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Inhibition of BCAT1-mediated cytosolic leucine metabolism regulates Th17 responses via the mTORC1-HIF1α pathway.

ABSTRACT: Branched-chain amino acids (BCAAs), particularly leucine, are indispensable AAs for immune regulation through metabolic rewiring. However, the molecular mechanism underlying this phenomenon remains unclear. Our investigation revealed that T-cell receptor (TCR)-activated human CD4⁺ T cells increase the expression of BCAT1, a cytosolic enzyme responsible for BCAA catabolism, and SLC7A5, a major BCAA transporter. This upregulation facilitates increased leucine influx and catabolism, which are particularly crucial for Th17 responses. Activated CD4⁺ T cells induce an alternative pathway of cytosolic leucine catabolism, generating a pivotal metabolite, β-hydroxy β-methylbutyric acid (HMB), by acting on BCAT1 and 4-hydroxyphenylpyruvate dioxygenase (HPD)/HPD-like protein (HPDL). Inhibition of BCAT1-mediated cytosolic leucine metabolism, either with BCAT1 inhibitor 2 (Bi2) or through BCAT1, HPD, or HPDL silencing using shRNA, attenuates IL-17 production, whereas HMB supplementation abrogates this effect. Mechanistically, HMB contributes to the regulation of the mTORC1-HIF1α pathway, a major signaling pathway for IL-17 production, by increasing the mRNA expression of HIF1α. This finding was corroborated by the observation that treatment with L-β-homoleucine (LβhL), a leucine analog and competitive inhibitor of BCAT1, decreased IL-17 production by TCR-activated CD4⁺ T cells. In an in vivo experimental autoimmune encephalomyelitis (EAE) model, blockade of BCAT1-mediated leucine catabolism, either through a BCAT1 inhibitor or LβhL treatment, mitigated EAE severity by decreasing HIF1α expression and IL-17 production in spinal cord mononuclear cells. Our findings elucidate the role of BCAT1-mediated cytoplasmic leucine catabolism in modulating IL-17 production via HMB-mediated regulation of mTORC1-HIF1α, providing insights into its relevance to inflammatory conditions.

SUBMITTER: Kang YJ

PROVIDER: S-EPMC11372109 | biostudies-literature | 2024 Aug

REPOSITORIES: biostudies-literature

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Inhibition of BCAT1-mediated cytosolic leucine metabolism regulates Th17 responses via the mTORC1-HIF1α pathway.

Kang Yeon Jun YJ Song Woorim W Lee Su Jeong SJ Choi Seung Ah SA Chae Sihyun S Yoon Bo Ruem BR Kim Hee Young HY Lee Jung Ho JH Kim Chulwoo C Cho Joo-Youn JY Kim Hyun Je HJ Lee Won-Woo WW

Experimental & molecular medicine 20240801 8

Branched-chain amino acids (BCAAs), particularly leucine, are indispensable AAs for immune regulation through metabolic rewiring. However, the molecular mechanism underlying this phenomenon remains unclear. Our investigation revealed that T-cell receptor (TCR)-activated human CD4<sup>+</sup> T cells increase the expression of BCAT1, a cytosolic enzyme responsible for BCAA catabolism, and SLC7A5, a major BCAA transporter. This upregulation facilitates increased leucine influx and catabolism, whic ...[more]

PMID: 39085353

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Project description:Amino acids play crucial roles in the MTOR (mechanistic target of rapamycin kinase) complex 1 (MTORC1) pathway. However, the underlying mechanisms are not fully understood. Here, we establish a cell-free system to mimic the activation of MTORC1, by which we identify CANX (calnexin) as an essential regulator for leucine-stimulated MTORC1 pathway. CANX translocates to lysosomes after leucine deprivation, and its loss of function renders either the MTORC1 activity or the lysosomal translocation of MTOR insensitive to leucine deprivation. We further find that CANX binds to LAMP2 (lysosomal associated membrane protein 2), and LAMP2 is required for leucine deprivation-induced CANX interaction with the Ragulator to inhibit Ragulator activity toward RRAG GTPases. Moreover, leucine deprivation promotes the lysine (K) 525 crotonylation of CANX, which is another essential condition for the lysosomal translocation of CANX. Finally, we find that KAT7 (lysine acetyltransferase 7) mediates the K525 crotonylation of CANX. Loss of KAT7 renders the MTORC1 insensitivity to leucine deprivation. Our findings provide new insights for the regulatory mechanism of the leucine-stimulated MTORC1 pathway.Abbreviations: CALR: calreticulin; CANX: calnexin; CLF: crude lysosome fraction; EIF4EBP1: eukaryotic translation initiation factor 4E binding protein 1; ER: endoplasmic reticulum; GST: glutathione S-transferase; HA: hemagglutinin; HEK293T: human embryonic kidney-293T; KAT7: lysine acetyltransferase 7; Kcr; lysine crotonylation; KO: knockout; LAMP2: lysosomal associated membrane protein 2; LAMTOR/Ragulator: late endosomal/lysosomal adaptor: MAPK and MTOR activator; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; MTOR: mechanistic target of rapamycin kinase; PDI: protein disulfide isomerase; PTM: post-translational modification; RPS6KB1/p70S6 kinase 1: ribosomal protein S6 kinase B1; RPTOR: regulatory associated protein of MTOR complex 1; SESN2: sestrin 2; TMEM192: transmembrane protein 192; ULK1: unc-51 like autophagy activating kinase 1.

Dataset Information

Inhibition of BCAT1-mediated cytosolic leucine metabolism regulates Th17 responses via the mTORC1-HIF1α pathway.

Publications

Inhibition of BCAT1-mediated cytosolic leucine metabolism regulates Th17 responses via the mTORC1-HIF1α pathway.

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