Activator protein 2alpha inhibits tumorigenicity and represses vascular endothelial growth factor transcription in prostate cancer cells

Activator protein 2alpha suppresses intestinal tumorigenesis in the Apc(min) mouse

Activator protein 2alpha (AP-2alpha) is a putative tumor suppressor, and various reports have described the loss or reduction of AP-2alpha expression in cutaneous malignant melanomas, as well as in cancers of the prostate, breast and colon. Previously, AP-2alpha was shown to attenuate beta-catenin/T-cell factor-4 (TCF-4) nuclear interactions and beta-catenin/TCF-4-dependent transcriptional activity in human colorectal cancer cells [Q. Li, R.H. Dashwood, Activator protein 2alpha associates with adenomatous polyposis coli/beta-catenin and Inhibits beta-catenin/T-cell factor transcriptional activity in colorectal cancer cells, J. Biol. Chem. 279 (2004) 45669-45675]. Here, we show that in vivo gene delivery of AP-2alpha suppressed intestinal polyp formation in the Apc(min) mouse, and protected against the development of anemia and splenomegaly. Immunoblot analyses and immunohistochemistry following gene delivery revealed an increase in AP-2alpha expression in the mouse intestinal mucosa and liver. Co-immunoprecipitation experiments provided evidence for interactions between AP-2alpha, beta-catenin, and adenomatous polyposis coli (APC) proteins in mouse intestinal mucosa, as well as in a primary human colorectal cancer. Collectively, these studies support a tumor suppressor role for AP-2alpha in the gastrointestinal tract, and suggest that AP-2alpha represents a novel target for therapeutic intervention in human cancers characterized by dysregulated Wnt signaling.

Mutations in the SOD2 promoter reveal a molecular basis for an activating protein 2-dependent dysregulation of manganese superoxide dismutase expression in cancer cells

A primary antioxidant enzyme in mitochondria, manganese superoxide dismutase (MnSOD), plays a critical role in the survival of aerobic life. It is well documented that, compared with normal cell counterparts, MnSOD level is decreased in neoplastic transformed cells but is increased in aggressive cancers. However, the underlying mechanism for the observed dysregulation of MnSOD in cancer is unknown. We have identified previously a unique set of mutations located in the promoter region of the SOD2 gene in several types of cancer cells. We found that a C-to-T transition at -102 and an insertion of A at -93 down-regulate MnSOD transcription by interrupting the formation of a single-stranded loop that is essential for a high level of promoter activity. Here, we show that the additional downstream mutation, C-to-G transversion at -38, creates a binding site for the transcription factors specificity protein 1 (Sp1) and activating protein 2 (AP-2). The promoter function is regulated by the relative levels of Sp1 and AP-2. In cytokine-induced expression of the SOD2 gene, Sp1 cooperates with a transcriptional complex containing nuclear factor-kappaB and nucleophosmin. The presence of AP-2 attenuates this induction. Our results suggest that the high level of MnSOD observed in aggressive cancer cells may be due, in part, to the absence of AP-2 transcriptional repression.

Evolutionary conservation of zinc finger transcription factor binding sites in promoters of genes co-expressed with WT1 in prostate cancer

BACKGROUND

Gene expression analyses have led to a better understanding of growth control of prostate cancer cells. We and others have identified the presence of several zinc finger transcription factors in the neoplastic prostate, suggesting a potential role for these genes in the regulation of the prostate cancer transcriptome. One of the transcription factors (TFs) identified in the prostate cancer epithelial cells was the Wilms tumor gene (WT1). To rapidly identify coordinately expressed prostate cancer growth control genes that may be regulated by WT1, we used an in silico approach.

RESULTS

Evolutionary conserved transcription factor binding sites (TFBS) recognized by WT1, EGR1, SP1, SP2, AP2 and GATA1 were identified in the promoters of 24 differentially expressed prostate cancer genes from eight mammalian species. To test the relationship between sequence conservation and function, chromatin of LNCaP prostate cancer and kidney 293 cells were tested for TF binding using chromatin immunoprecipitation (ChIP). Multiple putative TFBS in gene promoters of placental mammals were found to be shared with those in human gene promoters and some were conserved between genomes that diverged about 170 million years ago (i.e., primates and marsupials), therefore implicating these sites as candidate binding sites. Among those genes coordinately expressed with WT1 was the kallikrein-related peptidase 3 (KLK3) gene commonly known as the prostate specific antigen (PSA) gene. This analysis located several potential WT1 TFBS in the PSA gene promoter and led to the rapid identification of a novel putative binding site confirmed in vivo by ChIP. Conversely for two prostate growth control genes, androgen receptor (AR) and vascular endothelial growth factor (VEGF), known to be transcriptionally regulated by WT1, regulatory sequence conservation was observed and TF binding in vivo was confirmed by ChIP.

CONCLUSION

Overall, this targeted approach rapidly identified important candidate WT1-binding elements in genes coordinately expressed with WT1 in prostate cancer cells, thus enabling a more focused functional analysis of the most likely target genes in prostate cancer progression. Identifying these genes will help to better understand how gene regulation is altered in these tumor cells.

