Peroxisome proliferator-activated receptor gamma and transforming growth factor-beta pathways inhibit intestinal epithelial cell growth by regulating levels of TSC-22

Comprehensive transcriptome and scRNA-seq analyses uncover the expression and underlying mechanism of SYNJ2 in papillary thyroid carcinoma

Synaptojanin 2 (SYNJ2) has crucial role in various tumors, but its role in papillary thyroid carcinoma (PTC) remains unexplored. This study first detected SYNJ2 protein expression in PTC using immunohistochemistry method and further assessed SYNJ2 mRNA expression through mRNA chip and RNA sequencing data and its association with clinical characteristics. Additionally, KEGG, GSVA, and GSEA analyses were conducted to investigate potential biological functions, while single-cell RNA sequencing data were used to explore SYNJ2's underlying mechanisms in PTC. Meanwhile, immune infiltration status in different SYNJ2 expression groups were analyzed. Besides, we investigated the immune checkpoint gene expression and implemented drug sensitivity analysis. Results indicated that SYNJ2 is highly expressed in PTC (SMD = 0.66 [95% CI: 0.17-1.15]) and could distinguish between PTC and non-PTC tissues (AUC = 0.74 [0.70-0.78]). Furthermore, the study identified 134 intersecting genes of DEGs and CEGs, mainly enriched in the angiogenesis and epithelial-mesenchymal transition (EMT) pathways. Subsequent analysis showed the above pathways were activated in PTC epithelial cells. PTC patients with high SYNJ2 expression showed higher sensitivity to the six common drugs. Summarily, SYNJ2 may promote PTC progression through angiogenesis and EMT pathways. High SYNJ2 expression is associated with better response to immunotherapy and chemotherapy.

Harnessing the Vnn1 pantetheinase pathway boosts short chain fatty acids production and mucosal protection in colitis

OBJECTIVE

In the management of patients with IBD, there is a need to identify prognostic markers and druggable biological pathways to improve mucosal repair and probe the efficacy of tumour necrosis factor alpha biologics. Vnn1 is a pantetheinase that degrades pantetheine to pantothenate (vitamin B₅, a precursor of coenzyme A (CoA) biosynthesis) and cysteamine. Vnn1 is overexpressed by inflamed colonocytes. We investigated its contribution to the tolerance of the intestinal mucosa to colitis-induced injury.

DESIGN

We performed an RNA sequencing study on colon biopsy samples from patients with IBD stratified according to clinical severity and modalities of treatment. We generated the VIVA mouse transgenic model, which specifically overexpresses Vnn1 on intestinal epithelial cells and explored its susceptibility to colitis. We developed a pharmacological mimicry of Vnn1 overexpression by administration of Vnn1 derivatives.

RESULTS

VNN1 overexpression on colonocytes correlates with IBD severity. VIVA mice are resistant to experimentally induced colitis. The pantetheinase activity of Vnn1 is cytoprotective in colon: it enhances CoA regeneration and metabolic adaptation of colonocytes; it favours microbiota-dependent production of short chain fatty acids and mostly butyrate, shown to regulate mucosal energetics and to be reduced in patients with IBD. This prohealing phenotype is recapitulated by treating control mice with the substrate (pantethine) or the products of pantetheinase activity prior to induction of colitis. In severe IBD, the protection conferred by the high induction of VNN1 might be compromised because its enzymatic activity may be limited by lack of available substrates. In addition, we identify the elevation of indoxyl sulfate in urine as a biomarker of Vnn1 overexpression, also detected in patients with IBD.

CONCLUSION

The induction of Vnn1/VNN1 during colitis in mouse and human is a compensatory mechanism to reinforce the mucosal barrier. Therefore, enhancement of vitamin B₅-driven metabolism should improve mucosal healing and might increase the efficacy of anti-inflammatory therapy.

PPARγ Agonists in Combination Cancer Therapies

Peroxisome proliferator-activated receptor-gamma (PPARγ) is a nuclear receptor acting as a transcription factor involved in the regulation of energy metabolism, cell cycle, cell differentiation, and apoptosis. These unique properties constitute a strong therapeutic potential that place PPARγ agonists as one of the most interesting and widely studied anticancer molecules. Although PPARγ agonists exert significant, antiproliferative and tumoricidal activity in vitro, their anticancer efficacy in animal models is ambiguous, and their effectiveness in clinical trials in monotherapy is unsatisfactory. However, due to pleiotropic effects of PPARγ activation in normal and tumor cells, PPARγ ligands interact with many antitumor treatment modalities and synergistically potentiate their effectiveness. The most spectacular example is a combination of PPARγ ligands with tyrosine kinase inhibitors (TKIs) in chronic myeloid leukemia (CML). In this setting, PPARγ activation sensitizes leukemic stem cells, resistant to any previous form of treatment, to targeted therapy. Thus, this combination is believed to be the first pharmacological therapy able to cure CML patients. Within the last decade, a significant body of data confirming the benefits of the addition of PPARγ ligands to various antitumor therapies, including chemotherapy, hormonotherapy, targeted therapy, and immunotherapy, has been published. Although the majority of these studies have been carried out in vitro or animal tumor models, a few successful attempts to introduce PPARγ ligands into anticancer therapy in humans have been recently made. In this review, we aim to summarize shines and shadows of targeting PPARγ in antitumor therapies.

Low levels of TSC22 enhance tumorigenesis by inducing cell proliferation in colorectal cancer

Transforming growth factor β-stimulated clone 22 domain 1 (TSC22) has been identified as a cancer suppressor gene in various kinds of cancers. The purpose of this study was to explore the expression of TSC22 in colorectal cancer (CRC) tissues and cell lines. 24 matched CRC and normal tissue samples by qPCR along with 18 pairs of them by Western blot demonstrated TSC22 level was decreased in CRC compared with normal tissue. The protein expression of TSC22 was examined in 310 CRC specimens. Results showed low expression of TSC22 was significantly correlated with tumor size (P = 0.048) and tumor infiltration (P = 0.016). Kaplan-Meier method suggested low expression of TSC22 was inversely associated with OS for 276 samples (P < 0.01). Multivariate Cox regression analysis confirmed TSC22 expression as independent predictors of the OS in CRC patients. Furthermore, we found TSC22 could suppress tumor by inhibiting cell proliferation in CRC cell lines.

Mechanism of Proliferation of Cultured Human Corneal Endothelial Cells

Because human corneal endothelial cells (HCECs) do not proliferate once the endothelial monolayer has formed, corneal wound healing is believed to be mediated by cell enlargement or migration, rather than by proliferation. However, the cellular mechanisms involved in wound healing by HCECs have not been fully determined. In this review, we focus on the effects of promyelocytic leukemia zinc finger (PLZF), a DNA-binding transcription factor, and transforming growth factor (TGF)-β2 on the proliferation and migration of cultured HCECs. Involvement of the mitogen-activated protein kinase (MAPK) signaling pathway in the migration of HCECs was also investigated. Expression of PLZF mRNA decreased as cell-cell contact was disrupted and returned to the original level as cell-cell contact was re-formed. Assessment with a real-time cell electronic sensing system revealed that proliferation of cultured HCECs was inhibited after infection with Ad-PLZF and exposure to TGF-β2. Migration of cultured HCECs was increased by TGF-β2 through p38 MAPK activation. We conclude that PLZF expression in cultured HCECs is closely related to the formation of cell-cell contact and that TGF-β2 suppresses proliferation of cultured HCECs, while promoting their migration through p38 MAPK activation.

