NK Family Research Articles

Evaluation possibility of the turbine disks using of converted aircraft engines of the NK family

The article examines the possibility of using converted aircraft engines for gas pumping units using the example of the main parts of the GTE - the disks of the NK-8-2U aircraft engine and the NK-16ST and NK-16-18ST ground engines. For all disks of the second stage of low-pressure turbines of three engines, the stress-strain state calculation was performed using the boundary integral equations method (BEM) and using the FEM in the Ansys program. For three disk stress concentrators, the theoretical stress concentration coefficient was determined and the maximum equivalent stresses were calculated. During long-term operation, the main parameters of engine operation change due to degradation changes (wear, erosion and corrosion, development of seals, contamination and resizing of flow parts). As a result, the main parameters of engine operation change, in particular, the rotation speed of the rotors and the gas temperature in the turbine, which determine the stress-strain state, which must be taken into account when predicting durability. The compliance of the results of the calculated study of the stress-strain state of turbine disks with their real load was confirmed by the data of their metallurgical study after prolonged operation. Using the Manson formula for the disks of three engines, their cyclic durability was determined before the formation of a crack of low-cycle fatigue. Using the linear damage summation hypothesis, the total damage rates (under static loading and under fatigue loading) for the disks of three engines were calculated. It is established that after the conversion of aircraft engines that have spent their life in flight operation, it is advisable to continue the use of turbine disks on ground-based GTU.

Influence of operating time on the strength reliability of the gas generator turbine disk of the aircraft drive for the GPA

This paper contains the analysis of characteristics changes of mechanical properties of the EI698-VD alloy depending on the duration of operation of the NK family gas turbine disks working as part of a gas generator turbine for GPA. Their stress-strain state was determined using the finite element method. The strength reserves are defined as characteristics of the disks’ strength reliability at different levels of the operating time.

Development and prospects for the introduction of a low-emission combustion system for ground-based gas turbine engines and gas turbine units

Today, more and more “stringent” requirements are established in the world for the emission of harmful substances in the combustion products of gas turbines operated and newly developed, which is why the issue of ensuring environmental safety is relevant. The article presents the basic principles of organizing low - emission fuel combustion based on a generalization of experience in the successful operation of gas turbines of the NK family, which ensured that modern requirements for reliability and environmental safety are met. An example is given of the modernization of the gas turbine combustion chamber in order to reduce the levels of emissions of harmful substances. The experience of introducing into serial production of additive technology for the manufacture of basic elements of low-emission combustion chamber using selective laser melting technology is described.

Study of Mechanical Properties Stability in the Production of Turbine Disks for Gas Compressor Units

A statistical analysis of the baseline strength characteristics of the EI698-VD alloy disks of high-pressure turbines of the NK family engines operating as a part of gas compressor units is performed. The results of the assessment of mechanical properties stability in the disk production during the period 1998–2015 are presented.

Expression of NK genes that are not part of the NK cluster in the onychophoran Euperipatoides rowelli (Peripatopsidae)

BackgroundNK genes are a group of homeobox transcription factors that are involved in various molecular pathways across bilaterians. They are typically divided into two subgroups, the NK cluster (NKC) and NK-linked genes (NKL). While the NKC genes have been studied in various bilaterians, corresponding data of many NKL genes are missing to date. To further investigate the ancestral roles of NK family genes, we analyzed the expression patterns of NKL genes in the onychophoran Euperipatoides rowelli.ResultsThe NKL gene complement of E. rowelli comprises eight genes, including BarH, Bari, Emx, Hhex, Nedx, NK2.1, vax and NK2.2, of which only NK2.2 was studied previously. Our data for the remaining seven NKL genes revealed expression in different structures associated with the developing nervous system in embryos of E. rowelli. While NK2.1 and vax are expressed in distinct medial regions of the developing protocerebrum early in development, BarH, Bari, Emx, Hhex and Nedx are expressed in late developmental stages, after all major structures of the nervous system have been established. Furthermore, BarH and Nedx are expressed in distinct mesodermal domains in the developing limbs.ConclusionsComparison of our expression data to those of other bilaterians revealed similar patterns of NK2.1, vax, BarH and Emx in various aspects of neural development, such as the formation of anterior neurosecretory cells mediated by a conserved molecular mechanism including NK2.1 and vax, and the development of the central and peripheral nervous system involving BarH and Emx. A conserved role in neural development has also been reported from NK2.2, suggesting that the NKL genes might have been primarily involved in neural development in the last common ancestor of bilaterians or at least nephrozoans (all bilaterians excluding xenacoelomorphs). The lack of comparative data for many of the remaining NKL genes, including Bari, Hhex and Nedx currently hampers further evolutionary conclusions. Hence, future studies should focus on the expression of these genes in other bilaterians, which would provide a basis for comparative studies and might help to better understand the role of NK genes in the diversification of bilaterians.

