TY  - GEN
AV  - public
KW  - TOR 
KW  -  MAP4K3 
KW  -  4EBP1
N2  - Cells in a multicellular organism need to monitor their environment for nutritional cues, growth and stress signals in order to adapt their metabolism and growth to the changing conditions. The Target of Rapamycin (TOR) signaling pathway is an evolutionary conserved cellular protein network that controls responses to these signals. TOR signaling is a major research topic because of its role in several prevalent human disorders, including cancer and diabetes, but our understanding of TOR pathway is still far from complete. This work is aimed at improving our understanding of TOR signaling in two ways: by developing new research tools to dissect the dynamics of TOR signaling in cells and by characterizing the function of a novel component in the TOR pathway. The first chapter presents the project to develop a probe, based on the Fluorescence Resonance Energy Transfer (FRET) method, for measuring TOR activity in cell culture. I used several approaches to design a FRET probe, based on a substrate of TOR kinase called 4EBP1. These probes did not prove to be useful because fusions to fluorophore domains abolished biological regulation of 4EBP1. An alternative strategy whereby a small tag was introduced into 4EBP1 and then used for in vivo labeling, could solve this problem. Unfortunately, when this probe was expressed in the cells, its interaction with a corresponding partner did not produce a reliable FRET signal, as determined by three different methods. Nevertheless, the obtained results can be used as a basis for future attempts to develop probes for TOR kinase. The second chapter describes the genetic analysis of the MAP4K3 function in Drosophila. MAP4K3 is a new component of the TOR pathway proposed to mediate nutrient sensing by TOR. I identified a strong hypomorphic MAP4K3 mutant and investigated the phenotypes caused by absence of this protein. MAP4K3 mutant flies were viable but weak. Mutant animals demonstrated delayed growth, reduced cell and organ size. Furthermore, they were lean, displaying reduced fat, which could be rescued by genetically increasing TOR activity. This suggests that the observed metabolic defect is due to low TOR activity. The mechanism of MAP4K3 action may involve the MAP kinase pathway and/or modifying activity of Rag GTPases, which can interact with MAP4K3 in cell culture. These results establish MAP4K3 as a regulator of metabolism and growth and open up new possibilities for manipulating TOR signaling. 
A1  - Bryk, Boris
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/9043/
ID  - heidok9043
TI  - TOR signaling : from FRET probes development to function of MAP4K3 in Drosophila
Y1  - 2008///
ER  -