Purine homeostasis is essential for numerous cellular processes. Although purine metabolite accumulation occurs in various pathological and therapeutic contexts, the cellular consequences and underlying mechanisms remain poorly understood. In this study, we utilized gain-of-function mutations in phosphoribosylpyrophosphate synthetase 1 (PRPS1) as a model of intracellular purine accumulation and discovered that elevated purines—particularly deoxyguanosine (dG)—suppressed the mTORC1 signaling pathway. We identified elongation factor Tu (TUFM) as a novel regulator of RHEB by stabilizing its GTP/GDP binding. Accumulation of dG enhanced phosphorylation of RHEB at Ser130, triggering dissociation of both TUFM and guanine nucleotides from RHEB, thereby reducing RHEB activity and downstream mTORC1 signaling. Notably, similar suppression of mTORC1 and loss of TUFM binding were observed upon inhibition of xanthine dehydrogenase/oxidase, another condition associated with purine buildup. Together, these findings reveal a previously unrecognized regulatory crosstalk between purine metabolism and the mTORC1 pathway, mediated through the TUFM-RHEB axis.
Podocyte injury is a major determinant of glomerular diseases. Although considerable advances have been made in the understanding of the mechanisms that trigger podocyte injury, effective cell-specific therapies remain clinically unavailable. In particular, recent studies have revealed that podocyte adhesion dysfunction and aberrant migration are pivotal events in the pathogenesis of podocyte loss and injury. Therefore, identifying candidate pathways for therapeutic intervention in podocyte migration has significant clinical importance. Here, we found that diacylglycerol kinase epsilon (DGKE) expression level is reduced in kidney biopsies from patients with glomerular diseases, which correlates with estimated glomerular filtration rate (eGFR). Moreover, urinary migrasome levels, a marker of migration, were significantly elevated in patients and negatively correlated with DGKE levels. Podocyte-specific overexpression of DGKE attenuated podocyte injury and proteinuria in three independent mouse models, adriamycin (ADR)-, puromycin aminonucleoside (PAN)- and streptozotocin plus high-fat diet (STZ/HFD)-induced nephropathy. Mechanistically, DGKE regulates podocyte migration through the urokinase plasminogen activator receptor (uPAR)/β3 integrin axis and its downstream Rac1/Cdc42 signaling cascades. Collectively, our findings provide new insights into the pivotal role of DGKE in maintaining podocyte function and suggest that DGKE may represent a potential therapeutic target for treating patients with glomerular diseases.
Osteoclastogenesis requires precise coordination between mitochondrial bioenergetics and anabolic programs, yet the underlying mechanisms remain unclear. Here, we identify the mitochondrial citrate carrier (CIC, encoded by SLC25A1) as a crucial link that couples mitochondrial bioenergetics to glutathione (GSH)-dependent redox regulation during osteoclastogenesis. CIC expression was elevated in the osteoclast-lineage cells from postmenopausal osteoporosis (PMOP) patients and ovariectomized (OVX) mice, and was positively correlated with classical osteoclast markers. During osteoclastogenesis, CIC was progressively upregulated. Pharmacologic inhibition of CIC with CTPI-2 not only suppressed osteoclastogenesis but also disrupted core metabolic processes, including tricarboxylic acid cycle engagement, amino acid biosynthesis, and mitochondrial respiration. Integrative transcriptomic and metabolomic profiling further revealed a compensatory shift toward enhanced GSH synthesis. Mechanistically, CIC associated with the glutamate-cysteine ligase modifier subunit (GCLM), linking mitochondrial metabolic regulation to the GSH synthetic machinery. CIC inhibition increased GCL activity, intracellular GSH content, and the GSH/GSSG ratio, accompanied by reduced reactive oxygen species accumulation. The functional importance of the GSH axis was evident, as GCL inhibition by buthionine sulfoximine partially reversed the anti-osteoclastogenic effects of CIC inhibition. Consistently, osteoclast-targeted silencing of CIC in OVX mice mitigated bone loss. Collectively, these findings support a role for CIC as a metabolic integrator of energy and redox metabolism in osteoclasts, and highlight its potential as a candidate target for limiting excessive bone resorption in PMOP.
Third-generation EGFR tyrosine kinase inhibitors (TKIs), such as osimertinib, have demonstrated promising clinical efficacy in the treatment of EGFR-mutant non–small cell lung cancer (NSCLC). Despite substantial progress with EGFR-TKIs, the development of acquired resistance remains a major clinical challenge. Notably, the addition of immune checkpoint blockade after TKI resistance has not resulted in significant survival benefits compared to chemotherapy. In this study, we performed a comprehensive transcriptomic analysis of established osimertinib-resistant tumor models and found that the expression of the ectonucleotide phosphodiesterase ENPP1, a key regulator of extracellular cGAMP signaling, was significantly upregulated in resistant tumors compared to the parental TKI-sensitive NSCLC tumors. Mechanistically, upregulated ENPP1 in resistant cells promoted the hydrolysis of extracellular cGAMP, suppressing the cGAS–STING pathway in immune cells and subsequently impairing immune cell activation and function, thereby promoting immune suppression and tumor progression. Genetic depletion or pharmacological inhibition of ENPP1 enhanced immune cell–mediated cytotoxicity against TKI-resistant tumor cells. Furthermore, the use of ENPP1 inhibitors both in vitro and in vivo enhanced immune cell activity and antitumor efficacy in TKI-resistant lung cancers with high ENPP1 expression. Importantly, these observations were further validated by paired clinical tumor samples, which demonstrated increased ENPP1 expression following the development of acquired EGFR-TKI resistance. Collectively, our study highlights a critical role for ENPP1 in mediating immune evasion through suppression of the cGAMP–STING pathway in the tumor immune microenvironment, supporting ENPP1 as a promising therapeutic target to enhance immunotherapy efficacy in EGFR-TKI–resistant NSCLC.
Recovery from tissue stress requires the elimination of damaged cells and the commensurate production of healthy cells. How these two processes are coordinated to ensure tissue recovery remains poorly understood. Here we show that the c-Jun N-terminal kinase (JNK) pathway orchestrates apoptosis and proliferation, two seemingly opposite cellular behaviours, in response to epithelial stress. We took advantage of new optogenetic tools to trigger a pulse of JNK signalling activity in a defined domain of Drosophila wing primordia and mapped the response in time and space. Within 3 h after induction, the cells within the activation domain arrest proliferation, while a subset undergo apoptosis. As JNK signalling returns to background level, apoptosis subsides and proliferation resumes to allow completion of development with high fidelity. Using a sensitive reporter, we find that while JNK triggers apoptosis, the level of JNK activity does not correlate with apoptosis on a cell-by-cell basis. We show that the cell cycle phase modulates the pro-apoptotic activity of JNK signalling: G2 arrest is protective, while, in G1, mild JNK signalling activity suffices to trigger apoptosis. Transcriptomic analysis identified the genes encoding Dally and Dally-like protein (Dlp) among the most upregulated by excess JNK signalling. We show that these glypicans contribute to tissue repair by enhancing surface retention of the ligands Wingless (a Wnt) and Dpp (a BMP). We suggest that the resulting local increase in morphogen signalling provides subsequent protection from the pro-apoptotic effect of JNK signalling, allowing surviving cells to re-enter the cell cycle and resume development. Accordingly, recovery from ribosomal protein deficiency or irradiation-induced stress is impaired upon reduction of Dlp activity. Our work shows how a single stress pathway can selectively trigger apoptosis while protecting cells that can contribute to tissue recovery during resumption of normal development.
