Biomedical subjects

Hong Yu

Publications and source records attributed to Hong Yu.

At least 19 recordsLinked to original sources

PubMed2026

DEK::AFF2 Fusion-Associated Sinonasal Carcinoma With Intracranial and Orbital Involvement.

Sinonasal carcinomas encompass a molecularly heterogeneous group of malignancies. DEK::AFF2 fusion-associated carcinoma is a recently recognized subtype of nonkeratinizing squamous cell carcinoma characterized by deceptively bland morphology yet clinically aggressive behavior. We report the case of a 67-year-old woman who presented with a rapidly enlarging sinonasal mass with extensive local invasion involving both the intracranial compartment and orbit. Histologically, the tumor was composed of cytologically bland cells with monotonous nuclei and exhibited a combination of exophytic and endophytic growth patterns that closely mimicked a sinonasal papilloma. Although the tumor shows predominantly squamous differentiation, focal extracellular mucin was also present. The brain-invasive foci demonstrated tumor cells in sheets and nests floating within pools of mucin, a pattern focally reminiscent of mucinous adenocarcinoma. RNA sequencing identified a DEK::AFF2 fusion with breakpoints at DEK exon 7 and AFF2 exon 6, confirming the diagnosis. The tumor demonstrated positive PD-L1 expression with a combined positive score (CPS) of 40 and a low tumor mutational burden (TMB) of 0.5 mutations/Mb. This case highlights the diagnostic challenges posed by DEK::AFF2 fusion-associated carcinoma, underscores the importance of molecular profiling for accurate classification, and demonstrates the aggressive clinical behavior of this rare entity.

Journal Article↗

PubMed2026

A three-gene radioresistance signature predicts tumor progression in cervical cancer.

BACKGROUND: As a primary curative treatment for locally advanced cervical cancer, radiotherapy is frequently undermined by radioresistant tumor cells that evade cell death and subsequently drive post-treatment tumor progression. This study aimed to identify candidate genes associated with radioresistance in cervical cancer and to explore their potential in predicting unfavorable outcomes among radioresistant patients, thereby providing a reference for future research. METHODS: We screened for co-expressed genes using transcriptomic data from radiation non-complete response (NCR) cervical cancer patients in Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) databases. Cox regression analyses were conducted to identify the most significant radioresistance-associated genes for constructing a prognostic model. The predictive performance of this model was further validated through logistic regression, weighted gene co-expression network analysis (WGCNA), and pan-cancer analyses. Quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) was performed to quantify the expression levels of key genes in cervical cancer tissue samples from radiosensitive and radioresistant patients. RESULTS: The resulting prognostic model comprised three genes: MTMR11, VANGL1, and CD46. This gene panel was significantly associated with the prognosis of cervical cancer patients receiving radiotherapy and showed acceptable predictive performance across multiple cancer types. qRT-PCR analysis revealed that the expression patterns of MTMR11 and VANGL1 were generally consistent with radioresistance of cervical cancer, whereas CD46 exhibited an unexpected expression trend. CONCLUSIONS: Our findings indicate that MTMR11, VANGL1, and CD46 are associated with radioresistance and prognosis in cervical cancer. Their potential clinical utility, especially in predicting radiotherapy response at the individual patient level, requires further validation in larger, independent, and prospective cohorts.

Cervical cancer↗

PubMed2026

Genome-wide identification and expression profiling of HSD3B and SDR42E1 genes in the Pacific oyster (Crassostrea gigas): potential associations with gonadal development.

