Pigment epithelium-derived factor restoration increases bone mass and improves bone plasticity in a model of osteogenesis imperfecta type VI via Wnt3a blockade.

Null mutations in for pigment epithelium-derived factor (PEDF), the protein product of the SERPINF1 gene, are the cause of osteogenesis imperfecta (OI) type VI. The PEDF-knockout (KO) mouse captures crucial elements of the human disease, including diminished bone mineralization and propensity to fracture. Our group and others have demonstrated that PEDF directs human mesenchymal stem cell (hMSC) commitment to the osteoblast lineage and modulates Wnt/ß-catenin signaling, a major regulator of bone development; however, the ability of PEDF to restore bone mass in a mouse model of OI type VI has not been determined. In this study, PEDF delivery increased trabecular bone volume/total volume by 52% in 6-mo-old PEDF-KO mice but not in wild-type mice. In young (19-d-old) PEDF-KO mice, PEDF restoration increased bone volume fraction by 35% and enhanced biomechanical parameters of bone plasticity. A Wnt-green fluorescent protein reporter demonstrated dynamic changes in Wnt/ß-catenin signaling characterized by early activation and marked suppression during terminal differentiation of hMSCs. Continuous Wnt3a exposure impeded mineralization of hMSCs, whereas the combination of Wnt3a and PEDF potentiated mineralization. Interrogation of the PEDF sequence identified a conserved motif found in other Wnt modulators, such as the dickkopf proteins. Mutation of a single amino acid on a 34-mer PEDF peptide increased mineralization of hMSC cultures compared with the native peptide sequence. These results indicate that PEDF counters Wnt signaling to allow for osteoblast differentiation and provides a mechanistic insight into how the PEDF null state results in OI type VI.-Belinsky, G. S., Sreekumar, B., Andrejecsk, J. W., Saltzman, W. M., Gong, J., Herzog, R. I., Lin, S., Horsley, V., Carpenter, T. O., Chung, C. Pigment epithelium-derived factor restoration increases bone mass and improves bone plasticity in a model of osteogenesis imperfecta type VI via Wnt3a blockade.

Connexin hemichannels contribute to spontaneous electrical activity in the human fetal cortex.

Before the human cortex is able to process sensory information, young postmitotic neurons must maintain occasional bursts of action-potential firing to attract and keep synaptic contacts, to drive gene expression, and to transition to mature membrane properties. Before birth, human subplate (SP) neurons are spontaneously active, displaying bursts of electrical activity (plateau depolarizations with action potentials). Using whole-cell recordings in acute cortical slices, we investigated the source of this early activity. The spontaneous depolarizations in human SP neurons at midgestation (17-23 gestational weeks) were not completely eliminated by tetrodotoxin--a drug that blocks action potential firing and network activity--or by antagonists of glutamatergic, GABAergic, or glycinergic synaptic transmission. We then turned our focus away from standard chemical synapses to connexin-based gap junctions and hemichannels. PCR and immunohistochemical analysis identified the presence of connexins (Cx26/Cx32/Cx36) in the human fetal cortex. However, the connexin-positive cells were not found in clusters but, rather, were dispersed in the SP zone. Also, gap junction-permeable dyes did not diffuse to neighboring cells, suggesting that SP neurons were not strongly coupled to other cells at this age. Application of the gap junction and hemichannel inhibitors octanol, flufenamic acid, and carbenoxolone significantly blocked spontaneous activity. The putative hemichannel antagonist lanthanum alone was a potent inhibitor of the spontaneous activity. Together, these data suggest that connexin hemichannels contribute to spontaneous depolarizations in the human fetal cortex during the second trimester of gestation.

Pharmacological inhibition of Mdm2 triggers growth arrest and promotes DNA breakage in mouse colon tumors and human colon cancer cells.

