In situ visualization and detection of protein sulfenylation responses in living cells through a dimedone-based fluorescent probe

Oxidative stress-mediated protein sulfenylation in human diseases: Past, present, and future

Reactive Oxygen Species (ROS) refer to a variety of derivatives of molecular oxygen that play crucial roles in regulating a wide range of physiological and pathological processes. Excessive ROS levels can cause oxidative stress, leading to cellular damage and even cell demise. However, moderately elevated levels of ROS can mediate the oxidative post-translational modifications (oxPTMs) of redox-sensitive proteins, thereby affecting protein functions and regulating various cellular signaling pathways. Among the oxPTMs, ROS-induced reversible protein sulfenylation represents the initial form of cysteine oxidation for sensing redox signaling. In this review, we will summarize the discovery, chemical formation, and detection approaches of protein sulfenylation. In addition, we will highlight recent findings for the roles of protein sulfenylation in various diseases, including thrombotic disorders, diabetes, cardiovascular diseases, neurodegenerative diseases, and cancer.

Reactive Oxygen Species Induced p53 Activation: DNA Damage, Redox Signaling, or Both?

Significance: The p53 tumor suppressor has been dubbed the "guardian of genome" because of its various roles in the response to DNA damage such as DNA damage repair, cell cycle arrest, senescence, and apoptosis, all of which are in place to prevent mutations from being passed on down the lineage. Recent Advances: Reactive oxygen species (ROS), for instance hydrogen peroxide derived from mitochondrial respiration, have long been regarded mainly as a major source of cellular damage to DNA and other macromolecules. Critical Issues: More recently, ROS have been shown to also play important physiological roles as second messengers in so-called redox signaling. It is, therefore, not clear whether the observed activation of p53 by ROS is mediated through the DNA damage response, redox signaling, or both. In this review, we will discuss the similarities and differences between p53 activation in response to DNA damage and redox signaling in terms of upstream signaling and downstream transcriptional program activation. Future Directions: Understanding whether and how DNA damage and redox signaling-dependent p53 activation can be dissected could be useful to develop anti-cancer therapeutic p53-reactivation strategies that do not depend on the induction of DNA damage and the resulting additional mutational load.

Adenine-based small molecule fluorescent probe for imaging mitochondrial nucleic acid

A small molecule fluorescent probe (probe 1) based on adenine-coumarin derivative was designed and synthesized in this paper. Probe 1 exhibited a significant fluorescence-enhancing response to nucleic acids at 495 nm (for DNA) and 487 nm (for RNA). The fluorescence enhancement of probe 1 for DNA and RNA was 5.68 and 9.73 times respectively, the fluorescence quantum yield was changed from 2.5% to 11.7% and 22.5% accordingly. Meanwhile, an excellent linear relationship of fluorescence intensity at 495 nm or 487 nm versus the nucleic acid concentration (1 μM for probe 1, 0-350 μg/mL for DNA and 0-300 μg/mL for RNA) was obtained. Co-staining and nucleic acid digestion experiments showed that probe 1 could selectively image nucleic acids in mitochondria and nucleoli in HeLa cells.

Mitochondria-targeted Probes for Imaging Protein Sulfenylation

Mitochondrial reactive oxygen species (ROS) are essential regulators of cellular signaling, metabolism and epigenetics underlying the pathophysiology of numerous diseases. Despite the critical function of redox regulation in mitochondria, currently there are limited methods available to monitor protein oxidation in this key subcellular organelle. Here, we describe compounds for imaging sulfenylated proteins in mitochondria: DCP-NEt₂-Coumarin (DCP-NEt₂C) and rhodamine-based DCP-Rho1. Side-by-side comparison studies are presented on the reactivity of DCP-NEt₂C and DCP-Rho1 with a model protein sulfenic acid (AhpC-SOH) and mitochondrial localization to identify optimized experimental conditions for labeling and visualization of protein sulfenylation that would be independent of mitochondria membrane potential and would not impact mitochondrial function. These probes are applied to image mitochondrial protein sulfenylation under conditions of serum starvation and in a cell culture model of lung cancer exposed to ionizing radiation and silver nanoparticles, agents serving dual functions as environmental stressors and cancer therapeutics.

