Qualitative analysis of sequence specific binding of flavones to DNA using restriction endonuclease activity assays

Flavones, found in nature as secondary plant metabolites, have shown efficacy as anti-cancer agents. We have examined the binding of two flavones, 5,7-dihydroxy-3,6,8-trimethoxy-2-phenyl-4H-chromen-4-one (5,7-dihydroxy-3,6,8-trimethoxy flavone; FlavA) and 3,5-dihydroxy-6,7,8-trimethoxy-2-phenyl-4H-chromen-4-one (3,5-dihydroxy-6,7,8-trimethoxy flavone; FlavB), to phiX174 RF DNA using restriction enzyme activity assays employing the restriction enzymes Alw44, AvaII, BssHII, DraI, MluI, NarI, NciI, NruI, PstI, and XhoI. These enzymes possess differing target and flanking sequences allowing for observation of sequence specificity analysis. Using restriction enzymes that cleave once with a mixture of supercoiled and relaxed DNA substrates provides for observation of topological effects on binding. FlavA and FlavB show differing sequence specificities in their respective binding to phiX. For example, with relaxed DNA, FlavA shows inhibition of cleavage with DraI (reaction site (5') TTTAAA) but not BssHII ((5') GCGCGC) while FlavB shows the opposite results. Evidence for tolological specificity is also observed, Molecular modeling and conformational analysis of the flavones suggests that the phenyl ring of FlavB is coplanar with the flavonoid ring while the phenyl ring of FlavA is at an angle relative to the flavonoid ring. This may account for aspects of the observed sequence and topological specificities in the effects on restriction enzyme activity.

Abstract 2106: Gamma-tocotrienol upregulates the ceramide transporter, Arv-1, in pancreatic cancer cells

Pancreatic cancer is the fourth leading cause of cancer-related death in the United States. Treatment options are limited and novel therapeutic agents that can inhibit signaling pathways implicated in the proliferation and survival of pancreatic cancer cells are of interest. Tocotrienols are members of the vitamin E family but, unlike tocopherols, possess an unsaturated isoprenoid side-chain that confers superior and mechanistically different anti-cancer properties on pancreatic cancer cells. The ability of tocotrienols to selectively inhibit the HMG CoA reductase pathway through post-translational degradation of HMG CoA reductase, inhibit the PI3/Akt, ERK pathways through downregulation of Her2/ErbB2 receptors as well as suppression of the activity of transcription factor NF kappa B, could be the basis for some of these properties.

Recent studies have shown increase in cellular ceramide levels in cancer cells treated with tocopherols, leading to arrest in tumor proliferation and apoptosis. The actual mechanism of increase in ceramide levels is not clearly understood and is thought to be due to increased synthesis. We explored the hypothesis that the increase in ceramide on the cellular membrane could be due to increased transport from the ER to the membrane. The ARV1 (ACAT-related enzyme-2 required for viability) gene encodes an ER- localized protein involved in lipid homeostasis and ceramide transport in yeast and mammals. Deletion of the ARV-1 gene in yeast causes accumulation of ceramide in cytoplasm. Our previous work indicated that gamma-tocotrienol (GT3) has potent anti-proliferative activity in k-ras mutated pancreatic cancer cell (MIA-Paca-2) through the inhibitory effect on Akt, Ras/Raf/Erk and ErBb2 receptor as well as induction of apoptotic pathways through Fox-03 and GSK-3b. Our current data shows GT3 may decrease expression of caveolin, a cell survival marker, and cause up-regulation of ARV-1 that encodes a ceramide transport protein. We further show via HPLC (Babraham Bioscience Technologies Ltd, Cambridge, U.K) that total ceramide levels remain unchanged in the cell. There may be a change in ceramide (monoclonal anti-ceramide IgM, Sigma Chemicals) cellular distribution as indicated by immunofluorescence data.

Upregulation of ARV-1 may be involved in increase in cellular ceramide transport or redistribution of ceramide to the cell membrane. Transport of ceramide to membrane lipid rafts or mitochondrial membrane channels may cause loss of survival signaling and induce apoptosis. Thus it is likely that GT3 apoptotic effect on k-ras mutated MIA-Paca2 cells is related not to changes in the total ceramide levels, but rather to its increased transport and redistribution. Further work is necessary in order to better understand the role of GT3 in ceramide redistribution in pancreatic cancer cells.

