Redox Regulation of Nonmuscle Myosin Heavy Chain during Integrin Engagement

The role of reactive oxygen species in the regulation of the blood-brain barrier

The blood-brain barrier (BBB) regulates the exchange of metabolites and cells between the blood and brain, and maintains central nervous system homeostasis. Various factors affect BBB barrier functions, including reactive oxygen species (ROS). ROS can act as stressors, damaging biological molecules, but they also serve as secondary messengers in intracellular signaling cascades during redox signaling. The impact of ROS on the BBB has been observed in multiple sclerosis, stroke, trauma, and other neurological disorders, making blocking ROS generation a promising therapeutic strategy for BBB dysfunction. However, it is important to consider ROS generation during normal BBB functioning for signaling purposes. This review summarizes data on proteins expressed by BBB cells that can be targets of redox signaling or oxidative stress. It also provides examples of signaling molecules whose impact may cause ROS generation in the BBB, as well as discusses the most common diseases associated with BBB dysfunction and excessive ROS generation, open questions that arise in the study of this problem, and possible ways to overcome them.

LRRC8A anion channels modulate vascular reactivity via association with myosin phosphatase rho interacting protein

Leucine-rich repeat containing 8A (LRRC8A) volume regulated anion channels (VRACs) are activated by inflammatory and pro-contractile stimuli including tumor necrosis factor alpha (TNFα), angiotensin II and stretch. LRRC8A associates with NADPH oxidase 1 (Nox1) and supports extracellular superoxide production. We tested the hypothesis that VRACs modulate TNFα signaling and vasomotor function in mice lacking LRRC8A exclusively in vascular smooth muscle cells (VSMCs, Sm22α-Cre, Knockout). Knockout (KO) mesenteric vessels contracted normally but relaxation to acetylcholine (ACh) and sodium nitroprusside (SNP) was enhanced compared to wild type (WT). Forty-eight hours of ex vivo exposure to TNFα (10 ng/mL) enhanced contraction to norepinephrine (NE) and markedly impaired dilation to ACh and SNP in WT but not KO vessels. VRAC blockade (carbenoxolone, CBX, 100 μM, 20 min) enhanced dilation of control rings and restored impaired dilation following TNFα exposure. Myogenic tone was absent in KO rings. LRRC8A immunoprecipitation followed by mass spectroscopy identified 33 proteins that interacted with LRRC8A. Among them, the myosin phosphatase rho-interacting protein (MPRIP) links RhoA, MYPT1 and actin. LRRC8A-MPRIP co-localization was confirmed by confocal imaging of tagged proteins, Proximity Ligation Assays, and IP/western blots. siLRRC8A or CBX treatment decreased RhoA activity in VSMCs, and MYPT1 phosphorylation was reduced in KO mesenteries suggesting that reduced ROCK activity contributes to enhanced relaxation. MPRIP was a target of redox modification, becoming oxidized (sulfenylated) after TNFα exposure. Interaction of LRRC8A with MPRIP may allow redox regulation of the cytoskeleton by linking Nox1 activation to impaired vasodilation. This identifies VRACs as potential targets for treatment or prevention of vascular disease.

Redox Regulation of the Actin Cytoskeleton in Cell Migration and Adhesion: On the Way to a Spatiotemporal View

The actin cytoskeleton of eukaryotic cells is a dynamic, fibrous network that is regulated by the concerted action of actin-binding proteins (ABPs). In particular, rapid polarization of cells in response to internal and external stimuli is fundamental to cell migration and invasion. Various isoforms of ABPs in different tissues equip cells with variable degrees of migratory and adhesive capacities. In addition, regulation of ABPs by posttranslational modifications (PTM) is pivotal to the rapid responsiveness of cells. In this context, phosphorylation of ABPs and its functional consequences have been studied extensively. However, the study of reduction/oxidation (redox) modifications of oxidation-sensitive cysteine and methionine residues of actin, ABPs, adhesion molecules, and signaling proteins regulating actin cytoskeletal dynamics has only recently emerged as a field. The relevance of such protein oxidations to cellular physiology and pathophysiology has remained largely elusive. Importantly, studying protein oxidation spatiotemporally can provide novel insights into localized redox regulation of cellular functions. In this review, we focus on the redox regulation of the actin cytoskeleton, its challenges, and recently developed tools to study its physiological and pathophysiological consequences.

Mitochondrial morphology and activity regulate furrow ingression and contractile ring dynamics in Drosophila cellularization

Mitochondria are maternally inherited in many organisms. Mitochondrial morphology and activity regulation is essential for cell survival, differentiation, and migration. An analysis of mitochondrial dynamics and function in morphogenetic events in early metazoan embryogenesis has not been carried out. In our study we find a crucial role of mitochondrial morphology regulation in cell formation in Drosophila embryogenesis. We find that mitochondria are small and fragmented and translocate apically on microtubules and distribute progressively along the cell length during cellularization. Embryos mutant for the mitochondrial fission protein, Drp1 (dynamin-related protein 1), die in embryogenesis and show an accumulation of clustered mitochondria on the basal side in cellularization. Additionally, Drp1 mutant embryos contain lower levels of reactive oxygen species (ROS). ROS depletion was previously shown to decrease myosin II activity. Drp1 loss also leads to myosin II depletion at the membrane furrow, thereby resulting in decreased cell height and larger contractile ring area in cellularization similar to that in myosin II mutants. The mitochondrial morphology and cellularization defects in Drp1 mutants are suppressed by reducing mitochondrial fusion and increasing cytoplasmic ROS in superoxide dismutase mutants. Our data show a key role for mitochondrial morphology and activity in supporting the morphogenetic events that drive cellularization in Drosophila embryos.

