Pub Date : 2026-01-28DOI: 10.1016/j.jbc.2026.111212
Karla K Frietze,Alyssa Brown,Dividutta Das,Raymond Franks,Pranavi Jagadeesan,Joseph T Nickels
The prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH) has reached epidemic proportions globally. Understanding the molecular mechanisms that underlie these conditions offers significant potential for identifying new therapeutic targets. In this study, interleukin-21 receptor-deficient mice were used to investigate the role of IL-21 signaling in obesity-induced MASLD and MASH. Findings reveal that IL21R+/+ mice exposed to a high-fat diet develop MASLD/MASH, with hepatic activation of IL-21 signaling driving de novo lipogenesis through JAK1-STAT5-dependent induction of hypoxia-induced transcription factor 2α (HIF-2a). HIF-2α elevation stimulates genes involved in de novo lipogenesis, contributing to increased hepatic lipid accumulation and MASLD progression. Elevated levels of TGF-β1 and increased collagen deposition indicate hepatic stellate cell activation, facilitating the development of liver fibrosis. Moreover, upregulation of HIF-2α enhances expression of the amino acid transporter SLC7A5, leading to mTORC1-mediated inhibition of autophagy. In contrast, il21r-/- mice exhibited diminished JAK1-STAT5 signaling and were protected from MASLD/MASH. Livers from individuals afflicted with fatty liver disease or nodular cirrhosis show increased IL-21R protein that co-localized with CD4, implicating activated T cells as a potential source of IL-21 for receptor activation. Collectively, these results indicate that targeting IL-21 receptor signaling may represent a promising strategy for reducing MASLD/MASH.
{"title":"HIF-2α induction in de novo lipogenesis in metabolic dysfunction-associated steatohepatitis is dependent on IL-21 signaling.","authors":"Karla K Frietze,Alyssa Brown,Dividutta Das,Raymond Franks,Pranavi Jagadeesan,Joseph T Nickels","doi":"10.1016/j.jbc.2026.111212","DOIUrl":"https://doi.org/10.1016/j.jbc.2026.111212","url":null,"abstract":"The prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH) has reached epidemic proportions globally. Understanding the molecular mechanisms that underlie these conditions offers significant potential for identifying new therapeutic targets. In this study, interleukin-21 receptor-deficient mice were used to investigate the role of IL-21 signaling in obesity-induced MASLD and MASH. Findings reveal that IL21R+/+ mice exposed to a high-fat diet develop MASLD/MASH, with hepatic activation of IL-21 signaling driving de novo lipogenesis through JAK1-STAT5-dependent induction of hypoxia-induced transcription factor 2α (HIF-2a). HIF-2α elevation stimulates genes involved in de novo lipogenesis, contributing to increased hepatic lipid accumulation and MASLD progression. Elevated levels of TGF-β1 and increased collagen deposition indicate hepatic stellate cell activation, facilitating the development of liver fibrosis. Moreover, upregulation of HIF-2α enhances expression of the amino acid transporter SLC7A5, leading to mTORC1-mediated inhibition of autophagy. In contrast, il21r-/- mice exhibited diminished JAK1-STAT5 signaling and were protected from MASLD/MASH. Livers from individuals afflicted with fatty liver disease or nodular cirrhosis show increased IL-21R protein that co-localized with CD4, implicating activated T cells as a potential source of IL-21 for receptor activation. Collectively, these results indicate that targeting IL-21 receptor signaling may represent a promising strategy for reducing MASLD/MASH.","PeriodicalId":15140,"journal":{"name":"Journal of Biological Chemistry","volume":"8 1","pages":"111212"},"PeriodicalIF":4.8,"publicationDate":"2026-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146088990","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-28DOI: 10.1016/j.jbc.2026.111211
Julie Charpentier,Yan Lu,Serena Gallozzi,Shubhangi Seth,Mark P Hodson,James R Krycer,Severine Navarro
The biologically active metabolite of Vitamin A, retinoic acid, is essential for regulating immune tolerance, development, and metabolism. A key regulator of retinoic acid signalling is its synthesis by retinaldehyde dehydrogenase, whose expression is tightly regulated and cell-type specific. Current cell-based assays for retinaldehyde dehydrogenase activity rely on fluorescent aldehyde substrates, which lack specificity, limiting their accuracy and interpretability. Here, we developed a sensitive, cell-based assay that directly quantifies retinaldehyde dehydrogenase activity by measuring a panel of retinoids, including all-trans-retinoic acid, using liquid chromatography-mass spectrometry. Employing cultured conventional dendritic cells, we demonstrate that retinoic acid synthesis is time-, substrate-, and enzyme-dependent. Compared to fluorescence-based assays, our assay avoided artefactual signals influenced by cell density and provided a direct, quantitative measure of enzymatic activity in the context of broader retinoid metabolism. This assay offers additional practical advantages, including flexibility in sample processing and compatibility with other downstream metabolite analyses. Together, our protocol provides a robust, specific, and functionally-relevant approach that complements existing fluorescence-based approaches to study retinoic acid biosynthesis in immune cells and beyond.