Citation Format: Kanishka Chakraborty, Victoria P. Ramsauer, Janet W. Lightner, William L. Stone, Koyamangalath Krishnan. Gamma-tocotrienol upregulates the ceramide transporter, Arv-1, in pancreatic cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2106. doi:10.1158/1538-7445.AM2013-2106

Anti-neoplastic activity of two flavone isomers derived from Gnaphalium elegans and Achyrocline bogotensis

Over 4000 flavonoids have been identified so far and among these, many are known to have antitumor activities. The basis of the relationships between chemical structures, type and position of substituent groups and the effects these compounds exert specifically on cancer cells are not completely elucidated. Here we report the differential cytotoxic effects of two flavone isomers on human cancer cells from breast (MCF7, SK-BR-3), colon (Caco-2, HCT116), pancreas (MIA PaCa, Panc 28), and prostate (PC3, LNCaP) that vary in differentiation status and tumorigenic potential. These flavones are derived from plants of the family Asteraceae, genera Gnaphalium and Achyrocline reputed to have anti-cancer properties. Our studies indicate that 5,7-dihydroxy-3,6,8-trimethoxy-2-phenyl-4H-chromen-4-one (5,7-dihydroxy-3,6,8-trimethoxy flavone) displays potent activity against more differentiated carcinomas of the colon (Caco-2), and pancreas (Panc28), whereas 3,5-dihydroxy-6,7,8-trimethoxy-2-phenyl-4H-chromen-4-one (3,5-dihydroxy-6,7,8-trimethoxy flavone) cytototoxic action is observed on poorly differentiated carcinomas of the colon (HCT116), pancreas (Mia PaCa), and breast (SK-BR3). Both flavones induced cell death (>50%) as proven by MTT cell viability assay in these cancer cell lines, all of which are regarded as highly tumorigenic. At the concentrations studied (5-80 µM), neither flavone demonstrated activity against the less tumorigenic cell lines, breast cancer MCF-7 cells, androgen-responsive LNCaP human prostate cancer line, and androgen-unresponsive PC3 prostate cancer cells. 5,7-dihydroxy-3,6,8-trimethoxy-2-phenyl-4H-chromen-4-one (5,7-dihydroxy-3,6,8-trimethoxy flavone) displays activity against more differentiated carcinomas of the colon and pancreas, but minimal cytotoxicity on poorly differentiated carcinomas of these organs. On the contrary, 3,5-dihydroxy-6,7,8-trimethoxy-2-phenyl-4H-chromen-4-one (3,5-dihydroxy-6,7,8-trimethoxy flavone) is highly cytotoxic to poorly differentiated carcinomas of the colon, pancreas, and breast with minimal activity against more differentiated carcinomas of the same organs. These differential effects suggest activation of distinct apoptotic pathways. In conclusion, the specific chemical properties of these two flavone isomers dictate mechanistic properties which may be relevant when evaluating biological responses to flavones.

Differential effects of pravastatin and simvastatin on the growth of tumor cells from different organ sites

3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) inhibitors, commonly known as statins, may possess cancer preventive and therapeutic properties. Statins are effective suppressors of cholesterol synthesis with a well-established risk-benefit ratio in cardiovascular disease prevention. Mechanistically, targeting HMGCR activity primarily influences cholesterol biosynthesis and prenylation of signaling proteins. Pravastatin is a hydrophilic statin that is selectively taken up by a sodium-independent organic anion transporter protein-1B1 (OATP1B1) exclusively expressed in liver. Simvastatin is a hydrophobic statin that enters cells by other mechanisms. Poorly-differentiated and well-differentiated cancer cell lines were selected from various tissues and examined for their response to these two statins. Simvastatin inhibited the growth of most tumor cell lines more effectively than pravastatin in a dose dependent manner. Poorly-differentiated cancer cells were generally more responsive to simvastatin than well-differentiated cancer cells, and the levels of HMGCR expression did not consistently correlate with response to statin treatment. Pravastatin had a significant effect on normal hepatocytes due to facilitated uptake and a lesser effect on prostate PC3 and colon Caco-2 cancer cells since the OATP1B1 mRNA and protein were only found in the normal liver and hepatocytes. The inhibition of cell growth was accompanied by distinct alterations in mitochondrial networks and dramatic changes in cellular morphology related to cofilin regulation and loss of p-caveolin. Both statins, hydrophilic pravastatin and hypdrophobic simvastatin caused redistribution of OATP1B1 and HMGCR to perinuclear sites. In conclusion, the specific chemical properties of different classes of statins dictate mechanistic properties which may be relevant when evaluating biological responses to statins.