Sex steroids are lipid-soluble signaling molecules that regulate sex differentiation, reproductive development and physiological homeostasis in animals. 3β-Hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase (3β-HSD) is a key steroidogenic enzyme, whereas SDR42E1, an extended short-chain dehydrogenase/reductase, has been implicated in sterol- and steroid-related metabolism. However, the composition, evolutionary relationships and expression patterns of the HSD3B- and SDR42E1-related genes in bivalve gonadal development remain poorly characterized. In this study, five PF01073-containing genes, comprising three CgHsd3b and two CgSdr42e1 genes, were identified in the Pacific oyster Crassostrea gigas. Phylogenetic analysis separated the proteins into HSD3B-related and SDR42E1-related groups, and gene-structure and motif analyses indicated subfamily-level divergence. All five proteins retained the SDR domain but differed in exon-intron structure and motif composition. Each contained the extended-SDR TGxxGxxG motif, whereas exact classical [ST]GxxxGxG and NNAG motifs were absent. Tyr- and Lys-equivalent residues were conserved, while the HSD3B1 Ser-equivalent position contained Thr in two C. gigas proteins and Ser in one. These features support their classification as extended-SDR proteins but do not establish enzymatic activity or substrate specificity. The three CgHsd3b genes were dispersed on one chromosome, whereas CgSdr42e1-1 and CgSdr42e1-2 were adjacent on another chromosome, suggesting a possible local duplication event for the CgSdr42e1 pair. Public RNA-seq data showed distinct tissue- and gonadal-stage expression patterns, with several genes displaying gonad-biased or female-stage-associated expression. Independent RT-qPCR profiling of the representative genes CgHsd3b-3 and CgSdr42e1-1 detected stage-dependent expression, although tissue rankings differed from those in the public RNA-seq datasets. These differences may reflect the use of independent biological samples, tissue composition, normalization procedures, and platform-specific measurements. Because enzymatic assays, metabolite measurements, cellular localization, and functional perturbation were not performed, the results identify candidate genes whose expression is associated with gonadal development rather than demonstrating regulatory roles. This study provides a comparative framework for future functional investigation of sterol- and steroid-related metabolism in bivalves.

Animals↗

PubMed2026

Genomic identification and functional characterization of the nuclear receptor gene family in relation to sex determination and gonad development in the Pacific oyster (Crassostrea gigas).

Nuclear receptors (NRs) are a large superfamily of transcription factors that control a wide range of physiological processes by modulating the expression of downstream target genes. Numerous studies have confirmed that NR family members play critical and conserved roles in sex determination and gonadal development across metazoans. However, in mollusks, systematic characterization of NRs and their potential functions in gonadal regulation remain largely unexplored. In this study, 46 NR gene family members in the Pacific oyster (Crassostrea gigas) were identified and assigned to eight subfamilies. All NR family members contain at least one of the two core domains (DNA-binding domain, DBD; ligand-binding domain, LBD), and conserved exon-intron structures were observed within the same subgroup, indicating their evolutionary conservation. Furthermore, expression profiling revealed high expression of CgNR2F, CgNR5A1-1, and CgNR0B1 in undifferentiated gonads, suggesting their potential involvement in sex determination. CgNR1A and CgNR2E5 were specifically expressed in female gonads and exhibited female-biased expression patterns, indicating a putative role in ovarian development. Moreover, CgNR3A and CgNR3B showed high expression levels during the undifferentiated stage and early male development stage, implying their possible participation in male gonadal development and gametogenesis. These results expand the understanding of the NR gene family in C. gigas and help elucidate the potential functions of NR genes in sex determination and gonadal development.

Animals↗

PubMed2026

LLPS-based classification and a novel prognostic signature reveal NRF1 as a therapeutic target in pancreatic cancer.

BACKGROUND: Aberrant liquid-liquid phase separation (LLPS) can alter biomolecular condensate functions and may influence pancreatic tumorigenesis and progression, but the specific role of LLPS regulators in prognosis and the tumor immune microenvironment (TIME) in pancreatic ductal adenocarcinoma (PDAC) remains unclear. METHODS: We integrated transcriptome data of LLPS regulator-related differentially expressed genes (DEGs; n = 298) in a cohort of 176 PDAC patients from TCGA. Three LLPS regulator subtypes (LS1-LS3) were identified through multi-omics analyses, and a prognostic LLPS subtype-related risk model (LRRPC) was developed and validated. Chromatin immunoprecipitation confirmed NRF1 binding to promoters of key risk genes, and in vitro and in vivo experiments assessed the effects of NRF1 targeting on tumor growth. RESULTS: The three LLPS regulator subtypes exhibited significant differences in prognosis, clinical features, genomic alterations, TIME patterns and predicted immunotherapy response. The LRRPC signature predicted prognosis and immunotherapy efficacy across cohorts and was associated with tumor biomarkers and immune infiltration. Nuclear Respiratory Factor 1 (NRF1) directly regulated hub genes such as FAM83A, RHOV and ITGB6, promoting PDAC cell proliferation, while its inhibition induced apoptosis and reduced tumor growth. CONCLUSIONS: This study proposes an LLPS-based stratification framework for PDAC, and the LRRPC model provides an LLPS subtype-related risk score that may assist personalized prognostic assessment and immunotherapy stratification. NRF1 emerges as a promising therapeutic candidate whose targeting can inhibit tumor progression in PDAC experimental models and warrants further evaluation.

