Defense Date

2013

Document Type

Thesis

Degree Name

Master of Science

Department

Biochemistry

First Advisor

Xianjun Fang

Abstract

Lysophosphatidic acid (LPA), a naturally-occurring, simple phospholipid, is present at elevated levels in the blood and ascites of ovarian cancer patients. LPA is a ligand of seven cell surface G protein-coupled receptors. It has been known as an oncogenic growth factor in ovarian cancer and other types of human malignancies. However, the precise biological functions of LPA in ovarian oncogenesis remain to be fully elucidated. Our laboratory is interested in studying the potential role of LPA, as a tumor microenvironment factor, in regulation of cancer cell metabolism. A fundamental change associated with most cancer is the switch of glucose metabolism from mitochondrial oxidative phosphorylation to aerobic glycolysis, a phenomenon described by Otto Warburg nearly a century ago. This seems to be necessary to meet bioenergetic and biosynthetic demands of rapidly dividing tumor cells. However, the mechanism underlying the switch from aerobic respiration to aerobic glycolysis in cancer cells remains poorly understood. In this thesis project, my goal was to explore the effect of LPA on glycolysis and to compare LPA with other important growth factors in their capability to promote the glycolytic pathway in ovarian cancer cells. We demonstrated that LPA stimulated aerobic glycolysis as well as cell proliferation in ovarian cancer cell lines. The two parallel responses were LPA dose dependent. To determine whether LPA is unique in driving glycolysis, we compared the effect of LPA with other growth factors, including EGF, insulin and IGF-1 which are all involved in pathogenesis of ovarian cancer. While doses of these growth factors could be adjusted to achieve similar levels of cell proliferation, LPA and EGF were much more potent than insulin and IGF-1 in stimulation of glycolytic flux and lactate production. Therefore, we identified LPA and EGF as highly glycolytic factors relevant to the development and maintenance of the glycolytic phenotype of ovarian cancer cells. The next part of my study was focused on the molecular mechanism for the differential effects of LPA, EGF, insulin and IGF-1 on glycolytic metabolism. We used the glucose metabolism RT-PCR array to profile expression of glycolytic genes. The most remarkable change induced by LPA and EGF was the robust induction of hexokinase 2 (HK2) that stimulates irreversible entry of glucose to the glycolytic pathway. However, insulin and IGF-1 only weakly induced HK2 expression. Further experimental evidence using HK2 inhibitors indicated that HK2 up-regulation was the critical mediator of LPA-induced glycolysis. Further, the cells grown in LPA and EGF-stimulated conditions appear to show larger volume compared to insulin and IGF-1-treated cells, consistent with the hypothesis that active glycolysis contributes to biosynthetic processes to maintain cell sizes. Taken together, these findings of the current study revealed high glycolytic effects of LPA and EGF in ovarian cancer and the underlying HK2-mediated mechanism that distinguishes LPA and EGF from other growth factors such as insulin and IGF-1.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

May 2013

Available for download on Wednesday, May 09, 2018

Share

COinS