Zinc-finger Transcription Factor Snail Research Articles

The antibiotic drug trimethoprim suppresses tumour growth and metastasis via targeting Snail

The zinc finger transcription factor Snail is aberrantly activated in many human cancers and strongly associated with poor prognosis. As a transcription factor, Snail has been traditionally considered an 'undruggable' target. Here, we identified a potent small-molecule inhibitor of Snail, namely trimethoprim, and investigated its potential antitumour effects and the underlying mechanisms. The inhibitory action of trimethoprim on Snail protein and the related molecular mechanisms were revealed by molecular docking, biolayer interferometry, immunoblotting, immunoprecipitation, qRT-PCR, pull-down and cycloheximide pulse-chase assays. The anti-proliferative and anti-metastatic effects of trimethoprim via targeting Snail were tested in multiple cell-based assays and animal models. This study identified trimethoprim, an antimicrobial drug, as a potent antitumour agent via targeting Snail. Molecular modelling analysis predicted that trimethoprim directly binds to the arginine-174 pocket of Snail protein. We further discovered that trimethoprim strongly interrupts the interaction of Snail with CREB-binding protein (CBP)/p300, which consequently suppresses Snail acetylation and promotes Snail degradation through the ubiquitin-proteasome pathway. Furthermore, trimethoprim sufficiently inhibited the proliferation, epithelial-mesenchymal transition (EMT) and migration of cancer cells in vitro via specifically targeting Snail. More importantly, trimethoprim effectively reduced Snail-driven tumour growth and metastasis to vital organs such as lung, bone and liver. These findings indicate, for the first time, that trimethoprim suppresses tumour growth and metastasis via targeting Snail. This study provides insights for a better understanding of the anticancer effects of trimethoprim and offers a potential anticancer therapeutic agent for clinical treatment.

A potent CBP/p300-Snail interaction inhibitor suppresses tumor growth and metastasis in wild-type p53-expressing cancer.

The zinc finger transcription factor Snail is aberrantly activated in many human cancers and associated with poor prognosis. Therefore, targeting Snail is expected to exert therapeutic benefit in patients with cancer. However, Snail has traditionally been considered "undruggable," and no effective pharmacological inhibitors have been identified. Here, we found a small-molecule compound CYD19 that forms a high-affinity interaction with the evolutionarily conserved arginine-174 pocket of Snail protein. In aggressive cancer cells, CYD19 binds to Snail and thus disrupts Snail's interaction with CREB-binding protein (CBP)/p300, which consequently impairs CBP/p300-mediated Snail acetylation and then promotes its degradation through the ubiquitin-proteasome pathway. Moreover, CYD19 restores Snail-dependent repression of wild-type p53, thus reducing tumor growth and survival in vitro and in vivo. In addition, CYD19 reverses Snail-mediated epithelial-mesenchymal transition (EMT) and impairs EMT-associated tumor invasion and metastasis. Our findings demonstrate that pharmacologically targeting Snail by CYD19 may exert potent therapeutic effects in patients with cancer.

Snail-Overexpression Induces Epithelial-mesenchymal Transition and Metabolic Reprogramming in Human Pancreatic Ductal Adenocarcinoma and Non-tumorigenic Ductal Cells.

The zinc finger transcription factor Snail is a known effector of epithelial-to-mesenchymal transition (EMT), a process that underlies the enhanced invasiveness and chemoresistance of common to cancerous cells. Induction of Snail-driven EMT has also been shown to drive a range of pro-survival metabolic adaptations in different cancers. In the present study, we sought to determine the specific role that Snail has in driving EMT and adaptive metabolic programming in pancreatic ductal adenocarcinoma (PDAC) by overexpressing Snail in a PDAC cell line, Panc1, and in immortalized, non-tumorigenic human pancreatic ductal epithelial (HPDE) cells. Snail overexpression was able to induce EMT in both pancreatic cell lines through suppression of epithelial markers and upregulation of mesenchymal markers alongside changes in cell morphology and enhanced migratory capacity. Snail-overexpressed pancreatic cells additionally displayed increased glucose uptake and lactate production with concomitant reduction in oxidative metabolism measurements. Snail overexpression reduced maximal respiration in both Panc1 and HPDE cells, with further reductions seen in ATP production, spare respiratory capacity and non-mitochondrial respiration in Snail overexpressing Panc1 cells. Accordingly, lower expression of mitochondrial electron transport chain proteins was observed with Snail overexpression, particularly within Panc1 cells. Modelling of 13C metabolite flux within both cell lines revealed decreased carbon flux from glucose in the TCA cycle in snai1-overexpressing Panc1 cells only. This work further highlights the role that Snail plays in EMT and demonstrates its specific effects on metabolic reprogramming of glucose metabolism in PDAC.