The p53 tumor suppressor protein performs a number of cellular functions, ranging from the induction of cell cycle arrest and apoptosis to effects on DNA repair. Modulating p53 activity with Mdm2 inhibitors is a promising approach for treating cancer; however, it is presently unclear how the in vivo application of Mdm2 inhibitors impact the myriad processes orchestrated by p53. Since approximately half of all colon cancers (predominately cancers with microsatellite instability) are p53-normal, we assessed the anticancer activity of the Mdm2 inhibitor Nutlin-3 in the mouse azoxymethane (AOM) colon cancer model, in which p53 remains wild type. Using a cell line derived from an AOM-induced tumor, we found that four daily exposures to Nutlin-3 induced persistent p53 stabilization and cell cycle arrest without significant apoptosis. A 4-day dosing schedule in vivo generated a similar response in colon tumors; growth arrest without significantly increased apoptosis. In adjacent normal colon tissue, Nutlin-3 treatment reduced both cell proliferation and apoptosis. Surprisingly, Nutlin-3 induced a transient DNA damage response in tumors but not in adjacent normal tissue. Nutlin-3 likewise induced a transient DNA damage response in human colon cancer cells in a p53-dependent manner, and enhanced DNA strand breakage and cell death induced by doxorubicin. Our findings indicate that Mdm2 inhibitors not only trigger growth arrest, but may also stimulate p53's reported ability to slow homologous recombination repair. The potential impact of Nutlin-3 on DNA repair in tumors suggests that Mdm2 inhibitors may significantly accentuate the tumoricidal actions of certain therapeutic modalities.

The contribution of methotrexate exposure and host factors on transcriptional variance in human liver.

Long-term administration of methotrexate (MTX) for management of chronic inflammatory diseases is associated with risk of liver damage. In this study, we examined the transcriptional profiles of livers from patients treated with MTX. The possibility that expression signatures correlate with grade of fibrosis or underlying rheumatic disease was evaluated. Twenty-seven patients taking MTX were accrued for this study. Ten non-MTX-exposed normal liver specimens were used as controls. Global mRNA expression was assayed using oligonucleotide arrays. A total of 205 genes were significantly altered in MTX-exposed livers. Six of these genes were validated by qPCR. Two genes, CLN8 and ANKH that map to chromosomal locations previously associated with rheumatoid arthritis, were found to be elevated in MTX-exposed samples. Subsequent pathway analysis indicates that MTX exposure is associated with the following key alterations: (1) upregulation of lipid biosynthetic genes, consistent with MTX-induced steatosis, (2) downregulation of proinflammatory chemokines, consistent with the anti-inflammatory effects of MTX, and (3) elevation of complement pathway gene expression. Complement 5, shown earlier to be correlated with liver fibrosis in mice, was found to be elevated (twofold) in MTX-exposed livers. In conclusion, we have found the expression of a number of genes associated with rheumatic disease and/or MTX exposure to be significantly different. Differences in complement expression provide the rationale for future correlative studies between MTX-induced liver fibrosis and C5 alleles in order to identify patients with increased risk for fibrosis.

Cytoplasmic phospholipase A2 deletion enhances colon tumorigenesis.

Cellular pools of free arachidonic acid are tightly controlled through enzymatic release of the fatty acid and subsequent utilization by downstream enzymes including the cyclooxygenases. Arachidonic acid cleavage from membrane phospholipids is accomplished by the actions of phospholipase A(2) (PLA(2)). Upon release, free arachidonic acid provides substrate for the synthesis of eicosanoids. However, under certain conditions, arachidonic acid may participate in ceramide-mediated apoptosis. Disruption of arachidonic acid homeostasis can shift the balance of cell turnover in favor of tumorigenesis, via overproduction of tumor-promoting eicosanoids or alternatively by limiting proapoptotic signals. In the following study, we evaluated the influence of genetic deletion of a key intracellular phospholipase, cytoplasmic PLA(2) (cPLA(2)), on azoxymethane-induced colon tumorigenesis. Heterozygous and null mice, upon treatment with the organotropic colon carcinogen, azoxymethane, developed a significant (P < 0.05) increase in colon tumor multiplicity (7.2-fold and 5.5-fold, respectively) relative to their wild-type littermates. This enhanced tumor sensitivity may be explained, in part, by the attenuated levels of apoptosis observed by terminal deoxynucleotidyl transferase-mediated nick end labeling staining within the colonic epithelium of heterozygous and null mice ( approximately 50% of wild type). The lower frequency of apoptotic cells corresponded with reduced ceramide levels (69% and 46% of wild-type littermates, respectively). Remarkably, increased tumorigenesis resulting from cPLA(2) deletion occurred despite a significant reduction in prostaglandin E(2) production, even in cyclooxygenase-2-overexpressing tumors. These data contribute new information that supports a fundamental role of cPLA(2) in the control of arachidonic acid homeostasis and cell turnover. Our findings indicate that the proapoptotic role of cPLA(2) in the colon may supercede its contribution to eicosanoid production in tumor development.