Immunotherapy↗

PubMed2025

Beta-catenin/sirtuin 1/farnesoid X receptor pathway promotion of portal vein ligation and parenchymal transection-induced rapid liver regeneration.

BACKGROUND: By accelerating the regeneration of the future liver remnant, portal vein ligation and parenchymal transection allows for more extensive hepatectomy. Given that the mechanism remains poorly understood, the aim of this study was to investigate the mechanism of portal vein ligation and parenchymal transection-induced liver regeneration. METHODS: A portal vein ligation and parenchymal transection-induced liver regeneration mouse model was established, followed by RNA microarray analysis to identify candidate molecules. Genomic deletion and chemical manipulation of target molecules were used to explore their functions in portal vein ligation and parenchymal transection-induced liver regeneration. Validation was conducted using a diseased liver model and human samples. RESULTS: Portal vein ligation and parenchymal transection-induced liver regeneration was significantly accelerated compared with that in sham-operated mice (P < .05). An RNA microarray revealed that Sirtuin 1 is a crucial molecule in the proliferation of the future liver remnant. Regardless of whether Sirtuin 1 is inhibited chemically or through genetic deletion, portal vein ligation and parenchymal transection-induced liver regeneration is distinctly attenuated. Further investigation revealed that Sirtuin 1 promoted portal vein ligation and parenchymal transection-induced liver regeneration via the farnesoid X receptor. In addition, beta-catenin also was found to participate in the process of future liver remnant proliferation. Chemical inhibition of beta-catenin markedly impaired but activation of WNT/beta-catenin mildly enhanced portal vein ligation and parenchymal transection-induced liver regeneration (P < .05). Deletion of Sirtuin 1 blocked the facilitating effect of beta-catenin on portal vein ligation and parenchymal transection-induced liver regeneration. These findings were validated in diseased liver models and patient samples, confirming the correlation between the beta-catenin/Sirtuin 1/farnesoid X receptor pathway and portal vein ligation and parenchymal transection-induced liver regeneration. CONCLUSION: Activation of the beta-catenin/Sirtuin 1/farnesoid X receptor pathway offers critical mechanistic insights into accelerating portal vein ligation and parenchymal transection-induced liver regeneration. Modulation of beta-catenin/Sirtuin 1/farnesoid X receptor may therefore improve clinical outcomes in patients receiving staged hepatectomy.

Liver Regeneration↗

PubMed2007

Role of hyperactive cerebellum and motor cortex in Parkinson's disease.

Previous neuroimaging studies have found hyperactivation in the cerebellum and motor cortex and hypoactivation in the basal ganglia in patients with Parkinson's disease (PD) but the relationship between the two has not been established. This study examined whether cerebellar and motor cortex hyperactivation is a compensatory mechanism for hypoactivation in the basal ganglia or is a pathophysiological response that is related to the signs of the disease. Using a BOLD contrast fMRI paradigm PD patients and healthy controls performed automatic and cognitively controlled thumb pressing movements. Regions of interest analysis quantified the BOLD activation in motor areas, and correlations between the hyperactive and hypoactive regions were performed, along with correlations between the severity of upper limb rigidity and BOLD activation. There were three main findings. First, the putamen, supplementary motor area (SMA) and pre-SMA were hypoactive in PD patients. The left and right cerebellum and the contralateral motor cortex were hyperactive in PD patients. Second, PD patients had a significant negative correlation between the BOLD activation in the ipsilateral cerebellum and the contralateral putamen. The correlation between the putamen and motor cortex was not significant. Third, the BOLD activation in the motor cortex was positively correlated with the severity of upper limb rigidity, but the BOLD activation in the cerebellum was not correlated with rigidity. Further, the activation in the motor cortex was not correlated with upper extremity bradykinesia. These findings provide new evidence supporting the hypothesis that hyperactivation in the ipsilateral cerebellum is a compensatory mechanism for the defective basal ganglia. Our findings also provide the first evidence from neuroimaging that hyperactivation in the contralateral primary motor cortex is not a compensatory response but is directly related to upper limb rigidity.

Aged↗

PubMed2006

Hypophosphorylation of residue Y1045 leads to defective downregulation of EGFRvIII.