Peroxisome Proliferator-Activated Receptor Gamma in Obesity and Colorectal Cancer: the Role of Epigenetics

Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear receptor that is deregulated in obesity. PPARγ exerts diverse antineoplastic effects. Attempting to determine the clinical relevance of the epigenetic mechanisms controlling the expression PPARγ and susceptibility to colorectal cancer (CRC) in obese subjects, this study investigated the role of some microRNAs and DNA methylation on the deregulation of PPARγ. Seventy CRC patients (34 obese and 36 lean), 22 obese and 24 lean healthy controls were included. MicroRNA levels were measured in serum. PPARγ promoter methylation was evaluated in peripheral blood mononuclear cells (PBMC). PPARγ level was evaluated by measuring mRNA level in PBMC and protein level in serum. The tested microRNAs (miR-27b, 130b and 138) were significantly upregulated in obese and CRC patients. Obese and CRC patients had significantly low levels of PPARγ. A significant negative correlation was found between PPARγ levels and the studied microRNAs. There was a significant PPARγ promoter hypermethylation in CRC patients that correlated to low PPARγ levels. Our results suggest that upregulation of microRNAs 27b, 130b and 138 is associated with susceptibility to CRC in obese subjects through PPARγ downregulation. Hypermethylation of PPARγ gene promoter is associated with CRC through suppression of PPARγ regardless of BMI.

Sub-micromolar concentrations of retinoic acid induce morphological and functional neuronal phenotypes in SK-N-SH neuroblastoma cells

Neuroblastoma cells are neural crest derivatives that can differentiate into neuron-like cells in response to exogenous agents, and are known to be particularly sensitive to retinoic acid. The spectrum of neuroblastoma responses, ranging from proliferation, migration, differentiation, or apoptosis, is difficult to predict due to the heterogeneity of these tumors and to the broad effective range of retinoic acid. Our study focused on the effects of nanomolar concentrations of retinoic acid on neuroblastoma differentiation in two cell lines cells: SK-N-SH (HTB-11) and IMR-32. Each cell line was treated with retinoic acid from 1 to 100 nM for up to 6 d. Morphological changes were quantified; immunocytochemistry was used to observe changes in neuronal protein expression and localization, while live-cell calcium imaging utilizing pharmacological agents was conducted to identify neuron-like activity. Retinoic acid-treated HTB-11 but not IMR-32 cells developed specific neuronal phenotypes: acquisition of long neurite-like processes, expression of neurofilament-200, increased responsiveness to acetylcholine, and decreased responsiveness to nicotine and epinephrine. In addition, nanomolar levels of retinoic acid elicited increased nuclear trafficking of the CRABP2, which is traditionally associated with gene expression of cellular pathways related to neuronal differentiation. Collectively, these results show that nanomolar concentrations of retinoic acid are capable of inducing both structural and functional neuron-like features in HTB-11 cells using CRABP2, suggesting differentiation in neuroblastoma cells into neuronal phenotypes. These have important implications for both chemotherapeutic design and for the use of neuroblastomas as in vitro models for neuron differentiation.

Bunched and Madm Function Downstream of Tuberous Sclerosis Complex to Regulate the Growth of Intestinal Stem Cells in Drosophila

The Drosophila adult midgut contains intestinal stem cells that support homeostasis and repair. We show here that the leucine zipper protein Bunched and the adaptor protein Madm are novel regulators of intestinal stem cells. MARCM mutant clonal analysis and cell type specific RNAi revealed that Bunched and Madm were required within intestinal stem cells for proliferation. Transgenic expression of a tagged Bunched showed a cytoplasmic localization in midgut precursors, and the addition of a nuclear localization signal to Bunched reduced its function to cooperate with Madm to increase intestinal stem cell proliferation. Furthermore, the elevated cell growth and 4EBP phosphorylation phenotypes induced by loss of Tuberous Sclerosis Complex or overexpression of Rheb were suppressed by the loss of Bunched or Madm. Therefore, while the mammalian homolog of Bunched, TSC-22, is able to regulate transcription and suppress cancer cell proliferation, our data suggest the model that Bunched and Madm functionally interact with the TOR pathway in the cytoplasm to regulate the growth and subsequent division of intestinal stem cells.

Transcriptional Regulation of Human Cytosolic Sulfotransferase 1C3 by Peroxisome Proliferator-Activated Receptor γ in LS180 Human Colorectal Adenocarcinoma Cells

Cytosolic sulfotransferase 1C3 (SULT1C3) is the least characterized of the three human SULT1C subfamily members. Originally identified as an orphan SULT by computational analysis of the human genome, we recently reported that SULT1C3 is expressed in human intestine and LS180 colorectal adenocarcinoma cells and is upregulated by agonists of peroxisome proliferator-activated receptor (PPAR) α and γ To determine the mechanism responsible for PPAR-mediated upregulation, we prepared reporter plasmids containing fragments of the SULT1C3 5'-flanking region. During initial attempts to amplify a 2.8-kb fragment from different sources of human genomic DNA, a 1.9-kb fragment was sometimes coamplified with the expected 2.8-kb fragment. Comparison of the 1.9-kb fragment sequence to the published SULT1C3 5'-flanking sequence revealed an 863-nt deletion (nt -146 to -1008 relative to the transcription start site). Transfection analysis in LS180 cells demonstrated that PPARα, δ, and γ agonist treatments induced luciferase expression from a reporter plasmid containing the 2.8-kb but not the 1.9-kb fragment. The PPAR agonists also activated a 1-kb reporter containing the 863-nt deletion region. Computational analysis identified three peroxisome proliferator response elements (PPREs) within the 863-nt region and serial deletions and site-directed mutations indicated that the most distal PPRE (at nt -769) was essential for obtaining PPAR-mediated transcriptional activation. Although agonists of all three PPARs could activate SULT1C3 transcription, RNA interference analysis indicated the predominance of PPARγ These data demonstrate that the PPARγ regulatory network includes SULT1C3 and imply that this enzyme contributes to the control of such PPARγ-regulated intestinal processes as growth, differentiation, and metabolism.

Yeast two-hybrid screening identified WDR77 as a novel interacting partner of TSC22D2

Transforming growth factor β-stimulated clone 22 domain family, member 2 (TSC22D2), a member of the TSC22D family, has been implicated as a tumor-associated gene, but its function remains unknown. To further explore its biological role, yeast two-hybrid screening combined with multiple bioinformatics tools was used to identify 44 potential interacting partners of the TSC22D2 protein that were mainly involved in gene transcription, cellular metabolism, and cell cycle regulation. The protein WD repeat domain 77 (WDR77) was selected for further validation due to its function in the cell cycle and tumor development, as well as its high detection frequency in the yeast two-hybrid assay. Immunoprecipitation and immunofluorescence experiments confirmed an interaction between the TSC22D2 and WDR77 proteins. Our work greatly expands the putative protein interaction network of TSC22D2 and provides deeper insight into the biological functions of the TSC22D2 and WDR77 proteins.

Overexpression of TSC-22 (transforming growth factor- β-stimulated clone-22) causes marked obesity, splenic abnormality and B cell lymphoma in transgenic mice

In this study, we generated transgenic (Tg) mice, which overexpressed transforming growth factor (TGF)-β stimulated clone-22 (TSC-22), and investigate the functional role of TSC-22 on their development and pathogenesis. We obtained 13 Tg-founders (two mice from C57BL6/J and 11 mice from BDF1). Three of 13 Tg-founders were sterile, and the remaining Tg-founders also could generate only a limited number of the F1 generation. We obtained 32 Tg-F1 mice. Most of the Tg-mice showed marked obesity. Histopathological examination could be performed on 31 Tg-mice; seventeen mice died by some disease in their entire life and 14 mice were killed for examination. Most of the Tg-mice examined showed splenic abnormality, in which marked increase of the megakaryocytes, unclearness of the margin of the red pulp and the white pulp, and the enlargement of the white pulp was observed. B cell lymphoma was developed in 10 (71%) of 14 disease-died F1 mice. These results indicate that constitutive over-expression of TSC-22 might disturb the normal embryogenesis and the normal lipid metabolism, and induce the oncogenic differentiation of hematopoietic cells.

