Redox sensitivity of actin toward an exogenous oxidative stress has recently been reported. We report here the first evidence of in vivo actin redox regulation by a physiological source of reactive oxygen species, specifically those species generated by integrin receptors during cell adhesion. Actin oxidation takes place via the formation of a mixed disulfide between cysteine 374 and glutathione; this modification is essential for spreading and for cytoskeleton organization. Impairment of actin glutathionylation, either through GSH depletion or expression of the C374A redox-insensitive mutant, greatly affects cell spreading and the formation of stress fibers, leading to inhibition of the disassembly of the actinomyosin complex. These data suggest that actin glutathionylation is essential for cell spreading and cytoskeleton organization and that it plays a key role in disassembly of actinomyosin complex during cell adhesion.Actin is the main component of the cytoskeleton and exists as monomeric G-actin, able upon extracellular stimuli to polymerize into filamentous F-actin. Different structures of F-actin are produced by elongation of preformed filaments by accessory proteins, such as profilin, actin-related protein 2/3, actindepolymerizing factor/cofilin complexes, and many others. These actin-interacting proteins may act through different mechanisms, as forming transversal branching filaments or blocking the extensive elongation at the cell margins (1, 2).Actin cytoskeleton is modified by integrin signal in response to extracellular matrix (ECM) 3 transforming actin architecture from a cortical ring to a plain structure of stress fibers in complete adherent cells. Integrin-mediated cell adhesion proceeds in a step-like program: cells contact the substratum, integrins ligate to the ECM proteins and clusterize, focal contacts form, the cell spreads and finally organizes the actin filaments in stress fibers for mechanical resistance. The control of cytoskeleton organization is mainly due by the action of the members of the family of the small GTPases Rho like Cdc42, Rho, and Rac. In response to growth or chemotactic factors and cell-cell or cell-matrix interaction, Rho is activated thus inducing the formation of actin stress fibers. In contrast, activated Rac provokes actin-dependent membrane ruffling and Cdc42 causes protrusion of actin-rich microspikes from the cell surface (1).Much evidence supports the idea that reactive oxygen species (ROS) act as second messengers thus modulating the activity of signaling proteins upon growth factors and cytokines stimulation. The downstream effect of ROS production is the reversible oxidation of redox-sensible proteins through a direct modification of the thiol group of reactive cysteines (3). Redoxregulated proteins include tyrosine phosphatases, several transcription factors, p53, and the p21Ras family of proto-oncogenes (4). Recently, Chiarugi et al. (5) proposed a redox regulation of integrin signaling during cell adhesion. In this new model, integrin activation is join...

Background Whether patients with autoimmune rheumatic diseases (ARD) have a higher risk for SARS-CoV-2 infection (COVID-19) and how SARS-CoV-2 pandemic impacts on adherence to therapy has not been fully elucidated. We assessed the rate and clinical presentation of COVID-19, and adherence to therapy in a large cohort of patients with ARD followed-up in a tertiary University-Hospital in Northeast Italy. Methods Between April 9th and April 25th , 2020, after SARS-CoV-2 infection peak, a telephone survey investigating the impact of COVID-19 on patients with systemic lupus erythematosus (SLE), systemic sclerosis (SSc), rheumatoid arthritis (RA), ANCA-associated vasculitis (AAV), and idiopathic inflammatory myopathies (IIM) was administered. Demographics, disease activity status, therapy, occupational exposure, and adherence to social distancing advise were also collected. Results 916 patients (397 SLE, 182 AAV, 176 SSc, 111 RA, 50 IIM) completed the survey. 148 patients developed at least one symptom compatible with COVID-19 (cough 96, sore throat 64, fever 64, arthromyalgias 59, diarrhea 26, conjunctivitis 18, ageusia/hyposmia, 18). Among the 916 patients, 65 (7.1%) underwent SARS-CoV-2 nasopharyngeal swab (18 symptomatic and 47 asymptomatic), 2 (0.21%) tested positive, a proportion similar to that observed in the general population of the Veneto region. No deaths occurred. 31 patients (3.4%) withdrew ≥1 medication, mainly immunosuppressants or biologics. Adoption of social distancing was observed by 860 patients (93.9%), including 335 (36.6%) who adopted it before official lockdown. Conclusions COVID-19 incidence seems to be similar in our cohort compared to the general population. Adherence to therapy and to social distancing advise was high.

