Loss of Rb1 Enhances Glycolytic Metabolism in Kras-Driven Lung Tumors In Vivo.

Lindsey R Conroy,Ramon C Sun,Stephanie Metcalf,Xinmin Yin,Xiang Zhang,Lyndsay E.A Young,Liqing He,Brian F Clem,Susan Dougherty,Sengodagounder Arumugam,Pawel Lorkiewicz,Traci Kruer

doi:10.3390/cancers12010237

Lindsey R Conroy, Ramon C Sun + Show 10 more

Open Access

https://doi.org/10.3390/cancers12010237

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Abstract

Dysregulated metabolism is a hallmark of cancer cells and is driven in part by specific genetic alterations in various oncogenes or tumor suppressors. The retinoblastoma protein (pRb) is a tumor suppressor that canonically regulates cell cycle progression; however, recent studies have highlighted a functional role for pRb in controlling cellular metabolism. Here, we report that loss of the gene encoding pRb (Rb1) in a transgenic mutant Kras-driven model of lung cancer results in metabolic reprogramming. Our tracer studies using bolus dosing of [U-13C]-glucose revealed an increase in glucose carbon incorporation into select glycolytic intermediates. Consistent with this result, Rb1-depleted tumors exhibited increased expression of key glycolytic enzymes. Interestingly, loss of Rb1 did not alter mitochondrial pyruvate oxidation compared to lung tumors with intact Rb1. Additional tracer studies using [U-13C,15N]-glutamine and [U-13C]-lactate demonstrated that loss of Rb1 did not alter glutaminolysis or utilization of circulating lactate within the tricarboxylic acid cycle (TCA) in vivo. Taken together, these data suggest that the loss of Rb1 promotes a glycolytic phenotype, while not altering pyruvate oxidative metabolism or glutamine anaplerosis in Kras-driven lung tumors.

Highlights

Lung cancer is the leading cause of cancer-related deaths for both men and women worldwide, with the 5-year survival rate being less than 18% [1]
We have utilized a combination of steady-state and stable isotope-labeled metabolomics to assess global changes in metabolism resulting from pRb dysfunction in Kras-driven lung tumors in vivo (Figure 1A)
We found that loss of Rb1 qualitatively increased glucose transporter 1 (Glut1), hexokinase 2 (Hk2), and pyruvate kinase M2 (Pkm2) in Kras-driven lung tumors compared to those with intact Rb1 and normal lung tissue (Figure 4)

Summary

Introduction

Lung cancer is the leading cause of cancer-related deaths for both men and women worldwide, with the 5-year survival rate being less than 18% [1]. Cancers 2020, 12, 237 major driver of tumorigenesis, and aberrant expression of cell cycle proteins in the retinoblastoma protein–E2F factor (pRb–E2F) pathway has been found to play a key role in the pathogenesis of NSCLC [3,4]. PRb functions to regulate cell cycle progression by repressing the transcriptional activity of the E2F family of transcription factors, thereby inhibiting S-phase entry [5]. Advances in our understanding of pRb function have highlighted additional biochemical pathways under pRb regulation beyond cell cycle progression. Emerging evidence supports a direct role for pRb in regulating metabolic pathways, such as glycolysis, glutaminolysis, lipogenesis, mitochondrial oxidative phosphorylation, and reactive oxygen species metabolism [8,9,10,11]. Acute loss of Rb1 increases mitochondrial pyruvate oxidation in normal lung tissue; the metabolic effects of Rb1 loss during lung cancer development are largely unknown

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