1,720,982 research outputs found
Glycobiological Regulation of Breast Cancer Invasion
No full textInvasiveness of cancer is the predominant reason behind mortality associated with the disease. Although long under active investigation, fundamental aspects of the early steps of cancer invasion and metastasis are still poorly understood. One such aspect, the aberrant expression of glycans and their binding proteins (lectins), is among the earliest-demonstrated and pervasive hallmarks of malignant transformation, the consequences of which remain elusive. In this thesis, two glycopathological questions relating to breast cancer progression are investigated.
In the first problem, evidence is presented for heterogeneity of a specific glycan linkage: α2,6-linked sialic acids within breast cancer epithelia. Upon sorting out two populations with moderate- and relatively higher- cell surface expression of α2,6-linked sialic acids, from the triple negative breast cancer cell line MDA-MB-231, both populations (denoted as medium- and high- 2,6-Sial cells respectively) are shown to stably retain their levels in early passages. The medium 2,6-Sial cells shows greater plasticity (recapitulating eventually the heterogeneity of the unsorted population), and higher adhesion to, and invasion through, ECM, than the high 2,6-Sial cells. The expression of 2,6-Sial and the associated phenotypes is shown to be dependent on the expression of a specific glycosyltransferase, ST6GAL1. The differential adhesion between the two populations is proposed to have consequences for the ‘unjamming’ transition and localization of medium 2,6-Sial cells to the edge of growing tumoroid-like cultures. Notwithstanding the dynamics of cell-surface α2,6-linked sialic acids, an intriguing localization of α2,3-linked sialic acids is observed in the ECM proximal to breast cancer cells.
In the second problem, the role of Galectin-9 (GAL-9) in breast cancer invasion is investigated. A member of the tandem-repeat (having two distinct carbohydrate recognition domains (bi-CRD)) class of galectins, mRNA levels of GAL-9 are shown to be elevated in invasive breast cancer cell lines and the protein is elevated in tumor epithelia from sections of patients with breast cancer. Perturbing GAL-9 levels is shown to correlate with the adhesion and invasion of
cancer epithelia to, and through, ECM, respectively. Intriguingly, the consequences of GAL-9 on invasion is observed to be dependent on its cleavage to monoCRD galectins with the N-CRD fragment (but not C-CRD fragment) able to phenocopy the effects of the full-length counterpart.
Taken together, the above observations add an unexplored (glycobiological) dimension to the interactions between cancer cells and their surrounding ECM, enriching our understanding of how the tumor microenvironment contributes to cancer progression
A study of extracellular matrix dynamics in epithelial cancer progression with a special focus on ovarian cancer spheroidogenesis
No full textEpithelial ovarian cancer (EOC) is one of the most debilitating gynecological cancers in women worldwide due to its insidious symptoms. The predominant subtype of ovarian cancer: high-grade serous ovarian carcinoma (HGSOC), is responsible for 75% of all fatalities associated with EOC. 90% of EOC patients have already reached an advanced stage of metastasis when they are diagnosed with the disease. Metastasis is frequently associated with ascites: an abnormal accumulation of fluid in the peritoneal cavity due to the occurrence of spheroids, clusters of disseminated malignant EOC cells. Spheroids contribute significantly to the morbidity and mortality associated with EOC. Despite this, the mechanisms associated with the formation of EOC spheroids are ill-understood.
Investigations indicate intricate connections between these signaling modules with elements of reciprocal and hierarchical connections that underlie spheroidal morphogenesis and may provide insights into the identification of targets for future therapeutic strategies for EOC
Investigating the role of AMPK in mammary gland alveologenesis and lactation
No full textAMP-activated kinase (AMPK) is an energy sensor that regulates cell growth and metabolism. Reports from our laboratory and others have shown the context-specific role of AMPK signaling in breast cancer. However, its role in normal mammary gland growth and function is unclear. Here, we showed that AMPK expression and activity within murine mammary epithelia increased from puberty to pregnancy, reaching its highest levels during lactation, and then declined post-lactation. Further, induction of prolactin (PRL) signaling increased AMPK expression and activity in ex vivo organotypic cultures of mammary epithelial cells (MECs), whereas PRL failed to do so in 2D monolayer culture of MECs. To understand the role of AMPK in mammary gland morphogenesis in vivo, we generated mice with conditional knockout of the catalytic AMPK isoforms 1 and 2 (AMPK⍺1,⍺2 homo cDKO) in mammary gland. Whole mount analysis of AMPK⍺1,⍺2 homo cDKO mammary glands demonstrated precocious alveolar development with increased epithelial content due to enhanced proliferation and altered differentiation. This was corroborated by ex vivo organotypic cultures wherein pharmacological inhibition of AMPK in primary MECs led to the formation of bigger acini with a significantly increased number of cells AMPK⍺1,⍺2 homo cDKO mice also showed increased beta-casein expression with significantly increased pups’ weight when compared with wild-type control mice. Interestingly, AMPK⍺1,⍺2 homo cDKO epithelia showed increased phosphorylated STAT5 which is known to drive alveologenesis downstream of PRL signaling, suggesting a negative correlation between the two pathways. Interestingly, Akt inhibition led to reversal of phenotype in AMPK⍺1,⍺2 homo cDKO MECs cultured in 3D LrECM, demonstrating a negative cross talk between AMPK and Akt in maintaining cellular homeostasis during alveolar morphogenesis. Our study thus identifies a novel interplay between AMPK and Akt that determines mammary alveologenesis and differentiation through PRL-JAK2-STAT5 signaling
