Date of Degree

9-2015

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biology

Advisor(s)

David A. Foster

Committee Members

Derrick Brazill

Patricia Rockwell

John Blenis

Ming Li

Subject Categories

Biochemistry | Molecular Biology

Keywords

cancer biology

Abstract

Over the last decade, metabolic dysregulation in cancer cells has stimulated a significant amount of interest in basic research. It has been established that cancer cells increase glucose uptake and alter the fate of glycolytic and tricarboxylic acid (TCA) cycle intermediates for the synthesis of biological molecules to accommodate high rates of cellular growth and proliferation. Moreover, it is more prominent that some metabolic dysregulations are specific to particular oncogenes. Exploiting the dysregulated metabolic dependency of cancer cells with therapeutic means could represent a novel approach for clinical aspect.

To meet the need of increased anabolic metabolism cancer cells engage in significant induction in uptake of glutamine, conditionally essential amino acid along with glucose. We investigated the impact of glutamine deprivation on cancer cell cycle progression and report here that K-Ras driven cancer cells override a glutamine mediated G1 cell cycle checkpoint and arrest in S-phase of cell cycle. Moreover this differential sensitivity to glutamine in K-Ras mutant cancer cells can be exploited using phase specific cytotoxic drugs. We also show that interfering with anaplerotic utilization of glutamine sensitizes K-Ras driven cancer cells to the cytotoxic effects of cell cycle phase specific drugs. This study provides the rational for targeting metabolic deregulations in cancer cells.

Next we investigated the connection between the AMP activated protein kinase (AMPK) and phospholipase D (PLD). AMPK, cellular energy sensor, is dysregulated in most cancers whereas PLD is elevated in many cancers. PLD generated phosphatidic acid (PA) is a central metabolite of lipid biosynthesis and regulator of mTOR (mammalian/ mechanistic target of rapamycin) signaling node. Although negative impact of AMPK on mTOR has been reported previously little is known about the impact of mTOR on AMPK signaling. We have found that AMPK negatively regulates PLD activity in human cancer cells and in doing so it also suppresses the production of PLD generated PA, which positively regulates mTOR. We also show that PLD and PA suppresses AMPK in an mTOR dependent manner. This study suggests a negative feedback mechanism involving AMPK and PLD/mTOR signals in cancer cells.

To continue our study, we checked the effect of AMPK activator, AICAR (5-Aminoimidazole-4-Carboxamide-1-β-4Ribofuranoside) combined with mTORC1 inhibitor rapamycin on cell cycle progression. Rapamycin induces apoptosis in human cancer cells but in higher doses, which are not tolerable in the clinic. We report here that in presence of AICAR, rapamycin inhibits mTOR and induces apoptosis at clinically tolerable doses. We have demonstrated here that by inhibiting PLD activity, AICAR suppresses the production of PLD generated PA, which interacts with mTOR in a competitive manner with rapamycin. The reduced level of PA sensitizes mTORC2 complexes to rapamycin in tolerable doses leading to suppressed Akt-dependent survival signals and causes apoptosis. This study provides the evidence that tolerable doses of rapamycin in combination with AICAR induces apoptosis in human cancer cells which could be a viable therapeutic option in the clinical.

 
 

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