http://hdl.handle.net/10362/3655 Fri, 24 May 2013 23:26:47 GMT 2013-05-24T23:26:47Z http://hdl.handle.net/10362/8574 Title: The role of Rac1-modulated gene transcription in tumorigenesis Authors: Barros, Patrícia Abstract: Gene expression regulation is a dynamic and multi-step process, in which transcription plays a major role. Transcription initiation depends on binding of transcription regulators to DNA elements located in promoter or enhancer regions, a process often controlled by signalling pathways. One such pathway is regulated by Rac1, a member of the Rho family of small GTPases involved in cell proliferation, adhesion and migration. In this work, novel links between Rac1 signalling and transcriptional regulation in colorectal tumour cells are described. First, it is shown that Rac1 activation leads to PAK1-mediated phosphorylation of the transcriptional repressor BCL-6 in colorectal cancer cells, inactivating its repressor function. In the presence of active Rac1, BCL-6 redistribution within the nucleus, a reduction in its affinity to chromatin and increased expression of the endogenous target genes NFKB1 and CD44, and of a BCL-6-controlled luciferase reporter construct were observed. Next, it was found that Rac1 signalling promotes gene transcription by inducing a transcriptional switch from the repressor BCL-6 to the activator STAT5A at the promoter of certain target genes. Using chromatin immunoprecipitation, it is demonstrated in different colorectal cell lines that active Rac1 promotes release of BCL-6 with concomitant nuclear translocation and binding of STAT5A at the same promoter site. Three endogenous cell-cycle-related genes (CCND2, CDKN2B, SUMO1) were identified to be inversely regulated by BCL-6 and STAT5A and shown to respond to Rac1 signalling with promoter occupancy switches that correlate directly with changes in their expression levels.(...) Description: Dissertation presented to obtain the Ph.D degree in Biology Mon, 01 Oct 2012 00:00:00 GMT http://hdl.handle.net/10362/8574 2012-10-01T00:00:00Z http://hdl.handle.net/10362/6864 Title: Protein glycosylation of exosomes from ovarian carcinoma cells: structures and biological roles Authors: Escrevente, Cristina Abstract: Exosomes are small membrane vesicles that are secreted by several cell types including tumour cells. They are formed intracellularly by an inward budding of the membrane of endosomal compartments which are converted to multivesicular bodies. Exosomes are then released into the extracellular environment after fusion of the multivesicular bodies with the plasma membrane. Upon internalization by other cells they may transfer proteins and RNA among cells. Tumour-derived exosomes can promote angiogenesis, cell proliferation, tumour cell invasion and immune evasion. These vesicles have been found in biological fluids such as malignant ascites and blood and can therefore be used not only to identify potential biomarkers of disease but also in vaccination.(...) Description: Dissertation presented to obtain the Ph.D. degree in Biology Sat, 01 Oct 2011 00:00:00 GMT http://hdl.handle.net/10362/6864 2011-10-01T00:00:00Z http://hdl.handle.net/10362/4042 Title: Characterization of the glycosylation of human tumor cells Authors: Machado, Eda Abstract: Ovarian cancer is within the most lethal gynecological malignancies in woman. Therefore, many investigators study its biological aspects with the purpose of discovering more rapid diagnostic methods and efficient treatment. Resembling many other tumors, in ovarian cancer, aberrant glycosylation occurs with the appearance of novel or altered carbohydrate structures. These can be terminal motifs, such as the Lewis determinants, or entire carbohydrate sequences, which have been related to tumorigenesis and its outcome.(...) Sat, 01 May 2010 00:00:00 GMT http://hdl.handle.net/10362/4042 2010-05-01T00:00:00Z http://hdl.handle.net/10362/3666 Title: Fucosyltransferase IX: characterization and biological role Authors: Brito, Catarina Abstract: α3/4-Fucosyltransferases (α3/4-FUTs) are glycosyltransferases (GTs) that catalyze the transfer of fucose in an α3/4-linkage onto the N-acetylglucosamine residue from acceptors containing the type II or type I (Galβ4/3GlcNAc, respectively) structures, thus synthesizing the fucosylated Lewis (Le) carbohydrate determinants. Fucosyltransferase IX (FUT9), the most recently identified member of the family, presents the higher divergence from the other FUTs and its sequence is the only highly conserved among species. FUT9 synthesizes the Lewisx (Lex) epitope (Galβ4(Fucα3)GlcNAc). Recent evidence has suggested that it is the enzyme responsible for the synthesis of Lex in the mouse brain. Lex expression has been described in glycoproteins, proteoglycans and glycolipids from the central nervous system (CNS) of diverse species, including rodents and humans. Sat, 01 Sep 2007 00:00:00 GMT http://hdl.handle.net/10362/3666 2007-09-01T00:00:00Z