Sp1-decoy oligodeoxynucleotide inhibits high glucose-induced mesangial cell proliferation

AMPK-SP1-Guided Dynein Expression Represents a New Energy-Responsive Mechanism and Therapeutic Target for Diabetic Nephropathy

Key Points

AMP kinase senses diabetic stresses in podocytes, subsequently upregulates specificity protein 1–mediated dynein expression and promotes podocyte injury. Pharmaceutical restoration of dynein expression by targeting specificity protein 1 represents an innovative therapeutic strategy for diabetic nephropathy.

Background

Diabetic nephropathy (DN) is a major complication of diabetes. Injury to podocytes, epithelial cells that form the molecular sieve of a kidney, is a preclinical feature of DN. Protein trafficking mediated by dynein, a motor protein complex, is a newly recognized pathophysiology of diabetic podocytopathy and is believed to be derived from the hyperglycemia-induced expression of subunits crucial for the transportation activity of the dynein complex. However, the mechanism underlying this transcriptional signature remains unknown.

Methods

Through promoter analysis, we identified binding sites for transcription factor specificity protein 1 (SP1) as the most shared motif among hyperglycemia-responsive dynein genes. We demonstrated the essential role of AMP-activated protein kinase (AMPK)–regulated SP1 in the transcription of dynein subunits and dynein-mediated trafficking in diabetic podocytopathy using chromatin immunoprecipitation quantitative PCR and live cell imaging. SP1-dependent dynein-driven pathogenesis of diabetic podocytopathy was demonstrated by pharmaceutical intervention with SP1 in a mouse model of streptozotocin-induced diabetes.

Results

Hyperglycemic conditions enhance SP1 binding to dynein promoters, promoted dynein expression, and enhanced dynein-mediated mistrafficking in cultured podocytes. These changes can be rescued by chemical inhibition or genetic silencing of SP1. The direct repression of AMPK, an energy sensor, replicates hyperglycemia-induced dynein expression by activating SP1. Mithramycin inhibition of SP1-directed dynein expression in streptozotocin-induced diabetic mice protected them from developing podocytopathy and prevented DN progression.

Conclusions

Our work implicates AMPK-SP1–regulated dynein expression as an early mechanism that translates energy disturbances in diabetes into podocyte dysfunction. Pharmaceutical restoration of dynein expression by targeting SP1 offers a new therapeutic strategy to prevent DN.

Decoys as potential therapeutic tools for diabetes

Current therapeutic approaches for diabetes are focused on improving glycemic control to prevent diabetes-related complications, but such approached are not completely successful. Decoy technologies such as decoy oligodeoxynucleotides (ODNs) and decoy peptides have emerged as therapeutic tools in diabetes. Decoy ODNs carry a DNA recognition motif for the binding of transcription factors in order to trap them and block their effects, whereas decoy peptides mimic the binding structure of the receptor protein, bind to the docking site of the target ligand, and prevent the interaction of the ligand and receptor. This review summarizes the technologies that have been developed to date and the studies that have investigated the therapeutic effects of decoy ODNs and peptides in diabetes.

Cilostazol ameliorates diabetic nephropathy by inhibiting highglucose- induced apoptosis

Diabetic nephropathy (DN) is a hyperglycemia-induced progressive development of renal insufficiency. Excessive glucose can increase mitochondrial reactive oxygen species (ROS) and induce cell damage, causing mitochondrial dysfunction. Our previous study indicated that cilostazol (CTZ) can reduce ROS levels and decelerate DN progression in streptozotocin (STZ)-induced type 1 diabetes. This study investigated the potential mechanisms of CTZ in rats with DN and in high glucose-treated mesangial cells. Male Sprague-Dawley rats were fed 5 mg/kg/day of CTZ after developing STZ-induced diabetes mellitus. Electron microscopy revealed that CTZ reduced the thickness of the glomerular basement membrane and improved mitochondrial morphology in mesangial cells of diabetic kidney. CTZ treatment reduced excessive kidney mitochondrial DNA copy numbers induced by hyperglycemia and interacted with the intrinsic pathway for regulating cell apoptosis as an antiapoptotic mechanism. In high-glucose-treated mesangial cells, CTZ reduced ROS production, altered the apoptotic status, and down-regulated transforming growth factor beta (TGF-β) and nuclear factor kappa light chain enhancer of activated B cells (NF-κB). Base on the results of our previous and current studies, CTZ deceleration of hyperglycemia-induced DN is attributable to ROS reduction and thereby maintenance of the mitochondrial function and reduction in TGF-β and NF-κB levels.

