abstract / Clinical Oncology / Doctoral / Doctor of Philosophy

Thesis (Ph.D.)--University of Delaware, 2008. / Principal faculty advisors: Norman J. Wagner, Dept. of Chemical Engineering, University of Delaware; Eric Wickstrom, Dept. of Biochemistry and Molecular Biology, Thomas Jefferson University. Includes bibliographical references.

Thesis (Ph. D.)--University of Hawaii at Manoa, 2003. / Includes bibliographical references (leaves 122-177).

Thesis (Ph. D.)--University of Hawaii at Manoa, 2003. / Includes bibliographical references (leaves 122-177). Also available by subscription via World Wide Web.

Thesis (M. Med. Sc.)--University of Hong Kong, 2005.

Thesis (M. Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Although it was previously reported that Dictyostelium discoideum possessed a single ras gene (Ddras) that was maximally expressed during the pseudoplasmodial stage of development, a second ras gene (DdrasG), has been isolated and characterized. It encodes a protein that is similar to the protein encoded by Ddras and the human ras proteins. However, in contrast to Ddras, the DdrasG gene was only expressed during growth and early development. The two ras proteins may fulfill different functions: the DdrasG protein having a role during cell growth and the Ddras protein having a role in signal transduction during multicellular development. However, the expression of the DdrasG gene throughout development did not appear to have a detrimental effect on differentiation. Although other eukaryotic organisms possess more than one ras gene, D. discoideum is thus far unique in expressing different ras genes at different stages of development. Ras genes are members of a large ras-related multigene family that has been found in a wide variety of organisms. A ras-related gene was isolated from D. discoideum that hybridized to both the Ddras and DdrasG genes under low, but not under high stringency conditions. The predicted amino acid sequence shows a high degree of sequence identity with the human rap proteins and thus has been designated Ddrapl. During vegetative and early development a single 1.1 kb mRNA was present, but by aggregation this transcript was no longer detected and two new transcripts of 1.0 and 1.3 kb were observed and were present throughout the remainder of development. The maximum levels of the Ddrapl specific mRNAs appeared during aggregation and culmination, developmental stages where the levels of DdrasG and Ddras messages were declining. The reciprocal nature of the Ddrapl gene expression with respect to that of the two ras genes suggests the possibility that the ras and rap gene products in D. discoideum have antagonistic roles. Antibodies that are specific for the Ddras, DdrasG and Ddrapl proteins have been generated and can be used to help elucidate the biological functions of the individual proteins. / Science, Faculty of / Microbiology and Immunology, Department of / Graduate

Cellular transformation is accomplished in vitro through the concerted action of growth factors and oncogenes. This association has demonstrated that malignant growth results from aberrations in pathways that normally operate to control proliferation. Activation of genes that code for growth factors, their receptors, and/or molecules essential in the transduction of signals from the cell surface to the nucleus are all potential mechanisms by which tumor cells could establish a selective growth advantage over normal cells. This dissertation addresses the question of what oncogenic mechanisms are important in the development and progression of human melanoma. These studies show that melanoma growth is regulated by endogenous substances produced by the melanoma cells themselves (autocrine stimulation), as well as by exogenous substances supplied by neighboring cells and platelets (paracrine stimulation). These factors work to drive the expression of the transformed phenotype for melanoma as evidenced by induction of serum-free soft agar growth. Human platelets were found to the the richest source of paracrine growth promoters. The factor from human platelets was characterized and partially purified. Melanoma cells respond to this 60,000 molecular weight, disulfide-bond-containing protein in colony formation assays. In addition, the protein has endothelial cell growth factor activity. Purified fractions which promoted optimal colony formation for human melanoma cells also maximally stimulated monolayer growth of bovine aortic endothelial cells, while melanocytes were nonresponsive. This implies that melanoma cells are expressing receptors for a protein which plays no known or apparent role in the normal growth of melanocytes. Melanoma cells are sensitive to growth regulatory molecules of autocrine and paracrine nature. This dissertation provides clues to the genetic lesions which have occurred in these melanoma cells to influence their proliferation. The aberrations appear to reside in those genes important in growth factor pathways at the level of endogenous production and misguided response to exogenous factors through receptor expression. We can not hope to fully inhibit the proliferation of tumor cells until we identify and understand those forces which drive their growth. These studies have increased our knowledge of those signals which stimulate melanoma cellular proliferation, and thus provide insight into important therapeutic targets.

published_or_final_version / abstract / Surgery / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Clinical Oncology / Doctoral / Doctor of Philosophy