Circumvention and reactivation of the p53 oncogene checkpoint in mouse colon tumors.

The p53 tumor suppressor protein is sequence-normal in azoxymethane (AOM)-induced mouse colon tumors, making them a good model for human colon cancers that retain a wild type p53 gene. Cellular localization and co-immunoprecipitation experiments using a cell line derived from an AOM-induced colon tumor (AJ02-NM(0) cells) pointed to constitutively expressed Mdm2 as being an important negative regulator of p53 in these cells. Although the Mdm2 inhibitory protein p19/ARF was expressed in AJ02-NM(0) cells, its level of expression was not sufficient for p53 activation. We tested the response of AJ02-NM(0) cells to the recently developed Mdm2 inhibitor, Nutlin-3. Nutlin-3 was found to activate p53 DNA binding in AJ02-NM(0) cells, to a level comparable to doxorubicin and 5-fluorouracil (5-FU). In addition, Nutlin-3 increased expression of the p53 target genes Bax and PERP to a greater extent than doxorubicin or 5-FU, and triggered a G2/M phase arrest in these cells, compared to a G1 arrest triggered by doxorubicin and 5-FU. The differences in the cellular response may be related to differences in the kinetics of p53 activation and/or its post-translational modification status. In an ex vivo experiment, Nutlin-3 was found to activate p53 target gene expression and apoptosis in AOM-induced tumor tissue, but not in normal adjacent mucosa. Our data indicate that Mdm2 inhibitors may be an effective means of selectively targeting colon cancers that retain a sequence-normal p53 gene while sparing normal tissue and that the AOM model is an appropriate model for the preclinical development of these drugs.

Pigment epithelium-derived factor (PEDF) normalizes matrix defects in iPSCs derived from Osteogenesis imperfecta Type VI.

Osteogenesis imperfecta (OI) Type VI is characterized by a defect in bone mineralization, which results in multiple fractures early in life. Null mutations in the PEDF gene, Serpinf1, are the cause of OI VI. Whether PEDF restoration in a murine model of OI Type VI could improve bone mass and function was previously unknown. In Belinsky et al, we provided evidence that PEDF delivery enhanced bone mass and improved parameters of bone function in vivo. Further, we demonstrated that PEDF temporally inhibits Wnt signaling to enhance osteoblast differentiation. Here, we demonstrate that generation of induced pluripotent stem cells (iPSCs) from a PEDF null patient provides additional evidence for PEDF's role in regulating extracellular matrix proteins secreted from osteoblasts. PEDF null iPSCs have marked abnormalities in secreted matrix proteins, capturing a key feature of human OI Type VI, which were normalized by exogenous PEDF. Lastly, we place our recent findings within the broader context of PEDF biology and the developmental signaling pathways that are implicated in its actions.

Pigment Epithelium-Derived Factor (PEDF) Inhibits Wnt/ß-catenin Signaling in the Liver.