High Glucose Up-regulates ADAM17 through HIF-1α in Mesangial Cells

We previously showed that ADAM17 mediates high glucose-induced matrix production by kidney mesangial cells. ADAM17 expression is increased in diabetic kidneys, suggesting that its up-regulation may augment high glucose profibrotic responses. We thus studied the effects of high glucose on ADAM17 gene regulation. Primary rat mesangial cells were treated with high glucose (30 mm) or mannitol as osmotic control. High glucose dose-dependently increased ADAM17 promoter activity, transcript, and protein levels. This correlated with augmented ADAM17 activity after 24 h versus 1 h of high glucose. We tested involvement of transcription factors shown in other settings to regulate ADAM17 transcription. Promoter activation was not affected by NF-κB or Sp1 inhibitors, but was blocked by hypoxia-inducible factor-1α (HIF-1α) inhibition or down-regulation. This also prevented ADAM17 transcript and protein increases. HIF-1α activation by high glucose was shown by its increased nuclear translocation and activation of the HIF-responsive hypoxia-response element (HRE)-luciferase reporter construct. Assessment of ADAM17 promoter deletion constructs coupled with mutation analysis and ChIP studies identified HIF-1α binding to its consensus element at -607 as critical for the high glucose response. Finally, inhibitors of epidermal growth factor receptor (EGFR) and downstream PI3K/Akt, or ADAM17 itself, prevented high glucose-induced HIF-1α activation and ADAM17 up-regulation. Thus, high glucose induces ADAM17 transcriptional up-regulation in mesangial cells, which is associated with augmentation of its activity. This is mediated by HIF-1α and requires EGFR/ADAM17 signaling, demonstrating the potentiation by ADAM17 of its own up-regulation. ADAM17 inhibition thus provides a potential novel therapeutic strategy for the treatment of diabetic nephropathy.

Kidney glycosphingolipids are elevated early in diabetic nephropathy and mediate hypertrophy of mesangial cells

Glycosphingolipids (GSLs) play a role in insulin resistance and diabetes, but their role in diabetic nephropathy (DN) has received limited attention. We used 9- and 17-wk-old nondiabetic db/m and diabetic db/db mice to examine the role of GSLs in DN. Cerebrosides or monoglycosylated GSLs [hexosylceramides (HexCers); glucosyl- and galactosylceramides] and lactosylceramide (LacCers) were elevated in db/db mouse kidney cortices, specifically in glomeruli, and also in urine. In our recent paper (25), we observed that the kidneys exhibited glomerular hypertrophy and proximal tubular vacuolization and increased fibrosis markers at these time points. Mesangial cells contribute to hyperglycemia-induced glomerular hypertrophy in DN. Hyperglycemic culture conditions, similar to that present in diabetes, were sufficient to elevate mesangial cell HexCers and increase markers of fibrosis, extracellular matrix proteins, and cellular hypertrophy. Inhibition of glucosylceramide synthase or lowering glucose levels decreased markers of fibrosis and extracellular matrix proteins and reversed mesangial cell hypertrophy. Hyperglycemia increased phosphorylated (p)SMAD3 and pAkt levels and reduced phosphatase and tensin homolog levels, which were reversed with glucosylceramide synthase inhibition. These data suggest that inhibition of glucosylceramide synthase reversed mesangial cell hypertrophy through decreased pAkt and pSmad3 and increased pathways responsible for protein degradation. Importantly, urinary GSL levels were higher in patients with DN compared with healthy control subjects, implicating a role for these lipids in human DN. Thus, hyperglycemia in type II diabetes leads to renal dysfunction at least in part by inducing accumulation of HexCers and LacCers in mesangial cells, resulting in fibrosis, extracellular matrix production, and hypertrophy.

