Abstract 465: Human enhancer of filamentation 1 is a mediator of hypoxia-inducible factor-1 alpha-mediated migration in colorectal carcinoma cells

Human enhancer of filamentation 1 (HEF1, also known as NEDD9 or Cas-L) is a scaffolding protein that is implicated in regulating diverse cellular processes, including cellular attachment, motility, cell cycle progression, apoptosis and inflammation. Here, we identify HEF1 as a novel hypoxia-inducible factor-1α (HIF-1α) regulating gene and reveal that HEF1 mediates hypoxia-induced migration of colorectal cancer (CRC) cells. Moreover, we found that HIF-1α binds to a hypoxia-responsive element (HRE) of the HEF1 promoter to activate its transcription under hypoxic conditions. We further demonstrate that inhibition of HIF-1α expression abolished hypoxia-induced HEF1 expression and promoter activity in CRC cells. Importantly, silencing of HEF1 significantly inhibited hypoxia-stimulated HIF-1α transcriptional activity by preventing the interaction between HIF-1α and the transcriptional coactivator p300. HEF1 silencing also reduced the expression of hypoxia-inducible genes including those regulating cell motility and inhibited cell migration under hypoxic conditions. Thus, the positive feedback loop may contribute to adaptive responses by CRC cells that encounter hypoxia during CRC progression.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 465.

Abstract 5298: Human enhancer of filamentation 1 induction by Prostaglandin E2 enhances the cell motility of colorectal cancer cells

Prostaglandin (PG) E2 promotes cell motility during colorectal carcinogenesis. The mechanism by which PGE2 signaling regulates cell motility is not completely understood. Here, we demonstrated that PGE2 treatment induces HEF1 expression that links with cell motility in colorectal cancer cells. PGE2 rapidly stimulated HEF1 expression in colorectal cancer cells. Both PGE2 treatment and HEF1 overexpression activated Rac 1 and resulted in similar effects on cell spreading. Moreover, knockdown of HEF1 using shRNA suppressed PGE2-driven cell spreading. PKA activator forskolin induced HEF1 expression and cell spreading in a similar manner as PGE2. Inhibition of PKA activity by H-89 attenuated HEF1 expression induced by PGE2. Furthermore, PKA knockdown by siRNA blocked the HEF1 expression and cell spreading induced by PGE2. These data suggest that PGE2 induces HEF1 expression to promote cell motility through a PKA-involved pathway.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5298.

Cyclooxygenase-2 and cancer treatment: understanding the risk should be worth the reward

Targeting the prostaglandin (PG) pathway is potentially a critical intervention for the prevention and treatment of cancer. Central to PG biosynthesis are two isoforms of cyclooxygenase (COX 1 and 2), which produce prostaglandin H(2) (PGH(2)) from plasma membrane stores of fatty acids. COX-1 is constitutively expressed, whereas COX-2 is an inducible isoform upregulated in many cancers. Differences between COX-1 and COX-2 catalytic sites enabled development of selective inhibitors. Downstream of the COX enzymes, prostaglandin E(2) synthase converts available PGH(2) to prostaglandin E(2) (PGE(2)), which can stimulate cancer progression. Significant research efforts are helping identify more selective targets and fully elucidate the downstream targets of prostaglandin E(2)-mediated oncogenesis. Nonetheless, as a key rate-limiting control point of PG biosynthesis, COX-2 continues to be an important anticancer target. As we embark upon a new era of individualized medicine, a better understanding of the individual risk and/or benefit involved in COX-2 selective targeting is rapidly evolving. This review endeavors to summarize developments in our understanding of COX-2 and its downstream targets as vital areas of anticancer research and to provide the current status of an exciting aspect of molecular medicine.

HEF1 is a crucial mediator of the proliferative effects of prostaglandin E(2) on colon cancer cells

Prostaglandin E(2) (PGE(2)), one of the downstream products of cyclooxygenase-2 enzymatic activity, promotes colorectal carcinogenesis in part by stimulating cell division. In this study, we define a critical mechanism in this process by showing that the prometastatic adapter protein human enhancer of filamentation 1 (HEF1; NEDD9) links PGE(2) to the cell cycle machinery in colorectal cancer cells. PGE(2) rapidly induced expression of HEF1 mRNA and protein in colorectal cancer cells. HEF1 overexpression elicited the same effects as PGE(2) treatment on cell proliferation, cell cycle progression, and tumor growth. Conversely, HEF1 knockdown suppressed PGE(2)-driven cell proliferation and cell cycle progression. Cell cycle alterations involved HEF1 fragmentation as well as co-distribution of HEF1 and cell cycle kinase Aurora A along spindle asters during cell division. Moreover, Aurora A co-immunoprecipitated with HEF1 and was activated by HEF1. Consistent with a role for HEF1 in colorectal carcinogenesis, we found elevated expression of HEF1 expression in 50% of human colorectal cancers examined, relative to paired normal tissues. These findings establish that PGE(2) induces HEF1 expression, which in turn promotes cell cycle progression through its interaction with and activation of Aurora A. Further, they establish that HEF1 is a crucial downstream mediator of PGE(2) action during colorectal carcinogenesis.