AP-2alpha and AP-2gamma regulate tumor progression via specific genetic programs

The events occurring during tumor formation and progression display similarities to some of the steps in embryonic morphogenesis. The family of AP-2 proteins consists of five different transcription factors (alpha, beta, gamma, delta, and epsilon) that play relevant roles in embryonic development, as demonstrated by the phenotypes of the corresponding knockout mice. Here, we show that AP-2alpha and AP-2gamma proteins play an essential role in tumorigenesis. Down-modulation of AP-2 expression in tumor cells by RNA interference (RNAi) led to enhanced tumor growth and reduced chemotherapy-induced cell death, as well as migration and invasion. Most of these biological modulations were rescued by AP-2 overexpression. We observed that increased xenotransplant growth was mostly due to highly enhanced proliferation of the tumor cells together with reduced innate immune cell recruitment. Moreover, we showed that migration impairment was mediated, at least in part, by secreted factors. To identify the genetic programs involved in tumorigenesis, we performed whole genome microarray analysis of AP-2alpha knockdown cells and observed that AP-2alpha regulates specific genes involved in cell cycle, cell death, adhesion, and migration. In particular, we showed that ESDN, EREG, and CXCL2 play a major role in AP-2 controlled migration, as ablation of any of these genes severely altered migration.

Regulation of poly(ADP-ribose) polymerase-1 (PARP-1) gene expression through the post-translational modification of Sp1: a nuclear target protein of PARP-1

Background

Poly(ADP-ribose) polymerase-1 (PARP-1) is a nuclear enzyme that plays critical functions in many biological processes, including DNA repair and gene transcription. The main function of PARP-1 is to catalyze the transfer of ADP-ribose units from nicotinamide adenine dinucleotide (NAD⁺) to a large array of acceptor proteins, which comprises histones, transcription factors, as well as PARP-1 itself. We have previously demonstrated that transcription of the PARP-1 gene essentially rely on the opposite regulatory actions of two distinct transcription factors, Sp1 and NFI. In the present study, we examined whether suppression of PARP-1 expression in embryonic fibroblasts derived from PARP-1 knockout mice (PARP-1^-/-) might alter the expression and/or DNA binding properties of Sp1 and NFI. We also explored the possibility that Sp1 or NFI (or both) may represent target proteins of PARP-1 activity.

Results

Expression of both Sp1 and NFI was found to be considerably reduced in PARP-1^-/- cells. Co-immunoprecipitation assays revealed that PARP-1 physically interacts with Sp1 in a DNA-independent manner, but neither with Sp3 nor NFI, in PARP-1^+/+ cells. In addition, in vitro PARP assays indicated that PARP-1 could catalyze the addition of polymer of ADP-ribose to Sp1, which also translated into a reduction of Sp1 binding to its consensus DNA target site. Transfection of the PARP-1 promoter into both PARP-1^+/+ and PARP-1^-/- cells revealed that the lack of PARP-1 expression in PARP-1^-/- cells also results in a strong increase in PARP-1 promoter activity. This influence of PARP-1 was found to rely on the presence of the Sp1 sites present on the basal PARP-1 promoter as their mutation entirely abolished the increased promoter activity observed in PARP-1^-/- cells. Subjecting PARP-1^+/+ cells to an oxidative challenge with hydrogen peroxide to increase PARP-1 activity translated into a dramatic reduction in the DNA binding properties of Sp1. However, its suppression by the inhibitor PJ34 improved DNA binding of Sp1 and led to a dramatic increase in PARP-1 promoter function.

Conclusion

Our results therefore recognized Sp1 as a target protein of PARP-1 activity, the addition of polymer of ADP-ribose to this transcription factor restricting its positive regulatory influence on gene transcription.

Wwox Suppresses Prostate Cancer Cell Growth through Modulation of ErbB2-Mediated Androgen Receptor Signaling

The expression of the WWOX tumor suppressor gene is lost or reduced in a large fraction of various cancers, including prostate cancer. We previously reported that Wwox overexpression induced apoptosis and suppressed prostate cancer growth in vitro and in vivo. In this study, pathways through which Wwox contributes to control of prostate cancer cell growth have been investigated. We found that Wwox interacts with Ap2gamma and prevents it from entering the nucleus to bind the ERBB2 promoter region to activate transcription of ERBB2, a mediator of androgen receptor activity and prostate cancer cell growth at limiting androgen concentration. Ectopic expression of Wwox reduced ErbB2 protein expression in vitro and expression of Wwox protein inversely correlated with expression of ErbB2 protein in prostate cancer tissues. Furthermore, Wwox suppressed Ap2gamma/ErbB2-induced prostate cancer cell growth and suppressed prostate-specific antigen secretion through interaction with Ap2gamma and down-modulation of ErbB2, an effect that required functional androgen receptor.

