, bone, and brain more often. Interestingly, while KLF6-SV1 overexpression increased metastasis, it did not affect localized tumor growth. KLF6-SV1 inhibition using RNAi induced spontaneous apoptosis in cultured PCa cell lines and suppressed tumor growth in mice. Together, these findings demonstrate that KLF6-SV1 expression levels in PCa tumors at the time of diagnosis can predict the metastatic behavior of the tumor; thus, KLF-SV1 may represent a novel therapeutic target.

KLF6 induces apoptosis in prostate cancer cells through up-regulation of ATF3

KLF6 (Kruppel-like factor 6) is a zinc finger transcription factor and a tumor suppressor that is frequently mutated in prostate cancer. KLF6 suppresses tumor growth and induces apoptosis in cancer cells through mechanisms still not defined. Here we show that KLF6 induces apoptosis in prostate cancer cells by ATF3 (activating transcription factor 3) expression. KLF6 binds directly to and activates the ATF3 promoter. ATF3 induced apoptosis when ectopically expressed in cells, whereas knockdown of ATF3 by small interference RNA blocked KLF6-induced apoptosis. KLF6 mutants derived from clinical prostate cancers failed to activate the ATF3 promoter and were unable to induce apoptosis. Furthermore, stress conditions (exposure to staurosporine and hypoxia induced by sodium azide) caused significant increase in ATF3 expression and induced apoptosis, whereas knockdown of KLF6 by small interference RNA blocked the increase of ATF3 as well as the induction of apoptosis in these conditions. Thus, ATF3 is a key mediator of KLF6-induced apoptosis in prostate cancer cells.

Role of Kruppel-like factor 6 in transforming growth factor-beta1-induced epithelial-mesenchymal transition of proximal tubule cells

Krüppel-like factor 6 (KLF6) is a DNA-binding protein containing a triple zinc-fingered motif and plays a key role in the regulation of cell proliferation, differentiation, and development. More recently it has been implicated in hepatic fibrosis via its binding to the transforming growth factor (TGF)-beta control element. In the kidney, epithelial-mesenchymal transition (EMT) is a major contributor to the pathogenesis of renal fibrosis, with TGF-beta1 being a key mediator of EMT. The present study aimed to determine the role of KLF6 and TGF-beta1 in EMT in proximal tubule cells. To determine the relevance in clinical disease, KLF6 was measured in kidneys of streptozotocin-induced diabetic Ren-2 rats and in cells exposed to high (30 mM) glucose. TGF-beta1 was confirmed to induce EMT by morphological change, loss of E-cadherin, and gain in vimentin expression. KLF6 mRNA expression was concomitantly measured. To determine the role of KLF6 in EMT, the above markers of EMT were determined in KLF6-silenced (small interfering RNA) and KLF6-overexpressing proximal tubule cells. KLF6 overexpression significantly promoted a phenotype consistent with EMT. High glucose induced KLF6 in proximal tubule cells (P < 0.05). This increase in KLF6 in response to high glucose was TGF-beta1 mediated. In an in vivo model of diabetic nephropathy KLF6 increased at week 8 (P < 0.05). KLF6 plays a permissive role in TGF-beta1-induced EMT in proximal tubule cells. Its upregulation in in vivo models of diabetic nephropathy suggests it as a potential therapeutic target.

Identification of an evolutionarily conserved transcriptional signature of CD8 memory differentiation that is shared by T and B cells

After Ag encounter, naive lymphocytes differentiate into populations of memory cells that share a common set of functions including faster response to Ag re-exposure and the ability to self-renew. However, memory lymphocytes in different lymphocyte lineages are functionally and phenotypically diverse. It is not known whether discrete populations of T and B cells use similar transcriptional programs during differentiation into the memory state. We used cross-species genomic analysis to examine the pattern of genes up-regulated during the differentiation of naive lymphocytes into memory cells in multiple populations of human CD4, CD8, and B cell lymphocytes as well as two mouse models of memory development. We identified and validated a signature of genes that was up-regulated in memory cells compared with naive cells in both human and mouse CD8 memory differentiation, suggesting marked evolutionary conservation of this transcriptional program. Surprisingly, this conserved CD8 differentiation signature was also up-regulated during memory differentiation in CD4 and B cell lineages. To validate the biologic significance of this signature, we showed that alterations in this signature of genes could distinguish between functional and exhausted CD8 T cells from a mouse model of chronic viral infection. Finally, we generated genome-wide microarray data from tetramer-sorted human T cells and showed profound differences in this differentiation signature between T cells specific for HIV and those specific for influenza. Thus, our data suggest that in addition to lineage-specific differentiation programs, T and B lymphocytes use a common transcriptional program during memory development that is disrupted in chronic viral infection.

Increased alternative splicing of the KLF6 tumour suppressor gene correlates with prognosis and tumour grade in patients with pancreatic cancer

The aim of this study was to correlate the status of the KLF6 tumour suppressor gene including loss of heterozygosity (LOH), mutation and alternative splicing in human pancreatic cancer with tumour grade and survival. Whereas neither KLF6 loss nor mutation was identified, expression of the KLF6 alternative splice forms was significantly increased in pancreatic tumour samples and cell lines. These cancers demonstrated marked cytoplasmic KLF6 expression, consistent with over-expression and accumulation of KLF6 splice form(s), which lack a nuclear localisation signal. In addition, KLF6 splicing correlated significantly with tumour stage and survival. In summary, pancreatic cancer displays a novel pattern of KLF6 dysregulation through selectively increased expression of KLF6 splice variants. Therefore, determination of KLF6 mRNA splicing levels may represent a novel biomarker predicting prognosis.