Abstract B39: Prostaglandin E2 induces human enhancer of filamentation 1 to promote the cell motility of colorectal carcinoma cells

PGE2 promotes cell motility during colorectal carcinogenesis. The mechanism by which PGE2 signaling regulates cell motility is not completely understood. Here, we demonstrated that PGE2 treatment induces HEF1 expression that links with cell motility in colorectal cancer cells. PGE2 rapidly stimulated HEF1 expression in colorectal cancer cells. Both PGE2 treatment and HEF1 overexpression activated Rac 1 and resulted in similar effects on cell spreading. Moreover, knockdown of HEF1 using shRNA suppressed PGE2-driven cell spreading. PKA activator forskolin induced HEF1 expression and cell spreading in a similar manner as PGE2. Inhibition of PKA activity by H-89 attenuated HEF1 expression induced by PGE2. Furthermore, PKA knockdown by siRNA blocked the HEF1 expression and cell spreading induced by PGE2. These data suggest that PGE2 induces HEF1 expression to promote cell motility through a PKA-involved pathway.

Citation Information: Cancer Prev Res 2010;3(1 Suppl):B39.

Oleandrin-mediated inhibition of human tumor cell proliferation: importance of Na,K-ATPase alpha subunits as drug targets

Cardiac glycosides such as oleandrin are known to inhibit the Na,K-ATPase pump, resulting in a consequent increase in calcium influx in heart muscle. Here, we investigated the effect of oleandrin on the growth of human and mouse cancer cells in relation to Na,K-ATPase subunits. Oleandrin treatment resulted in selective inhibition of human cancer cell growth but not rodent cell proliferation, which corresponded to the relative level of Na,K-ATPase alpha3 subunit protein expression. Human pancreatic cancer cell lines were found to differentially express varying levels of alpha3 protein, but rodent cancer cells lacked discernable expression of this Na,K-ATPase isoform. A correlation was observed between the ratio of alpha3 to alpha1 isoforms and the level of oleandrin uptake during inhibition of cell growth and initiation of cell death; the higher the alpha3 expression relative to alpha1 expression, the more sensitive the cell was to treatment with oleandrin. Inhibition of proliferation of Panc-1 cells by oleandrin was significantly reduced when the relative expression of alpha3 was decreased by knocking down the expression of alpha3 isoform with alpha3 siRNA or increasing expression of the alpha1 isoform through transient transfection of alpha1 cDNA to the cells. Our data suggest that the relative lack of alpha3 (relative to alpha1) in rodent and some human tumor cells may explain their unresponsiveness to cardiac glycosides. In conclusion, the relatively higher expression of alpha3 with the limited expression of alpha1 may help predict which human tumors are likely to be responsive to treatment with potent lipid-soluble cardiac glycosides such as oleandrin.

Activator protein-1 has an essential role in pancreatic cancer cells and is regulated by a novel Akt-mediated mechanism

Activator protein-1 (AP-1) regulates the expression of several genes involved in human tumorigenesis. However, there is little known about this transcription factor in pancreatic ductal adenocarcinoma. We recently found high levels of AP-1-binding activities and multiple AP-1/DNA complexes containing c-Jun, JunD, Fra1, and Fra2 in pancreatic cancer cells. Transient transfection assays indicated that AP-1 was functional and capable of transactivating its gene targets. Furthermore, a c-Jun transactivation mutant inhibited anchorage-dependent and anchorage-independent proliferation, suggesting that AP-1 had an essential role in pancreatic cancer cells. Our study also uncovered a novel mechanism by which protein kinase Akt controls c-Jun activity in pancreatic cancer cells. Indeed, distinct from its known ability to induce c-fos and fra1 and to stabilize c-Jun, Akt appeared to directly regulate the transcriptional activity of c-Jun independently of the phosphorylation sites targeted by c-Jun NH(2)-terminal kinase (Ser(63)/Ser(73)) and glycogen synthase kinase-3 (Thr(239)). Our data also suggest that growth factors might use this Akt-regulated mechanism to potently induce c-Jun targets such as cyclin D1. Collectively, our findings indicate that AP-1 has an important function in pancreatic cancer cells and provide evidence for a previously unknown Akt-mediated mechanism of c-Jun activation.

Selenium and vitamin E: cell type- and intervention-specific tissue effects in prostate cancer

BACKGROUND

Secondary analyses of two randomized, controlled phase III trials demonstrated that selenium and vitamin E could reduce prostate cancer incidence. To characterize pharmacodynamic and gene expression effects associated with use of selenium and vitamin E, we undertook a randomized, placebo-controlled phase IIA study of prostate cancer patients before prostatectomy and created a preoperative model for prostatectomy tissue interrogation.