Tocotrienols inhibit AKT and ERK activation and suppress pancreatic cancer cell proliferation by suppressing the ErbB2 pathway

Tocotrienols are members of the vitamin E family but, unlike tocopherols, possess an unsaturated isoprenoid side chain that confers superior anti-cancer properties. The ability of tocotrienols to selectively inhibit the HMG-CoA reductase pathway through posttranslational degradation and to suppress the activity of transcription factor NF-κB could be the basis for some of these properties. Our studies indicate that γ- and δ-tocotrienols have potent antiproliferative activity in pancreatic cancer cells (Panc-28, MIA PaCa-2, Panc-1, and BxPC-3). Indeed both tocotrienols induced cell death (>50%) by the MTT cell viability assay in all four pancreatic cancer cell lines. We also examined the effects of the tocotrienols on the AKT and the Ras/Raf/MEK/ERK signaling pathways by Western blotting analysis. γ- and δ-tocotrienol treatment of cells reduced the activation of ERK MAP kinase and that of its downstream mediator RSK (ribosomal protein S6 kinase) in addition to suppressing the activation of protein kinase AKT. Suppression of activation of AKT by γ-tocotrienol led to downregulation of p-GSK-3β and upregulation accompanied by nuclear translocation of Foxo3. These effects were mediated by the downregulation of Her2/ErbB2 at the messenger level. Tocotrienols but not tocopherols were able to induce the observed effects. Our results suggest that the tocotrienol isoforms of vitamin E can induce apoptosis in pancreatic cancer cells through the suppression of vital cell survival and proliferative signaling pathways such as those mediated by the PI3-kinase/AKT and ERK/MAP kinases via downregulation of Her2/ErbB2 expression. The molecular components for this mechanism are not completely elucidated and need further investigation.

An elective course to engage pharmacy students in research activities

OBJECTIVE

To implement problem-based learning exercises in a pharmacy research elective course and assess the impact on students' knowledge and confidence in their ability to analyze, design, and present basic research projects relevant to clinical areas.

DESIGN

Hands-on learning activities, including discussions on experimental design, development of collective diagrams, research planning, results analysis, data evaluation, and presentation design, were incorporated into the course and developed as team-based learning experiences.

ASSESSMENT

Students gave a seminar presentation to peers and faculty members at the end of the semester and created posters for presentations at professional meetings. Students who decided to work on a continuation project during the following semester were expected to produce data that might be sufficient for the development of manuscripts for submission to scientific journals.

CONCLUSIONS

Feedback from students revealed an appreciation and renewed interest in analyzing clinical issues with a much wider focus as well as increased understanding of and confidence in using data derived from basic science research.

Early response to ErbB2 over-expression in polarized Caco-2 cells involves partial segregation from ErbB3 by relocalization to the apical surface and initiation of survival signaling

In several human cancers, ErbB2 over-expression facilitates the formation of constitutively active homodimers resistant to internalization which results in progressive signal amplification from the receptor, conducive to cell survival, proliferation, or metastasis. Here we report on studies of the influence of ErbB2 over-expression on localization and signaling in polarized Caco-2 and MDCK cells, two established models to study molecular trafficking. In these cells, ErbB2 is not over-expressed and shares basolateral localization with ErbB3. Over-expression of ErbB2 by transient transfection resulted in partial separation of the receptors by relocalization of ErbB2, but not ErbB3, to the apical surface, as shown by biotinylation of the apical or basolateral surfaces. These results were confirmed by immunofluorescence and confocal microscopy. Polarity controls indicated that the relocalization of ErbB2 is not the result of depolarization of the cells. Biotinylation and confocal microscopy also showed that apical, but not basolateral ErbB2 is activated at tyrosine 1139. This phosphotyrosine binds adaptor protein Grb2, as confirmed by immunoprecipitation. However, we found that it does not initiate the canonical Grb2-Ras-Raf-Erk pathway. Instead, our data supports the activation of a survival pathway via Bcl-2. The effects of ErbB2 over-expression were abrogated by the humanized anti-ErbB2 monoclonal antibody Herceptin added only from the apical side. The ability of apical ErbB2 to initiate an altered downstream cascade suggests that subcellular localization of the receptor plays an important role in regulating ErbB2 signaling in polarized epithelia.

