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PROX1 Orchestrates Tumor Metabolic Plasticity by Integrating LKB1-AMPK Signaling with BCAA Catabolism (ATAC-Seq)

ABSTRACT: Tumor cell metabolic plasticity is essential for tumor progression and therapeutic response, but the mechanism for regulation of metabolic plasticity remain poorly explored. Here, we identify PROX1 as an essential determinant for tumor metabolic plasticity. Notably, PROX1 is significantly reduced in response to metabolic stress or AMPK activation and is elevated in LKB1-deficient tumors in mice and human. Furthermore, the Ser79 phosphorylation of PROX1 by AMPK significantly alters its protein activity and allows a rapid recruitment of CUL4-DDB1 E3 ubiquitin ligase to promote PROX1 degradation under glucose starvation, a critical event that drives BCAA metabolism rewiring to suppress mTOR signaling. Importantly, PROX1 loss or Ser79 phosphorylation in HCC shows therapeutic resistance to metformin. Consistently, genetic ablation of PROX1 renders LKB1‐deficient KRAS-driven lung cancer resistant to phenformin treatment. Conversely, mice harboring non-phosphorylated PROX1 mutant or LKB1 mutant exhibit high PROX1 stabilization, promoting liver and lung cancer progression. Clinically, AMPK-PROX1 axis in human cancers is important for patient clinical outcomes. Collectively, our results demonstrate that the deficiency in the LKB1-AMPK axis in cancers reactivates PROX1 to sustain intracellular BCAA pools, resulting in enhanced mTOR signaling, and facilitating tumorigenesis and aggressiveness.

ORGANISM(S): Mus musculus

PROVIDER: GSE214193 | GEO | 2022/09/27

REPOSITORIES: GEO

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Project description:Purpose: Mutations in STK11 (LKB1) occur in 17% of lung adenocarcinoma (LUAD) and drive a suppressive (cold) tumor immune microenvironment (TME) and resistance to immunotherapy. The mechanisms underpin the establishment and maintenance of a cold TME in LKB1 mutant LUAD remain poorly understood and the identification of downstream effectors is critical to inform therapeutic strategies to invigorate antitumor immunity. In this study, we investigated the association between inactivation of AMPK, one of the downstream substrates of LKB1, and immune evasion in human LUAD as well as the causal role of AMPK on TME in genetically engineered mouse model (GEMM) of LUAD. Experimental Design: We modeled AMPK inactivation in vivo using GEMM by deleting both AMPKα1 (Prkaa1) and AMPKα2 (Prkaa2) in KrasG12D-driven LUAD (KAA). Furthermore, we investigated the impact of AMPK inactivation on immune cell infiltration and global gene-expression programs of murine LUAD. Gene expression signature from AMPK-deficient murine LUAD was further compared to that of Lkb1 deficient murineLUAD as well as human LUAD with either LKB1 mutation or attenuated AMPK phosphorylation. Results: Inactivation of both AMPKα1 and AMPKα2 accelerates KrasG12D-driven LUAD. AMPK-deficient tumors are characterized with reduced infiltration of CD8+/CD4+ T cells and gene signatures associated with compromised immune microenvironment, which resembles LKB1-deficient murine and human LUAD (KL) as well as LKB1-wildtype LUAD with reduced AMPK phosphorylation. Attenuation of the MHC Class 1 component ß2 microglobulin (ß2M) was identified as a shared feature in KL and KAA murine LUAD as well as in human LUAD with either LKB1 mutations or reduced AMPK phosphorylation. Furthermore, reactivation of AMPK by expression of constitutive active form of AMPKα1 leads to restoration of ß2M level in LKB1 mutant LUAD cells. Conclusions: The results identify attenuation of the LKB1 substrate AMPK as an important mechanism for decreased MHC Class 1 expression and immune evasion in LKB1 mutant LUAD. Translational relevance: LKB1 loss-of-function mutations rank as the third most common genetic alterations found in lung adenocarcinoma and associated with immune evasion. In the current study, on the basis of GEMM of LUAD we established the causal relationship between inactivation of the LKB1 substrate AMPK and immune evasion. Furthermore we find that the status of AMPK phosphorylation is more sensitive than LKB1 mutation in predicting impaired tumor immune microenvironment and likely also for the resistance to immunotherapy. The results also suggest that restoration of AMPK activity could increase the number of patients benefiting from immunotherapy.

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PROX1 Orchestrates Tumor Metabolic Plasticity by Integrating LKB1-AMPK Signaling with BCAA Catabolism (ATAC-Seq)

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