Pharmacologic or Genetic Targeting of Glutamine Synthetase Skews Macrophages toward an M1-like Phenotype and Inhibits Tumor Metastasis

Publication date: 15 August 2017
Source:Cell Reports, Volume 20, Issue 7
Author(s): Erika M. Palmieri, Alessio Menga, Rosa Martín-Pérez, Annamaria Quinto, Carla Riera-Domingo, Giacoma De Tullio, Douglas C. Hooper, Wouter H. Lamers, Bart Ghesquière, Daniel W. McVicar, Attilio Guarini, Massimiliano Mazzone, Alessandra Castegna
Glutamine-synthetase (GS), the glutamine-synthesizing enzyme from glutamate, controls important events, including the release of inflammatory mediators, mammalian target of rapamycin (mTOR) activation, and autophagy. However, its role in macrophages remains elusive. We report that pharmacologic inhibition of GS skews M2-polarized macrophages toward the M1-like phenotype, characterized by reduced intracellular glutamine and increased succinate with enhanced glucose flux through glycolysis, which could be partly related to HIF1α activation. As a result of these metabolic changes and HIF1α accumulation, GS-inhibited macrophages display an increased capacity to induce T cell recruitment, reduced T cell suppressive potential, and an impaired ability to foster endothelial cell branching or cancer cell motility. Genetic deletion of macrophagic GS in tumor-bearing mice promotes tumor vessel pruning, vascular normalization, accumulation of cytotoxic T cells, and metastasis inhibition. These data identify GS activity as mediator of the proangiogenic, immunosuppressive, and pro-metastatic function of M2-like macrophages and highlight the possibility of targeting this enzyme in the treatment of cancer metastasis.

Graphical abstract

Teaser

Palmieri et al. show that inhibiting glutamine synthetase activity in M2 macrophages skews their polarization toward an HIF1α-mediated M1 state, which impairs cytotoxic T cell recruitment and angiogenesis. As a consequence of a more pronounced immunostimulatory and antiangiogenic effect, GS ablation in macrophages translates into prevention of metastasis.


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