SPSB3 targets SNAIL for degradation in GSK-3β phosphorylation-dependent manner and regulates metastasis.

Epithelial-mesenchymal transition (EMT) is a process during which normal epithelial cells acquire mesenchymal characteristics. EMT has a critical role in various human diseases especially in cancer. EMT facilitates tumor initiation and progression by mediating cancer cell stemness and motility. Zinc finger transcription factor SNAIL is one of the most important initiators of EMT. Therefore, it is of great significance to understand the regulating mechanism of SNAIL. In this study, we carried out a luciferase-based genome-wide screening using small interfering RNA library against ~200 of E3 ligases and ubiquitin-related genes and identified SOCS box protein SPSB3 as a novel E3 ligase component that targets SNAIL into polyubiquitination and degradation in response to GSK-3β phosphorylation of SNAIL. Functionally, we observed that SPSB3 overexpression greatly inhibits tumor metastasis by regulating SNAIL degradation both in vitro and in vivo. The expression of SPSB3 and SNAIL are negatively correlated in human esophageal squamous cell carcinoma tissues, and low SPSB3 expression indicates lymph node metastasis. Moreover, high SPSB3 expression indicates good survivals in various kinds of cancer. Collectively, these findings suggest that SPSB3-mediated SNAIL degradation has a vital role in regulating EMT and cancer progression.

PPARGC1A is upregulated and facilitates lung cancer metastasis

Lung cancer remains a leading cause of cancer-related mortality, with metastatic progression remaining the single largest cause of lung cancer mortality. Hence it is imperative to determine reliable biomarkers for lung cancer prognosis. We performed quantitative real-time PCR (qRT-PCR) analysis to explore epithelial-mesenchymal transition (EMT) inducers that regulate EMT process in three patients with advanced lung cancer disease. Peroxisome proliferator-activated receptor gamma (PPARGC1A) was uniformly the topmost overexpressed gene in all three human non-small cell lung cancer (NSCLC) patient samples. Further evaluation in human normal lung and metastatic lung cancer cell lines revealed that the expression of PPARGC1A was upregulated in metastatic lung cancer cell lines. Metagenomic analysis revealed direct correlation among PPARGC1A, zinc-finger transcription factor snail homolog 1 (SNAI1), and metastatic lung disease. Upregulation of PPARGC1A transcript expression was independent of a differential upregulation of the upstream AMP-dependent protein kinase (AMPK) activation or steady state expression of the silent mating type information regulation 2 homolog 1 (SIRT1). Xenograft tail vein colonization assays proved that the high expression of PPARGC1A was a prerequisite for metastatic progression of lung cancer to brain. Our results indicate that PPARGC1A might be a potential biomarker for lung cancer prognosis.

Snail/Slug binding interactions with YAP/TAZ control skeletal stem cell self-renewal and differentiation

Bone marrow-derived skeletal stem/stromal cell (SSC) self-renewal and function are critical to skeletal development, homeostasis and repair. Nevertheless, the mechanisms controlling SSC behavior, particularly bone formation, remain ill-defined. Using knockout mouse models that target the zinc-finger transcription factors, Snail, Slug or Snail and Slug combined, a regulatory axis has been uncovered wherein Snail and Slug cooperatively control SSC self-renewal, osteoblastogenesis and bone formation. Mechanistically, Snail/Slug regulate SSC function by forming complexes with the transcriptional co-activators, YAP and TAZ, in tandem with the inhibition of the Hippo pathway-dependent regulation of YAP/TAZ signaling cascades. In turn, the Snail/Slug-YAP/TAZ axis activates a series of YAP/TAZ/TEAD and Runx2 downstream targets that control SSC homeostasis and osteogenesis. Together, these results demonstrate that SSCs mobilize Snail/Slug-YAP/TAZ complexes to control stem cell function.