{"title":"A cell-based assay for retinaldehyde dehydrogenase activity: retinoid quantification as an alternative to current fluorescence-based approaches.","authors":"Julie Charpentier,Yan Lu,Serena Gallozzi,Shubhangi Seth,Mark P Hodson,James R Krycer,Severine Navarro","doi":"10.1016/j.jbc.2026.111211","DOIUrl":"https://doi.org/10.1016/j.jbc.2026.111211","url":null,"abstract":"The biologically active metabolite of Vitamin A, retinoic acid, is essential for regulating immune tolerance, development, and metabolism. A key regulator of retinoic acid signalling is its synthesis by retinaldehyde dehydrogenase, whose expression is tightly regulated and cell-type specific. Current cell-based assays for retinaldehyde dehydrogenase activity rely on fluorescent aldehyde substrates, which lack specificity, limiting their accuracy and interpretability. Here, we developed a sensitive, cell-based assay that directly quantifies retinaldehyde dehydrogenase activity by measuring a panel of retinoids, including all-trans-retinoic acid, using liquid chromatography-mass spectrometry. Employing cultured conventional dendritic cells, we demonstrate that retinoic acid synthesis is time-, substrate-, and enzyme-dependent. Compared to fluorescence-based assays, our assay avoided artefactual signals influenced by cell density and provided a direct, quantitative measure of enzymatic activity in the context of broader retinoid metabolism. This assay offers additional practical advantages, including flexibility in sample processing and compatibility with other downstream metabolite analyses. Together, our protocol provides a robust, specific, and functionally-relevant approach that complements existing fluorescence-based approaches to study retinoic acid biosynthesis in immune cells and beyond.","PeriodicalId":15140,"journal":{"name":"Journal of Biological Chemistry","volume":"96 1","pages":"111211"},"PeriodicalIF":4.8,"publicationDate":"2026-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146088991","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-28DOI: 10.1016/j.jbc.2026.111217
Drew Barber,Fiona Naughton,Niek van Hilten,Michael Grabe,Aviv Paz
The organic anion transporting polypeptide (OATP)-1B1 and -1B3 are liver-specific transporters that govern the uptake of numerous endogenous molecules and drugs before their metabolism and excretion by the hepatocytes. Structurally, these two transporters are members of the major facilitator superfamily, operating by the alternating access mechanism that facilitates the movement of solutes between extracellular and intracellular compartments. Given their dynamic nature, salt bridges often modulate the conformations of transporters and participate in the orchestration of conformational changes. In this study, we identified and characterized a network of salt bridges within the internal cavities of OATP1B1 and OATP1B3 by cell-based uptake assays, uptake kinetics, and molecular dynamics simulations. These experiments revealed that a salt bridge network centered around E185 is crucial for uptake activities in these two proteins, as it stabilizes the inward cavity of the proteins and bridges the N- and C- bundles of the protein. Interestingly, this salt bridge network changes as a function of conformation. Furthermore, the residues studied do not participate in ligand coordination in the published structures nor in our simulations. These findings advance our understanding of the elaborate network of ionic interactions that govern the structure and dynamics of OATP1B1, OATP1B3, and other MFS transporters.