Small-nucleic-acid-based therapeutic strategy targeting the transcription factors regulating the vascular inflammation, remodeling and fibrosis in atherosclerosis

Atherosclerosis arises when injury to the arterial wall induces an inflammatory cascade that is sustained by a complex network of cytokines, together with accumulation of lipids and fibrous material. Inflammatory cascades involve leukocyte adherence and chemotaxis, which are coordinated by the local secretion of adhesion molecules, chemotactic factors, and cytokines. Transcription factors are critical to the integration of the various steps of the cascade response to mediators of vascular injury, and are induced in a stimulus-dependent and cell-type-specific manner. Several small-nucleic-acid-based therapeutic strategies have recently been developed to target transcription factors: antisense oligodeoxynucleotides, RNA interference, microRNA, and decoy oligodeoxynucleotides. The aim of this review was to provide an overview of these particular targeted therapeutic strategies, toward regulation of the vascular inflammation, remodeling and fibrosis associated with atherosclerosis.

Transcription factor Sp1, also known as specificity protein 1 as a therapeutic target

INTRODUCTION

Specificity protein (Sp) transcription factors (TFs) are members of the Sp/Kruppel-like factor family, and Sp proteins play an important role in embryonic and early postnatal development. Sp1 has been the most extensively investigated member of this family, and expression of this protein decreases with age, whereas Sp1 and other family members (Sp3 and Sp4) are highly expressed in tumors and cancer cell lines.

AREA COVERED

The prognostic significance of Sp1 in cancer patients and the functional pro-oncogenic activities of Sp1, Sp3 and Sp4 in cancer cell lines are summarized. Several different approaches have been used to target downregulation of Sp TFs and Sp-regulated genes, and this includes identification of different structural classes of antineoplastic agents including NSAIDs, natural products and their synthetic analogs and several well-characterized drugs including arsenic trioxide, aspirin and metformin. The multiple pathways involved in drug-induced Sp downregulation are also discussed.

EXPERT OPINION

The recognition by the scientific and clinical community that experimental and clinically used antineoplastic agents downregulate Sp1, Sp3 and Sp4, and pro-oncogenic Sp-regulated genes will facilitate future clinical applications for individual drug and drug combination therapies that take advantage of their unusual effects.

The impact of thiamine treatment in the diabetes mellitus

Thiamine acts as a coenzyme for transketolase (Tk) and for the pyruvate dehydrogenase and α-ketoglutarate dehydrogenase complexes, enzymes which play a fundamental role for intracellular glucose metabolism. The relationship between thiamine and diabetes mellitus (DM) has been reported in the literature. Thiamine levels and thiamine-dependent enzyme activities have been reduced in DM. Genetic studies provide opportunity to link the relationship between thiamine and DM (such as Tk, SLC19A2 gene, transcription factor Sp1, α-1-antitrypsin, and p53). Thiamine and its derivatives have been demonstrated to prevent the activation of the biochemical pathways (increased flux through the polyol pathway, formation of advanced glycation end-products, activation of protein kinase C, and increased flux through the hexosamine biosynthesis pathway) induced by hyperglycemia in DM.Thiamine definitively has a role in the diabetic endothelial vascular diseases (micro and macroangiopathy), lipid profile, retinopathy, nephropathy, cardiopathy, and neuropathy.

SREBP-1 activation by glucose mediates TGF-β upregulation in mesangial cells

Glomerular matrix accumulation is a hallmark of diabetic nephropathy. Recent studies showed that overexpression of the transcription factor sterol-responsive element-binding protein (SREBP)-1 induces pathology reminiscent of diabetic nephropathy, and SREBP-1 upregulation was observed in diabetic kidneys. We thus studied whether SREBP-1 is activated by high glucose (HG) and mediates its profibrogenic responses. In primary rat mesangial cells, HG activated SREBP-1 by 30 min, seen by the appearance of its cleaved nuclear form (nSREBP-1), EMSA, and by activation of an SREBP-1 response element (SRE)-driven green fluorescent protein construct. Activation was dose dependent and not induced by an osmotic control. Site 1 protease was required, since its inhibition by AEBSF prevented SREBP-1 activation. SCAP, the ER-associated chaperone for SREBP-1, was also necessary since its inhibitor fatostatin also blocked SREBP-1 activation. Signaling through the EGFR/phosphatidylinositol 3-kinase (PI3K) pathway, which we previously showed mediates HG-induced TGF-β1 upregulation, and through RhoA, were upstream of SREBP-1 activation (Wu D, Peng F, Zhang B, Ingram AJ, Gao B, Krepinsky JC. Diabetologia 50: 2008–2018, 2007; Wu D, Peng F, Zhang B, Ingram AJ, Kelly DJ, Gilbert RE, Gao B, Krepinsky JC. J Am Soc Nephrol 20: 554–566, 2009). Fatostatin and AEBSF prevented HG-induced TGF-β1 upregulation by Northern blot analysis, and HG-induced TGF-β1 promoter activation was inhibited by both fatostatin and dominant negative SREBP-1a. Chromatin immunoprecipitation analysis confirmed that HG led to SREBP-1 binding to the TGF-β1 promoter in a region containing a putative SREBP-1 binding site (SRE). Thus HG-induced SREBP-1 activation requires EGFR/PI3K/RhoA signaling and SCAP-mediated transport to the Golgi for its proteolytic cleavage. Activated SREBP-1 binds to the TGF-β promoter, resulting in TGF-β1 upregulation in response to HG. SREBP-1 thus provides a potential novel therapeutic target for the treatment of diabetic nephropathy.

