Asparagine promotes cancer cell proliferation through use as an amino acid exchange factor

Abstract

Cellular amino acid uptake is critical for mTOR complex 1 (mTORC1) activation and cell proliferation. However, the regulation of amino acid uptake is not well-understood. Here we describe a role for asparagine as an amino acid exchange factor: intracellular asparagine exchanges with extracellular amino acids. Through asparagine synthetase knockdown and altering of media asparagine concentrations, we show that intracellular asparagine levels regulate uptake of amino acids, especially serine, arginine and histidine. Through its exchange factor role, asparagine regulates mTORC1 activity and protein synthesis. In addition, we show that asparagine regulation of serine uptake influences serine metabolism and nucleotide synthesis, suggesting that asparagine is involved in coordinating protein and nucleotide synthesis. Finally, we show that maintenance of intracellular asparagine levels is critical for cancer cell growth. Collectively, our results indicate that asparagine is an important regulator of cancer cell amino acid homeostasis, anabolic metabolism and proliferation.

ATF4-Induced Metabolic Reprograming Is a Synthetic Vulnerability of the p62-Deficient Tumor Stroma

“…Because the activation of autophagy results in p62 degradation (Moscat and Diaz-Meco, 2011; Moscat et al, 2016), we can speculate that in a nutrient-stressed tumor microenvironment, stromal cells activate autophagy to generate Ala, and simultaneously downregulate p62 to promote the metabolic reprogramming necessary to generate Asn by upregulating ATF4. The generation of Asn and their utilization by cancer cells have attracted recent interest in the cancer metabolism field (Krall et al, 2016; Ye et al, 2010; Zhang et al, 2014), and our data further support its relevance in cancer. Whereas our results indicate that Asn provides the nitrogen necessary for cells to grow under Gln-deficient conditions, other roles equally important can also be envisioned.…”

“…However, label incorporation was similar, or less than that from [ 15 N]NH 4 + (Figure 6N). Since overall biosynthesis (Figure 6M) was not increased by ammonium supplementation, these data suggest that Asn availability generally enhances tumor cell growth through signaling (Krall et al, 2016; Zhang et al, 2014), and also by limiting the need for Gln to be diverted to Asn production rather than directly providing nitrogen. Altogether, these data support a model whereby p62-deficient stroma reprograms its metabolism under Gln scarce conditions to provide Asn to support epithelial growth in an ATF4-dependent mechanism (Figure 6O).…”

“…In fact, addition of Asn to sgC stromal cells co-cultured with PC3 cells in low Gln conditions was able to mimic the response of sgp62 cells (Figures 6K and 6L). These are important observations because Asn has been shown to be critical for the survival and growth of cancer cells in several settings (Krall et al, 2016; Zhang et al, 2014). Moreover, they established that stromal cells can produce the Asn necessary to withstand Gln deprivation in the tumor microenvironment and sustain epithelial cancer cell growth under nutrient challenging conditions.…”

“…Whereas our results indicate that Asn provides the nitrogen necessary for cells to grow under Gln-deficient conditions, other roles equally important can also be envisioned. This might include the ability of Asn to maintain mTORC1 activation through its actions as an exchange factor to promote the uptake of amino acids (Krall et al, 2016), or its ability to prevent Chop-driven cell death upon the accumulation of ATF4, its upstream regulator (Zhang et al, 2014). …”

SHMT2 Desuccinylation by SIRT5 Drives Cancer Cell Proliferation

“…Furthermore, we found that the function of SIRT5 on regulating nonessential amino acid metabolism was not universal. Although asparagine can promote tumor cell growth (40) and aspartate is the material for de novo asparagine synthesis, SIRT5 KO cells showed the same pattern on metabolic index change and cell growth rate change as SIRT5 WT cells under aspartate/asparagine starvation ( Supplementary Fig. S2G-S2J), indicating the specificity of the involvement of SIRT5 on serine/glycine metabolism.…”