Quantitative genetic screening reveals a Ragulator-FLCN feedback loop that regulates the mTORC1 pathway

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Forward genetic screens in mammalian cells, including RNAi and CRISPR-Cas9, are vital for understanding signaling pathways.
• The mechanistic target of rapamycin complex 1 (mTORC1) pathway is a crucial regulator of cell growth, sensing metabolic conditions.
• Human haploid cells offer a powerful platform for comparative genetic screening.

Purpose of the Study:

• To identify novel regulatory mechanisms of mTORC1 signaling using quantitative forward genetic screens.
• To validate human haploid cells as a screening platform for complex signaling pathways.
• To explore the interplay between mTORC1, lysosomal function, and metabolic states.

Main Methods:

• Utilized human haploid cells for quantitative forward genetic screens.
• Applied chemical (rapamycin) and genetic (LAMTOR4 ablation) perturbations.
• Performed iterative "perturb and observe" screening strategies.

Main Results:

• Validated known mTORC1 signaling complexes and their link to lysosomal function.
• Discovered differential roles of LAMTOR4 and LAMTOR5 in mTORC1 regulation under fed vs. starved conditions.
• Uncovered a novel synthetic-sick interaction between tumor suppressor folliculin and LAMTOR4.

Conclusions:

• Human haploid cells are an effective platform for dissecting complex signaling networks like mTORC1.
• The study identified new regulators and interactions within the mTORC1 pathway with potential therapeutic implications.
• Findings advance the understanding of cell growth control and its dysregulation in diseases such as cancer.