Expression of NK cluster genes in the onychophoran Euperipatoides rowelli: implications for the evolution of NK family genes in nephrozoans

BackgroundUnderstanding the evolution and development of morphological traits of the last common bilaterian ancestor is a major goal of the evo-devo discipline. The reconstruction of this “urbilaterian” is mainly based on comparative studies of common molecular patterning mechanisms in recent model organisms. The NK homeobox genes are key players in many of these molecular pathways, including processes regulating mesoderm, heart and neural development. Shared features seen in the expression patterns of NK genes have been used to determine the ancestral bilaterian characters. However, the commonly used model organisms provide only a limited view on the evolution of these molecular pathways. To further investigate the ancestral roles of NK cluster genes, we analyzed their expression patterns in the onychophoran Euperipatoides rowelli.ResultsWe identified nine transcripts of NK cluster genes in E. rowelli, including single copies of NK1, NK3, NK4, NK5, Msx, Lbx and Tlx, and two copies of NK6. All of these genes except for NK6.1 and NK6.2 are expressed in different mesodermal organs and tissues in embryos of E. rowelli, including the anlagen of somatic musculature and the heart. Furthermore, we found distinct expression patterns of NK3, NK5, NK6, Lbx and Msx in the developing nervous system. The same holds true for the NKL gene NK2.2, which does not belong to the NK cluster but is a related gene playing a role in neural patterning. Surprisingly, NK1, Msx and Lbx are additionally expressed in a segment polarity-like pattern early in development—a feature that has been otherwise reported only from annelids.ConclusionOur results indicate that the NK cluster genes were involved in mesoderm and neural development in the last common ancestor of bilaterians or at least nephrozoans (i.e., bilaterians to the exclusion of xenacoelomorphs). By comparing our data from an onychophoran to those from other bilaterians, we critically review the hypothesis of a complex “urbilaterian” with a segmented body, a pulsatile organ or heart, and a condensed mediolaterally patterned nerve cord.

Can the NK Family of Osteoblast Homeodomain Transcription Factors Signaling Be a Magic Bullet to Reverse Calcification-Induced Vasculopathy in Diabetes?

Human vascular calcification burden has existed for at least 5 millennia and has long been a major area of interest in the cardiovascular physiopathology research. Abnormal calcium deposition occurs in almost all arterial beds in both the media and intima in metabolic and diabetic diseases. Calcification of arteries reduces arterial elastance and compromises cardiovascular hemodynamics, which are high risk factors for cardiovascular diseases such stroke and ischemic heart disease (1). Despite the wealth of information regarding the effects of vascular calcification in atherosclerosis, metabolic syndrome, hypertension, and diabetes, the molecular mechanism of arteriosclerosis remains poorly understood. Therefore, understanding the mechanism by which diabetes and metabolic disease induce vascular calcification is crucial to identify effective new therapeutic strategies to intervene with the disease. Interestingly in this issue, Cheng et al. (2) determined the in vivo contribution of members of the highly conserved NK family of osteoblast homeodomain transcription factors 1 ( Msx1 ) and 2 ( Msx2 ) signaling in arteriosclerosis and vascular stiffness in diabetic mice. The study by Cheng et al. provides new insight into the molecular mechanism that drives arteriosclerosis in diabetes and suggests a potential target for future therapy. Thus, targeting Msx1 …

Methodology of modernizing the serial converted gas turbine unit

The ways and special features of modernizing the ground-based power plants that are converted from the aircraft gas turbine engines as well as the appearing problems are considered by an example of the NK family engines being developed.