BACKGROUND & AIMS: Pigment epithelium-derived factor (PEDF) is a secretory protein that inhibits multiple tumor types. PEDF inhibits the Wnt coreceptor, low-density lipoprotein receptor-related protein 6 (LRP6), in the eye, but whether the tumor-suppressive properties of PEDF occur in organs such as the liver is unknown. METHODS: Wnt-dependent regulation of PEDF was assessed in the absence and presence of the Wnt coreceptor LRP6. Whole genome expression analysis was performed on PEDF knockout (KO) and control livers (7 months). Interrogation of Wnt/ß-catenin signaling was performed in whole livers and human hepatocellular carcinoma (HCC) cell lines after RNA interference of PEDF and restoration of a PEDF-derived peptide. Western diet feeding for 6 to 8 months was used to evaluate whether the absence of PEDF was permissive for HCC formation (n = 12/group). RESULTS: PEDF levels increased in response to canonical Wnt3a in an LRP6-dependent manner but were suppressed by noncanonical Wnt5a protein in an LRP6-independent manner. Gene set enrichment analysis (GSEA) of PEDF KO livers revealed induction of pathways associated with experimental and human HCC and a transcriptional profile characterized by Wnt/ß-catenin activation. Enhanced Wnt/ß-catenin signaling occurred in KO livers, and PEDF delivery in vivo reduced LRP6 activation. In human HCC cells, RNA interference of PEDF led to increased levels of activated LRP6 and ß-catenin, and a PEDF 34-mer peptide decreased LRP6 activation and ß-catenin signaling, and reduced Wnt target genes. PEDF KO mice fed a Western diet developed sporadic well-differentiated HCC. Human HCC specimens demonstrated decreased PEDF staining compared with hepatocytes. CONCLUSIONS: PEDF is an endogenous inhibitor of Wnt/ß-catenin signaling in the liver.

Polarization of the vacuolar adenosine triphosphatase delineates a transition to high-grade pancreatic intraepithelial neoplasm lesions.

OBJECTIVES: A functional vacuolar adenosine triphosphatase (v-ATPase) complex regulates canonical Wnt/ß-catenin signaling. The goal of this study was to identify the distribution of the v-ATPase in human and murine models of pancreatic intraepithelial neoplasms (PanINs) and assess its role in Wnt/ß-catenin signaling. METHODS: We evaluated the immunolabeling pattern of the v-ATPase in human PanIN specimens and murine PanIN-1 and PanIN-2 lesions obtained from Ptf1a(Cre/+); LSL-Kras(G12D) mice. Wnt/ß-catenin signaling was interrogated in primary PanIN cells by examining the phosphorylated levels of its surface coreceptor, low-density lipoprotein receptor-related protein-6 (LRP6), and its intracellular effector, nonphosphorylated ß-catenin. The response of primary PanIN cells to epidermal growth factor (EGF) was assessed in the absence and presence of the v-ATPase inhibitor, concanamycin. RESULTS: In advanced (PanIN-2), but not early (PanIN-1), lesions, the v-ATPase assumed a polarized phenotype. Blocking the v-ATPase disrupted Wnt/ß-catenin signaling in primary PanIN cells despite significantly higher levels of the total and activated Wnt cell surface coreceptor, LRP6. Vacuolar adenosine triphosphatase blockade significantly decreased the total and activated levels of EGF receptor, a determinant of PanIN progression. The activation of EGF receptor and its intracellular mediator, p44/42 mitogen-activated protein kinase, was also reduced by v-ATPase blockade. This led to diminished proliferation in response to EGF ligand. CONCLUSIONS: The v-ATPase regulates Wnt/ß-catenin and EGF receptor signaling in PanINs.

Patch-clamp recordings and calcium imaging followed by single-cell PCR reveal the developmental profile of 13 genes in iPSC-derived human neurons.

Molecular genetic studies are typically performed on homogenized biological samples, resulting in contamination from non-neuronal cells. To improve expression profiling of neurons we combined patch recordings with single-cell PCR. Two iPSC lines (healthy subject and 22q11.2 deletion) were differentiated into neurons. Patch electrode recordings were performed on 229 human cells from Day-13 to Day-88, followed by capture and single-cell PCR for 13 genes: ACTB, HPRT, vGLUT1, ßTUBIII, COMT, DISC1, GAD1, PAX6, DTNBP1, ERBB4, FOXP1, FOXP2, and GIRK2. Neurons derived from both iPSC lines expressed ßTUBIII, fired action potentials, and experienced spontaneous depolarizations (UP states) ~2 weeks before vGLUT1, GAD1 and GIRK2 appeared. Multisite calcium imaging revealed that these UP states were not synchronized among hESC-H9-derived neurons. The expression of FOXP1, FOXP2 and vGLUT1 was lost after 50 days in culture, in contrast to other continuously expressed genes. When gene expression was combined with electrophysiology, two subsets of genes were apparent; those irrelevant to spontaneous depolarizations (including vGLUT1, GIRK2, FOXP2 and DISC1) and those associated with spontaneous depolarizations (GAD1 and ERBB4). The results demonstrate that in the earliest stages of neuron development, it is useful to combine genetic analysis with physiological characterizations, on a cell-to-cell basis.