Targeted blockage of signal transducer and activator of transcription 5 signaling pathway with decoy oligodeoxynucleotides suppresses leukemic K562 cell growth

The protein signal transducer and activator of transcription 5 (STAT5) of the JAK/STAT pathway is constitutively activated because of its phosphorylation by tyrosine kinase activity of fusion protein BCR-ABL in chronic myelogenous leukemia (CML) cells. This study investigated the potential therapeutic effect of STAT5 decoy oligodeoxynucleotides (ODN) using leukemia K562 cells as a model. Our results showed that transfection of 21-mer-long STAT5 decoy ODN into K562 cells effectively inhibited cell proliferation and induced cell apoptosis. Further, STAT5 decoy ODN downregulated STAT5 targets bcl-xL, cyclinD1, and c-myc at both mRNA and protein levels in a sequence-specific manner. Collectively, these data demonstrate the therapeutic effect of blocking the STAT5 signal pathway by cis-element decoy for cancer characterized by constitutive STAT5 activation. Thus, our study provides support for STAT5 as a potential target downstream of BCR-ABL for CML treatment and helps establish the concept of targeting STAT5 by decoy ODN as a novel therapy approach for imatinib-resistant CML.

Melittin suppresses PMA-induced tumor cell invasion by inhibiting NF-kappaB and AP-1-dependent MMP-9 expression

Matrix metalloproteinase-9 (MMP-9) plays an important role in the invasion and metastasis of cancer cells. In this study, we examined the inhibitory effect of bee venom (BV) and its major peptides, melittin and apamin, on PMA-induced invasion induced by MMP-9 expression in Caki-1 renal cancer cells. BV and melittin, but not apamin, significantly suppressed PMA-induced invasion by inhibiting MMP-9 expression in Caki-1 cells. Furthermore, as evidenced by MMP-9 promoter assays, melittin inhibited MMP-9 gene expression by blocking the PMA-stimulated activations of activator protein-1 (AP-1) and nuclear factor-kappa B (NF-kappaB). In addition, melittin suppressed the PMA-induced phosphorylations of ERK and JNK mitogen-activated protein kinases, upstream factors involved in Ap-1 and NF-kappaB. These results suggest that the suppression of MMP-9 expression contributes to the anti-tumor properties of melittin.

Transcription factors in the pathogenesis of diabetic nephropathy

Approximately a third of patients with diabetes develop diabetic kidney disease, and diabetes is the leading cause of end-stage renal disease in most developed countries. Hyperglycaemia is known to activate genes that ultimately lead to extracellular matrix accumulation, the hallmark of diabetic nephropathy. Several transcription factors have been implicated in glucose-mediated expression of genes involved in diabetic nephropathy. This review focuses on the transcription factors upstream stimulatory factors 1 and 2 (USF1 and 2), activator protein 1 (AP-1), nuclear factor (NF)-kappaB, cAMP-response-element-binding protein (CREB), nuclear factor of activated T cells (NFAT), and stimulating protein 1 (Sp1). In response to high glucose, several of these transcription factors regulate the gene encoding the profibrotic cytokine transforming growth factor beta, as well as genes for a range of other proteins implicated in inflammation and extracellular matrix turnover, including thrombospondin 1, the chemokine CCL2, osteopontin, fibronectin, decorin, plasminogen activator inhibitor 1 and aldose reductase. Identifying the molecular mechanisms by which diabetic nephropathy occurs has important clinical implications as therapies can then be tailored to target those at risk. Strategies to specifically target transcription factor activation and function may be employed to halt the progression of diabetic nephropathy.