Rad51 overexpression contributes to chemoresistance in human soft tissue sarcoma cells: a role for p53/activator protein 2 transcriptional regulation

We investigated whether Rad51 overexpression plays a role in soft tissue sarcoma (STS) chemoresistance as well as the regulatory mechanisms underlying its expression. The studies reported here show that Rad51 protein is overexpressed in a large panel of human STS specimens. Human STS cell lines showed increased Rad51 protein expression, as was also observed in nude rat STS xenografts. STS cells treated with doxorubicin exhibited up-regulation of Rad51 protein while arrested in the S-G(2) phase of the cell cycle. Treatment with anti-Rad51 small interfering RNA decreased Rad51 protein expression and increased chemosensitivity to doxorubicin. Because we previously showed that reintroduction of wild-type p53 (wtp53) into STS cells harboring a p53 mutation led to increased doxorubicin chemosensitivity, we hypothesized that p53 participates in regulating Rad51 expression in STS. Reintroduction of wtp53 into STS cell lines resulted in decreased Rad51 protein and mRNA expression. Using luciferase reporter assays, we showed that reconstitution of wtp53 function decreased Rad51 promoter activity. Deletion constructs identified a specific Rad51 promoter region containing a p53-responsive element but no p53 consensus binding site. Electrophoretic mobility shift assays verified activator protein 2 (AP2) binding to this region and increased AP2 binding to the promoter in the presence of wtp53. Mutating this AP2 binding site eliminated the wtp53 repressive effect. Furthermore, AP2 knockdown resulted in increased Rad51 expression. In light of the importance of Rad51 in modulating STS chemoresistance, these findings point to a potential novel strategy for molecular-based treatments that may be of relevance to patients burdened by STS.

Tumor-specific activation of human telomerase reverses transcriptase promoter activity by activating enhancer-binding protein-2beta in human lung cancer cells

The up-regulated expression and telomerase activity of human telomerase reverse transcriptase (hTERT) are hallmarks of tumorigenesis. The hTERT promoter has been shown to promote hTERT gene expression selectively in tumor cells but not in normal cells. However, little is known about how tumor cells differentially activate hTERT transcription and induce telomerase activity. In this study, we identified activating enhancer-binding protein-2beta (AP-2beta) as a novel transcription factor that specifically binds to and activates the hTERT promoter in human lung cancer cells. AP-2beta was detected in hTERT promoter DNA-protein complexes formed in nuclear extracts prepared only from lung cancer cells but not from normal cells. We verified the tumor-specific binding activity of AP-2beta for the hTERT promoter in vitro and in vivo and detected high expression levels of AP-2beta in lung cancer cells. We found that ectopic expression of AP-2beta reactivated hTERT promoter-driven reporter green fluorescent protein (GFP) gene and endogenous hTERT gene expression in normal cells, enhanced GFP gene expression in lung cancer cells, and prolonged the life span of primary lung bronchial epithelial cells. Furthermore, we found that inhibition of endogenous AP-2beta expression by AP-2beta gene-specific small interfering RNAs effectively attenuated hTERT promoter-driven GFP expression, suppressed telomerase activity, accelerated telomere shortening, and inhibited tumor cell growth by induction of apoptosis in lung cancer cells. Our results demonstrate the tumor-specific activation of the hTERT promoter by AP-2beta and imply the potential of AP-2beta as a novel tumor marker or a cancer therapeutic target.

Activator protein-2 in carcinogenesis with a special reference to breast cancer-A mini review

Activator protein-2 (AP-2) transcription factors are involved in the regulation of cell proliferation, differentiation, apoptosis and carcinogenesis. AP-2alpha has been suggested to function as a tumor suppressor in many cancers and AP-2gamma to be a marker of testicular and germ cell malignancies. At least 3 of the 5 AP-2 family members identified to date, AP-2alpha, AP-2beta and AP-2gamma, are known to be expressed in breast tissue and thought to coordinate the growth and development of the breast via regulation of several breast-related genes such as human epidermal growth factor receptor-2 (HER2) and estrogen receptor (ER). The function of AP-2alpha seems to be tumor suppressive in breast tissue, whereas the role of the other AP-2 family members is less well known. In this review, we summarize the current knowledge of AP-2 in carcinogenesis, especially in breast cancer.

Loss of AP-2alpha results in deregulation of E-cadherin and MMP-9 and an increase in tumorigenicity of colon cancer cells in vivo

Activator protein-2 (AP-2) is a transcription factor that regulates proliferation and differentiation in mammalian cells and has been implicated in the acquisition of the metastatic phenotype in several types of cancer. Herein, we examine the role of AP-2alpha in colon cancer progression. We provide evidence for the lack of AP-2alpha expression in the late stages of colon cancer cells. Re-expression of the AP-2alpha gene in the AP-2alpha-negative SW480 colon cancer cells suppressed their tumorigenicity following orthotopic injection into the cecal wall of nude mice. The inhibition of tumor growth could be attributed to the increased expression of E-cadherin and decreased expression and activity of matrix-metalloproteinase-9 (MMP-9) in the transfected cells, as well as a substantial loss of their in vitro invasive properties. Conversely, targeting constitutive expression of AP-2alpha in AP-2-positive KM12C colon cancer cells with small interfering RNA resulted in an increase in their invasive potential, downregulation of E-cadherin and increased expression of MMP-9. In SW480 cells, re-expression of AP-2alpha resulted in a fourfold increase in the activity of E-cadherin promoter, and a 5-14-fold decrease in the activity of MMP-9 promoter, indicating transcriptional regulation of these genes by AP-2alpha. Chromatin immunoprecipitation assay showed that re-expressed AP-2alpha directly binds to the promoter of E-cadherin, where it has been previously reported to act as a transcriptional activator. Furthermore, chromatin immunoprecipitation assay revealed AP-2alpha binding to the MMP-9 promoter, which ensued by decreased binding of transcription factor Sp-1 and changes in the recruitment of transcription factors to a distal AP-1 element, thus, contributing to the overall downregulation of MMP-9 promoter activity. Collectively, our data provide evidence that AP-2alpha acts as a tumor suppressor gene in colon cancer..