Mild hypothermia inhibits differentiation of human embryonic and induced pluripotent stem cells.

Culture of pluripotent stem cells at 35°C strikingly reduces unwanted spontaneous differentiation during hESC and iPSC maintenance compared with 37°C. Growth at 35°C did not affect expression of pluripotency mRNAs nor induce expression of cold-inducible genes. Colony size was somewhat reduced at 35°C. Thus, growth at 35°C is a convenient, simple method to reduce the labor of removing spontaneously differentiated colonies when maintaining pluripotent cells.

Dopamine receptors in human embryonic stem cell neurodifferentiation.

We tested whether dopaminergic drugs can improve the protocol for in vitro differentiation of H9 human embryonic stem cells (hESCs) into dopaminergic neurons. The expression of 5 dopamine (DA) receptor subtypes (mRNA and protein) was analyzed at each protocol stage (1, undifferentiated hESCs; 2, embryoid bodies [EBs]; 3, neuroepithelial rosettes; 4, expanding neuroepithelium; and 5, differentiating neurons) and compared to human fetal brain (gestational week 17-19). D2-like DA receptors (D2, D3, and D4) predominate over the D1-like receptors (D1 and D5) during derivation of neurons from hESCs. D1 was the receptor subtype with the lowest representation in each protocol stage (Stages 1-5). D1/D5-agonist SKF38393 and D2/D3/D4-agonist quinpirole (either alone or combined) evoked Ca(2+) responses, indicating functional receptors in hESCs. To identify when receptor activation causes a striking effect on hESC neurodifferentiation, and what ligands and endpoints are most interesting, we varied the timing, duration, and drug in the culture media. Dopaminergic agonists or antagonists were administered either early (Stages 1-3) or late (Stages 4-5). Early DA exposure resulted in more neuroepithelial colonies, more neuronal clusters, and more TH(+) clusters. The D1/D5 antagonist SKF83566 had a strong effect on EB morphology and the expression of midbrain markers. Late exposure to DA resulted in a modest increase in TH(+) neuron clusters (∼75%). The increase caused by DA did not occur in the presence of dibutyryl cAMP (dbcAMP), suggesting that DA acts through the cAMP pathway. However, a D2-antagonist (L741) decreased TH(+) cluster counts. Electrophysiological parameters of the postmitotic neurons were not significantly affected by late DA treatment (Stages 4-5). The mRNA of mature neurons (VGLUT1 and GAD1) and the midbrain markers (GIRK2, LMX1A, and MSX1) were lower in hESCs treated by DA or a D2-antagonist. When hESCs were neurodifferentiated on PA6 stromal cells, DA also increased expression of tyrosine hydroxylase. Although these results are consistent with DA's role in potentiating DA neurodifferentiation, dopaminergic treatments are generally less efficient than dbcAMP alone.

Physiological properties of neurons derived from human embryonic stem cells using a dibutyryl cyclic AMP-based protocol.

