Molecular cloning of novel antimicrobial peptide genes from the skin of the Chinese brown frog, Rana chensinensis

Efflux pump inhibitor chlorpromazine effectively increases the susceptibility of Escherichia coli to antimicrobial peptide Brevinin-2CE

Aim: The response of E. coli ATCC8739 to Brevinin-2CE (B2CE) was evaluated as a strategy to prevent the development of antimicrobial peptide (AMP)-resistant bacteria. Methods: Gene expression levels were detected by transcriptome sequencing and RT-PCR. Target genes were knocked out using CRISPR-Cas9. MIC was measured to evaluate strain resistance. Results: Expression of acrZ and sugE were increased with B2CE stimulation. ATCC8739ΔacrZ and ATCC8739ΔsugE showed twofold and fourfold increased sensitivity, respectively. The survival rate of ATCC8739 was reduced in the presence of B2CE/chlorpromazine (CPZ). Combinations of other AMPs with CPZ also showed antibacterial effects. Conclusion: The results indicate that combinations of AMPs/efflux pump inhibitors (EPIs) may be a potential approach to combat resistant bacteria.

Temporins: Multifunctional Peptides from Frog Skin

Temporins are short peptides secreted by frogs from all over the world. They exert antimicrobial activity, mainly against Gram-positive bacteria, including resistant pathogens; recent studies highlight other possible applications of these peptides as anticancer or antiviral agents. This review is meant to describe the main features of temporins produced by different ranid genera. Due to the abundance of published papers, we focus on the most widely investigated peptides. We report studies on their mechanism of action and three-dimensional structure in model systems mimicking bacterial membranes or in the presence of cells. The design and the antimicrobial activity of peptide analogues is also described, with the aim of highlighting elements that are crucial to improve the bioactivity of peptides while reducing their toxicity. Finally, a short section is dedicated to the studies aimed at applying these peptides as drugs, to produce new antimicrobial materials or in other technological uses.

Truncated analog Brevinin2-CE-N26V5K: Revelation the Augmentation of Antimicrobial Activity

Brevinin2-CE (B2CE), a natural peptide containing 37 amino acids, was first isolated from the skin secretions of the Chinese forest frog Rana chensinensis. B2CE shows good antibacterial activity. In this study, a series of B2CE analogs with differences in cationicity, α-helicity, hydrophobicity and amphipathic properties were designed through chain-length deletion and amino acid substitution. The most potent, nontoxic analog, B2CE-N26V5K, was identified by examination of its antibacterial activity, hemolytic activity, and stability under physiological conditions. The increased cationicity, hydrophobicity and more obvious hydrophilic and hydrophobic surface of B2CE-N26-N16WA18KG23K did not improve the antibacterial activity but increased the hemolytic activity of this modified peptide. The helicity might promote antibacterial activity for brevinin-2 peptides, as the 15-aa analogs with lower helicity show decreased potency against different test bacteria (approximately 2- to 72-fold) compared to B2CE-N26V5K. Additionally, the results indicated that the "Rana box" does not affect the antimicrobial activity of brevinin-2 peptides, as B2CE, B2CE-nonDS and B2CE-C31-37 S have similar strong inhibitory effects on both gram-positive and gram-negative bacteria. However, the "Rana box" does affect the hemolytic activity, as the HC₅₀ values of the 3 peptides range from 25 ~ 130 µM. Furthermore, B2CE-N26V5K caused obvious morphological alterations of the bacterial surfaces, as shown by atomic force microscopy. Additionally, B2CE-N26V5K exhibited strong membrane-disrupting activity when examined using the LIVE/DEAD Bac Light Bacterial Viability Kit. Thus, the antibacterial effect of B2CE-N26V5K on gram-negative and gram-positive bacteria may be caused by cell membrane attack. In conclusion, the excellent candidate B2CE-N26V5K was obtained and has application prospects as a novel anti-infective agent.

The Prepropalustrin-2CE2 and Preprobrevinin-2CE3 Gene from Rana Chensinensis: Gene Expression, Genomic Organization, and Functional Analysis of the Promoter Activity

BACKGROUND

Palustrin-2CE2 and brevinin-2CE3 are antimicrobial peptides from Rana chensinensis. In R. chensinensis tadpoles, the expression of prepropalustrin-2CE2 and preprobrevinin-2CE3 increased with the developmental stage. In addition, the expression of the two genes was dramatically upregulated with stimulation by Escherichia coli, Staphylococcus aureus, and the chemical lipopolysaccharide (LPS). The genomic organization of the two antimicrobial peptide genes was confirmed. Both prepropalustrin-2CE2 and preprobrevinin-2CE3 contain three exons separated by two large introns. Additionally, several presumed transcription factor binding sites were identified in the promoter sequence. Functional analysis of the promoter was performed using a luciferase reporter system, and further confirmed by yeast one-hybrid experiment and EMSA assay. The results indicated that the transcription factors NF-κB and RelA are involved in regulating the expression of prepropalustrin-2CE2 and preprobrevinin-2CE3. As amphibian populations decline globally, this study provides new data demonstrating how frogs defend against pathogens from the environment by regulating AMP expression. For amphibians, antimicrobial peptides are innate immune molecules that resist adverse external environmental stimuli. However, the regulation mechanism of antimicrobial peptide gene expression in frogs is still unclear.

