Mikhail Ryzhikov

Mechanism of RecO recruitment to DNA by single-stranded DNA binding protein

RecO is a recombination mediator protein (RMP) important for homologous recombination, replication repair and DNA annealing in bacteria. In all pathways, the single-stranded (ss) DNA binding protein, SSB, plays an inhibitory role by protecting ssDNA from annealing and recombinase binding. Conversely, SSB may stimulate each reaction through direct interaction with RecO. We present a crystal structure of Escherichia coli RecO bound to the conserved SSB C-terminus (SSB-Ct). SSB-Ct binds the hydrophobic pocket of RecO in a conformation similar to that observed in the ExoI/SSB-Ct complex. Hydrophobic interactions facilitate binding of SSB-Ct to RecO and RecO/RecR complex in both low and moderate ionic strength solutions. In contrast, RecO interaction with DNA is inhibited by an elevated salt concentration. The SSB mutant lacking SSB-Ct also inhibits RecO-mediated DNA annealing activity in a salt-dependent manner. Neither RecO nor RecOR dissociates SSB from ssDNA. Therefore, in E. coli, SSB recruits RMPs to ssDNA through SSB-Ct, and RMPs are likely to alter the conformation of SSB-bound ssDNA without SSB dissociation to initiate annealing or recombination. Intriguingly, Deinococcus radiodurans RecO does not bind SSB-Ct and weakly interacts with the peptide in the presence of RecR, suggesting the diverse mechanisms of DNA repair pathways mediated by RecO in different organisms.

A dual role for mycobacterial RecO in RecA-dependent homologous recombination and RecA-independent single-strand annealing

Mycobacteria have two genetically distinct pathways for the homology-directed repair of DNA double-strand breaks: homologous recombination (HR) and single-strand annealing (SSA). HR is abolished by deletion of RecA and reduced in the absence of the AdnAB helicase/nuclease. By contrast, SSA is RecA-independent and requires RecBCD. Here we examine the function of RecO in mycobacterial DNA recombination and repair. Loss of RecO elicits hypersensitivity to DNA damaging agents similar to that caused by deletion of RecA. We show that RecO participates in RecA-dependent HR in a pathway parallel to the AdnAB pathway. We also find that RecO plays a role in the RecA-independent SSA pathway. The mycobacterial RecO protein displays a zinc-dependent DNA binding activity in vitro and accelerates the annealing of SSB-coated single-stranded DNA. These findings establish a role for RecO in two pathways of mycobacterial DNA double-strand break repair and suggest an in vivo function for the DNA annealing activity of RecO proteins, thereby underscoring their similarity to eukaryal Rad52.

Role of adenosine signaling in the pathogenesis of breast cancer

The plasma level of adenosine increases under ischemic and inflamed conditions in tumor microenvironment. Adenosine elicits a range of signaling pathways in tumors, resulting in either inhibition or enhancement of tumor growth depending upon different subtypes of adenosine receptors activation and type of cancer. Metabolism of adenosine‐5′‐triphosphate (ATP) and its derivatives including adenosine is dysregulated in the breast tumor microenvironment, supporting the role of this metabolite in the pathogenesis of breast cancer. Adenosine regulates inflammation, apoptosis, cell proliferation, and metastasis in breast cancer cells. This review summarizes the role of adenosine in the pathogenesis of breast cancer for a better understanding and hence a better management of this disease.

Role of Wnt5a in the Pathogenesis of Inflammatory Diseases

Wnt5a initiates pro‐inflammatory responses through activation of non‐canonical Wnt signaling pathway. Pro‐inflammatory functions of Wnt5a trigger pro‐inflammatory signaling cascades and increase secretion of pro‐inflammatory cytokines and chemokines. Wnt5a as a potent signaling molecule is strongly implicated in a number of diseases including cancer, diabetes, metabolic disorders, and of special interest in this review, inflammatory diseases. This review summarizes the role of Wnt5a in the pathogenesis of inflammatory diseases including atherosclerosis, rheumatoid arthritis, psoriasis vulgaris and sepsis, promoting greater understanding, and clinical management of these diseases. J. Cell. Physiol. 232: 1611–1616, 2017.

