Improved mitochondrial function in the hearts of sarcolipin-deficient dystrophin and utrophin double-knockout mice

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disease associated with cardiomyopathy. DMD cardiomyopathy is characterized by abnormal intracellular Ca2+ homeostasis and mitochondrial dysfunction. We used dystrophin and utrophin double-knockout (mdx:utrn-/-) mice in a sarcolipin (SLN) heterozygous-knockout (sln+/-) background to examine the effect of SLN reduction on mitochondrial function in the dystrophic myocardium. Germline reduction of SLN expression in mdx:utrn-/- mice improved cardiac sarco/endoplasmic reticulum (SR) Ca2+ cycling, reduced cardiac fibrosis, and improved cardiac function. At the cellular level, reducing SLN expression prevented mitochondrial Ca2+ overload, reduced mitochondrial membrane potential loss, and improved mitochondrial function. Transmission electron microscopy of myocardial tissues and proteomic analysis of mitochondria-associated membranes showed that reducing SLN expression improved mitochondrial structure and SR-mitochondria interactions in dystrophic cardiomyocytes. These findings indicate that SLN upregulation plays a substantial role in the pathogenesis of cardiomyopathy and that reducing SLN expression has clinical implications in the treatment of DMD cardiomyopathy.

Research advances of MAL family members in tumorigenesis and tumor progression (Review)

The myelin and lymphocyte protein (MAL) family is a novel gene family first identified and characterized in 2002. This family is comprised of seven members, including MAL, MAL2, plasmolipin, MALL, myeloid differentiation‑associated marker (MYADM), MYADML2 and CMTM8, which are located on different chromosomes. In addition to exhibiting extensive activity during transcytosis, the MAL family plays a vital role in the neurological, digestive, respiratory, genitourinary and other physiological systems. Furthermore, the intimate association between MAL and the pathogenesis, progression and metastasis of malignancies, attributable to several mechanisms such as DNA methylation has also been elucidated. In the present review, an overview of the structural and functional properties of the MAL family and the latest research findings regarding the relationship between several MAL members and various cancers is provided. Furthermore, the potential clinical and scientific significance of MAL is discussed and directions for future research are summarized.

Sarcolipin relates to fattening, but not sarco/endoplasmic reticulum Ca2+-ATPase uncoupling, in captive migratory gray catbirds

In order to complete their energetically demanding journeys, migratory birds undergo a suite of physiological changes to prepare for long-duration endurance flight, including hyperphagia, fat deposition, reliance on fat as a fuel source, and flight muscle hypertrophy. In mammalian muscle, SLN is a small regulatory protein which binds to sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) and uncouples Ca2+ transport from ATP hydrolysis, increasing energy consumption, heat production, and cytosolic Ca2+ transients that signal for mitochondrial biogenesis, fatigue resistance and a shift to fatty acid oxidation. Using a photoperiod manipulation of captive gray catbirds (Dumetella carolinensis), we investigated whether SLN may play a role in coordinating the development of the migratory phenotype. In response to long-day photostimulation, catbirds demonstrated migratory restlessness and significant body fat stores, alongside higher SLN transcription while SERCA2 remained constant. SLN transcription was strongly correlated with h-FABP and PGC1α transcription, as well as fat mass. However, SLN was not significantly correlated with HOAD or CD36 transcripts or measurements of SERCA activity, SR membrane Ca2+ leak, Ca2+ uptake rates, pumping efficiency or mitochondrial biogenesis. Therefore, SLN may be involved in the process of storing fat and shifting to fat as a fuel, but the mechanism of its involvement remains unclear.

Reduced Proteolipid Protein 2 promotes endoplasmic reticulum stress-related apoptosis and increases drug sensitivity in acute myeloid leukemia

BACKGROUND

The Proteolipid Protein 2 (PLP2), a protein in the Endoplasmic Reticulum (ER) membrane, has been reported to be highly expressed in various tumors. Previous studies have demonstrated that the reduced PLP2 can induce apoptosis and autophagy through ER stress-related pathways, leading to a decreased proliferation and aggressiveness. However, there is no research literature on the role of PLP2 in Acute Myeloid Leukemia (AML).

METHODS

PLP2 expression, clinical data, genetic mutations, and karyotype changes from GEO, TCGA, and timer2.0 databases were analyzed through the R packages. The possible functions and pathways of cells were explored through GO, KEGG, and GSEA enrichment analysis using the clusterProfiler R package. Immuno-infiltration analysis was conducted using the Cibersort algorithm and the Xcell R package. RT-PCR and western blot techniques were employed to identify the PLP2 expression, examine the knockdown effects in THP-1 cells, and assess the expression of genes associated with endoplasmic reticulum stress and apoptosis. Flow cytometry was utilized to determine the apoptosis and survival rates of different groups.

RESULTS

PLP2 expression was observed in different subsets of AML and other cancers. Enrichment analyses revealed that PLP2 was involved in various tumor-related biological processes, primarily apoptosis and lysosomal functions. Additionally, PLP2 expression showed a strong association with immune cell infiltration, particularly monocytes. In vitro, the knockdown of PLP2 enhanced endoplasmic reticulum stress-related apoptosis and increased drug sensitivity in THP-1 cells.

CONCLUSIONS

PLP2 could be a novel therapeutic target in AML, in addition, PLP2 is a potential endoplasmic reticulum stress regulatory gene in AML.

Functional characterization of obscure puffer ToNK-lysin: A novel immunomodulator possessing anti-bacterial and anti-inflammatory properties

NK-lysins are one of the most abundant antimicrobial peptides produced by cytotoxic T lymphocytes (CTLs) and natural killer cells (NKs), and identified as a new class of intrinsically disordered proteins, playing critical roles in the cell-mediated cytotoxicity response, as well as immunomodulatory and antimicrobial activities upon a significant range of pathogens. In the present study, an NK-lysin was identified from Obscure puffer Takifugu obscurus (ToNK-lysin). The open reading frame of ToNK-lysin sequence spans 423 bp, encoding a peptide with 140 amino acids which shares a moderate residue identity (18%-60%) with NK-lysin of mammals and other teleost species. Phylogenetic analysis revealed that ToNK-lysin was most closely related to NK-lysins from the Pleuronectiformes (Bastard halibut Paralichthys olivaceus and Pacific halibut Hippoglossus stenolepis). Comprehensive computational analysis revealed that ToNK-lysin have substantial level of intrinsic disorder, which might be contribute to its multifunction. The transcripts of the ToNK-lysin were detected in multiple examined tissues and most abundant in gills. After bacterial and Poly I:C challenge, the transcriptional levels of ToNK-lysin were significantly up-regulated in the head kidney, liver and spleen at different time points. The recombinant ToNK-lysin showed significant antibacterial activity against Vibrio harveyi and Escherichia coli, and the ToNK-lysin treatment not only reduced the bacterial loads in liver and head kidney, but also alleviated the pathogen-mediated upregulation of immune-related genes. In addition, the co-incubation with rToNK-lysin protein remarkably degraded bacterial genomic DNA, suggesting the potential mechanism of ToNK-lysin against microbes. These results suggest that ToNK-lysin possess antibacterial and immunoregulatory function both in vivo and in vitro, which may allow it a potential applicability to the aquaculture industry.

Antibacterial and anticancer activity of two NK-lysin-derived peptides from the Antarctic teleost Trematomus bernacchii

The NK-lysin antimicrobial peptide, first identified in mammals, possesses both antibacterial and cytotoxic activity against cancer cell lines. Homologue peptides isolated from different fish species have been examined for their functional characteristics in the last few years. In this study, a NK-lysin transcript was identified in silico from the head kidney transcriptome of the Antarctic teleost Trematomus bernacchii. The corresponding amino acid sequence, slightly longer than NK-lysins of other fish species, contains six cysteine residues that in mammalian counterparts form three disulphide bridges. Real time-PCR analysis indicated its predominant expression in T. bernacchii immune-related organs and tissues, with greatest mRNA abundance detected in gills and spleen. Instead of focusing on the full T. bernacchii derived NK-lysin mature molecule, we selected a 27 amino acid residue peptide (named NKL-WT), corresponding to the potent antibiotic NK-2 sequence found in human NK-lysin. Moreover, we designed a mutant peptide (named NKL-MUT) in which two alanine residues substitute the two cysteines found in the NKL-WT. The two peptides were obtained by solid phase organic synthesis to investigate their functional features. NKL-WT and NKL-MUT displayed antibacterial activity against the human pathogenic bacterium Enterococcus faecalis and the ESKAPE pathogen Acinetobacter baumannii, respectively. Moreover, at the determined Minimum Inhibitory Concentration and Minimum Bactericidal Concentration values against these pathogens, both peptides showed high selectivity as they did not exhibit any haemolytic activity on erythrocytes or cytotoxic activity against mammalian primary cell lines. Finally, the NKL-MUT selectively triggers the killing of the melanoma cell line B16F10 by means of a pro-apoptotic pathway at a concentration range in which no effects were found in normal mammalian cell lines. In conclusion, the two peptides could be considered as promising candidates in the fight against antibiotic resistance and tumour proliferative action, and also be used as innovative adjuvants, either to decrease chemotherapy side effects or to enhance anticancer drug activity.

