Spatial Compartmentalization of mTORC1 to the Nucleus to Regulate Transcription and Impact Nuclear Erk Signaling

Abstract

<b>Abstract ID 16953</b> <b>Poster Board 330</b> Mechanistic target of Rapamycin (mTOR) complex 1 (mTORC1) integrates inputs from multiple pathways and senses diverse signals to regulate cell growth, protein translation, and proliferation. Given that signal compartmentalization can enhance signaling specificity and efficiency, spatial regulation of mTORC1 appears to be critical for this multifaceted signaling complex as it has been reported at many subcellular locations. For example, mTORC1 at the lysosome is regulated by both amino acids and growth factors and functions to promote translation and suppress autophagy. We have also previously reported a nuclear pool of mTORC1 that is regulated by nuclear Akt, by a regulatory mode distinct from the lysosomal pool of mTORC1. However, the functions of subcellular pools of mTORC1, in particular in the nucleus, are not well understood. A major limitation in the field is the availability of tools to assess the activity and function of spatially compartmentalized signaling enzymes in living cells. We have developed a genetically encodable inhibitor of mTORC1, TerminaTOR, that can be spatially compartmentalized to specifically inhibit a subcellular pool of mTORC1. Using TerminaTOR, we conducted a phosphoproteomics study to elucidate the role of nuclear mTORC1 in regulating transcriptional proteins. Several transcription-related proteins were differentially expressed or phosphorylated upon nuclear mTORC1 inhibition. Furthermore, the phosphoproteomics data revealed interesting crosstalk between nuclear mTORC1 and Erk activity, which we investigated more in depth by imaging and biochemical assays. Based on our findings, we hypothesize that there is a mechanism of spatially regulated crosstalk between nuclear Erk and nuclear mTORC1 that may play a role in transcription.