Chemoselective ratiometric imaging of protein S-sulfenylation

Here we report a ratiometric fluorescent probe for chemoselective conjugation to sulfenic acids in living cells. Our approach couples an α-fluoro-substituted dimedone to an aminonaphthalene fluorophore (F-DiNap), which upon sulfenic acid conjugation is locked as the 1,3-diketone, changing the fluorophore excitation. F-DiNap reacts with S-sulfenylated proteins at equivalent rates to current probes, but the α-fluorine substitution blocks side-reactions with biological aldehydes.

Live-cell imaging approaches for the investigation of xenobiotic-induced oxidant stress

BACKGROUND

Oxidant stress is arguably a universal feature in toxicology. Research studies on the role of oxidant stress induced by xenobiotic exposures have typically relied on the identification of damaged biomolecules using a variety of conventional biochemical and molecular techniques. However, there is increasing evidence that low-level exposure to a variety of toxicants dysregulates cellular physiology by interfering with redox-dependent processes.

SCOPE OF REVIEW

The study of events involved in redox toxicology requires methodology capable of detecting transient modifications at relatively low signal strength. This article reviews the advantages of live-cell imaging for redox toxicology studies.

MAJOR CONCLUSIONS

Toxicological studies with xenobiotics of supra-physiological reactivity require careful consideration when using fluorogenic sensors in order to avoid potential artifacts and false negatives. Fortunately, experiments conducted for the purpose of validating the use of these sensors in toxicological applications often yield unexpected insights into the mechanisms through which xenobiotic exposure induces oxidant stress.

GENERAL SIGNIFICANCE

Live-cell imaging using a new generation of small molecule and genetically encoded fluorophores with excellent sensitivity and specificity affords unprecedented spatiotemporal resolution that is optimal for redox toxicology studies. This article is part of a Special Issue entitled Air Pollution, edited by Wenjun Ding, Andrew J. Ghio and Weidong Wu.

T cells and reactive oxygen species

Reactive oxygen species (ROS) have been long considered simply as harmful by-products of metabolism, which damage cellular proteins, lipids, and nucleic acids. ROS are also known as a weapon of phagocytes, employed against pathogens invading the host. However, during the last decade, an understanding has emerged that ROS also have important roles as signaling messengers in a multitude of pathways, in all cells, tissues, and organs. T lymphocytes are the key players of the adaptive immune response, which both coordinate other immune cells and destroy malignant and virus-infected cells. ROS have been extensively implicated in T-cell hyporesponsiveness, apoptosis, and activation. It has also become evident that the source, the kinetics, and the localization of ROS production all influence cell responses. Thus, the characterization of the precise mechanisms by which ROS are involved in the regulation of T-cell functions is important for our understanding of the immune response and for the development of new therapeutic treatments against immune-mediated diseases. This review summarizes the 30-year-long history of research on ROS in T lymphocytes, with the emphasis on the physiological roles of ROS.

Cysteine sulfur chemistry in transcriptional regulators at the host-bacterial pathogen interface

Hosts employ myriad weapons to combat invading microorganisms as an integral feature of the host-bacterial pathogen interface. This interface is dominated by highly reactive small molecules that collectively induce oxidative stress. Successful pathogens employ transcriptional regulatory proteins that sense these small molecules directly or indirectly via a change in the ratio of reduced to oxidized low-molecular weight (LMW) thiols that collectively comprise the redox buffer in the cytoplasm. These transcriptional regulators employ either a prosthetic group or reactive cysteine residue(s) to effect changes in the transcription of genes that encode detoxification and repair systems that is driven by regulator conformational switching between high-affinity and low-affinity DNA-binding states. Cysteine harbors a highly polarizable sulfur atom that readily undergoes changes in oxidation state in response to oxidative stress to produce a range of regulatory post-translational modifications (PTMs), including sulfenylation (S-hydroxylation), mixed disulfide bond formation with LMW thiols (S-thiolation), di- and trisulfide bond formation, S-nitrosation, and S-alkylation. Here we discuss several examples of structurally characterized cysteine thiol-specific transcriptional regulators that sense changes in cellular redox balance, focusing on the nature of the cysteine PTM itself and the interplay of small molecule oxidative stressors in mediating a specific transcriptional response.

Highly efficient detection of hydrogen peroxide in solution and in the vapor phase via fluorescence quenching

Herein we report the highly efficient and sensitive detection of hydrogen peroxide in both aqueous solution and in the vapor phase via fluorescence quenching (turn-off mechanism) of the amplified fluorescent conjugated polymer-titanium complex induced by hydrogen peroxide. Inter- and intra-polymer energy migration leads to extremely high sensitivity.