METHODS

Thirty-nine men with prostate cancer were randomly assigned to treatment with 200 microg of selenium, 400 IU of vitamin E, both, or placebo. Laser capture microdissection of prostatectomy biopsy specimens was used to isolate normal, stromal, and tumor cells. Gene expression in each cell type was studied with microarray analysis and validated with a real-time polymerase chain reaction (PCR) and immunohistochemistry. An analysis of variance model was fit to identify genes differentially expressed between treatments and cell types. A beta-uniform mixture model was used to analyze differential expression of genes and to assess the false discovery rate. All statistical tests were two-sided.

RESULTS

The highest numbers of differentially expressed genes by treatment were 1329 (63%) of 2109 genes in normal epithelial cells after selenium treatment, 1354 (66%) of 2051 genes in stromal cells after vitamin E treatment, and 329 (56%) of 587 genes in tumor cells after combination treatment (false discovery rate = 2%). Validation of 21 representative genes across all treatments and all cell types yielded Spearman correlation coefficients between the microarray analysis and the PCR validation ranging from 0.64 (95% confidence interval [CI] = 0.31 to 0.79) for the vitamin E group to 0.87 (95% CI = 0.53 to 0.99) for the selenium group. The increase in the mean percentage of p53-positive tumor cells in the selenium-treated group (26.3%), compared with that in the placebo-treated group (5%), showed borderline statistical significance (difference = 21.3%; 95% CI = 0.7 to 41.8; P = .051).

CONCLUSIONS

We have demonstrated the feasibility and efficiency of the preoperative model and its power as a hypothesis-generating engine. We have also identified cell type- and zone-specific tissue effects of interventions with selenium and vitamin E that may have clinical implications.

Survivin expression in normal human bronchial epithelial cells: an early and critical step in tumorigenesis induced by tobacco exposure

The inhibitor of apoptosis protein survivin is selectively expressed in tumor cells. The tobacco component nicotine increases the transcription of the survivin gene in non-small cell lung cancer cells. However, the role of survivin expression induced by tobacco component is not clear during lung carcinogenesis. We investigated the effects of the tobacco components nicotine and its related carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) on survivin expression in normal human bronchial epithelial (NHBE) cells and examined the role of survivin in the malignant transformation of normal human bronchial epithelial (HBE) cells induced by these components. We found that survivin messenger RNA (mRNA) expression was detected in 41% (7 of 17) of bronchial brush specimens from heavy smokers. Nicotine and NNK increased survivin mRNA and protein expression levels in primary cultured NHBE cells and immortalized HBE cells. Bronchial epithelium in mice administered NNK also showed increased staining for survivin. Nicotine and NNK stimulated the Akt-mammalian target of rapamycin (mTOR) pathway in NHBE cells, leading to increased de novo synthesis of survivin protein. Induced survivin expression increased the survival potential of the cells, which was blocked by transfection with survivin-specific small interfering RNA (siRNA). siRNA-induced down-regulation of survivin expression also suppressed the tumorigenic potential of premalignant and malignant HBE cells exposed to the tobacco components. These findings suggest that NNK and nicotine induce survivin protein synthesis in NHBE cells by activating the Akt-mTOR pathway and thus blockade of the pathway effectively inhibits the tobacco-induced malignant transformation of HBE cells.

Establishment of three-dimensional cultures of human pancreatic duct epithelial cells

Three-dimensional (3D) cultures of epithelial cells offer singular advantages for studies of morphogenesis or the role of cancer genes in oncogenesis. In this study, as part of establishing a 3D culture system of pancreatic duct epithelial cells, we compared human pancreatic duct epithelial cells (HPDE-E6E7) with pancreatic cancer cell lines. Our results show, that in contrast to cancer cells, HPDE-E6E7 organized into spheroids with what appeared to be apical and basal membranes and a luminal space. Immunostaining experiments indicated that protein kinase Akt was phosphorylated (Ser473) and CTMP, a negative Akt regulator, was expressed in both HPDE-E6E7 and cancer cells. However, a nuclear pool of CTMP was detectable in HPDE-E6E7 cells that showed a dynamic concentrated expression pattern, a feature that further distinguished HPDE-E637 cells from cancer cells. Collectively, these data suggest that 3D cultures of HPDE-E6E7 cells are useful for investigating signaling and morphological abnormalities in pancreatic cancer cells.