Intermediate filaments: a role in epithelial polarity

Intermediate filaments have long been considered mechanical components of the cell that provide resistance to deformation stress. Practical experimental problems, including insolubility, lack of good pharmacological antagonists, and the paucity of powerful genetic models have handicapped the research of other functions. In single-layered epithelial cells, keratin intermediate filaments are cortical, either apically polarized or apico-lateral. This review analyzes phenotypes of genetic manipulations of simple epithelial cell keratins in mice and Caenorhabditis elegans that strongly suggest a role of keratins in apico-basal polarization and membrane traffic. Published evidence that intermediate filaments can act as scaffolds for proteins involved in membrane traffic and signaling is also discussed. Such a scaffolding function would generate a highly polarized compartment within the cytoplasm of simple epithelial cells. While in most cases mechanistic explanations for the keratin-null or overexpression phenotypes are still missing, it is hoped that investigators will be encouraged to study these as yet poorly understood functions of intermediate filaments.

Membrane Mucin Muc4 Induces Density-dependent Changes in ERK Activation in Mammary Epithelial and Tumor Cells

The membrane mucin Muc4 has been shown to alter cellular behavior through both anti-adhesive effects on cell-cell and cell-extracellular matrix interactions and its ability to act as an intramembrane ligand for the receptor tyrosine kinase ErbB2. The ERK pathway is regulated by both cell-matrix and cell-cell adhesion. An analysis of the effects of Muc4 expression on ERK phosphorylation in mammary tumor and epithelial cells, which exhibit both adhesion-dependent growth and contact inhibition of growth, showed that the effects are density dependent, with opposing effects on proliferating cells and contact-inhibited cells. In these cells, cell-matrix interactions through integrins are required for activation of the ERK mitogenesis pathway. However, cell-cell interactions via cadherins inhibit the ERK pathway. Expression of Muc4 reverses both of these effects. In contact-inhibited cells, Muc4 appears to activate the ERK pathway at the level of Raf-1; this activation does not depend on Ras activation. The increase in ERK activity correlates with an increase in cyclin D(1) expression in these cells. This abrogation of contact inhibition is dependent on the number of mucin repeats in the mucin subunit of Muc4, indicative of an anti-adhesive effect. The mechanism by which Muc4 disrupts contact inhibition involves a Muc4-induced relocalization of E-cadherin from adherens junctions at the lateral membrane of the cells to the apical membrane. Muc4-induced abrogation of contact inhibition may be an important mechanism by which tumors progress from an early, more benign state to invasiveness.

Muc4-ErbB2 complex formation and signaling in polarized CACO-2 epithelial cells indicate that Muc4 acts as an unorthodox ligand for ErbB2

Muc4 serves as an intramembrane ligand for the receptor tyrosine kinase ErbB2. The time to complex formation and the stoichiometry of the complex were determined to be <15 min and 1:1 by analyses of Muc4 and ErbB2 coexpressed in insect cells and A375 tumor cells. In polarized CACO-2 cells, Muc4 expression causes relocalization of ErbB2, but not its heterodimerization partner ErbB3, to the apical cell surface, effectively segregating the two receptors. The apically located ErbB2 is phosphorylated on tyrosines 1139 and 1248. The phosphorylated ErbB2 in CACO-2 cells recruits the cytoplasmic adaptor protein Grb2, consistent with previous studies showing phosphotyrosine 1139 to be a Grb2 binding site. To address the issue of downstream signaling from apical ErbB2, we analyzed the three MAPK pathways of mammalian cells, Erk, p38, and JNK. Consistent with the more differentiated phenotype of the CACO-2 cells, p38 phosphorylation was robustly increased by Muc4 expression, with a consequent activation of Akt. In contrast, Erk and JNK phosphorylation was not changed. The ability of Muc4 to segregate ErbB2 and other ErbB receptors and to alter downstream signaling cascades in polarized epithelial cells suggests that it has a role in regulating ErbB2 in differentiated epithelia.

