| Guanosine triphosphatases (GTPases) are signaling mediators involved in regulation of diverse cellular processes including regulation of the actin cytoskeleton, gene transcription, cell cycle regulation, apoptosis and transformation. Regulatory proteins including G protein coupled receptors (GPCR), GTPase activating proteins (GAP) and guanine nucleotide exchange factors (GEF) influence the activity of GTPases. This thesis addresses the contributions of GTPase regulators in cellular growth control, differentiation and transformation.; Over-expression of G2A or PAR-1, two GPCRs, in NIH 3T3 fibroblasts induced a full range of phenotypes characteristic of oncogenic transformation. Co-expression of dominant negative Rho or LscRGS (Lbc's second cousin regulator of G protein signaling domain), a negative regulator of Gα12 and Ga13 GTPases, suppressed transformation via these GPCRs. Activation of Gα 12, Gα13 and Rho GTPases are thus required for transformation via these GPCRs.; To elucidate the role of Gα12 and Gα13 GTPases in lymphocyte development, transgenic mice expressing LscRGS were generated. Analyses of lymphocytes from these mice revealed that LscRGS expression did not overtly affect lymphocyte development. These results indicate that Gα12 and Gα13 are not required for lymphocyte development.; Previous studies by others demonstrated that loss of Rho function partially blocked differentiation and survival of CD4−/CD8 − double negative (DN) thymocytes and expression of another Rho family GTPase, Cdc42, enhanced the proliferative capacity of DN thymocytes. In addition, results from other studies revealed that expression of activated Rho augments positive selection and induces CD4+/CD8 − and CD4−/CD8+ single positive (SP) thymocyte hypersensitivity to TCR-induced proliferation in vitro . Dbs is a Rho- and Cdc42-activating GEF normally expressed in thymus. To determine how Dbs influences lymphocyte development, transgenic mice were generated expressing an activated form of Dbs. Expression of activated Dbs in lymphocytes promoted the accumulation of early thymocytes and restricted the production of mature thymocytes. Activated Dbs expression also led to increased proliferation of DN thymocytes. The Dbs transgene caused reduced numbers of SP thymocytes and mature splenic T lymphocytes. In addition, transgenic CD4+/CD8+ double positive (DP) thymocytes expressed higher levels of T cell receptor (TCR) and were hypersensitive to apoptosis induced by injection of anti-CD3. (Abstract shortened by UMI.)... |
