Biomedical subjects

Ian P Newton

Publications and source records attributed to Ian P Newton.

6 recordsLinked to original sources

PubMed2007

Loss of APC induces polyploidy as a result of a combination of defects in mitosis and apoptosis.

Mutations in the adenomatous polyposis coli (APC) tumor suppressor gene initiate a majority of colorectal cancers. Acquisition of chromosomal instability is an early event in these tumors. We provide evidence that the loss of APC leads to a partial loss of interkinetochore tension at metaphase and alters mitotic progression. Furthermore, we show that inhibition of APC in U2OS cells compromises the mitotic spindle checkpoint. This is accompanied by a decrease in the association of the checkpoint proteins Bub1 and BubR1 with kinetochores. Additionally, APC depletion reduced apoptosis. As expected from this combination of defects, tetraploidy and polyploidy are consequences of APC inhibition in vitro and in vivo. The removal of APC produced the same defects in HCT116 cells that have constitutively active beta-catenin. These data show that the loss of APC immediately induces chromosomal instability as a result of a combination of mitotic and apoptotic defects. We suggest that these defects amplify each other to increase the incidence of tetra- and polyploidy in early stages of tumorigenesis.

Adenomatous Polyposis Coli Protein↗

PubMed2006

Lack of adenomatous polyposis coli protein correlates with a decrease in cell migration and overall changes in microtubule stability.

Most sporadic colorectal tumors carry truncation mutations in the adenomatous polyposis coli (APC) gene. The APC protein is involved in many processes that govern gut tissue. In addition to its involvement in the regulation of beta-catenin, APC is a cytoskeletal regulator with direct and indirect effects on microtubules. Cancer-related truncation mutations lack direct and indirect binding sites for microtubules in APC, suggesting that loss of this function contributes to defects in APC-mutant cells. In this study, we show that loss of APC results in disappearance of cellular protrusions and decreased cell migration. These changes are accompanied by a decrease in overall microtubule stability and also by a decrease in posttranslationally modified microtubules in the cell periphery particularly the migrating edge. Consistent with the ability of APC to affect cell shape, the overexpression of APC in cells can induce cellular protrusions. These data demonstrate that cell migration and microtubule stability are linked to APC status, thereby revealing a weakness in APC-deficient cells with potential therapeutic implications.

Acetylation↗

PubMed2006

Open microscopy environment and findspots: integrating image informatics with quantitative multidimensional image analysis.

Biomedical research and drug development increasingly involve the extraction of quantitative data from digital microscope images, such as those obtained using fluorescence microscopy. Here, we describe a novel approach for both managing and analyzing such images. The Open Microscopy Environment (OME) is a sophisticated open-source scientific image management database that coordinates the organization, storage, and analysis of the large volumes of image data typically generated by modern imaging methods. We describe FindSpots, a powerful image-analysis package integrated in OME that will be of use to those who wish to identify and measure objects within microscope images or time-lapse movies. The algorithm used in FindSpots is in fact only one of many possible segmentation (object detection) algorithms, and the underlying data model used by OME to capture and store its results can also be used to store results from other segmentation algorithms. In this report, we illustrate how image segmentation can be achieved in OME using one such implementation of a segmentation algorithm, and how this output subsequently can be displayed graphically or processed numerically using a spreadsheet.

Algorithms↗

PubMed2004

Loss of Apc in vivo immediately perturbs Wnt signaling, differentiation, and migration.

Although Apc is well characterized as a tumor-suppressor gene in the intestine, the precise mechanism of this suppression remains to be defined. Using a novel inducible Ahcre transgenic line in conjunction with a loxP-flanked Apc allele we, show that loss of Apc acutely activates Wnt signaling through the nuclear accumulation of beta-catenin. Coincidentally, it perturbs differentiation, migration, proliferation, and apoptosis, such that Apc-deficient cells maintain a "crypt progenitor-like" phenotype. Critically, for the first time we confirm a series of Wnt target molecules in an in vivo setting and also identify a series of new candidate targets within the same setting.

Adenomatous Polyposis Coli Protein↗

PubMed2004

Induced somatic inactivation of STAT3 in mice triggers the development of a fulminant form of enterocolitis.

We have generated mice in which the gene encoding the transcription factor STAT3 can be inactivated in multiple cell types by triggering the endogenous production of type I interferon. Gene inactivation is particularly effective in the liver and the adipose tissue, as well as in macrophages and gut epithelial cells. Upon induction of the mutation, mice develop a wasting syndrome culminating in an aggressive and fatal form of enterocolitis, limited to the large intestine, within 2-3 weeks after the treatment. The disease is characterised by massive infiltration of the gut mucosa by macrophages, granulocytes and CD4+ cells, increased expression of endothelial adhesion molecules and high production of the cytokines interleukin (IL)-6, IL-12, interferon-gamma and IL-10. IL-12 p40 plays a pivotal role in disease development as in vivo treatment with neutralising antibodies completely prevents its onset. Interestingly, oral treatment with wide spectrum antibiotics does not have any effect on either the onset or the development of colitis. Taken together, these data show that STAT3 plays a crucial role in the maintenance of intestinal homeostasis and possibly in mediating specialised cell functions in the intestinal epithelium.

Animals↗

PubMed2004

The adenomatous polyposis coli protein is required for the formation of robust spindles formed in CSF Xenopus extracts.

Mutations in the adenomatous polyposis coli (APC) protein occur early in colon cancer and correlate with chromosomal instability. Here, we show that depletion of APC from cystostatic factor (CSF) Xenopus extracts leads to a decrease in microtubule density and changes in tubulin distribution in spindles and asters formed in such extracts. Addition of full-length APC protein or a large, N-terminally truncated APC fragment to APC-depleted extracts restored normal spindle morphology and the intact microtubule-binding site of APC was necessary for this rescue. These data indicate that the APC protein plays a role in the formation of spindles that is dependent on its effect on microtubules. Spindles formed in cycled extracts were not sensitive to APC depletion. In CSF extracts, spindles predominantly formed from aster-like intermediates, whereas in cycled extracts chromatin was the major site of initial microtubule polymerization. These data suggest that APC is important for centrosomally driven spindle formation, which was confirmed by our finding that APC depletion reduced the size of asters nucleated from isolated centrosomes. We propose that lack of microtubule binding in cancer-associated mutations of APC may contribute to defects in the assembly of mitotic spindles and lead to missegregation of chromosomes.

Adenomatous Polyposis Coli Protein↗