The Kruppel-like factor 6 genotype is associated with fibrosis in nonalcoholic fatty liver disease

BACKGROUND & AIMS

Although nonalcoholic fatty liver disease (NAFLD) is increasingly common, only a minority of affected individuals develop fibrotic liver disease. Based on its role in liver growth and repair, we explored whether Kruppel-like factor 6 (KLF6) plays a role in NAFLD progression.

METHODS

KLF6 expression in 31 fibrosis scored NAFLD liver biopsy specimens was assessed by real-time polymerase chain reaction. Transfected minigene constructs were used to study the effect of a polymorphism, KLF6-IVS1-27G>A, that promotes KLF6 alternative splicing in vitro. We genotyped KLF6-IVS1-27G>A in 3 groups of patients (UK group 1, n = 306; Italian group 2, n = 109; trio group 3, n = 61 children and parents).

RESULTS

KLF6 expression was increased in association with increased steatosis, inflammation, and fibrosis in NAFLD livers. KLF6-IVS1-27G>A promoted alternative splicing of KLF6 and abrogated the up-regulation of both alpha-smooth muscle actin and collagen 1 in LX-2 cells. Group 1 genotyping identified KLF6-IVS1-27G>A in 44 of 306 (14.4%) patients. Notably, KLF6-IVS1-27G>A was associated significantly with milder NAFLD, with only 25% having more advanced fibrosis compared with 45% of wild-type (wt) individuals. This trend was confirmed in group 2. A linear regression analysis including all 415 patients, adjusted for age, sex, body mass index, and blood glucose level, confirmed that presence of the wt KLF6 allele was an independent predictor of fibrotic NAFLD. Furthermore, we have shown preferential transmission of the wt allele to children with fibrotic NAFLD.

CONCLUSIONS

We report a functional polymorphism in the KLF6 gene associated with advanced NAFLD and believe further study of KLF6 may enhance our understanding of this disease process.

Molecular alterations in prostate cancer

Prostate tumors display a range of clinical phenotypes, from indolent to aggressively metastatic. Numerous gene expression profiling studies have been conducted toward the potential molecular staging of these pathologies, however the identification of genetic markers that predict aggressive disease has not yet been demonstrated in the clinical setting. A recent survey of the literature has shown that molecular alterations in prostate carcinomas can occur through a variety of different mechanisms, ranging from upstream epigenetic changes and genetic polymorphisms to downstream modulations through alternative splicing and other post-translational processes, some of which could involve noncoding RNAs. A summary of these results and recommendations for future work are the subject of this review.

DAPK2 is a novel E2F1/KLF6 target gene involved in their proapoptotic function

Death-associated protein kinase 2 (DAPK2) belongs to a family of proapoptotic Ca(2+)/calmodulin-regulated serine/threonine kinases. We recently identified DAPK2 as an enhancing factor during granulocytic differentiation. To identify transcriptional DAPK2 regulators, we cloned 2.7 kb of the 5'-flanking region of the DAPK2 gene. We found that E2F1 and Krüppel-like factor 6 (KLF6) strongly activate the DAPK2 promoter. We mapped the E2F1 and KLF6 responsive elements to a GC-rich region 5' of exon 1 containing several binding sites for KLF6 and Sp1 but not for E2F. Moreover, we showed that transcriptional activation of DAPK2 by E2F1 and KLF6 is dependent on Sp1 using Sp1/KLF6-deficient insect cells, mithramycin A treatment to block Sp1-binding or Sp1 knockdown cells. Chromatin immunoprecipitation revealed recruitment of Sp1 and to lesser extent that of E2F1 and KLF6 to the DAPK2 promoter. Activation of E2F1 in osteosarcoma cells led to an increase of endogenous DAPK2 paralleled by cell death. Inhibition of DAPK2 expression resulted in significantly reduced cell death upon E2F1 activation. Similarly, KLF6 expression in H1299 cells increased DAPK2 levels accompanied by cell death that is markedly decreased upon DAPK2 knockdown. Moreover, E2F1 and KLF6 show cooperation in activating the DAPK2 promoter. In summary, our findings establish DAPK2 as a novel Sp1-dependent target gene for E2F1 and KLF6 in cell death response.

Genetic changes and DNA damage responses in the prostate

The integrity of genomic DNA is challenged by genotoxic stress originating during normal cellular metabolism or by external insults. Cellular responses to DNA damage involve elegant checkpoint cascades enforcing cell cycle arrest, damage repair, apoptosis or cellular senescence. The loss or alterations of genes involved in the damage response pathways have been reported in many cancer susceptibility syndromes and in sporadic tumors. Furthermore, this surveillance pathway is activated during early tumourigenesis presumably due to uncontrolled replicative cycles and has been recognized as one of the main barriers against the development of cancer. This review discusses the relevance of prostatic epithelial cells in prostate tumourigenesis and highlights common molecular changes associated with prostate cancer. Furthermore, DNA damage responses of primary cultures of human prostatic epithelial cells and fresh human prostate tissues are discussed providing evidence for alterations in crucial DNA damage checkpoint molecules. New insights connecting prostate tumourigenesis to alterations and defects in the pathways maintaining genomic integrity will be discussed.

Ras promotes growth by alternative splicing-mediated inactivation of the KLF6 tumor suppressor in hepatocellular carcinoma

BACKGROUND & AIMS

Hepatocellular carcinoma (HCC) is the fifth most prevalent cancer worldwide and the third most lethal. Dysregulation of alternative splicing underlies a number of human diseases, yet its contribution to liver cancer has not been explored fully. The Krüppel-like factor 6 (KLF6) gene is a zinc finger transcription factor that inhibits cellular growth in part by transcriptional activation of p21. KLF6 function is abrogated in human cancers owing to increased alternative splicing that yields a dominant-negative isoform, KLF6 splice variant 1 (SV1), which antagonizes full-length KLF6-mediated growth suppression. The molecular basis for stimulation of KLF6 splicing is unknown.

