Graduation Date

Fall 12-18-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Cancer Research

First Advisor

Robert E Lewis

Abstract

Metabolic alterations are a hallmark of cancer and the mechanism by which these adaptations sustain cancer cell growth are complex and dependent on tissue type. In colon cancer, Peroxisome Proliferator Activated Receptor γ Coactivator 1 β(PGC1𝛽) and Estrogen-Related Receptor α (ERR𝛼) are overexpressed and contribute to tumor growth. Previous studies have shown that PGC1𝛽 and ERR𝛼 regulate many metabolic processes by controlling vital gene expression. Here, we show that PGC1𝛽 and ERR𝛼 drive oxidative phosphorylation and glycolysis in colon cancer cell lines and we evaluated downstream effectors and processes.

A dysfunction in the reductive and oxidative capacity of the cell often aligns with dysfunction in metabolism. Data presented here show that Nrf2, a transcription factor that activates antioxidant response genes, also regulates PGC1𝛽 and ERR𝛼protein expression. Similarly, we also showed K-Ras, a common oncogenic driver in colon cancer, as a regulator of Nrf2 protein expression. However, we determined that the mitochondria following PGC1𝛽 depletion were at optimal polarity compared to the control cells, but not with Nrf2 knockdown, suggesting PGC1𝛽 can function independently of its regulation by Nrf2. These data led to the investigation of downstream effectors of PGC1𝛽 and ERR𝛼 to understand the mechanism by which the metabolic alterations occur.

Our data further determined that mitochondrial phosphoenolpyruvate carboxykinase 2 (PCK2), an essential enzyme at the junction of the TCA cycle and glycolysis, is regulated by both PGC1𝛽 and ERR𝛼 expression. While depletion of PCK2 has a minimal effect on the metabolism and cell viability of immortalized, non-transformed human colon epithelial cells, PCK2 knockdown suppresses oxidative phosphorylation and glycolytic metabolism and decreases cell survival in human colon cancer cells. Elevated concentrations of glucose, but not glutamine, rescue the metabolic effect of PCK2 depletion. PCK2 depletion also leads to a significant buildup in TCA cycle intermediate oxaloacetate, significantly altering flux through malate dehydrogenase correlating with diminished glycolytic and oxidative phosphorylation processes. These findings suggest that the PGC1𝛽 and ERR𝛼-dependent regulation of PCK2 represents a molecular mechanism used by colon cancer cells to maximize metabolic processes and promote cancer growth and survival. Overall, the PGC1𝛽 signaling axis is a vital hub of redox and metabolic regulation to enhance cancer cell health, which is not present in normal cells.

Available for download on Tuesday, June 01, 2021

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