Molecular mechanism of glutaminase activation through filamentation and the role of filaments in mitophagy protection

TGFB signaling induces mitophagy via PLSCR3-mediated cardiolipin externalization in conjunction with a BNIP3L/NIX-, BNIP3-, and FUNDC1-dependent mechanism

Selective clearance of damaged mitochondria through mitophagy is crucial for the maintenance of mitochondrial homeostasis. While mitophagy can be activated by various mitochondrial toxins, the physiologically relevant signal that triggers mitophagy is less studied. TGFB/TGFβ signaling has been linked to autophagic induction, but its specific role in mitophagy is not well understood. Here, we discovered a novel mitophagy induction paradigm stimulated by TGFB1. The mitophagic response is exclusively mediated by SMAD2, SMAD3, and SMAD4 underlying the TGFB receptor signaling. The transcriptional regulation activates genes involved in the canonical autophagic pathway which is required for the TGFB1-induced mitophagy. Moreover, TGFB1 signaling promotes mitophagic flux by upregulating PLSCR3 that externalizes cardiolipin in conjunction with the MAP1LC3/LC3/GABARAPs-interacting receptor proteins (BNIP3L/NIX, BNIP3, and FUNDC1)-dependent mechanism. Overall, our study characterized the essential components engaged in the TGFB1-induced mitophagy and demonstrated that TGFB is an important signal that induces mitophagy.Abbreviations ATG5: autophagy related 5; ATG8: mammalian homolog of yeast Atg8; ATG9A: autophagy related 9A; ATG13: autophagy related 13; ATG101: autophagy related 101; BNIP3: BCL2 interacting protein 3; BNIP3L/NIX: BCL2 interacting protein 3 like; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; Cardiolipin: 1,3-bis(sn-3'-phosphatidyl)-sn-glycerol; CERS1: ceramide synthase 1; FUNDC1: FUN14 domain containing 1; GABARAP: GABA type A receptor-associated protein; GABARAPL1: GABA type A receptor-associated protein like 1; GABARAPL2: GABA type A receptor-associated protein like 2; GLS: glutaminase; KO: knockout; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MitoIP: mitochondrial immunoprecipitation; MMP: mitochondrial membrane potential; NRBF2: nuclear receptor binding factor 2; OPTN: optineurin; PINK1: PTEN induced kinase 1; PLSCR3: phospholipid scramblase 3; PRKN: parkin RBR E3 ubiquitin protein ligase; RB1CC1/FIP200: RB1 inducible coiled-coil 1; TGFB/TGFβ: transforming growth factor beta; ULK1: unc-51 like autophagy activating kinase 1.

HIF2α inhibits glutaminase clustering in mitochondria to sustain growth of clear cell Renal Cell Carcinoma

Clear cell renal cell carcinomas (ccRCC) are largely driven by HIF2α and are avid consumers of glutamine. However, inhibitors of glutaminase1 (GLS1), the first step in glutaminolysis, have not shown benefit in phase III trials, and HIF2α inhibition, recently FDA-approved for treatment of ccRCC, shows great but incomplete benefits, underscoring the need to better understand the roles of glutamine and HIF2α in ccRCC. Here, we report that glutamine deprivation rapidly redistributes GLS1 into isolated clusters within mitochondria across diverse cell types, but not in ccRCC. GLS1 clustering is rapid (1-3 hours) and reversible, is specifically driven by reduced intracellular glutamate, and is mediated by mitochondrial fission. Clustered GLS1 markedly enhances glutaminase activity and promotes cell death under glutamine-deprived conditions. HIF2α prevents GLS1 clustering, independently of its transcriptional activity, thereby protecting ccRCC cells from cell death induced by glutamine deprivation. Reversing this protection, by genetic expression of GLS1 mutants that constitutively cluster, enhances ccRCC cell death in culture and suppresses ccRCC growth in vivo. These findings provide multiple insights into cellular glutamine handling, including a novel metabolic pathway by which HIF2α promotes ccRCC, and reveals a potential therapeutic avenue to synergize with HIF2α inhibition in the treatment of ccRCC.

Protein aggregation in health and disease: A looking glass of two faces

Protein molecules organize into an intricate alphabet of twenty amino acids and five architecture levels. The jargon "one structure, one functionality" has been challenged, considering the amount of intrinsically disordered proteins in the human genome and the requirements of hierarchical hetero- and homo-protein complexes in cell signaling. The assembly of large protein structures in health and disease is now viewed through the lens of phase separation and transition phenomena. What drives protein misfolding and aggregation? Or, more fundamentally, what hinders proteins from maintaining their native conformations, pushing them toward aggregation? Here, we explore the principles of protein folding, phase separation, and aggregation, which hinge on crucial events such as the reorganization of solvents, the chemical properties of amino acids, and their interactions with the environment. We focus on the dynamic shifts between functional and dysfunctional states of proteins and the conditions that promote protein misfolding, often leading to disease. By exploring these processes, we highlight potential therapeutic avenues to manage protein aggregation and reduce its harmful impacts on health.

ω-Amidase and Its Substrate α-Ketoglutaramate (the α-Keto Acid Analogue of Glutamine) as Biomarkers in Health and Disease

A large literature exists on the biochemistry, chemistry, metabolism, and clinical importance of the α-keto acid analogues of many amino acids. However, although glutamine is the most abundant amino acid in human tissues, and transamination of glutamine to its α-keto acid analogue (α-ketoglutaramate; KGM) was described more than seventy years ago, little information is available on the biological importance of KGM. Herein, we summarize the metabolic importance of KGM as an intermediate in the glutamine transaminase - ω-amidase (GTωA) pathway for the conversion of glutamine to anaplerotic α-ketoglutarate. We describe some properties of KGM, notably its occurrence as a lactam (2-hydroxy-5-oxoproline; 99.7% at pH 7.2), and its presence in normal tissues and body fluids. We note that the concentration of KGM is elevated in the cerebrospinal fluid of liver disease patients and that the urinary KGM/creatinine ratio is elevated in patients with an inborn error of the urea cycle and in patients with citrin deficiency. Recently, of the 607 urinary metabolites measured in a kidney disease study, KGM was noted to be one of five metabolites that was most significantly associated with uromodulin (a potential biomarker for tubular functional mass). Finally, we note that KGM is an intermediate in the breakdown of nicotine in certain organisms and is an important factor in nitrogen homeostasis in some microorganisms and plants. In conclusion, we suggest that biochemists and clinicians should consider KGM as (i) a key intermediate in nitrogen metabolism in all branches of life, and (ii) a biomarker, along with ω-amidase, in several diseases.

Identifying protein conformational states in the Protein Data Bank: Toward unlocking the potential of integrative dynamics studies

Studying protein dynamics and conformational heterogeneity is crucial for understanding biomolecular systems and treating disease. Despite the deposition of over 215 000 macromolecular structures in the Protein Data Bank and the advent of AI-based structure prediction tools such as AlphaFold2, RoseTTAFold, and ESMFold, static representations are typically produced, which fail to fully capture macromolecular motion. Here, we discuss the importance of integrating experimental structures with computational clustering to explore the conformational landscapes that manifest protein function. We describe the method developed by the Protein Data Bank in Europe - Knowledge Base to identify distinct conformational states, demonstrate the resource's primary use cases, through examples, and discuss the need for further efforts to annotate protein conformations with functional information. Such initiatives will be crucial in unlocking the potential of protein dynamics data, expediting drug discovery research, and deepening our understanding of macromolecular mechanisms.