Tyrosine phosphorylation of ACLY regulates lipid metabolism and oncogenesis in ALK positive Anaplastic Large Cell Lymphoma

Abstract

A fundamental requirement for growth of rapidly proliferating cells is metabolic adaptation to promote synthesis of biomass1. ATP citrate lyase (ACLY) is a critical enzyme responsible for synthesis of cytosolic acetyl-CoA, the key building component for de novo fatty acid synthesis and links vital pathways such as carbohydrate and lipid metabolism2. The mechanisms of ACLY regulation are not completely understood and the regulation of ACLY function by tyrosine phosphorylation is unknown. Here we show using mass-spectrometry-driven phosphoproteomics and metabolomics that ACLY is phosphorylated and functionally regulated at an evolutionary conserved residue, Y682. Physiologic signals promoting rapid cell growth such as epidermal growth factor stimulation in epithelial cells and T-cell receptor activation in primary human T-cells result in rapid phosphorylation of ACLY at Y682. In vitro kinase assays demonstrate that Y682 is directly phosphorylated by multiple tyrosine kinases, including ALK, ROS1, SRC, JAK2 and LTK. Oncogenically activating structural alterations such as gene-fusions, amplification or point mutations of ALK tyrosine kinase result in constitutive phosphorylation of ACLY in diverse forms of primary human cancer such as lung cancer, anaplastic large cell lymphoma (ALCL) and neuroblastoma. Expression of a phosphorylation-defective ACLY-Y682F mutant in NPM-ALK+ ALCL decreases ACLY activity and attenuates lipid synthesis. Metabolomic analyses reveal that ACLY-Y682F expression results in increased {beta}-oxidation of 13C-oleic acid-labeled fatty acid with increased labeling of +2-citrate (p<0.01) and +18-oleyol carnitine (p<0.001). Similarly, oxygen consumption rate (OCR) is significantly increased in cells expressing ACLY-Y682F (p<0.001). Moreover, expression of ACLY-Y682F dramatically decreases cell proliferation, impairs clonogenicity and abrogates tumor growth in vivo. Our results reveal a novel mechanism for direct ACLY regulation that is subverted by multiple oncogenically-activated tyrosine kinases in diverse human cancers. These findings have significant implications for novel therapies targeting ACLY in cancer and metabolism.