Snail, a transcriptional regulator, represses adiponectin expression by directly binding to an E-box motif in the promoter

ObjectiveAdiponectin is a hormone that modulates many metabolic processes and is exclusively expressed in adipose tissue. However, complete understanding of the factors that regulate adiponectin expression is lacking. The following were investigated: (1) functional analysis of the human adiponectin promoter, (2) putative adiponectin repressor sequence activity in 3T3-L1 adipocytes using promoter mutagenesis, (3) whether Snail, an E-box binding transcription factor, binds this repressor sequence, (4) if Snail regulates adiponectin expression in 3T3-L1 pre-adipocytes. Materials/MethodsTo further understand how adiponectin expression is regulated, we isolated the human adiponectin promoter and analyzed its activity after serial deletions. ResultsWe found a negative cis-regulatory element located in the adiponectin proximal promoter sequence (−174 to −152bp), which contained an E-box site (CAACTG). The DNA binding activity of this putative negative regulatory factor was found to be sequence-specific and the binding activity is decreased during adipocyte differentiation time-dependently. Affinity chromatography identified the zinc-finger transcription factor Snail (SNAI1) as the putative negative regulatory factor. Chromatin immunoprecipitation assay and electrophoretic mobility shift assay confirmed that Snail binds to this negative cis-regulatory element in pre-adipocytes, exclusively. Inhibition of Snail expression using small interfering RNA techniques increased adiponectin expression in 3T3-L1 adipocytes, while overexpression of Snail reduced adiponectin expression. Furthermore, we observed an inverse relation between the expression of Snail and the expression of CCAAT-enhancer-binding protein alpha and peroxisome proliferator-activated receptor gamma, which are transcription factors that regulate adipogenesis. ConclusionsSnail is a novel regulator of adiponectin expression and probably has a role in regulating adipogenesis.

Regulation of Transcription Factor Twist Expression by the DNA Architectural Protein High Mobility Group A2 during Epithelial-to-Mesenchymal Transition

Deciphering molecular mechanisms that control epithelial-to-mesenchymal transition (EMT) contributes to our understanding of how tumor cells become invasive and competent for intravasation. We have established that transforming growth factor β activates Smad proteins, which induce expression of the embryonic factor high mobility group A2 (HMGA2), which causes mesenchymal transition. HMGA2 associates with Smad complexes and induces expression of an established regulator of EMT, the zinc finger transcription factor Snail. We now show that HMGA2 can also induce expression of a second regulator of EMT, the basic helix-loop-helix transcription factor Twist. Silencing of endogenous Twist demonstrated that this protein acts in a partially redundant manner together with Snail. Double silencing of Snail and Twist reverts mesenchymal HMGA2-expressing cells to a more epithelial phenotype when compared with single silencing of Snail or Twist. Furthermore, HMGA2 can directly associate with A:T-rich sequences and promote transcription from the Twist promoter. The new evidence proposes a model whereby HMGA2 directly induces multiple transcriptional regulators of the EMT program and, thus, is a potential biomarker for carcinomas displaying EMT during progression to more advanced stages of malignancy.

Expression of transcription factor Snai1 and tubulointerstitial fibrosis in progressive nephropathy

Tubulointerstitial fibrosis (TIF) is seen as the final stage of progressive nephropathy, and the degree of TIF is reported to be a major determinant in renal outcomes. In recent years, epithelial-mesenchymal transition (EMT) and the zinc-finger transcription factor snail homolog 1 (Snai1) have each been implicated in the mechanism of TIF. The relationship between EMT and these transcription factors is unclear, however, so in this study we attempted to elucidate the correlation between the expression of Snai1 and clinical markers. We performed immunohistochemical staining on human renal tissue obtained from patients with diabetic nephropathy (DN), IgA nephropathy (IgAN), minimal change disease (MCD) and minor glomerular abnormality (MGA) using anti-Snai1 and anti-vimentin antibodies. We counted Snai1-positive and Snai1/vimentin double positive tubular epithelial cells. Snai1 protein was mainly observed in the nuclei of flattened, damaged tubular epithelial cells, especially in IgAN and DN, and positive cell numbers were significantly higher in IgAN than in MGA, MCD or DN. Snai1/vimentin double staining showed that some vimentin-positive tubular epithelial cells also contained Snai1-positive nuclei, and double positive cell numbers were increased in IgAN and DN. Statistical analysis revealed positive correlations between Snai1/vimentin double positive cell numbers and proteinuria and creatinine in IgAN. Positive correlations were also seen between Snai1/vimentin double positive cell numbers and the severity of proteinuria in DN. The results of this study indicate that Snai1 plays an important role in TIF in patients with progressive nephropathy.

