Thesis (M. Phil.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

Exosomes are small secreted vesicles of endocytic origin with a size range of 50-150 nm. They are secreted by many cell types and display multiple biological functions including immune-activation, immune-suppression, antigen presentation, and the shuttling of mRNA and miRNA, as well as other cargo. We have characterised the exosomes secreted from two breast cancer cell lines, MDA-MB-231 and MCF7. Exosomes secreted from both cell lines display typical markers including ALIX, Tsg101, CD9 and CD63, and were capable of inducing apoptosis of the Jurkat T cell line, indicating the potential immune-suppressive function of such tumour-derived exosomes. To further investigate the biological potential of exosomes, we loaded purified exosomes with gene specific siRNAs using electroporation, and observed the targeted inhibition of both a known component of the exosome pathway, Rab27a, and also the arthritis associated gene ERAP1, demonstrating the potential novel use of exosomes as therapeutic gene delivery vectors. We have also shown that exosomes derived from MDA-MB-231 cells and the parental cells have different lipid composition, as analysed by lipidomics study. Nanoparticle tracking analysis (NTA), which allows the rapid detection of size and concentration of nanoparticles within the size range 10 nm-1000 nm was tested for its ability to accurately measure size and concentration of exosomes and microvesicles under different conditions. NTA was capable of detecting apoptotic vesicles induced by Taxol and Curcumin treatment. Immunodepletion was used to determine the percentage of CD9 and CD63 positive vesicles. Our data suggest that NTA is a useful technique for measuring size and concentration of exosomes and microvesicles. We hypothesized that NTA could assist in the screening of agents that interfere or promote exosome release. NTA was therefore used to detect increases in exosomes secretion induced by Tamoxifen and Thimerosal treatment, and to monitor the inhibition of exosome secretion from MDA-MB-231 breast cancer cells expressing inhibitory RNA targeted for Rab27a, a component of the exosome pathway. Increases in exosome release induced by Tamoxifen and Thimerosal was detected by NTA and a significant reduction in the release of exosomes by inhibition of Rab27a expression was also observed. Treatment with the known exosomal pathway inhibitor DMA also reduced exosome release, establishing the principle of NTA as a screening technique. We further compared the siRNA targeted cells for their ability to migrate, invade and form anchorage-independent colonies, which were all significantly reduced. Supplementation with MDA-MB-231 derived exosomes restored the ability to form colonies, suggesting exosomes may contribute to metastatic lesion formation. These data suggest that the exosomal pathway is a valid target to disrupt the behaviour of tumour cells and NTA can be used to monitor its activity.

Indiana University-Purdue University Indianapolis (IUPUI) / The addition and removal of phosphate groups is a key regulatory mechanism for many cellular processes. The balance between phosphorylation and dephosphorylation is delicate and must be maintained in order for proper cell functions to be carried out. Protein kinases and phosphatases are the keepers of this balance with kinases adding phosphate groups and phosphatases removing them. As such, mutation and/or altered regulation of these proteins can be the driving factor in disease. Phosphatase of Regenerating Liver (PRL) is a family novel of three dual specificity phosphatases (DSPs) first discovered in the regenerating liver tissue of rats. PRLs have also been shown to act as oncogenes in cell culture and in animal models. However, the physiological substrate and mechanisms of the PRLs are not yet known. Recently, our lab has developed a PRL 2 knockout mouse and found several striking phenotypes all of which correspond to a significant increase in PTEN. We also found that PRL 2 is targetable by small molecular inhibitors that can potentially be used to disrupt tumor growth and spermatogenesis. Furthermore, a PTEN heterozygous mouse model crossed into our PRL 2 knockout line was generated to investigate the relevance of PRL interaction with PTEN in cancer.

Indiana University-Purdue University Indianapolis (IUPUI) / Phosphatase of Regenerating Liver 3 (PRL3) is suspected to be a causative factor toward cellular metastasis when overexpressed. To date, the molecular basis for PRL3 function remains an enigma, justifying the use of 'shot-gun'-style phosphoproteomic strategies to define the PRL3-mediated signaling network. On the basis of aberrant Src tyrosine kinase activation following ectopic PRL3 expression, phosphoproteomic data reveal a signal transduction network downstream of a mitogenic and chemotactic PDGF (α and β), Eph (A2, B3, B4), and Integrin (β1 and β5) receptor array known to be utilized by migratory mesenchymal cells during development and acute wound healing in the adult animal. Tyrosine phosphorylation is present on a multitude of signaling effectors responsible for Rho-family GTPase, PI3K-Akt, Jak-STAT3, and Ras-ERK1/2 pathway activation, linking observations made by the field as a whole under Src as a primary signal transducer. Our phosphoproteomic data paint the most comprehensive picture to date of how PRL3 drives pro-metastatic molecular events through Src activation. The Src-homology 2 (SH2) domain-containing tyrosine phosphatase 2 (SHP2), encoded by the Ptpn11 gene, is a bona-fide proto-oncogene responsible for the activation of the Ras/ERK1/2 pathway following mitogen stimulation. The molecular basis for SHP2 function is pTyr-ligand-mediated alleviation of intramolecular autoinhibition by the N-terminal SH2 domain (N-SH2 domain) upon the PTP catalytic domain. Pathogenic mutations that reside within the interface region between the N-SH2 and PTP domains are postulated to weaken the autoinhibitory interaction leading to SHP2 catalytic activation in the open conformation. Conversely, a subset of mutations resides within the catalytic active site and cause catalytic impairment. These catalytically impaired SHP2 mutants potentiate the pathogenesis of LEOPARD-syndrome (LS), a neuro-cardio-facial-cutaneous (NCFC) syndrome with very similar clinical presentation to related Noonan syndrome (NS), which is known to be caused by gain-of-function (GOF) SHP2 mutants. Here we apply hydrogen-deuterium exchange mass spectrometry (H/DX-MS) to provide direct evidence that LS-associated SHP2 mutations which cause catalytic impairment also weaken the autoinhibitory interaction that the N-SH2 domain makes with the PTP domain. Our H/DX-MS study shows that LS-SHP2 mutants possess a biophysical property that is absolutely required for GOF-effects to be realized, in-vivo.