High glucose induces transactivation of the human paraoxonase 1 gene in hepatocytes

Human serum paraoxonase 1 (PON1) is associated with high-density lipoprotein and inhibits oxidative modification of low-density lipoprotein in vitro. Therefore, PON1 is expected to protect against atherosclerosis in vivo. We and other investigators have shown that PON1 enzymatic activity is decreased in diabetic patients; however, an alteration in hepatic PON1 synthesis under hyperglycemic conditions remains unclear. We previously demonstrated that Sp1 is a positive regulator of PON1 transcription and that an interaction between Sp1 and protein kinase C (PKC) is a crucial mechanism for the effect of Sp1 on PON1 transcription in cultured HepG2 cells. Because several PKC isoforms are activated under hyperglycemic conditions, we examined the effect of d-glucose, which can activate the diacylglycerol-PKC pathway, on the transcription and expression of PON1. For a reporter gene assay, Huh7 human hepatocyte cell line incorporated with PON1 (-1232/-6)-luciferase expression vector was established using a cationic lipid method. d-Glucose dose dependently enhanced PON1 promoter activity. d-Glucose also enhanced both messenger RNA and protein expression of PON1. Increased PON1 expression was also detected in primary human hepatocytes treated with high d-glucose concentrations. Bisindolylmaleimide, a PKC inhibitor, significantly inhibited d-glucose-induced transactivation of PON1; and mithramycin, an inhibitor of Sp1, completely abrogated the transactivation. Our data suggest that high glucose concentrations transactivate the PON1 gene through Sp1 activation by PKC in cultured hepatocytes. Up-regulated hepatic PON1 expression under high glucose conditions may be a compensatory mechanism in diabetes in which antioxidant capacity, including PON1 enzymatic activity, is attenuated.

Decoy oligodeoxynucleotide targeting activator protein-1 (AP-1) attenuates intestinal inflammation in murine experimental colitis

Various therapies are used for inflammatory bowel diseases (IBD), though none seem to be extremely effective. AP-1 is a major transcription factor that upregulates genes involved in immune and proinflammatory responses. We investigated decoy oligodeoxynucleotide (ODN) targeting AP-1 to prevent dextran sulfate sodium (DSS)-induced colitis in mice. Functional efficacies of synthetic decoy and scrambled ODNs were evaluated in vitro by a reporter gene luciferase assay and measuring flagellin-induced IL-8 expression by HCT-15 cells transfected with ODNs. Experimental colitis was induced in mice with a 2.5% DSS solution in drinking water for 7 days, and decoy or scrambled ODNs were intraperitoneally injected from days 2 to 5. Colitis was assessed by weight loss, colon length, histopathology, and detection of myeloperoxidase (MPO), IL-1beta, and TNF-alpha in colon tissue. Therapeutic effects of AP-1 and NF-kappaB decoy ODNs were compared. Transfection of AP-1 decoy ODN inhibited AP-1 transcriptional activity in reporter assays and flagellin-induced IL-8 production in vitro. In mice, AP-1 decoy ODN, but not scrambled ODN, significantly inhibited weight loss, colon shortening, and histological inflammation induced by DSS. Further, AP-1 decoy ODN decreased MPO, IL-1beta, and TNF-alpha in colonic tissue of mice with DSS-induced colitis. The AP-1 decoy therapeutic effect was comparable to that of NF-kappaB decoy ODN, which also significantly decreased intestinal inflammation. Double-strand decoy ODN targeting AP-1 effectively attenuated intestinal inflammation associated with experimental colitis in mice, indicating the potential of targeting proinflammatory transcription factors in new therapies for IBD.

Glucose enhances protein tyrosine phosphatase 1B gene transcription in hepatocytes

Protein tyrosine phosphatase 1B (PTP1B) is a negative regulator of the insulin receptor signal transduction pathway. We investigated the effects of glucose on PTP1B transcription in the human hepatocyte cell line Huh7. Using a reporter gene assay, we found that D-glucose dose-dependently enhanced the PTP1B promoter activity. Real-time PCR demonstrated that D-glucose also increased PTP1B mRNA expression. Protein kinase C (PKC) inhibitors partially but significantly inhibited the transactivation by D-glucose. Mithramycin, a Sp1 inhibitor, completely abrogated this transactivation. The deletion of three possible Sp1 sites in the promoter region of PTP1B significantly reduced the basal promoter activity and transactivation by D-glucose. Sp1 activation by PKC is one of the key mechanisms in the regulation of several gene expressions. Our data suggested that glucose enhanced PTP1B transcription through Sp1 activation by PKC. Increased hepatic PTP1B expression may partly explain glucose toxicity in diabetes.