NKHs27, a sevenband grouper NK-Lysin peptide that possesses immunoregulatory and antimicrobial activity

As an effective and broad-spectrum antimicrobial peptide, NK-Lysin is attracted more and more attention at present. However, the functions and action mechanism of NK-Lysin peptides are still not comprehensive enough at present. In this study, a sevenband grouper (Hyporthodus septemfasciatus) NK-Lysin peptide, NKHs27, was identified and synthesized, and its biological functions were studied. The results indicated that NKHs27 shares 44.44%∼88.89% overall sequence identities with other teleost NK-Lysin peptides. The following antibacterial activity assay exhibited that NKHs27 was active against both Gram-negative and Gram-positive bacteria, including Staphylococcus aureus, Listonella anguillarum, Vibrio parahaemolyticus and Vibrio vulnificus. Additionally, NKHs27 showed a synergistic effect when it was combined with rifampicin or erythromycin. In the process of interaction with the L. anguillarum cells, NKHs27 changed the cell membrane permeability and retained its morphological integrity, then penetrated into the cytoplasm to act on genomic DNA or total RNA. Then, in vitro studies showed that NKHs27 could enhance the respiratory burst ability of macrophages and upregulate immune-related genes expression in it. Moreover, NKHs27 incubation improved the proliferation of peripheral blood leukocytes significantly. Finally, in vivo studies showed that administration of NKHs27 prior to bacterial infection significantly reduced pathogen dissemination and replication in tissues. In summary, these results provide new insights into the function of NK-Lysin peptides in teleost and support that NKHs27, as a novel broad-spectrum antibacterial peptide, has potential applications in aquaculture against pathogenic infections.

Genomic Variant in NK-Lysin Gene Is Associated with T Lymphocyte Subpopulations in Pigs

As an antimicrobial peptide, NK-lysin (NKL) plays an important role in the innate immune system of organisms. In this study, 300 piglets (68 Landrace pigs, 158 Large White pigs and 74 Songliao Black pigs) were used to further explore the function of NLK gene in porcine immune system. The quantitative real-time PCR analysis detected the NKL gene's expression, and the result demonstrated that NKL mRNA was expressed in lung, spleen, stomach, kidney, liver and heart, and the expression level decreased sequentially. A single-nucleotide polymorphism (SNP, g.59070355 G > A) in intron 3 of the NKL gene was detected by PCR amplification and sequencing. The results of the Chi-square (χ2) test showed that the genotype of the SNP was consistent with the Hardy-Weinberg equilibrium. What's more, association analysis results showed the SNP in NKL gene was significantly associated with T lymphocyte subpopulations. Different genotypes had significant effects on the proportion of CD4-CD8-, CD4-CD8+, CD4+CD8+, CD8+, CD4+/CD8+ in peripheral blood (p < 0.05). These results further suggested that NKL could be recognized as a promising immune gene for swine disease resistance breeding.

Knockdown of sarcolipin (SLN) impairs substrate utilization in human skeletal muscle cells

BACKGROUND

Recent studies have highlighted that uncoupling of sarco-/endoplasmic reticulum Ca2+-ATPase (SERCA) by sarcolipin (SLN) increases ATP consumption and contributes to heat liberation. Exploiting this thermogenic mechanism in skeletal muscle may provide an attractive strategy to counteract obesity and associated metabolic disorders. In the present study, we have investigated the role of SLN on substrate metabolism in human skeletal muscle cells.

METHODS AND RESULTS

After generation of skeletal muscle cells with stable SLN knockdown (SLN-KD), cell viability, glucose and oleic acid (OA) metabolism, mitochondrial function, as well as gene expressions were determined. Depletion of SLN did not influence cell viability. However, glucose and OA oxidation were diminished in SLN-KD cells compared to control myotubes. Basal respiration measured by respirometry was also observed to be reduced in cells with SLN-KD. The metabolic perturbation in SLN-KD cells was reflected by reduced gene expression levels of peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α) and forkhead box O1 (FOXO1). Furthermore, accumulation of OA was increased in cells with SLN-KD compared to control cells. These effects were accompanied by increased lipid formation and incorporation of OA into complex lipids. Additionally, formation of complex lipids and free fatty acid from de novo lipogenesis with acetate as substrate was enhanced in SLN-KD cells. Detection of lipid droplets using Oil red O staining also showed increased lipid accumulation in SLN-KD cells.

CONCLUSIONS

Overall, our study sheds light on the importance of SLN in maintaining metabolic homeostasis in human skeletal muscle. Findings from the current study suggest that therapeutic strategies involving SLN-mediated futile cycling of SERCA might have significant implications in the treatment of obesity and associated metabolic disorders.

Antimicrobial and immunoregulatory activities of the derived peptide of a natural killer lysin from black rockfish (Sebastes schlegelii)

Natural killer lysin (NK-lysin) is a small molecule antimicrobial peptide secreted by natural killer cells and T lymphocytes. In this study, we characterized a cDNA sequence encoding an NK-lysin homologue (SsNKL1) from black rockfish, Sebastes schlegelii. The open reading frame (ORF) of SsNKL1 encodes a putative protein of 149 amino acids and shares 44%-87% overall sequence identities with other teleost NK-lysins. SsNKL1 possesses conserved NK-lysin family features, including a signal sequence and a surfactant-associated protein B (SapB) domain, sequence analysis revealed that SsNKL1 is most closely related to false kelpfish (Sebastiscus marmoratus) NK-lysin (with 87% sequence identity). SsNKL1 transcripts were detected in all the tested tissues, with the highest level in the kidney, followed by the spleen and gills. Upon Listonella anguillarum infection, the mRNA expression of SsNKL1 in the black rockfish was significantly up-regulated in the liver and kidney. The derived peptide SsNKLP27 from SsNKL1 was synthesized, and its biological function was studied. SsNKLP27 showed direct antibacterial activity against Gram-negative and Gram-positive bacteria, including Staphylococcus aureus, Bacillus subtilis, L. anguillarum, Vibrio parahaemolyticus, Vibrio alginolyticus and Vibrio vulnificus. SsNKLP27 treatment facilitated the bactericidal process of erythromycin by enhancing the permeability of the outer membrane. In the process of interaction with the target bacterial cells, SsNKLP27 changed the permeability and retained the morphological integrity of the cell membrane, then penetrated into the cytoplasm, and induced the degradation of genomic DNA and total RNA. In vivo studies showed that administration of SsNKLP27 before bacterial and viral infection significantly reduced the transmission and replication of pathogens in tissues. In vitro analysis showed that SsNKLP27 could enhance the respiratory burst ability and regulate the expression of some immune-related genes of macrophages. In summary, these results provided new insights into the function of NK-lysins in teleost fish and support that SsNKLP27 is a new broad-spectrum antimicrobial peptide that has a potential application prospect in aquaculture against pathogenic infection.

Barbel steed (Hemibarbus labeo) NK-lysin protects against Aeromonas hydrophila infection via immunomodulatory activity

NK-lysins (NKLs) are a family of multifunctional antimicrobial peptides that have activity against various microorganisms. However, the immunomodulatory activity of NKL in fish remains unclear. In this study, the cDNA sequence of barbel steed (Hemibarbus labeo) NKL gene was cloned. Barbel steed NKL amino acid sequence comprised a signal peptide and a mature peptide. The saposin B domain in the mature peptide has six conserved cysteines that form three disulfide bonds. Phylogenetic analysis showed that the barbel steed NKL was most closely related to that of the common carp (Cyprinus carpio) NKL. Differential expression analysis showed that the barbel steed NKL gene was expressed in all tested tissues, with the highest expression in the spleen. In response to Aeromonas hydrophila infection, NKL was significantly upregulated in the liver, spleen, head kidney, and gill. The barbel steed NKL showed strong antibacterial activity against Vibrio parahaemolyticus, V. alginolyticus, V. vulnificus, and Listeria monocytogenes. However, NKL had no antibacterial activity against the pathogenic bacteria A. hydrophila. Lactate dehydrogenase release assays showed that NKL damaged the V. parahaemolyticus cell membrane. NKL significantly increased barbel steed survival rate after A. hydrophila infection and upregulated IL-1β and TNF-α expression in the spleen and head kidney. NKL induced monocyte/macrophage chemotaxis and enhanced the respiratory burst and proinflammatory cytokine expression. Our study shows that fish NKL exhibits immunomodulatory effects and protects the host from pathogenic infections independent of direct bacterial clearance.