TSC-22 Promotes Interleukin-2-Deprivation Induced Apoptosis in T-Lymphocytes

Originally described as a TGF-β-inducible gene, tsc-22 (Transforming growth factor-beta Stimulated Clone 22) encodes a transcriptional regulator affecting biological processes such as cell growth, differentiation, or apoptosis. Along with GILZ (Glucocorticoid-Induced Leucine Zipper), TSC-22 belongs to the evolutionary conserved TSC-22 Domain family. We previously showed that, in T-lymphocytes, GILZ expression was induced upon IL-2 withdrawal, delaying apoptosis through down-regulation of the pro-apoptotic protein BIM expression. The aim of this work was then to elucidate the respective roles of GILZ and TSC-22 upon IL-2 deprivation-induced apoptosis. We report here that these two highly homologous genes are concomitantly expressed in most human tissues and in primary T-lymphocytes and that expression of TSC-22 promotes T-lymphocytes apoptosis by inhibiting GILZ functions. Indeed, we demonstrated that TSC-22 expression in the murine lymphoid CTLL-2 cell line promoted IL-2 deprivation-induced apoptosis. BIM expression and caspases-9 and -3 activities were markedly increased in TSC-22 expressing clones compared to control clones. Analysis of GILZ expression revealed that TSC-22 prevented the induction of the GILZ protein upon IL-2 deprivation, by inhibiting gilz mRNA transcription. These results suggested that TSC-22 could counteract the protective effect of GILZ on IL-2-deprivation-induced apoptosis. Moreover, TSC-22-induced inhibition of GILZ expression was also found in CTLL-2 cells treated with glucocorticoids or TGF-β. In the human NKL cell line deprived of IL-2, TSC-22 showed the same effect and thus may represent a potent repressor of GILZ expression in IL-2-dependent cells, independently of the cell type, or the stimulus, leading to an increase of IL-2-deprived T-cells apoptosis. J. Cell. Biochem. 117: 1855-1868, 2016. © 2016 Wiley Periodicals, Inc.

Hepatic transforming growth factor-β 1 stimulated clone-22 D1 controls systemic cholesterol metabolism

Disturbances in lipid homeostasis are hallmarks of severe metabolic disorders and their long-term complications, including obesity, diabetes, and atherosclerosis. Whereas elevation of triglyceride (TG)-rich very-low-density lipoproteins (VLDL) has been identified as a risk factor for cardiovascular complications, high-density lipoprotein (HDL)-associated cholesterol confers atheroprotection under obese and/or diabetic conditions. Here we show that hepatocyte-specific deficiency of transcription factor transforming growth factor β 1-stimulated clone (TSC) 22 D1 led to a substantial reduction in HDL levels in both wild-type and obese mice, mediated through the transcriptional down-regulation of the HDL formation pathway in liver. Indeed, overexpression of TSC22D1 promoted high levels of HDL cholesterol in healthy animals, and hepatic expression of TSC22D1 was found to be aberrantly regulated in disease models of opposing energy availability. The hepatic TSC22D1 transcription factor complex may thus represent an attractive target in HDL raising strategies in obesity/diabetes-related dyslipidemia and atheroprotection.

Multiple TSC22D4 iso-/phospho-glycoforms display idiosyncratic subcellular localizations and interacting protein partners

Proteins of the TSC22 domain (TSC22D) family, including TSC22D1 and TSC22D4, play pivotal roles in cell proliferation, differentiation and apoptosis, interacting with other factors in a still largely unknown manner. This study explores this issue by biochemically characterizing various TSC22D4 forms (both iso- and glyco-phospho-, namely the splice variants 42 and 55 kDa and the post-translationally modified 67 and 72 kDa forms) and their subcellular localization and protein partners during cerebellar granule neuron (CGN) differentiation. The TSC22D4-42 form is mostly cytosolic, and is the only TSC22D4 form that associates with TSC22D1.2 in undifferentiated but not differentiated CGNs. In contrast, TSC22D4-55 is prominently associated with the nuclear matrix in differentiated but not undifferentiated CGNs. As for TSC22D4-67, it is localized in the cytosol and nuclei of undifferentiated CGNs and enters mitochondria of differentiated CGNs, associating with apoptosis-inducing factor. TSC22D4-72 is modified by O-linked beta-N-acetylglucosamine (O-GlcNAcylated) and phosphorylated and is always associated with chromatin irrespective of CGN differentiation. The various subcellular localization patterns and interacting protein partners of TSC22D4 forms during CGN differentiation suggest the existence of form-specific function(s) and provide a novel framework to further investigate the biological functions of TSC22D proteins.

N-3 PUFAs have antiproliferative and apoptotic effects on human colorectal cancer stem-like cells in vitro

The n-3 polyunsaturated fatty acids have been shown to inhibit the induction and progression of many kinds of tumor and to increase the therapeutic effects of numerous chemotherapeutics, but their anticancer effect on cancer stem cells from colorectal cancer has not been described previously. In the present study, we cultivated spheres from the SW620 cell line in serum-free medium and evaluated the features of the spheres by immunofluorescence, cell cycle distribution, resistance to chemotherapeutics and soft agar clone formation, and the spheres were shown to be cancer stem-like cells through tumorigenicity in athymic nude mice. Reverse transcriptase polymerase chain reaction analysis of pluripotency genes, such as Sox-2, Oct-4 and Bmi-1, showed that the spheres were generated by dedifferentiation of SW620 cells. The study explored the use of n-3 polyunsaturated fatty acids (PUFAs) in spheres, which were treated with two n-3 PUFAs [docosahexaenoic acid (DHA)/eicosapentaenoic acid (EPA)]. Treatment of the spheres with DHA and EPA alone or in combination for 72 h led to apoptosis and the progressive loss of viability and DNA fragmentation and an increase in annexin V expression. DHA and EPA can enhance the chemotherapeutic sensitivity effect of 5-Fu and mitomycin C, especially DHA combined with EPA. Taken together, these results provide evidence that n-3 PUFAs exert a direct anticancer action that may contribute to their antiproliferative and proapoptotic effect on the cancer stem-like cells.

PPARG Epigenetic Deregulation and Its Role in Colorectal Tumorigenesis

Peroxisome proliferator-activated receptor gamma (PPARγ) plays critical roles in lipid storage, glucose metabolism, energy homeostasis, adipocyte differentiation, inflammation, and cancer. Its function in colon carcinogenesis has largely been debated; accumulating evidence, however, supports a role as tumor suppressor through modulation of crucial pathways in cell differentiation, apoptosis, and metastatic dissemination. Epigenetics adds a further layer of complexity to gene regulation in several biological processes. In cancer, the relationship with epigenetic modifications has provided important insights into the underlying molecular mechanisms. These studies have highlighted how epigenetic modifications influence PPARG gene expression in colorectal tumorigenesis. In this paper, we take a comprehensive look at the current understanding of the relationship between PPARγ and cancer development. The role that epigenetic mechanisms play is also addressed disclosing novel crosstalks between PPARG signaling and the epigenetic machinery and suggesting how this dysregulation may contribute to colon cancer development.

Differential gene expression analysis in fracture callus of patients with regular and failed bone healing

OBJECTIVE

Although several systemic and local factors are known to impair fracture healing, there is still no explanation, why some patients with sufficient fracture stability, showing none of the existing risk factors, still fail to heal normally. An investigation of local gene expression patterns in the fracture gap of patients with non-unions could decisively contribute to a better understanding of the pathophysiology of impaired fracture healing. For the first time, this study compares the expression of a large variety of osteogenic and chondrogenic genes in patients with regular and failed fracture healing.

METHODS

Between March 2006 and May 2007, a total of 130 patients who were surgically treated at the Berufsgenossenschaftliche Unfallklink Ludwigshafen were screened for the study. Tissue samples of patients with normal and failed fracture healing were collected intraoperatively. Patients were divided into groups depending on the fracture date, and only patients with fractures two to four weeks old and patients with non-unions more than 9 months old were included in the final analysis. For the gene expression analysis, a customised cDNA array - containing 226 genes involved in osteo- and chondrogenesis - was used.

RESULTS

In the cDNA array analysis, the expression of eight genes was significantly elevated two-fold or more in the group with failed fracture healing relative to the normal controls. Conversely, no genes were found to be expressed at a higher level in the control group. The identified genes are supposed to be involved in extracellular matrix assembly, cytoskeletal structure, and differentiative and proliferative processes.

CONCLUSIONS

The differences in gene expression pattern indicate a change in the composition and structure of the extracellular matrix, and a possible turn in the healing programme towards fibrous scar tissue formation, leading to non-union.

