The gamma-tubulin meshwork as a therapeutic target

Abstract: Cancer is a heterogeneous disease and treatment regime is dependent on type and location of the tumor. Several of the commonly used chemotherapeutics target the functions of the microtubules. One of the major problems with these drugs is the adverse effects associated with their use. Another problem many of the chemotherapeutics today face is resistance. Therefore there is a constant need for development of new drugs in the fight against cancer. Many tumors achieve independent growth by carrying mutations in the retinoblastoma (pRB) signaling pathway. It has been shown that reduced protein levels of nuclear gamma-tubulin in tumor cells lacking pRB expression induce cell death. Consequently inhibiton of gamma-tubulin might be used as a new strategy for therapy of pRB-negative tumors with fewer side-effects.The aim of this thesis was to evaluate gamma-tubulins’ potential as a novel therapeutic target in the treatment of tumors with a deregulated pRB and to characterize the gamma-tubulin meshwork. We searched for compounds that specifically interfere with the nuclear activity of gamma-tubulin and the effect of the substances were studied in silico, in vitro and in vivo. Among the tested substances we found one, citral dimethyl acetal (CDA), that was specific for gamma-tubulin. CDA caused cell death in cell lines with non-functional pRB and reduced tumor growth in a mice xenograft model. We also showed that CDA interact with gamma-tubulin at the amino acid cysteine 13 at the GTPase domain of gamma-tubulin. Our results demonstrate that it is possible to develop new chemotherapeutics that target the nuclear activity of gamma-tubulin and give rise to fewer side-effects.We also observed that gamma-tubulin form a meshwork in cells that connects the nuclear and cytoplasmic compartments. The network is important in mitosis during formation of the nuclear envelope (NE) where it is responsible for recruitment of the lamina to the chromatin. We also observed that gamma-tubulin form cytosolic tubules together with several other proteins, including GCP2, GCP3, GCP6 and pericentrin. The gamma-tubulin meshwork also interacts with the mitochondria. In addition, we provide evidence for that the gamma-tubulin GTPase domain is involved in regulation of mitochondria organization and homeostasis.