A novel NK-lysin in hybrid crucian carp can exhibit cytotoxic activity in fish cells and confer protection against Aeromonas hydrophila infection in comparison with Carassius cuvieri and Carassius auratus red var

NK-lysin, an effector of natural killer (NK) cells and cytotoxic T lymphocytes (CTLs), not only exhibits cytotoxic effect in fish cells, but also participates in the immune defense against pathogenic infection. In this study, ORF sequences of RCC-NK-lysin, WCC-NK-lysin and WR-NK-lysin were 369 bp. Tissue-specific analysis revealed that the highest expressions of RCC-NK-lysin and WCC-NK-lysin were observed in gill, while the peaked level of WR-NK-lysin mRNA was observed in spleen. A. hydrophila infection sharply increased RCC-NK-lysin, WCC-NK-lysin and WR-NK-lysin mRNA expression in liver, trunk kidney and spleen. In addition, elevated levels of NK-lysin mRNA were observed in cultured fin cell lines of red crucian carp (RCC), white crucian carp (WCC) and their hybrid offspring (WR) after Lipopolysaccharide (LPS) challenge. RCC-NK-lysin, WCC-NK-lysin and WR-NK-lysin exerted regulatory roles in inducing ROS generation, modulating mitochondrial membrane potential, decreasing fish cell viability and antagonizing survival signalings, respectively. RCC/WCC/WR-NK-lysin-overexpressing fish could up-regulate expressions of inflammatory cytokines and decrease bacterial loads in spleen. These results indicated that NK-lysin in hybrid fish contained close sequence similarity to those of its parents, possessing the capacities of cytotoxicity and immune defense against bacterial infection.

Structure and regulation of the NK-lysin (1-4) and NK-lysin like (a and b) antimicrobial genes in rainbow trout (Oncorhynchus mykiss)

Nk-lysin (Nkl), an antimicrobial peptide (AMP) product of natural killer cells and cytotoxic T cells in mammals, has recently been characterized in a number of finfish species. In this study, we identified six genes with sequence homology to Nkl and characterized their patterns of mRNA expression and abundances in rainbow trout (Oncorhynchus mykiss). The cDNA sequences for the six Nkls encoded precursor peptides of 128-133 aa in length, and mature peptides of 109-111 aa in length. Genomic DNA of the nkl1-4 genes consisted of five exons and four introns, whereas the nkl-like a & b genes consisted of four exons and three introns. Chromosomal locations of these peptides show that nkl1 was located on chromosome arm 25q, whereas the other five nkl genes were clustered on chromosome arm 19q. Phylogenetic analysis revealed a conserved structure of Nkls among the teleosts and further protein sequence analyses suggests that all six nkl genes fall within the Nkl sub-family of the Saposin family of proteins. Patterns of tissue-specific mRNA expression were asymmetric among the six trout Nkl homologues, with nkl1, nkl3, and nkl-like a & b occurring in immune competent organs such as spleen, gill, intestine and kidney, as well as pineal gland, brain and oocytes. However, nkl2 and nkl4, showed primary abundances in brain, pineal gland and oocyte tissues. Using mRNA sequencing, in whole-body pools of juvenile trout fry (1 g bw) exposed to Flavobacterium psychrophilum infection, we observed modest up-regulation (2-3 fold) of five (nkl 2-4 and nkl-like a & b) of the six nkl mRNAs over the five-day post-challenge time-course. However, no upregulation could be recorded in spleen tissue measured by qPCR in juvenile trout (270 g bw). Using mRNA sequencing again, mRNA abundances were determined in gill of juvenile trout (~57.7 g bw) exposed to various aquaculture stressors. The results indicated that all six nkls (nkl1-4 and nkl-like a and nkl-like b) were downregulated when exposed to high temperature, and that nkl1 was significantly downregulated following salinity challenge. Overall, these newly characterized AMPs may contribute to host innate immunity as they are modulated following pathogen challenge and by physiological stressors.

Sarcolipin haploinsufficiency prevents dystrophic cardiomyopathy in mdx mice

Sarcolipin (SLN) is an inhibitor of sarco/endoplasmic reticulum (SR) Ca2+-ATPase (SERCA) and expressed at high levels in the ventricles of animal models for and patients with Duchenne muscular dystrophy (DMD). The goal of this study was to determine whether the germline ablation of SLN expression improves cardiac SERCA function and intracellular Ca2+ (Ca2+i) handling and prevents cardiomyopathy in the mdx mouse model of DMD. Wild-type, mdx, SLN-haploinsufficient mdx (mdx:sln+/-), and SLN-deficient mdx (mdx:sln-/-) mice were used for this study. SERCA function and Ca2+i handling were determined by Ca2+ uptake assays and by measuring single-cell Ca2+ transients, respectively. Age-dependent disease progression was determined by histopathological examinations and by echocardiography in 6-, 12-, and 20-mo-old mice. Gene expression changes in the ventricles of mdx:sln+/- mice were determined by RNA-Seq analysis. SERCA function and Ca2+i cycling were improved in the ventricles of mdx:sln+/- mice. Fibrosis and necrosis were significantly decreased, and cardiac function was enhanced in the mdx:sln+/- mice until the study endpoint. The mdx:sln-/- mice also exhibited similar beneficial effects. RNA-Seq analysis identified distinct gene expression changes including the activation of the apelin pathway in the ventricles of mdx:sln+/- mice. Our findings suggest that reducing SLN expression is sufficient to improve cardiac SERCA function and Ca2+i cycling and prevent cardiomyopathy in mdx mice.NEW & NOTEWORTHY First, reducing sarcopolin (SLN) expression improves sarco/endoplasmic reticulum Ca2+ uptake and intracellular Ca2+ handling and prevents cardiomyopathy in mdx mice. Second, reducing SLN expression prevents diastolic dysfunction and improves cardiac contractility in mdx mice Third, reducing SLN expression activates apelin-mediated cardioprotective signaling pathways in mdx heart.

A lung tropic AAV vector improves survival in a mouse model of surfactant B deficiency

Surfactant protein B (SP-B) deficiency is an autosomal recessive disorder that impairs surfactant homeostasis and manifests as lethal respiratory distress. A compelling argument exists for gene therapy to treat this disease, as de novo protein synthesis of SP-B in alveolar type 2 epithelial cells is required for proper surfactant production. Here we report a rationally designed adeno-associated virus (AAV) 6 capsid that demonstrates efficiency in lung epithelial cell transduction based on imaging and flow cytometry analysis. Intratracheal administration of this vector delivering murine or human proSFTPB cDNA into SP-B deficient mice restores surfactant homeostasis, prevents lung injury, and improves lung physiology. Untreated SP-B deficient mice develop fatal respiratory distress within two days. Gene therapy results in an improvement in median survival to greater than 200 days. This vector also transduces human lung tissue, demonstrating its potential for clinical translation against this lethal disease.

Functional characterization of NK-lysin in golden pompano Trachinotus ovatus (Linnaeus 1758)

NK-lysin is an important part of the innate immune defence system and plays an important role in resisting the invasion of pathogenic microorganisms. In this study, NK-lysin from golden pompano (Trachinotus ovatus) was characterized and its expression in response to Photobacterium damselae was investigated. The full-length NK-lysin cDNA was 731 bp, which comprised a 5'-UTR of 63 bp, an ORF of 444 bp, and a 3'-UTR of 224 bp, and encoded 147 amino acids; NK-lysin consisted of a conserved saposin B domain and six conserved cysteines that formed three pairs of disulfide bonds. The genomic organization of NK-lysin was also determined and the gene consisted of four introns and five exons. The predicted promoter region of ToNK-lysin contained several putative transcription factor binding sites. Quantitative real-time (qRT-PCR) analysis indicated that ToNK-lysin was ubiquitously expressed in all examined tissues; the highest mRNA levels were observed in the skin, kidney and intestine, while the lowest expression level was detected in the stomach. After P. damselae stimulation, the expression level of NK-lysin mRNA was significantly upregulated in various tissues of golden pompano. In addition, SDS-PAGE showed that the molecular mass of recombinant NK-lysin expressed in pGEX-6P-1 was approximately 37 kDa. The purified recombinant protein showed antibacterial activity against gram-positive and gram-negative bacteria. The results indicate that golden pompano NK-lysin has potential antimicrobial roles in fish innate immunity.

NK-lysin is highly conserved in European sea bass and gilthead seabream but differentially modulated during the immune response

Fish NK-lysin (NKL), an orthologous to human granulysin, exerts a dual role as an antimicrobial peptide (AMP) and as a direct executor of T cytotoxic and natural killer cells during the cell-mediated cytotoxic (CMC) response. Although its best-known function is as AMP against bacteria, recent studies point to a special role of NKL in antiviral responses. Nodavirus (NNV) is a spreading threat in Mediterranean aquaculture. In this study, we have identified and compared the expression pattern of European sea bass and gilthead seabream NKL and evaluated its transcription in different tissues and its regulation in head-kidney leucocyte (HKLs) stimulated in vitro with different immunostimulants, under CMC response and upon an in vivo infection with NNV. Our results showed that nkl transcription is highly expressed in spleen, thymus and skin with species-specific differences. Interestingly, the expression pattern in both species was very different upon treatment. While sea bass nkl transcription was increased in HKLs by the T mitogen phytohemagglutinin all the stimulators inhibited it in seabream HKLs. Similar results occurred in NNV-infected fish where the transcription was increased in sea bass tissues and down-regulated in seabream. Curiously, during CMC assays, nkl transcription was significantly increased in seabream HKLs against NNV-infected fish cell lines but this was not observed in sea bass leucocytes. The potential role of NKL as CMC effector molecule or as AMP in fish will be discussed.