Transcriptional Regulation of ULBP1, a Human Ligand of the NKG2D Receptor

Tumor cells expressing ligands of the NKG2D receptor stimulate anti-tumor immunity mediated by natural killer and T cells. In humans, NKG2D ligands (NKG2DL) are encoded by MIC and ULBP proteins. NKG2DL exhibit highly restricted expression in healthy tissues but are widely expressed in tumors. However, regulation of each NKG2DL differs substantially in different cancer cells. In this study, we characterized the mechanisms that regulate the expression of ULBP1. We show that the transcription of ULBP1 strictly depends on the binding of Sp1 and Sp3 to a CRE(1) site located in the ULBP1 minimal promoter. The mutation or deletion of this Sp1/Sp3 binding site abolished the transcription of ULBP1. It also diminished the transactivation of ULBP1 promoter by Sp3 overexpression, but not by Sp1, indicating that Sp3 is the main transcription factor that regulates ULBP1 through the CRE(1) site. Experiments in SL2 cells showed that the ULBP1 promoter was inactive in the absence of the Sp proteins and indicate that Sp3 is the essential activator of ULBP1 transcription, because the overexpression of Sp3 up-regulated its promoter activity > 500-fold. Additionally, we demonstrated that AP-2alpha repressed the expression of ULBP1 in HeLa cells by interfering with the binding of Sp3 and Sp1 to the ULBP1 promoter. These data indicate that Sp1, Sp3, and AP-2alpha may play an important role in the immunosurveillance against cancer. Finally, the definition of ULBP1 regulation may have implications for development of new therapeutic strategies against cancer cells.

AP-2gamma induces p21 expression, arrests cell cycle, and inhibits the tumor growth of human carcinoma cells

Activating enhancer-binding protein 2gamma (AP-2gamma) is a member of the developmentally regulated AP-2 transcription factor family that regulates the expression of many downstream genes. Whereas the effects of AP-2alpha overexpression on cell growth are fairly well established, the cellular effects of AP-2gamma overexpression are less well studied. Our new findings show that AP-2gamma significantly upregulates p21 mRNA and proteins, inhibits cell growth, and decreases clonogenic survival. Cell cycle analysis revealed that forced AP-2gamma expression induced G1-phase arrest, decreased DNA synthesis, and decreased the fraction of cells in S phase. AP-2gamma expression also led to cyclin D1 repression, decreased Rb phosphorylation, and decreased E2F activity in breast carcinoma cells. AP-2gamma binding to the p21 promoter was observed in vivo, and the absence of growth inhibition in response to AP-2gamma expression in p21(-/-) cells demonstrated that p21 caused, at least in part, AP-2-induced cell cycle arrest. Finally, the tumor growth of human breast carcinoma cells in vivo was inhibited by the expression of AP-2gamma relative to empty vector-infected cells, suggesting that AP-2gamma acts as a tumor suppressor. In summary, expression of either AP-2gamma or AP-2alpha inhibited breast carcinoma cell growth; thus, these genes may be therapeutic targets for breast cancer.

Jak3- and JNK-dependent vascular endothelial growth factor expression in cutaneous T-cell lymphoma

Biopsies from patients with cutaneous T-cell lymphoma (CTCL) exhibit stage-dependent increase in angiogenesis. However, the molecular mechanisms responsible for the increased angiogenesis are unknown. Here we show that malignant CTCL T cells spontaneously produce the potent angiogenic protein, vascular endothelial growth factor (VEGF). Dermal infiltrates of CTCL lesions show frequent and intense staining with anti-VEGF antibody, indicating a steady, high production of VEGF in vivo. Moreover, the VEGF production is associated with constitutive activity of Janus kinase 3 (Jak3) and the c-Jun N-terminal kinases (JNKs). Sp600125, an inhibitor of JNK activity and activator protein-1 (AP-1) binding to the VEGF promoter, downregulates the VEGF production without affecting Jak3 activity. Similarly, inhibitors of Jak3 inhibit the VEGF production without affecting JNK activity. Downregulation of Stat3 with small interfering RNA has no effect, whereas curcumin, an inhibitor of both Jak3 and the JNKs, almost completely blocks the VEGF production. In conclusion, we provide evidence of VEGF production in CTCL, which is promoted by aberrant activation of Jak3 and the JNKs. Inhibition of VEGF-inducing pathways or neutralization of VEGF itself could represent novel therapeutic modalities in CTCL.

Apoptosis induction by activator protein 2alpha involves transcriptional repression of Bcl-2

