Biology subjects

Hanna, D. A.

Publications and source records attributed to Hanna, D. A..

8 recordsLinked to original sources

bioRxiv2026

Hydrogen sulfide dynamically upregulates copper uptake and localization

The reactivity of copper, an essential micronutrient that undergoes facile cycling between Cu1+ and Cu2+ redox states, is carefully controlled within the confines of protein binding sites, and by sequestration in storage vesicles, or harnessed to kill pathogens by active pumping of Cu1+ into phagosomes. We have discovered that hydrogen sulfide, a signaling metabolite generated in copious quantities at the host-microbiome interface, upregulates Cu accumulation in diffusely dispersed puncta across the cell, as visualized by X-ray fluorescence microscopy. The Cu is predominantly in the Cu2+ state with oxygen/nitrogen ligands. Cu import occurs via the non- canonical ZNT1 transporter, while export, following sulfide withdrawal, is ATP7A-dependent. Cu accumulates at the apices of colon crypts in a mouse model of elevated sulfide exposure due to SQOR deficiency in the intestinal epithelium, establishing in vivo relevance. Our study reveals that sulfide is a dynamic regulator of the Cu pool, stimulating Cu2+ influx into highly concentrated puncta.

cell biology↗

bioRxiv2025

Iron addicted colorectal cancers exploit Heme-Complex II axis to resist oxidative cell death

Colorectal cancer (CRC) cells are addicted to iron, which fuels nucleotide synthesis, mitochondrial respiration, and rapid proliferation. Yet paradoxically, high intracellular iron is cytotoxic to most other cells, raising the question of how CRC cells tolerate and exploit iron-rich environments. One pathway thought to mediate iron toxicity is ferroptosis, an iron-dependent form of cell death. However, most ferroptosis regulators were identified through synthetic chemical screens or small molecule activators, and it remains unclear whether these canonical pathways explain how iron itself triggers cell death, particularly in vivo. Here, using multi-omics profiling, CRISPR screening, and in vivo models, we uncover a heme-succinate dehydrogenase (SDH)-Coenzyme Q (CoQ) axis that enables CRC cells to buffer iron-induced oxidative stress. Heme-dependent SDH reduces CoQ, which redistributes to mitochondrial and plasma membranes to detoxify lipid ROS as a radical trapping antioxidant. This pathway functions alongside, and in some contexts independently of, canonical ferroptosis regulators. These findings reveal that CRCs co-opt metabolic cofactors not only for growth but also for survival under physiologically toxic iron levels, uncovering new vulnerabilities for therapy.

cancer biology↗

bioRxiv2025

Hydrogen sulfide increases intracellular oxygen and regulates the HIF response

O2 sensing by hypoxia-inducible factor (HIF) is a principal mechanism by which aerobic organisms adjust cellular energy metabolism and adapt to O2 limitation. In this study, we show that H2S, a product of host and microbial metabolism, profoundly influences the threshold for HIF-dependent hypoxia-sensing by increasing intracellular O2. The dose-dependent destabilization of HIF by H2S is inversely correlated with sulfide quinone oxidoreductase, which oxidizes sulfide in the mitochondrion. Hypoxia sensors provide a quantitative estimate of the magnitude of H2S-induced perturbation. The O2 concentration in cells grown in a 2% O2 atmosphere is sensed as 5 or 15 % O2 in the presence of 25 or 100 ppm H2S, respectively. Sustained exposure to H2S elicits the hallmarks of hyperoxia-associated cytotoxicity, including loss of Fe-S proteins in cellular and murine models. H2S thus emerges as a powerful regulator of O2 sensing and signaling with possible implications for dysregulation in O2 toxicity diseases. Significance StatementThe mitochondrial electron transport chain (ETC) accounts for [~]90% of whole body O2 consumption. However, our understanding of how metabolites modify ETC flux and therefore, intracellular O2 availability, are poor. In this study, we demonstrate that hydrogen sulfide (H2S), which is produced by host and gut microbes alike, increases intracellular O2 by decreasing ETC flux, and destabilizes the principal hypoxia sensor, HIF-1. The upshift in intracellular O2 levels is quantitatively significant, such that 2% O2 is sensed as 5-15% O2 at varying H2S concentrations, with concomitant destabilization of Fe-S proteins, a signature of cellular hyperoxia. Our study identifies H2S as a HIF-1 regulator with important implications for the large class of mitochondrial diseases characterized by dysregulated O2 metabolism.

cell biology↗

bioRxiv2024

H2S remodels mitochondrial ultrastructure and destabilizes respiratory supercomplexes

Mitochondrial form and function are intimately interconnected, responding to cellular stresses and changes in energy demand. Hydrogen sulfide, a product of amino acid metabolism, has dual roles as an electron transport chain substrate and complex IV (CIV) inhibitor, leading to a reductive shift, which has pleiotropic metabolic consequences. Luminal sulfide concentration in colon is high due to microbial activity, and in this study, we demonstrate that chronic sulfide exposure of colonocyte-derived cells leads to lower Mic60 and Mic19 expression that is correlated with a profound loss of cristae and lower mitochondrial networking. Sulfide-induced depolarization of the inner mitochondrial membrane activates Oma1-dependent cleavage of Opa1 and is associated with a profound loss of CI and CIV activities associated with respirasomes. Our study reveals a potential role for sulfide as an endogenous modulator of mitochondrial dynamics and suggests that this regulation is corrupted in hereditary or acquired diseases associated with elevated sulfide. Significance StatementHydrogen sulfide is a product of host as well as gut microbial metabolism and has the dual capacity for activating respiration as a substrate, and inhibiting it at the level of complex IV. In this study, we report that chronic albeit low-level sulfide exposure elicits profound changes in mitochondrial architecture in cultured human cells. Disruption of mitochondrial networks is reversed upon removal of sulfide from the growth chamber atmosphere. Sulfide-dependent depolarization of the inner mitochondrial membrane is associated with loss of cristae and respiratory supercomplexes. Our study reveals the potential for sulfide to be an endogenous regulator of mitochondrial ultrastructure and function via modulation of electron flux and for this process to be corrupted in sulfide dysregulated diseases.