Glycogen synthase kinase 3β-dependent Snail degradation directs hepatocyte proliferation in normal liver regeneration

Liver regeneration proceeds under the well-orchestrated control of multiple transcription factors that lead hepatocytes to reenter the cell cycle, proliferate, and renew quiescence. Here, we found an important role of the zinc-finger transcription factor Snail in liver regeneration. Snail was typically expressed in quiescent adult hepatocytes, but was rapidly degraded when the liver needed to regenerate itself. Decreased levels of Snail induced DNA synthesis in hepatocytes through up-regulation of cell cycle-related proteins. Snail degradation was dependent on phosphorylation by glycogen synthase kinase (GSK)-3β, whose quantity and activity were immediately increased after loss of liver mass or hepatic injury. Inactivation of GSK-3β resulted in suppression of Snail degradation and DNA synthesis in hepatocytes, leading to impaired liver growth during regeneration. This GSK-3β-dependent Snail degradation occurred as a result of cytokine, growth factor, and bile acid signals that are known to drive liver regeneration. Thus, GSK-3β-dependent Snail degradation acts as a fundamental cue for the initiation of hepatocyte proliferation in liver regeneration.

Abstract 4812: Collagen regulation of Snail expression in pancreatic cancer involves TGF-β1 signaling

Abstract Pancreatic cancer, the fourth leading cause of cancer death in the U.S., is associated with pronounced desmoplastic reaction; however, the role of this collagen-rich fibrotic reaction in pancreatic cancer progression is poorly understood. Previously, we had shown that the collagen increased expression of the key proteinase membrane type 1-matrix metalloproteinase (MT1-MMP). Now we show that collagen can also increase expression of the zinc-finger transcription factor Snail to enhance pancreatic cancer invasion. Relative to cells grown on tissue culture plastic, PDAC cells grown in 3D collagen gels induced Snail. As we had previously published that TGF-β1 increases Snail levels, we examined the contribution of TGF-β1 signaling to collagen-induced Snail expression. Inhibiting TGF-β1 signaling with siRNA against TGF-β1 receptor type I (TbRI) or with a highly specific inhibitor of TbRI kinase activity attenuated the effect of collagen on Snail levels. To further examine the role of Snail in PDAC progression, we generated Snail-inducible PDAC cells lines. Expression of Snail in PDAC cells grown in 3D collagen gels enhanced invasion, which was blocked in the presence of the MMP inhibitor GM6001. Overexpression of Snail in PDAC cells increased MT1-MMP, while siRNA against Snail decreased MT1-MMP and also attenuated collagen-induced MT1-MMP expression. Snail expression of MT1-MMP requires ERK1/2 signaling and blocking ERK1/2 phosphorylation inhibited Snail-induced invasion in 3D collagen gels. To provide in vivo support for our findings that Snail can regulate MT1-MMP, we examined the expression of Snail and MT1-MMP in human PDAC tumors and found a statistically significant positive correlation between MT1-MMP and Snail in these tumors. Overall, our data demonstrate that collagen-rich milieu can increase the expression of Snail, and suggests that the desmoplastic reaction actively contributes to PDAC progression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4812.

