Studies into the antiapoptotic signalling of protein kinase By

One of the most important roles for growth factors such as insulin and IGF-1 in certain cells is the promotion of cell survival and protection against apoptosis. Growth factors achieve this antiapoptotic signalling via complex intracellular signalling pathways mediated by protein kinases and phosphatases. A recently cloned protein kinase, protein kinase B (PKB) has been shown to be a key component of growth factor signalling pathways and in particular has been implicated as a crucial mediator in antiapoptoic signalling. In this study I report the cloning of PKBy, the third and least studied of the PKB isoforms, from rat and mouse brain tissue and production of two different constitutively active mutants of PKBy, the first a membrane targeted mutant and the second a phosphorylation site active mutant. These mutants were then used to stabily transfect Madin-Darby Canine embryonic Kidney (MDCK) cells in order to investigate the role of PKBy in antiapoptotic signalling. Using these stable cell lines it was established that GSK-3 is a downstream target of PKBy and expression of the constitutively active PKBy mutants was found to protect the stable cells against apoptosis induced by growth factor withdrawal. In addition, a dominant negative rat PKBy was cloned and found to induce apoptosis when transfected into wild-type MDCK cells, even in the presence of serum. TTakfai togp^Wier thesx; SHig%*est dbat PKJByiiBS a (%ucial role to fdsry in gfovfdi factor stimulated cell survival signalling. This research may have important implications for research into cancer, diabetes and neurodegenerative disease since PKBy has been found to be upregulated in breast cancer and prostate cancer cell lines and downregulation of PKB may be a central cause of insulin resistance and Alzheimers disease.