15-Lipoxygenase-2 gene regulation by its product 15-(S)-hydroxyeicosatetraenoic acid through a negative feedback mechanism that involves peroxisome proliferator-activated receptor gamma

An inverse relationship exists between the expression of 15-lipoxygenase-2 (15-LOX-2) and peroxisome proliferator-activated receptor gamma (PPARgamma) in normal prostate epithelial cells (PrECs) compared with their expression in prostate carcinoma cells (PC-3). The reason for this difference, however, is unknown. We hypothesized that this inverse expression partly involves the 15-LOX-2 promoter and 15-S-hydroxyeicosatetraenoic acid (15-(S)-HETE), a product of 15-LOX-2 that binds to PPARgamma. We identified an active steroid nuclear receptor half-site present in the 15-LOX-2 promoter fragment F-5 (-618/+177) that can interact with PPARgamma. After forced expression of wild-type PPARgamma, 15-(S)-HETE (1 microM) decreased F-5 reporter activity in PrECs whereas forced expression of 15-LOX-2 resulted in 15-(S)-HETE production which enhanced F-5 activity in PC-3. In contrast, the expression of dominant-negative PPARgamma reversed the transcriptional activation of F-5 by enhancing it 202-fold in PrEC or suppressing it in PC-3; the effect in PC-3 was positively increased 150-fold in the presence of 15-(S)-HETE (1 microM). Peroxisome proliferator-activated receptor gamma interacted with 15-LOX-2 promoter sequences in pulldown experiments using biotinylated 15-LOX-2 (-560/-596 bp) oligonucleotides. In gelshift analyses PPARgamma and orphan receptor RORalpha were shown to interact with the F-5 fragment in PC-3 cells. These data suggest that crosstalk mechanisms exist between the 15-LOX-2 gene and PPARgamma to counterbalance expression and help explain the inverse relationship of these genes in normal versus cancer cells.

Selenium Accumulation in Prostate Tissue During a Randomized, Controlled Short-term Trial of l-Selenomethionine: a Southwest Oncology Group Study

PURPOSE

Epidemiologic and clinical data suggest that selenium could prevent prostate cancer, but it has not been shown that supplemental selenium leads to an increased concentration of selenium in prostate tissue compared with adjacent tissue.

EXPERIMENTAL DESIGN

We conducted a randomized, controlled, short-term trial of l-selenomethionine (SeMet) versus observation in men with organ-confined prostate cancer. The primary endpoint was the measurement of selenium concentration in prostate tissue and seminal vesicle (SV). We assessed baseline selenium levels in serum and in toenail specimens (reflecting long-term intake) and post-intervention selenium levels in serum, and in prostate and SV tissues using hydride generation atomic fluorescence spectroscopy.

RESULTS

Sixty-six eligible patients were randomly assigned to the SeMet (n = 34) or observation (n = 32) arm; both arms had similar baseline patient characteristics. Baseline serum selenium was similar in the two groups (P = 0.64). Baseline toenail selenium levels were slightly higher in the SeMet group than in the control group (P = 0.07). After the intervention, the mean serum selenium level increased 15% in the SeMet arm and was higher than in the observation arm (P = 0.001). The selenium concentration in prostate tissue was 22% higher in the SeMet arm (n = 26) than in the observation arm (n = 25; 1.80 versus 1.47 ppm; P = 0.003, Wilcoxon rank sum test) and remained significantly higher after adjusting for chronic selenium intake (P = 0.021, ANCOVA). SV selenium concentration was similar in both groups (P = 0.384) and was lower than in prostate tissue.

CONCLUSIONS

The present study is the first to show that selenium taken as oral supplementation accumulates preferentially in the human prostate gland as opposed to the SV. These findings support the hypothesis that oral selenium supplementation may contribute to the cancer preventive effects of selenium.

Suppression of prostate tumor cell growth by stromal cell prostaglandin D synthase-derived products

Stromal-epithelial interactions and the bioactive molecules produced by these interactions maintain tissue homeostasis and influence carcinogenesis. Bioactive prostaglandins produced by prostaglandin synthases and secreted by the prostate into seminal plasma are thought to support reproduction, but their endogenous effects on cancer formation remain unresolved. No studies to date have examined prostaglandin enzyme production or prostaglandin metabolism in normal prostate stromal cells. Our results show that lipocalin-type prostaglandin D synthase (L-PGDS) and prostaglandin D2 (PGD2) metabolites produced by normal prostate stromal cells inhibited tumor cell growth through a peroxisome proliferator-activated receptor gamma (PPARgamma)-dependent mechanism. Enzymatic products of stromal cell L-PGDS included high levels of PGD2 and 15-deoxy-delta(12,14)-PGD2 but low levels of 15-deoxy-delta(12,14)-prostaglandin J2. These PGD2 metabolites activated the PPARgamma ligand-binding domain and the peroxisome proliferator response element reporter systems. Thus, growth suppression of PPARgamma-expressing tumor cells by PGD2 metabolites in the prostate microenvironment is likely to be an endogenous mechanism involved in tumor suppression that potentially contributes to the indolence and long latency period of this disease.