Role of Thrombin in the Pathogenesis of Central Nervous System Inflammatory Diseases

Thrombin initiates proinflammatory signaling responses through activation of protease‐activated receptors (PARs) in in vitro and in vivo systems. Proinflammatory signaling function of thrombin increases secretion of proinflammatory cytokines and chemokines, triggers vascular permeability, promotes leukocyte migration, and induces adhesion molecule expression. Thrombin as a potent signaling molecule is strongly implicated in a number of proinflammatory disorders including severe sepsis, cancer, cardiovascular disease, and of special interest in this review neurodegenerative disorders. This review summarizes the role of thrombin in the pathogenesis of central nervous system (CNS) inflammatory diseases, including Alzheimers disease (AD) and Parkinsons disease (PD), promoting greater understanding and clinical management of these diseases. J. Cell. Physiol. 232: 482–485, 2017.

Adenosine: an endogenous mediator in the pathogenesis of gynecological cancer†

Extracellular concentration of adenosine increases in the hypoxic tumor microenvironment. Adenosine signaling regulates apoptosis, angiogenesis, metastasis, and immune suppression in cancer cells. Adenosine‐induced cell responses depend upon different subtypes of adenosine receptors activation and type of cancer. Suppression of adenosine signaling via inhibition of adenosine receptors or adenosine generating enzymes including CD39 and CD73 on ovarian or cervical cancer cells is a potentially novel therapeutic approach for gynecological cancer patients. This review summarizes the role of adenosine in the pathogenesis of gynecological cancer for a better understanding and hence a better management of this disease.

Structural Studies of SSB Interaction with RecO

Interaction of recombination protein RecO with single-stranded (ss) DNA-binding protein (SSB) is essential for DNA damage repair and restart of stalled replication (Cox, Crit Rev Biochem Mol Biol 42(1):41-63, 2007). To understand mechanism of this interaction and its role in DNA repair, we deciphered a high-resolution structure of RecO complex with C-terminal tail of SSB (SSB-Ct). The structure revealed a key role of hydrophobic interactions between two proteins and suggests the mechanism of RecO recruitment to DNA during homologous recombination and strand annealing.

Therapeutic potentials of adenosine receptors agonists and antagonists in colitis; current status and perspectives†

Increasing evidence suggests that adenosine is dysregulated in ulcerative colitis (UC), potentially affecting UC pathogenesis, diagnosis, and therapy. Dysregulation of the activity of adenosine generating enzymes including adenosine deaminase in serum of patients with acute colitis supports the role of this omnipresent metabolite in the pathogenesis of colitis. Adenosine regulates inflammatory responses including epithelial barrier hyper‐permeability, myeloperoxidase activity, and neuromuscular motility in colitis, supporting the therapeutic potency of adenosine receptors agonists and antagonists in this disease. Depending upon the adenosine receptor subtype, activation or suppression of the receptor with pharmacological agonists or antagonists attenuates colitis pathological symptoms in colitis model. This review summarizes the role of adenosine receptors agonists and antagonists in the pathogenesis of colitis for a better understanding and hence a better management of this disease.

RecO Protein Initiates DNA Recombination and Strand Annealing through Two Alternative DNA Binding Mechanisms

Background: RecO anneals DNA and initiates homologous recombination. Results: Binding of RecO to DNA/SSB is regulated by zinc during annealing and by RecR during recombination. Conclusion: Alternative DNA repair reactions are supported by different DNA binding mechanisms of RecO. Significance: Results explain how the same RMP supports multiple reactions during DNA repair and chromosome maintenance. Recombination mediator proteins (RMPs) are important for genome stability in all organisms. Several RMPs support two alternative reactions: initiation of homologous recombination and DNA annealing. We examined mechanisms of RMPs in both reactions with Mycobacterium smegmatis RecO (MsRecO) and demonstrated that MsRecO interacts with ssDNA by two distinct mechanisms. Zinc stimulates MsRecO binding to ssDNA during annealing, whereas the recombination function is zinc-independent and is regulated by interaction with MsRecR. Thus, different structural motifs or conformations of MsRecO are responsible for interaction with ssDNA during annealing and recombination. Neither annealing nor recombinase loading depends on MsRecO interaction with the conserved C-terminal tail of single-stranded (ss) DNA-binding protein (SSB), which is known to bind Escherichia coli RecO. However, similarly to E. coli proteins, MsRecO and MsRecOR do not dismiss SSB from ssDNA, suggesting that RMPs form a complex with SSB-ssDNA even in the absence of binding to the major protein interaction motif. We propose that alternative conformations of such complexes define the mechanism by which RMPs initiate the repair of stalled replication and support two different functions during recombinational repair of DNA breaks.

Therapeutic potency of pharmacological adenosine receptor agonist/antagonist in angiogenesis, current status and perspectives

Adenosine concentration significantly increases in tumour microenvironment contributing to tumorigenic processes including cell proliferation, survival, invasion and of special interest in this review angiogenesis.