Neurons derived from human embryonic stem cells hold promise for the therapy of neurological diseases. Quality inspection of human embryonic stem cell-derived neurons has often been based on immunolabeling for neuronal markers. Here we put emphasis on their physiological properties. Electrophysiological measurements were carried out systematically at different stages of neuronal in vitro development, including the very early stage, neuroepithelial rosettes. Developing human neurons are able to generate action potentials (APs) as early as 10 days after the start of differentiation. Tyrosine hydroxylase (TH)-positive (putative dopaminergic, DA) neurons tend to aggregate into clumps, and their overall yield per coverslip is relatively low (8.3%) because of areas void of DA neurons. On the same in vitro day, neighboring neurons can be in very different stages of differentiation, including repetitive AP firing, single full-size AP, and abortive AP. Similarly, the basic electrophysiological parameters (resting membrane potential, input resistance, peak sodium, and peak potassium currents) are scattered in a wide range. Visual appearance of differentiating neurons, and number of primary and secondary dendrites cannot be used to predict the peak sodium current or AP firing properties of cultured neurons. Approximately 13% of neurons showed evidence of hyperpolarization-induced current (I(h)), a characteristic of DA neurons; however, no neurons with repetitive APs showed I(h). The electrophysiological measurements thus indicate that a standard DA differentiation (dibutyryl cyclic AMP-based) protocol, applied for 2-5 weeks, produces a heterogeneous ensemble of mostly immature neurons. The overall quality of human neurons under present conditions (survival factors were not used) begins to deteriorate after 12 days of differentiation.

DNA damage response to the Mdm2 inhibitor nutlin-3.

Mdm2 inhibitors represent a promising class of p53 activating compounds that may be useful in cancer treatment and prevention. However, the consequences of pharmacological p53 activation are not entirely clear. We observed that Nutlin-3 triggered a DNA damage response in azoxymethane-induced mouse AJ02-NM(0) colon cancer cells, characterized by the phosphorylation of H2AX (at Ser-139) and p53 (at Ser-15). The DNA damage response was highest in cells showing robust p53 stabilization, it could be triggered by the active but not the inactive Nutlin-3 enantiomer, and it was also activated by another pharmacological Mdm2 inhibitor (Caylin-1). Quantification of gamma H2AX-positive cells following Nutlin-3 exposure showed that approximately 17% of cells in late S and G2/M were mounting a DNA damage response (compared to a approximately 50% response to 5-fluorouracil). Nutlin-3 treatment caused the formation of double-strand DNA strand breaks, promoted the formation of micronuclei, accentuated strand breakage induced by doxorubicin and sensitized the mouse colon cancer cells to DNA break-inducing topoisomerase II inhibitors. Although the HCT116 colon cancer cells did not mount a significant DNA damage response following Nutlin-3 treatment, Nutlin-3 enhanced the DNA damage response to the nucleotide synthesis inhibitor hydroxyurea in a p53-dependent manner. Finally, p21 deletion also sensitized HCT116 cells to the Nutlin-3-induced DNA damage response, suggesting that cell cycle checkpoint abnormalities may promote this response. We propose that p53 activation by Mdm2 inhibitors can result in the slowing of double-stranded DNA repair. Although this effect may suppress illegitimate homologous recombination repair, it may also increase the risk of clastogenic events.

cPLA2 is protective against COX inhibitor-induced intestinal damage.

Cytosolic phospholipase A(2) (cPLA(2)) is the rate-limiting enzyme responsible for the generation of prostaglandins (PGs), which are bioactive lipids that play critical roles in maintaining gastrointestinal (GI) homeostasis. There has been a long-standing association between administration of cyclooxygenase (COX) inhibitors and GI toxicity. GI injury is thought to be induced by suppressed production of GI-protective PGs as well as direct injury to enterocytes. The present study sought to determine how pan-suppression of PG production via a genetic deletion of cPLA(2) impacts the susceptibility to COX inhibitor-induced GI injury. A panel of COX inhibitors including celecoxib, rofecoxib, sulindac, and aspirin were administered via diet to cPLA(2)(-/-) and cPLA(2)(+/+) littermates. Administration of celecoxib, rofecoxib, and sulindac, but not aspirin, resulted in acute lethality (within 2 weeks) in cPLA(2)(-/-) mice, but not in wild-type littermates. Histomorphological analysis revealed severe GI damage following celecoxib exposure associated with acute bacteremia and sepsis. Intestinal PG levels were reduced equivalently in both genotypes following celecoxib exposure, indicating that PG production was not likely responsible for the differential sensitivity. Gene expression profiling in the small intestines of mice identified drug-related changes among a panel of genes including those involved in mitochondrial function in cPLA(2)(-/-) mice. Further analysis of enterocytic mitochondria showed abnormal morphology as well as impaired ATP production in the intestines from celecoxib-exposed cPLA(2)(-/-) mice. Our data demonstrate that cPLA(2) appears to be an important component in conferring protection against COX inhibitor-induced enteropathy, which may be mediated through affects on enterocytic mitochondria.