{"title":"A conserved salt bridge network stabilizes the hepatic organic anion transporters OATP1B1 and OATP1B3.","authors":"Drew Barber,Fiona Naughton,Niek van Hilten,Michael Grabe,Aviv Paz","doi":"10.1016/j.jbc.2026.111217","DOIUrl":"https://doi.org/10.1016/j.jbc.2026.111217","url":null,"abstract":"The organic anion transporting polypeptide (OATP)-1B1 and -1B3 are liver-specific transporters that govern the uptake of numerous endogenous molecules and drugs before their metabolism and excretion by the hepatocytes. Structurally, these two transporters are members of the major facilitator superfamily, operating by the alternating access mechanism that facilitates the movement of solutes between extracellular and intracellular compartments. Given their dynamic nature, salt bridges often modulate the conformations of transporters and participate in the orchestration of conformational changes. In this study, we identified and characterized a network of salt bridges within the internal cavities of OATP1B1 and OATP1B3 by cell-based uptake assays, uptake kinetics, and molecular dynamics simulations. These experiments revealed that a salt bridge network centered around E185 is crucial for uptake activities in these two proteins, as it stabilizes the inward cavity of the proteins and bridges the N- and C- bundles of the protein. Interestingly, this salt bridge network changes as a function of conformation. Furthermore, the residues studied do not participate in ligand coordination in the published structures nor in our simulations. These findings advance our understanding of the elaborate network of ionic interactions that govern the structure and dynamics of OATP1B1, OATP1B3, and other MFS transporters.","PeriodicalId":15140,"journal":{"name":"Journal of Biological Chemistry","volume":"149 1","pages":"111217"},"PeriodicalIF":4.8,"publicationDate":"2026-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146088957","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-28DOI: 10.1016/j.jbc.2026.111210
Rachel M Golonka,Lauren E Intravaia,Ala M Shaqra,Qi Li,Yongzhi Chen,Fiachra Humphries,Nese Kurt-Yilmaz,Kate A Fitzgerald,Celia A Schiffer,Yang Wang,Lisa A Cavacini
The COVID-19 pandemic accelerated the development of monoclonal antibodies (mAb) targeting SARS-CoV-2, with IgG1-based mAbs dominating the therapeutic landscape. However, IgA-the predominant immunoglobulin at mucosal surfaces-represents a promising alternative for respiratory infections due to its natural role in immune exclusion and pathogen neutralization. Here, we engineered IgA-Fc fusion proteins conjugated with nanobodies (VHH-IgA) derived from immunized llamas to neutralize SARS-CoV-2 variants. Phage display libraries generated from Delta and Omicron receptor-binding domain (RBD) immunized llamas yielded 248 unique VHH sequences, with fifty candidates selected based on binding reactivity and neutralization potency. VHH-IgA fusion proteins were expressed in Expi293 cells, and top candidates exhibited high binding affinities (EC50 < 0.2nM) and potent neutralization (IC50 < 40pM) against multiple SARS-CoV-2 variants, including Omicron Ba.1 and XBB. Structural modeling predicted that the leading VHH-IgA candidates 2D4, 1C2, and 2D10 adopt distinct binding conformations to accommodate amino acid sequence variations on the Omicron RBD domain. In vitro assays demonstrated that 2D4, 1C2, and 2D10 neutralized authentic Omicron variants of concern, with 2D4 exhibiting the broadest activity. In vivo, intranasal administration of 2D4 VHH-IgA significantly reduced SARS-CoV-2 XBB viral loads in the lungs of infected K18-hACE2 mice. These findings highlight the therapeutic potential of IgA-based nanobody fusion proteins as mucosal antivirals against SARS-CoV-2. Our work positions VHH-IgA fusion proteins as a platform for developing next-generation biologics to combat respiratory pathogens at mucosal surfaces.
{"title":"Engineered IgA-Fc fusion protein with bioactive nanobody neutralizes SARS-CoV-2 variants with mucosal delivery potential.","authors":"Rachel M Golonka,Lauren E Intravaia,Ala M Shaqra,Qi Li,Yongzhi Chen,Fiachra Humphries,Nese Kurt-Yilmaz,Kate A Fitzgerald,Celia A Schiffer,Yang Wang,Lisa A Cavacini","doi":"10.1016/j.jbc.2026.111210","DOIUrl":"https://doi.org/10.1016/j.jbc.2026.111210","url":null,"abstract":"The COVID-19 pandemic accelerated the development of monoclonal antibodies (mAb) targeting SARS-CoV-2, with IgG1-based mAbs dominating the therapeutic landscape. However, IgA-the predominant immunoglobulin at mucosal surfaces-represents a promising alternative for respiratory