# Defining the Biochemical Functions of the TSC Tumor Suppressors in mTORC1 Signaling

> **NIH NIH F31** · HARVARD UNIVERSITY D/B/A HARVARD SCHOOL OF PUBLIC HEALTH · 2021 · $2,500

## Abstract

Project Summary/Abstract
Many growth factor signaling pathways converge on the tuberous sclerosis complex (TSC) complex to activate
the mechanistic target of rapamycin complex 1 (mTORC1), a key event in the promotion of anabolic processes
underlying cell growth. The TSC complex is composed of the tumor suppressors, TSC1 and TSC2, and the
protein TBC1D7. Within the complex, TSC2 acts as a GTPase activating protein (GAP) towards the small G-
protein Rheb, which potently activates mTORC1 when it is GTP bound. The pathways that control mTORC1
are comprised of some of the most common oncogenes and tumor suppressors genetically altered in human
cancers. Moreover, mutations found in TSC1 and TSC2 themselves, have been identified in sporadic cancers.
In these settings, mTORC1 is aberrantly activated and results in uncontrolled cell growth. Although significant
progress has been made in understanding the mTORC1 signaling network, many longstanding questions
underlying the mechanistic function of the TSC complex and its regulation of Rheb remain unanswered. Our
lab recently established that specific phosphorylation events on TSC2 by the growth factor signaling kinase,
Akt, regulates mTORC1 activity through spatial localization of the TSC complex. However, a deeper
mechanistic understanding of how phosphorylation impacts TSC2-Rheb binding and the Rheb-GDP/GTP state,
and whether additional kinases regulate localization of the complex is needed. Moreover, how TSC2 binds to
Rheb in different nucleotide-bound states and whether the TSC complex contains regulatory functions towards
Rheb independent of GAP activity are unknown. This proposal will address these unanswered questions
regarding the molecular determinants of TSC complex regulation and function through biochemical studies
including in vitro TSC2-Rheb binding, Rheb nucleotide exchange and TSC2 kinase assays as well as cell
based immunofluorescence microscopy and mTORC1 signaling experiments. Collectively, these mechanistic
studies will provide novel molecular insights into the regulation and function of the TSC tumor suppressors and
their regulation of Rheb and mTORC1 in both normal settings and cancer. To investigate these questions, I
propose the following aims: 1) Map the TSC2-Rheb binding domains and characterize novel regulatory
functions inherent to these regions. 2) Determine how multi-site phosphorylation of TSC2 by upstream kinases
influences TSC2-Rheb binding and regulation. The research outlined in this proposal will take place at the
Harvard T.H. Chan school of Public Health in the lab of Dr. Brendan Manning. Dr. Manning is an expert in the
mTORC1 field and has extensive expertise in biochemical techniques and experimental design. Additionally,
many of the proposed reagents and protocols have already been established in the Manning lab.

## Key facts

- **NIH application ID:** 10392665
- **Project number:** 3F31CA239432-01A1S1
- **Recipient organization:** HARVARD UNIVERSITY D/B/A HARVARD SCHOOL OF PUBLIC HEALTH
- **Principal Investigator:** Sophie Morgan Evarts
- **Activity code:** F31 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $2,500
- **Award type:** 3
- **Project period:** 2021-05-01 → 2021-09-29

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10392665

## Citation

> US National Institutes of Health, RePORTER application 10392665, Defining the Biochemical Functions of the TSC Tumor Suppressors in mTORC1 Signaling (3F31CA239432-01A1S1). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10392665. Licensed CC0.

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