Abstract
5-Aminoimidazole-4-carboxamide ribonucleotide (known as ZMP) is a metabolite produced in de novo purine biosynthesis and histidine biosynthesis, but only utilized in the cell by a homodimeric bifunctional enzyme (called ATIC) that catalyzes the last two steps of de novo purine biosynthesis. ZMP is known to act as an allosteric activator of the cellular energy sensor adenosine monophosphate-activated protein kinase (AMPK), when exogenously administered as the corresponding cell-permeable ribonucleoside. Here, we demonstrate that endogenous ZMP, produced by the aforementioned metabolic pathways, is also capable of activating AMPK. Using an inhibitor of ATIC homodimerization to block the ninth step of de novo purine biosynthesis, we demonstrate that the subsequent increase in endogenous ZMP activates AMPK and its downstream signaling pathways. We go on to illustrate the viability of using this approach to AMPK activation as a therapeutic strategy with an in vivo mouse model for metabolic disorders.
Highlights
AMP-activated protein kinase (AMPK) is the master regulator of cellular energy homeostasis, monitoring and responding to changes in the intracellular AMP/ATP ratio
Homodimerization of aminoimidazole carboxamide ribonucleotide transformylase/inosine monophosphate cyclohydrolase (ATIC) is essential for its aminoimidazole carboxamide ribonucleotide transformylase (AICART) activity, as the active site of this enzyme is formed at the interface of two interacting ATIC monomers, with each molecule contributing residues (Greasley et al, 2001)
Inhibition of ATIC Homodimerization with Cpd14 Up-regulates Intracellular ZMP, and Leads to AMPK Activation We began by measuring changes in the intracellular ZMP levels in MCF-7 cells treated with 250 mM Cpd14; the dose was chosen based on our previously reported effects of this compound on the viability of MCF-7 cells (Spurr et al, 2012)
Summary
Asby et al report a new approach to AMPK activation. Using an inhibitor of AICAR transformylase homodimerization, the ninth step of de novo purine biosynthesis is blocked, causing a rise in endogenous ZMP, which activates AMPK and its downstream effectors. Highlights d AICAR transformylase is targeted in cells with an ATIC homodimerization inhibitor d The resulting increase in endogenous ZMP is sufficient to activate AMPK d Downstream AMPK signaling is activated, significantly altering cell metabolism d A mouse model of metabolic syndrome is used to show therapeutic viability.
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