published_or_final_version / abstract / Biological Sciences / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Biological Sciences / Master / Master of Philosophy

published_or_final_version / Pathology / Master / Master of Philosophy

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

Ovarian cancer is a highly metastatic disease having a poor prognosis (<25%). The factors and underlying mechanisms that regulate ovarian cancer metastasis, however, are still incompletely understood. p70 S6 kinase (p70S6K), a serine/threonine kinase, is frequently activated in high-grade malignant human ovarian cancer. The aim of this study is to investigate the molecular mechanisms by which p70S6K may promote ovarian cancer metastasis. The results show that p70S6K is a critical regulator of the actin cytoskeleton, peritoneal adhesion and dissemination, and multicellular aggregates/spheroids formation in the acquisition of the metastatic phenotype. The regulation of p70S6K on the actin cytoskeleton is through two important functions: as an actin cross-linking protein and as a Rho family GTPase-activating protein. Ectopic expression of constitutively active p70S6K induced a marked reorganization of the actin cytoskeleton and directional migration of ovarian cancer cells. Actin binding and immunofluorescence studies showed that p70S6K had a direct interaction with the actin filaments with no other proteins involved. This interaction did not affect actin polymerization kinetics but cross-linked the actin filaments to inhibit cofilin-induced actin depolymerization. In addition, p70S6K mediated the activation of Rac1 and Cdc42 GTPases and their downstream effector p21-activated kinase 1, but not RhoA. Peritoneal adhesion and dissemination is regulated by p70S6K through integrin expression. Expression of p70S6K siRNA efficiently inhibited ovarian cancer cell adhesion to fibronectin and laminin among different peritoneal extracellular matrix components, as well as to human primary peritoneal mesothelial cells. These effects were associated with the expression of alpha5 and beta1 integrin. Studies into the mechanisms suggest that p70S6K may upregulate alpha5 integrin by a transcriptional mechanism whereas beta1 integrin is regulated at a post-transcriptional level. Enhanced expression of alpha5 and beta1 integrin by active p70S6K mediated the subsequent peritoneal adhesion. In ovarian cancer xenografts, p70S6K and beta1 integrin interference significantly inhibited peritoneal dissemination through reduction in the number and weight of tumors. Multicellular spheroids are present in the malignant ascites of ovarian cancer patients. Using a 3-dimensional culture system, expression of p70S6K siRNA resulted in inhibition of multicellular spheroid formation, which was mediated by N-cadherin but not E- or P-cadherin. In addition to spheroid formation, inhibition of p70S6K was associated with reduced growth of spheroids and disaggregation capabilities on different extracellular matrix components. Taken together, these findings indicate that p70S6K plays an important role in the biology of ovarian cancer metastasis through regulation of several critical steps in dissemination and migration, suggesting that p70S6K could be explored as a potential therapeutic target in ovarian cancer. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

published_or_final_version / Pathology / Master / Master of Medical Sciences

published_or_final_version / Pathology / Master / Master of Medical Sciences

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / Obstetrics and Gynaecology / Doctoral / Doctor of Philosophy

published_or_final_version / Obstetrics and Gynaecology / Doctoral / Doctor of Philosophy