Abstract 2310: Snail-induced epigenetic regulation and its implication in plasticity of cellular morphology

Abstract Epithelial and mesenchymal cells exhibit distinct phenotypic and functional characteristics, yet the two cell types possess substantial plasticity and are interconvertable. Bidirectional transitions between epithelial and mesenchymal cells play crucial roles in physiological and pathological processes. Both epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) are fundamental to embryonic development. In human cancer, EMT confers migratory and invasive properties on carcinoma cells, thereby promoting tumor invasion and dissemination. Moreover, EMT may endow cells with stem cell-like traits. After migrating tumor cells reach ectopic organ sites, conversion of mesenchymal tumor cells to epithelial cells through MET (including differentiation of tumor stem cells) may facilitate macrometastatic growth. However, despite its critical relevance in normal development and cancer metastasis, the molecular basis underpinning the interconvertibility between epithelial and mesenchymal states remains incompletely understood. The zinc-finger transcription factor Snail induces EMT by directly repressing E-cadherin, a defining marker of epithelial cells. Here we show that Snail physically interacts with and recruits the histone demethylase LSD1 to the E-cadherin promoter to remove dimethylation of lysine 4 on histone H3 (H3K4m2), a histone modification associated with active chromatin. Furthermore, demethylation of H3K4m2 by LSD1 is essential for Snail-mediated transcriptional repression. In contrast to H3K4me2, the active trimethylated H3K4 (H3K4m3) mark is not a substrate for LSD1 and it remains at high levels at the inactive E-cadherin promoter despite Snail expression. In addition, Snail induces H3K27 trimethylation (H3K27m3), a repressive chromatin mark. As a consequence, the Snail-repressed E-cadherin promoter simultaneously possesses opposite H3K4m3 and H3K27m3 marks, a pattern characteristic of bivalent chromatin modifications. Bivalent chromatin domains were initially identified and are enriched in stem cells. Bivalent promoters are inactive but are poised for activation. Although it awaits to be determined whether Snail-induced chromatin bivalency might contribute to cellular stemness, this observation suggests that the E-cadherin gene repressed by Snail remains in a transcriptionally ready state for re-activation, which may be critical for MET. These results exemplify how a bivalent chromatin state is established and provide new insights into epigenetic regulation of E-cadherin transcription and the plasticity of cellular morphology. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2310.

Expression of the Transcription Factor Snail and Its Target Gene Twist Are Associated with Malignancy in Pheochromocytomas

One of the best known functions of the zinc-finger transcription factor Snail is to induce epithelial-mesenchymal transition (EMT). Twist, a target genes of Snail, is known to promote the development of distant metastases in mice. Increasing evidence suggests that EMT plays a pivotal role in tumor progression and metastatic spread. Snail, Twist, and E-cadherin expression were assessed by immunohistochemistry and real-time quantitative reverse transcriptase-polymerase chain reaction in 12 malignant and 35 benign pheochromocytomas (PCC). Data were correlated with clinical characteristics and genetics. We found Snail expression in 13 (28%) of 47 primary PCC samples. Twist was expressed in 31 (66%) of 47 cases. Only one of 47 PCC showed E-cadherin expression. We observed Snail expression in 7 (58%) of 12 malignant PCC, whereas only 6 (17%) of 35 apparently benign PCC revealed Snail expression (P = 0.01). Furthermore, 11 (92%) of 12 malignant PCC, but only 20 (57%) of 35 benign PCC, revealed Twist expression (P = 0.03). Interestingly, all five metastases showed Snail and Twist expression. In normal adrenal medulla, Snail, Twist, and E-cadherin expression could not be detected. We describe for the first time that EMT markers Snail and Twist are expressed in PCC and that their expression is associated with malignancy. Our study supports a role for EMT in the malignant transformation of PCC.

Expression of the zinc-finger transcription factor Snail in adrenocortical carcinoma is associated with decreased survival