Inverse relationship between 15-lipoxygenase-2 and PPAR-gamma gene expression in normal epithelia compared with tumor epithelia

15-Lipoxygenase-2 (15-LOX-2) synthesizes 15-S-hydroxyeicosatetraenoic acid (15-S-HETE), an endogenous ligand for the nuclear receptor, peroxisome proliferator-activated receptor-gamma (PPAR-gamma). Several studies have described an inverse relationship between 15-LOX-2 and PPAR-gamma expression in normal versus tumor samples. To systematically determine if this is a ubiquitous phenomenon, we used a variety of epithelial and nonepithelial cells and some tissues to further evaluate the extent of this inverse relationship. The levels of mRNA or protein were measured by reverse transcriptase polymerase chain reaction or Western gray level intensity, whereas distribution was determined by in situ hybridization or immunofluorescence. 15-S-HETE was measured by liquid chromatography/tandem mass spectrometry. Normal epithelial cells/samples generally expressed high levels of 15-LOX-2 along with the enzyme product 15-S-HETE, but both levels were reduced in cancer cells/samples. In contrast, most cancer cells expressed high levels of PPAR-gamma mRNA and protein, which were absent from normal epithelial cells. Overall, the inverse relationship between these two genes was primarily restricted to epithelial samples. Forced expression of PPAR-gamma reduced 15-LOX-2 protein levels in normal cells, whereas forced expression of 15-LOX-2 in tumor cells suppressed PPAR-gamma protein levels. These results suggest that feedback mechanisms may contribute to the loss of 15-LOX-2 pathway components, which coincide with an increase in PPAR-gamma in many epithelial cancers.

Differential peroxisome proliferator-activated receptor-gamma isoform expression and agonist effects in normal and malignant prostate cells

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is being studied intensively for its role in carcinogenesis and in mediating the effects of prostate cancer treatment and prevention drugs. Prostate cancers express abundant and higher constitutive levels of PPAR-gamma than do normal prostate cells and are growth inhibited by ligand activation of PPAR-gamma. However, little is known about the role of PPARs in tumorigenesis or in normal prostate epithelial cells (EC). We examined the expression, phosphorylation patterns, and functions of the human PPAR (hPPAR)-gamma1 and hPPAR-gamma2 isoforms in normal prostate ECs to determine if activation of the receptor is sufficient for PPAR-gamma ligand activity in prostate cells. We found that ECs did not express either PPAR-gamma1 or PPAR-gamma2 protein and were not sensitive to growth inhibition by the PPAR-gamma ligand 15-deoxy-Delta12,14-prostaglandin J(2) (15d-PGJ(2)). In contrast, prostate cancer cells (PC-3), which express PPAR-gamma1 receptor isoform, are growth inhibited by PPAR-gamma ligand. Forced expression of hPPAR-gamma1 or hPPAR-gamma2 made ECs sensitive to 15d-PGJ(2) and led to reduced cellular viability. The direct repeat-1 promoter containing PPAR response elements was transactivated in ECs expressing exogenous PPAR-gamma1 or PPAR-gamma2, indicating that either isoform can be active in these cells. 15-Lipoxygenase-2, expressed at high levels in ECs, was down-regulated by transfecting PPAR-gamma expression construct (either gamma1 or gamma2 isoform) into ECs. Addition of PPAR-gamma ligand 15-hydroxyeicosatetraenoic acid in the presence of PPAR-gamma expression caused further down-regulation of 15-lipoxygenase-2. Our data illustrate that a PPAR-gamma ligand (15d-PGJ(2)) activates PPAR-gamma1 and selectively induces cell death in human prostate cancer cells but not in normal prostate ECs. These findings have important implications for the development of PPAR-gamma-targeting agents that prevent or treat prostate cancer and spare normal prostate cells.

Peroxisome Proliferator-Activated Receptor-γ Suppresses Cyclooxygenase-2 Expression in Human Prostate Cells

Recent studies have found that cyclooxygenase-2 (COX-2) protein expression was low and inducible with cytokines in prostate cancer cells (in the absence of serum) and that, in contrast, COX-2 expression was high in normal prostate epithelial cells (EC). Peroxisome proliferator-activated receptor-γ (PPAR-γ) was expressed at high levels in the prostate cancer cell line PC-3 but not in ECs. In contrast to previous findings by others, PPAR-γ ligands did not induce PPAR-γ expression in EC or PC-3. The present study examined the relationship between PPAR-γ and COX-2 expression patterns in EC and PC-3 in the presence and absence of serum and/or the PPAR-γ agonist 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2). We also evaluated the effects that the forced expression of PPAR-γ1 and PPAR-γ2 had on COX-2 in ECs. We found that expression of PPAR-γ and COX-2 protein was inversely correlated in ECs and PC-3. Low COX-2 expression in PC-3 was up-regulated by serum, and 15d-PGJ2 blocked serum-induced COX-2 expression and activity in a dose-dependent manner. 15d-PGJ2 had no effect on COX-2 expression in ECs or PPAR-γ expression in either cell type. However, forced expression of PPAR-γ1 or PPAR-γ2 in ECs suppressed the high level of endogenous COX-2. This effect was not isoform specific and was augmented by 15d-PGJ2. The present study showed that PPAR-γ activation can be an important regulator of COX-2 in prostate cells and may be an important target for prostate cancer chemoprevention.

