Biomedical subjects

Stephen W Byers

Publications and source records attributed to Stephen W Byers.

9 recordsLinked to original sources

PubMed2006

Pathway-specific differences between tumor cell lines and normal and tumor tissue cells.

BACKGROUND: Cell lines are used in experimental investigation of cancer but their capacity to represent tumor cells has yet to be quantified. The aim of the study was to identify significant alterations in pathway usage in cell lines in comparison with normal and tumor tissue. METHODS: This study utilized a pathway-specific enrichment analysis of publicly accessible microarray data and quantified the gene expression differences between cell lines, tumor, and normal tissue cells for six different tissue types. KEGG pathways that are significantly different between cell lines and tumors, cell lines and normal tissues and tumor and normal tissue were identified through enrichment tests on gene lists obtained using Significance Analysis of Microarrays (SAM). RESULTS: Cellular pathways that were significantly upregulated in cell lines compared to tumor cells and normal cells of the same tissue type included ATP synthesis, cell communication, cell cycle, oxidative phosphorylation, purine, pyrimidine and pyruvate metabolism, and proteasome. Results on metabolic pathways suggested an increase in the velocity nucleotide metabolism and RNA production. Pathways that were downregulated in cell lines compared to tumor and normal tissue included cell communication, cell adhesion molecules (CAMs), and ECM-receptor interaction. Only a fraction of the significantly altered genes in tumor-to-normal comparison had similar expressions in cancer cell lines and tumor cells. These genes were tissue-specific and were distributed sparsely among multiple pathways. CONCLUSION: Significantly altered genes in tumors compared to normal tissue were largely tissue specific. Among these genes downregulation was a major trend. In contrast, cell lines contained large sets of significantly upregulated genes that were common to multiple tissue types. Pathway upregulation in cell lines was most pronounced over metabolic pathways including cell nucleotide metabolism and oxidative phosphorylation. Signaling pathways involved in adhesion and communication of cultured cancer cells were downregulated. The three way pathways comparison presented in this study brings light into the differences in the use of cellular pathways by tumor cells and cancer cell lines.

Biosynthetic Pathways↗

PubMed2006

The molecular basis of vitamin D receptor and beta-catenin crossregulation.

The signaling/oncogenic activity of beta-catenin can be repressed by activation of the vitamin D receptor (VDR). Conversely, high levels of beta-catenin can potentiate the transcriptional activity of 1,25-dihydroxyvitamin D3 (1,25D). We show here that the effects of beta-catenin on VDR activity are due to interaction between the activator function-2 (AF-2) domain of the VDR and C terminus of beta-catenin. Acetylation of the beta-catenin C terminus differentially regulates its ability to activate TCF or VDR-regulated promoters. Mutation of a specific residue in the AF-2 domain, which renders the VDR trancriptionally inactive in the context of classical coactivators, still allows interaction with beta-catenin and ligand-dependent activation of VDRE-containing promoters. VDR antagonists, which block the VDRE-directed activity of the VDR and recruitment of classical coactivators, do allow VDR to interact with beta-catenin, which suggests that these and perhaps other ligands would permit those functions of the VDR that involve beta-catenin interaction.

Acetylation↗

PubMed2005

The role of TGF-beta and Wnt signaling in gastrointestinal stem cells and cancer.

The past three decades have seen an unremitting quest to identify and understand gastrointestinal stem cells, their plasticity in differentiating across cell types, as well as their role in normal, regenerative, and cancer cells. A fascinating hallmark of stem cells is their ability to undergo assymetric cell division, which entails replication of the DNA followed by division of the nucleus and partitioning of the cytoplasm to yield two different daughter cells: a stem cell as well as a committed progenitor cell, the latter proliferating into differentiated progeny. We are only just beginning to understand how normally quiescent, tissue-specific stem cells interpret a vast array of signals to develop into the gastrointestinal system. These signaling pathways include the transforming growth factor-beta (TGF-beta) superfamily, Wnt, FGFs, Hedgehog, Hox proteins that originate from surrounding mesodermal/stromal tissue as well as endodermal/epithelial tissue. TGF-beta and wnt proteins are key morphogens that ultimately influence cell division and cell fate, so that gut endodermal stem cells enter the cell cycle, and undergo cell division that ultimately leads to differentiated cells such as functional hepatocytes, gastric parietal cells, or gut epithelial cells. Disruptions and errors in this process usually lead to tissue-specific gastrointestinal cancers such as hepatocellular cancers, gastric adenocarcinomas, and colonic adenocarcinomas. An increasingly complex and coherent view of stem/progenitor cell signaling networks, which coordinate cell growth, proliferation, stress management, and survival, is helping to define the fragile areas where malignancies are likely to develop and shows promise for the development of better cancer therapies.

