Nitric oxide receptor soluble guanylyl cyclase undergoes splicing regulation in differentiating human embryonic cells

Soluble guanylyl cyclase beta1 subunit targets epithelial-to-mesenchymal transition and downregulates Akt pathway in human endometrial and cervical cancer cells

Endometrial and cervical cancer are among the most frequently diagnosed malignancies globally. Nitric oxide receptor-soluble guanylyl cyclase (sGC) is a heterodimeric enzyme composed of two subunits, α1 and β1. Previously we showed that sGCα1 subunit promotes cell survival, proliferation, and migration, but the role of sGCβ1 subunit has not been addressed. The aim of the present work was to study the impact of sGCβ1 restoration in proliferation, survival, migration, and cell signaling in endometrial and cervical cancer cells. We found that sGCβ1 transcript levels are reduced in endometrial and cervical tumors vs normal tissues. We confirmed nuclear enrichment of sGCβ1, unlike sGCα1. Overexpression of sGCβ1 reduced cell viability and augmented apoptotic index. Cell migration and invasion were also negatively affected. All these sGCβ1-driven effects were independent of sGC enzymatic activity. sGCβ1 reduced the expression of epithelial-to-mesenchymal transition factors such as N-cadherin and β-catenin and increased the expression of E-cadherin. sGCβ1 impacted signaling in endometrial and cervical cancer cells through significant downregulation of Akt pathway affecting some of its main targets such as GSK-3β and c-Raf. Our results show for the first time that sGCβ1 exerts several antiproliferative actions in ECC-1 and HeLa cell lines by targeting key regulatory pathways.

Soluble Guanylate Cyclase β1 Subunit Represses Human Glioblastoma Growth

Malignant glioma is the most common and deadly brain tumor. A marked reduction in the levels of sGC (soluble guanylyl cyclase) transcript in the human glioma specimens has been revealed in our previous studies. In the present study, restoring the expression of sGCβ1 alone repressed the aggressive course of glioma. The antitumor effect of sGCβ1 was not associated with enzymatic activity of sGC since overexpression of sGCβ1 alone did not influence the level of cyclic GMP. Additionally, sGCβ1-induced inhibition of the growth of glioma cells was not influenced by treatment with sGC stimulators or inhibitors. The present study is the first to reveal that sGCβ1 migrated into the nucleus and interacted with the promoter of the TP53 gene. Transcriptional responses induced by sGCβ1 caused the G0 cell cycle arrest of glioblastoma cells and inhibition of tumor aggressiveness. sGCβ1 overexpression impacted signaling in glioblastoma multiforme, including the promotion of nuclear accumulation of p53, a marked reduction in CDK6, and a significant decrease in integrin α6. These anticancer targets of sGCβ1 may represent clinically important regulatory pathways that contribute to the development of a therapeutic strategy for cancer treatment.

Advances, Perspectives and Potential Engineering Strategies of Light-Gated Phosphodiesterases for Optogenetic Applications

The second messengers, cyclic adenosine 3'-5'-monophosphate (cAMP) and cyclic guanosine 3'-5'-monophosphate (cGMP), play important roles in many animal cells by regulating intracellular signaling pathways and modulating cell physiology. Environmental cues like temperature, light, and chemical compounds can stimulate cell surface receptors and trigger the generation of second messengers and the following regulations. The spread of cAMP and cGMP is further shaped by cyclic nucleotide phosphodiesterases (PDEs) for orchestration of intracellular microdomain signaling. However, localized intracellular cAMP and cGMP signaling requires further investigation. Optogenetic manipulation of cAMP and cGMP offers new opportunities for spatio-temporally precise study of their signaling mechanism. Light-gated nucleotide cyclases are well developed and applied for cAMP/cGMP manipulation. Recently discovered rhodopsin phosphodiesterase genes from protists established a new and direct biological connection between light and PDEs. Light-regulated PDEs are under development, and of demand to complete the toolkit for cAMP/cGMP manipulation. In this review, we summarize the state of the art, pros and cons of artificial and natural light-regulated PDEs, and discuss potential new strategies of developing light-gated PDEs for optogenetic manipulation.

Effects of the nitric oxide releasing biomimetic nanomatrix gel on pulp-dentin regeneration: Pilot study

Successful disinfection alongside complete endodontic tissue regeneration and revascularization are the most desired clinical outcomes of regenerative endodontics. Despite reported clinical successes, significant limitations to the current regenerative endodontic procedure (REP) have been elucidated. To improve the current REP, an antibiotics and nitric oxide (NO) releasing biomimetic nanomatrix gel was developed. The study evaluates antibacterial effects of an antibiotics and NO releasing biomimetic nanomatrix gel on multispecies endodontic bacteria. Antibiotics, ciprofloxacin (CF) and metronidazole (MN) were mixed and encapsulated within the NO releasing biomimetic nanomatrix gel. The gel was synthesized and self-assembled from peptide amphiphiles containing various functional groups. Antibacterial effects of the antibiotics and NO releasing biomimetic nanomatrix gel were evaluated using bacterial viability assays involving endodontic microorganisms including clinical samples. Pulp-dentin regeneration was evaluated via animal-model experiments. The antibiotics and NO releasing biomimetic nanomatrix gel demonstrated a concentration dependent antibacterial effect. In addition, NO alone demonstrated a concentration dependent antibacterial effect on endodontic microorganism. An in vivo analysis demonstrated the antibiotics and NO releasing biomimetic nanomatrix gel promoted tooth revascularization with maturation of root canals. An optimal concentration of and NO releasing nanomatrix gel is suggested for its potential as a root treatment material for REP and an appropriate protocol for human trials. Further investigation is required to obtain a larger sample size and decide upon ideal growth factor incorporation.