infections due to its natural role in immune exclusion and pathogen neutralization. Here, we engineered IgA-Fc fusion proteins conjugated with nanobodies (VHH-IgA) derived from immunized llamas to neutralize SARS-CoV-2 variants. Phage display libraries generated from Delta and Omicron receptor-binding domain (RBD) immunized llamas yielded 248 unique VHH sequences, with fifty candidates selected based on binding reactivity and neutralization potency. VHH-IgA fusion proteins were expressed in Expi293 cells, and top candidates exhibited high binding affinities (EC50 < 0.2nM) and potent neutralization (IC50 < 40pM) against multiple SARS-CoV-2 variants, including Omicron Ba.1 and XBB. Structural modeling predicted that the leading VHH-IgA candidates 2D4, 1C2, and 2D10 adopt distinct binding conformations to accommodate amino acid sequence variations on the Omicron RBD domain. In vitro assays demonstrated that 2D4, 1C2, and 2D10 neutralized authentic Omicron variants of concern, with 2D4 exhibiting the broadest activity. In vivo, intranasal administration of 2D4 VHH-IgA significantly reduced SARS-CoV-2 XBB viral loads in the lungs of infected K18-hACE2 mice. These findings highlight the therapeutic potential of IgA-based nanobody fusion proteins as mucosal antivirals against SARS-CoV-2. Our work positions VHH-IgA fusion proteins as a platform for developing next-generation biologics to combat respiratory pathogens at mucosal surfaces.","PeriodicalId":15140,"journal":{"name":"Journal of Biological Chemistry","volume":"76 1","pages":"111210"},"PeriodicalIF":4.8,"publicationDate":"2026-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146088988","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-28DOI: 10.1016/j.jbc.2026.111139
Herbert Michlmayr,Anastassios C Papageorgiou
{"title":"Author response to \"Commentary on detoxification of deoxynivalenol by pathogen-inducible tau-class glutathione transferases from wheat\" by Dr. Latika Shendre.","authors":"Herbert Michlmayr,Anastassios C Papageorgiou","doi":"10.1016/j.jbc.2026.111139","DOIUrl":"https://doi.org/10.1016/j.jbc.2026.111139","url":null,"abstract":"","PeriodicalId":15140,"journal":{"name":"Journal of Biological Chemistry","volume":"180 1","pages":"111139"},"PeriodicalIF":4.8,"publicationDate":"2026-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146073282","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mammalian cells exploit diverse metabolic pathways to regulate cell fates during glucose deprivation. We previously reported that glucose deprivation lowers the metabolic activity of mannose pathway that is interconnected with glycolysis, leading to biosynthetic arrest and degradation of the glycan precursors for asparagine-linked glycosylation (N-glycosylation) in the endoplasmic reticulum (ER). However, the cellular role of this sequential metabolic response remains unknown, largely due to metabolic complications caused by glucose deprivation. Here, we genetically engineered cells to separate mannose pathway from glycolysis, allowing precise control of mannose pathway activity by adjusting mannose supply levels instead of changing glucose supply. Moderate decrease in mannose supply severely suppressed N-glycosylation, leading to activation of pro-survival PERK-eIF2 signals. Although further decrease in mannose supply to the minimal levels did not compromise cell survival, it depleted luminal protective glycocalyx of lysosomes and increased a risk of cell death by impairing lysosome integrity. These results indicate that low metabolic flux of glucose into mannose pathway initiates alterations in homeostasis of the ER and lysosomes, at least in part through N-glycosylation defects, leading to cell fate decisions.
{"title":"Mannose metabolic pathway senses glucose supply and regulates cell fate decisions.","authors":"Ziwei Wang,Yasuhide Miyamoto,Takehiro Suzuki,Miki Tanaka-Okamoto,Yu Mizote,Naoshi Dohmae,Hideaki Tahara,Naoyuki Taniguchi,Yoichiro Harada","doi":"10.1016/j.jbc.2026.111213","DOIUrl":"https://doi.org/10.1016/j.jbc.2026.111213","url":null,"abstract":"Mammalian cells exploit diverse metabolic pathways to regulate cell fates during glucose deprivation. We previously reported that glucose deprivation lowers the metabolic activity of mannose pathway that is interconnected with glycolysis, leading to biosynthetic arrest and degradation of the glycan precursors for asparagine-linked glycosylation (N-glycosylation) in the endoplasmic reticulum (ER). However, the cellular role of this sequential metabolic response remains unknown, largely due to metabolic