Metabolic orchestration driven by GGCT: diverting glutamine to glutathione biosynthesis while enhancing glucose...

Glutamine (Gln) metabolism serves dual metabolic roles: it fuels the tricarboxylic acid (TCA) cycle, while concurrently sustaining redox balance through glutathione (GSH) synthesis. γ-Glutamylcyclotransferase (GGCT), a key metabolic enzyme frequently overexpressed in various cancers, has an undefined role in directing glutamine metabolic flux during tumorigenesis. This study demonstrated that glutamine promotes cancer cell growth by regulating GSH and reactive oxygen species (ROS) levels, with this process being closely associated with GGCT expression. Knockdown of GGCT significantly inhibited tumor growth, depleted GSH, and elevated ROS levels, whereas overexpression of GGCT exerted the opposite effects. Furthermore, we refined and established the Gln/c-Myc/miR-29b-3p/GGCT regulatory axis. Notably, GGCT knockdown markedly altered mitochondrial morphology and impaired oxidative phosphorylation and glycolysis capacity. Targeted metabolomics analysis revealed that GGCT knockdown significantly reduced the abundance of TCA cycle intermediates, while GGCT overexpression substantially increased their levels. [U-¹³C]glutamine isotope tracing experiments showed that GGCT overexpression reduced Gln contribution to the TCA cycle and diverted it preferentially to the GSH synthesis pathway for ROS regulation. In contrast, [U-¹³C]glucose isotope tracing results demonstrated a significant increase in TCA cycle intermediates derived from glucose when GGCT was overexpressed. Additional, supplementation of sodium pyruvate and JX06 in GGCT-knockdown cells confirmed that this regulatory effect of GGCT-mediated changes in ROS was independent of energy metabolism pathways. Collectively, this study identifies GGCT as a metabolic switch that diverts Gln flux toward GSH synthesis to maintain redox homeostasis, while enhancing glucose-fueled anaplerosis into the TCA cycle to sustain cell proliferation. These findings highlight GGCT as a potential therapeutic target for disrupting cancer redox adaptation and metabolic plasticity.