The Role of Reactive Oxygen and Nitrogen Species in the Expression and Splicing of Nitric Oxide Receptor

SIGNIFICANCE

Nitric oxide (NO)-dependent signaling is critical to many cellular functions and physiological processes. Soluble guanylyl cyclase (sGC) acts as an NO receptor and mediates the majority of NO functions. The signaling between NO and sGC is strongly altered by reactive oxygen and nitrogen species. Recent Advances: Besides NO scavenging, sGC is affected by oxidation/loss of sGC heme, oxidation, or nitrosation of cysteine residues and phosphorylation. Apo-sGC or sGC containing oxidized heme is targeted for degradation. sGC transcription and the stability of sGC mRNA are also affected by oxidative stress.

CRITICAL ISSUES

Studies cited in this review suggest the existence of compensatory processes that adapt cellular processes to diminished sGC function under conditions of short-term or moderate oxidative stress. Alternative splicing of sGC transcripts is discussed as a mechanism with the potential to both enhance and reduce sGC function. The expression of α1 isoform B, a functional and stable splice variant of human α1 sGC subunit, is proposed as one of such compensatory mechanisms. The expression of dysfunctional splice isoforms is discussed as a contributor to decreased sGC function in vascular disease.

FUTURE DIRECTIONS

Targeting the process of sGC splicing may be an important approach to maintain the composition of sGC transcripts that are expressed in healthy tissues under normal conditions. Emerging new strategies that allow for targeted manipulations of RNA splicing offer opportunities to use this approach as a preventive measure and to control the composition of sGC splice isoforms. Rational management of expressed sGC splice forms may be a valuable complementary treatment strategy for existing sGC-directed therapies. Antioxid. Redox Signal. 26, 122-136.

Pluripotent Stem Cells and DNA Damage Response to Ionizing Radiations

Pluripotent stem cells (PSCs) hold great promise in regenerative medicine, disease modeling, functional genomics, toxicological studies and cell-based therapeutics due to their unique characteristics of self-renewal and pluripotency. Novel methods for generation of pluripotent stem cells and their differentiation to the specialized cell types such as neuronal cells, myocardial cells, hepatocytes and beta cells of the pancreas and many other cells of the body are constantly being refined. Pluripotent stem cell derived differentiated cells, including neuronal cells or cardiac cells, are ideal for stem cell transplantation as autologous or allogeneic cells from healthy donors due to their minimal risk of rejection. Radiation-induced DNA damage, ultraviolet light, genotoxic stress and other intrinsic and extrinsic factors triggers a series of biochemical reactions known as DNA damage response. To maintain genomic stability and avoid transmission of mutations into progenitors cells, stem cells have robust DNA damage response signaling, a contrast to somatic cells. Stem cell transplantation may protect against radiation-induced late effects. In particular, this review focuses on differential DNA damage response between stem cells and derived differentiated cells and the possible pathways that determine such differences.

The G-protein regulator LGN modulates the activity of the NO receptor soluble guanylate cyclase

sGC (soluble guanylate cyclase) is the main mediator of NO signalling. Biochemical and physiological studies suggest that, besides NO, in vivo regulation of sGC involves direct interaction with other proteins. Using yeast two-hybrid screening, we identified that the multidomain LGN (Leu-Gly-Asn repeat-enriched protein) interacts with both α1 and β1 sGC subunits. LGN and sGC co-localized in the cell cytoplasm, and the LGN-sGC complex was co-immunoprecipitated from cells expressing both proteins and from native tissues. Their interaction requires the N-terminal tetratricopeptide repeats of LGN, but does not require the N-terminal portions of α1 or β1 sGC subunits. Overexpression of LGN decreases the activity of cellular sGC, whereas knockdown of LGN mRNA and protein correlated with increased sGC activity. Although purified LGN interacts directly with purified sGC, the inhibitory effect in vitro is observed only after supplementation of cell lysate to the reaction. Although resting sGC and sGC activated by the stimulator BAY41-2272 have very similar LGN-IC50 values to the NO-stimulated sGC, they have a much higher Hill coefficient, suggesting co-operative binding with respect to LGN in the low-activated state of sGC. AGS3 (activator of G-protein signalling 3), the closest LGN homologue, also inhibits sGC. The interaction of sGC with these scaffolding proteins may expand the cross-talk between NO/cGMP signalling and other cellular pathways and tailor sGC function to specific tissues or signals.