Transforming growth factor-β-stimulated clone-22 is a negative-feedback regulator of Ras / Raf signaling: Implications for tumorigenesis

Transforming growth factor-β (TGF-β)-stimulated clone-22 (TSC-22), also called TSC22D1-2, is a putative tumor suppressor. We previously identified TSC-22 downstream of an active mutant of fms-like tyrosine kinase-3 (Flt3). Here, we show that TSC-22 works as a tumor suppressor through inhibiting Ras/Raf signaling. Notably, TSC-22 was upregulated by Ras/Raf activation, whereas its upregulation was inhibited by concurrent STAT5 activation. Although TSC-22 was normally retained in the cytoplasm by its nuclear export signal (NES), Ras/Raf activation caused nuclear translocation of TSC-22, but not TSC22D1-1. Unlike glucocorticoid-induced leucine zipper (GILZ/TSC22D3-2) previously characterized as a negative regulator of Ras/Raf signaling, TSC-22 failed to interact physically with Ras/Raf. Importantly, transduction with TSC-22, but not TSC22D1-1, suppressed the growth, transformation and tumorigenesis of NIH3T3 cells expressing oncogenic H-Ras: this suppression was enhanced by transduction with a TSC-22 mutant lacking NES that had accumulated in the nucleus. Collectively, upregulation and nuclear translocation of TSC-22 played an important role in the feedback suppression of Ras/Raf signaling. Consistently, TSC22D1-deficient mice were susceptible to tumorigenesis in a mouse model of chemically-induced liver tumors bearing active mutations of Ras/Raf. Thus, TSC-22 negatively regulated Ras/Raf signaling through a mechanism different from GILZ, implicating TSC-22 as a novel suppressor of oncogenic Ras/Raf-induced tumors.

Regulation of TGF-β signaling by PKC depends on Tsc-22 inducibility

Interactions between various signaling pathways enable a fine control of cellular activities. When the cells are subjected to activation of TGF-β signaling and PKC signaling, PKC phosphorylation of Smad3 abrogates binding and transcriptional activity of Smad3 leading to suppression of TGF-β response. We studied this interaction between Smads and PKC in different cell types to examine cell specificity of the interaction. We found that the outcome of the interaction between Smads and PKC depends on cell types and inducibility of a regulatory molecule Tsc-22. In this report, we showed that induced Tsc-22 leads to enhancement of TGF-β-dependent signaling and the enhancement was blocked by expression of a dominant-negative Tsc-22 mutant. Its effect on cellular differentiation was also examined.

Pathophysiological Roles of PPARgamma in Gastrointestinal Epithelial Cells

Although the highest levels of PPARγ expression in the body have been reported in the gastrointestinal epithelium, little is known about the physiological functions of that receptor in the gut. Moreover, there is considerable controversy concerning the effects of thiazolidinedione PPARγ agonists on the two major diseases of the gastrointestinal track: colorectal cancer and inflammatory bowel disease. We will undertake to review both historical and recently published data with a view toward summarizing what is presently known about the roles of PPARγ in both physiological and pathological processes in the gastrointestinal epithelium.

PPARgamma: The Portrait of a Target Ally to Cancer Chemopreventive Agents

Peroxisome proliferator-activated receptor-gamma (PPARγ), one of three ligand-activated transcription factors named PPAR, has been identified as a molecular target for cancer chemopreventive agents. PPARγ was initially understood as a regulator of adipocyte differentiation and glucose homeostasis while later on, it became evident that it is also involved in cell differentiation, apoptosis, and angiogenesis, biological processes which are deregulated in cancer. It is now established that PPARγ ligands can induce cell differentiation and yield early antineoplastic effects in several tumor types. Moreover, several bioactive natural products with cancer protecting potential are shown to operate through activation of PPARγ. Overall, PPARγ appears to be a prevalent target ally to cancer chemopreventive agents and therefore pursuing research in this area is of great relevance.

Peroxisome proliferator-activated receptors and progression of colorectal cancer

The peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily. These receptors are also ligand-dependent transcription factors responsible for the regulation of cellular events that range from glucose and lipid homeostases to cell differentiation and apoptosis. The importance of these receptors in lipid homeostasis and energy balance is well established. In addition to these metabolic and anti-inflammatory properties, emerging evidence indicates that PPARs can function as either tumor suppressors or accelerators, suggesting that these receptors are potential candidates as drug targets for cancer prevention and treatment. However, conflicting results have emerged regarding the role of PPARs on colon carcinogenesis. Therefore, further investigation is warranted prior to considering modulation of PPARs as an efficacious therapy for colorectal cancer chemoprevention and treatment.

Inhibitory effect of rosiglitazone on the acid-induced intracellular generation of hydrogen peroxide in cultured feline esophageal epithelial cells

Peroxisome proliferator-activated receptor-gamma (PPARγ) agonists have been reported to enhance antioxidant defenses by increasing levels of catalase and copper-zinc superoxide dismutase (Cu/Zn SOD) in oligodendrocyte progenitor cells. In this study, we investigated the effects of the PPARγ agonist, rosiglitazone, on hydrogen peroxide (H(2)O(2)) generation by acidified medium at pH 5.5 (AM5.5), which is in the pH range of duodenogastric refluxates, in primary cultured feline esophageal epithelial cells (EEC). Successful isolation of EEC was identified by immunocytochemistry. AM5.5- and rosiglitazone-induced cell viabilities were determined using 3-(4,5-dimethylthiozol-2-yl)-2,5-diphenyltetrazolium bromide assays. The NAD(P)H oxidase activity was measured, and expression of catalase or SOD protein by AM5.5 in the absence and presence of rosiglitazone was assessed using western blotting analysis. PPARγ protein and mRNA were constitutively expressed in EEC. In the incubation with rosiglitazone alone, cell viability was shown more than 90% at 0-10 μM for 72 h. After exposure to AM5.5 for 8 h, intracellular H(2)O(2) was significantly generated. Treatment with rosiglitazone prior to and during exposure to AM5.5 inhibited the H(2)O(2) generation whereas the specific PPARγ antagonist GW9662 offsets the inhibitory action of rosiglitazone. H(2)O(2) generation was also prevented by a nonspecific ROS scavenger N-acetylcysteine or an inhibitor of NADPH oxidase diphenyleneiodonium. The enhanced AM5.5-induced NAD(P)H oxidase activity was not suppressed by rosiglitazone. Instead, the pretreatment of rosiglitazone enhanced the protein expression of catalase, Cu/Zn SOD, and Mn SOD, which are endogenous antioxidative enzymes. These findings indicate that rosiglitazone inhibits AM5.5-induced intracellular H(2)O(2) production, which occurs via NAD(P)H oxidase activation, by using a PPARγ-dependent pathway, and that the underlying mechanism involves an increase in the expression of catalase and SOD proteins.

The transcriptional programme of contact-inhibition

Proliferation of non-transformed cells is regulated by cell-cell contacts, which are referred to as contact-inhibition. Vice versa, transformed cells are characterised by a loss of contact-inhibition. Despite its generally accepted importance for cell-cycle control, little is known about the intracellular signalling pathways involved in contact-inhibition. Unravelling the molecular mechanisms of contact-inhibition and its loss during tumourigenesis will be an important step towards the identification of novel target genes in tumour diagnosis and treatment. To better understand the underlying molecular mechanisms we identified the transcriptional programme of contact-inhibition in NIH3T3 fibroblast using high-density microarrays. Setting the cut off: >or=1.5-fold, P <or= 0.05, 853 genes and 73 cDNA sequences were differentially expressed in confluent compared to exponentially growing cultures. Importing these data into GenMAPP software revealed a comprehensive list of cell-cycle regulatory genes mediating G0/G1 arrest, which was confirmed by RT-PCR and Western blot. In a narrow analysis (cut off: >or=2-fold, P <or= 0.002), we found 110 transcripts to be differentially expressed representing 107 genes and 3 cDNA sequences involved, for example, in proliferation, signal transduction, transcriptional regulation, cell adhesion and communication. Interestingly, the majority of genes was upregulated indicating that contact-inhibition is not a passive state, but actively induced. Furthermore, we confirmed differential expression of eight genes by semi-quantitative RT-PCR and identified the potential tumour suppressor transforming growth factor-beta (TGF-beta)-1-induced clone 22 (TSC-22; tgfb1i4) as a novel protein to be induced in contact-inhibited cells.