OBJECTIVE

The two antimicrobial peptides, palustrin-2CE2 and brevinin-2CE3, are produced under external stimulation in Rana chensinensis. Using this model, we analyzed the gene structure and regulatory elements of the two antimicrobial peptide genes and explored the regulatory effects of related transcription factors on the two genes.

METHOD

Different stimuli such as E. coli, S. aureus, and chemical substance lipopolysaccharide (LPS) were applied to Rana chensinensis tadpoles at different developmental stages, and antimicrobial peptide expression levels were detected by RT-PCR. Bioinformatics analysis and 5'-RACE and genome walking technologies were employed to analyze the genome structure and promoter region of the antimicrobial peptide genes. With dual-luciferase reporter gene assays, yeast one-hybrid experiment and EMSA assays, we assessed the regulatory effect of the endogenous regulators of the cell on the antimicrobial peptide promoter.

RESULTS

The transcription levels of prepropalustrin-2CE2 and preprobrevinin-2CE3 were significantly upregulated after different stimulations. Genomic structure analysis showed that both genes contained three exons and two introns. Promoter analysis indicated that there are binding sites for regulatory factors of the NF-κB family in the promoter region, and experiments showed that endogenous NF-κB family regulatory factors in frog cells activate the promoters of the antimicrobial peptide genes. Yeast one-hybrid experiment and EMSA assay demonstrated that RelA and NF-κB1 might interact with specific motifs in the prepropalustrin-2CE2 promoter.

CONCLUSION

In this paper, we found that the gene expression levels of the antimicrobial peptides, palustrin-2CE2 and brevinin-2CE3, in R. chensinensis will increase under environmental stimuli, and we verified that the changes in gene expression levels are affected by the transcription factors RelA and NF-κB1. The yeast one-hybrid experiment and EMSA assay confirmed that RelA and NF-κB1 could directly interact with the frog antimicrobial peptide gene promoter, providing new data for the regulatory mechanism of antimicrobial peptides in response to environmental stimuli.

Brevinin-2 Drug Family—New Applied Peptide Candidates Against Methicillin-Resistant Staphylococcus aureus and Their Effects on Lys-7 Expression of Innate Immune Pathway DAF-2/DAF-16 in Caenorhabditis elegans

The issue of Staphylococcus aureus (MRSA) developing a resistance to drugs such as methicillin has long been the focus for new drug development. In recent years, antimicrobial peptides, such as small molecular peptides with broad-spectrum antibacterial activity and special antibacterial mechanism, have shown a strong medicinal potential. In particular, the Brevinin-2 family has been shown to have a significant inhibitory effect against gram-positive bacteria (G+). In this study, we researched the influence of MRSA on the behavior and survival rate of nematodes. We established an assay of Caenorhabditis elegans–MRSA antimicrobial peptides to screen for new potent anti-infective peptides against MRSA. From the Brevinin-2 family, 13 peptides that had shown strong effects on G+ were screened for their ability to prolong the lifespan of infected worms. Real-time Polymerase Chain Reaction (PCR) tests were used to evaluate the effect on the innate immune pathway dauer formation defective (DAF)-2/DAF-16 of C. elegans. The assay successfully screened and filtered out four of the 13 peptides that significantly improved the survival rate of MRSA-infected worms. The result of real-time PCR indicated that the mRNA and protein expression levels of lys-7 were consistently upregulated by being treated with four of the Brevinin-2 family. The Brevinin-2 family peptides, including Brevinin-2, Brevinin-2-OA3, Brevinin-2ISb, and Brevinin-2TSa, also played an active role in the DAF-2/DAF-16 pathway in C. elegans. We successfully demonstrated the utility of anti-infective peptides that prolong the survival rate of the MRSA-infected host and discovered the relationship between antibacterial peptides and the innate immune system of C. elegans. We demonstrated the antimicrobial effects of Brevinin-2 family peptides, indicating their potential for use as new drug candidates against MRSA infections.

Oviductus ranae protein hydrolysate (ORPH) inhibits the growth, metastasis and glycolysis of HCC by targeting miR-491-5p/PKM2 axis

BACKGROUND

Oviductus Ranae (OR) is a valuable Chinese crude drug and has been reported to have a range of biological activities. Protein hydrolysate extracted from OR (ORPH) was previously found to have immune regulatory effect and anti-glioma activity. This study was aimed to investigate the effects of ORPH on hepatocellular carcinoma (HCC) progression.

