AMPK Reprograms Gene Expression and Promotes Adaptation/Survival in Response to Metabolic Stress through Binding to a Chromatin-Associated Transcription Complex in Acute Lymphoblastic Leukemia
Authors: Sun Guangyan , Leclerc Guy Jacques , Shvab Anna , Barredo Julio C 
Published: November 2021

Abstract
Survival rates for relapsed/refractory acute lymphoblastic leukemia (ALL), the most common cancer in children and adolescents, remain dismal. We and others have reported that ALL cells are vulnerable to conditions inducing energy/ER-stress mediated by AMP-activated protein kinase (AMPK) activation. AMPK has been reported to interact with chromatin-associated proteins (e.g., histone H2B) in MEF cells to epigenetically regulate gene expression in response to environmental/cellular stress (Bungard et al. Science, 2010; 329:1201). To identify genome-wide genes regulated by direct association of AMPK to chromatin in response to energy/metabolic stress, we first constructed Bp-ALL (NALM6, REH) and T-ALL (CCRF-CEM, KE-37) stable cell lines expressing HA-AMPKα1 or HA-AMPKα2. Next, using HA and RNA pol II antibodies, we performed ChIP-seq assays in CCRF-CEM/HA-AMPKα2 (CN2) grown in glucose-free RPMI for 24 h. ChIP-seq differentially identified 171 candidate genes in CN2 treated with no-glucose vs. 431 genes in untreated controls. Data analysis using the Encode and ChEA database identified the TATA-Box Binding Protein Associated Factor, CCAAT Enhancer Binding Protein Delta (CEBPD), the negative elongation factor complex member E (NELFE), and the Promyelocytic leukemia protein (PML) among highly ranked transcription factors (TFs) may associated with AMPKα2 on chromatin. To correlate the level of gene mRNA expression and recruitment of AMPKα2 to chromatin gene loci regulated in response to energy/metabolic stress, we performed RNA-seq assays in CN2 cells treated with or without glucose deprivation for 24 h. RNA-seq data analysis indicated that of the 3497 genes altered by AMPK activation, two thirds were downregulated whereas the remaining were upregulated. Kyoto Encyclopedia of Genes and Genomes gene set and BioPlanet 2019 gene set analysis identified metabolic pathways, DNA replication/metabolism, and cell cycle as the main biological processes altered in CN2 cells in response to metabolic stress. Among downregulated genes in response to metabolic stress, we uncovered a cluster of histone genes. To confirm and validate our data, we used RT-qPCR and ChIP-qPCR assays on selected histone gene candidates (H1-2/ HIST1H1C, H1-3/HIST1H1D, H4C4/HIST1H4D) which exhibited both decreased recruitment of HA-AMPKα2 to chromatin and mRNA downregulation in response to metabolic stress. Further ChIP-qPCR assays using an AMPKα2 antibody confirmed these data in KASUMI-2 cells (Bp-ALL). Similar data were also observed in CN2 cells treated with AICAR, another AMPK activator. Additional experiments were conducted using the allosteric AMPK activators compound 991 and PF-06409577. Using Co-IP experiments, we uncovered that AMPKα2 interacted with putative members of an AMPK/chromatin-associated transcription factor complex which included the TATA-Box Binding Protein Associated Factor (TAF), integrator (INT), and RNA polymerase II. To investigate the role of AMPK kinase activity on AMPKα2-associated chromatin regulated gene targets, we determined the effect of genetic constructs encoding a constitutively active (CA) form of AMPKα2 on histone gene mRNA expression in CCRF-CEM and MEF AMPKα1/AMPKα2 double knockout (DKO) cells, and found that in both cell types the expression of the full-length CA-AMPKα2 (T172D) lead to decreased mRNA expression of the histone genes examined, suggesting AMPK kinase activity is required to regulate histone genes in response to energy/metabolic stress. In conclusion, our data show that in response to metabolic stress, AMPK binds directly to a multi-protein complex on chromatin to reprogram gene expression to promote cellular adaptation/survival in ALL. Further elucidation of AMPK's interactions with members of the putative AMPK/chromatin-associated transcription complex may lead to unique opportunities for epigenetic-based therapeutic interventions and combination strategies to exploit synthetic lethality in relapse/refractory ALL and other hematological malignancies.

Disclosures
No relevant conflicts of interest to declare.