Peroxisome proliferator activated receptor-γ and the ubiquitin-proteasome system in colorectal cancer

Peroxisome proliferator activated receptor-γ (PPARγ), a transcription factor of the nuclear receptor superfamily plays a significant role in colorectal cancer pathogenesis. In most experimental systems PPARγ activation has tumor suppressing effects in the colon. PPARγ is regulated at multiple levels by the ubiquitin-proteasome system (UPS). At a first level, UPS regulates PPARγ transcription. This regulation involves both PPARγ transcription specific factors and the general transcription machinery. At a second level UPS regulates PPARγ and its co-factors themselves, as PPARγ and many co-factors are proteasome substrates. At a third level of regulation, transduction pathways working in parallel but also having interrelations with PPARγ are regulated by the UPS, creating a network of regulation in the colorectal carcinogenesis-related pathways that are under UPS control. Activation of PPARγ transcription by direct pharmacologic activators and by stabilization of its molecule by proteasome inhibitors could be strategies to be exploited in colorectal cancer treatment.

Transforming Growth Factor-{beta}-Stimulated Clone-22 Is an Androgen-Regulated Gene That Enhances Apoptosis in Prostate Cancer following Insulin-Like Growth Factor-I Receptor Inhibition

PURPOSE: Inhibition of insulin-like growth factor (IGF) signaling using the human IGF-I receptor monoclonal antibody A12 is most effective at inducing apoptosis in prostate cancer xenografts in the presence of androgen. We undertook this study to determine mechanisms for increased apoptosis by A12 in the presence of androgens. Experimental Methods: The castrate-resistant human xenograft LuCaP 35 V was implanted into intact or castrate severe combined immunodeficient mice and treated with A12 weekly. After 6 weeks of tumor growth, animals were sacrificed and tumors were removed and analyzed for cell cycle distribution/apoptosis and cDNA arrays were done. RESULTS: In castrate mice, the tumors were delayed in G(2) with no apoptosis; in contrast, tumors from intact mice underwent apoptosis with either G(1) or G(2) delay. Transforming growth factor-beta-stimulated clone-22 (TSC-22) was significantly elevated in tumors from the intact mice compared with castrate mice, especially in those tumors with the highest levels of apoptosis. To further determine the function of TSC-22, we transfected various human prostate cancer cell lines with a plasmid expressing TSC-22. Cell lines overexpressing TSC-22 showed an increase in apoptosis and a delay in G(1). When these cell lines were placed subcutaneously in athymic nude mice, a decreased number of animals formed tumors and the rate of tumor growth was decreased compared with control tumors. CONCLUSIONS: These data indicate that IGF-I receptor inhibition in the presence of androgen has an enhanced effect on decreasing tumor growth, in part, through increased expression of the tumor suppressor gene TSC-22. (Clin Cancer Res 2009;15(24):7634-41).

KLF4-dependent, PPARgamma-induced expression of GPA33 in colon cancer cell lines

The glycoprotein A33 (GPA33) is a colon cancer antigen. Phase I trials with 131I and 125I monoclonal antibody A33 in colon carcinoma patients showed excellent localization to colorectal cancer and some evidence of tumor response. Using DNA microarrays, we have identified the GPA33 gene as a target of PPARgamma in HT29-Cl.16E colon cancer cells. Treatment of HT29-Cl.16E, Caco2, SW1116 and LS174T colon cancer cells with the PPARgamma agonist GW7845 induced a 2- to 6-fold increase in GPA33 mRNA as determined by real-time PCR. This induction was also found in HT29-Cl.16E cells treated with rosiglitazone and ciglitazone and was prevented by cotreatment with the PPARgamma antagonist GW9662, indicating that this regulation was PPARgamma dependent. No canonical PPAR responsive element was found in the GPA33 promoter. We therefore analyzed the expression of transcription factors involved in GPA33 expression. CDXl, CDX2 and KLF5 expression was not modified by PPARgamma activation. By contrast, a significant increase in KLF4 was seen, both at mRNA and protein levels. Furthermore, chromatin immunoprecipitation studies demonstrated that an increased amount of KLF4 protein was bound to the GPA33 promoter in cells treated with rosiglitazone. Finally, downregulation of KLF4 expression by siRNA reduced rosiglitazone-induced GPA33 expression. This indicates that PPARgamma activation induces KLF4 expression, which in turn increases GPA33 expression. We also demonstrate that PPARgamma activation leads to increased (p21WAF1/Cip1 and keratin 19) or decreased (cyclin D1) expression of known KLF4 targets, suggesting that KLF4 is a nodal player in a network of PPARgamma-regulated genes.

Therapeutic potential of n-3 polyunsaturated fatty acids in disease

PURPOSE

The potential therapeutic benefits of supplementation with n-3 polyunsaturated fatty acids (PUFAs) in various diseases are reviewed, and the antiinflammatory actions, activity, and potential drug interactions and adverse effects of n-3 PUFAs are discussed.

SUMMARY

Fish oils are an excellent source of long-chain n-3 PUFAs, such as eicosapentaenoic acid and docosahexaenoic acid. After consumption, n-3 PUFAs can be incorporated into cell membranes and reduce the amount of arachidonic acid available for the synthesis of proinflammatory eicosanoids (e.g., prostaglandins, leukotrienes). Likewise, n-3 PUFAs can also reduce the production of inflammatory cytokines, such as tumor necrosis factor alpha, interleukin-1, and interleukin-6. Considerable research has been conducted to evaluate the potential therapeutic effects of fish oils in numerous conditions, including arthritis, coronary artery disease, inflammatory bowel disease, asthma, and sepsis, all of which have inflammation as a key component of their pathology. Additional investigations into the use of supplementation with fish oils in patients with neural injury, cancer, ocular diseases, and critical illness have recently been conducted. The most commonly reported adverse effects of fish oil supplements are a fishy aftertaste and gastrointestinal upset. When recommending an n-3 PUFA, clinicians should be aware of any possible adverse effect or drug interaction that, although not necessarily clinically significant, may occur, especially for patients who may be susceptible to increased bleeding (e.g., patients taking warfarin).

CONCLUSION

The n-3 PUFAs have been shown to be efficacious in treating and preventing various diseases. The wide variation in dosages and formulations used in studies makes it difficult to recommend dosages for specific treatment goals.

TSC-22 contributes to hematopoietic precursor cell proliferation and repopulation and is epigenetically silenced in large granular lymphocyte leukemia

Aberrant methylation of tumor suppressor genes can lead to their silencing in many cancers. TSC-22 is a gene silenced in several solid tumors, but its function and the mechanism(s) responsible for its silencing are largely unknown. Here we demonstrate that the TSC-22 promoter is methylated in primary mouse T or natural killer (NK) large granular lymphocyte (LGL) leukemia and this is associated with down-regulation or silencing of TSC-22 expression. The TSC-22 deregulation was reversed in vivo by a 5-aza-2'-deoxycytidine therapy of T or NK LGL leukemia, which significantly increased survival of the mice bearing this disease. Ectopic expression of TSC-22 in mouse leukemia or lymphoma cell lines resulted in delayed in vivo tumor formation. Targeted disruption of TSC-22 in wild-type mice enhanced proliferation and in vivo repopulation efficiency of hematopoietic precursor cells (HPCs). Collectively, our data suggest that TSC-22 normally contributes to the regulation of HPC function and is a putative tumor suppressor gene that is hypermethylated and silenced in T or NK LGL leukemia.

The effect of Saccharomyces boulardii on human colon cells and inflammation in rats with trinitrobenzene sulfonic acid-induced colitis

Saccharomyces boulardii (S. boulardii) has beneficial effects in the treatment of intestinal inflammation; however, little is known about the mechanisms by which these effects occur. We investigated the effects of S. boulardii on the expression of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) and interleukin-8 (IL-8), using human HT-29 colonocytes and a rat model of trinitrobenzene sulfonic acid (TNBS)-induced colitis. The effect of S. boulardii on gene expression was assessed by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR), and Northern blot and Western blot assays. Pharmacological inhibitors for various signaling pathways were used to determine the signaling pathways implicated in the S. boulardii regulation of PPAR-gamma and IL-8. We found that S. boulardii up-regulated and down-regulated PPAR-gamma and IL-8 expression at the transcription level, both in vitro and in vivo (P < 0.05, respectively). Saccharomyces boulardii blocked tumor necrosis factor-alpha (TNF-alpha) regulation of PPAR-gamma and IL-8 through disruption of TNF-alpha-mediated nuclear factor kappa B (NF-kappaB) activation. Furthermore, S. boulardii suppressed colitis and expression of pro-inflammatory cytokine genes in vivo (P < 0.05, respectively). Our study demonstrated that S. boulardii reduces colonic inflammation and regulates inflammatory gene expression.