Identification and characterization of five Nk-lysins from Pseudocrossocheilus bamaensis and their diverse expression patterns in response to bacterial infection

Nk-lysin is an effector protein of cytotoxic T lymphocytes and natural killer cells. It is known to possess anti-bacterial, anti-fungal, anti-viral, and anti-tumor activity. Here we describe five Nk-lysin genes (PbNkla, PbNklb, PbNklc, PbNkld, and PbNkle) from Pseudocrossocheilus bamaensis, a rare indigenous species distributed in Guangxi, China. The open reading frames (ORFs) consisted of 426 (PbNkla), 435 (PbNklb), 369 (PbNklc), 366 (PbNkld), and 339 (PbNkle) bp nucleic acids. The surfactant-associated protein B (SapB) domain and six conserved cysteine residues were identified in each PbNkl gene. Phylogenetic analysis revealed similar results to homology comparison that PbNkla and PbNklb consist of five exons and four introns and grouped together, whereas PbNklc and PbNkld each contain four exons and three introns and formed a separate clade. PbNkle had three exons and two introns and formed an independent clade separate from the four other PbNkls. qPCR analysis demonstrated that PbNkla, PbNklc, PbNkld, and PbNkle were ubiquitously expressed in all tissues examined, whereas PbNklb was expressed only after bacterial infection. Aeromonas hydrophila challenge significantly up- and down-regulated PbNkls at different time points post-injection and in different immune-related tissues. These results suggested that PbNkls were conserved immune molecules that may be involved in the immune response to pathogen invasion.

Molecular characterization of the NK-lysin in a teleost fish, Boleophthalmus pectinirostris: Antimicrobial activity and immunomodulatory activity on monocytes/macrophages

NK-lysin (NKL) is a cationic host defense peptide that plays an important role in host immune responses against various pathogens. However, the immunomodulatory activity of NKL in fishes is rarely investigated. In this study, we characterized a cDNA sequence encoding an NK-lysin homolog (BpNKL) from the fish, mudskipper (Boleophthalmus pectinirostris). Sequence analysis revealed that BpNKL is most closely related to tiger puffer (Takifugu rubripes) NKL. BpNKL transcript was detected in all the tested tissues, with the highest level in the gill, followed by the spleen and kidney. Upon Edwardsiella tarda infection, the mRNA expression of BpNKL in the mudskipper was significantly upregulated in the spleen, kidney, and gill. A shortened peptide derived from BpNKL, BpNKLP40, was then chemically synthesized and its biological functions were investigated. BpNKLP40 exhibited a direct antibacterial activity against some Gram-negative bacteria, including E. tarda, Vibrio parahaemolyticus, Vibrio alginolyticus, and Vibrio harveyi, and induced hydrolysis of E. tarda genomic DNA. Intraperitoneal injection of 1.0 μg/g BpNKLP40 significantly improved the survival of mudskipper following E. tarda infection and reduced the bacterial burden in tissues and blood. Moreover, 1.0 μg/ml BpNKLP40 treatment had an enhanced effect on the intracellular killing of E. tarda by monocytes/macrophages (MO/MФ) as well as on the mRNA expression of pro-inflammatory cytokines in MO/MФ. In conclusion, our study reveals that BpNKL plays a role against E. tarda infection in the mudskipper by not only directly killing bacteria but also through an immunomodulatory activity on MO/MФ.

In vitro immunomodulatory activities of peptides derived from Salmo salar NK-lysin and cathelicidin in fish cells

Antimicrobial peptides (AMPs) are amphipathic peptides, which play an important role in innate defence. These peptides are gene-encoded and either constitutively expressed and/or upregulated during an infection. NK-lysins are AMPs with a three-dimensional globular structure. They are larger molecules, which comprise 74-78 amino acid residues and six conserved cysteine residues forming three disulphide bonds. Cathelicidins are a family of antimicrobial peptides that act as important components of the innate immune system with a broad spectrum of antimicrobial activity and immunomodulatory properties. Although they are widely studied in mammals, little is known about their immunomodulatory function. In the present study, we identified and characterized for the first time four NK-lysin-like transcripts from Atlantic salmon (Salmo salar) based on EST reported sequences. In vitro, NK-lysin derived peptides were able to induce the expression of IL-1β and IL-8 in Salmo salar head kidney leukocytes. We also tested Salmo salar cathelicidin 1 derived peptide in a similar assay, showing its ability to induce the expression of IFN-γ. These results indicate that NK-lysin and cathelicidin 1 derived peptides are able to modulated immune response, suggesting their potential use to enhance immune response in fish.

Turbot (Scophthalmus maximus) Nk-lysin induces protection against the pathogenic parasite Philasterides dicentrarchi via membrane disruption

P. dicentrarchi is one of the most threatening pathogens for turbot aquaculture. This protozoan ciliate is a causative agent of scuticociliatosis, which is a disease with important economic consequences for the sector. Neither vaccines nor therapeutic treatments are commercially available to combat this infection. Numerous antimicrobial peptides (AMPs) have demonstrated broad-spectrum activity against bacteria, viruses, fungi, parasites and even tumor cells; an example is Nk-lysin (Nkl), which is an AMP belonging to the saposin-like protein (SAPLIP) family with an ability to interact with biological membranes. Following the recent characterization of turbot Nkl, an expression plasmid encoding Nkl was constructed and an anti-Nkl polyclonal antibody was successfully tested. Using these tools, we demonstrated that although infection did not clearly affect nkl mRNA expression, it induced changes at the protein level. Turbot Nkl had the ability to inhibit proliferation of the P. dicentrarchi parasite both in vivo and in vitro. Moreover, a shortened peptide containing the active core of turbot Nkl (Nkl71-100) was synthesized and showed high antiparasitic activity with a direct effect on parasite viability that probably occurred via membrane disruption. Therefore, the nkl gene may be a good candidate for genetic breeding selection of fish, and either the encoded peptide or its shortened analog is a promising antiparasitic treatment in aquaculture.

Proteolipid Protein 2 Overexpression Indicates Aggressive Tumor Behavior and Adverse Prognosis in Human Gliomas

Proteolipid protein 2 (PLP2), a membrane protein of the endoplasmic reticulum, is related to tumor proliferation and metastasis in some human cancers, but not in gliomas. First, we performed western-blot analysis, real-time quantitative PCR and immunohistochemical stains to detect PLP2 expression in 4 glioma cell lines and human glioma tissues. In addition, we used small interfering RNA (SiPLP2) and short hairpin RNA (shPLP2) to knockdown PLP2 expression in GBM8401 and LN229 glioma cell lines. After then, the alteration of PLP2 suppressed glioma cells behavior were examined by cell proliferation, wound healing, cell invasion, and colonies formation assays. Finally, the possible mechanism of PLP2 was analyzed by detecting the expression of the proteins related to cell-cycle checkpoints, cell-proliferative signaling factors, and cell-matrix interaction. Compared with normal brain cell lysates and mRNA, all glioma cell lines displayed PLP2 protein and mRNA overexpression. Besides, higher PLP2 IHC staining significantly correlated with more advanced tumor grades and poorer prognosis in human gliomas. Both siPLP2 transfected gliomas showed a clear inhibition of glioma cell proliferation, migration, and invasion as well as down-regulating p-p38, p-ERK, MMP-2, and MMP-9 expression. In conclusion, we successfully demonstrated that PLP2 overexpression played an oncogenic role in glioma development and aggressive tumor behavior.

Identification, expression analysis, and antibacterial activity of NK-lysin from common carp Cyprinus carpio

Natural killer lysin (NK-lysin), produced by cytotoxic T lymphocytes and natural killer cells, is a cationic antimicrobial peptide that has a broad antimicrobial spectrum, including bacteria, viruses, and parasites. Nevertheless, the implication of NK-lysin in the protection against bacterial infection is not aware in common carp. In this study, six different NK-lysin genes (nkl1, nkl2, nkl3, nkl4, nkl5 and nkl6) were identified in the common carp genome. Each of the mature peptides of common carp NK-lysin has six well-conserved cysteine residues, and shares a Saposin B domain, characteristic of saposin-like protein (SALIP) family. The gene nkl1 contains 5 extrons and 4 introns, and nkl2, nkl3, nkl4 or nkl5 contains 4 extrons and 3 introns, however, the nkl6 has 3 extrons and 2 introns. By quantitative real-time PCR, nkl2 transcripts were predominantly expressed in spleen of healthy common carp, while elevated mainly in gill and spleen upon Aeromonas hydrophila infection. The recombinant NK-lysin-2 purified from Pichia pastoris shows antibacterial activity against Staphylococcus aureus (Gram-positive), and Escherichia coli M15, Aeromonas hydrophila, as well as Edwardsiella tarda (Gram-negative), the latter two are important pathogens of aquaculture. Our results indicate that NK-lysin in common carp might play an important role in fish immune response by enhancing antibacterial defense against bacterial pathogens.