complications caused by glucose deprivation. Here, we genetically engineered cells to separate mannose pathway from glycolysis, allowing precise control of mannose pathway activity by adjusting mannose supply levels instead of changing glucose supply. Moderate decrease in mannose supply severely suppressed N-glycosylation, leading to activation of pro-survival PERK-eIF2 signals. Although further decrease in mannose supply to the minimal levels did not compromise cell survival, it depleted luminal protective glycocalyx of lysosomes and increased a risk of cell death by impairing lysosome integrity. These results indicate that low metabolic flux of glucose into mannose pathway initiates alterations in homeostasis of the ER and lysosomes, at least in part through N-glycosylation defects, leading to cell fate decisions.","PeriodicalId":15140,"journal":{"name":"Journal of Biological Chemistry","volume":"1 1","pages":"111213"},"PeriodicalIF":4.8,"publicationDate":"2026-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146088958","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-28DOI: 10.1016/j.jbc.2026.111214
Christopher Dirks,Ann-Kathrin Schlotterbeck,Pontus Pettersson,Axel Leppert,Michael Landreh,Si Min Zhang,Sean G Rudd
SAMHD1 is a deoxyribonucleoside triphosphate (dNTP) hydrolase that controls intracellular dNTP pools and plays diverse roles in human health and disease. Notably, this enzymatic activity also confers chemotherapy resistance by hydrolysing the active triphosphate forms of nucleoside analogue drugs, thereby reducing their efficacy and contributing to worse treatment outcomes in cancer patients. The dNTPase activity of SAMHD1 is tightly regulated by allosteric activation and oligomerisation through binding of (d)NTPs to two allosteric sites, the first of which - allosteric site 1 (AS1) - requires binding of a guanine nucleotide. In the present study, we investigated strategies to pharmacologically modulate SAMHD1 dNTPase activity via AS1. Using a variety of biochemical and biophysical assays, we demonstrate that the antiviral guanine nucleotide analogues acyclovir- and ganciclovir-triphosphate are potent AS1 binders that induce the formation of enzymatically competent SAMHD1 tetramers, however with reduced enzymatic activity. Furthermore, we show that AS1 activator identity can fine-tune dNTPase activity towards different dNTP substrates, providing a new avenue to pharmacologically control SAMHD1. This differential activity of acyclovir- and ganciclovir-triphosphate-activated SAMHD1 can be explained by distinct kinetic profiles that deviate from Michaelis-Menten kinetics. Furthermore, based on an apparent synergistic activation between these nucleotide analogues and the physiological AS1 activator GTP, we also propose the existence of mixed-occupancy SAMHD1 tetramers. Our work therefore provides new insights into the allosteric activation and oligomerisation process of SAMHD1 and opens new avenues to pharmacologically control the dNTPase activity utilising non-natural allosteric ligands.
{"title":"Allosteric targeting with antiviral nucleotide analogues allows fine-tuning of SAMHD1 dNTPase activity.","authors":"Christopher Dirks,Ann-Kathrin Schlotterbeck,Pontus Pettersson,Axel Leppert,Michael Landreh,Si Min Zhang,Sean G Rudd","doi":"10.1016/j.jbc.2026.111214","DOIUrl":"https://doi.org/10.1016/j.jbc.2026.111214","url":null,"abstract":"SAMHD1 is a deoxyribonucleoside triphosphate (dNTP) hydrolase that controls intracellular dNTP pools and plays diverse roles in human health and disease. Notably, this enzymatic activity also confers chemotherapy resistance by hydrolysing the active triphosphate forms of nucleoside analogue drugs, thereby reducing their efficacy and contributing to worse treatment outcomes in cancer patients. The dNTPase activity of SAMHD1 is tightly regulated by allosteric activation and oligomerisation through binding of (d)NTPs to two allosteric sites, the first of which - allosteric site 1 (AS1) - requires binding of a guanine nucleotide. In the present study, we investigated strategies to pharmacologically modulate SAMHD1 dNTPase activity via AS1. Using a variety of biochemical and biophysical assays, we demonstrate that the antiviral guanine nucleotide analogues acyclovir- and ganciclovir-triphosphate are potent AS1 binders that induce the formation of enzymatically competent SAMHD1 tetramers, however with reduced enzymatic activity. Furthermore, we show that AS1 activator identity can fine-tune dNTPase activity towards different dNTP substrates, providing a new avenue to pharmacologically control