Hydrogen peroxide alters splicing of soluble guanylyl cyclase and selectively modulates expression of splicing regulators in human cancer cells

Background

Soluble guanylyl cyclase (sGC) plays a central role in nitric oxide (NO)-mediated signal transduction in the cardiovascular, nervous and gastrointestinal systems. Alternative RNA splicing has emerged as a potential mechanism to modulate sGC expression and activity. C-α1 sGC is an alternative splice form that is resistant to oxidation-induced protein degradation and demonstrates preferential subcellular distribution to the oxidized environment of endoplasmic reticulum (ER).

Methodology/Principal Findings

Here we report that splicing of C-α1 sGC can be modulated by H₂O₂ treatment in BE2 neuroblastoma and MDA-MD-468 adenocarcinoma human cells. In addition, we show that the H₂O₂ treatment of MDA-MD-468 cells selectively decreases protein levels of PTBP1 and hnRNP A2/B1 splice factors identified as potential α1 gene splicing regulators by in silico analysis. We further demonstrate that down-regulation of PTBP1 by H₂O₂ occurs at the protein level with variable regulation observed in different breast cancer cells.

Conclusions/Significance

Our data demonstrate that H₂O₂ regulates RNA splicing to induce expression of the oxidation-resistant C-α1 sGC subunit. We also report that H₂O₂ treatment selectively alters the expression of key splicing regulators. This process might play an important role in regulation of cellular adaptation to conditions of oxidative stress.

Nitric oxide-cyclic GMP signaling in stem cell differentiation

The nitric oxide-cyclic GMP (NO-cGMP) pathway mediates important physiological functions associated with various integrative body systems including the cardiovascular and nervous systems. Furthermore, NO regulates cell growth, survival, apoptosis, proliferation, and differentiation at the cellular level. To understand the significance of the NO-cGMP pathway in development and differentiation, studies have been conducted both in developing embryos and in stem cells. Manipulation of the NO-cGMP pathway, by employing activators and inhibitors as pharmacological probes, and genetic manipulation of NO signaling components have implicated the involvement of this pathway in the regulation of stem cell differentiation. This review focuses on some of the work pertaining to the role of NO-cGMP in the differentiation of stem cells into cells of various lineages, particularly into myocardial cells, and in stem cell-based therapy.

The amino-terminus of nitric oxide sensitive guanylyl cyclase α₁ does not affect dimerization but influences subcellular localization

Background

Nitric oxide sensitive guanylyl cyclase (NOsGC) is a heterodimeric enzyme formed by an α- and a β₁-subunit. A splice variant (C-α₁) of the α₁-subunit, lacking at least the first 236 amino acids has been described by Sharina et al. 2008 and has been shown to be expressed in differentiating human embryonic cells. Wagner et al. 2005 have shown that the amino acids 61–128 of the α₁-subunit are mandatory for quantitative heterodimerization implying that the C-α₁-splice variant should lose its capacity to dimerize quantitatively.

Methodology/Principal Findings

In the current study we demonstrate preserved quantitative dimerization of the C-α₁-splice by co-purification with the β₁-subunit. In addition we used fluorescence resonance energy transfer (FRET) based on fluorescence lifetime imaging (FLIM) using fusion proteins of the β₁-subunit and the α₁-subunit or the C-α₁ variant with ECFP or EYFP. Analysis of the respective combinations in HEK-293 cells showed that the fluorescence lifetime was significantly shorter (≈0.3 ns) for α₁/β₁ and C-α₁/β₁ than the negative control. In addition we show that lack of the amino-terminus in the α₁ splice variant directs it to a more oxidized subcellular compartment.

Conclusions/Significance

We conclude that the amino-terminus of the α₁-subunit is dispensable for dimerization in-vivo and ex-vivo, but influences the subcellular trafficking.

RNA splicing in regulation of nitric oxide receptor soluble guanylyl cyclase

Soluble guanylyl cyclase (sGC) is a key protein in the nitric oxide (NO)/-cGMP signaling pathway. sGC activity is involved in a number of important physiological processes including smooth muscle relaxation, neurotransmission and platelet aggregation and adhesion. Regulation of sGC expression and activity emerges as a crucial factor in control of sGC function in normal and pathological conditions. Recently accumulated evidence strongly indicates that the regulation of sGC expression is a complex process modulated on several levels including transcription, post-transcriptional regulation, translation and protein stability. Presently our understanding of mechanisms governing regulation of sGC expression remains very limited and awaits systematic investigation. Among other ways, the expression of sGC subunits is modulated at the levels of mRNA abundance and transcript diversity. In this review we summarize available information on different mechanisms (including transcriptional activation, mRNA stability and alternative splicing) involved in the modulation of mRNA levels of sGC subunits in response to various environmental clues. We also summarize and cross-reference the information on human sGC splice forms available in the literature and in genomic databases. This review highlights the fact that the study of the biological role and regulation of sGC splicing will bring new insights to our understanding of NO/cGMP biology.