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(PGC1��) and Estrogen-Related Receptor α (ERR��) are overexpressed and contribute to tumor growth. Previous studies have shown that PGC1�� and ERR�� regulate many metabolic processes by controlling vital gene expression. Here, we show that PGC1�� and ERR�� 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 PGC1�� and ERR��protein 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 PGC1�� depletion were at optimal polarity compared to the control cells, but not with Nrf2 knockdown, suggesting PGC1�� can function independently of its regulation by Nrf2. These data led to the investigation of downstream effectors of PGC1�� and ERR�� 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 PGC1�� and ERR�� 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 PGC1�� and ERR��-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 PGC1�� signaling axis is a vital hub of redox and metabolic regulation to enhance cancer cell health, which is not present in normal cells.

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