Downregulation of the EGF receptor is the net result of receptor degradation and recycling. Cbl functions by specifically targeting activated ErbB receptors for ubiquitination, facilitating ligand-induced desensitization of EGFR. The interaction between EGFR and c-Cbl has been shown to depend upon receptor phosphorylation at tyrosine residue 1045, the major docking site for c-Cbl. To better understand the biological consequences of EGFR mutants in human cancers, we compared wild-type EGFR and EGFRvIII internalization, as well as gefitinib sensitive and resistant EGFR kinase mutations found in non-small cell lung carcinoma. We observed that Cbl failed to associate with EGFRvIII as well as an inability of the receptor to undergo ubiquitination and degradation. The most intriguing observation is that EGFRvIII tyrosine 1045 residue is either un-phosphorylated or hypophosphorylated. This is in contrast to other tyrosine residues in EGFRvIII, such as Y1173, which exhibit levels of phosphorylation comparable to those of wild-type EGFR. These results suggest that hypophosphorylation of tyrosine residue 1045 is likely to be the cause for EGFRvIII escape from c-Cbl-induced ubiquitination and degradation, enhancing EGFRvIII's ability to increase proliferation in breast cancer cells. Interestingly, inefficient degradation was only observed in the gefitinib resistant EGFR kinase mutant, despite the fact that this mutant receptor is capable of recruiting c-Cbl and undergoes ubiquitination. The gefitinib sensitive EGFR kinase mutant exhibits similar ubiquitination and degradation patterns as the wild-type EGFR. Collectively, different EGFR mutations exert various negative mechanisms that have the potential to modify receptor internalization and degradation, and may play a critical role in resistance to tyrosine kinase inhibitory treatments.

Amino Acid Sequence↗

PubMed2006

[The application of selective portal inflow occlusion in laparoscopic hepatectomy].

OBJECTIVE: To discuss the safety and the feasibility of laparoscopic selective portal inflow occlusion. METHODS: From January 2005 to February 2006, 7 patients were performed by laparoscopic hepatectomy with selective portal inflow occlusion. The patients included 1 male and 6 females, the mean age was 48.9 years, ranged from 31 to 70 years. Procedure included left lateral segmentectomies (4 patients), left hemihepatectomies (2 patients), and right hemihepatectomies (1 patient). Portal vein, hepatic artery and their branches were exposed by blunt dissection and performed selective portal occlusion with absorbable clips. RESULTS: There is no conversion, no mortality, and no postoperative complication. Seven selective portal inflow occlusions were performed successfully. The mean operating time was 188.7 min (range 70 min to 300 min), the mean intraoperative blood loss was 625 ml (range 350 ml to 1000 ml), and the mean postoperative hospital stay was 8.4 days. CONCLUSIONS: Laparoscopic selective portal inflow occlusion is a safe and feasible technique.

Adult↗

PubMed2006

Natural language processing and visualization in the molecular imaging domain.

Molecular imaging is at the crossroads of genomic sciences and medical imaging. Information within the molecular imaging literature could be used to link to genomic and imaging information resources and to organize and index images in a way that is potentially useful to researchers. A number of natural language processing (NLP) systems are available to automatically extract information from genomic literature. One existing NLP system, known as BioMedLEE, automatically extracts biological information consisting of biomolecular substances and phenotypic data. This paper focuses on the adaptation, evaluation, and application of BioMedLEE to the molecular imaging domain. In order to adapt BioMedLEE for this domain, we extend an existing molecular imaging terminology and incorporate it into BioMedLEE. BioMedLEE's performance is assessed with a formal evaluation study. The system's performance, measured as recall and precision, is 0.74 (95% CI: [.70-.76]) and 0.70 (95% CI [.63-.76]), respectively. We adapt a JAVA viewer known as PGviewer for the simultaneous visualization of images with NLP extracted information.

Animals↗

PubMed2006

Nuclear exclusion of separase prevents cohesin cleavage in interphase cells.

During mitosis, equal transmission of the duplicated chromosomes demands a strict regulation of separase, which cleaves cohesin and triggers sister chromatid separation in anaphase. Vertebrate separase is inhibited by securin and the inhibitory phosphorylation of separase. However, knockout experiments indicate that securin is dispensable and the inhibitory phosphorylation was observed only in M phase cells. This begs the question how cohesin cleavage by separase is prevented in the absence these two mechanisms. Here we show that separase is excluded from cohesin by the nuclear envelope, which forms in telophase and disassembles in mitosis. The exclusion is achieved passively by its large physical mass and may be backed up by the CRM1-dependent nuclear export. A functional NES motif is identified in separase. We demonstrated that the nuclear envelope is sufficient to prevent active separase from cleaving nuclear cohesin. We propose that the nuclear exclusion is important to prevent cohesin cleavage during interphase in the absence of securin and the phosphorylation inhibition.