Genetic deletion of mPGES-1 suppresses intestinal tumorigenesis.

Elevated levels of prostaglandin E(2) (PGE(2)) are often found in colorectal cancers. Thus, nonsteroidal anti-inflammatory drugs, including selective cyclooxygenase-2 (COX-2) inhibitors, are among the most promising chemopreventive agents for colorectal cancer. However, their long-term use is restricted by the occurrence of adverse events believed to be associated with a global reduction in prostaglandin production. In the present study, we evaluated the chemopreventive efficacy of targeting the terminal synthase microsomal PGE(2) synthase 1 (mPGES-1), which is responsible for generating PGE(2), in two murine models of intestinal cancer. We report for the first time that genetic deletion of mPGES-1 in Apc-mutant mice results in marked and persistent suppression of intestinal cancer growth by 66%, whereas suppression of large adenomas (>3 mm) was almost 95%. This effect occurred despite loss of Apc heterozygosity and beta-catenin activation. However, we found that mPGES-1 deficiency was associated with a disorganized vascular pattern within primary adenomas as determined by CD31 immunostaining. We also examined the effect of mPGES-1 deletion on carcinogen-induced colon cancer. The absence of mPGES-1 reduced the size and number of preneoplastic aberrant crypt foci (ACF). Importantly, mPGES-1 deletion also blocked the nuclear accumulation of beta-catenin in ACF, confirming that beta-catenin is a critical target of PGE(2) procarcinogenic signaling in the colon. Our data show the feasibility of targeting mPGES-1 for cancer chemoprevention with the potential for improved tolerability over traditional nonsteroidal anti-inflammatory drugs and selective COX-2 inhibitors.

Expression of secretory phospholipase A2 in colon tumor cells potentiates tumor growth.

Secretory phospholipase A2 (sPLA2-IIA) has been shown to attenuate intestinal tumorigenesis in Apc(Min) mice, demonstrating that it is a tumor modifier. To further explore the actions of sPLA2-IIA in tumorigenesis, sPLA2-IIA was overexpressed in two cell lines where it is normally absent, the murine colon tumor cell line AJ02nm0, and human colon carcinoma cell line HCT-116. Two allelic variants of sPLA2-IIA were tested in this study; sPLA2-IIA(AKR) and sPLA2-IIA(SWR), which are derived from AKR/J and SWR/J mice, respectively, and differ by a single amino acid at position 63 in the calcium- and receptor-binding domain. There was no change in cell-doubling time for either allele when compared to vector controls. Furthermore, sodium butyrate and arachidonic acid (AA)-induced cell death were unchanged in control and transfected cells. Addition of the sPLA2 substrate, palmitoyl-arachidonoyl-phosphatidic acid (PAPA), to AJ02nm0 cells resulted in a modest (12%-24%), but significant (P < 0.01), inhibition of growth that was dependent on sPLA2-IIA expression. However, when AJ02nm0 and HCT-116 cells were injected subcutaneously (sc) into nude mice, Pla2g2a expression resulted in a 2.5-fold increase in tumor size. In addition, sPLA2-IIA expressing HCT-116 tumors were found to be more infiltrative than controls. We conclude that the ability of sPLA2-IIA to slow tumor cell growth is dependent upon the availability of substrate, and that in some instances sPLA2-IIA may actually enhance tumor growth. Mechanisms that may account for differences between the tumor explant model versus the Apc(Min) model of intestinal cancer are discussed.

Utilizing endoscopic technology to reveal real-time proteomic alterations in response to chemoprevention.