SAMHD1. This differential activity of acyclovir- and ganciclovir-triphosphate-activated SAMHD1 can be explained by distinct kinetic profiles that deviate from Michaelis-Menten kinetics. Furthermore, based on an apparent synergistic activation between these nucleotide analogues and the physiological AS1 activator GTP, we also propose the existence of mixed-occupancy SAMHD1 tetramers. Our work therefore provides new insights into the allosteric activation and oligomerisation process of SAMHD1 and opens new avenues to pharmacologically control the dNTPase activity utilising non-natural allosteric ligands.","PeriodicalId":15140,"journal":{"name":"Journal of Biological Chemistry","volume":"43 1","pages":"111214"},"PeriodicalIF":4.8,"publicationDate":"2026-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146088954","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-27DOI: 10.1016/j.jbc.2026.111195
Mingkui Wei,Zhiqi Tian,Lei Song,Rongrong Xue,Handong Li,Hong Ji,Jian Sun
Obesity significantly burdens global health. Conversely, some animals efficiently store substantial fat during food abundance while maintaining metabolic health, offering unique insights into mechanisms of healthy adipose expansion. Understanding these short-term physiological adaptations is therefore crucial. Here, using the grass carp (Ctenopharyngodon idellus) as a model, which exhibits remarkable fat storage capacity, we found that adipose tissue responded to energy overload first and expanded through adipocyte hypertrophy and hyperplasia. Mechanistically, hypoxia inducible factor 1αa (HIF1αa) was activated in mature adipocytes after short-term high-energy intake, thereby bidirectionally regulating adipose triglyceride lipase (ATGL) to drive healthy expansion of adipose tissue in grass carp: (1) HIF1αa downregulates ATGL protein levels via the ubiquitin-proteasome pathway, promoting adipocyte hypertrophy; (2) HIF1αa upregulates ATGL transcription to sustain basal lipolysis, releasing free fatty acids that activate peroxisome proliferator-activated receptor γ (PPARγ) in preadipocytes to promote adipocyte hyperplasia. Crucially, unlike obese mice requiring 7 weeks, grass carp exhibited rapid adipocyte hyperplasia. This not only increases the energy storage limit but also prevents excessive hypertrophy of adipocytes. Taken together, our study reveals how grass carp utilizes hypoxia signal (a signal often associated with metabolic disorders in mammals) to coordinate the pattern of adipose tissue expansion, achieving rapid and healthy lipid storage. Our findings redefine hypoxia's role as a metabolic orchestrator rather than a stress indicator, providing a theoretical basis for addressing obesity-related diseases in humans caused by excessive energy intake.
{"title":"Hypoxia-Inducible Factor 1αa Regulates Lipid Metabolism to Coordinate Adipocyte Hypertrophy and Hyperplasia in Grass Carp.","authors":"Mingkui Wei,Zhiqi Tian,Lei Song,Rongrong Xue,Handong Li,Hong Ji,Jian Sun","doi":"10.1016/j.jbc.2026.111195","DOIUrl":"https://doi.org/10.1016/j.jbc.2026.111195","url":null,"abstract":"Obesity significantly burdens global health. Conversely, some animals efficiently store substantial fat during food abundance while maintaining metabolic health, offering unique insights into mechanisms of healthy adipose expansion. Understanding these short-term physiological adaptations is therefore crucial. Here, using the grass carp (Ctenopharyngodon idellus) as a model, which exhibits remarkable fat storage capacity, we found that adipose tissue responded to energy overload first and expanded through adipocyte hypertrophy and hyperplasia. Mechanistically, hypoxia inducible factor 1αa (HIF1αa) was activated in mature adipocytes after short-term high-energy intake, thereby bidirectionally regulating adipose triglyceride lipase (ATGL) to drive healthy expansion of adipose tissue in grass carp: (1) HIF1αa downregulates ATGL protein levels via the ubiquitin-proteasome pathway, promoting adipocyte hypertrophy; (2) HIF1αa upregulates ATGL transcription to sustain basal lipolysis, releasing free fatty acids that activate peroxisome proliferator-activated receptor γ (PPARγ) in preadipocytes to promote adipocyte hyperplasia. Crucially, unlike obese mice requiring 7 weeks, grass carp exhibited rapid adipocyte hyperplasia. This not only increases the energy storage limit but also prevents excessive hypertrophy of adipocytes. Taken together, our study reveals how grass carp utilizes hypoxia signal (a signal often associated with metabolic disorders in mammals) to coordinate the pattern of adipose tissue expansion, achieving rapid and healthy lipid storage. Our findings redefine hypoxia's role as a metabolic orchestrator rather than a stress indicator, providing a theoretical basis for addressing obesity-related diseases in humans caused by excessive energy intake.","PeriodicalId":15140,"journal":{"name":"Journal of Biological Chemistry","volume":"93 1","pages":"111195"},"PeriodicalIF":4.8,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146073280","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-23DOI: 10.1016/j.jbc.2026.111190