NK-lysin from Oreochromis niloticus improves antimicrobial defence against bacterial pathogens

NK-lysin, an effector of cytotoxic T cells and natural killer cells, is a potent antimicrobial peptide widely distributed in mammals. Homologues of NK-lysin have been discovered in several teleost species, but only several of their natural functions was recorded so far. Here we identified an NK-lysin from Nile tilapia (Oreochromis niloticus), On-NKL, and analysed its expression model and biological effects on pathogen infection. The open reading frame of On-NKL sequence spans 432 bp, codes for 143 amino acids and shares 27%-62% overall sequence identities with NK-lysin of other species. The deduced mature peptide of On-NKL possesses a saposin B domain and six well-conserved cysteine residues that essential for antimicrobial activity by forming three intrachain disulphide bonds. The results of qRT-PCR showed that On-NKL expression was observed in multiple tissues and head kidney leucocytes and nonspecific cytotoxic cells (NCCs) and is most abundant in gills. After bacterial challenge, On-NKL expression significantly varied in different tissues and NCCs. Following bacterial infection, On-NKL-overexpressing fish featured significantly lower pathogen loads in tissues than control fish. On-NKL-overexpressing fish also exhibited 33.3% relative percent survival compare with control groups. Findings suggested that On-NKL could be the potential effector of NCCs and act as immune-related gene that enhances antimicrobial defence.

Interactions between small ankyrin 1 and sarcolipin coordinately regulate activity of the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA1)

SERCA1, the sarco(endo)plasmic reticulum Ca2+-ATPase of skeletal muscle, is essential for muscle relaxation and maintenance of low resting Ca2+ levels in the myoplasm. We recently reported that small ankyrin 1 (sAnk1) interacts with the sarco(endo)plasmic reticulum Ca2+-ATPase in skeletal muscle (SERCA1) to inhibit its activity. We also showed that this interaction is mediated at least in part through sAnk1's transmembrane domain in a manner similar to that of sarcolipin (SLN). Earlier studies have shown that SLN and phospholamban, the other well studied small SERCA-regulatory proteins, oligomerize either alone or together. As sAnk1 is coexpressed with SLN in muscle, we sought to determine whether these two proteins interact with one another when coexpressed exogenously in COS7 cells. Coimmunoprecipitation (coIP) and anisotropy-based FRET (AFRET) assays confirmed this interaction. Our results indicated that sAnk1 and SLN can associate in the sarcoplasmic reticulum membrane and after exogenous expression in COS7 cells in vitro but that their association did not require endogenous SERCA2. Significantly, SLN promoted the interaction between sAnk1 and SERCA1 when the three proteins were coexpressed, and both coIP and AFRET experiments suggested the formation of a complex consisting of all three proteins. Ca2+-ATPase assays showed that sAnk1 ablated SLN's inhibition of SERCA1 activity. These results suggest that sAnk1 interacts with SLN both directly and in complex with SERCA1 and reduces SLN's inhibitory effect on SERCA1 activity.

HEK293 cells exposed to microcystin-LR show reduced protein phosphatase 2A activity and more stable cytoskeletal structure when overexpressing α4 protein

Microcystin-LR (MC-LR) is one of the most toxic members of microcystins released by freshwater cyanobacterial. The major mechanism of MC-LR toxicity has been attributed to its inhibition of protein phosphatases 1 (PP1) and 2A (PP2A). In our prior research, α4 protein, a regulator of PP2A, was found not only crucial for PP2A regulation but also for the overall response of HEK 293 cells encountering MC-LR. To explore the role of α4 in MC-LR toxicity via PP2A regulation, here, HEK 293 cells overexpressing α4 protein were exposed to MC-LR and PP2A, cytoskeletal organization, and cytoskeleton-related proteins were investigated. The results showed that PP2A activity decreased and PP2A/C subunit expression and phosphorylation at Tyr307 increased significantly in the group exposed to high MC-LR. Vimentin IF became concentrated and formed perinuclear bundles. However, the assembly of actin filament and microtubules remained unchanged and the expression and phosphorylation of the cytoskeleton-related proteins HSP27 and VASP did not increase significantly. Some of these results differ from those of our previous study in which normal HEK293 cells were exposed to MC-LR. Our results indicate that elevated α4 expression confers some resistance to MC-LR-induced cytoskeletal change These new findings provide helpful insights into the mechanism of MC-LR toxicity and the role of α4 in regulating PP2A function. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 255-264, 2017.

Sarcolipin: A Key Thermogenic and Metabolic Regulator in Skeletal Muscle

Skeletal muscle constitutes ∼40% of body mass and has the capacity to play a major role as thermogenic, metabolic, and endocrine organ. In addition to shivering, muscle also contributes to nonshivering thermogenesis via futile sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase (SERCA) activity. Sarcolipin (SLN), a regulator of SERCA activity in muscle, plays an important role in regulating muscle thermogenesis and metabolism. Uncoupling of SERCA by SLN increases ATP hydrolysis and heat production, and contributes to temperature homeostasis. SLN also affects whole-body metabolism and weight gain in mice, and is upregulated in various muscle diseases including muscular dystrophy, suggesting a role for SLN during increased metabolic demand. In this review we also highlight the physiological roles of skeletal muscle beyond contraction.

Identification, expression and antibacterial activities of an antimicrobial peptide NK-lysin from a marine fish Larimichthys crocea

As fundamental immunologic mechanism, the innate immunity system is more important than the specific immunity system in teleost fishes during pathogens infection. Antimicrobial peptides are integral parts of the innate immune system, and play significant roles against pathogens infection. NK-lysin, the compounds of the natural killer cells and cytotoxic T cells, are potent and effective antimicrobial peptides widely distributed in animals. In this study, we reported the sequence characteristics, expression profiles and antibacterial activities of a NK-lysin gene (Lc-NK-lysin) from a commercially important marine fish, the large yellow croaker (Larimichthys crocea). The open reading frame of Lc-NK-lysin cDNA sequence was 447 bp in length, coding 148 amino acids. The genomic DNA of Lc-NK-lysin has the common features of NK-lysin family, consisting of five exons and four introns, and in its deduced mature peptide, there are six well-conserved cysteine residues and a Saposin B domain. Lc-NK-lysin was expressed in all tested tissues (skin, muscle, gill, brain, head kidney, heart, liver, spleen, stomach and intestine) with different expression patterns. In pathogens infection the expression profiles of Lc-NK-lysin varied significantly in gill, head kidney, spleen and liver, indicating its role in immune response. Two peptides (Lc-NK-lysin-1 and Lc-NK-lysin-2) divided from the core region of the Lc-NK-lysin mature polypeptide were chemically synthesized and their antibacterial activities were examined; the potential function on the inhibition of bacteria propagation was revealed. Our results suggested that Lc-NK-lysin is a typical member of the NK-lysin family and as an immune-related gene it involves in the immune response when pathogens invasion.

Expression of the Bovine NK-Lysin Gene Family and Activity against Respiratory Pathogens

Unlike the genomes of many mammals that have a single NK-lysin gene, the cattle genome contains a family of four genes, one of which is expressed preferentially in the lung. In this study, we compared the expression of the four bovine NK-lysin genes in healthy animals to animals challenged with pathogens known to be associated with bovine respiratory disease (BRD) using transcriptome sequencing (RNA-seq). The expression of several NK-lysins, especially NK2C, was elevated in challenged relative to control animals. The effects of synthetic peptides corresponding to functional region helices 2 and 3 of each gene product were tested on both model membranes and bio-membranes. Circular dichroism spectroscopy indicated that these peptides adopted a more helical secondary structure upon binding to an anionic model membrane and liposome leakage assays suggested that these peptides disrupt membranes. Bacterial killing assays further confirmed the antimicrobial effects of these peptides on BRD-associated bacteria, including both Pasteurella multocida and Mannhemia haemolytica and an ultrastructural examination of NK-lysin-treated P. multocida cells by transmission electron microscopy revealed the lysis of target membranes. These studies demonstrate that the expanded bovine NK-lysin gene family is potentially important in host defense against pathogens involved in bovine respiratory disease.

Transmembrane dynamics of the Thr-5 phosphorylated sarcolipin pentameric channel

Sarcolipin (SLN), an important membrane protein expressed in the sarcoplasmic reticulum (SR), regulates muscle contractions in cardiac and skeletal muscle. The phosphorylation at amino acid Thr5 of the SLN protein modulates the amount of Ca(2+) that passes through the SR. Using molecular dynamics simulation, we evaluated the phosphorylation at Thr5 of pentameric SLN (phospho-SLN) channel's energy barrier and pore characteristics by calculating the potential of mean force (PMF) along the channel pore and determining the diffusion coefficient. The results indicate that pentameric phospho-SLN promotes penetration of monovalent and divalent ions through the channel. The analysis of PMF, pore radius and diffusion coefficient indicates that Leu21 is the hydrophobic gate of the pentameric SLN channel. In the channel, water molecules near the Leu21 pore demonstrated a clear hydrated-dehydrated transition; however, the mutation of Leu21 to an Alanine (L21A) destroyed the hydrated-dehydrated transitions. These water-dynamic behaviors and PMF confirm that Leu21 is the key residue that regulates the ion permeability of the pentameric SLN channel. These results provide the structural-basis insights and molecular-dynamic information that are needed to understand the regulatory mechanisms of ion permeability in the pentameric SLN channel.

