Metabolic regulation of mammalian cell growth and proliferation

Abstract

Proliferation requires that cells acquire sufficient biomass to produce two daughter cells. To accomplish this, cells must utilize available nutrients to generate new components of cell mass, including proteins, lipids, and nucleic acids. In addition, cells must coordinate biosynthesis and production of specific macromolecules with the events that enable cell cycle progression. A cell’s ability to fulfill these anabolic requirements is impacted by environmental factors that influence how the metabolic network is used. This dissertation examines how cells regulate their biosynthesis to enable coordinated growth and division, and how metabolic dependencies impact proliferation. We first investigated why cells that genetically upregulate serine synthesis still rely on consuming large amounts of serine from the environment. We found that serine synthesis is constrained by availability of the oxidizing cofactor NAD+, and that decreased production of purine nucleotides downstream of serine limits proliferation. These findings demonstrate that regeneration of NAD+ can be a limitation for serine and nucleotide synthesis that constrains proliferation. We next determined how cells respond to perturbations to relative levels of nucleotide species. We found that imbalanced nucleotides inhibit cell proliferation, but do not constrain cell growth, allowing cells to grow excessively large. Instead, nucleotide imbalance is not sensed until cells enter S phase, when the replication stress response becomes critical for cell survival. Moreover, we found that replication stress sensing promotes nucleotide availability during normal S phases, suggesting that proliferating cells enter S phase without sensing whether they have sufficient nucleotides. Together, these studies contribute new insights into how metabolism is regulated to support cell growth and division.