Glycoprotein contributions to mammary gland and mammary tumor structure and function: roles of adherens junctions, ErbBs and membrane MUCs

Mammary function is dependent on its three-dimensional organization, which is established and maintained by cell adhesive junctions linked through the membrane to the cell cytoskeleton. These junctions serve not only as structural elements, but also function as initiators and integrators of cell signals. In this review we discuss three types of glycoproteins whose interactions impinge on the function of mammary cell-cell junctions, cadherins, ErbB receptor tyrosine kinases and membrane mucins, as a microcosm of events regulating mammary cell behaviors. Actions of these components are integrated by the critical signaling element beta-catenin. When functioning properly, these glycoproteins, beta-catenin and associated signaling pathways mesh into a highly structured program for development and function of the gland. However, disruption or dysfunction of these glycoproteins or the signaling elements can lead to disorganization of the epithelia and ultimately to neoplasia.

Muc4/sialomucin complex, the intramembrane ErbB2 ligand, translocates ErbB2 to the apical surface in polarized epithelial cells

Muc4/Sialomucin complex (SMC) acts as an intramembrane ligand for the receptor tyrosine kinase ErbB2, inducing a limited phosphorylation of the receptor. Because Muc4/SMC is found at the apical surfaces of polarized epithelial cells and ErbB2 is often basolateral, the question arises as to whether these components become associated in polarized cells. To address this question, we examined the localization of these proteins in polarized human colon carcinoma CACO-2 cells. Dual color immunofluorescence analysis by confocal microscopy demonstrated the basolateral localization of the ErbB2 in these cells; it is primarily co-localized with E-cadherin at adherens junctions. Expression of apical Muc4/SMC in these cells by transient transfection results in the localization of the ErbB2 at the apical surface. Two-color confocal microscopy indicated that ErbB2 is colocalized with Muc4/SMC in the transfected cells but not in untransfected cells in the same culture. The change of localization of ErbB2 was confirmed by cell surface biotinylation of apical and basolateral proteins, followed by streptavidin precipitation and the subsequent detection of ErbB2 by immunoblotting. In contrast, Na+/K+-ATPase maintains its basolateral localization in Muc4/SMC-transfected cells, indicating that the translocation of ErbB2 is not the result of depolarization of the cells. A potential physiological role for the apical localization of ErbB2 is indicated by the fact that ErbB2 phosphorylated at tyrosine 1248 is found predominantly in Muc4/SMC-transfected cells, but not in untransfected cells, and is co-localized with the apical Muc4/SMC. The ability of Muc4/SMC to alter the localization of ErbB2, particularly a phosphorylated form of it, in epithelial cells, suggests that it has an important role in regulating ErbB2 signaling.

Cell signaling through membrane mucins

MUC1 and MUC4 are the two membrane mucins that have been best characterized. Although they have superficially similar structures and have both been shown to provide steric protection of epithelial surfaces, recent studies have also implicated them in cellular signaling. They act by substantially different mechanisms, MUC4 as a receptor ligand and MUC1 as a docking protein for signaling molecules. MUC4 is a novel intramembrane ligand for the receptor tyrosine kinase ErbB2/HER2/Neu, triggering a specific phosphorylation of the ErbB2 in the absence of other ErbB ligands and potentiating phosphorylation and signaling through the ErbB2/ErbB3 heterodimeric receptor complex formed in the presence of neuregulin. In contrast, MUC1 has a highly conserved cytoplasmic tail, which binds beta-catenin, a key component of adherens junctions and a regulator of transcription, in a process that is tightly regulated by MUC1 phosphorylation. The specific localization of these membrane mucins to the apical surfaces of epithelial cells suggests that their signaling functions may be important as sensor mechanisms in response to invasion or damage of epithelia.