The elongation factor eEF3 (Yef3) interacts with mRNA in a translation independent manner

BACKGROUND

mRNA binding proteins (RBPs) constitute 10-15% of the eukaryotic proteome and play important part in post-transcriptional regulation of gene expression. Due to the instability of RNA and the transient nature its interaction with RBPs, identification of novel RBPs is a significant challenge. Recently, a novel methodology for RBP purification and identification (termed RaPID) was presented, which allows high affinity purification of RBPs while associated with mRNA in vivo.

RESULTS

We performed a RaPID screen for proteins that interact with PMP1 mRNA in order to identify novel mRNA binding proteins. PMP1 mRNA was tagged in its 3' UTR with multiple MS2 loops and co-expressed with MS2-binding protein fused to streptavidin binding protein (SBP). RNA-protein complexes were cross-linked in vivo and isolated through streptavidin beads. The eluted proteins were subjected to mass spectroscopy analysis. The screen identified many proteins, about half of them were previously shown to bind RNA. We focused on eEF3 (YEF3), an essential translation elongation factor that interacts with ribosomes. Purification of TAP-tagged Yef3 with its associated RNAs confirmed that the native PMP1 transcript is associated with it. Intriguingly, high association with Yef3-TAP was observed when purification was performed in the presence of EDTA, and with PMP1 that contains stop codons immediately downstream to the initiation codon. Furthermore, high association was observed with a transcript containing only the 3' UTR of PMP1. Complementary, RaPID isolation of MS2-tagged 3' UTRs with their associated proteins revealed that Yef3 can efficiently interact with these regions.

CONCLUSIONS

This study identifies many novel proteins that interact with PMP1 mRNA. Importantly, the elongation factor Yef3 was found to interact with mRNA in non-coding regions and in a translation independent manner. These results suggest an additional, non-elongation function for this factor.

Loss of MiR-664 Expression Enhances Cutaneous Malignant Melanoma Proliferation by Upregulating PLP2

Proteolipid protein 2 (PLP2) has been shown to be upregulated in several cancers, including breast cancer, hepatocellular carcinoma, osteosarcoma, and melanoma. PLP2 specifically binds to phosphatidylinositol 3 kinase to activate the protein kinase B pathway to enhance cell proliferation, adhesion, and invasion in melanoma cells. Therefore, we speculated that PLP2 exhibits oncogenic potential. However, the regulatory mechanisms of PLP2 in cancer cells remain unclear.Herein, we found that microRNA (miR)-664 expression was significantly downregulated in cutaneous malignant melanoma (CMM) cells and tissues compared with normal human melanocytes and benign melanocytic naevi. MiR-664 expression level was significantly correlated with patient survival. Ectopic expression of miR-664 reduced CMM cell proliferation and anchorage-independent growth, whereas the inhibition of miR-664 induced these effects. Furthermore, inhibition of miR-664 in CMM cells resulted in modulation of their entry into the G1/S transitional phase, which was caused by downregulation of the cyclin-dependent kinase inhibitor P21 and upregulation of the cell-cycle regulator cyclin D1. Moreover, we demonstrated that miR-664 downregulated PLP2 expression by directly targeting the PLP2 untranslated region.Taken together, our results suggest that miR-664 may play an important role in suppressing proliferation of CMM cells and present a novel mechanism of miR-mediated direct suppression of PLP2 expression in cancer cells.

Zebrafish Nk-lysins: First insights about their cellular and functional diversification

Nk-lysins are antimicrobial proteins produced by cytotoxic T lymphocytes and natural killer cells with a broad antimicrobial spectrum (including bacteria, fungi and parasites). Nevertheless, the implication of these proteins in the protection against viral infections is still poorly understood. In this work, four different Nk-lysin genes (nkla, nklb, nklc and nkld) were identified in the zebrafish genome. That means that zebrafish is the species with the higher repertoire of Nk-lysin genes described so far. The differential expression pattern of the Nk-lysins in several tissues, during ontogeny, among the different kidney cell populations, as well as between Rag1(-/-) and Rag1(+/+) individuals, could suggest a certain specialization of different cell types in the production of different Nk-lysin. Moreover, only two of these genes (nkla and nkld) were significantly up-regulated after viral infection, and this observation could be also a consequence of a functional diversification of the zebrafish Nk-lysins.

Cardiac specific expression of threonine 5 to alanine mutant sarcolipin results in structural remodeling and diastolic dysfunction

The functional importance of threonine 5 (T5) in modulating the activity of sarcolipin (SLN), a key regulator of sarco/endoplasmic reticulum (SR) Ca²⁺ ATPase (SERCA) pump was studied using a transgenic mouse model with cardiac specific expression of threonine 5 to alanine mutant SLN (SLNT5A). In these transgenic mice, the SLNT5A protein replaces the endogenous SLN in atria, while maintaining the total SLN content. The cardiac specific expression of SLNT5A results in severe cardiac structural remodeling accompanied by bi-atrial enlargement. Biochemical analyses reveal a selective downregulation of SR Ca²⁺ handling proteins and a reduced SR Ca²⁺ uptake both in atria and in the ventricles. Optical mapping analysis shows slower action potential propagation in the transgenic mice atria. Doppler echocardiography and hemodynamic measurements demonstrate a reduced atrial contractility and an impaired diastolic function. Together, these findings suggest that threonine 5 plays an important role in modulating SLN function in the heart. Furthermore, our studies suggest that alteration in SLN function can cause abnormal Ca²⁺ handling and subsequent cardiac remodeling and dysfunction.

NKLP27: a teleost NK-lysin peptide that modulates immune response, induces degradation of bacterial DNA, and inhibits bacterial and viral infection

NK-lysin is an antimicrobial protein produced by cytotoxic T lymphocytes and natural killer cells. In this study, we examined the biological property of a peptide, NKLP27, derived from tongue sole (Cynoglossus semilaevis) NK-lysin. NKLP27 is composed of 27 amino acids and shares little sequence identity with known NK-lysin peptides. NKLP27 possesses bactericidal activity against both Gram-negative and Gram-positive bacteria including common aquaculture pathogens. The bactericidal activity of NKLP27 was dependent on the C-terminal five residues, deletion of which dramatically reduced the activity of NKLP27. During its interaction with the target bacterial cells, NKLP27 destroyed cell membrane integrity, penetrated into the cytoplasm, and induced degradation of genomic DNA. In vivo study showed that administration of tongue sole with NKLP27 before bacterial and viral infection significantly reduced pathogen dissemination and replication in tissues. Further study revealed that fish administered with NKLP27 exhibited significantly upregulated expression of the immune genes including those that are known to be involved in antibacterial and antiviral defense. These results indicate that NKLP27 is a novel antimicrobial against bacterial and viral pathogens, and that the observed effect of NKLP27 on bacterial DNA and host gene expression adds new insights to the action mechanism of fish antimicrobial peptides.

Identification and purification of human induced pluripotent stem cell-derived atrial-like cardiomyocytes based on sarcolipin expression

The use of human stem cell-derived cardiomyocytes to study atrial biology and disease has been restricted by the lack of a reliable method for stem cell-derived atrial cell labeling and purification. The goal of this study was to generate an atrial-specific reporter construct to identify and purify human stem cell-derived atrial-like cardiomyocytes. We have created a bacterial artificial chromosome (BAC) reporter construct in which fluorescence is driven by expression of the atrial-specific gene sarcolipin (SLN). When purified using flow cytometry, cells with high fluorescence specifically express atrial genes and display functional calcium handling and electrophysiological properties consistent with atrial cardiomyocytes. Our data indicate that SLN can be used as a marker to successfully monitor and isolate hiPSC-derived atrial-like cardiomyocytes. These purified cells may find many applications, including in the study of atrial-specific pathologies and chamber-specific lineage development.

Differential expression of genes involved in the calcium homeostasis in masticatory muscles of MDX mice

Duchenne Muscular Dystrophy (DMD) and its murine model, mdx, are characterized by Ca(2+) induced muscle damage and muscle weakness followed by distorted dentofacial morphology. In both, DMD patients and in mdx mice, could be proven so far that only the extraocular muscles (EOM) are not affected by muscular dystrophy. The EOMs are protected against calcium overload by enhanced expression of genes involved in the Ca(2+) homeostasis. We could recently demonstrate that masticatory muscles of mdx mice are differentially affected by muscle dystrophy. The dystrophic masseter and temporalis shows muscle histology comparable to all other skeletal muscles in this animal model, whereas dystrophic tongue muscles seem to develop a milder phenotype. Due to this fact it is to hypothesize that an altered Ca(2+) homeostasis seems to underlie the mdx masticatory muscle pathology. Aim of this study was to examine the mRNA and protein levels of the sarcoplasmic reticulum Ca(2+) ATPases SERCA1 and SERCA2, the plasma membrane Ca(2+) ATPases Atp2b1 and Atp2b4, the sodium/calcium exchanger NCX1, the ryanodine receptor 1, parvalbumin, sarcolipin, phospholamban and the L-type Ca(2+) channel alpha-1 subunit (Cacna1s) in Musculus masseter, temporalis, and tongue of 100 day old control and mdx mice. In mdx masseter muscle significant increased mRNA levels of NCX1 and Cacna1s were found compared to control mice. In contrast, the mRNA amount of RYR1 was significant reduced in mdx temporalis muscle, whereas ATP2b4 was significant increased. In mdx tongue a down-regulation of the ATP2b1, sarcolipin and parvalbumin mRNA expression was found, whereas the phospholamban mRNA level was significantly increased compared to controls. These data were verified by western blot analyses. Our findings revealed that mdx masticatory muscles showed an unequally altered expression of genes involved in the Ca(2+) homeostasis that can support the differences in masticatory muscles response to dystrophin deficiency.