Active Transport, Cell Nucleus↗

PubMed2006

SerpinB2 is an inducible host factor involved in enhancing HIV-1 transcription and replication.

The serine protease inhibitor SerpinB2 (plasminogen activator inhibitor-2) is a major product of activated monocytes and macrophages and is substantially induced during most inflammatory processes. Distinct from its widely described extracellular role as an inhibitor of urokinase plasminogen activator, SerpinB2 has recently been shown to have an intracellular role as a retinoblastoma protein (Rb)-binding protein that inhibits Rb degradation. Here we show that HIV-1 infection and gp120 treatment of human peripheral blood mononuclear cells resulted in induction of SerpinB2. Furthermore, SerpinB2 expression in THP-1 monocyte/macrophage, Jurkat T, and HeLa cell lines increased replication of HIV-1 and enhanced transcription from the HIV-1 long terminal repeat (LTR) promoter by 3-10-fold. Increased HIV-1 gene expression and transcription was also observed in activated macrophages from SerpinB2+/+ mice compared with macrophages from SerpinB2-/- mice. The SerpinB2-mediated elevation of Rb protein levels appeared to be responsible for enhancing transcription from the core promoter region of the LTR by relieving HDM2-mediated inhibition of Sp1 and/or by increasing the Sp1/Sp3 expression ratios. This is the first report associating HIV-1 replication with SerpinB2 expression and illustrates that SerpinB2 is a potentially important inducible host factor that significantly promotes HIV-1 replication.

Animals↗

PubMed2006

Hierarchical modularity of nested bow-ties in metabolic networks.

BACKGROUND: The exploration of the structural topology and the organizing principles of genome-based large-scale metabolic networks is essential for studying possible relations between structure and functionality of metabolic networks. Topological analysis of graph models has often been applied to study the structural characteristics of complex metabolic networks. RESULTS: In this work, metabolic networks of 75 organisms were investigated from a topological point of view. Network decomposition of three microbes (Escherichia coli, Aeropyrum pernix and Saccharomyces cerevisiae) shows that almost all of the sub-networks exhibit a highly modularized bow-tie topological pattern similar to that of the global metabolic networks. Moreover, these small bow-ties are hierarchically nested into larger ones and collectively integrated into a large metabolic network, and important features of this modularity are not observed in the random shuffled network. In addition, such a bow-tie pattern appears to be present in certain chemically isolated functional modules and spatially separated modules including carbohydrate metabolism, cytosol and mitochondrion respectively. CONCLUSION: The highly modularized bow-tie pattern is present at different levels and scales, and in different chemical and spatial modules of metabolic networks, which is likely the result of the evolutionary process rather than a random accident. Identification and analysis of such a pattern is helpful for understanding the design principles and facilitate the modelling of metabolic networks.

Algorithms↗

PubMed2006

Accessing bioscience images from abstract sentences.

Images (e.g., figures) are important experimental results that are typically reported in bioscience full-text articles. Biologists need to access images to validate research facts and to formulate or to test novel research hypotheses. On the other hand, biologists live in an age of information explosion. As thousands of biomedical articles are published every day, systems that help biologists efficiently access images in literature would greatly facilitate biomedical research. We hypothesize that much of image content reported in a full-text article can be summarized by the sentences in the abstract of the article. In our study, more than one hundred biologists had tested this hypothesis and more than 40 biologists had evaluated a novel user-interface BioEx that allows biologists to access images directly from abstract sentences. Our results show that 87.8% biologists were in favor of BioEx over two other baseline user-interfaces. We further developed systems that explored hierarchical clustering algorithms to automatically identify abstract sentences that summarize the images. One of the systems achieves a precision of 100% that corresponds to a recall of 4.6%.

Abstracting and Indexing↗

PubMed2006

Complex adenovirus-vectored vaccine protects guinea pigs from three strains of Marburg virus challenges.

The Marburg virus (MARV), an African filovirus closely related to the Ebola virus, causes a deadly hemorrhagic fever in humans, with up to 90% mortality. Currently, treatment of disease is only supportive, and no vaccines are available to prevent spread of MARV infections. In order to address this need, we have developed and characterized a novel recombinant vaccine that utilizes a single complex adenovirus-vectored vaccine (cAdVax) to overexpress a MARV glycoprotein (GP) fusion protein derived from the Musoke and Ci67 strains of MARV. Vaccination with the cAdVaxM(fus) vaccine led to efficient production of MARV-specific antibodies in both mice and guinea pigs. Significantly, guinea pigs vaccinated with at least 5 x 10(7) pfu of cAdVaxM(fus) vaccine were 100% protected against lethal challenges by the Musoke, Ci67 and Ravn strains of MARV, making it a vaccine with trivalent protective efficacy. Therefore, the cAdVaxM(fus) vaccine serves as a promising vaccine candidate to prevent and contain multi-strain infections by MARV.

