Myeloid folliculin balances mTOR activation to maintain innate immunity homeostasis
Jia Li, Shogo Wada, Lehn K. Weaver, Chhanda Biswas, Edward M. Behrens, Zoltan Arany
Jia Li, Shogo Wada, Lehn K. Weaver, Chhanda Biswas, Edward M. Behrens, Zoltan Arany
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Research Article Cell biology Immunology

Myeloid folliculin balances mTOR activation to maintain innate immunity homeostasis

Abstract

The mTOR pathway is central to most cells. How mTOR is activated in macrophages and how it modulates macrophage physiology remain poorly understood. The tumor suppressor folliculin (FLCN) is a GAP for RagC/D, a regulator of mTOR. We show here that LPS potently suppresses FLCN in macrophages, allowing nuclear translocation of the transcription factor TFE3, leading to lysosome biogenesis, cytokine production, and hypersensitivity to inflammatory signals. Nuclear TFE3 additionally activates a transcriptional RagD-positive feedback loop that stimulates FLCN-independent canonical mTOR signaling to S6K and increases cellular proliferation. LPS thus simultaneously suppresses the TFE3 arm and activates the S6K arm of mTOR. In vivo, mice lacking myeloid FLCN reveal chronic macrophage activation, leading to profound histiocytic infiltration and tissue disruption, with hallmarks of human histiocytic syndromes, such as Erdheim-Chester disease. Our data thus identify a critical FLCN-mTOR-TFE3 axis in myeloid cells, modulated by LPS, that balances mTOR activation and curbs innate immune responses.

Authors

Jia Li, Shogo Wada, Lehn K. Weaver, Chhanda Biswas, Edward M. Behrens, Zoltan Arany

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Figure 1

FLCN deletion in myeloid/macrophage cell lineage leads to constitutive activation of TFE3.

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FLCN deletion in myeloid/macrophage cell lineage leads to constitutive a...
(A) Western blot of FLCN, phospho-TFE3 (Ser320), and TFE3 in the FLCN-KO and nontarget control (NTC) RAW 264.7 cells. (B) Immunofluorescence staining of TFE3 (green) in the FLCN-KO and NTC RAW 264.7 cells. (C) Relative mRNA expression in the FLCN-KO and NTC RAW 264.7 cells was quantified by quantitative reverse transcription–PCR (qRT-PCR). The data were normalized to a reference gene, 36B4. Values are represented as mean ± SEM from 3 independent experiments. **P < 0.01 vs. NTC, determined by Student’s t test. (D) Relative mRNA expression in primary cultured bone marrow–derived macrophages (BMDMs) isolated from FLCNlox/lox mice (WT) and FLCNlox/lox Lyz2 Cre mice (FLCN KO). Values are represented as mean ± SEM from 3 independent experiments. **P < 0.01 vs. WT, determined by Student’s t test. (E) Immunofluorescence staining of TFE3 (green) in the WT and FLCN-KO BMDMs. Scale bar: 10 μm. (F) Immunofluorescence staining of FLCN-HA (red) and TFE3 (green) in the FLCN-KO BMDMs overexpressed by doxycycline-inducible FLCN-HA. TFE3 was distributed in the cytoplasm of cells with successful FLCN-HA transfection (white arrows) but retained in the nuclear of FLCN-deleted BMDMs without transfection. Scale bar: 10 μm. (G) Relative mRNA expression of lysosome genes in the WT and FLCN-KO BMDMs. Values are represented as mean ± SEM from 3 independent experiments. *P < 0.05, **P < 0.01 vs. WT, determined by Student’s t test. (H) Immunofluorescence staining of LAMP2 (red) in the WT and FLCN-KO BMDMs. Scale bar: 10 μm.