Huaping Qin,Lennis B Orduña-Castillo,Olivia Molinar-Inglis,Monica L Gonzalez Ramirez,Miguel A Lopez-Ramirez,Carolyne Bardeleben,JoAnn Trejo
G protein-coupled receptors (GPCRs) display bias towards either G proteins or GPCR kinase (GRK)-mediated β-arrestin signaling depending on the agonist stabilized receptor conformation. The cellular context and subcellular location of GPCRs can also influence biased signaling through mechanisms that are not well understood. The protease-activated receptor-1 (PAR1) exhibits signaling bias in response to thrombin and activated protein C (APC). APC-induced β-arrestin-2 (βarr2) biased signaling requires PAR1 compartmentalization in caveolae, a subtype of lipid rafts, whereas thrombin-activated PAR1 G protein signaling does not. Caveolin-1 (Cav1) is the principal structural component of caveolae and regulates protein-protein interactions. The mechanisms by which Cav1 contributes to APC/PAR1-induced βarr2 biased signaling are not known. Here we report that a substantial population of endogenous PAR1 colocalizes with Cav1 in endothelial cells and is modulated by APC assessed by single molecule super-resolution stochastic optical reconstruction microscopy imaging. APC activation of PAR1 also induces Cav1 tyrosine-14 phosphorylation through a βarr2- and c-Src-dependent pathway, which disrupts PAR1-Cav1 co-association. A smaller population of endogenous GRK5 was also found to colocalize with Cav1 in endothelial cells and was modestly altered by APC-activation of PAR1. Moreover, GRK5 was found to interact with Cav1 in intact cells through an N-terminal aromatic-rich Cav1 binding motif. Mutation of this motif disrupts GRK5-Cav1 binding, shifts GRK5 predominantly to the cytoplasm rather than the plasma membrane and perturbs GRK5-mediated βarr2 recruitment to APC-activated PAR1. Thus, beyond its structural function, Cav1 participates in protein-protein interactions with PAR1 and GRK5, two key effectors that enable APC-induced βarr2 signaling.
{"title":"Activated protein C drives β-arrestin-2- and c-Src-dependent phosphorylation of Cav1 and modulates Cav1 association with PAR1 and GRK5.","authors":"Huaping Qin,Lennis B Orduña-Castillo,Olivia Molinar-Inglis,Monica L Gonzalez Ramirez,Miguel A Lopez-Ramirez,Carolyne Bardeleben,JoAnn Trejo","doi":"10.1016/j.jbc.2026.111190","DOIUrl":"https://doi.org/10.1016/j.jbc.2026.111190","url":null,"abstract":"G protein-coupled receptors (GPCRs) display bias towards either G proteins or GPCR kinase (GRK)-mediated β-arrestin signaling depending on the agonist stabilized receptor conformation. The cellular context and subcellular location of GPCRs can also influence biased signaling through mechanisms that are not well understood. The protease-activated receptor-1 (PAR1) exhibits signaling bias in response to thrombin and activated protein C (APC). APC-induced β-arrestin-2 (βarr2) biased signaling requires PAR1 compartmentalization in caveolae, a subtype of lipid rafts, whereas thrombin-activated PAR1 G protein signaling does not. Caveolin-1 (Cav1) is the principal structural component of caveolae and regulates protein-protein interactions. The mechanisms by which Cav1 contributes to APC/PAR1-induced βarr2 biased signaling are not known. Here we report that a substantial population of endogenous PAR1 colocalizes with Cav1 in endothelial cells and is modulated by APC assessed by single molecule super-resolution stochastic optical reconstruction microscopy imaging. APC activation of PAR1 also induces Cav1 tyrosine-14 phosphorylation through a βarr2- and c-Src-dependent pathway, which disrupts PAR1-Cav1 co-association. A smaller population of endogenous GRK5 was also found to colocalize with Cav1 in endothelial cells and was modestly altered by APC-activation of PAR1. Moreover, GRK5 was found to interact with Cav1 in intact cells through an N-terminal aromatic-rich Cav1 binding motif. Mutation of this motif disrupts GRK5-Cav1 binding, shifts GRK5 predominantly to the cytoplasm rather than the plasma membrane and perturbs GRK5-mediated βarr2 recruitment to APC-activated PAR1. Thus, beyond its structural function, Cav1 participates in protein-protein interactions with PAR1 and GRK5, two key effectors that enable APC-induced βarr2 signaling.","PeriodicalId":15140,"journal":{"name":"Journal of Biological Chemistry","volume":"40 1","pages":"111190"},"PeriodicalIF":4.8,"publicationDate":"2026-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146044545","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-23DOI: 10.1016/j.jbc.2026.111202