Identification of PLP2 and RAB5C as novel TPD52 binding partners through yeast two-hybrid screening

Tumor protein D52 (TPD52) is overexpressed in different cancers, but its molecular functions are poorly defined. A large, low-stringency yeast two-hybrid screen using full-length TPD52 bait identified known partners (TPD52, TPD52L1, TPD52L2, MAL2) and four other preys that reproducibly bound TPD52 and TPD52L1 baits (PLP2, RAB5C, GOLGA5, YIF1A). PLP2 and RAB5 interactions with TPD52 were confirmed in pull down assays, with interaction domain mapping experiments indicating that both proteins interact with a novel binding region of TPD52. This study provides insights into TPD52 functions, and ways to maximise the efficiency of low-stringency yeast two-hybrid screens.

Co-expression of SERCA isoforms, phospholamban and sarcolipin in human skeletal muscle fibers

Sarcolipin (SLN) and phospholamban (PLN) inhibit the activity of sarco(endo)plasmic reticulum Ca²⁺-ATPases (SERCAs) by reducing their apparent affinity for Ca²⁺. A ternary complex between SLN, PLN, and SERCAs results in super-inhibition of SERCA activity. Analysis of skeletal muscle homogenate has limited our current understanding of whether SLN and PLN regulate SERCA1a, SERCA2a, or both in skeletal muscle and whether SLN and PLN are co-expressed in skeletal muscle fibers. Biopsies from human vastus lateralis were analyzed through single fiber Western blotting and immunohisto/fluorescence staining to circumvent this limitation. With a newly generated SLN antibody, we report for the first time that SLN protein is present in human skeletal muscle. Addition of the SLN antibody (50 µg) to vastus lateralis homogenates increased the apparent Ca²⁺ affinity of SERCA (K_Ca, pCa units) (-Ab, 5.85 ± 0.02 vs. +Ab, 5.95 ± 0.02) and maximal SERCA activity (μmol/g protein/min) (-Ab, 122 ± 6.4 vs. +Ab, 159 ± 11) demonstrating a functional interaction between SLN and SERCAs in human vastus lateralis. Specifically, our results suggest that although SLN and PLN may preferentially regulate SERCA1a, and SERCA2a, respectively, physiologically they both may regulate either SERCA isoform. Furthermore, we show that SLN and PLN co-immunoprecipitate in human vastus lateralis homogenate and are simultaneously expressed in 81% of the fibers analyzed with Western blotting which implies that super-inhibition of SERCA may exist in human skeletal muscle. Finally, we demonstrate unequivocally that mouse soleus contains PLN protein suggesting that super-inhibition of SERCA may also be important physiologically in rodent skeletal muscle.

Haploid genetic screens identify an essential role for PLP2 in the downregulation of novel plasma membrane targets by viral E3 ubiquitin ligases

The Kaposi's sarcoma-associated herpesvirus gene products K3 and K5 are viral ubiquitin E3 ligases which downregulate MHC-I and additional cell surface immunoreceptors. To identify novel cellular genes required for K5 function we performed a forward genetic screen in near-haploid human KBM7 cells. The screen identified proteolipid protein 2 (PLP2), a MARVEL domain protein of unknown function, as essential for K5 activity. Genetic loss of PLP2 traps the viral ligase in the endoplasmic reticulum, where it is unable to ubiquitinate and degrade its substrates. Subsequent analysis of the plasma membrane proteome of K5-expressing KBM7 cells in the presence and absence of PLP2 revealed a wide range of novel K5 targets, all of which required PLP2 for their K5-mediated downregulation. This work ascribes a critical function to PLP2 for viral ligase activity and underlines the power of non-lethal haploid genetic screens in human cells to identify the genes involved in pathogen manipulation of the host immune system.

Musa paradisica RCI complements AtRCI and confers Na+ tolerance and K+ sensitivity in Arabidopsis

The mechanisms involved in Na⁺/K⁺ uptake and extrusion are important in plant salt tolerance. In this study, we investigated the physiological role of a plasma membrane (PM)-localized protein, MpRCI, from plantain in transgenic Arabidopsis under NaCl and KCl stress and determined its effect on PM fluidity and H⁺-ATPase activity. The MpRCI gene exhibited high homology to the AtRCI2 gene family in Arabidopsis and was therefore able to complement for loss of the yeast AtRCI2-related PMP3 gene. Results of phenotypic espial and atomic emission spectrophotometer (AES) assays indicated that MpRCI overexpression in the AtRCI2A knockout mutant with reduced shoot Na⁺ and increased K⁺ exhibited increased Na⁺-tolerance and K⁺-sensitivity under NaCl or KCl treatments, respectively. Furthermore, comparisons of PM fluidity and H⁺-ATPase activity in shoots, with expression or absence of MpRCI/AtRCI2A expression under NaCl or KCl stress, showed MpRCI maintained PM fluidity and H⁺-ATPase activity under stress conditions. Results suggest that MpRCI plays an essential role in Na⁺/K⁺ flux in plant cells.

Integrity of the network sarcoplasmic reticulum in skeletal muscle requires small ankyrin 1

Small ankyrin 1 (sAnk1; Ank1.5) is a ~20 kDa protein of striated muscle that concentrates in the network compartment of the sarcoplasmic reticulum (nSR). We used siRNA targeted to sAnk1 to assess its role in organizing the sarcoplasmic reticulum (SR) of skeletal myofibers in vitro. siRNA reduced sAnk1 mRNA and protein levels and disrupted the organization of the remaining sAnk1. Sarcomeric proteins were unchanged, but two other proteins of the nSR, SERCA and sarcolipin, decreased significantly in amount and segregated into distinct structures containing sarcolipin and sAnk1, and SERCA, respectively. Exogenous sAnk1 restored SERCA to its normal distribution. Ryanodine receptors and calsequestrin in the junctional SR, and L-type Ca(2+) channels in the transverse tubules were not reduced, although their striated organization was mildly altered. Consistent with the loss of SERCA, uptake and release of Ca(2+) were significantly inhibited. Our results show that sAnk1 stabilizes the nSR and that its absence causes the nSR to fragment into distinct membrane compartments.

Interaction of PLP with GFP-MAL2 in the human oligodendroglial cell line HOG

The velocity of the nerve impulse conduction of vertebrates relies on the myelin sheath, an electrically insulating layer that surrounds axons in both the central and peripheral nervous systems, enabling saltatory conduction of the action potential. Oligodendrocytes are the myelin-producing glial cells in the central nervous system. A deeper understanding of the molecular basis of myelination and, specifically, of the transport of myelin proteins, will contribute to the search of the aetiology of many dysmyelinating and demyelinating diseases, including multiple sclerosis. Recent investigations suggest that proteolipid protein (PLP), the major myelin protein, could reach myelin sheath by an indirect transport pathway, that is, a transcytotic route via the plasma membrane of the cell body. If PLP transport relies on a transcytotic process, it is reasonable to consider that this myelin protein could be associated with MAL2, a raft protein essential for transcytosis. In this study, carried out with the human oligodendrocytic cell line HOG, we show that PLP colocalized with green fluorescent protein (GFP)-MAL2 after internalization from the plasma membrane. In addition, both immunoprecipitation and immunofluorescence assays, indicated the existence of an interaction between GFP-MAL2 and PLP. Finally, ultrastructural studies demonstrated colocalization of GFP-MAL2 and PLP in vesicles and tubulovesicular structures. Taken together, these results prove for the first time the interaction of PLP and MAL2 in oligodendrocytic cells, supporting the transcytotic model of PLP transport previously suggested.

Epigenetic silencing of MAL, a putative tumor suppressor gene, can contribute to human epithelium cell carcinoma

BACKGROUND

To identify new and useful candidate biomarkers in head and neck squamous cell carcinoma (HNSCC), we performed a genome-wide survey and found that Myelin and lymphocyte-associated protein (MAL) was a gene that was markedly down-regulated in HNSCC. Hence, we investigated the mechanism of MAL silencing and the effects of MAL on the proliferation, invasion, and apoptotic potential in HNSCC.