THG-1pit moves to nucleus at the onset of cerebellar granule neurons apoptosis

Thg-1pit (Tsc22d4), a murine gene belonging to the TGF-beta1-stimulated clone 22 domain (TSC22D) family, is expressed in developing and adult cerebellar granule neurons and mature Purkinje cells. We have studied THG-1pit function in primary cultures of mouse cerebellar granule neurons maintained in vitro in the presence of a medium containing 25 mM K+ (differentiating condition) or 5 mM K+ (pro-apoptotic condition), and determined the effect of culture medium, TGF-beta1 and IGF-1 on THG-1pit expression and intracellular localization. Thg-1pit encoded a 42 kDa MW protein and other, higher MW and developmentally-regulated forms. Cell exposure to 5 mM K+ elicited early and/or late waves of Thg-1pit transcription, depending on the presence/absence of TGF-beta1, and caused THG-1pit to massively and transiently move from cytoplasm and neurites to the nucleus. THG-1pit nuclear entrance was concomitant to that of AIF, suggesting that THG-1pit is involved in the induction of granule neuron apoptosis.

Peroxisome proliferator-activated receptor gamma down-regulates follistatin in intestinal epithelial cells through SP1

Activation of peroxisome proliferator-activated receptor gamma (PPARgamma) down-regulates the expression of follistatin mRNA in intestinal epithelial cells in vivo. The mechanism of PPARgamma-mediated down-regulation of follistatin was investigated using non-transformed, rat intestinal epithelial cells (RIE-1). RIE cells expressed activin A, the activin receptors ActRI and ActRII, and the follistatin-315 mRNA. RIE-1 cells responded to endogenous activin A, and this response was antagonized by follistatin, as evidenced by changes in cell growth and regulation of an activin-responsive reporter. Using RIE-1 cells, we show that activation of PPARgamma by rosiglitazone reduced follistatin mRNA levels in a dose- and concentration-dependent manner. Down-regulation of follistatin by rosiglitazone required the DNA binding domain of PPARgamma and was dependent upon dimerization with the retinoid X receptor. Inhibition of follistatin expression by rosiglitazone was not associated with decreased follistatin mRNA stability, suggesting that regulation may be at the promoter level. Analysis of the follistatin promoter revealed consensus binding sites for AP-1, AP-2, and Sp1. Targeting the AP-1 pathway with SP600125, an inhibitor of JNK, and TAM67, a dominant negative c-Jun, had no effect on PPARgamma-mediated down-regulation of follistatin. However, the follistatin promoter was dramatically regulated by Sp1, and this regulation was inhibited by PPARgamma expression. Knockdown of Sp1 expression relieved repression of follistatin levels by rosiglitazone. Moreover, PPARgamma was found to interact with Sp1 and repress its transcriptional activation function. Collectively, our data indicate that repression of Sp1 transcriptional activity by PPARgamma is the underlying mechanism responsible for PPARgamma-mediated regulation of follistatin expression.

Identification of the transcriptional response of human intestinal mucosa to Lactobacillus plantarum WCFS1 in vivo

Background

There is limited knowledge on the extent and dynamics of the mucosal response to commensal and probiotic species in the human intestinal lumen. This study aimed to identify the acute, time-dependent responses of intestinal mucosa to commensal Lactobacillus plantarum WCFS1 in vivo in two placebo-controlled human intervention studies in healthy volunteers. Transcriptional changes in duodenal mucosa upon continuous intraduodenal infusion of L. plantarum WCFS1 for one- and six h, respectively, were studied using oro- and nasogastric intubations with dedicated orogastric catheters and tissue sampling by standard flexible gastroduodenoscopy.

Results

One- and six-h exposure of small intestinal mucosa to L. plantarum WCFS1 induced differential expression of 669 and 424 gene reporters, respectively. While short-term exposure to L. plantarum WCFS1 inhibited fatty acid metabolism and cell cycle progression, cells switched to a more proliferative phase after prolonged exposure with an overall expression profile characterized by upregulation of genes involved in lipid metabolism, cellular growth and development. Cell death and immune responses were triggered, but cell death-executing genes or inflammatory signals were not expressed. Proteome analysis showed differential expression of several proteins. Only the microsomal protein 'microsomal triglyceride transfer protein' was regulated on both the transcriptional and the protein level in all subjects.

Conclusion

Overall, this study showed that intestinal exposure to L. plantarum WCFS1 induced consistent, time-dependent transcriptional responses in healthy intestinal mucosa. This extensive exploration of the human response to L. plantarum WCFS1 could eventually provide molecular support for specific or probiotic activity of this strain or species, and exemplifies the strength of the applied technology to identify the potential bio-activity of microbes in the human intestine.

The Drosophila homolog of human tumor suppressor TSC-22 promotes cellular growth, proliferation, and survival

TSC22D1, which encodes transforming growth factor beta-stimulated clone 22 (TSC-22), is thought to be a tumor suppressor because its expression is lost in many glioblastoma, salivary gland, and prostate cancers. TSC-22 is the founding member of the TSC-22/DIP/Bun family of leucine zipper transcription factors; its functions have not been investigated in a multicellular environment. Genetic studies in the model organism Drosophila melanogaster often provide fundamental insights into mechanisms disrupted in carcinogenesis, because of the strong evolutionary conservation of molecular mechanisms between flies and humans. Whereas humans and mice have four TSC-22 domain genes with numerous isoforms, Drosophila has only one TSC-22 domain gene, bunched (bun), which encodes both large and small protein isoforms. Surprisingly, Drosophila Bun proteins promote cellular growth and proliferation in ovarian follicle cells. Loss of both large isoforms has the strongest phenotypes, including increased apoptosis. Cultured S2 cells depleted for large Bun isoforms show increased apoptosis and less frequent cell division, with decreased cell size. Altogether, these data indicate that Drosophila TSC-22/DIP/Bun proteins are necessary for cellular growth, proliferation, and survival both in culture and in an epithelial context. Previous work demonstrated that bun prevents recruitment of epithelial cells to a migratory fate and, thus, maintains epithelial organization. We speculate that reduced TSC22D1 expression generally reduces cellular fitness and only contributes to carcinogenesis in specific tissue environments.

TSC22D1 and PSAP predict clinical outcome of tamoxifen treatment in patients with recurrent breast cancer

Purpose Two genes, TSC22 domain family, member 1 (TSC22D1) and prosaposin (PSAP) were identified in an in vitro functional screen for genes having a causative role in tamoxifen resistance. These genes were also present in our previously established 81-gene signature for resistance to first-line tamoxifen therapy. The aim of this study was to investigate the predictive value of these genes for tamoxifen therapy failure in patients with recurrent breast cancer. Experimental Design The mRNA levels of TSC22D1 and PSAP were analyzed by quantitative real-time polymerase chain reaction (qRT-PCR) in 223 estrogen receptor-positive primary breast tumors of patients with recurrent disease treated with first-line tamoxifen therapy. The main objective of this study was the length of progression-free survival (PFS). Results High mRNA levels of TSC22D1 and PSAP were significantly associated with shorter PFS and both were independent of the traditional predictive factors (HR = 1.30, 95% CI = 1.04-1.64 P = 0.023; and HR = 1.40, 95% CI = 1.03-1.88, P = 0.029, respectively). In multivariate analysis, patients with high mRNA levels of both genes associated significantly with no clinical benefit (OR = 0.19, 95% CI = 0.06-0.62, P = 0.006) and had the shortest PFS (HR = 2.05, 95% CI = 1.29-3.25, P = 0.002). Conclusion These results confirm our previous in vitro and tumor-related findings and are indicative for the failure of tamoxifen treatment in breast-cancer patients. Both TSC22D1 and PSAP are associated with clinical outcome and may have a functional role in therapy resistance.

