Xiao-yong Zhang

Mammalian cells fuel their growth and proliferation through the catabolism of two main substrates: glucose and glutamine. Most of the remaining metabolites taken up by proliferating cells are not catabolized, but instead are used as building blocks during anabolic macromolecular synthesis. Investigations of phosphoinositol 3-kinase (PI3K) and its downstream effector AKT have confirmed that these oncogenes play a direct role in stimulating glucose uptake and metabolism, rendering the transformed cell addicted to glucose for the maintenance of survival. In contrast, less is known about the regulation of glutamine uptake and metabolism. Here, we report that the transcriptional regulatory properties of the oncogene Myc coordinate the expression of genes necessary for cells to engage in glutamine catabolism that exceeds the cellular requirement for protein and nucleotide biosynthesis. A consequence of this Myc-dependent glutaminolysis is the reprogramming of mitochondrial metabolism to depend on glutamine catabolism to sustain cellular viability and TCA cycle anapleurosis. The ability of Myc-expressing cells to engage in glutaminolysis does not depend on concomitant activation of PI3K or AKT. The stimulation of mitochondrial glutamine metabolism resulted in reduced glucose carbon entering the TCA cycle and a decreased contribution of glucose to the mitochondrial-dependent synthesis of phospholipids. These data suggest that oncogenic levels of Myc induce a transcriptional program that promotes glutaminolysis and triggers cellular addiction to glutamine as a bioenergetic substrate.

The c-myc oncogene is among the most commonly overexpressed genes in human cancer. c-myc encodes a basic helix-loop-helix/leucine zipper (bHLH/LZ) transcription factor (c-MYC) that activates a cascade of downstream targets that ultimately mediate cellular transformation. Although a large number of genes are regulated by c-MYC, only a few have been functionally linked to c-MYC-mediated transformation. By expression profiling, the metastasis-associated protein 1 (MTA1) gene was identified here as a target of the c-MYC oncoprotein in primary human cells, a result confirmed in human cancer cells. MTA1 itself has been previously implicated in cellular transformation, in part through its ability to regulate the epithelial-to-mesenchymal transition and metastasis. MTA1 is a component of the Mi-2/nucleosome remodeling and deacetylating (NURD) complex that contains both histone deacetylase and nucleosome remodeling activity. The data reported here demonstrate that endogenous c-MYC binds to the genomic MTA1 locus and recruits transcriptional coactivators. Most importantly, short hairpin RNA (shRNA)-mediated knockdown of MTA1 blocks the ability of c-MYC to transform mammalian cells. These data implicate MTA1 and the Mi-2/NURD complex as one of the first downstream targets of c-MYC function that are essential for the transformation potential of c-MYC.

// Amanda R. Oran 1 , Clare M. Adams 1 , Xiao-yong Zhang 1 , Victoria J. Gennaro 1 , Harla K. Pfeiffer 1 , Hestia S. Mellert 2 , Hans E. Seidel 3 , Kirsten Mascioli 1 , Jordan Kaplan 1 , Mahmoud R. Gaballa 1 , Chen Shen 4,5 , Isidore Rigoutsos 1 , Michael P. King 6 , Justin L. Cotney 7 , Jamie J. Arnold 8 , Suresh D. Sharma 8 , Ubaldo E. Martinez-Outschoorn 1 , Christopher R. Vakoc 4 , Lewis A. Chodosh 3 , James E. Thompson 9 , James E. Bradner 10 , Craig E. Cameron 8 , Gerald S. Shadel 11,12 , Christine M. Eischen 1 and Steven B. McMahon 1 1 Department of Cancer Biology, Thomas Jefferson University, Philadelphia, PA, USA 2 Biomedical Graduate Studies, University of Pennsylvania, Philadelphia, PA, USA 3 Department of Cancer Biology and Abramson Family Cancer Research Institute, University of Pennsylvania School of Medicine, Philadelphia, PA, USA 4 Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, USA 5 Molecular and Cellular Biology Program, Stony Brook University, Stony Brook, NY, USA 6 Department of Biochemistry, Thomas Jefferson University, Philadelphia, PA, USA 7 Genetics and Genome Sciences, University of Connecticut Health, Farmington, CT, USA 8 Department of Biochemistry & Molecular Biology, The Pennsylvania State University, University Park, PA, USA 9 Leukemia Service, Department of Medicine, Roswell Park Cancer Institute, Buffalo, NY, USA 10 Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA,USA 11 Department of Pathology, Yale School of Medicine, New Haven, CT, USA 12 Department of Genetics, Yale School of Medicine, New Haven, CT, USA Correspondence to: Steven B. McMahon, email: // Keywords : MYC, mitochondria, mitochondrial gene expression, tigecycline, synthetic lethality Received : June 08, 2016 Accepted : August 25, 2016 Published : August 31, 2016 Abstract Despite ubiquitous activation in human cancer, essential downstream effector pathways of the MYC transcription factor have been difficult to define and target. Using a structure/function-based approach, we identified the mitochondrial RNA polymerase (POLRMT) locus as a critical downstream target of MYC. The multifunctional POLRMT enzyme controls mitochondrial gene expression, a process required both for mitochondrial function and mitochondrial biogenesis. We further demonstrate that inhibition of this newly defined MYC effector pathway causes robust and selective tumor cell apoptosis, via an acute, checkpoint-like mechanism linked to aberrant electron transport chain complex assembly and mitochondrial reactive oxygen species (ROS) production. Fortuitously, MYC-dependent tumor cell death can be induced by inhibiting the mitochondrial gene expression pathway using a variety of strategies, including treatment with FDA-approved antibiotics. In vivo studies using a mouse model of Burkitt’s Lymphoma provide pre-clinical evidence that these antibiotics can successfully block progression of MYC-dependent tumors.