Over the last decade, a dual character of cell response to oxidative stress, eustress versus distress, has become increasingly recognized. A growing body of evidence indicates that under physiological conditions, low concentrations of reactive oxygen and nitrogen species (RONS) maintained by the activity of endogenous antioxidant system (AOS) allow reversible oxidative/nitrosative modifications of key redox-sensitive residues in regulatory proteins. The reversibility of redox modifications such as Cys S-sulphenylation/S-glutathionylation/S-nitrosylation/S-persulphidation and disulphide bond formation, or Tyr nitration, which occur through electrophilic attack of RONS to nucleophilic groups in amino acid residues provides redox switches in the activities of signalling proteins. Key requirement for the involvement of the redox modifications in RONS signalling including ROS-MAPK, ROS-PI3K/Akt, and RNS-TNF-α/NF-kB signalling is their specificity provided by a residue microenvironment and reaction kinetics. Glutathione, glutathione peroxidases, peroxiredoxins, thioredoxin, glutathione reductases, and glutaredoxins modulate RONS level and cell signalling, while some of the modulators (glutathione, glutathione peroxidases and peroxiredoxins) are themselves targets for redox modifications. Additionally, gene expression, activities of transcription factors, and epigenetic pathways are also under redox regulation. The present review focuses on RONS sources (NADPH-oxidases, mitochondrial electron-transportation chain (ETC), nitric oxide synthase (NOS), etc.), and their cross-talks, which influence reversible redox modifications of proteins as physiological phenomenon attained by living cells during the evolution to control cell signalling in the oxygen-enriched environment. We discussed recent advances in investigation of mechanisms of protein redox modifications and adaptive redox switches such as MAPK/PI3K/PTEN, Nrf2/Keap1, and NF-κB/IκB, powerful regulators of numerous physiological processes, also implicated in various diseases.

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Endogenous inhibitors of angiogenesis are proved to be a major factor preventing the emergence of clinically manifested stages of human cancer. The protein endostatin, a 20-kD proteolytic fragment of type XVIII collagen, is one of the most active natural inhibitors of angiogenesis. Endostatin specifically inhibits the in vitro and in vivo proliferation of endothelial cells, inducing their apoptosis through inhibition of cyclin D1. On the surface of endothelial cells, endostatin binds with the integrin alpha(5)beta(1) that activates the Src-kinase pathway. The binding of endostatin with integrins also down-regulates the activity of RhoA GTPase and inhibits signaling pathways mediated by small kinases of the Ras and Raf families. All these events promote disassembly of the actin cytoskeleton, disorders in cell-matrix interactions, and decrease in endotheliocyte mobility, i.e., promote the suppression of angiogenesis. Endostatin displays a high antitumor activity in vivo: it inhibits the progression of more than 60 types of tumors. This review summarizes results of numerous studies concerning the biological activity and action mechanism of endostatin.

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The epidermal growth factor (EGF) receptor is expressed at high levels on many types of tumor cells, such as squamous carcinoma, breast cancer and endothelial cells. We studied targeted delivery of the anticancer drug doxorubicin (DOX) using EGF and its receptor-binding fragment (EGFfr) to cells able to overexpress EGF receptors. EGF-DOX and EGFfr-DOX conjugates were synthesized via a glutaraldehyde bridge. The cytotoxic activities (CTA) of the conjugates were studied in vitro in different tumor cell lines (MCF-7Wt, MCF-7AdrR, B16) and endothelial cells using MTT-test. The antitumor effects of the conjugates were examined in vivo in mice with a subcutaneous B16 model. In the case of MCF-7Wt cells, CTA of EGF-DOX and EGFfr-DOX conjugates exceeded 7.7- and 68-fold that of free DOX. Besides, the conjugates effectively decreased the drug resistance of MCF-7AdrR cells. CTA of the conjugates against endothelial cell cultures markedly exceeded that of free DOX. It is of note that proliferating endothelial cells were much more sensitive to the effects of the conjugates than confluent endothelial cells. Administration of EGF-DOX and EGFfr-DOX conjugates significantly inhibited tumor growth and increased the mean life span of experimental animals by 46 and 48.5%, respectively.