Stacks and D-Brane Bundles

In this paper we describe explicitly how the twisted ``bundles'' on a D-brane worldvolume in the presence of a nontrivial B field, can be understood in terms of sheaves on stacks. We also take this opportunity to provide the physics community with a readable introduction to stacks and generalized spaces.Comment: 24 pages, LaTeX; v2: references adde

Role of Id-2 in the maintenance of a differentiated and noninvasive phenotype in breast cancer cells. Cancer Res

ABSTRACT Id proteins are inhibitors of basic helix-loop-helix transcription factors and generally stimulate cell proliferation and inhibit differentiation. We have shown that ectopic expression of Id-1 in murine mammary epithelial cells resulted in loss of differentiation and gain of invasive and proliferative abilities. Moreover, Id-1 was highly expressed in aggressive breast cancer cells in culture and in biopsies from infiltrating carcinomas. In contrast to Id-1, we found that, in vitro and in vivo, Id-2 mRNA and protein were up-regulated as mammary epithelial cells lost proliferative capacity and initiated differentiation. We further determined that this up-regulation of Id-2 was a necessary step toward a fully differentiated phenotype in breast cells. Here we show that one of the components of the extracellular matrix network, laminin, is responsible for the increase in Id-2 expression during differentiation. We also show that Id-2 expression is inversely correlated with the rate of proliferation in murine mammary epithelial cells and that Id-2 is expressed at a higher level in differentiated human breast cancer cells in comparison with very aggressive and metastatic cells. When reintroduced in aggressive breast cancer cells, Id-2 is able to reduce their proliferative and invasive phenotypes and decrease their level of matrix metalloproteinase 9 secretion as well as increase syndecan-1 expression. Moreover, little Id-2 protein expression is detectable in human biopsies from aggressive and invasive carcinomas in comparison with in situ carcinomas. In conclusion, Id-2 expression not only follows a pattern opposite to that of Id-1 during mammary gland development and breast cancer progression but also appears to act as an important protein for the maintenance of a differentiated and noninvasive phenotype in normal and transformed breast cells

Differential AP2 binding to the <i>BST2</i> promoter in primary breast cancer cell lines of varying histologic grade.

<p><b><i>A.</i></b> Schematic of the <i>BST2</i> promoter region spanning 239 bp upstream of the transcriptional start site, including 111 bp of exon 1. Numbering is relative to the translation start site, highlighted in green (+1). Potential <i>cis</i>-regulatory elements shown are either on the plus (+) or minus (–) DNA strands. Regulatory binding sequences: AP2 (blue), STAT1 (red) and STAT3 (purple). <b><i>B.</i></b><b><i>Top panel</i></b> - Chromatin immunoprecipitation (ChIP) performed with anti AP2, or control IgG in 8 breast cancer cell lines. Significant AP2 recruitment to the <i>BST2</i> promoter observed only in grade 1 (CCdl22, CCdl68, CCdl67) & grade 2 (CCdl66, CCdl61) cell lines. <b><i>Bottom panel</i></b><b> -</b> DNA from ChIP samples in top panel analyzed by QPCR. Primers encompassing putative AP2 binding sites from −221 to +6 were used. Melt curves were analyzed to ensure amplification of a single product. Each reaction was performed in triplicate. The plot represents relative binding efficiency determined by 2^-ΔΔC_T, where ΔC_T is the difference between input C_T and immunoprecipitated C_T; ΔΔC_T is the difference between AP2-immunoprecipitated ΔC_T and IgG-immunoprecipitated ΔC_T. Asterisks represent statistical significance (p<0.01). <b><i>C</i></b><i>.</i> Inhibition of AP2 binding to the <i>BST2</i> promoter in TGFβ-responsive primary breast cancer cell lines. Prior to processing for ChIP, cells were treated with vehicle, 4 ng/ml TGFβ, or 20 uM TGFβ inhibitor - SB-431542<b>.</b> Note striking reduction in AP2 binding in the presence of SB-431542 in 3 independent test cell lines. <b><i>D.</i></b> Hypothetical representation of <i>BST2</i> transcriptional regulation by the TGFβ axis. Intact TGFβ regulation mediated by AP2 binding to the <i>BST2</i> promoter enables maintenance of low baseline expression in grade 1 & 2 breast cancer cells.</p

Differential BST2 expression in primary breast cancer of varying histological grade is maintained in tumor-derived cell lines.