METHODS

In human HCC samples and cell lines, we functionally link oncogenic Ras signaling to increased alternative splicing of KLF6 through signaling by phosphatidylinositol-3 kinase and Akt, mediated by the splice regulatory protein ASF/SF2.

RESULTS

In 67 human HCCs, there is a significant correlation between activated Ras signaling and increased KLF6 alternative splicing. In cultured cells, Ras signaling increases the expression of KLF6 SV1, relative to full-length KLF6, thereby enhancing proliferation. Abrogation of oncogenic Ras signaling by small interfering RNA (siRNA) or a farnesyl-transferase inhibitor decreases KLF6 SV1 and suppresses growth. Growth inhibition by farnesyl-transferase inhibitor in transformed cell lines is overcome by ectopic expression of KLF6 SV1. Down-regulation of the splice factor ASF/SF2 by siRNA increases KLF6 SV1 messenger RNA levels. KLF6 alternative splicing is not coupled to its transcriptional regulation.

CONCLUSIONS

Our findings expand the role of Ras in human HCC by identifying a novel mechanism of tumor-suppressor inactivation through increased alternative splicing mediated by an oncogenic signaling cascade.

The Pathobiology of Krüppel-like Factors in Colorectal Cancer

The Krüppel-like factor (KLF) proteins are zinc finger-containing transcription factors that exert important functions in regulating diverse biologic processes such as growth, proliferation, differentiation, development, inflammation, and apoptosis. Many KLFs have also been shown to play significant roles in tumorigenesis of various organs and tissues. Three in particular-KLF4, KLF5, and KLF6-are often dysregulated in tumors of the gastrointestinal tract, including colorectal cancer. This article reviews the functions of these three KLFs in normal gastrointestinal biology and their pathobiologic roles in colorectal cancer.

Insulin-like growth factor-i regulates Kruppel-like factor-6 gene expression in a p53-dependent manner

High-circulating IGF-I concentrations are associated with an increased risk for breast, prostate, and colorectal cancer. Krüppel-like factor-6 (KLF6) is a zinc finger tumor suppressor inactivated in prostate and other types of cancer. We have previously demonstrated that KLF6 is a potent transactivator of the IGF-I receptor promoter. The aim of the present study was to examine the potential regulation of KLF6 gene expression by IGF-I. The human colon cancer cell lines HCT116 +/+ and -/- (with normal and disrupted p53, respectively) were treated with IGF-I. Western blots, quantitative RT-PCR, and transfection assays were used to evaluate the effect of IGF-I on KLF-6 production. Signaling pathway inhibitors were used to identify the mechanisms responsible for regulation of KLF6 expression. Small interfering RNA against p53 and KLF6 was used to assess the role of p53 in regulation of KLF6 expression by IGF-I and to evaluate KLF6 involvement in cell cycle control. Results obtained showed that IGF-I stimulated KLF-6 transcription in cells with normal, but not disrupted, p53, suggesting that KLF6 is a downstream target for IGF-I action. Stimulation of KLF6 expression by IGF-I in a p53-dependent manner may constitute a novel mechanism of action of IGF-I, with implications in normal cell cycle progression and cancer biology.

Tumor suppressor and hepatocellular carcinoma

A few signaling pathways are driving the growth of hepatocellular carcinoma. Each of these pathways possesses negative regulators. These enzymes, which normally suppress unchecked cell proliferation, are circumvented in the oncogenic process, either the over-activity of oncogenes is sufficient to annihilate the activity of tumor suppressors or tumor suppressors have been rendered ineffective. The loss of several key tumor suppressors has been described in hepatocellular carcinoma. Here, we systematically review the evidence implicating tumor suppressors in the development of hepatocellular carcinoma.

A functional role for KLF6-SV1 in lung adenocarcinoma prognosis and chemotherapy response

Kruppel-like factor 6 (KLF6) is a tumor suppressor gene that is functionally inactivated in human cancer by loss of heterozygosity, somatic mutation, decreased expression, and increased alternative splicing into an oncogenic splice variant, KLF6-SV1. Here we show that increased expression of KLF6-SV1 is associated with decreased survival in patients with lung adenocarcinoma. In addition, KLF6-SV1 is a novel antiapoptotic protein in lung cancer cell lines, and targeted reduction of KLF6-SV1 using siRNA induces apoptosis both alone and in combination with the chemotherapeutic drug cisplatin. Together, these findings highlight a critical role for KLF6-SV1 in lung cancer, and show a potential novel therapeutic strategy for the treatment of lung cancer.

Dynamic down-regulation of Krüppel-like factor 4 in colorectal adenoma-carcinoma sequence

PURPOSE

To explore the clinical significance of Krüppel-like factors 4 (KLF4) expression in colorectal cancer initiation and progression.

METHODS

We used quantitative real-time PCR to detect KLF4 mRNA expression in 49 colorectal cancer samples with individual-matched normal mucosa and eight concurrent adenomas. We also analysed the immunostaining pattern of KLF4 in additional 129 colorectal cancers and 48 sporadic colorectal adenomas with matched normal mucosa and correlated KLF4 staining with clinicopathological parameters and prognosis. KLF4 expression change was detected in SW480, SW620 and RKO cell lines after treatment of 5-aza-dC (10 microM) or butyrate sodium (4 mM).

