Biology subjects

Chiang, J.-C.

Publications and source records attributed to Chiang, J.-C..

3 recordsLinked to original sources

bioRxiv2025

LIPT1 loss confers replication stress and PARP inhibitor sensitivity through PrimPol-mediated ssDNA gaps

Replication stress (RS) and altered metabolism are two hallmarks of cancer, yet how metabolic perturbations contribute to RS remains poorly understood. Lipotransferase 1 (LIPT1) catalyzes the covalent attachment of lipoic acid to mitochondrial 2-ketoacid dehydrogenases, sustaining flux through the tricarboxylic acid (TCA) cycle. Loss of LIPT1 causes accumulation of 2-hydroxyglutarate (2-HG), which is known to inhibit -ketoglutarate (-KG)-dependent histone demethylases and promotes heterochromatin formation. Here, we show that 2-HG-driven heterochromatin impedes replication fork progression, causing fork stalling and RS in LIPT1-deficient cancer cells. To bypass stalled forks, PrimPol-mediated repriming resumes DNA synthesis but leaves behind single-stranded DNA (ssDNA), which requires poly (ADP-ribose) polymerase 1 (PARP1) for repair. Furthermore, nascent DNA at reprimed forks undergoes MRE11-dependent degradation, further destabilizing replication fork integrity. Consequently, LIPT1 deficiency promotes replication and genome instability, and therapeutic vulnerability to PARP inhibitor. Together, these findings reveal a mechanistic link between mitochondrial lipoylation and replication fork stability, uncovering a metabolic basis for genome instability in cancer.

cell biology↗

bioRxiv2025

NUDT5 regulates purine metabolism and thiopurine sensitivity by interacting with PPAT

Cells generate purine nucleotides through both de novo purine biosynthesis (DNPB) and purine salvage. Purine accumulation represses energetically costly DNPB through feedback inhibition of the enzymatic steps that produce the precursor phosphoribosylamine. Excessive DNPB is associated with human diseases including neurological dysfunction and hyperuricemia. However, the mechanisms explaining how cells balance DNPB and purine salvage are incompletely understood. Data from a genome-wide CRISPR loss-of-function screen and extensive stable isotope tracing identified Nudix hydrolase 5 (NUDT5) as a suppressor of DNPB during purine salvage. NUDT5 ablation allows DNPB to persist in the presence of either native purines or thiopurine drugs; this renders NUDT5-deficient cells insensitive to thiopurine treatment. Surprisingly, this regulation occurs independently of NUDT5s known function in hydrolyzing ADP-ribose to AMP and ribose-5-phosphate. Rather, NUDT5 interacts with phosphoribosyl pyrophosphate amidotransferase (PPAT), the rate-limiting enzyme in DNPB that generates phosphoribosylamine. Upon induction of purine salvage, the PPAT-NUDT5 interaction is required to trigger disassembly of the purinosome, a cytosolic metabolon involved in efficient DNPB. Mutations that disrupt NUDT5s interaction with PPAT but leave its catalytic activity intact permit excessive DNPB during purine salvage, inducing thiopurine resistance. Collectively, our findings identify NUDT5 as a regulator governing the balance between DNPB and purine salvage, underscoring its impact on nucleotide metabolism and efficacy of thiopurine treatment.

biochemistry↗

bioRxiv2022

In-vivo characterization of glutamine metabolism identifies therapeutic targets in clear cell renal cell carcinoma

Targeting metabolic vulnerabilities has been proposed as a therapeutic strategy in renal cell carcinoma (RCC). Here, we analyzed metabolism in patient-derived xenografts (tumorgrafts) from diverse forms of RCC. Tumorgrafts from VHL-mutant clear cell RCC (ccRCC) retained metabolic features of human ccRCC and engage in oxidative and reductive glutamine metabolism. We used several approaches to suppress glutamine metabolism and test the effect on tumor growth. Genetic silencing of isocitrate dehydrogenase-1 or -2 impaired reductive labeling of TCA cycle intermediates and suppressed tumor growth. Glutaminase inhibition resulted in modest growth suppression and variable effects on glutamine metabolism in vivo. Infusions with [amide-15N]glutamine revealed persistent amidotransferase activity during glutaminase inhibition, and blocking these activities with the amidotransferase inhibitor JHU-083 also reduced tumor growth. We conclude that ccRCC tumorgrafts catabolize glutamine via multiple pathways, perhaps explaining why it has been challenging to achieve therapeutic responses in patients by inhibiting glutaminase. TeaserGlutamine fuels the TCA cycle and amidotransferase pathways in clear cell renal cell carcinoma.

cancer biology↗