3-phosphoinositide-dependent kinase-1 (PDK-1) was identified by its ability to phosphorylate and activate protein kinase B (PKB), a key protein kinase in mediating PI3-kinase-dependent signal transduction. PDK-1 has subsequently been demonstrated to phosphorylate a number of additional protein kinases in the AGC kinase sub-family, on a homologous activating phosphorylation site in the activation loop. Some of these are also activated by PI3-kinase-dependent signals (eg p70S6 and SGK), whereas others are thought to be PI3- kinase-independent (eg p90rsk). The critical role for PDK-1 in mediating the activation of these protein kinases is demonstrated by the fact that their activity is abolished in PDK-1 null ES cells. Tumor cells are thought to rely on the activity of several of these protein kinases for their proliferation and survival. In addition, over-expression of PDK-1 has been shown to be oncogenic. Therefore, inhibition of PDK-1 would be predicted to inhibit tumor growth. However, it is not known which tumors would be most sensitive to PDK-1 inhibition, or how toxic PDK-1 inhibition would be to an intact organism. Mice lacking PDK-1 die early in embryogenesis. To circumvent these obstacles analyzing the effects of PDK-1 inhibition during tumorigenesis in a mammalian organism, we propose to create a knock-in mouse whereby the ATP binding pocket in PDK-1 is enlarged, allowing specific inhibition by small molecules that should be inert to other protein kinases. We will use cells derived from these animals to demonstrate the biochemical and biological consequences of acute PDK-1 inhibition. In addition, we will initiate tumor formation in these to examine the consequences of acute and specific PDK-1 inhibition. We propose two well-defined mouse tumor models to define the requirement for PDK-1 activity. The first is a chemical carcinogen induced skin tumor model, whereby DMBA initiates and TPA causes progression of epidermal papillomas. The second is a myeloid leukemia model whereby activated K-Ras expressed under its endogenous promoter in hematopoietic cells causes a fatal myeloproliferative disorder. These experiments will determine whether PDK-1 inhibition represents an effective and non-toxic approach to curb tumorigenesis.
|Tamguney, Tanja; Zhang, Chao; Fiedler, Dorothea et al. (2008) Analysis of 3-phosphoinositide-dependent kinase-1 signaling and function in ES cells. Exp Cell Res 314:2299-312|
|Stokoe, David (2005) The phosphoinositide 3-kinase pathway and cancer. Expert Rev Mol Med 7:1-22|