RESULTS

The large clinicopathological survey with combined methods confirmed a dynamic downregulation of KLF4 in individual-matched normal mucosa, adenoma and cancer (P < 0.05). The quantitative analysis of immunostaining pattern showed that KLF4 staining cells were more frequently seen in the upper zones than that in the lower zones of both normal mucosa and adenoma (P < 0.05). Survival analysis implied a trend toward better overall survival in KLF4-positive colorectal cancer patients with lymph node metastasis than that in KLF4-negative cancer with lymph node metastasis. In vitro study found elevated KLF4 mRNA expression in SW620 and RKO cells with 5-aza-dC treatment, implicating the underlying aberrant epigenetic modifications in regulating KLF4 expression at least in a subset of colorectal cancers.

CONCLUSIONS

KLF4 is associated with terminal differentiation in colorectal epithelium and drastically downregulated in colorectal adenomas and cancers via possible epigenetic modifications. Loss of KLF4 protein expression might contribute to assessing prognosis in colorectal cancer with lymph node metastasis.

Modeling genomic diversity and tumor dependency in malignant melanoma

The classification of human tumors based on molecular criteria offers tremendous clinical potential; however, discerning critical and "druggable" effectors on a large scale will also require robust experimental models reflective of tumor genomic diversity. Here, we describe a comprehensive genomic analysis of 101 melanoma short-term cultures and cell lines. Using an analytic approach designed to enrich for putative "driver" events, we show that cultured melanoma cells encompass the spectrum of significant genomic alterations present in primary tumors. When annotated according to these lesions, melanomas cluster into subgroups suggestive of distinct oncogenic mechanisms. Integrating gene expression data suggests novel candidate effector genes linked to recurrent copy gains and losses, including both phosphatase and tensin homologue (PTEN)-dependent and PTEN-independent tumor suppressor mechanisms associated with chromosome 10 deletions. Finally, sample-matched pharmacologic data show that FGFR1 mutations and extracellular signal-regulated kinase (ERK) activation may modulate sensitivity to mitogen-activated protein kinase/ERK kinase inhibitors. Genetically defined cell culture collections therefore offer a rich framework for systematic functional studies in melanoma and other tumors.

Genetic and genomic analysis modeling of germline c-MYC overexpression and cancer susceptibility

BACKGROUND

Germline genetic variation is associated with the differential expression of many human genes. The phenotypic effects of this type of variation may be important when considering susceptibility to common genetic diseases. Three regions at 8q24 have recently been identified to independently confer risk of prostate cancer. Variation at 8q24 has also recently been associated with risk of breast and colorectal cancer. However, none of the risk variants map at or relatively close to known genes, with c-MYC mapping a few hundred kilobases distally.

RESULTS

This study identifies cis-regulators of germline c-MYC expression in immortalized lymphocytes of HapMap individuals. Quantitative analysis of c-MYC expression in normal prostate tissues suggests an association between overexpression and variants in Region 1 of prostate cancer risk. Somatic c-MYC overexpression correlates with prostate cancer progression and more aggressive tumor forms, which was also a pathological variable associated with Region 1. Expression profiling analysis and modeling of transcriptional regulatory networks predicts a functional association between MYC and the prostate tumor suppressor KLF6. Analysis of MYC/Myc-driven cell transformation and tumorigenesis substantiates a model in which MYC overexpression promotes transformation by down-regulating KLF6. In this model, a feedback loop through E-cadherin down-regulation causes further transactivation of c-MYC.

CONCLUSION

This study proposes that variation at putative 8q24 cis-regulator(s) of transcription can significantly alter germline c-MYC expression levels and, thus, contribute to prostate cancer susceptibility by down-regulating the prostate tumor suppressor KLF6 gene.

Expression of the transcription factor Klf6 in cirrhosis, macronodules, and hepatocellular carcinoma

BACKGROUND AND AIMS

Macronodules (MN) occurring in cirrhosis are considered to be precursor lesions for hepatocellular carcinoma (HCC). However, early molecular events in hepatocellular carcinogenesis are poorly understood. The aim of this study was to compare gene expression profiling between cirrhotic tissues, MN, and HCC, to identify genes early involved in liver carcinogenesis.

METHODS

Tissues were obtained from explanted livers: nine cirrhosis, 10 MN, and seven HCC. Total RNAs were extracted by RNeasy and reverse transcribed with labelled [(33)P]-alpha ATP. Hybridations were performed on Atlas Human Cancer 1.2 membranes (1176 genes).

RESULTS

A two-way hierarchical clustering algorithm successfully isolated specific gene expression profiles when comparing MN, cirrhosis, and HCC. A total of 16 and 14 genes were up- and down-expressed, respectively, in HCC as compared to cirrhotic tissues. The molecular signature of MN was characterized by the down-expression of 23 and 42 genes as compared to cirrhosis and HCC, respectively. Among them, Klf6 was down-expressed in all MN samples whereas it was over-expressed in cirrhosis and HCC. This result was confirmed at RNA level by quantitative real time-polymerase chain reaction and at protein level by Western blotting. However, no mutation in the exon 2 of Klf6 was detected.

CONCLUSION

We identified a molecular signature of MN characterized by a down-expression of several genes. One of them, Klf6 was found to be down-expressed in all MN without evidence of somatic mutations in the exon 2. This gene could be involved at an early stage of hepatocarcinogenesis.

Microarrays--identifying molecular portraits for prostate tumors with different Gleason patterns

We present in this chapter the combined use of several recently introduced methodologies for the analysis of microarray datasets. These computational techniques are varied in type and very powerful when combined. We have selected a prostate cancer dataset which is available in the public domain to allow for further comparisons with existing methods. The task is to identify biomarkers that correlate with the clinical phenotype of interest, i.e., Gleason patterns 3, 4, and 5. A supervised method, based on the mathematical formalism of (alpha, beta)-k-feature sets (1), is used to select differentially expressed genes. After these "molecular signatures" are identified, we applied an unsupervised method (a memetic algorithm) to order the samples (2). The objective is to maximize a global measure of correlation in the two-dimensional display of gene expression profiles. With the resulting ordering and taxonomy we are able to identify samples that have been assigned a certain Gleason pattern, and have gene expression patterns different from most of the other samples in the group. We reiterate the approach to obtain molecular signatures that produce coherent patterns of gene expression in each of the three Gleason pattern groups, and we analyze the statistically significant patterns of gene expression that seem to be implicated in these different stages of disease.

Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver

The hepatic stellate cell has surprised and engaged physiologists, pathologists, and hepatologists for over 130 years, yet clear evidence of its role in hepatic injury and fibrosis only emerged following the refinement of methods for its isolation and characterization. The paradigm in liver injury of activation of quiescent vitamin A-rich stellate cells into proliferative, contractile, and fibrogenic myofibroblasts has launched an era of astonishing progress in understanding the mechanistic basis of hepatic fibrosis progression and regression. But this simple paradigm has now yielded to a remarkably broad appreciation of the cell's functions not only in liver injury, but also in hepatic development, regeneration, xenobiotic responses, intermediary metabolism, and immunoregulation. Among the most exciting prospects is that stellate cells are essential for hepatic progenitor cell amplification and differentiation. Equally intriguing is the remarkable plasticity of stellate cells, not only in their variable intermediate filament phenotype, but also in their functions. Stellate cells can be viewed as the nexus in a complex sinusoidal milieu that requires tightly regulated autocrine and paracrine cross-talk, rapid responses to evolving extracellular matrix content, and exquisite responsiveness to the metabolic needs imposed by liver growth and repair. Moreover, roles vital to systemic homeostasis include their storage and mobilization of retinoids, their emerging capacity for antigen presentation and induction of tolerance, as well as their emerging relationship to bone marrow-derived cells. As interest in this cell type intensifies, more surprises and mysteries are sure to unfold that will ultimately benefit our understanding of liver physiology and the diagnosis and treatment of liver disease.

Tissue factor pathway inhibitor-2 was repressed by CpG hypermethylation through inhibition of KLF6 binding in highly invasive breast cancer cells

Background

Tissue factor pathway inhibitor-2 (TFPI-2) is a matrix-associated Kunitz inhibitor that inhibits plasmin and trypsin-mediated activation of zymogen matrix metalloproteinases involved in tumor progression, invasion and metastasis. Here, we have investigated the mechanism of DNA methylation on the repression of TFPI-2 in breast cancer cell lines.

Results

We found that both protein and mRNA of TFPI-2 could not be detected in highly invasive breast cancer cell line MDA-MB-435. To further investigate the mechanism of TFPI-2 repression in breast cancer cells, 1.5 Kb TFPI-2 promoter was cloned, and several genetic variations were detected, but the promoter luciferase activities were not affected by the point mutation in the promoter region and the phenomena was further supported by deleted mutation. Scan mutation and informatics analysis identified a potential KLF6 binding site in TFPI-2 promoter. It was revealed, by bisulfite modified sequence, that the CpG island in TFPI-2 promoter region was hypermethylated in MDA-MB-435. Finally, using EMSA and ChIP assay, we demonstrated that the CpG methylation in the binding site of KLF-6 diminished the binding of KLF6 to TFPI-2 promoter.

Conclusion

In this study, we found that the CpG islands in TFPI-2 promoter was hypermethylated in highly invasive breast cancer cell line, and DNA methylation in the entire promoter region caused TFPI-2 repression by inducing inactive chromatin structure and decreasing KLF6 binding to its DNA binding sequence.

Plexin-B1 mutations in prostate cancer

Semaphorins are a large class of secreted or membrane-associated proteins that act as chemotactic cues for cell movement via their transmembrane receptors, plexins. We hypothesized that the function of the semaphorin signaling pathway in the control of cell migration could be harnessed by cancer cells during invasion and metastasis. We now report 13 somatic missense mutations in the cytoplasmic domain of the Plexin-B1 gene. Mutations were found in 89% (8 of 9) of prostate cancer bone metastases, in 41% (7 of 17) of lymph node metastases, and in 46% (41 of 89) of primary cancers. Forty percent of prostate cancers contained the same mutation. Overexpression of the Plexin-B1 protein was found in the majority of primary tumors. The mutations hinder Rac and R-Ras binding and R-RasGAP activity, resulting in an increase in cell motility, invasion, adhesion, and lamellipodia extension. These results identify a key role for Plexin-B1 and the semaphorin signaling pathway it mediates in prostate cancer.

Caffeine regulates alternative splicing in a subset of cancer-associated genes: a role for SC35

Alternative splicing of pre-mRNA contributes significantly to human proteomic complexity, playing a key role in development, gene expression and, when aberrant, human disease onset. Many of the factors involved in alternative splicing have been identified, but little is known about their regulation. Here we report that caffeine regulates alternative splicing of a subset of cancer-associated genes, including the tumor suppressor KLF6. This regulation is at the level of splice site selection, occurs rapidly and reversibly, and is concentration dependent. We have recapitulated caffeine-induced alternative splicing of KLF6 using a cell-based minigene assay and identified a "caffeine response element" within the KLF6 intronic sequence. Significantly, a chimeric minigene splicing assay demonstrated that this caffeine response element is functional in a heterologous context; similar elements exist within close proximity to caffeine-regulated exons of other genes in the subset. Furthermore, the SR splicing factor, SC35, was shown to be required for induction of the alternatively spliced KLF6 transcript. Importantly, SC35 is markedly induced by caffeine, and overexpression of SC35 is sufficient to mimic the effect of caffeine on KLF6 alternative splicing. Taken together, our data implicate SC35 as a key player in caffeine-mediated splicing regulation. This novel effect of caffeine provides a valuable tool for dissecting the regulation of alternative splicing of a large gene subset and may have implications with respect to splice variants associated with disease states.

