Dissertations, Theses, and Capstone Projects

Date of Degree

9-2018

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biochemistry

Advisor

David Foster

Committee Members

Jill Bargonetti

Diego Loayza

Richard Possemato

Steven Gross

Subject Categories

Biochemistry | Cancer Biology

Keywords

mTORC1, Phospholipase D (PLD), Phosphatidic acid (PA), Rag GTPase, Arf1, Rheb, RalA, alpha-ketoglutarate

Abstract

Glutamine, the conditionally essential amino acid and most abundant amino acid in human sera, is a key nutrient required for sustaining cell proliferation. Glutamine is essential for nucleotide, protein, and lipid synthesis, all of which are essential for cell proliferation. The mammalian target of rapamycin complex 1 (mTORC1) is a highly conserved protein complex that acts as a sensor of nutrients, relaying signals for the shift from catabolic to anabolic metabolism. While glutamine plays an important role in activating mTORC1, the mechanism is not completely clear. Here we describe a Rag-independent mechanism of mTORC1 activation by glutamine that is dependent on phospholipase D (PLD). PLD catalyzes the hydrolysis of phosphatidylcholine to generate phosphatidic acid (PA) – a metabolite required for the stability and activity of both mTORC1 and mTORC2. Suppressing the production of PA by PLD blocked mTORC1 activation by glutamine. It has been reported that glutamine stimulates mTORC1 through an amino acid transporter that exchanges glutamine for leucine. However, our data suggests that glutamine can stimulate PLD and mTORC1 independently of leucine, in an ADP-ribosylation factor 1 (Arf1), RalA, and Rheb-dependent manner. α-ketoglutarate, a downstream metabolite of glutamine, was able to rescue mTORC1 activation following glutamine deprivation and also required Arf1 and PLD, but not Rag GTPases. Collectively, our data describe a novel mechanism by which glutamine stimulates mTORC1 in a PLD-PA-dependent manner. This pathway runs parallel to the leucine-dependent, Rag-GTPase pathway for mTORC1 activation and likely represents a compensatory mechanism for glutamine to activate mTORC1 in the absence of leucine.

Download

Share

COinS