The role of Nkx3.2 in chondrogenesis

Transcription factor, Nkx3.2, is a member of the NK family of developmental genes and is expressed during embryogenesis in a variety of mammalian model organisms, including chicken and mouse. It was first identified in Drosophila as the Bagpipe (bap) gene, where it has been demonstrated to be essential during formation of the midgut musculature. However, mammalian homolog Nkx3.2 has been shown to play a significant role in axial and limb skeletogenesis; in particular, the human skeletal disease, spondylo-megaepiphyseal-metaphyseal dysplasia (SMMD), is associated with mutations of the Nkx3.2 gene. In this review, we highlight the role of Nkx3.2 during musculoskeletal development, with an emphasis on the factor's role in determining chondrogenic cell fate and its subsequent role in endochondral ossification and chondrocyte survival.

Protein Kinase D3 Is a Pivotal Activator of Pathological Cardiac Hypertrophy by Selectively Increasing the Expression of Hypertrophic Transcription Factors

Fetal cardiac gene reactivation is a hallmark of pathological cardiac hypertrophy (PCH) driven by cardiac transcription factors (TFs) such as nuclear factor of activated T-cells (NFATs). Nuclear import of dephosphorylated NFATs catalyzed by calcineurin (CaN) is a well-established hypertrophic mechanism. Here we report that NFATc4 expression is also up-regulated by newly expressed protein kinase D3 (PKD3) to induce PCH. In both in vitro and in vivo cardiac hypertrophic models, the normally undetectable PKD3 was profoundly up-regulated by isoproterenol followed by overt expression of cardiac TFs including NFATc4, NK family of transcription factor 2.5 (Nkx2.5), GATA4 and myocyte enhancer factor 2 (MEF2). Using gene silencing approaches, we demonstrate PKD3 is required for increasing the expression of NFATc4, Nkx2.5, and GATA4 while PKD1 is required for the increase in MEF2D expression. Upstream induction of PKD3 is driven by nuclear entry of CaN-activated NFATc1 and c3 but not c4. Therefore, PKD3 is a pivotal mediator of the CaN-NFATc1/c3-PKD3-NFATc4 hypertrophic signaling cascade and a potential new drug target for the PCH.

Local Optima Networks of NK Landscapes With Neutrality

In previous work, we have introduced a network based model that abstracts many details of the underlying landscape and compresses the landscape information into a weighted, oriented graph which we call the local optima network. The vertices of this graph are the local optima of the given fitness landscape, while the arcs are transition probabilities between local optima basins. Here, we extend this formalism to neutral fitness landscapes, which are common in difficult combinatorial search spaces. The study is based on two neutral variants of the well-known NK family of landscapes (where N stands for the chromosome length, and K for the number of gene epistatic interactions within the chromosome). By using these two NK variants, probabilistic (NKp), and quantified NK (NKq), in which the amount of neutrality can be tuned by a parameter, we show that our new definitions of the optima networks and the associated basins are consistent with the previous definitions for the non-neutral case. Moreover, our empirical study and statistical analysis show that the features of neutral landscapes interpolate smoothly between landscapes with maximum neutrality and non-neutral ones. We found some unknown structural differences between the two studied families of neutral landscapes. But overall, the network features studied confirmed that neutrality, in landscapes with percolating neutral networks, may enhance heuristic search. Our current methodology requires the exhaustive enumeration of the underlying search space. Therefore, sampling techniques should be developed before this analysis can have practical implications. We argue, however, that the proposed model offers a new perspective into the problem difficulty of combinatorial optimization problems and may inspire the design of more effective search heuristics.

Msx1 and Msx2are required for endothelial-mesenchymal transformation of the atrioventricular cushions and patterning of the atrioventricular myocardium