Bunched, the Drosophila homolog of the mammalian tumor suppressor TSC-22, promotes cellular growth

BACKGROUND

Transforming Growth Factor-beta1 stimulated clone-22 (TSC-22) is assumed to act as a negative growth regulator and tumor suppressor. TSC-22 belongs to a family of putative transcription factors encoded by four distinct loci in mammals. Possible redundancy among the members of the TSC-22/Dip/Bun protein family complicates a genetic analysis. In Drosophila, all proteins homologous to the TSC-22/Dip/Bun family members are derived from a single locus called bunched (bun).

RESULTS

We have identified bun in an unbiased genetic screen for growth regulators in Drosophila. Rather unexpectedly, bun mutations result in a growth deficit. Under standard conditions, only the long protein isoform BunA - but not the short isoforms BunB and BunC - is essential and affects growth. Whereas reducing bunA function diminishes cell number and cell size, overexpression of the short isoforms BunB and BunC antagonizes bunA function.

CONCLUSION

Our findings establish a growth-promoting function of Drosophila BunA. Since the published studies on mammalian systems have largely neglected the long TSC-22 protein version, we hypothesize that the long TSC-22 protein is a functional homolog of BunA in growth regulation, and that it is antagonized by the short TSC-22 protein.

Role of promyelocytic leukemia zinc finger protein in proliferation of cultured human corneal endothelial cells

PURPOSE

To review the role of promyelocytic leukemia zinc finger (PLZF), a transcriptional repressor and negative regulator of cell cycling, in the proliferation of cultured human corneal endothelial cells (HCECs).

METHODS

The expression pattern of PLZF mRNA was determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and real-time quantitative PCR in HCECs and normal human corneal epithelia. The effect of cell-cell contact on expression of the PLZF gene was studied after incubation of the cultured HCECs in EDTA. The proliferation rate of cultured HCECs was assayed by a real-time electronic sensing (RT-CES) system, and DNA microarray analysis was performed to find the PLZF-regulating genes in cultured HCECs infected with LacZ- and PLZF-carrying adenoviruses (Ad-LacZ, Ad-PLZF).

RESULTS

PLZF mRNA was expressed in HCECs in vivo and in completely confluent HCECs but not in subconfluent HCECs in vitro. Real-time PCR showed that the expression of PLZF mRNA was decreased by approximately 20-fold when incubated with EDTA and returned to a normal level as the cell-cell contact reformed. Cell proliferation assay by the RT-CES system showed that infection of cultured HCECs with Ad-PLZF inhibited proliferation.

CONCLUSIONS

These findings suggest that PLZF plays an important role in the suppression of proliferation of HCECs.

Functional genomic analysis reveals cross-talk between peroxisome proliferator-activated receptor gamma and calcium signaling in human colorectal cancer cells

Activation of PPARgamma in MOSER cells inhibits anchorage-dependent and anchorage-independent growth and invasion through Matrigel-coated transwell membranes. We carried out a longitudinal two-class microarray analysis in which mRNA abundance was measured as a function of time in cells treated with a thiazolidinedione PPARgamma agonist or vehicle. A statistical machine learning algorithm that employs an empirical Bayesian implementation of the multivariate HotellingT2 score was used to identify differentially regulated genes. HotellingT2 scores, MB statistics, and maximum median differences were used as figures of merit to interrogate genomic ontology of these targets. Three major cohorts of genes were regulated: those involved in metabolism, DNA replication, and migration/motility, reflecting the cellular phenotype that attends activation of PPARgamma. The bioinformatic analysis also inferred that PPARgamma regulates calcium signaling. This response was unanticipated, because calcium signaling has not previously been associated with PPARgamma activation. Ingenuity pathway analysis inferred that the nodal point in this cross-talk was Down syndrome critical region 1 (DSCR1). DSCR1 is an endogenous calcineurin inhibitor that blocks dephosphorylation and activation of members of the cytoplasmic component of nuclear factor of activated T cells transcription factors. Lentiviral short hairpin RNA-mediated knockdown of DSCR1 blocks PPARgamma inhibition of proliferation and invasion, indicating that DSCR1 is required for suppression of transformed properties of early stage colorectal cancer cells by PPARgamma. These data reveal a novel, heretofore unappreciated link between PPARgamma and calcium signaling and indicate that DSCR1, which has previously been thought to function by suppression of the angiogenic response in endothelial cells, may also play a direct role in transformation of epithelial cells.

A dominant negative allele of the Drosophila leucine zipper protein Bunched blocks bunched function during tissue patterning

The bunched (bun) gene encodes the Drosophila member of the TSC-22/GILZ family of leucine zipper transcriptional regulators. The bun locus encodes multiple BUN protein isoforms and has diverse roles during patterning of the eye, wing margin, dorsal notum and eggshell. Here we report the construction and activity of a dominant negative allele (BunDN) of the BUN-B isoform. In the ovary, BunDN expression in the follicle cells (FC) resulted in epithelial defects including aberrant accumulation of DE-cadherin and failure to rearrange into columnar FC cell shapes. BunDN expression in the posterior FC led to loss of epithelial integrity associated with extensive apoptosis. BunDN FC phenotypes collectively resemble loss-of-function bun mutant phenotypes. BunDN expression using tissue-specific imaginal disk drivers resulted in characteristic cuticular patterning defects that were enhanced by bun mutations and suppressed by co-expression of the BUN-B protein isoform. These data indicate that BunDN has dominant negative activity useful to identify bun functions and genetic interactions that occur during tissue patterning.

Peroxisome proliferator-activated receptor γ (PPARγ) and colorectal carcinogenesis

Peroxisome proliferator-activated receptor gamma (PPARgamma) a member of the nuclear transcription factor superfamily is playing a role in colon carcinogenesis. Although not all in vivo models agree, PPARgamma seems to have suppressive effects in this process favoring apoptosis and inhibiting the cell cycle by inducing expression of apoptosis and senescence proteins. With the recent discovery that anti-diabetic class of drugs thiazolidinediones act through activation of PPARgamma, interest in this transcription factor has increased as it can now be pharmacologically activated in order to obtain tumor suppression. In addition, thiazolidinediones and other PPARgamma agonists possess PPARgamma-independent anti-tumor effects. Although PPARgamma agonists may not by themselves be capable to induce clinical tumor regression, their combination with chemotherapy drugs or other targeted therapies is worth pursuing in the treatment of colorectal carcinoma.

TSC-box is essential for the nuclear localization and antiproliferative effect of XTSC-22

Transforming growth factor-beta1-stimulated clone 22 (TSC-22) encodes a leucine zipper-containing protein that is highly conserved among various species. Mammalian TSC-22 is a potential tumor suppressor gene. It translocates into nuclei and suppresses cell division upon antiproliferative stimuli. In human colon carcinoma cells, TSC-22 inhibits cell growth by upregulating expression of the p21 gene, a cyclin-dependent kinase (Cdk) inhibitor. We previously showed that the Xenopus laevis homologue of the TSC-22 gene (XTSC-22) is required for cell movement during gastrulation through cell cycle regulation. In this report, we investigated the molecular mechanism of the antiproliferative effect of XTSC-22. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis suggested that XTSC-22 did not affect the expression levels of the p21 family of Cdk inhibitors or other cell cycle regulators. Analysis of deletion mutants of XTSC-22 revealed that nuclear localization of the N-terminal TSC-box is necessary for cell cycle inhibition by XTSC-22. Further experiments suggested that p27Xic1, a key Cdk inhibitor in Xenopus, interacts with XTSC-22. Because p27Xic1 is a cell cycle inhibitor with a nuclear localization signal, it is possible that XTSC-22 suppresses cell division by translocating into the nucleus with p27Xic1, where it may potentiate the intranuclear action of p27Xic1.