Lixia Hu,Hao Zhang,Ao Xiao,Haiwen Qiu,Xinxin Meng,Yi You,Mingxiao Wang
Endothelin-1 (ET-1) from renal-tubule-epithelial-cells inhibits NaCl reabsorption via ETB receptor in an autocrine manner and inhibition of ETB receptors leads to salt-sensitive-hypertension. In the distal-convoluted-tubule (DCT), NaCl enters the cell via NaCl-cotransporter (NCC) and Cl- exits the cell in part by ClC-K2 channels, which plays a role in regulating With-No-lysine kinase 4 (WNK4). The aim of the study is to explore whether ET-1-induced inhibition of NaCl absorption is also achieved by inhibiting the basolateral Cl- channels in the DCT. Patch-clamp and immunoblotting assessed ET-1 effects on DCT Cl- channels and NCC. Immunofluoresence images detected ETB-receptor was expressed in parvalbumin-positive DCT. Application of ET-1 decreased NPPB-sensitive Cl- currents and reduced 10-pS Cl- channel activity (ClC-K2), defined by NPo (A product of channel number and open probability), an effect was absent in the presence of ETB receptor-inhibitor. Application of L-NAME (nitric oxyside sunthase inhibitor), ODQ (soluable guanisine cyclase inhibitor) or Bay-60-7550 (phosphadiesterase-2-inhibitor) per-se had no effect on Cl- channels, but it abolished inhibitory effect of ET-1. In contrast, application of NO-donor or cGMP inhibited ClC-K2 channel activity of the DCT. Moreover, ET-1 had no additional inhibitory effect of ET-1 on ClC-K2 in the presence of NO-donor or cGMP. Immunoblotting demonstrated that ET-1 treatment (200 nM) of renal cortex decreased NCC phosphorylation and total NCC expression, an effect was abolished by inhibiting phosphadiesterase-2 but not by KT-5823 (PKG-inhibitor). In conclusion, ET-1 inhibits NCC and ClC-K2 in DCT by NO-sGMP-phosphadiesterase-2 dependent-pathway.
{"title":"Nitric Oxide Mediates ET-1-induced-Inhibition of NPPB-Sensitive Cl- Currents in Early Distal Convoluted Tubule of the Mouse Kidney.","authors":"Lixia Hu,Hao Zhang,Ao Xiao,Haiwen Qiu,Xinxin Meng,Yi You,Mingxiao Wang","doi":"10.1016/j.jbc.2026.111202","DOIUrl":"https://doi.org/10.1016/j.jbc.2026.111202","url":null,"abstract":"Endothelin-1 (ET-1) from renal-tubule-epithelial-cells inhibits NaCl reabsorption via ETB receptor in an autocrine manner and inhibition of ETB receptors leads to salt-sensitive-hypertension. In the distal-convoluted-tubule (DCT), NaCl enters the cell via NaCl-cotransporter (NCC) and Cl- exits the cell in part by ClC-K2 channels, which plays a role in regulating With-No-lysine kinase 4 (WNK4). The aim of the study is to explore whether ET-1-induced inhibition of NaCl absorption is also achieved by inhibiting the basolateral Cl- channels in the DCT. Patch-clamp and immunoblotting assessed ET-1 effects on DCT Cl- channels and NCC. Immunofluoresence images detected ETB-receptor was expressed in parvalbumin-positive DCT. Application of ET-1 decreased NPPB-sensitive Cl- currents and reduced 10-pS Cl- channel activity (ClC-K2), defined by NPo (A product of channel number and open probability), an effect was absent in the presence of ETB receptor-inhibitor. Application of L-NAME (nitric oxyside sunthase inhibitor), ODQ (soluable guanisine cyclase inhibitor) or Bay-60-7550 (phosphadiesterase-2-inhibitor) per-se had no effect on Cl- channels, but it abolished inhibitory effect of ET-1. In contrast, application of NO-donor or cGMP inhibited ClC-K2 channel activity of the DCT. Moreover, ET-1 had no additional inhibitory effect of ET-1 on ClC-K2 in the presence of NO-donor or cGMP. Immunoblotting demonstrated that ET-1 treatment (200 nM) of renal cortex decreased NCC phosphorylation and total NCC expression, an effect was abolished by inhibiting phosphadiesterase-2 but not by KT-5823 (PKG-inhibitor). In conclusion, ET-1 inhibits NCC and ClC-K2 in DCT by NO-sGMP-phosphadiesterase-2 dependent-pathway.","PeriodicalId":15140,"journal":{"name":"Journal of Biological Chemistry","volume":"50 1","pages":"111202"},"PeriodicalIF":4.8,"publicationDate":"2026-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146044706","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：