BackgroundMsx1 and Msx2, which belong to the highly conserved Nk family of homeobox genes, display overlapping expression patterns and redundant functions in multiple tissues and organs during vertebrate development. Msx1 and Msx2 have well-documented roles in mediating epithelial-mesenchymal interactions during organogenesis. Given that both Msx1 and Msx2 are crucial downstream effectors of Bmp signaling, we investigated whether Msx1 and Msx2 are required for the Bmp-induced endothelial-mesenchymal transformation (EMT) during atrioventricular (AV) valve formation.ResultsWhile both Msx1-/- and Msx2-/- single homozygous mutant mice exhibited normal valve formation, we observed hypoplastic AV cushions and malformed AV valves in Msx1-/-; Msx2-/- mutants, indicating redundant functions of Msx1 and Msx2 during AV valve morphogenesis. In Msx1/2 null mutant AV cushions, we found decreased Bmp2/4 and Notch1 signaling as well as reduced expression of Has2, NFATc1 and Notch1, demonstrating impaired endocardial activation and EMT. Moreover, perturbed expression of chamber-specific genes Anf, Tbx2, Hand1 and Hand2 reveals mispatterning of the Msx1/2 double mutant myocardium and suggests functions of Msx1 and Msx2 in regulating myocardial signals required for remodelling AV valves and maintaining an undifferentiated state of the AV myocardium.ConclusionOur findings demonstrate redundant roles of Msx1 and Msx2 in regulating signals required for development of the AV myocardium and formation of the AV valves.

Role of Scavenger Receptors in the Binding and Internalization of Heat Shock Protein 70

Extracellular heat shock protein 70 (Hsp70) exerts profound effects both in mediating tumor rejection by Hsp70-based vaccines and in autoimmunity. Further progress in this area, however, awaits the identification of the cell surface receptors for extracellular Hsp70 that mediate its immune functions. We have examined a wide range of candidate Hsp70 receptors and find significant binding through two main families of cell surface proteins, including 1) the scavenger receptor (SR) family and 2) C-type lectins of the NK family. In addition, given that the anticancer effects of Hsp70 vaccines have been shown to involve uptake of Ags by APC exposed to Hsp70-tumor Ag complexes, we have examined the ability of the receptors identified here to internalize Hsp70-peptide complexes. Our findings indicate that three members of the SR family (lectin-like oxidized low density lipoprotein receptor 1; fasciclin, epidermal growth factor-like, laminin-type epidermal growth factor-like, and link domain-containing scavenger receptor-1; and SR expressed by endothelial cells-1) are able to bind Hsp70-peptide complexes and mediate its efficient internalization. Indeed, each of the SR was able to mediate efficient uptake of Hsp70 when transfected into Chinese hamster ovary cells previously null for uptake. Curiously, Hsp70 internalization occurs independently of the intracellular domains of the SR, and Hsp70 uptake could be detected when the entire intracellular domain of lectin-like oxidized low density lipoprotein receptor 1 or SR expressed by endothelial cells-1 was truncated. The existence of a wide repertoire of cell surface Hsp70-binding structures may permit intracellular responses to extracellular Hsp70 that are cell specific and discriminate between Hsp70 family members.

Physical and Functional Interactions between the Prostate Suppressor Homeoprotein NKX3.1 and Serum Response Factor

The NKX3.1 transcription factor is an NK family homeodomain protein and a tumor suppressor gene that is haploinsufficient and down-regulated in the early phases of prostate cancer. Like its cardiac homolog, NKX2.5, NKX3.1 acts synergistically with serum response factor (SRF) to activate expression from the smooth muscle γ-actin (SMGA) gene promoter. Using NMR spectroscopy, three conserved motifs in a construct containing the N-terminal region and homeodomain of NKX3.1 were observed to interact with the MADS box domain of SRF. These motifs interacted both in the absence of DNA and when both proteins were bound to a SMGA promoter DNA sequence. No significant interaction was seen between the homeodomain and SRF MADS box. One of the SRF-interacting regions was the tinman (TN) or engrailed homology-1 motif (EH-1), residues 29–35 (FLIQDIL), which for other NK proteins is the site of interaction with the repressor protein Groucho. A second hydrophobic interacting region was designated the SRF-interacting (SI) motif and included residues 99–105 (LGSYLLD). A third interacting motif was the acidic region adjacent to the SI motif including residues 88–96 (ETLAETEPE). The acidic domain (AD) motif signals also showed strengthening upon the NKX3.1 homeodomain binding to DNA in the absence of SRF, consistent with the acidic region weakly interacting with the homeodomain in the unbound state. The importance of these linear motifs in the transcriptional interaction of NKX3.1 and SRF was demonstrated by targeted mutagenesis of an NKX3.1 expression vector in a SMGA reporter assay. The results implicate the NKX3.1 N-terminal region in regulation of transcriptional activity of this tumor suppressor.

Lymphoblastoid cells express HLA-B27 homodimers both intracellularly and at the cell surface following endosomal recycling.