Activator protein 2alpha (AP-2alpha) induces cytotoxicity by inducing cell cycle arrest and apoptosis. In this study we investigated the mechanism of apoptosis induction by AP-2alpha. We found that AP-2alpha induced apoptosis efficiently in cells treated with benzyloxycar-bonyl-IETD-fluoromethyl ketone or FADD-silenced cells but failed to do so in benzyloxycarbonyl-LEHD-fluoromethyl ketone-treated or apoptosis protease activation factor-1 (Apaf1)-silenced cells, suggesting the central role of mitochondria in AP-2alpha-induced apoptosis. In good correlation, cells overexpressing AP-2alpha showed a reduction in mitochondrial membrane potential (Deltapsi(m)), cytochrome c and Smac/DIABLO release into cytosol, and Bax translocation into mitochondria. We found that the pro-apoptotic protein Bax is important for AP-2alpha-induced apoptosis as adenovirus AP2 failed to induce apoptosis in HCT116 Bax(-/-) cells. However, we found the IAP (inhibitor of apoptosis) inhibitor Smac/DIABLO may have a limited role in AP-2alpha-induced apoptosis as we found the IAP member Survivin down-regulated by AP-2alpha. Although the total Bax level remains unaltered, we found a time-dependent increase in the activated form of Bax in adenovirus AP2-infected cells. In addition, we show that AP-2alpha transcriptionally represses Bcl-2 by binding to its promoter both in vitro and in vivo and that this is essential for AP-2alpha-induced apoptosis as ectopic expression of Bcl-2 efficiently inhibited apoptosis induced by AP-2alpha. Furthermore, we show that chemotherapy-induced endogenous AP-2alpha down-regulates Bcl-2 and induces apoptosis in an AP-2alpha-dependent manner. Moreover, we demonstrate that inhibition of okadaic acid or staurosporine-sensitive pathways in AP-2alpha overexpressing breast cancer cells resulted in AP-2alpha-dependent apoptosis induction. These results suggest that AP-2alpha induces apoptosis by down-regulating Bcl-2 and utilizing a bax/cytochrome c/Apaf1/caspase 9-dependent mitochondrial pathway.

Proteomics profiling of nuclear proteins for kidney fibroblasts suggests hypoxia, meiosis, and cancer may meet in the nucleus

Proteomics methods were used to characterize proteins that change their form or abundance in the nucleus of NRK49F rat kidney fibroblasts during prolonged hypoxia (1% O(2), 12 h). Of the 791 proteins that were monitored, about 20% showed detectable changes. The 51 most abundant proteins were identified by mass spectrometry. Changes in nuclear receptor transcription factors (THRalpha1, RORalpha4, HNF4alpha, NUR77), other transcription factors (GATA1, AP-2alpha, OCT1, ATF6alpha, ZFP161, ZNF354A, PDCD2), and transcription cofactors (PC4, PCAF, MTA1, TCEA1, JMY) are indicative of major, co-ordinated changes in transcription. Proteins involved in DNA repair/recombination, ribosomal RNA synthesis, RNA processing, nuclear transport, nuclear organization, protein translation, glycolysis, lipid metabolism, several protein kinases (PKCdelta, MAP3K4, GRK3), as well as proteins with no established functional role were also observed. The observed proteins suggest nuclear regulatory roles for proteins involved in cytosolic processes such as glycolysis and fatty acid metabolism, and roles in overall nuclear structure/organization for proteins previously associated with meiosis and/or spermatogenesis (synaptonemal complex proteins 1 and 2 (SYCP1, SYCP2), meiosis-specific nuclear structural protein 1 (MNS1), LMNC2, zinc finger protein 99 (ZFP99)). Proteins associated with cytoplasmic membrane functions (ACTN4, hyaluronan mediated motility receptor (RHAMM), VLDLR, GRK3) and/or endocytosis (DNM2) were also seen. For 30% of the identified proteins, new isoforms indicative of alternative transcription were detected (e.g., GATA1, ATF6alpha, MTA1, MLH1, MYO1C, UBF, SYCP2, EIF3S10, MAP3K4, ZFP99). Comparison with proteins involved in cell death, cancer, and testis/meiosis/spermatogenesis suggests commonalities, which may reflect fundamental mechanisms for down-regulation of cellular function.

Activator Protein 2α Status Determines the Chemosensitivity of Cancer Cells: Implications in Cancer Chemotherapy

Cancer chemotherapeutic drugs induce apoptosis by several pathways. Inactivation of proapoptotic genes, or activation of survival signaling, leads to chemoresistance. Activator protein 2alpha (AP-2alpha), a developmentally regulated sequence-specific DNA-binding transcription factor, has been shown to function like a tumor suppressor. Here, we show that controlled expression of AP-2alpha, using tetracycline-inducible system, increased the chemosensitivity of cancer cells by severalfold by sensitizing cells to undergo apoptosis upon chemotherapy. Under these conditions, neither AP-2alpha expression nor drug treatment resulted in apoptosis induction, whereas in combination the cancer cells underwent massive apoptosis. We found that endogenous AP-2alpha protein is induced posttranscriptionally by various chemotherapeutic drugs. Blocking the endogenous AP-2alpha by small interfering RNA in human cancer cells lead to decreased apoptosis, increased colony formation, and chemoresistance irrespective of their p53 status upon chemotherapy. We further show that 5-aza-2'-deoxycytidine induced reexpression of AP-2alpha in MDA-MB-231 breast cancer cells (wherein AP-2alpha expression is silenced by hypermethylation), resulted in massive apoptosis induction, increased chemosensitivity, decreased colony formation, and loss of tumorigenesis upon chemotherapy. However, in MDA-MB-231 cells transfected with AP-2alpha small interfering RNA, 5-aza-2'-deoxycytidine treatment failed to increase apoptosis and chemosensitivity. The treatment also resulted in increased colony formation and efficient tumor formation upon chemotherapy. These results establish an important role for AP-2alpha in cancer cell chemosensitivity and provide new insights for modifying the chemosensitivity of cancer cells by activating apoptotic pathways.