Animals↗

PubMed2004

Cyclin D1 genetic heterozygosity regulates colonic epithelial cell differentiation and tumor number in ApcMin mice.

Constitutive beta-catenin/Tcf activity, the primary transforming events in colorectal carcinoma, occurs through induction of the Wnt pathway or APC gene mutations that cause familial adenomatous polyposis. Mice carrying Apc mutations in their germ line (ApcMin) develop intestinal adenomas. Here, the crossing of ApcMin with cyclin D1-/- mice reduced the intestinal tumor number in animals genetically heterozygous or nullizygous for cyclin D1. Decreased tumor number in the duodenum, intestines, and colons of ApcMin/cyclin D1+/- mice correlated with reduced cellular proliferation and increased differentiation. Cyclin D1 deficiency reduced DNA synthesis and induced differentiation of colonic epithelial cells harboring mutant APC but not wild-type APC cells in vivo. In previous studies, the complete loss of cyclin D1 through homozygous genetic deletion conveyed breast tumor resistance. The protection of mice, genetically predisposed to intestinal tumorigenesis, through cyclin D1 heterozygosity suggests that modalities that reduce cyclin D1 abundance could provide chemoprotection.

Adenomatous Polyposis Coli Protein↗

PubMed2003

Up-regulation of fibroblast growth factor-binding protein, by beta-catenin during colon carcinogenesis.

Fibroblast growth factor-binding protein (FGF-BP) releases immobilized FGFs from the extracellular matrix and can function as an angiogenic switch molecule in cancer. Here we show that FGF-BP is up-regulated in early dysplastic lesions of the human colon that are typically associated with a loss of adenomatous polyposis coli and up-regulation of beta-catenin. In addition, FGF-BP expression is induced in dysplastic lesions in ApcMin/+ mice in parallel with the up-regulation of beta-catenin. Also, in cell culture studies FGF-BP is induced by beta-catenin through direct activation of the FGF-BP gene promoter. We conclude that FGF-BP is a target gene of beta-catenin.

Adenoma↗

PubMed2003

Trans-repression of beta-catenin activity by nuclear receptors.

The signaling/oncogenic activity of beta-catenin can be repressed by the activation of nuclear receptors such as the vitamin A, vitamin D, and androgen receptors. Although these receptors directly interact with beta-catenin and can sequester it away from its transcription factor partner T-cell factor, it is not known if this is the mechanism of trans-repression. Using several different promoter constructs and nuclear receptors and mammalian two-hybrid and mutation analyses we now show that interaction with the co-activator, p300, underlies the trans-repression of beta-catenin signaling by nuclear receptors and their ligands.

Blotting, Western↗

PubMed2003

IKKalpha regulates mitogenic signaling through transcriptional induction of cyclin D1 via Tcf.