In this study, we evaluate whether Snail is expressed in adrenocortical cancer (ACC) and if its expression is related to patient outcome. One of the best known functions of the zinc-finger transcription factor Snail is to induce epithelial-to-mesenchymal transition (EMT). Increasing evidence suggests that EMT plays a pivotal role in tumour progression and metastatic spread. Snail and E-cadherin expression were assessed by immunohistochemistry in 26 resected ACCs and real-time quantitative RT–PCR expression analysis was performed. Data were correlated with clinical outcome and in particular with overall patient survival. Seventeen of 26 (65%) ACC tumour samples expressed Snail when assessed by immunohistochemistry. Snail expression was neither detected in normal adrenocortical tissue, nor in benign adrenocortical adenomas. Expression levels were confirmed on the mRNA level by Real-Time–PCR. Survival rates were significantly decreased in Snail-positive tumours compared to Snail-negative tumours: 10 out of 16 vs one out of eight patients succumbed to disease after a median follow up of 14.5 and 28.5 months, respectively (P=0.03). Patients with Snail-expressing ACCs presented in advanced disease (11 out of 12 vs 6 out of 14, P=0.01) and tend to develop distant metastases more frequently than patients with negative staining (7 out of 11 vs two out of eight, P=0.19). In conclusion, we describe for the first time that Snail is expressed in a large subset of ACCs. Furthermore, Snail expression is associated with decreased survival, advanced disease and higher risk of developing distant metastases.

Precise measurement of the E-cadherin repressor Snail in formalin-fixed endometrial carcinoma using protein lysate microarrays

Over-expression of the zinc finger transcription factor Snail leads to down-regulation of the epithelial proteins E-cadherin and Cytokeratin 18 and to upregulation of the mesenchymal protein Vimentin. The aim of our study was to characterize for the first time Snail protein expression in formalin-fixed primary tumour tissues using protein lysate microarrays and correlate Snail with E-cadherin, Cytokeratin 18, and Vimentin protein abundances. In a first feasibility study, we examined 17 formalin-fixed endometrioid adenocarcinomas by protein lysate microarrays. Snail expression showed a statistical significant inverse correlation with the expression of E-cadherin (P<0.001). A trend for correlation between Snail and Cytokeratin 18 (P=0.043) and the tumour grade (P=0.074) was seen. For Snail and Vimentin no correlation was found (P=0.384). In conclusion, our results fit to the proposed function of Snail as a transcriptional repressor of E-cadherin and Cytokeratin 18 in primary human carcinomas and demonstrate the usefulness of protein lysate microarrays for the precise determination of proteins involved in epithelial-mesenchymal-transition.

An NF-κB and Slug Regulatory Loop Active in Early Vertebrate Mesoderm

BackgroundIn both Drosophila and the mouse, the zinc finger transcription factor Snail is required for mesoderm formation; its vertebrate paralog Slug (Snai2) appears to be required for neural crest formation in the chick and the clawed frog Xenopus laevis. Both Slug and Snail act to induce epithelial to mesenchymal transition (EMT) and to suppress apoptosis.Methodology & Principle FindingsMorpholino-based loss of function studies indicate that Slug is required for the normal expression of both mesodermal and neural crest markers in X. laevis. Both phenotypes are rescued by injection of RNA encoding the anti-apoptotic protein Bcl-xL; Bcl-xL's effects are dependent upon IκB kinase-mediated activation of the bipartite transcription factor NF-κB. NF-κB, in turn, directly up-regulates levels of Slug and Snail RNAs. Slug indirectly up-regulates levels of RNAs encoding the NF-κB subunit proteins RelA, Rel2, and Rel3, and directly down-regulates levels of the pro-apopotic Caspase-9 RNA.Conclusions/SignificanceThese studies reveal a Slug/Snail–NF-κB regulatory circuit, analogous to that present in the early Drosophila embryo, active during mesodermal formation in Xenopus. This is a regulatory interaction of significance both in development and in the course of inflammatory and metastatic disease.

Transcription Factor Snail Modulates Hormone Expression in Established Endocrine Pancreatic Cell Lines

The development of differentiated cells from undifferentiated progenitor cells is one of the central tenets of developmental biology. However, under conditions of tissue morphogenesis, regeneration, and cancer, this process of development is reversed and fully differentiated cells transition to an undifferentiated phenotype. Here we present evidence that the zinc-finger transcription factor Snail modulates this transition in differentiated pancreatic endocrine cell lines. During passage and growth of these cell lines, Snail expression is induced in a subset of cells within the culture, concomitant with a decrease in insulin and/or glucagon expression. As the cells cluster and exit the cell division cycle, nuclear levels of Snail are reduced and hormone expression is resumed. Snail represses proinsulin and proglucagon gene transcription, and reduction of Snail levels by small interfering RNA treatment increases proinsulin gene expression. We propose that Snail modulates the dynamic balance between differentiated and dedifferentiated cells allowing their migration and proliferation. These findings may be relevant to providing approaches for the enhancement of beta-cell growth in individuals with diabetes mellitus.

