The effect of reactive oxygen and nitrogen species on the structure of cytoglobin: A potential tumor suppressor

Abstract

Many current anti-cancer therapies rely on increasing the intracellular reactive oxygen and nitrogen species (RONS) contents with the aim to induce irreparable damage, which subsequently results in tumor cell death. A novel tool in cancer therapy is the use of cold atmospheric plasma (CAP), which has been found to be very effective in the treatment of many different cancer cell types in vitro as well as in vivo, mainly through the vast generation of RONS. One of the key determinants of the cell's fate will be the interaction of RONS, generated by CAP, with important proteins, i.e. redox-regulatory proteins. One such protein is cytoglobin (CYGB), a recently discovered globin proposed to be involved in the protection of the cell against oxidative stress. In this study, the effect of plasma-produced RONS on CYGB was investigated through the treatment of CYGB with CAP for different treatment times. Spectroscopic analysis of CYGB showed that although chemical modifications occur, its secondary structure remains intact. Mass spectrometry experiments identified these modifications as oxidations of mainly sulfur-containing and aromatic amino acids. With longer treatment time, the treatment was also found to induce nitration of the heme. Furthermore, the two surface-exposed cysteine residues of CYGB were oxidized upon treatment, leading to the formation of intermolecular disulfide bridges, and potentially also intramolecular disulfide bridges. In addition, molecular dynamics and docking simulations confirmed, and further show, that the formation of an intramolecular disulfide bond, due to oxidative conditions, affects the CYGB 3D structure, thereby opening the access to the heme group, through gate functioning of His117. Altogether, the results obtained in this study (1) show that plasma-produced RONS can extensively oxidize proteins and (2) that the oxidation status of two redox-active cysteines lead to different conformations of CYGB.

Cytoglobin Attenuates Neuroinflammation in Lipopolysaccharide-Activated Primary Preoptic Area Cells via NF-κB Pathway Inhibition

“…Systemic exposure to insults, such as toxins or bacterial infection, triggers an inflammatory response associated with the release of inflammatory mediators, such as free radicals, cytokines, and chemokines (Milatovic et al, 2017). As a NO scavenger, Cygb has been reported as an anti-inflammatory and antitumor agent (De Backer et al, 2018;Yassin et al, 2018). Ou et al (2018) showed that Cygb prevents atherosclerosis by functioning as an NO dioxygenase enzyme and ROS scavenger, favoring the protection of the body against unbalanced homeostasis.…”

Cytoglobin ameliorates the stemness of hepatocellular carcinoma via coupling oxidative‐nitrosative stress signals

“…However, the anti‐tumor mechanisms are complex and not clear. Cygb performs the activities of peroxidase and nitric oxide dioxygenase (NOD) at O2‐dependent manner . In this study, we observed that Cygb consumes intracellular ROS/RNS and NO storage (Figures A and C), whereas Cygb knockdown aggravates intracellular ROS/RNS and NO accumulation (Figures B and D).…”

“…Cygb performs the activities of peroxidase and nitric oxide dioxygenase (NOD) at O2-dependent manner. 12,14,33,34 In this study, we observed that Cygb consumes Thus we proposed that Cygb-mediated ONS control may be a crucial mechanism that determines the function of six-coordinated hemoglobin as tumor suppressors against HCC tumorigenesis and progression.…”

“…It is a dynamic mediator in the maintenance of redox homeostasis and performs the activities of peroxidase and nitric oxide dioxygenase (NOD), which catalyzes nitric oxide (NO) or nitrite to nitrate in rat hepatocytes. [11][12][13][14] Emerging evidences indicated that Cygb is negatively associated with liver fibrosis and HCC tumorigenesis via regulating oxidative stress pathways. [15][16][17][18][19] Cygb absence accounts for a high incidence of multiple malignancies including liver, lung and colon cancer and lymphoma in aged Cygb −/− mice, compared with wide-type mice.…”

“…Cytoglobin is a ubiquitously expressed hexacoordinate hemoglobin. It is a dynamic mediator in the maintenance of redox homeostasis and performs the activities of peroxidase and nitric oxide dioxygenase (NOD), which catalyzes nitric oxide (NO) or nitrite to nitrate in rat hepatocytes . Emerging evidences indicated that Cygb is negatively associated with liver fibrosis and HCC tumorigenesis via regulating oxidative stress pathways .…”