Differential Peroxisome Proliferator-Activated Receptor-γ Isoform Expression and Agonist Effects in Normal and Malignant Prostate Cells

Peroxisome proliferator-activated receptor-γ (PPAR-γ) is being studied intensively for its role in carcinogenesis and in mediating the effects of prostate cancer treatment and prevention drugs. Prostate cancers express abundant and higher constitutive levels of PPAR-γ than do normal prostate cells and are growth inhibited by ligand activation of PPAR-γ. However, little is known about the role of PPARs in tumorigenesis or in normal prostate epithelial cells (EC). We examined the expression, phosphorylation patterns, and functions of the human PPAR (hPPAR)-γ1 and hPPAR-γ2 isoforms in normal prostate ECs to determine if activation of the receptor is sufficient for PPAR-γ ligand activity in prostate cells. We found that ECs did not express either PPAR-γ1 or PPAR-γ2 protein and were not sensitive to growth inhibition by the PPAR-γ ligand 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2). In contrast, prostate cancer cells (PC-3), which express PPAR-γ1 receptor isoform, are growth inhibited by PPAR-γ ligand. Forced expression of hPPAR-γ1 or hPPAR-γ2 made ECs sensitive to 15d-PGJ2 and led to reduced cellular viability. The direct repeat-1 promoter containing PPAR response elements was transactivated in ECs expressing exogenous PPAR-γ1 or PPAR-γ2, indicating that either isoform can be active in these cells. 15-Lipoxygenase-2, expressed at high levels in ECs, was down-regulated by transfecting PPAR-γ expression construct (either γ1 or γ2 isoform) into ECs. Addition of PPAR-γ ligand 15-hydroxyeicosatetraenoic acid in the presence of PPAR-γ expression caused further down-regulation of 15-lipoxygenase-2. Our data illustrate that a PPAR-γ ligand (15d-PGJ2) activates PPAR-γ1 and selectively induces cell death in human prostate cancer cells but not in normal prostate ECs. These findings have important implications for the development of PPAR-γ-targeting agents that prevent or treat prostate cancer and spare normal prostate cells.

Peroxisome proliferator-activated receptor-gamma suppresses cyclooxygenase-2 expression in human prostate cells

Recent studies have found that cyclooxygenase-2 (COX-2) protein expression was low and inducible with cytokines in prostate cancer cells (in the absence of serum) and that, in contrast, COX-2 expression was high in normal prostate epithelial cells (EC). Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) was expressed at high levels in the prostate cancer cell line PC-3 but not in ECs. In contrast to previous findings by others, PPAR-gamma ligands did not induce PPAR-gamma expression in EC or PC-3. The present study examined the relationship between PPAR-gamma and COX-2 expression patterns in EC and PC-3 in the presence and absence of serum and/or the PPAR-gamma agonist 15-deoxy-Delta12,14-prostaglandin J(2) (15d-PGJ(2)). We also evaluated the effects that the forced expression of PPAR-gamma1 and PPAR-gamma2 had on COX-2 in ECs. We found that expression of PPAR-gamma and COX-2 protein was inversely correlated in ECs and PC-3. Low COX-2 expression in PC-3 was up-regulated by serum, and 15d-PGJ(2) blocked serum-induced COX-2 expression and activity in a dose-dependent manner. 15d-PGJ(2) had no effect on COX-2 expression in ECs or PPAR-gamma expression in either cell type. However, forced expression of PPAR-gamma1 or PPAR-gamma2 in ECs suppressed the high level of endogenous COX-2. This effect was not isoform specific and was augmented by 15d-PGJ(2). The present study showed that PPAR-gamma activation can be an important regulator of COX-2 in prostate cells and may be an important target for prostate cancer chemoprevention.

Formation and antiproliferative effect of prostaglandin E(3) from eicosapentaenoic acid in human lung cancer cells

We investigated the formation and pharmacology of prostaglandin E(3) (PGE(3)) derived from fish oil eicosapentaenoic acid (EPA) in human lung cancer A549 cells. Exposure of A549 cells to EPA resulted in the rapid formation and export of PGE(3.) The extracellular ratio of PGE(3) to PGE(2) increased from 0.08 in control cells to 0.8 in cells exposed to EPA within 48 h. Incubation of EPA with cloned ovine or human recombinant cyclooxygenase 2 (COX-2) resulted in 13- and 18-fold greater formation of PGE(3), respectively, than that produced by COX-1. Exposure of A549 cells to 1 microM PGE(3) inhibited cell proliferation by 37.1% (P < 0.05). Exposure of normal human bronchial epithelial (NHBE) cells to PGE(3), however, had no effect. When A549 cells were exposed to EPA (25 microM) or a combination of EPA and celecoxib (a selective COX-2 inhibitor), the inhibitory effect of EPA on the growth of A549 cells was reversed by the presence of celecoxib (at both 5 and 10 microM). This effect appears to be associated with a 50% reduction of PGE(3) formation in cells treated with a combination of EPA and celecoxib compared with cells exposed to EPA alone. These data indicate that exposure of lung cancer cells to EPA results in a decrease in the COX-2-mediated formation of PGE(2), an increase in the level of PGE(3), and PGE(3)-mediated inhibition of tumor cell proliferation.