Adenoviridae↗

PubMed2006

Characterization of Bacillus thuringiensis strain Bt185 toxic to the Asian cockchafer: Holotrichia parallela.

A new Bacillus thuringiensis strain, Bt185, was isolated from HeBei soil samples in China. Observations after transmission electron microscopy found that the strain produced spherical parasporal inclusions similar to that of the B. thuringiensis subsp. japonensis Buibui strain, which showed toxicity to both Anomala corpulenta and Popillia japonica. The plasmid profile seen on an agarose gel revealed that Bt185 contained six large bands of 191 kb, 161 kb, 104 kb, 84 kb, 56 kb, and 37 kb. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed one major band with an estimated molecular mass of 130 kDa. Polymerase chain reaction-restriction fragment length polymorphism results showed that a novel cry8-type gene sequence was found in the Bt185 strain. When we screened for this novel gene sequence, an additional novel cry8-type gene was isolated, having a partial sequence of 2340 bp and encoding a protein of 780 amino acids. Bioassay results showed that Bt185 had no toxicity against several Coleopteran and Lepidopteran pests. However, Bt185 exhibited toxicity against larvae of the Asian cockchafer, Holotrichia parallela. This is the first report of the occurrence of a Bacillus strain that has insecticidal activity against Holotrichia parallela larvae.

Animals↗

PubMed2006

Using MEDLINE as a knowledge source for disambiguating abbreviations and acronyms in full-text biomedical journal articles.

Biomedical abbreviations and acronyms are widely used in biomedical literature. Since many of them represent important content in biomedical literature, information retrieval and extraction benefits from identifying the meanings of those terms. On the other hand, many abbreviations and acronyms are ambiguous, it would be important to map them to their full forms, which ultimately represent the meanings of the abbreviations. In this study, we present a semi-supervised method that applies MEDLINE as a knowledge source for disambiguating abbreviations and acronyms in full-text biomedical journal articles. We first automatically generated from the MEDLINE abstracts a dictionary of abbreviation-full pairs based on a rule-based system that maps abbreviations to full forms when full forms are defined in the abstracts. We then trained on the MEDLINE abstracts and predicted the full forms of abbreviations in full-text journal articles by applying supervised machine-learning algorithms in a semi-supervised fashion. We report up to 92% prediction precision and up to 91% coverage.

Artificial Intelligence↗

PubMed2006

Hydrogen peroxide-mediated isoniazid activation catalyzed by Mycobacterium tuberculosis catalase-peroxidase (KatG) and its S315T mutant.

Inhibition of the enzyme Mycobacterium tuberculosis InhA (enoyl-acyl carrier protein reductase) due to formation of an isonicotinoyl-NAD adduct (IN-NAD) from isoniazid (INH) and nicotinamide adenine dinucleotide cofactor is considered central to the mode of action of INH, a first-line treatment for tuberculosis infection. INH action against mycobacteria requires catalase-peroxidase (KatG) function, and IN-NAD adduct formation is catalyzed in vitro by M. tuberculosis KatG under a variety of conditions, yet a physiologically relevant approach to the process has not emerged that allows scrutiny of the mechanism and the origins of INH resistance in the most prevalent drug-resistant strain bearing KatG[S315T]. In this report, we describe how hydrogen peroxide, delivered at very low concentrations to ferric KatG, leads to efficient inhibition of InhA due to formation of the IN-NAD adduct. The rate of adduct formation mediated by wild-type KatG was about 20-fold greater than by the isoniazid-resistant KatG[S315T] mutant under optimal conditions (H2O2 supplied along with NAD+ and INH). Slow adduct formation also occurs starting with NADH and INH, in the presence of KatG even in the absence of added peroxide, due to endogenous peroxide. The poor efficiency of the KatG[S315T] mutant can be enhanced merely by increasing the concentration of INH, consistent with this enzyme's reduced affinity for INH binding to the resting enzyme and the catalytically competent enzyme intermediate (Compound I). Origins of drug resistance in the KatG[S315T] mutant enzyme are analyzed at the structural level through examination of the three-dimensional X-ray crystal structure of the mutant enzyme.

Bacterial Proteins↗