<p><b><b><i>A</i></b></b><i>.</i> QPCR based <i>BST2</i> transcript levels in 17 breast cancer cell lines normalized to expression in non-malignant breast epithelium. <b><i>B.</i></b> Western blot analysis of BST2 protein (25–35 kd) in breast cancer cells. Tubulin used as a loading control. <b><i>C.</i></b> Microscopic images of BST2 immunostaining (green) in fixed, permeabilized breast cancer cells. Nuclei counterstained with propidium iodide (red). Bar –50 µm. <b><i>D.</i></b> BST2 immunolocalized at the cell membrane in live, unfixed breast cancer cells. Bar –25 µm.</p

BST2 overexpression is associated with high histological grade of primary breast cancer.

<p><b><b><i>A.</i></b></b> Low grade invasive primary breast tumor showing weak or no BST2 expressing cancer cells. Blue – hematoxylin counterstain. <b><i>B.</i></b> High grade invasive primary breast tumor displaying strong BST2 localization in cancer cells (brown). <b><i>C.</i></b> Homogeneous BST2 immunostaining in cells of coexisting ductal carcinoma <i>in situ</i> (DCIS), and invasive tumor. Bar –50 µm.</p

Biomarker Expression and Risk of Subsequent Tumors After Initial Ductal Carcinoma In Situ Diagnosis

BACKGROUND: Studies have failed to identify characteristics of women who have been diagnosed with ductal carcinoma in situ (DCIS) and have a high or low risk of subsequent invasive cancer. METHODS: We conducted a nested case-control study in a population-based cohort of 1162 women who were diagnosed with DCIS and treated by lumpectomy alone from 1983 to 1994. We collected clinical characteristics and information on subsequent tumors, defined as invasive breast cancer or DCIS diagnosed in the ipsilateral breast containing the initial DCIS lesion or at a regional or distant site greater than 6 months after initial treatment of DCIS (N = 324). We also conducted standardized pathology reviews and immunohistochemical staining for the estrogen receptor (ER), progesterone receptor, Ki67 antigen, p53, p16, epidermal growth factor receptor-2 (ERBB2, HER2/neu oncoprotein), and cyclooxygenase-2 (COX-2) on the initial paraffin-embedded DCIS tissue. Competing risk models were used to determine factors associated with risk of subsequent invasive cancer vs DCIS, and cumulative incidence survival functions were used to estimate 8-year risk. RESULTS: Factors associated with subsequent invasive cancer differed from those associated with subsequent DCIS. Eight-year risk of subsequent invasive cancer was statistically significantly (P = .018) higher for women with initial DCIS lesions that were detected by palpation or that were p16, COX-2, and Ki67 triple positive (p16(+)COX-2(+)Ki67(+)) (19.6%, 95% confidence interval [CI] = 18.0% to 21.3%) than for women with initial lesions that were detected by mammography and were p16, COX-2, and Ki67 triple negative (p16(-)COX-2(-)Ki67(-)) (4.1%, 95% CI = 3.4% to 5.0%). In a multivariable model, DCIS lesions that were p16(+)COX-2(+)Ki67(+) or those detected by palpation were statistically significantly associated with subsequent invasive cancer, but nuclear grade was not. Eight-year risk of subsequent DCIS was highest for women with DCIS lesions that had disease-free margins of 1 mm or greater combined with either ER(-)ERBB2(+)Ki67(+) or p16(+)COX-2(-)Ki67(+) status (23.6%, 95% CI = 18.1% to 34.0%). CONCLUSION: Biomarkers can identify which women who were initially diagnosed with DCIS are at high or low risk of subsequent invasive cancer, whereas histopathology information cannot