RESULTS

MAL was significantly down-regulated in 91.7% of HNSCC specimens at the mRNA level as compared with adjacent normal tissues (P = 0.0004). Moreover, the relative transcript levels of the MAL gene were remarkably decreased by five-fold in nine HNSCC cell lines as compared with normal head and neck epithelium cells. MAL gene expression was restored in 44%, 67%, and 89% in HNSCC cell lines treated with TSA, 5-Aza-dC, and TSA plus 5-Aza-dC, respectively. Furthermore, bisulfate-treated DNA sequencing demonstrated that the two CpG islands (that is, M1 and M2) located in MAL promoter region were completely methylated in the HNSCC cell lines (CpG methylated ratio was more than 90%), and only one CpG island (that is, M1) was partially methylated in HNSCC tissues (CpG methylated ratio between 20% and 90%). A significant reduction in cell proliferation and a change in the cell cycle profile were also observed in MAL transfectants. Matrigel assay demonstrated that the invasiveness of HNSCC cells significantly decreased. A significant increase in the population of apoptotic cells was observed in MAL transfected cells. The exogenous expression of the MAL gene suppressed malignant phenotypes, while the cell death induced by MAL gene transfer was a result of apoptosis as demonstrated by the induction of cleavage of the poly (that is, ADP-ribose) polymerase. Additionally, tumor growth was suppressed in cells expressing MAL as compared with cells not expressing MAL.

CONCLUSION

Our data suggest that the epigenetic inactivation of MAL, as a candidate tumor suppressor gene, can contribute to human epithelial cell carcinoma and may be served as a biomarker in HNSCC.

Sequence analysis and characterization of vacuolar-type H+-ATPase proteolipid transcript fromAcanthus ebracteatusVahl

The vacuolar-type H+ -ATPase (V-ATPase) is a multimeric enzyme with diverse functions in plants such as nutrient transport, flowering, stress tolerance, guard cell movement and development. A partial sequence of V-ATPase proteolipid was identified among the expressed sequence tags (ESTs) generated from Acanthus ebracteatus, and selected for full-length sequencing. The 876-nucleotide cDNA consists of an open reading frame of 165 amino acids. The deduced amino acid sequence displays high similarity (81%) with its homologs from Arabidopsis thaliana, Avecinnia marina and Gossypium hirsutum with the four transmembrane domains characteristics of the 16 kDa proteolipid subunit c of V-ATPase well conserved in this protein. Southern analysis revealed the existence of several members of proteolipid subunit c of V-ATPase in A. ebracteatus. The mRNA of this gene was detected in leaf, floral, stem and root tissues, however, the expression level was lower in stem and root tissues.

Mucin 1 (MUC1) is a novel partner for MAL2 in breast carcinoma cells

BACKGROUND

The MAL2 gene, encoding a four-transmembrane protein of the MAL family, is amplified and overexpressed in breast and other cancers, yet the significance of this is unknown. MAL-like proteins have trafficking functions, but their molecular roles are largely obscure, partly due to a lack of known binding partners.

METHODS

Yeast two-hybrid screening of a breast carcinoma cDNA expression library was performed using a full-length MAL2 bait, and subsequent deletion mapping experiments were performed. MAL2 interactions were confirmed by co-immunoprecipitation analyses and confocal microscopy was employed to compare protein sub-cellular distributions. Sucrose density gradient centrifugation of membranes extracted in cold Triton X-100 was employed to compare protein distributions between Triton X-100-soluble and -insoluble fractions.

RESULTS

The tumor-associated protein mucin 1 (MUC1) was identified as a potential MAL2 partner, with MAL2/MUC1 interactions being confirmed in myc-tagged MAL2-expressing MCF-10A cells using co-immunoprecipitation assays. Deletion mapping experiments demonstrated a requirement for the first MAL2 transmembrane domain for MUC1 binding, whereas the MAL2 N-terminal domain was required to bind D52-like proteins. Confocal microscopy identified cytoplasmic co-localisation of MUC1 and MAL2 in breast cell lines, and centrifugation of cell lysates to equilibrium in sucrose density gradients demonstrated that MAL2 and MUC1 proteins were co-distributed between Triton X-100-soluble and -insoluble fractions. However co-immunoprecipitation analyses detected MAL2/MUC1 interactions in Triton X-100-soluble fractions only. Myc-MAL2 expression in MCF-10A cells was associated with both increased MUC1 detection within Triton X-100-soluble and -insoluble fractions, and increased MUC1 detection at the cell surface.

CONCLUSION

These results identify MUC1 as a novel MAL2 partner, and suggest a role for MAL2 in regulating MUC1 expression and/or localisation.

Expression of transcripts for myelin related genes in postmortem brain from cocaine abusers

Chronic abuse of cocaine is known to cause neuroadaptive changes in the nucleus accumbens (NAc) and ventral tegmental area (VTA). In addition, altered expression of the myelin-related genes MBP, MOBP, PLP1 as well as of MAL2 in NAc was recently reported by gene array analysis in brains from cocaine abusers. In the present study we used in situ hybridization to quantify transcript expression of these four genes, as well as for the myelin-related transcripts encoding quaking, EDG2, claudin-11, transferrin, CNP, and MAG in caudate, putamen, internal capsule, and NAc in postmortem brain from cocaine abusers and matched comparison subjects. Most transcripts were not different between these groups in these striatal regions, and contrary to previous reports, we did not detect any changes in the NAc. However, expression of the transcript encoding PLP1 was significantly decreased in ventral and dorsal regions of the caudate, putamen, and in the internal capsule. Additionally, expression of claudin-11 and transferrin was decreased in the caudate and internal capsule, respectively. PLP1 is expressed at very high levels in oligodendrocytes and is essential in maintaining stability of myelin sheets. Based on these findings, altered expression of PLP1 in most areas of the striatum suggests that widespread changes to the myelin structure could be associated with the adaptive changes following chronic cocaine abuse.

The 3'-UTR mediates the cellular localization of an mRNA encoding a short plasma membrane protein

Cotranslational synthesis of proteins into the endoplasmic reticulum is preceded by targeting of the translating mRNA once a signal peptide emerges from the ribosome exit tunnel. Many mRNAs, however, are unlikely to be targeted by this process because they encode proteins that do not contain a signal peptide or because they are too short to be recognized by the signal recognition particle. Herein we tested the possible involvement of the 3'-UTR in the localization of an mRNA that encodes a very short Saccharomyces cerevisiae protein (Pmp1). We found by ribosome density mapping, sedimentation analysis, differential centrifugation, and fluorescent in situ hybridization that the 3'-UTR is essential for the association of the transcript with membrane compartments. Fusion of the 3'-UTR to heterologous open reading frames conferred on them a sedimentation and cellular localization pattern resembling that of PMP1. Mutation analysis revealed that a repeating UG-rich sequence within the 3'-UTR is important for membrane association. Taken together, our results reveal an essential role for elements within the 3'-UTR in the localization of an mRNA that is likely to be ignored by the standard signal-dependant mechanism.

Surfactant protein B deficiency caused by a novel mutation involving multiple exons of the SP-B gene

BACKGROUND

Inability to produce surfactant protein (SP)-B causes fatal neonatal respiratory disease. Homozygosity for a frameshift mutation (121ins2) in the gene encoding SP-B (SFTPB) is the predominant but not the exclusive cause of disease.

OBJECTIVES

To report a novel mutation in the SFTB gene.

METHODS

We analyzed tracheal aspirates, lung tissue obtained by in vivo lung biopsy and DNA from a newborn infant with lethal respiratory failure.

RESULTS

DNA analysis revealed a large homozygous genomic deletion encompassing exon 7 and 8 of SFTPB gene, a mutation we described as c.673-1248del2959. The parents were both heterozygous carriers. Analysis of the SP profile in tracheal aspirates and lung tissue by immunohistochemistry, routine and electron microscopy supported the diagnosis of SP-B deficiency and suggested that this large mutation might lead to abnormal routing and processing of proSP-B and proSP-C.

CONCLUSIONS

This report shows that SP-B deficiency can also be caused by a multi exon deletion in the SFTPB gene and this finding emphasizes the importance of using modern DNA analysis techniques capable of detecting multi exon deletions.

Mammaglobin and lipophilin B expression in breast tumors and their lack of effect on breast cancer cell proliferation

BACKGROUND

Mammaglobin (SCGB2A2) and lipophilin B (SCGB1D2) are members of the secretoglobin polypeptide family. Mammaglobin has been shown to be overexpressed in breast tumor tissue, indicating that mammaglobin might confer a growth advantage to mammaglobin-expressing tumor cells.

MATERIALS AND METHODS

The mammaglobin and lipophilin B mRNA expression levels were investigated in seven breast tumors and matched nonneoplastic tissues from the same patients using quantitative real-time RT-PCR. The effect of mammaglobin and lipophilin B expression on breast cancer cell proliferation rates was investigated by analyzing retrovirally transduced Hs578T cell clones. Cell proliferation rates were determined during the exponential growth phase by analyzing the change in lactate dehydrogenase activity over time.

RESULTS

All analyzed breast cancer tumors had lower expression levels of mammaglobin and lipophilin B than the respective mean level of the nonneoplastic breast tissues; no prominent overexpression was evident. There was high variability in the expression of mammaglobin and lipophilin B among the non-neoplastic samples, showing that caution should be taken when evaluating their over- and underexpression in tumors. The expression levels of mammaglobin and lipophilin B correlated with each other in the analyzed samples (p = 0.001). Ectopic overexpression of mammaglobin and lipophilin B did not affect the cell proliferation rate of Hs578T breast carcinoma cells in vitro.

CONCLUSION

Our findings suggest that the overexpression of mammaglobin observed in certain breast tumors is an epiphenomenon not causally involved in breast carcinogenesis.