Cancer chemoprevention approaches use either pharmacological or dietary agents to impede, arrest or reverse the carcinogenic process. Although several agents have shown effectiveness against colon cancer, present intervention strategies provide only partial reduction. In this study, we utilized high-resolution endoscopy to obtain colon tumor biopsy specimens from Apc mutant mice before and after 2-wk sulindac intervention. To acquire information beyond genomics, proteome analysis using the ProteomeLab PF2D platform was implemented to generate 2-D protein expression maps from biopsies. Chromatograms produced common signature profiles between sulindac and nonsulindac treated samples, and contrasting profiles termed "fingerprints". We selected a double peak that appeared in tumor biopsies from sulindac-treated mice. Further analyses using MS sequencing identified this protein as histone H2B. The location of H2B in the 1(st) dimension strongly suggested PTM, consistent with identification of two oxidized methionines. While further studies on sulindac proteomic fingerprints are underway, this study demonstrates the feasibility and advantages of "real-time" proteomic analysis for obtaining information on biomarker discovery and drug activity that would not be revealed by a genetic assay. This approach should be broadly applicable for assessing lesion responsiveness in a wide range of translational and human clinical studies.

Epigenetic alterations in RASSF1A in human aberrant crypt foci.

CpG island methylation (CIM) is an epigenetic mechanism for transcriptional silencing that occurs at various stages of colon tumorigenesis. CIM has been found in serrated adenomas and hyperplastic polyps. There is also evidence for hypermethylation in aberrant crypt foci (ACF) that are found in resected colons from cancer patients. Our study addresses promoter methylation of a tumor suppressor gene, RASSF1A, within the colonic epithelium of subjects undergoing screening colonoscopies in the absence of synchronous tumors. Patients included in this study were at elevated risk for colorectal cancer (CRC) based on family history, but without a previously occurring or synchronous colon carcinoma. ACF were identified using close-focus magnifying chromendoscopy and collected by biopsy in situ. We isolated ACF and adjacent normal colonic epithelium by laser capture microdissection (LCM) and studied methylation of the RASSF1A promoter region in ACF and in adjacent normal mucosa. Expression of RASSF1A was verified using quantitative real-time polymerase chain reaction (QRT-PCR). We found that 8.6% (3 out of 35) of ACF had K-ras mutations and 24% (6 out of 25) had RASSF1A hypermethylation. Our results demonstrate that RASSF1A hypermethylation and K-ras mutations are not mutually exclusive and are present in patients at elevated risk of CRC. Importantly, CIM of RASSF1A is an early epigenetic aberration, occurring in the absence of synchronous colon tumors and is not accompanied by field effects into the surrounding epithelium.

Vascular endothelial growth factor and enhanced angiogenesis do not promote metastatic conversion of a newly established azoxymethane-induced colon cancer cell line.

The organo-specific carcinogen, azoxymethane (AOM), produces colon tumors in mice that share many pathological features with sporadic human colorectal cancer (CRC). An important distinction between AOM-induced CRC and human CRC is lack of mucosal invasion in the murine model. To assess the role of the microenvironment in preventing the invasive phenotype, multiple benign in situ adenocarcinomas were harvested from AOM-treated mice and cultured in vitro. However, tumor cell growth was extremely limiting under standard culturing conditions. Thus, we injected tumor cells directly into nude mice and performed two serial transplants, and successfully explanted a rapidly growing epithelial tumor cell line (AJ02nm(0)). When injected subcutaneously (sc) into nude mice, AJ02nm(0) cells formed well-differentiated adenocarcinomas with minimal tumor invasive capacity. To define whether metastatic and invasive potential were related to lack of angiogenic stimuli, the AJ02nm(0) cells were transfected to overexpress murine vascular endothelial growth factor-164 (VEGF(164)). AJ02nm-VEGF cells produced rapidly growing tumors in nude mice that exhibited extensive pseudo-epithelial ductal architecture and supporting vasculature, but without increased invasive potential compared to controls. The established murine colon epithelial cell line provides a useful experimental model to further elaborate genetic and epigenetic factors that may promote or inhibit colon tumorigenesis and metastasis.