SUMO Modifies GβL and Mediates mTOR Signaling

The mechanistic target of rapamycin (mTOR) signaling is influenced by multiple regulatory proteins and post-translational modifications, however, underlying mechanisms remains unclear. Here, we report a novel role of small ubiquitin-like modifier (SUMO) in mTOR complex assembly and activity. By investigating the SUMOylation status of core mTOR components, we observed that the regulatory subunit, G{beta}L, is modified by SUMO1, 2, and 3 isoforms. Using mutagenesis and mass spectrometry, we identified that G{beta}L is SUMOylated at lysine sites K86, K215, K245, K261 and K305. We found that SUMO depletion reduces mTOR-Raptor and mTOR-Rictor complex formation and diminishes nutrient-induced mTOR signaling. Furthermore, we found that reconstitution with WT G{beta}L but not SUMOylation defective KR mutant G{beta}L promote mTOR signaling in G{beta}L-depleted cells. Taken together, we report for the very first time that SUMO modifies G{beta}L, influences the assembly of mTOR protein complexes, and regulates mTOR activity.