Characterization of singlet oxygen-induced guanine residue damage after photochemical treatment of free nucleosides and DNA

Direct and Indirect Photochemical Reactions in Viral RNA Measured with RT-qPCR and Mass Spectrometry

RNA carries the genetic instructions for many viruses to replicate in their host cells. The photochemical reactions that take place in RNA and affect viral infectivity in natural and engineered environments, however, remain poorly understood. We exposed RNA oligomer segments from the genome of bacteriophage MS2 to UV₂₅₄, simulated sunlight, and singlet oxygen (¹O₂) and analyzed the oligomer reaction kinetics with reverse transcription quantitative PCR (RT-qPCR) and quantitative matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF) mass spectrometry (MS). Following UV₂₅₄ exposure, quantitative MALDI-TOF-MS detected significantly more RNA modifications than did RT-qPCR, suggesting that certain chemical modifications in the RNA were not detected by the reverse transcriptase enzyme. In contrast, MALDI-TOF-MS tracked as much ¹O₂-induced RNA damage as RT-qPCR. After 5 h of simulated sunlight exposure (5100 J/m² UVB and 1.2 × 10⁵ J/m² UVA), neither MALDI-TOF-MS nor RT-qPCR detected significant decreases in the oligomer concentrations. High-resolution electrospray ionization (ESI)-Orbitrap MS analyses identified pyrimidine photohydrates as the major UV₂₅₄ products, which likely contributed to the discrepancy between the MS- and RT-qPCR-based results. Reactions between RNA oligomers and ¹O₂ resulted in an unidentified major product with a mass change of +6 Da. These results shed light on the photochemical reactions that take place in RNA and suggest that the analytical techniques used to detect RNA reactivity could bias the observed reaction kinetics.

Mechanistic aspects of photoinactivation of Candida albicans by exogenous porphyrins

The mechanism of photoinactivation of Candida albicans by 3.5 μM uncharged, cationic or anionic porphyrins under blue light (407-420 nm) was found to be dependent on the uptake of porphyrins into yeast cells, and was also dependent on the presence or absence of proteins in the photosensitization medium. In a very protein-rich medium, a decrease in viability was observed only with the uncharged porphyrin. Photoinactivation by uncharged or cationic porphyrins in a protein-poorer medium resulted in total eradication, whereas no significant decrease was observed with the anionic porphyrin. Phototreatment in PBS resulted in eradication with all three porphyrins. X-ray microanalysis after phototreatment by the uncharged or cationic porphyrins in the protein-poor medium exhibited ion loss, indicating cell-membrane damage. Transmission electron microscopy indicated cellular and chromosomal damage. No ion loss or cell damage was observed in this medium with the anionic porphyrin. The efficiency of photoeradication of C. albicans is dependent on porphyrin uptake, which might lead (upon illumination) to processes that facilitate the formation of reactive oxygen species that damage the cells. Uptake of charged porphyrins is dependent on protein quantity and quality in the photosensitization microenvironment. This fact must be taken into account when using charged photosensitizers.

Targeted photodynamic therapy--a promising strategy of tumor treatment

Targeted therapy is a new promising therapeutic strategy, created to overcome growing problems of contemporary medicine, such as drug toxicity and drug resistance. An emerging modality of this approach is targeted photodynamic therapy (TPDT) with the main aim of improving delivery of photosensitizer to cancer tissue and at the same time enhancing specificity and efficiency of PDT. Depending on the mechanism of targeting, we can divide the strategies of TPDT into "passive", "active" and "activatable", where in the latter case the photosensitizer is activated only in the target tissue. In this review, contemporary strategies of TPDT are described, including new innovative concepts, such as targeting assisted by peptides and aptamers, multifunctional nanoplatforms with navigation by magnetic field or "photodynamic molecular beacons" activatable by enzymes and nucleic acid. The imperative of introducing a new paradigm of PDT, focused on the concepts of heterogeneity and dynamic state of tumor, is also called for.

Simultaneous determination of 8-oxo-2'-deoxyguanosine and 8-oxo-2'-deoxyadenosine in DNA using online column-switching liquid chromatography/tandem mass spectrometry