Expression of matrix metalloproteinase (MMP)-2 and MMP-9 in breast cancer with a special reference to activator protein-2, HER2, and prognosis

PURPOSE

In the present study, we investigated the expression and prognostic value of matrix metalloproteinase (MMP)-2 and MMP-9 in breast cancer as well as their relation to transcription factor activator protein (AP)-2 and HER2 oncogene. The role of invasion and metastasis-promoting MMPs and their potential regulators, AP-2 and HER2, is currently still unclear in breast cancer.

EXPERIMENTAL DESIGN

MMP-2 and MMP-9 expressions were analyzed immunohistochemically in a large prospective series of 421 breast cancer patients diagnosed and treated between 1990 and 1995 at Kuopio University Hospital (Kuopio, Finland). The relation of MMP-2 and MMP-9 expressions to AP-2, HER2, clinicopathological data, and survival was investigated.

RESULTS

Both MMP-2 and MMP-9 were expressed in the cytoplasm of malignant and stromal cells. High expression of MMPs in carcinoma cells was related to small tumors (T1, stage I), whereas positive stromal expression of MMPs was associated with aggressive factors. High expression of MMP-2 and MMP-9 in carcinoma cells, but not in stromal cells, was related to high AP-2 expression. Positive stromal MMP-2 expression was associated with HER2 overexpression in the whole patient group and in the node-negative patient subgroup. Positive stromal MMP-9 expression was related to HER2 overexpression in estrogen receptor (ER)-positive disease. In the univariate survival analysis, positive stromal MMP-9 predicted shorter recurrence-free survival (RFS; P=0.0389) and breast cancer-related survival (BCRS; P=0.0081) in ER+ disease, especially in the subgroup of ER+ tumors of < or =2 cm in diameter (T1; P=0.0031 for RFS, and P=0.0089 for BCRS). High MMP-9 expression in cancer cells predicted longer RFS (P=0.0351) in the whole patient group. In the multivariate analysis of the whole patient group, the independent predictors of shorter RFS were reduced MMP-9 expression in carcinoma cells (P=0.0248), HER2 overexpression (P=0.0001), and advanced-stage disease (P=0.0002). Shorter BCRS was predicted by advanced-stage disease (P <0.0001).

CONCLUSIONS

Expression of MMP-2 and MMP-9 in breast cancer seems to be partly related to expression of AP-2 and HER2. Positive stromal MMP-9 expression predicts poor survival in the hormone-responsive small tumors, whereas MMP-9 expression in carcinoma cells favors survival. Evaluation of MMP-9 expression seems to add valuable information on breast cancer prognosis.

Proof of concept for microarray-based detection of DNA-binding oncogenes in cell extracts

The function of DNA-binding proteins is controlled not just by their abundance, but mainly at the level of their activity in terms of their interactions with DNA and protein targets. Moreover, the affinity of such transcription factors to their target sequences is often controlled by co-factors and/or modifications that are not easily assessed from biological samples. Here, we describe a scalable method for monitoring protein–DNA interactions on a microarray surface. This approach was designed to determine the DNA-binding activity of proteins in crude cell extracts, complementing conventional expression profiling arrays. Enzymatic labeling of DNA enables direct normalization of the protein binding to the microarray, allowing the estimation of relative binding affinities. Using DNA sequences covering a range of affinities, we show that the new microarray-based method yields binding strength estimates similar to low-throughput gel mobility-shift assays. The microarray is also of high sensitivity, as it allows the detection of a rare DNA-binding protein from breast cancer cells, the human tumor suppressor AP-2. This approach thus mediates precise and robust assessment of the activity of DNA-binding proteins and takes present DNA-binding assays to a high throughput level.

Molecular markers of prostate cancer outcome

Molecular markers have the potential to serve not only as prognostic factors but may be targets for new therapeutic strategies and predictors of response in a range of cancers. Prostate cancer development and progression is predicated on a series of genetic and epigenetic events within the prostate cell and its milieu. Within this review, we identify candidate molecules involved in diverse processes such as cell proliferation, death and apoptosis, signal transduction, androgen receptor (AR) signalling, cellular adhesion and angiogenesis that are linked to outcome in prostate cancer. Current markers with potential prognostic value include p53, Bcl-2, p16INK4A, p27Kip1, c-Myc, AR, E-cadherin and vascular endothelial growth factor. Evolving technology permits the identification of an increasing number of molecular markers with prognosis and predictive potential. We also review the use of gene microarray analysis in gene discovery as a means of identifying and cosegregating novel markers of prostate cancer outcome. By integrating selected markers into prospective clinical trials, there is potential for us to provide specific targeted therapy tailored for an increasing number of patients.

Angiogenesis-targeted therapies in prostate cancer

Most patients with metastatic prostate cancer will respond initially to ablation of gonadal androgen production. Eventually, all patients will develop progressive disease despite continued androgen suppression, a condition called androgen-independent or hormone-refractory prostate cancer. Hormone-refractory prostate cancer is characterized by virulent biologic and clinical behavior. Recently, docetaxel-based chemotherapy has been shown to improve survival and quality of life in this disease when compared with mitoxantrone-based therapy. However, results remain suboptimal. Recently, there have been remarkable advances in the delineation of the mechanisms of cancer growth, metastasis, and the intricate interactions between tumor cells and the surrounding normal tissues. The accumulated evidence has confirmed the importance of angiogenesis in these processes and validated the theory that inhibition of neovascularization is a promising therapeutic anticancer strategy. Currently, dozens of compounds that interfere with different steps of the angiogenic cascade are in preclinical and clinical development. Some of these agents have exhibited promising antitumor activity in hormone-refractory prostate cancer. This review summarizes the molecular mechanisms implicating angiogenesis in the development and progression of advanced-stage prostate cancer, as well as the drug development efforts that are targeting this process.