The Wnt/beta-catenin/Tcf and IkappaB/NF-kappaB cascades are independent pathways involved in cell cycle control, cellular differentiation, and inflammation. Constitutive Wnt/beta-catenin signaling occurs in certain cancers from mutation of components of the pathway and from activating growth factor receptors, including RON and MET. The resulting accumulation of cytoplasmic and nuclear beta-catenin interacts with the Tcf/LEF transcription factors to induce target genes. The IkappaB kinase complex (IKK) that phosphorylates IkappaB contains IKKalpha, IKKbeta, and IKKgamma. Here we show that the cyclin D1 gene functions as a point of convergence between the Wnt/beta-catenin and IkappaB pathways in mitogenic signaling. Mitogenic induction of G(1)-S phase progression and cyclin D1 expression was PI3K dependent, and cyclin D1(-/-) cells showed reduced PI3K-dependent S-phase entry. PI3K-dependent induction of cyclin D1 was blocked by inhibitors of PI3K/Akt/IkappaB/IKKalpha or beta-catenin signaling. A single Tcf site in the cyclin D1 promoter was required for induction by PI3K or IKKalpha. In IKKalpha(-/-) cells, mitogen-induced DNA synthesis, and expression of Tcf-responsive genes was reduced. Reintroduction of IKKalpha restored normal mitogen induction of cyclin D1 through a Tcf site. In IKKalpha(-/-) cells, beta-catenin phosphorylation was decreased and purified IKKalpha was sufficient for phosphorylation of beta-catenin through its N-terminus in vitro. Because IKKalpha but not IKKbeta induced cyclin D1 expression through Tcf activity, these studies indicate that the relative levels of IKKalpha and IKKbeta may alter their substrate and signaling specificities to regulate mitogen-induced DNA synthesis through distinct mechanisms.

Binding Sites↗

PubMed2002

An alternatively spliced cadherin-11 enhances human breast cancer cell invasion.

Although reduced levels of the epithelial cell adhesion molecule E-cadherin are often associated with poorly differentiated breast cancers, recent studies show that expression of other cadherins such as N-cadherin, P-cadherin, and the mesenchymal cadherin-11 is actually elevated in invasive breast cancers and cell lines. Cadherin-11 is unique among cadherins in that it exists as two alternatively spliced forms that are expressed together in the same cell. We now show that expression of wild-type cadherin-11, with or without coexpression of the COOH-terminal truncated splice variant, promotes epithelial differentiation of the cadherin-negative SKBR3 cell line. Exogenous wild-type cadherin-11 association with and membrane recruitment of beta-catenin and p120 are unaffected by coexpression of the truncated variant. Cadherin-11-expressing cells exhibit modest changes in cell proliferation and no change in anchorage-independent growth. However, coexpression of wild-type cadherin-11 and the splice variant promotes a dramatic increase in the ability of SKBR3 cells and E-cadherin-positive MCF7 cells to traverse Matrigel-coated filters. Biochemical studies indicate that the truncated variant may be secreted from the cell and/or enter a detergent-insoluble compartment. These data suggest that the presence of the cadherin-11 splice variant promotes invasion of cadherin-11-positive breast cancer cells.

Adherens Junctions↗

PubMed2002

The role of cadherin, beta-catenin, and AP-1 in retinoid-regulated carcinoma cell differentiation and proliferation.

Vitamin A derivatives (retinoids) are potent regulators of cell proliferation and differentiation. Retinoids inhibit the function of the oncogenic AP-1 and beta-catenin/TCF pathways and also stabilize components of the adherens junction, a tumor suppressor complex. When treated with retinoic acid (RA), the breast cancer cell line, SKBR3, undergoes differentiation and reduction in cell proliferation. The present work demonstrates that in SKBR3 cells, which exhibit high AP-1 activity, RA-regulation of cadherin expression and function, but not changes in AP-1 (or beta-catenin/TCF) signaling, is responsible for the epithelial differentiation. However, cadherin function and recruitment of beta-catenin to the membrane is not required for RA to regulate DNA synthesis in these cells. RA also reduces the activity of an AP-1 and TCF-sensitive cyclin D1 reporter in SKBR3 cells in a manner that is independent of the TCF site. In contrast, in SW480 cells, which have high levels of beta-catenin/TCF signaling, the activity and retinoid responsiveness of the cyclin D1 promoter was markedly inhibited by mutation of the TCF site. These data indicate that the remarkably broad effects of RA on the growth and differentiation of many different epithelial cancers may well be explained by the ability of RA to differentially regulate the activity of RAR/RXR, AP-1, and beta-catenin/TCF pathways.

Cadherins↗