Cancer development induced by graded expression of Snail in mice

The zinc-finger transcription factor Snail is believed to trigger epithelial-mesenchymal transitions (EMTs) during cancer progression. This idea is supported by analysis of Snail knockout mice, which uncovered crucial role of Snail in gastrulation, and of individuals with cancer, in whom Snail expression is frequently upregulated. However, these results have not shown a direct link between Snail and the pathogenesis of cancer. Here we show that mice carrying hypomorphic tetracycline-repressible Snail transgenes, that increase Snail expression to 20% above normal levels, exhibit no morphological alterations and develop both epithelial and mesenchymal tumours (leukaemias). Suppression of the Snail transgene did not rescue the malignant phenotype, indicating that alterations induced by Snail are irreversible. CombitTA-Snail murine embryonic fibroblasts show similar migratory ability to that of control mouse embryonic fibroblasts (MEFs). However, CombitTA-Snail-MEFs induce tumour formation in nude mice. CombitTA-Snail expression results in increased radioprotection in vivo, although it does not affect p53 regulation in response to DNA damage. In concert with these results, Snail expression is repressed following DNA damage. This regulation of Snail by DNA damage is p53-independent. Our results connect DNA damage with the requirement of a critical level of an EMT regulator and provide genetic evidence that Snail plays essential roles in cancer development in mammals and thereby influences cell fate in the genotoxic stress response.

The zinc-finger transcription factor Snail downregulates proliferating cell nuclear antigen expression in colorectal carcinoma cells

The Snail family of zinc-finger protein is a transcription repressor that is involved in the development of vertebrate and invertebrate embryos as well as in tumor progression. This family leads to broad biological functions such as cell differentiation, cell motility, cell cycle regulation and apoptosis. However, the target genes of Snail remain little known. In this study, we found several potential Snail binding sequences in the 5'-flanking region of human PCNA gene. Cotransfection experiments showed that Snail reduces human PCNA gene promoter activity in colorectal carcinoma cell lines, HCT116 and Colo320HSR. Snail-reduced PCNA expression was detected in immunoblotting and immunochemistry. In BrdU incorporation experiment, Snail inhibited the BrdU incorporation. Electrophoretic mobility shift assays showed that Snail can bind to the potential Snail recognition sites in the human PCNA promoter. Taken together, our results suggest that Snail may have an inhibitory effect on cell proliferation through down-regulation of PCNA expression as a novel target.

Autocrine Motility Factor Signaling Enhances Pancreatic Cancer Metastasis

Autocrine motility factor (AMF)/phosphoglucose isomerase (PGI) is a ubiquitous cytosolic enzyme that plays a key role in glycolysis. AMF/PGI is also a multifunctional protein that acts in the extracellular milieu as a potent mitogen/cytokine. Increased expression of AMF/PGI and its receptor has been found in a wide spectrum of malignancies and is associated with cancer progression and metastasis. Recent studies indicated that AMF is induced by hypoxia and enhances the random motility of pancreatic cancer cells. In the present study, the role and regulation of AMF in the growth and metastasis of pancreatic cancer cells were determined. In this study, we assessed whether overexpression of AMF in human pancreatic cancer cells enhances the liver metastasis using an orthotopic mouse tumor model. We also investigated the intracellular signal transduction pathways of AMF in human pancreatic cancer cell lines. Overexpression of AMF stimulated in vitro invasion of MIA PaCa-2 cells. In vivo, after orthotopic implantation into the pancreas of nude mice, parental and empty vector-transfected MIA PaCa-2 cells produced locally relatively small tumors with no evidence of liver metastasis, whereas AMF-transfected MIA PaCa-2 cells produced the large tumors and liver metastases. In addition, over-expression of AMF leads to down-regulation of E-cadherin expression associated with the up-regulation of the zinc-finger transcription factor SNAIL expression. The data submitted here show that AMF expression significantly contributes to the aggressive phenotype of human pancreatic cancer and thus may provide a novel prognostic and therapeutic target.