Targeting multiple signaling pathways as a strategy for managing prostate cancer: multifocal signal modulation therapy

The aberrant behavior of cancer reflects upregulation of certain oncogenic signaling pathways that promote proliferation, inhibit apoptosis, and enable the cancer to spread and evoke angiogenesis. Theoretically, it should be feasible to decrease the activity of these pathways-or increase the activity of pathways that oppose them-with noncytotoxic agents. Since multiple pathways are dysfunctional in most cancers, and cancers accumulate new oncogenic mutations as they progress, the greatest and most durable therapeutic benefit will likely be achieved with combination regimens that address several targets. Thus, a multifocal signal modulation therapy (MSMT) of cancer is proposed. This concept has already been documented by researchers who have shown that certain combinations of signal modulators-of limited utility when administered individually-can achieve dramatic suppression of tumor growth in rodent xenograft models. The present essay attempts to guide development of MSMTs for prostate cancer. Androgen ablation is a signal-modulating measure already in standard use in the management of delocalized prostate cancer. The additional molecular targets considered here include the type 1 insulin-like growth factor receptor, the epidermal growth factor receptor, mammalian target of rapamycin, NF-kappaB, hypoxia-inducible factor-1alpha, hsp90, cyclooxygenase-2, protein kinase A type I, vascular endothelial growth factor, 5-lipoxygenase, 12-lipoxygenase, angiotensin II receptor type 1, bradykinin receptor type 1, c-Src, interleukin-6, ras, MDM2, bcl-2/bclxL, vitamin D receptor, estrogen receptor-beta, and PPAR-. Various nutrients and phytochemicals suspected to have potential utility in prostate cancer prevention and therapy, but whose key molecular targets are still unknown, might reasonably be incorporated into MSMTs for prostate cancer; these include lycopene, selenium, green tea polyphenols, genistein, and silibinin. MSMTs can be developed systematically by testing various combinations of signal-modulating agents, in concentrations that can feasibly be achieved and maintained clinically, on human prostate cancer cell lines; combinations that appear promising can then be tested in xenograft models and, ultimately, in the clinic. Some signal modulators can increase response to cytotoxic drugs by upregulating effectors of apoptosis. When MSMTs fail to raise the spontaneous apoptosis rate sufficiently to achieve tumor stasis or regression, incorporation of appropriate cytotoxic agents into the regimen may improve the clinical outcome.

KAI1 promoter activity is dependent on p53, junB and AP2: evidence for a possible mechanism underlying loss of KAI1 expression in cancer cells

A molecular mechanism to explain reduced KAI1 expression in invasive and metastatic tumour cells remains elusive. In this report, we extend an earlier study in bladder cells to confirm that a 76 bp region of the KAI1 promoter (residues -922 to -847), with binding motifs for p53, AP1 and AP2, is required for high level activity of a KAI1 reporter in prostate cancer cell lines. Gel shift and supershift experiments supported binding of p53, junB and heterodimers of AP2alpha/AP2gamma or AP2beta/AP2gamma to this sequence. Introduction of mutations into specific motifs demonstrated an essential requirement for p53 and junB to reporter activity, and that functional synergy between these two factors enhanced activity. A further elevation of reporter activity required AP2. Roles of individual p53, junB and AP2 proteins, as well as functional synergy between p53 and junB, were confirmed in transfection experiments. Western blotting analysis showed that an absence of wild-type p53, and/or a loss of junB and AP2 protein expression, correlated with downregulation of KAI1 mRNA levels in a series of prostate cancer cell lines. A loss of p53 function and/or expression of junB, combined with reduced expression of specific AP2 proteins may underly downregulated KAI1 expression in tumour cells.

Loss of the AP-2α Transcription Factor Is Associated with the Grade of Human Gliomas

Purpose: The activator protein (AP)-2α transcription factor plays a crucial role in the progression of several human tumors, including malignant melanoma, prostate, and breast cancer. Loss of AP-2α results in deregulation of several genes with AP-2α binding motifs such as E-cadherin, p21WAF1, MMP-2, MCAM/MUC18, VEGF, and c-KIT. The purpose of our study was to determine AP-2α expression distribution among grades of gliomas and any possible effect on prognosis.

Experimental Design: A tissue microarray was assembled from all surgical glioma cases with available tissue samples at M.D. Anderson Cancer Center since 1986 to include 72 glioblastomas, 49 anaplastic astrocytomas, 9 low-grade astrocytoma, 37 oligodendrogliomas, 37 anaplastic oligodendrogliomas, 15 mixed oligoastrocytomas, 20 anaplastic mixed oligoastrocytomas, and 7 gliosarcomas. The microarray included normal brain tissue, and AP-2α expression was determined by immunohistochemistry.