METHODS

MTT, BrdU, colony formation and transwell assays were used to determine proliferation and mobility of HCC cells in vitro. Glucose consumption and lactate production assays were carried out to measure the glycolysis of HCC cells. The subcutaneous tumor model and lung metastasis model in nude mice were established to detect tumor growth and metastasis of HCC in vivo. The direct binding of miR-491-5p to 3'UTR of pyruvate kinase M2 (PKM2) was confirmed by luciferase reporter assay.

RESULTS

In vitro experiments showed that ORPH significantly inhibited proliferation, migration, invasion, epithelial-to-mesenchymal transition (EMT) and glycolysis of HCC cells. Moreover, ORPH treatment prominently suppressed HCC growth and metastasis in mice. We demonstrated that ORPH effectively decreased the expression of PKM2 in HCC cells. Forced expression of PKM2 abrogated the inhibitory effects of ORPH on HCC cells. Mechanically, ORPH reduced PKM2 expression in a post-transcriptional manner by up-regulating miR-491-5p. miR-491-5p exhibited a similar tumor suppressive effects with ORPH in HCC cells. Moreover, ORPH exerted its inhibitory effects on HCC cells through regulating miR-491-5p/PKM2 axis. Lastly, decreased miR-491-5p level and increased PKM2 expression were correlated with unfavorable clinical features and poor prognosis of HCC patients.

CONCLUSIONS

In all, this study reveals that ORPH inhibits the growth, metastasis and glycolysis of HCC cells by targeting miR-491-5p/PKM2 axis. ORPH may be a potential effective anti-tumor agent for HCC.

Extraction and characterization of collagen hydrolysates from the skin of Rana chensinensis

The production of Hasma generates plentiful non-edible by-products in China and Central Asia. As one of main by-products, the skin of Rana chensinensis is discarded as waste without utilization. In this work, R. chensinensis skin collagen (RCSC) hydrolysates were extracted using pepsin under acidic conditions. The yield of RCSC is 15.1% (w/w). Amino acid analysis revealed that RCSC contained glycine (204.5/1000 residues) and imino acids (182/1000 residues). RCSC exhibited high solubility in acidic pH (1-4) and low NaCl concentrations (< 2%, w/v). Differential scanning calorimetry indicated that the denaturation temperature of RCSC was 33.5 °C. Scanning electron microscopy analysis confirmed their well-defined fibril morphologies. The results indicated that the skin of R. chensinensis is an alternative source of collagen hydrolysates, and RCSC can serve as a potential source applying in foodstuff and medical industry.

Molecular Cloning and Functional Characterization of Antimicrobial Peptides Brevinin-1ULf and Ulmin-1ULa in the Skin of the Newly Classified Ryukyu Brown Frog Rana ulma

Antimicrobial peptides (AMPs) were previously isolated from the skin of the Ryukyu brown frog Rana okinavana. However, this species has recently been reclassified as two species, i.e., Rana kobai and Rana ulma. As a result, it was determined that AMPs isolated from R. okinavana were in fact products of R. kobai, but not of R. ulma. In the present study, we collected skin samples from the species R. ulma and cloned twelve cDNAs encoding AMP precursors for the acyclic brevinin-1ULa--1ULf, the temporin-ULa-ULc, ranatuerin-2ULa, japonicin-1ULa, and a novel peptide using reverse-transcription polymerase chain reaction techniques. The deduced amino acid sequence of the novel peptide had a high similarity to those of Rana chensinensis chensinin-1CEa--1CEc, which were cloned by Zhao et al. ( 2011 ), but had a low similarity with R. chensinensis chensinin-1, which was cloned by Shang et al. ( 2009 ). To avoid confusion with these two different chensinin-1 families, we termed our peptide ulmin-1. Among these peptides, we focused on two peptides, brevinin-1ULf and ulmin-1ULa, and examined the antimicrobial and cytotoxic activity of their synthetic replicates. In broth microdilution assays, growth inhibitory activities against Staphylococcus aureus, Bacillus cereus, and Candida albicans were detected for brevinin-1ULf but not for ulmin-1ULa, whereas scanning electron microscopic observations revealed that both peptides induce morphological abnormalities in these microbes. In addition, binding activity of ulmin-1ULa to the bacterial cell wall component lipoteichoic acid was higher than that of brevinin-1ULf. In contrast, hemolytic and cytotoxic activities of brevinin-1ULf were stronger than those of ulmin-1ULa.