The MHC class I allele HLA-B27 is very strongly associated with development of autoimmune spondyloarthritis, although the disease mechanism remains unknown. Class I molecules classically associate in the endoplasmic reticulum (ER) with beta2-microglobulin (beta(2)m) and antigenic peptides for cell surface expression and presentation to T cells. We have previously shown that HLA-B27 is capable of forming beta(2)m-free disulfide-bonded homodimers in vitro. Here we show that HLA-B27 forms disulfide-bonded homodimers in vivo by two distinct pathways. HLA-B27 homodimers form in the ER but appear unable to egress to the cell surface in human cells. Cell surface HLA-B27 homodimers are abundantly expressed in a variety of lymphoid cell lines. Experiments with inhibitors indicate that HLA-B27 homodimers can arise from cell-surface heterodimers via an endosome-dependent recycling pathway. HLA-B27 homodimer expression on the cell surface of 721.220 is dependent on the unpaired cysteine(67) and is inhibited by restoration of tapasin function or by incubation with peptides that bind strongly to HLA-B27 heterodimers. Cell surface expressed HLA-B27 homodimers are likely to be immunologically reactive ligands for NK family immunoreceptors and, hence, could play a pathogenic role in spondyloarthritis.

A novel NK-type homeobox gene, ENK (early embryo specific NK), preferentially expressed in embryonic stem cells

In order to identify novel homeobox-containing genes involved in early embryonic development, we conducted a degenerate oligonucleotide polymerase chain reaction (PCR) screening of a murine embryonic stem (ES) cell cDNA library. ENK (early embryo specific expression NK family) was one of several genes isolated that was found to exhibit early embryo stage-specific expression. The full-length ENK cDNA was cloned and its genomic organization was characterized. Murine ENK spans 7.1 kb, encodes four exons and maps to mouse chromosome 6F2. Reverse transcriptase–PCR and Northern blot analyses show that ENK is preferentially expressed in pre-implantation mouse embryos and a higher level in blastocysts. Whole-mount in situ hybridization analysis further demonstrates that ENK mRNA is present predominantly in the inner cell mass of blastocysts. The expression of ENK is markedly higher in undifferentiated ES cells than in retinoic acid differentiated ES cells and embryonic bodies. ENK expression slightly decreased in early primitive ectoderm-like (EPL) cells and was absent after the 9.5-day embryo stages. ENK is one of the few homeobox-encoding genes preferentially expressed in ES cells during mammalian embryogenesis.

Sequence of a conserved region of a new sea urchin homeobox gene from the NK family.

The partial sequence of a novel homeobox-containing gene from Paracentrotus lividus is described. Both cDNA and genomic DNA were screened using probes from the vnd/NK-2 homeobox gene found in Drosophila melanogaster. The new DNA sequence found in P. lividus encodes a protein fragment that is closely related to the NK family of homeodomain transcriptional regulators originally discovered in the fruit fly. This study thus represents the first finding of a homeobox gene from the NK family in sea urchin. The DNA that was sequenced includes the most highly conserved region of the NK genes and contains the 180 basepair homeobox (i.e. the DNA segment that encodes the homeodomain), the NK-2 box that encodes the NK-2-specific domain (NK-2 SD), and the acidic box that encodes an acidic domain, but which is found only in a limited subset of the NK genes. In this deduced sequence, the 60 amino acid residue homeodomain contains tyrosine in position 54 and leucine in position 7, which implies that the protein will bind to an unusual sequence of DNA that contains 5'-CAAGTG-3' as its core. The presence of tyrosine in position 54 identifies the gene as a member of the NK-2 class of homeobox genes. Positions 37 and 56 of the homeodomain contain isoleucine and leucine, respectively, which is the first finding in the NK family of homeodomains of these particular amino acid residues in those positions. The presence of the NK-2 box is consistent with identification of the gene as a member of the NK-2 class, and suggests an important role for the C-terminal portion of the protein in transcriptional activation. The sequence homology of the NK-2 box and the spacing between it and the homeobox further suggest that this gene is a member of the NKx-2.2 subclass, whose genes typically are expressed in brain and play a role in axonal guidance, and whose full lengths often are of the order of 900 bases. Homologous NK genes have been found in such diverse invertebrate and vertebrate species, such as Amphioxus sp., Xenopus sp., Caenorhabditis elegans, zebra fish, chicken, hamster, mouse and humans. The finding of this new gene together with sequence comparisons suggests possible evolutionary relationships between sea urchins and vertebrates in the developmental pathways of their body plans.