Sp1 and Smad3 are required for high glucose-induced p21WAF1 gene transcription in LLC-PK1 cells

The cyclin-dependent kinase inhibitor p21(WAF1) is required for diabetic glomerular hypertrophy. High glucose-induced hypertrophy in proximal tubule cells is dependent on transforming growth factor-beta (TGF-beta). Many of the TGF-beta-induced effects are dependent on Smad2/3. Thus, the molecular mechanisms of high glucose-induced p21(WAF1) and hypertrophy were studied in high glucose-cultured proximal tubule-like LLC-PK(1) cells. We found that high glucose (30 mM) induced hypertrophy at 72 h. High glucose also increased the expression of p21(WAF1) protein and p21(WAF1) mRNA transcription and abundance at 48 h. The DNA element in the 5' regulatory region of p21(WAF1) gene essential for high glucose-induced p21(WAF1) gene transcription was identified as Sp1 by a series of the 5' regulatory region of p21(WAF1) gene deletion mutants. Moreover, high glucose activated Smad2/3 while increasing the Sp1 DNA-binding activity. High glucose also increased the Sp1-dependent transcriptional activity of p21(WAF1) gene. High glucose-induced hypertrophy was attenuated by p21(WAF1) short interfering RNA and Smad3 dominant-negative plasmid transfection. We concluded that high glucose induced hypertrophy via Sp1-Smad2/3-dependent activation of p21(WAF1) gene transcription in LLC-PK(1) cells.

Ring-Sp1 decoy oligonucleotide effectively suppresses extracellular matrix gene expression and fibrosis of rat kidney induced by unilateral ureteral obstruction

Tubulointerstitial fibrosis is the consequence of an injury characterized by the accumulation of excess collagen and other extracellular matrix components, resulting in the destruction of the normal kidney architecture and subsequent loss of function. A transcription factor Sp1, originally described as a ubiquitous transcription factor, is involved in the basal expression of extracellular matrix genes and may, therefore, be important in fibrotic processes. Here, we report on the design of a ring-Sp1 decoy oligonucleotide, containing the consensus Sp1 binding sequence in a single decoy molecule without an open end, to create a novel therapeutic strategy for fibrosis. The ring-Sp1 decoy oligonucleotide is highly resistant to degradation by nucleases or serum compared to the conventional phosphorothioated double-stranded Sp1 decoy oligonucleotide, and effectively suppressed the expression of transforming growth factor-beta1 and fibronectin, the binding of Sp1 to the promoter region of these genes, and proliferation in response to serum in normal rat kidney fibroblasts. Moreover, treatment with the ring-Sp1 decoy in vivo significantly attenuates extracellular matrix gene expression in the rat kidney in which a unilateral ureteral obstruction had been induced. These results suggest that the ring-Sp1 decoy oligonucleotide represents promising therapeutic alternative to the conventional treatment of fibrotic disorders.

Tolfenamic acid and pancreatic cancer growth, angiogenesis, and Sp protein degradation

BACKGROUND

Sp1, Sp3, and Sp4 are transcription factors that regulate cell proliferation and vascular endothelial growth factor (VEGF) expression and are overexpressed in many cancer cell lines. For some cancers, Sp1 overexpression is associated with poor survival. Cyclooxygenase inhibitors decrease Sp1 expression in cancer cells, and therefore different structural classes of nonsteroidal anti-inflammatory drugs (NSAIDs) were screened for their ability to decrease levels of Sp1, Sp3, and Sp4 and to decrease pancreatic tumor growth and metastasis in an in vivo model.

METHODS

Levels of Sp1, Sp3, Sp4, and VEGF proteins in pancreatic cancer cell lines were assessed by immunoblot analysis. mRNA was assessed by reverse transcription-polymerase chain reaction. Panc-1 pancreatic cancer cells transfected with VEGF promoter constructs were used to assess VEGF promoter activation. Pancreatic tumor weight and size and liver metastasis were assessed in an orthotopic mouse model of pancreatic cancer (groups of 10 mice). Protein expression in tumors was assessed immunohistochemically.