Glycogen synthase kinase-3 beta is involved in the phosphorylation and suppression of androgen receptor activity

Kinases can phosphorylate and regulate androgen receptor activity during prostate cancer progression. In particular, we showed that glycogen synthase kinase-3 beta phosphorylates the androgen receptor, thereby inhibiting androgen receptor-driven transcription. Conversely, the glycogen synthase kinase-3 beta inhibitor lithium chloride suppressed the glycogen synthase kinase-3 beta-mediated phosphorylation of the androgen receptor, thereby enabling androgen receptor-driven transcription to occur. The androgen receptor hinge and ligand-binding domains were important for both the phosphorylation and the inhibition of transcriptional activity of the receptor by glycogen synthase kinase-3 beta. Furthermore, androgen receptor phosphorylation was augmented by LY294002, an indirect inhibitor of protein kinase B/Akt that inhibits glycogen synthase kinase-3 beta. We also showed that the mutation of various phosphorylation sites on glycogen synthase kinase-3 beta affected the ability of these mutants to co-distribute with the androgen receptor in the cell nucleus, also that both glycogen synthase kinase-3beta and androgen receptor proteins can be found in cell nuclei of prostate cancer tissue samples. Because glycogen synthase kinase-3 beta activity is suppressed after the enzyme is phosphorylated by protein kinase B/Akt and Akt activity frequently increases during the progression of prostate cancer, nullification of the glycogen synthase kinase-3 beta-mediated suppression of androgen receptor activity by Akt likely contributes to prostate cancer progression.

Alleviating the suppression of glycogen synthase kinase-3beta by Akt leads to the phosphorylation of cAMP-response element-binding protein and its transactivation in intact cell nuclei

Glycogen synthase kinase-3beta (GSK-3beta) activity is suppressed when it becomes phosphorylated on serine 9 by protein kinase B (Akt). To determine how GSK-3beta activity opposes Akt function we used various methods to alleviate GSK-3beta suppression in prostate carcinoma cells. In some experiments, LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (a kinase involved in activating Akt) and tumor necrosis factor-alpha (TNF-alpha) were used to activate GSK-3beta. In other experiments mutant forms of GSK-3beta, GSK-3betadelta9 (a constitutively active deletion mutant of GSK-3beta) and GSK-3betaY216F (an inactive point mutant of GSK-3beta) were used to alter GSK-3beta activity. LY294002, TNF-alpha, and overexpression of wild-type GSK-3beta or of GSK-3betadelta9, but not GSK-3betaY216F, alleviated the suppression of GSK-3beta activity in prostate carcinoma cells and enhanced the turnover of beta-catenin. Forced expression of wild-type GSK-3beta or of GSK-3betadelta9, but not GSK-3betaY216F, suppressed cell growth and showed that the phosphorylation status of GSK-3beta can affect its intracellular distribution. When transcription factors activator protein-1 and cyclic AMP-response element (CRE)-binding protein were analyzed as targets of GSK-3beta activity, overexpression of wild-type GSK-3beta suppressed AP1-mediated transcription and activated CRE-mediated transcription. Overexpression of GSK-3betadelta9 caused an (80-fold) increase in CRE-mediated transcription, which was further amplified (up to 130-fold) by combining GSK-3betadelta9 overexpression with the suppression of Jun activity. This study also demonstrated for the first time that expression of constitutively active GSK-3betadelta9 results in the phosphorylation of CRE-binding protein on serine 129 and enhancement of CRE-mediated transcription in intact cell nuclei.

Cyclooxygenase 2 selective inhibitors in cancer treatment and prevention

Prostaglandin synthesis by a number of enzymes is important at all stages during the genesis of cancer. The availability of prostaglandin H(2) as a substrate for prostaglandin production is a critical control point in its synthesis. Cyclooxygenase (COX) occurs in two forms (COX-1 and -2) and acts as the rate-limiting enzyme that generates prostaglandin H(2). COX-1 is produced as a steady-state enzyme, while COX-2 is heavily involved in inflammation and tumorigenesis. Differences in the catalytic sites of these enzymes are utilised to generate COX-2 selective inhibitors. Certain chemical characteristics of non-steroidal anti-inflammatory drugs and COX-2 selective inhibitors make some of these inhibitors more effective against COX-2 than others. Epidemiological, animal and preclinical data demonstrate the promise of non-steroidal anti-inflammatory drugs and COX-2 selective inhibitors as anticancer agents. Ongoing clinical trials are designed to determine the efficacy of non-steroidal anti-inflammatory drugs and COX-2 selective inhibitors in the prevention and treatment of many types of cancer.

