Non-canonical functions of a mutant TSC2 protein in mitotic division
Mary-Bronwen L Chalkley1, Rachel B Mersfelder1, Maria Sundberg2
1Department of Cell & Developmental Biology, School of Medicine Basic Sciences, Vanderbilt University, Nashville, Tennessee, United States of America.
Abstract:
Tuberous Sclerosis Complex (TSC) is a debilitating developmental disorder characterized by a variety of clinical manifestations. TSC is caused by mutations in the TSC1 or TSC2 genes, which encode the hamartin/tuberin proteins respectively. These proteins function as a heterodimer that negatively regulates the mechanistic Target of Rapamycin Complex 1 (mTORC1). TSC research has focused on the effects of mTORC1, a critical signaling hub, on regulation of diverse cell processes including metabolism, cell growth, translation, and neurogenesis. However, non-canonical functions of TSC2 are not well studied, and the potential disease-relevant biological mechanisms of mutations affecting these functions are not well understood. We observed aberrant multipolar mitotic division, a novel phenotype, in TSC2 mutant iPSCs. The multipolar phenotype is not meaningfully affected by treatment with the inhibitor rapamycin. We further observed dominant negative activity of the mutant form of TSC2 in producing the multipolar division phenotype. These data expand the knowledge of TSC2 function and pathophysiology which will be highly relevant to future treatments for patients with TSC.
Insights
Tuberous Sclerosis Complex (TSC) involves mutations in TSC1/TSC2 genes, impacting mTORC1 signaling. Researchers discovered a novel multipolar cell division defect in TSC2 mutant cells, independent of mTORC1 inhibition, revealing new disease mechanisms.
Area of Science:
- Cell Biology
- Genetics
- Developmental Biology
Background:
- Tuberous Sclerosis Complex (TSC) is a genetic disorder caused by mutations in TSC1 or TSC2 genes.
- These genes encode proteins that form a complex regulating mTORC1 signaling, crucial for cell growth and metabolism.
- While mTORC1 pathways are well-studied in TSC, non-canonical functions of TSC2 remain underexplored.
Purpose of the Study:
- To investigate novel cellular phenotypes associated with TSC2 mutations beyond mTORC1 signaling.
- To explore the functional consequences of TSC2 mutations on cell division.
- To understand the potential disease relevance of these newly identified TSC2 functions.
Main Methods:
- Utilized induced pluripotent stem cells (iPSCs) derived from TSC2-mutant individuals.
- Observed and quantified mitotic division patterns, specifically looking for multipolar divisions.
- Assessed the effect of rapamycin, an mTORC1 inhibitor, on the observed phenotypes.
- Investigated the dominant-negative effects of mutant TSC2 proteins.
Main Results:
- Identified aberrant multipolar mitotic division as a novel phenotype in TSC2-mutant iPSCs.
- Demonstrated that rapamycin treatment did not significantly rescue the multipolar division phenotype.
- Showcased dominant-negative activity of mutant TSC2 in inducing multipolar divisions.
Conclusions:
- TSC2 has non-canonical functions in regulating cell division that are independent of mTORC1.
- Aberrant multipolar division represents a novel disease mechanism in TSC.
- These findings offer new insights into TSC pathophysiology and potential therapeutic targets.
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