Stem cell origin of death-from-cancer phenotypes of human prostate and breast cancers

In clinical terms, all human cancers diagnosed in individuals can be divided in two major categories: malignant tumors that will be cured with the existing cancer therapies and tumors that have therapy-resistant phenotypes and will return after initial treatment as incurable metastatic disease. These tumors manifesting clinically lethal death-from-cancer phenotypes represent the most formidable challenge of experimental, translational, and clinical cancer research. Clinical genomics data demonstrate that gene expression signatures associated with the "stemness" state of a cell are informative as molecular predictors of cancer therapy outcome and can help to identify cancer patients with therapy-resistant tumors. Here, we present experimental and clinical evidence in support of the BMI1 pathway rule indicating a genetic link between the stemness state and therapy-resistant death-from-cancer phenotypes. Our analysis demonstrates that therapy-resistant and therapy-responsive cancer phenotypes manifest distinct patterns of association with stemness/differentiation pathways, suggesting that therapy-resistant and therapy-responsive tumors develop within genetically distinct stemness/differentiation programs. These differences can be exploited for development of prognostic and therapy selection genetic tests utilizing a microarray-based cancer therapy outcome predictor algorithm. One of the major regulatory pathways manifesting distinct patterns of association with therapy-resistant and therapy-responsive cancer phenotypes is the Polycomb group proteins chromatin silencing pathway.

Gene expression analysis of zebrafish retinal ganglion cells during optic nerve regeneration identifies KLF6a and KLF7a as important regulators of axon regeneration

Unlike mammals, teleost fish are able to mount an efficient and robust regenerative response following optic nerve injury. Although it is clear that changes in gene expression accompany axonal regeneration, the extent of this genomic response is not known. To identify genes involved in successful nerve regeneration, we analyzed gene expression in zebrafish retinal ganglion cells (RGCs) regenerating their axons following optic nerve injury. Microarray analysis of RNA isolated by laser capture microdissection from uninjured and 3-day post-optic nerve injured RGCs identified 347 up-regulated and 29 down-regulated genes. Quantitative RT-PCR and in situ hybridization were used to verify the change in expression of 19 genes in this set. Gene ontological analysis of the data set suggests regenerating neurons up-regulate genes associated with RGC development. However, not all regeneration-associated genes are expressed in differentiating RGCs indicating the regeneration is not simply a recapitulation of development. Knockdown of six highly induced regeneration-associated genes identified two, KLF6a and KLF7a, that together were necessary for robust RGC axon re-growth. These results implicate KLF6a and KLF7a as important mediators of optic nerve regeneration and suggest that not all induced genes are essential to mount a regenerative response.

Higher frequency of familial clustering of prostate cancer in French-Canadian men

PURPOSE

Prostate cancer is the second cause of cancer related death in North American men. We investigated the frequency of familial clustering in a French-Canadian population of prostate cancer cases.

MATERIALS AND METHODS

Between October 2004 and September 2005, 179 consecutively seen patients with localized prostate cancer identified each of their parents as being of French-Canadian descent. They were asked for their family history of cancer in first-degree relatives, age at diagnosis, whether affected relatives were alive, age and markers of tumor aggressiveness, including prostate specific antigen, Gleason and disease stage. ANOVA was used to compare the distribution of quantitative factors according to qualitative factors identified in our population. Differences between qualitative factors were assessed by the Fisher exact test. All p values were 2-sided.

RESULTS

Mean age at diagnosis was 67 years. A total of 45 French-Canadian patients (25.1%) had at least 1 first-degree relative with prostate cancer, including 34 (19%) with 1 first-degree relative, 9 with a father-son pair, 25 with a brother-brother pair and 11 (6.1%) with at least 2 first-degree relatives. In our series the frequency of familial clustering defined by at least 1 relative with prostate cancer was high. We found a higher percent of French-Canadian men with at least 1 first-degree relative with prostate cancer than what was previously reported for an unselected population in Canada (25.1% vs 14.7%, p <0.0001).

CONCLUSIONS

Those preliminary results open a new perspective to a better understanding of familial prostate cancer in the Province of Quebec.

Involvement of Krüppel-like factor 6 (KLF6) mutation in the development of nonpolypoid colorectal carcinoma

AIM: To examine Krüppel-like factor 6 (KLF6) mutations in nonpolypoid-type tumors and alterations of K-ras, p53, and B-raf in relation between mutation and morphologic type, particularly nonpolypoid-type colorectal carcinomas.

METHODS: Fifty-five early nonpolypoid colorectal carcinomas were analyzed. Loss of heterozygosity (LOH) of KLF6 and p53 was determined by microsatellite assay. Mutations of KLF6, K-ras, and B-raf were examined by polymerase chain reaction-single-strand conformation polymorphism followed by direct sequencing. In LOH-positive and/or mutation-positive tumors, multiple (4-7) samples in each tumor were microdissected and examined for genetic alterations. p53 expression was evaluated by immunohistochemistry.

RESULTS: LOH of KLF6 and p53 was found in 14 of 29 (48.3%) and 14 of 31 (45.2%) tumors, respectively. In 10 of the 14 (71.4%) KLF6 LOH-positive tumors and 9 of the 14 (64.3%) p53 LOH-positive tumors, LOH was found in all of the microdissected samples. In 1 of the 10 (10.0%) KLF6 LOH-positive tumors, a single missense mutation was identified. K-ras and B-raf mutations were found in 5 of 55 (9.1%) and 6 of 55 (10.9%) tumors, respectively. However, these mutations were detected only in subsets of microdissected tumor samples.