A Triad of Serum Response Factor and the GATA and NK Families Governs the Transcription of Smooth and Cardiac Muscle Genes

Serum response factor and the (CC(A/T)(6)GG) (CArG) box interact to promote the transcription of c-fos and muscle genes; this tissue-specific activity may require co-regulators for serum response factor. The alpha(1) integrin promoter contains two cis-elements besides the CArG box: a TAAT sequence, a consensus binding site for homeoproteins, and a GATA-binding box. As a candidate TAAT-binding factor, we cloned an NK family homeobox gene, Nkx-3.2, which is expressed mainly in smooth muscle tissues and skeletal structures. Nkx-3.2, serum response factor, and GATA-6 were co-expressed only in the medial smooth muscle layer of arteries. These three transcription factors formed a complex with their corresponding cis-elements and cooperatively transactivated smooth muscle genes, including alpha(1) integrin, SM22alpha, and caldesmon. Cardiac muscle-specific members of the NK and GATA families exist, and the triad of Nkx-2.5, serum response factor, and GATA-4 also transactivated the cardiac atrial natriuretic factor gene, which contains a CArG-like box, a GATA-binding box, and an NK-binding element. Our findings demonstrate that smooth and cardiac muscle have a shared transcriptional machinery and that the GATA and NK families confer muscle specificity on the serum response factor/CArG interaction.

The role of Bapx1 (Nkx3.2) in the development and evolution of the axial skeleton.

The bagpipe-related homeobox-containing genes are members of the NK family, bagpipe (bap) was first identified in Drosophila and there are three different bagpipe-related genes in vertebrates. Only two of these are found in mammals, the Nkx3.1 and the Bapxl (Nkx3.2) gene. The targeted mutation in the mouse Bapxl gene shows a vertebral phenotype in which the ventromedial elements are lacking; these are the centra and the intervertebral discs. In addition, a region of gastric mesenchyme is abnormal. This mesenchyme surrounds the posterior region of the presumptive stomach and duodenum, and in the mutant fails to support normal development of the spleen. In Drosophila, bagpipe has a role in gut mesoderm and the mutant embryos have no midgut musculature. Thus bap related genes in mouse and Drosophila have roles in patterning gut mesoderm; however, neither of the mammalian genes has a discernible role in the gut musculature. In contrast, both mammalian genes have roles in developmental processes that have appeared recently in evolution. The Bapxl gene found in fish, amphibians, birds and mammals appears to have derived vertebrate specific functions sometime after the split between the jawless fish and gnathostomes.

DNA-binding sequence of the human prostate-specific homeodomain protein NKX3.1

NKX3.1 is a member of the NK class of homeodomain proteins and is most closely related to Drosophila NK-3. NKX3.1 has predominantly prostate-specific expression in the adult human. Previous studies suggested that NKX3.1 exerts a growth-suppressive effect on prostatic epithelial cells and controls differentiated glandular functions. Using a binding site selection assay with recombinant NKX3.1 protein we identified a TAAGTA consensus binding sequence that has not been reported for any other NK class homeoprotein. By electromobility shift assay we demonstrated that NKX3.1 preferentially binds the TAAGTA sequence rather than the binding site for Nkx2.1 (CAAGTG) or Msx1 (TAATTG). Using mutated binding sites in competitive gel shift assays, we analyzed the nucleotides in the TAAGTA consensus sequence that are important for NKX3.1 binding. The consensus binding site of a naturally occurring polymorphic NKX3.1 protein with arginine replaced by cysteine at position 52 was identical to the wild-type binding sequence. The binding affinities of wild-type and polymorphic NKX3.1 for the TAAGTA consensus site were very similar, with values of 20 and 22 nM, respectively. Wild-type and polymorphic NKX3.1 specifically repressed transcription of luciferase from a reporter vector with three copies of the NKX3.1-binding site upstream from a thymidine kinase promoter. The data show that among NK family proteins NKX3.1 binds a novel DNA sequence and can behave as an in vitro transcriptional repressor.