Notch signaling links interactions between the C/EBP homolog slow border cells and the GILZ homolog bunched during cell migration

In the follicle cell (FC) epithelium that surrounds the Drosophila egg, a complex set of cell signals specifies two cell fates that pattern the eggshell: the anterior centripetal FC that produce the operculum and the posterior columnar FC that produce the main body eggshell structure. We have previously shown that the long-range morphogen DPP represses the expression of the bunched (bun) gene in the anterior-most centripetal FC. bun, which encodes a homolog of vertebrate TSC-22/GILZ, in turn represses anterior gene expression and antagonizes Notch signaling to restrict centripetal FC fates in posterior cells. From a screen for novel targets of bun repression we have identified the C/EBP homolog slow border cells (slbo). At stage 10A, slbo expression overlaps bun in anterior FC; by stage 10B they repress each other's expression to establish a sharp slbo/bun expression boundary. The precise position of the slbo/bun expression boundary is sensitive to Notch signaling, which is required for both slbo activation and bun repression. As centripetal migration proceeds from stages 10B-14, slbo represses its own expression and both slbo loss-of-function mutations and overexpression approaches reveal that slbo is required to coordinate centripetal migration with nurse cell dumping. We propose that in anterior FC exposed to a Dpp morphogen gradient, high and low levels of slbo and bun, respectively, are established by modulation of Notch signaling to direct threshold cell fates. Interactions among Notch, slbo and bun resemble a conserved signaling cassette that regulates mammalian adipocyte differentiation.

Peroxisome proliferator-activated receptor-gamma regulates expression of PDX-1 and NKX6.1 in INS-1 cells

In the 60% pancreatectomy (Px) rat model of beta-cell adaptation, normoglycemia is maintained by an initial week of beta-cell hyperplasia that ceases and is followed by enhanced beta-cell function. It is unknown how this complex series of events is regulated. We studied isolated islets and pancreas sections from 14-day post-Px versus sham-operated rats and observed a doubling of beta-cell nuclear peroxisome proliferator-activated receptor (PPAR)-gamma protein, along with a 2-fold increase in nuclear pancreatic duodenal homeobox (Pdx)-1 protein and a 1.4-fold increase in beta-cell nuclear Nkx6.1 immunostaining. As PPAR-gamma activation is known to both lower proliferation and have prodifferentiation effects in many tissues, we studied PPAR-gamma actions in INS-1 cells. A 3-day incubation with the PPAR-gamma agonist troglitazone reduced proliferation and increased Pdx-1 and Nkx6.1 immunostaining, along with glucokinase and GLUT2. Also, a 75% knockdown of PPAR-gamma using RNA interference lowered the mRNA levels of Pdx-1, glucokinase, GLUT2, and proinsulin II by more than half. Our results show a dual effect of PPAR-gamma in INS-1 cells: to curtail proliferation and promote maturation, the latter via enhanced expression of Pdx-1 and Nkx6.1. Additional studies are needed to determine whether there is a regulatory role for PPAR-gamma signaling in the beta-cell adaptation following a 60% Px in rats.

Peroxisome proliferator-activated receptor gamma is a Zac target gene mediating Zac antiproliferation

Zac is a C2H2 zinc finger protein, which regulates apoptosis and cell cycle arrest through DNA binding and transactivation. During tumorigenesis and in response to mitogenic activation, Zac gene expression is down-regulated in a methylation-sensitive manner. As yet, no target genes have been identified that could explain the potent antiproliferative function of Zac. Here, applying genome-wide expression analysis, we identify peroxisome proliferator-activated receptor gamma (PPARgamma) as a new bona fide Zac target gene, which is induced by direct Zac binding to the proximal PPARgamma1 promoter. We show that in human colon carcinoma cells, ZAC activates expression of PPARgamma target genes in a PPARgamma-dependent manner. Moreover, we show that treatment of pituitary tumor cells with octreotide, a somatostatin analogue, leads to Zac induction and subsequent Zac-dependent up-regulation of PPARgamma, which thereupon mediates part of the antiproliferative activity of Zac. Our work provides a first step toward elucidating a functional relationship between Zac and PPARgamma that could be relevant to the understanding of tumorigenesis and diabetes as well.

Peroxisome proliferator-activated receptor gamma (PPARgamma) regulates trefoil factor family 2 (TFF2) expression in gastric epithelial cells

Although trefoil factor family 2 (TFF2) plays a critical role in the defense and repair of gastric mucosa, the regulatory mechanism of TFF2 expression is not fully understood. In this study, we investigated the regulation of TFF2 expression by peroxisome proliferator-activated receptor gamma (PPARgamma) in gastric epithelial cells. MKN45 gastric cells were used. TFF2 mRNA expression was analyzed by real-time quantitative RT-PCR. The promoter sequence of the human TFF2 gene was cloned into pGL3-basic vector for reporter gene assays. Ciglitazone was mainly used as a specific PPARgamma ligand. MKN45 cells expressed functional PPARgamma proteins. Endogenous TFF2 mRNA expression and TFF2 reporter gene transcription was significantly up-regulated by ciglitazone in a dose-dependent manner. Reporter gene assays showed that two distinct cis-elements are involved in the response to PAPRgamma activation. Within one of these element (nucleotides -558 to -507), we identified a functional peroxisome proliferator responsive element (PPRE) at -522 (5'-GGGACAAAGGGCA-3'). Electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) assay confirmed the binding of PPARgamma to this sequence. Another element (nucleotides -407 to -358) appeared to be a composite enhancer element indirectly regulated by PPARgamma and a combination of these two cis-elements was required for the full response of the human TFF2 gene expression to PPARgamma. These data demonstrate that human TFF2 gene is a direct target of PPARgamma in gastric epithelial cells. Since TFF2 is a critical gastroprotective agent, PPARgamma may be involved in the gastric mucosal defense through regulating TFF2 expression in humans.

Differential expression of TGFbeta-stimulated clone 22 in normal prostate and prostate cancer

The transforming growth factor-beta (TGFbeta) superfamily and its downstream effector genes are key regulators of epithelial homeostasis. Altered expression of these genes may be associated with malignant transformation of the prostate gland. The cDNA array analysis of differential expression of the TGFbeta superfamily and functionally related genes between patient-matched noncancerous prostate (NP) and prostate cancer (PC) bulk tissue specimens highlighted two genes, namely TGFbeta-stimulated clone-22 (TSC-22) and Id4. Verification of their mRNA expression by real-time PCR in patient-matched NP and PC bulk tissue, in laser-captured pure epithelial and cancer cells and in NP and PC cell lines confirmed TSC-22 underexpression, but not Id4 overexpression, in PC and in human PC cell lines. Immunohistochemical analysis showed that TSC-22 protein expression in NP is restricted to the basal cells and colocalizes with the basal cell marker cytokeratin 5. In contrast, all matched PC samples lack TSC-22 immunoreactivity. Likewise, PC cell lines do not show detectable TSC-22 protein expression as shown by immunoblotting. TSC-22 should be considered as a novel basal cell marker, potentially useful for studying lineage determination within the epithelial compartment of the prostate. Conversely, lack of TSC-22 seems to be a hallmark of malignant transformation of the prostate epithelium. Accordingly, TSC-22 immunohistochemistry may prove to be a diagnostic tool for discriminating benign lesions from malignant ones of the prostate. The suggested tumour suppressor function of TSC-22 warrants further investigation on its role in prostate carcinogenesis and on the TSC-22 pathway as a candidate therapeutic target in PC.

From molecular action to physiological outputs: peroxisome proliferator-activated receptors are nuclear receptors at the crossroads of key cellular functions

Peroxisome proliferator-activated receptors (PPARs) compose a family of three nuclear receptors which act as lipid sensors to modulate gene expression. As such, PPARs are implicated in major metabolic and inflammatory regulations with far-reaching medical consequences, as well as in important processes controlling cellular fate. Throughout this review, we focus on the cellular functions of these receptors. The molecular mechanisms through which PPARs regulate transcription are thoroughly addressed with particular emphasis on the latest results on corepressor and coactivator action. Their implication in cellular metabolism and in the control of the balance between cell proliferation, differentiation and survival is then reviewed. Finally, we discuss how the integration of various intra-cellular signaling pathways allows PPARs to participate to whole-body homeostasis by mediating regulatory crosstalks between organs.