CONCLUSION: These data suggest that KLF6 and p53 mutations are involved in the development of nonpolypoid colorectal carcinoma, whereas K-ras and B-raf mutations are not.

KLF5 promotes cell proliferation and tumorigenesis through gene regulation and the TSU-Pr1 human bladder cancer cell line

KLF5 is a transcription factor that plays important roles in multiple physical and pathological processes, including cell growth, cell cycle regulation, and angiogenesis. To better characterize KLF5 function in bladder carcinogenesis, we established stable TSU-Pr1 cell clones expressing different levels of KLF5. These clones were then characterized for cell growth, cell cycle progression, tumorigenesis, and alteration in gene expression. Overexpression of KLF5 promoted tumorigenesis of the TSU-Pr1 cancer cells in mice. Consistently, KLF5 increased G1 to S phase transition, which was accompanied by the upregulation of cyclin D1, phosphorylation of MAPK and Akt, and reduced protein levels for CDK inhibitors p27 and p15. Microarray analysis combined with expression verification in different cell systems identified a number of additional genes that are potentially regulated by KLF5, including HBP17, ITGA6, and RAIG1. These findings suggest that the KLF5 transcription factor plays an oncogenic role in the TSU-Pr1 bladder cancer cell line through the regulation of a subset of genes.

Manipulation of host Kruppel-like factor (KLF) function by exotoxins from diverse bacterial pathogens

Diverse pathogenic bacteria have developed similar mechanisms to subvert host cell responses. In this Progress article, we focus on bacterial virulence factors with different enzymatic activities that can increase the expression of the Kruppel-like factor (KLF) family of mammalian transcriptional regulators through their ability to modify the activity of a common host-cell target - the Rho protein family. By using a common virulence strategy, both Gram-negative and Gram-positive pathogens exploit the KLF regulatory cascade to modulate nuclear factor kappaB activation, pro-inflammatory cytokine expression, actin cytoskeletal dynamics and phagocytosis.

RASSF1A promoter methylation is frequently detected in both pre-malignant and non-malignant microdissected prostatic epithelial tissues

BACKGROUND

The RASSF1A gene is a tumor suppressor gene inactivated by hypermethylation in a very wide variety of malignant tumors including prostate cancer.

METHODS

In this study we have used laser capture microdissection to provide pure cell populations to investigate the methylation status of 16 CpG sites in the promoter region of this gene in prostatic intra-epithelial neoplasia, in histologically normal epithelial cells associated with these lesions and in epithelial cells from benign prostatic hyperplasia.

RESULTS

Unexpectedly, frequent methylation, detected by sequence analysis following bisulphite treatment, was observed in benign epithelium as well as in the lesions associated with prostatic intra-epithelial neoplasia and at high risk of cancer formation. Fifty percent or more CpG sites were methylated in 7/14 prostatic intra-epithelial neoplasms, 8/11 histologically normal epithelial cells and 8/12 specimens of benign prostatic tissue.

CONCLUSION

These observations suggest that methylation of the RASSF1A gene is present in both pre-malignant and benign epithelia and suggests quantitation is required for it to be an effective marker of early prostate cancer.

Difference in the Role of Loss of Heterozygosity at 10p15 (KLF6 Locus) in Colorectal Carcinogenesis between Sporadic and Familial Adenomatous Polyposis and Hereditary Nonpolyposis Colorectal Cancer Patients

OBJECTIVES

To clarify the role of the KLF6 (Kruppel-like factor 6) locus in multistep colorectal carcinogenesis, we analyzed loss of heterozygosity (LOH) at 10p15 (KLF6 locus) and mutations of the KLF6gene in 298 colorectal tumors at various pathological stages of sporadic and familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC) patients.

METHODS

10p15 LOH was analyzed using KLF6M1 and KLF6M2, and KLF6 gene mutation was analyzed using PCR-SSCP and sequencing.

RESULTS

It was found that the frequencies of LOH (sum of M1 and M2) were 4% in adenomas, 0% in intramucosal carcinomas, 35% in invasive carcinomas, and 33% in liver metastases in sporadic cases. Invasive carcinomas from FAP patients showed only 6% LOH, and invasive carcinomas from HNPCC patients exhibited 0% LOH. Mutation analysis of the KLF6 gene in 298 colorectal tumors detected no somatic mutations.

CONCLUSIONS

The present data suggest that LOH of the KLF6 locus at chromosome 10p15 contributes to the invasion step from an intramucosal carcinoma to an invasive carcinoma specifically in sporadic colorectal carcinogenesis, but is rarely involved in the carcinogenesis of FAP and HNPCC cases. Moreover, the absence of somatic mutations suggests the uncertainty of the KLF6 gene as a classical tumor suppressor gene at the lost 10p15 region in colorectal carcinogenesis.

Downregulation of KLF6 is an early event in hepatocarcinogenesis, and stimulates proliferation while reducing differentiation

BACKGROUND/AIMS

Hepatocellular carcinoma (HCC) has the most rapidly rising cancer incidence in the US and Europe. The KLF6 tumor suppressor is frequently inactivated in HCC by loss-of-heterozygosity (LOH) and/or mutation.

METHODS

Here we have analyzed 33 HBV- and 40 HCV-related HCCs for mRNA expression of wildtype KLF6 (wtKLF6) as well as the KLF6 variant 1 (SV1), a truncated, growth-promoting variant that antagonizes wtKLF6 function. The HCV-related tumors analyzed represented the full histologic spectrum from cirrhosis and dysplasia to metastatic cancer.

