Probing the membrane environment of the TOR kinases reveals functional interactions between TORC1, actin, and membrane trafficking in Saccharomyces cerevisiae-
Section of Molecular and Cellular Biology, College of Biological Sciences, University of California, Davis, Davis, CA 95616, USA-
Abstract: The TOR kinases are regulators of growth in eukaryotic cells that assemble into two distinct protein complexes, TORC1 and TORC2, where TORC1 is inhibited by the antibiotic rapamycin- Present models favor a view wherein TORC1 regulates cell mass accumulation, and TORC2 regulates spatial aspects of growth, including organization of the actin cytoskeleton- Here, we demonstrate that in yeast both TORC1 and TORC2 fractionate with a novel form of detergent-resistant membranes that are distinct from detergent-resistant plasma membrane "rafts-" Proteomic analysis of these TOR-associated membranes revealed the presence of regulators of endocytosis and the actin cytoskeleton- Genetic analyses revealed a significant number of interactions between these components and TORC1, demonstrating a functional link between TORC1 and actin-endocytosis-related genes- Moreover, we found that inhibition of TORC1 by rapamycin 1- disrupted actin polarization, 2- delayed actin repolarization after glucose starvation, and 3- delayed accumulation of lucifer yellow within the vacuole- By combining our genetic results with database mining, we constructed a map of interactions that led to the identification of additional genetic interactions between TORC1 and components involved in membrane trafficking- Together, these results reveal the broad scope of cellular processes influenced by TORC1, and they underscore the functional overlap between TORC1 and TORC2-