Deploying an Orthogonal Turn for Isolation of Rare Cell Populations from Vascular Environments
No full textCancer cells are shed from metastatic primary tumors, bearing the potential for blood-borne metastasis to distant vital organs. Metastasis is predominantly responsible for cancer-related deaths. These circulating tumor cells (also known as CTCs) are highly invasive and can be present in the vasculature as single cells or as clusters. CTCs have been proposed as an important biomarker to assess the aggressiveness of cancer, the effectiveness of the treatment, and disease progression. Although most of the cells have epithelial receptors on their surface, such as Epithelial Cell Adhesion Molecules (EpCAMs), the molecular diversity on the surfaces of such cells is still not completely characterized. The circulating tumor cells (or CTCs) tend to be larger in size and higher in density with respect to the rest of the blood cells and in their density. CTCs are extraordinarily rare, i.e., one among a billion blood cells which make their isolation difficult.
Existing technologies carry out CTC separation by either inducing external forces (active separation) or using intrinsic hydrodynamic forces (passive separation). In active separation, the external forces have to be larger than the flow-induced forces, which results in a limited throughput. Moreover, these techniques often involve biomarkers and labelling agents (usually EpCAM antibodies), which not only puts a question on the viability of the captured cells but also might fail to work for CTCs that do not express such markers. The passive separation method is carried out by simply controlling the hydrodynamic properties of the flow. Of these, inertial microfluidics separation has high throughput, whereby large sample volumes can be processed in a short time. High throughput vortex trapping and CTC separation has been described by Di Carlo et al. in their vortex-chip technology. However, the operation of their device requires drastically high flow velocities (particle velocity ̴ 4 m/s), which are prone to damage the cells and affect their viability.
In this dissertation, an inertial microfluidic vortex chip incorporating an orthogonal turn is investigated for the isolation and separation of CTCs. These chips function at significantly lower (38% of previously reported) flow velocities. Fluid flowing through the chip is constrained to exit the trapping chamber at right angles to that of its entry. Such a flow configuration leads to the formation of a vortex in the chamber and above a critical flow velocity, larger particles are trapped in the vortex, whereas smaller particles get ejected with the flow: we call this phenomenon the turn-effect.
I explain how different forces contribute to the turn-effect in the orthogonal design by acting on cells, and pushing them into specific vortices in a size- and velocity-dependent fashion. Furthermore, we have characterized the critical velocities for trapping particles of different sizes on chips with distinct entry-exit configurations. Optimal architectures for stable vortex trapping at low flow velocities are identified using polystyrene beads and blood cells.
Subsequently, I demonstrated selective trapping of human breast cancer cells mixed with whole blood at low concentrations. An isolation protocol to separate the trapped particles was developed and optimized on a scaled-up device that uses serialization and parallelization. After isolating spiked circulating cancer cells from diluted blood, we were also able to culture them.
In summary, a label-free inertial microfluidic vortex trapping setup incorporating an orthogonal turn was developed and optimized for the size-based gentle separation of CTCs which are larger and rarer than other blood cells. Some further design modifications were also suggested in the latter part of the work to increase the efficiency of enrichment
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Complexity: the organizing principle at the interface of biological (dis)order
No full textThe term complexity means several things to biologists. When qualifying morphological phenotype, on the one hand, it is used to signify the sheer complicatedness of living systems, especially as a result of the multicomponent aspect of biological form. On the other hand, it has been used to represent the intricate nature of the connections between constituents that make up form: a more process-based explanation. In the context of evolutionary arguments, complexity has been defined, in a quantifiable fashion, as the amount of information, an informatic template such as a sequence of nucleotides or amino acids stores about its environment. In this perspective, we begin with a brief review of the history of complexity theory. We then introduce a developmental and an evolutionary understanding of what it means for biological systems to be complex. We propose that the complexity of living systems can be understood through two interdependent structural properties: multiscalarity of interconstituent mechanisms and excitability of the biological materials. The answer to whether a system becomes more or less complex over time depends on the potential for its constituents to interact in novel ways and combinations to give rise to new structures and functions, as well as on the evolution of excitable properties that would facilitate the exploration of interconstituent organization in the context of their microenvironments and macroenvironments
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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