LOSS OF MITOCHONDRIAL PYRUVATE CARRIER ACTIVITY SHORT CIRCUITS HEPATOCELLULAR TUMORIGENESIS
Authors: Taylor Eric 
Published: June 2021

Hepatocellular carcinoma (HCC) is a prevalent, challenging to treat, and highly lethal cancer. The incidence of HCC resulting from obesity and accompanying metabolic and inflammatory liver injury is increasing dramatically. Thus, there is an urgent need to understand how metabolism influences HCC progression and initiation. HCCs exhibit a profound difference in metabolism compared to normal hepatocytes, the loss of gluconeogenic capacity. The Mitochondrial Pyruvate Carrier (MPC) gates gluconeogenesis by importing pyruvate into the mitochondrial matrix. Yet, data from the cancer genome atlas indicate that across numerous cancers, MPC transcript expression is greatest in HCC. We hypothesized that MPC function is repurposed in HCC to support tumor metabolism. To model the genetic heterogeneity of human HCCs, we employed a mutagen plus injury mouse model of HCC tumorigenesis. WT and MPC liver‐specific knockout mice (LivKO) were injected with a priming dose of N‐nitrosodiethylamine at age 15 days and then twice weekly with low dose carbon tetrachloride from age 8 to 22 weeks. Upon euthanasia at age 23 weeks tumor number was markedly decreased in MPC LivKO vs WT mice. We compared tumors and adjacent normal tissue by RNAseq and observed systematic differences in transcripts for glutathione metabolism between WT and MPC LivKO tumors. Biochemical tests for glutathione content and redox state revealed that WT but not MPC LivKO tumors significantly increased total glutathione content relative to adjacent normal tissue. Furthermore, relative reduced vs oxidized glutathione content was greater in WT vs MPC LivKO tumors. In cultured mouse hepatoma Hepa1–6 cells, simultaneously impairing glutathione synthesis and disrupting MPC activity synthetically decreased proliferation. Synthetic lethality was rescued by N‐acetylcysteine supplementation, consistent with protection from ROS. Furthermore, real‐time measurements of glutathione chemical conjugation in Hepa1–6 cells showed that acute inhibition of MPC activity decreased resistance to glutathione depletion. In primary mouse hepatocytes, MPC disruption impaired utilization of glutamine to regenerate glutathione content during acute chemical depletion. MPC disruption also increased primary hepatocyte loss of viability with tert‐butyl‐peroxide treatment. We propose that HCCs utilize mitochondrial pyruvate import to sustain essential TCA‐cycle activity, thereby sparing glutamine for glutathione synthesis. By this model, MPC disruption results in adaptive mitochondrial glutamine utilization, decrease glutathione synthetic capacity, and increased vulnerability to ROS, thereby impairing HCC initiation and progression. Thus, disrupting MPC activity breaks a metabolic circuit that may be common in HCCs and amenable to therapeutic targeting.

Support or Funding Information

NIH R01 DK104998, University of Iowa Carver College of Medicine and Holden Comprehensive Cancer Center

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.