RESULTS

Tolfenamic acid and structurally related biaryl derivatives induced degradation of Sp1, Sp3, and Sp4 in pancreatic cancer cells. Tolfenamic acid also inhibited VEGF mRNA and protein expression in pancreatic cancer cells; this inhibition was associated with the decreased Sp-dependent activation of the VEGF promoter. In the mouse model for pancreatic cancer, treatment with tolfenamic acid (50 mg/kg of body weight), compared with control treatment, statistically significantly decreased tumor growth and weight (P = .005), liver metastasis (P = .027), and levels of Sp3 and VEGF (P = .009) and Sp1 and Sp4 (P = .006) proteins in tumors. For example, tumors from mice treated with tolfenamic acid (50 mg/kg) had statistically significantly lower VEGF levels (45%, 95% confidence interval = 39% to 51%; P = .009) than tumors from control mice.

CONCLUSIONS

Tolfenamic acid is a new antipancreatic cancer NSAID that activates degradation of transcription factors Sp1, Sp3, and Sp4; reduces VEGF expression; and decreases tumor growth and metastasis.

Overexpression of Sp1 transcription factor induces apoptosis

Transcription factor Sp1 has recently been shown to be overexpressed in a number of human cancers and its overexpression contributes to malignant transformation. Sp1 regulates the expression of a number of genes participating in multiple aspects of tumorigenesis such as angiogenesis, cell growth and apoptosis resistance. To better understand the role of increased Sp1 levels on apoptosis regulation we have used retroviruses to overexpress this protein in haematopoietic Baf-3 cells and in 3T3 fibroblasts. We have also used inducible expression systems to control ectopic Sp1 levels in different cell types. Surprisingly, Sp1 overexpression on its own induces apoptosis in all the cellular models tested. The apoptotic pathways induced by Sp1 overexpression are cell type specific. Finally, using a truncated form of Sp1, we show that Sp1-induced apoptosis requires its DNA-binding domain. Our results highlight that Sp1 levels in untransformed cells must be tightly regulated as Sp1 overexpression leads to the induction of apoptosis. Our results also suggest that cancer cells overexpressing Sp1 can avoid Sp1-induced apoptosis.

Sp transcription factor family and its role in cancer

Specificity protein 1 (Sp1) and other Sp and Krüppel-like factor (KLF) proteins are members of a family of transcription factors which bind GC/GT-rich promoter elements through three C(2)H(2)-type zinc fingers that are present at their C-terminal domains. Sp1-Sp4 proteins regulate expression of multiple genes in normal tissues and tumours. There is growing evidence that some Sp proteins play a critical role in the growth and metastasis of many tumour types by regulating expression of cell cycle genes and vascular endothelial growth factor. Sp/KLF proteins are also potential targets for cancer chemotherapy.

Ascochlorin Inhibits Matrix Metalloproteinase-9 Expression by Suppressing Activator Protein-1-mediated Gene Expression through the ERK1/2 Signaling Pathway

The expression of matrix metalloproteinases (MMPs) has been implicated in the invasion and metastasis of cancer cells. Here we examined the effect of ascochlorin, a prenyl-phenol anti-tumor compound from the fungus Ascochyta viciae, on the regulation of signaling pathways that control MMP-9 expression in human renal carcinoma (Caki-1) cells. Ascochlorin reduced the invasive activity of Caki-1 cells and inhibited phorbol 12-myristate 13-acetate-induced increases in MMP-9 expression and activity in a dose-dependent manner. Reporter gene, electrophoretic mobility shift, kinase inhibitor assays, and in vitro kinase assay showed that ascochlorin inhibits MMP-9 gene expression by suppressing activation of the nuclear transcription factor activator protein-1 (AP-1) via the extracellular signal-regulated kinase 1 and 2 pathway. The AP-1 family member most specifically affected by ascochlorin was Fra-1. Ascochlorin did not affect the activation of the c-Jun N-terminal or p38 kinase pathways. Moreover, transfection of Caki-1 cells with AP-1 decoy oligodeoxynucleotides resulted in the suppression of phorbol 12-myristate 13-acetate-induced MMP-9 expression and invasion. In conclusion, ascochlorin represents a unique natural anti-tumor compound that specifically inhibits MMP-9 activity through suppression of AP-1-dependent induction of MMP-9 gene expression.