cell biology↗

bioRxiv2024

BRD4-mediated epigenetic regulation of endoplasmic reticulum-mitochondria contact sites is governed by the mitochondrial complex III

Inter-organellar communication is critical for cellular metabolic homeostasis. One of the most abundant inter-organellar interactions are those at the endoplasmic reticulum and mitochondria contact sites (ERMCS). However, a detailed understanding of the mechanisms governing ERMCS regulation and their roles in cellular metabolism are limited by a lack of tools that permit temporal induction and reversal. Through unbiased screening approaches, we identified fedratinib, an FDA-approved drug, that dramatically increases ERMCS abundance by inhibiting the epigenetic modifier BRD4. Fedratinib rapidly and reversibly modulates mitochondrial and ER morphology and alters metabolic homeostasis. Moreover, ERMCS modulation depends on mitochondria electron transport chain complex III function. Comparison of fedratinib activity to other reported inducers of ERMCS revealed common mechanisms of induction and function, providing clarity and union to a growing body of experimental observations. In total, our results uncovered a novel epigenetic signaling pathway and an endogenous metabolic regulator that connects ERMCS and cellular metabolism.

cell biology↗

bioRxiv2023

H2S preconditioning induces long-lived perturbations in O2 metabolism

Hydrogen sulfide exposure in moderate doses can induce profound but reversible hypometabolism in mammals. At a cellular level, H2S inhibits the electron transport chain (ETC), augments aerobic glycolysis, and glutamine-dependent carbon utilization via reductive carboxylation; however, the durability of these changes is unknown. We report that despite its volatility, H2S preconditioning increases P50(O2), the O2 pressure for half maximal cellular respiration, and has pleiotropic effects on oxidative metabolism that persist up to 24-48 h later. Notably, cyanide, another complex IV inhibitor, does not induce this type of metabolic memory. Sulfide-mediated prolonged fractional inhibition of complex IV by H2S is modulated by sulfide quinone oxidoreductase, which commits sulfide to oxidative catabolism. Since induced hypometabolism can be beneficial in disease settings that involve insufficient or interrupted blood flow, our study has important implications for attenuating reperfusion-induced ischemic injury, and/or prolonging shelf life of biologics like platelets.

biochemistry↗

bioRxiv2022

Depletion Assisted Hemin Affinity (DAsHA) Proteomics Reveals an Expanded Landscape of Heme Binding Proteins

Heme b (iron protoporphyrin IX) plays important roles in biology as a metallocofactor and signaling molecule. However, the targets of heme signaling and the network of proteins that mediate the exchange of heme from sites of synthesis or uptake to heme dependent or regulated proteins are poorly understood. Herein, we describe a quantitative mass spectrometry-based chemoproteomics strategy to identify exchange labile hemoproteins in human embryonic kidney HEK293 cells that may be relevant to heme signaling and trafficking. The strategy involves depleting endogenous heme with the heme biosynthetic inhibitor succinylacetone (SA), leaving putative heme binding proteins in their apo-state, followed by the capture of those proteins using hemin-agarose resin and finally elution and identification by mass spectrometry. By identifying only those proteins that interact with high specificity to hemin-agarose relative to control beaded agarose in a SA-dependent manner, we have expanded the number of proteins and ontologies that may be involved in binding and buffering labile heme or are targets of heme signaling. Notably, these include proteins involved in chromatin remodeling, DNA damage response, RNA splicing, cytoskeletal organization and vesicular trafficking, many of which have been associated with heme through complimentary studies published recently. Taken together, these results provide support for the emerging role for heme in an expanded set of cellular processes from genome integrity to protein trafficking and beyond.

biochemistry↗

bioRxiv2021

Heme oxygenase-2 (HO-2) binds and buffers labile heme, which is largely oxidized, in human embryonic kidney cells

Heme oxygenases (HO) detoxify heme by oxidatively degrading it into carbon monoxide, iron, and biliverdin, which is reduced to bilirubin and excreted. Humans express two isoforms: inducible HO-1, which is up-regulated in response to various stressors, including excess heme, and constitutive HO-2. While much is known about the regulation and physiological function of HO-1, comparatively little is known about the role of HO-2 in regulating heme homeostasis. The biochemical necessity for expressing constitutive HO-2 is largely dependent on whether heme is sufficiently abundant and accessible as a substrate under conditions in which HO-1 is not induced. By measuring labile heme, total heme, and bilirubin in human embryonic kidney HEK293 cells with silenced or over-expressed HO-2, and various HO-2 mutant alleles, we found that endogenous heme is too limiting to support HO-2 catalyzed heme degradation. Rather, we discovered that a novel role for HO-2 is to bind and buffer labile heme. Taken together, in the absence of excess heme, we propose that HO-2 regulates heme homeostasis by acting as a heme buffering factor in control of heme bioavailability. When heme is in excess, HO-1 is induced and both HO-2 and HO-1 can provide protection from heme toxicity by enzymatically degrading it. Our results explain why catalytically inactive mutants of HO-2 are cytoprotective against oxidative stress. Moreover, the change in bioavailable heme due to HO-2 overexpression, which selectively binds ferric over ferrous heme, is consistent with the labile heme pool being oxidized, thereby providing new insights into heme trafficking and signaling.

cell biology↗