Results: AP-2α expression was lost on 99% (P &lt; 0.001) and 98% (P &lt; 0.001) of glioblastomas and anaplastic astrocytomas, respectively, compared with grade 2 astrocytomas and normal brain, all of which (100%) maintained expression of AP-2α. The loss of AP-2α was a negative prognostic indicator within the overall category of gliomas by univariate analysis (rate ratio, 4.30; 95% confidence interval, 2.60-7.10; P &lt; 0.001). However, there was no significant effect of loss of AP-2α expression on survival observed after adjustment for patient age, Karnofsky Performance Scale score, tumor grade, and extent of resection (rate ratio, 1.2; 95% confidence interval, 0.6-2.2; P = 0.6).

Conclusions: AP-2α expression correlates inversely with glioma grade, suggesting a direct role in glioma tumorigenicity, possibly through subsequent deregulation of target genes. Of all the previously characterized markers of progression, the loss of AP-2α would be the most common (96.2%) molecular marker as an astrocytic tumor evolves from grade 2 to 3.

Identification of a novel functional androgen response element withinhPar1promoter: implications to prostate cancer progression

Human protease-activated receptor-1 (hPar1) plays a role in malignant and physiological invasion processes. We have identified a functional androgen response element (ARE) located in the hPar1 promoter upstream of the transcription start site at -1791 to -1777. Dihydrotestosterone treatment of the prostate cancer cell line LNCaP increased endogenous hPar1 mRNA levels, consistent with the threefold increase in promoter activity of hPar1-luciferase reporter construct. Specific binding of the hPar1-derived ARE to LNCaP nuclear extracts was demonstrated by electrophoretic mobility shift assay. This binding was abrogated by antiandrogen receptor (anti-AR) antibodies or excess cold oligonucleotide but not by a mutated oligonucleotide. Moreover, using chromatin immunoprecipitation assays, we confirm the in vivo interaction between the AR and ARE domain of the hPar1 promoter. In parallel, we show that hormone ablation therapy markedly reduces the otherwise high hPar1 expression levels in prostate cancer biopsy specimens. We suggest that the hPar1 gene is regulated transcriptionally by androgens, representing one of several target genes effectively reduced during hormone ablation therapy. A major limitation of hormonal deprivation is that it causes only a temporary remission, and the cancer eventually reappears in a more malignant, androgen-independent form. hPar1 is also overexpressed in CL1 cells, an aggressively metastasizing, hormone-independent subclone of LNCaP, and in PC3 prostate adenocarcinoma lacking AR in a mechanism yet to be fully elucidated. These data may imply that hPar1 expression correlates with prostate cancer progression in androgen-dependent and -independent phases and therefore, provides an instrumental, therapeutic target for treatment in prostate cancer.

Different signalling pathways regulate VEGF and IL-8 expression in breast cancer: implications for therapy

Elevated expression of pro-angiogenic cytokines is associated with aggressive tumour growth and decreased survival of patients with breast cancer. In general, the breast cancer cell lines with high vascular endothelial growth factor (VEGF) expression also express high levels of interleukin-8 (IL-8). The consequence of inhibiting mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3-kinase (PI3K), both implicated in regulation of these cytokines, was examined in four cell lines. Treatment with the mitogen-activated protein kinase/extracellular signal-related kinase (MEK) inhibitor U0126 reduced expression of VEGF and IL-8 in MDA-MB-231 cells, partially inhibited expression in MDA-MB-468 and Hs578T cells, with minimal effects in GI101A cells. Treatment with LY294002 reduced cytokine expression in GI101A and MDA-MB-468 cells, with partial reduction in Hs578T and less effect in MDA-MB-231 cells. Thus, IL-8 and VEGF were regulated by different signalling pathways in different cell lines; this suggests that inhibition of the dominantly active pathway can downregulate both angiogenic cytokines. Recognising which signalling pathway is active may identify targets for anti-angiogenic therapy of breast cancer.

Activator protein 2alpha associates with adenomatous polyposis coli/beta-catenin and Inhibits beta-catenin/T-cell factor transcriptional activity in colorectal cancer cells

In most human colorectal cancers, mutations in the adenomatous polyposis coli gene (APC) or CTNNB1 constitutively activate the beta-catenin/T-cell factor (TCF)/lymphoid enhancer factor (LEF) signaling pathway. Here, we show that the transcription factor activator protein (AP)-2alpha inhibited a beta-catenin/TCF-responsive reporter in human embryonic kidney 293 cells and in two human colorectal cancer lines, despite the fact that beta-catenin and TCF-4 protein levels were unchanged in the nucleus. Co-immunoprecipitation studies revealed that AP-2alpha formed a complex with APC and beta-catenin and that AP-2alpha disrupted beta-catenin/TCF-4 interactions in the nucleus. Thus, AP-2alpha.APC.beta-catenin complex formation appears to suppress beta-catenin transactivation by shifting the pool of nuclear beta-catenin toward an inactive form, having reduced binding to TCF/LEF transcription factors. Glutathione S-transferase pull-down assays showed that AP-2alpha physically associated with APC rather than with beta-catenin, and the AP-2alpha binding site was identified in the N terminus of APC, involving both the heptad and armadillo repeat domains, whereas the APC binding site in AP-2alpha was in the basic region of the C-terminal DNA binding domain. These findings provide the first evidence for a specific interaction between the tumor suppressor protein APC and the transcription factor AP-2alpha, and they suggest a link between the Wnt signaling pathway and various other pathways of development and differentiation associated with AP-2alpha.