Her-2/neu gene amplification in ductal carcinoma in situ of the breast

This study evaluated the relative frequencies of HER-2/neu gene amplification in ductal carcinoma in situ (DCIS)-associated invasive breast cancer and DCIS alone. We examined archival tissue samples of 100 DCIS lesions with an invasive component (cases) and 100 without an invasive component (controls), with cases and controls matched by pathologic nuclear grade. HER-2/neu gene amplification was determined by fluorescence in situ hybridization. We compared HER-2/neu gene amplification in DCIS lesions only, irrespective of the presence or absence of an invasive component. HER-2/neu gene amplification occurred significantly less frequently in the cases (26%) than in the controls (40%), with an odds ratio of 0.35 (95% confidence interval, 0.17-0.72; P < 0.004) after adjustment for pathologic and quantitative-image-analyzed morphometric nuclear grade. The HER-2/neu gene also was amplified more frequently in higher- than in lower-grade DCIS alone (56% versus 19%, respectively; P < 0.0001) or in higher- than in lower-grade DCIS with invasive cancer (44% versus 2%, respectively; P < 0.00001). Future studies should examine the potential roles of HER-2/neu and other biomarkers (e.g., p21 and Rb) as markers of the risk of DCIS patients for invasive breast cancer and as molecular targets of chemoprevention in breast intraepithelial neoplasia.

Computerized image analysis of Ki-67 in ductal breast carcinoma in situ

OBJECTIVE

To develop and determine the staining protocols and computerized image analysis methods that are the most effective combination for performing quantitative analysis of Ki-67.

STUDY DESIGN

We compared conventional bright-field light microscopy and refractive optical enhancement methods in combination with various immunodetection and filter enhancement methods, including immunogold in combination with epipolarization refractive optics and enzymatic conversion of chromogenic substrates in combination with optical filter enhancement. Initial Ki-67 tests were performed on lymph node tissues and cultured human breast cells and then applied to 200 ductal carcinoma in situ (DCIS) samples. DCIS acini were digitally acquired, and a region of interest was manually outlined in each one with a digital stylus to include only the cellular component; then the Ki-67 staining index was quantified by segmentation analysis.

RESULTS

Although combining epipolarization analysis with immunohistogold staining was the most sensitive detection method, nonspecific binding was too high. The streptavidin-horseradish-peroxidase enzymatic conversion of 3,3'-diaminobenzidine (DAB) in combination with optical enhancement filters was the most effective method tested. Ki-67 stain was associated with dense fibrillar structures of the nucleoli in the less intensely staining nuclei and was most intense in paired nuclei.

CONCLUSION

The method of measuring Ki-67 expression by DAB staining combined with optical enhancement filters and quantification via computer-assisted image analysis techniques produced objective and reproducible results. As such, this method can offer (1) less intraobserver and interobserver variability, (2) a digital archival record, and (3) a baseline for digital exchange of information between studies.

Differential expression of cyclooxygenase-2 and its regulation by tumor necrosis factor-alpha in normal and malignant prostate cells

Cyclooxygenase (COX)-2 expression is elevated in some malignancies; however, information is scarce regarding COX-2 contributions to the development of prostate cancer and its regulation by inflammatory cytokines. The present study compared and contrasted the expression levels and subcellular distribution patterns of COX-1 and COX-2 in normal prostate [prostate epithelial cell (PrEC), prostate smooth muscle (PrSM), and prostate stromal (PrSt)] primary cell cultures and prostatic carcinoma cell lines (PC-3, LNCaP, and DU145). The basal COX-2 mRNA and protein levels were high in normal PrEC and low in tumor cells, unlike many other normal cells and tumor cells. Because COX-2 levels were low in prostate smooth muscle cells, prostate stromal cells, and tumor cells, we also examined whether COX-1 and COX-2 gene expression was elevated in response to tumor necrosis factor-alpha (TNF-alpha), a strong inducer of COX-2 expression. Northern blot analysis and reverse transcription-PCR demonstrated different patterns and kinetics of expression for COX-1 and COX-2 among normal cells and tumor cells in response to TNF-alpha. In particular, COX-2 protein levels increased, and the subcellular distribution formed a distinct perinuclear ring in the normal cells at 4 h after TNF-alpha exposure. The COX-2 protein levels also increased in cancer cells, but the subcellular distribution was less organized; COX-2 protein appeared diffuse in some cells and accumulated as focal deposits in the cytoplasm of other cells. TNF-alpha induction of COX-2 and prostaglandin E2 correlated inversely with induction of apoptosis. We conclude that COX-2 expression may be important to PrEC cell function. Although it is low in stromal and tumor cells, COX-2 expression is induced by TNF-alpha in these cells, and this responsiveness may play an important role in prostate cancer progression.