Low molecular weight protein-tyrosine phosphatase (LMW-PTP) is an enzyme involved in mitogenic signaling and cytoskeletal rearrangement after platelet-derived growth factor (PDGF) stimulation. Recently, we demonstrated that LMW-PTP is regulated by a redox mechanism involving the two cysteine residues of the catalytic site, which turn reversibly from reduced to oxidized state after PDGF stimulation. Since recent findings showed a decrease of intracellular reactive oxygen species in contact inhibited cells and a lower tyrosine phosphorylation level in dense cultures in comparison to sparse ones, we studied if the level of endogenous LMW-PTP is regulated by growth inhibition conditions, such as cell confluence and differentiation. Results show that both cell confluence and cell differentiation up-regulate LMW-PTP expression in C2C12 and PC12 cells. We demonstrate that during myogenesis LMW-PTP is regulated at translational level and that the protein accumulates at the plasma membrane. Furthermore, we showed that both myogenesis and cell-cell contact lead to a dramatical decrease of tyrosine phosphorylation level of PDGF receptor. In addition, we observed an increased association of the receptor with LMW-PTP during myogenesis. Herein, we demonstrate that myogenesis decreases the intracellular level of reactive oxygen species, as observed in dense cultures. As a consequence, LMW-PTP turns from oxidized to reduced form during muscle differentiation, increasing its activity in growth inhibition conditions such as differentiation. These data suggest that LMW-PTP plays a crucial role in physiological processes, which require cell growth arrest such as confluence and differentiation.The control of protein tyrosine phosphorylation in vivo is regulated by the coordinated and competing actions of proteintyrosine kinases and protein-tyrosine phosphatases (PTPs) 1 (1). PTPs have been identified in eukaryotes, prokaryotes, plants, and virus and comprise a large family of enzymes, that rival protein-tyrosine kinases in structural diversity and complexity (2). PTPs may either antagonize or potentiate proteintyrosine kinase-induced signaling in vivo and have been implicated in fundamental physiological processes such as growth and proliferation, differentiation, and cytoskeletal functions (3). Most growth factors, when bind to their receptors, activate an intracellular cascade of events involving tyrosine phosphorylation of the receptor itself and of several other substrates, phosphotyrosine-dependent recruitment of multiple signal transducers to the cell membrane and, eventually, the delivery of mitogenic stimuli (4). With some exceptions, PTPs exert a general inhibitory effect on this intracellular cascade by attenuating the intensity of phosphorylation signals initiated by activated receptors and accelerating their extinction (2).LMW-PTP is an 18-kDa enzyme widely distributed in mammalian tissues (5). Previous findings demonstrated that PDGFr is an in vivo substrate of LMW-PTP and that this protein is involved in the control of...

Adiponectin/ACRP30 is an adipose tissue-derived hormone with antiatherogenic, antidiabetic, and insulin-sensitizing properties. Although the metabolic effects of adiponectin on glucose and lipid metabolism are well known, the signaling pathways triggered by adiponectin receptors remain to be elucidated. We report evidence that in hepatic cells, adiponectin stimulation produces a transient burst of reactive oxygen species (ROS) through activation of the small GTPase Rac1 and 5-lypoxigenase. Furthermore, adiponectin-induced oxidants cause the oxidation/inhibition of protein-tyrosine phosphatase (PTP) 1B, one of the major phosphotyrosine phosphatases involved in the control of insulin receptor phosphorylation. Adiponectin causes increased association of PTP1B to insulin receptor and the oxidation/ inhibition of the phosphatase, ultimately provoking the ligand-independent trans-phosphorylation of insulin receptor. We also report evidence that redox signaling plays a key role in both mitogen-activated protein kinase activation and hepatic glucose consumption induced by adiponectin. A diponectin/ACRP30 is an abundant adipocytederived circulating plasma protein with insulinsensitizing metabolic effects and vascular protective properties. 1 Adiponectin is composed of 2 structurally distinct domains, an N-terminal collagen-like domain and a C-terminal globular domain. Both the full-length and the globular form of the hormone have been observed in mammalian plasma. 2 Furthermore, adiponectin molecules can associate in the plasma to form trimers, hexamers, and high molecular weight forms whose biological activities are poorly understood. 3 Studies in humans and monkeys show that plasma adiponectin level significantly correlates with insulin sensitivity in the whole body. 4,5 Moreover, the hormone treatment improves diabetes in mice. 6 These findings identify adiponectin as an insulinsensitizing hormone and indicate that its reduced production might be related to the pathophysiology of insulin resistance. The physiological effects of adiponectin on glucose and lipid metabolism in the liver and in skeletal muscle are mediated by 2 receptors (AdipoR1 and AdipoR2) that have been identified recently. 7 These receptors contain 7-transmembrane domains but are structurally and functionally distinct from G-protein-coupled receptors. However, the signaling pathways responsible for the metabolic effects of adiponectin have been only partially elucidated. An involvement of AMP kinase (AMPK) activation has been indicated for both full-length and globular adiponectin (gAd) in muscle and only for the fulllength hormone in the liver, suggesting different organ targeting of the 2 adiponectin forms. 7 In muscle, AMPK activation has been correlated to fatty acid oxidation and

Protein tyrosine phosphorylation is one of the earliest signaling events detected in response to lymphocyte function-associated antigen-1 (LFA-1) engagement during lymphocyte adhesion. In particular, the focal adhesion kinase p125FAK, involved in the modulation and rearrangement of the actin cytoskeleton, seems to be a crucial mediator of LFA-1 signaling. Herein, we investigate the role of a FAK tyrosine phosphatase, namely low molecular weight phosphotyrosine phosphatase (