Redox regulation of the actin cytoskeleton and its role in the vascular system

The actin cytoskeleton is critical for form and function of vascular cells, serving mechanical, organizational and signaling roles. Because many cytoskeletal proteins are sensitive to reactive oxygen species, redox regulation has emerged as a pivotal modulator of the actin cytoskeleton and its associated proteins. Here, we summarize work implicating oxidants in altering actin cytoskeletal proteins and focus on how these alterations affect cell migration, proliferation and contraction of vascular cells. Finally, we discuss the role of oxidative modification of the actin cytoskeleton in vivo and highlight its importance for vascular diseases.

Redox molecular machines involved in tumor progression

SIGNIFICANCE

We herein review recent advances on the role exerted by protein redox machines engaged in tumor progression, focusing on cell adhesion and migration, regulation of transcriptional response, and tumor metabolic reprogramming, all features belonging to the new hallmarks of cancer.

RECENT ADVANCES

Several recent insights have reported that oxidative stress, either due to intracellular sources of oxidants, which are frequently deregulated in cancers or to microenvironment factors as hypoxia or stromal cell contact, plays a key role in tumor malignancy, as well as in metabolic pathways control. Indeed, many proteins behave as sensors of intracellular oxidative stress, including protein tyrosine kinases and phosphatases, transcription factors as p53, forkhead box class-Os, nuclear respiratory factor-2, nuclear factor-kB, hypoxia inducible factor, enzymes involved in glycolysis or penthose phosphate pathway as pyruvate kinase-M2 and adenylate monophosphate kinase, or DNA repair enzymes as Ataxia Teleangectasia Mutated. All these proteins have been reported to play essential roles during cancer progression and their sensitivity to oxidative stress has added new levels of complexity to the cancer field.

CRITICAL ISSUES

Main significant issues that need to be addressed in redox cancer biology are (i) sensitivity to a different level of oxidative stress of sensors, that is, they can respond to different oxidative insults/signals, and (ii) the real susceptibility of cancer cells to redox-based therapies due to the acknowledged plasticity of cancer cells to develop adoptive strategies.

FUTURE DIRECTIONS

Definitely, redox machines have the potentiality to develop into novel biomarkers and related target therapies should attain the goal of personalized medicine in the fight against cancer.

Proteomic and carbonylation profile analysis of rat skeletal muscles following acute swimming exercise

Previous studies by us and other groups characterized protein expression variation following long-term moderate training, whereas the effects of single bursts of exercise are less known. Making use of a proteomic approach, we investigated the effects of acute swimming exercise (ASE) on protein expression and carbonylation patterns in two hind limb muscles: the Extensor Digitorum Longus (EDL) and the Soleus, mostly composed of fast-twitch and slow-twitch fibres, respectively. Carbonylation is one of the most common oxidative modifications of proteins and a marker of oxidative stress. In fact, several studies suggest that physical activity and the consequent increase in oxygen consumption can lead to increase in reactive oxygen and nitrogen species (RONS) production, hence the interest in examining the impact of RONS on skeletal muscle proteins following ASE. Results indicate that protein expression is unaffected by ASE in both muscle types. Unexpectedly, the protein carbonylation level was reduced following ASE. In particular, the analysis found 31 and 5 spots, in Soleus and EDL muscles respectively, whose carbonylation is reduced after ASE. Lipid peroxidation levels in Soleus were markedly reduced as well. Most of the decarbonylated proteins are involved either in the regulation of muscle contractions or in the regulation of energy metabolism. A number of hypotheses may be advanced to account for such results, which will be addressed in future studies.

The role of mechanical force and ROS in integrin-dependent signals

Cells are exposed to several types of integrin stimuli, which generate responses generally referred to as “integrin signals”, but the specific responses to different integrin stimuli are poorly defined. In this study, signals induced by integrin ligation during cell attachment, mechanical force from intracellular contraction, or cell stretching by external force were compared. The elevated phosphorylation levels of several proteins during the early phase of cell attachment and spreading of fibroblast cell lines were not affected by inhibition of ROCK and myosin II activity, i.e. the reactions occurred independently of intracellular contractile force acting on the adhesion sites. The contraction-independent phosphorylation sites included ERK1/2 T202/Y204, AKT S473, p130CAS Y410, and cofilin S3. In contrast to cell attachment, cyclic stretching of the adherent cells induced a robust phosphorylation only of ERK1/2 and the phosphorylation levels of the other investigated proteins were not or only moderately affected by stretching. No major differences between signaling via α5β1 or αvβ3 integrins were detected. The importance of mitochondrial ROS for the integrin-induced signaling pathways was investigated using rotenone, a specific inhibitor of complex I in the respiratory chain. While rotenone only moderately reduced ATP levels and hardly affected the signals induced by cyclic cell stretching, it abolished the activation of AKT and reduced the actin polymerization rate in response to attachment in both cell lines. In contrast, scavenging of extracellular ROS with catalase or the vitamin C analog Asc-2P did not significantly influence the attachment-derived signaling, but caused a selective and pronounced enhancement of ERK1/2 phosphorylation in response to stretching. In conclusion, the results showed that “integrin signals” are composed of separate sets of reactions triggered by different types of integrin stimulation. Mitochondrial ROS and extracellular ROS had specific and distinct effects on the integrin signals induced by cell attachment and mechanical stretching.