Electrospun poly(l-lactide)/zein nanofiber mats loaded with Rana chensinensis skin peptides for wound dressing

Electrospun nanofiber mats can display impressive performance as an ideal wound dressing. In this study, poly(l-lactide)(PLLA)/zein nanofiber mats loaded with Rana chensinensis skin peptides (RCSPs) were successfully produced by two different electrospinning techniques, blend and coaxial, with the goal of developing a wound dressing material. The nanofiber mats were investigated by environmental scanning electron microscope (ESEM), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR), differential scanning calorimeter (DSC), water contact angle, mechanical tests and cell viability. The resulting nanofiber mats exhibited smooth surfaces, tiny diameters and different cross-sectional shapes from pure PLLA and zein nanofibers. The FTIR result showed that PLLA, zein and RCSPs were well dispersed, without chemical interactions. Compared with coaxial nanofiber mats, blending zein-RCSPs with PLLA enhanced hydrophilicity but decreased mechanical properties. Adding RCSPs into the electrospun nanofibers significantly improved the mechanical properties of the mats. Cell viability studies with human foreskin fibroblasts demonstrated that cell growth on PLLA/zein-RCSPs nanofiber mats was significantly higher than that on PLLA/zein nanofiber mats. The results indicate that nanofiber mats containing RCSPs are potential candidates for wound dressing.

Investigation of the anti-glioma activity of Oviductus ranae protein hydrolysate

Oviductus Ranae is the dry oviducts of Rana temporaria chensinensis, and it has been reported to have a range of biological activities. This study aimed to investigate the effects of Oviductus Ranae protein hydrolysate (ORPH) on human glioma C6 cell proliferation and apoptosis in vitro and in vivo. Following in vitro treatment, cell viability and colony formation assays showed that ORPH inhibited C6 cell proliferation. In addition, the results of western blotting also demonstrated that ORPH effectively regulated the expression of the apoptosis related proteins, cleaved caspase-3, Bax and Bcl-2, DNA staining and flow cytometry analysis demonstrated that ORPH significantly promoted apoptosis in this cell line, a finding that was confirmed in vivo using terminal deoxynucleotidyl transferase dUTP nick end labeling. Further investigation demonstrated that ORPH increased apoptosis by modulating the release of inflammatory cytokines and the phosphoinositide 3-kinase (PI3K)/AKT signaling pathway; this was demonstrated using a PI3K/AKT inhibitor (NVP-BEZ235). In summary, the present study suggested that ORPH promoted apoptosis and inhibited glioma cell proliferation by influencing the PI3K/AKT signaling pathway.

In vitro synergistic activities of antimicrobial peptide brevinin-2CE with five kinds of antibiotics against multidrug-resistant clinical isolates

Antimicrobial peptides are the promising candidates for withstanding multidrug-resistant bacteria (MDRB) which were caused by the misuse and extensive use of antibiotics. In this research, in vitro activities of one antimicrobial cationic peptide, brevinin-2CE alone and in combination with five kinds of antibiotics were assessed against clinical isolates of extended-spectrum β-lactamase-producing Escherichia coli and methicillin-resistant Staphylococcus aureus. The results showed that most of the combination groups had synergistic effects. Also, it was obvious that brevinin-2CE had more rapid and severe action on the tested MDRBs which demonstrated that brevinin-2CE and the antibiotics had different antimicrobial mechanisms. Thus, it was presumed that the antimicrobial peptides destroyed the bacterial cells via pore formation mechanisms which lead to the increasing of membrane permeability; and then the other compounds like antibiotics might enter into the cells and accomplish the antimicrobial activities more rapidly and efficiently.

Identification and structure-activity relationship of an antimicrobial peptide of the palustrin-2 family isolated from the skin of the endangered frog Odorrana ishikawae

Recently, we identified nine novel antimicrobial peptides from the skin of the endangered anuran species, Odorrana ishikawae, to assess its innate immune system. In this study an additional antimicrobial peptide was initially isolated based on antimicrobial activity against Escherichia coli. The new antimicrobial peptide belonging to the palustrin-2 family was named palustrin-2ISb. It consists of 36 amino acid residues including 7 amino acids C-terminal to the cyclic heptapeptide Rana box domain. The peptide's primary structure suggests a close relationship with the Chinese odorous frog, Odorrana grahami. The cloned cDNA encoding the precursor protein contained a signal peptide, an N-terminal acidic spacer domain, a Lys-Arg processing site and the C-terminal precursor antimicrobial peptide. It also contained 3 amino acid residues at the C-terminus not found in the mature peptide. Finally, the antimicrobial activities against four microorganisms (E. coli, Staphylococcus aureus, methicillin-resistant S. aureus and Candida albicans) were investigated using several synthetic peptides. A 29 amino acid truncated form of the peptide, lacking the 7 amino acids C-terminal to the Rana box, possessed greater antimicrobial activities than the native structure.