RESULTS

Expression of KLF6 mRNA is decreased in 73% of HBV-associated HCCs compared to matched surrounding tissue (ST), with reductions of approximately 80% in one-third of the patients. KLF6 mRNA expression is also reduced in dysplastic nodules from patients with HCV compared to cirrhotic livers (p<0.005), with an additional, marked decrease in the very advanced, metastatic stage (p<0.05). An increased ratio of KLF6SV1/wt KLF6 is present in a subset (6/33, 18%) of the HBV-related HCCs compared to matched ST. Reconstituting KLF6 in HepG2 cells by retroviral infection decreased proliferation and related markers including cyclin D1 and beta-catenin, increased cellular differentiation based on induction of albumin, E-cadherin, and decreased alpha fetoprotein.

CONCLUSIONS

We conclude that reduced KLF6 expression is common in both HBV- and HCV-related HCCs and occurs at critical stages during cancer progression. Effects of KLF6 are attributable to regulation of genes controlling hepatocyte growth and differentiation.

KLF6 transcription factor protects hepatocellular carcinoma-derived cells from apoptosis

Hepatocellular carcinoma (HCC) is a major public health concern because of the absence of early diagnosis and effective treatments. Efficient diagnosis modalities and therapies to treat HCC are needed. Kruppel-like factor (KLF) family members, such as KLF6, are involved in cell proliferation and differentiation. KLF6 is inactivated in solid tumors, which may contribute to pathogenesis. However, KLF6 status in HCC is controversial. Thus, we undertook the characterization of KLF6 expression and function in HCC and HCC-derived cell lines. We found that HCC, HepG2 and HuH7 cells expressed KLF6 messenger ribonucleic acid and protein. Next, using RNA interference, we demonstrated that inhibiting KLF6 expression in vitro strongly impaired cell proliferation-induced G1-phase arrest, inhibited cyclin-dependent kinase 4 and cyclin D1 expression, and subsequent retinoblastoma phosphorylation. Finally, KLF6 silencing caused p53 upregulation and inhibited Bcl-xL expression, to induce cell death by apoptosis. Taken together, these data demonstrated that KLF6 is essential for HCC-derived cells to evade apoptosis.

Functional Interaction between the Transcription Factor Krüppel-like Factor 5 and Poly(ADP-ribose) Polymerase-1 in Cardiovascular Apoptosis

Krüppel-like factor 5 (KLF5) is a transcription factor important in regulation of the cardiovascular response to external stress. KLF5 regulates pathological cell growth, and its acetylation is important for this effect. Its mechanisms of action, however, are still unclear. Analysis in KLF5-deficient mice showed that KLF5 confers apoptotic resistance in vascular lesions. Mechanistic analysis further showed that it specifically interacts with poly(ADP-ribose) polymerase-1 (PARP-1), a nuclear enzyme important in DNA repair and apoptosis. KLF5 interacted with a proteolytic fragment of PARP-1, and acetylation of KLF5 under apoptotic conditions increased their affinity. Moreover, KLF5 wild-type (but not a non-acetylatable point mutant) inhibited apoptosis as induced by the PARP-1 fragment. Collectively, we have found that KLF5 regulates apoptosis and targets PARP-1, and further, for acetylation to regulate these effects. Our findings thus implicate functional interaction between the transcription factor KLF5 and PARP-1 in cardiovascular apoptosis.

A module of negative feedback regulators defines growth factor signaling

Signaling pathways invoke interplays between forward signaling and feedback to drive robust cellular response. In this study, we address the dynamics of growth factor signaling through profiling of protein phosphorylation and gene expression, demonstrating the presence of a kinetically defined cluster of delayed early genes that function to attenuate the early events of growth factor signaling. Using epidermal growth factor receptor signaling as the major model system and concentrating on regulation of transcription and mRNA stability, we demonstrate that a number of genes within the delayed early gene cluster function as feedback regulators of immediate early genes. Consistent with their role in negative regulation of cell signaling, genes within this cluster are downregulated in diverse tumor types, in correlation with clinical outcome. More generally, our study proposes a mechanistic description of the cellular response to growth factors by defining architectural motifs that underlie the function of signaling networks.

In vivo regulation of p21 by the Kruppel-like factor 6 tumor-suppressor gene in mouse liver and human hepatocellular carcinoma

Kruppel-like factor (KLF) 6 is a tumor-suppressor gene functionally inactivated by loss of heterozygosity, somatic mutation and/or alternative splicing that generates a dominant-negative splice form, KLF6-SV1. Wild-type KLF6 (wtKLF6) expression is decreased in many human malignancies, which correlates with reduced patient survival. Additionally, loss of the KLF6 locus in the absence of somatic mutation in the remaining allele occurs in a number of human cancers, raising the possibility that haploinsufficiency of the KLF6 gene alone contributes to cellular growth dysregulation and tumorigenesis. Our earlier studies identified the cyclin-dependent kinase inhibitor p21 as a transcriptional target of the KLF6 gene in cultured cells, but not in vivo. To address this issue, we have generated two genetic mouse models to define the in vivo role of KLF6 in regulating cell proliferation and p21 expression. Transgenic overexpression of KLF6 in the liver resulted in a runted phenotype with decreased body and liver size, with evidence of decreased hepatocyte proliferation, increased p21 and reduced proliferating cell nuclear antigen expression. In contrast, mice with targeted deletion of one KLF6 allele (KLF6+/-) display increased liver mass with reduced p21 expression, compared to wild type littermates. Moreover, in primary hepatocellular carcinoma samples, there is a significant correlation between wtKLF6 and p21 mRNA expression. Combined, these data suggest that haploinsufficiency of the KLF6 gene may regulate cellular proliferation in vivo through decreased transcriptional activation of the cyclin-dependent kinase inhibitor p21.