Thesis (Ph. D.)--University of Chicago, Committee on Human Nutrition and Nutritional Biology, 2001. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 86-103).

Thesis (M.S. in Bio. E.)--School of Biomedical Engineering, Georgia Institute of Technology, 2004. Directed by Cheng Zhu. / Includes bibliographical references (leaves 79-84).

Thesis (Ph. D. in Cell and Developmental Biology)--Vanderbilt University, Dec. 2009. / Title from title screen. Includes bibliographical references.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1969. / Includes bibliographical references (p. 117-120).

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 189-230).

 In rat testes, at stage VIII of the epithelial cycle of spermatogenesis, two cellular events, namely blood-testis barrier (BTB) restructuring and spermiation, take place simultaneously but at the opposite ends of the seminiferous epithelium. BTB is constituted by tight junctions (TJs), basal ectoplasmic specializations (ES), gap junctions and desmosomes, which must disassemble intermittently at stage VIII to facilitate preleptotene spermatocyte migration across the barrier. Synchronously, spermiation occurs at the luminal edge of the tubule lumen, involving the disruption of the apical ES, the only anchoring device there, and the release of sperm. The mechanism coordinating these events is not well understood. In this dissertation, I provide evidence that intercellular adhesion molecule (ICAM)-1 and -2, are working in concert with sarcoma (Src) family kinases to regulate these events. ICAMs comprise an immunoglobulin subfamily of cell adhesion proteins expressed by hematopoietic, endothelial and epithelial cells. They are known to function in the transendothelial migration of leukocytes. In the rat testis, ICAM-1 was shown to localize to both BTB and apical ES stage-specifically, with its immunoreactivity highest at stage VIII at the BTB. Besides co-immunoprecipitation and co-localization with BTB proteins, such as occludin and N-cadherin, ICAM-1 was found to promote BTB integrity in that its over-expression (O-E) in Sertoli cells in vitro increased transepithelial electrical resistance (TER). However, O-E of a truncated form of ICAM-1 (sICAM-1) that only consisted of the extracellular domain resulted in decreased TER and down-regulation of several BTB constituent proteins, possibly via the Src/Pyk2 signaling pathway. O-E of sICAM-1 in vivo also compromised the BTB integrity. These findings illustrate that ICAM-1 is an important regulator of the BTB. On the other hand, the localization of ICAM-2 was restricted to the Sertoli-germ cell interface and absent from the BTB, and associated with β1-integrin, nectin-3 and F-actin at the apical ES. Further, ICAM-2 was shown to interact with Src and Pyk2, as well as annexin II, a phospholipid-binding protein. Intriguingly, ICAM-2, Src and annexin II were specifically up-regulated during CdCl2-induced germ cell loss. These results reveal that ICAM-2 actively participates in the restructuring of apical ES based on studies using the cadmium model. The function of c-Yes, a member of the Src family, was also investigated. It was found to be stage-specifically expressed at the BTB and the apical ES, and it structurally associated with BTB components (e.g., occludin and N-cadherin) and with the apical ES proteins (e.g., β1-integrin, laminin β3 and γ3). In the study, the knockdown of c-Yes by RNAi in vitro and in vivo affected BTB and apical ES function, causing changes in the distribution/localization of adhesion proteins at the BTB and the apical ES, inducing germ cell loss from the seminiferous epithelium, possibly via an interference with the F-actin network. These findings implicate that ICAMs and c-Yes are regulatory molecules of cell adhesion at the BTB and the apical ES, and are biomarkers for male contraceptive development. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / toc / Medicine / Doctoral / Doctor of Philosophy

Research has identified a linear relationship between saturated fat intake and colon cancer, and has demonstrated that high fat diets enhance tumorigenesis through elevation of secondary bile acids such as deoxycholic acid (DCA). We and others have shown that DCA can manipulate cell adhesion by decreasing expression of E-cadherin and increasing expression of beta-catenin. We have also shown that DCA significantly reduces EphB2 expression, which regulates cell positioning and segregation. Importantly, vitamin D can reinstate membranous E-cadherin/beta-catenin interactions and increase E-cadherin expression. In the present study, we sought to analyze the effects of DCA and vitamin D (cholecalciferol) treatment on EphB2 in colorectal cancer cells. Pre-treatment with cholecalciferol restored EphB2 expression in a dose-dependent manner, even with combined DCA treatment. This observation may be EGFR-dependent, suggesting that cholecalciferol may antagonize the effects of DCA. Taken together, these results suggest that cholecalciferol may represent an adjuvant therapy for colorectal cancer patients.

Stat3 (signal transducer and activator of transcription-3) is activated by a number of receptor and non-receptor tyrosine kinases, while a constitutively active form of Stat3 alone is sufficient to induce neoplastic transformation. Results presented in this thesis reveal that Stat3 can also be activated through homophilic interactions by the epithelial (E)-cadherin and cadherin-11, two members of the classical type I and II cadherin family of surface receptors, responsible for the formation of cell to cell junctions. Indeed, by plating cells onto surfaces coated with fragments encompassing the two outermost domains of these cadherins, we definitively demonstrate that cadherin engagement can activate Stat3, even in the absence of direct cell to cell contact. At the same time, levels of the extracellular signal regulated kinase (Erk)1/2, which is often coordinately activated by growth factor receptors and oncogenes, remain unchanged upon cadherin ligation. Most importantly, we report, for the first time, an unexpected surge in total Rac1 and Cdc42 protein levels, triggered by cadherin engagement, and an increase in Rac1 and Cdc42 activity, which is responsible for the Stat3 stimulation observed. Inhibition of cadherin interactions reduced Rac/Cdc42 and Stat3 levels and induced apoptosis, pointing to a significant role of this pathway in cell survival signalling, a finding which could also have important therapeutic implications. To better understand the role of Rac/Cdc42 in the cadherin-mediated Stat3 activation, we compared Stat3 activity in mouse HC11 cells before and after expression of the mutationally activated, RacV12. We demonstrate a dramatic increase in protein levels and activity of both the endogenous Rac and RacV12 with cell density, which was due to inhibition of proteasomal degradation. Moreover, we clearly show that RacV12 expression can activate Stat3 through an increase in expression of members of the IL6 family of cytokines, known potent Stat3 activators. In fact, knockdown experiments indicate that gp130 receptor function, and Stat3 activation, are essential for the migration and proliferation of RacV12-expressing cells, thereby demonstrating that the gp130/Stat3 axis represents an essential target of activated Rac in the regulation of both of these fundamental cellular functions. / Thesis (Ph.D, Pathology & Molecular Medicine) -- Queen's University, 2010-02-18 10:38:29.549