Sensitive and reliable methods are required for the assessment of oxidative DNA damage, which can result from reactive oxygen species that are generated endogenously from cellular metabolism and inflammatory responses, or by exposure to exogenous agents. The development of a liquid chromatography/tandem mass spectrometry (LC/MS/MS) selected reaction monitoring (SRM) method is described, that utilises online column-switching valve technology for the simultaneous determination of two DNA adduct biomarkers of oxidative stress, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8-oxo-7,8-dihydro-2'-deoxyadenosine (8-oxodA). To allow for the accurate quantitation of both adducts the corresponding [(15)N(5)]-labelled stable isotope internal standards were synthesised and added prior to enzymatic hydrolysis of the DNA samples to 2'-deoxynucleosides. The method required between 10 and 40 microg of hydrolysed DNA on-column for the analysis and the limit of detection for both 8-oxodG and 8-oxodA was 5 fmol. The analysis of calf thymus DNA treated in vitro with methylene blue (ranging from 5 to 200 microM) plus light showed a dose-dependent increase in the levels of both 8-oxodG and 8-oxodA. The level of 8-oxodG was on average 29.4-fold higher than that of 8-oxodA and an excellent linear correlation (r = 0.999) was observed between the two adducts. The influence of different DNA extraction procedures for 8-oxodG and 8-oxodA levels was assessed in DNA extracted from rat livers following dosing with carbon tetrachloride. The levels of 8-oxodG and 8-oxodA were on average 2.9 (p = 0.018) and 1.4 (p = 0.018) times higher, respectively, in DNA samples extracted using an anion-exchange column procedure than in samples extracted using a chaotropic procedure, implying artefactual generation of the two adducts. In conclusion, the online column-switching LC/MS/MS SRM method provides the advantages of increased sample throughput with reduced matrix effects and concomitant ionisation suppression, making the method ideally suited when used in conjunction with chaotropic DNA extraction for the determination of oxidative DNA damage.

The history of PDT in Norway Part one: Identification of basic mechanisms of general PDT

Photodynamic therapy (PDT) is now an established treatment of malignant and premalignant dysplasias. A number of first and second generation photosensitizers have been studied in Norway. The aim has been to improve PDT efficiency and applicability. Many critical details regarding the mechanisms of PDT were elucidated by researchers in Norway. In this review we focus on the most important findings related to these basic mechanisms, such as generation of singlet oxygen, estimations of its lifetime, the oxygen effect itself, the subcellular localization of photosensitizers with different properties, their photodegradation during PDT and their tumour selectivity.

Identification and characterization of human and mouse ovastacin: a novel metalloproteinase similar to hatching enzymes from arthropods, birds, amphibians, and fish

We have cloned and characterized human and mouse ovary cDNAs encoding a new protein of the astacin family of metalloproteinases, called ovastacin because of its predominant expression in ovarian tissues. Human and mouse ovastacins exhibit the same domain organization as other astacins, including signal sequence, propeptide, and metalloproteinase domain. However, ovastacins show an additional C-terminal domain of about 150 amino acids with no similarity to other ancillary domains present in the equivalent region of most astacins. Northern blot analysis of human tissues and cell lines revealed that ovastacin is only detected at significant levels in leukemia and lymphoma cells of different origin. In addition, RT-PCR analysis demonstrated that ovastacin is expressed in human and mouse ovary, in unfertilized mouse oocytes, and in 1.5-day-postcoitum preimplantation embryos. Further studies showed that superovulation caused a dramatic increase in the expression of mouse ovastacin, indicating that the production of this enzyme is under hormonal regulation. Human ovastacin was expressed in Escherichia coli and the purified recombinant protein hydrolyzed synthetic substrates used for assaying metalloproteinases. These activities were abolished by inhibitors of metalloproteinases, but not by inhibitors of other classes of proteases. On the basis of these results, we suggest that ovastacin could play in mammals a physiological function similar to that performed by hatching proteases in evolutionary distant species from arthropods to fish.

N-Benzoyl-L-tyrosyl-p-aminobenzoic acid hydrolase beta (human meprinbeta). A 13-amino-acid sequence is required for proteolyticprocessing and subsequent secretion

N-Benzoyl-L-tyrosyl-p-aminobenzoic acid hydrolase or human meprin (PPH) is a brush-border membrane enzyme of small intestinal epithelial cells. It is a type I integral membrane protein composed of two disulphide-bridged subunits (alpha and beta). PPH and its homologous counterparts in rodents belong to the astacin family of zinc-metalloendopeptidases. Although the amino-acid sequence of the beta subunits is 80-90% identical in these three species, processing is different. Expression of PPHbeta in simian virus 40-transformed African green monkey kidney cells (COS-1) and Madin Darby canine kidney (MDCK) cells results in its cell surface localization and secretion, whereas mouse meprinbeta is only found at the plasma membrane. To investigate proteolytic processing of PPHbeta and to identify the cleavage site, different C-terminal domains of wild-type PPHbeta were exchanged with the homologous domains of mouse meprinbeta. We identified a 13-amino-acid sequence (QIQLTPAPSVQDL) necessary for cleavage and subsequent secretion of PPHbeta. Using brefeldin A, the site of processing was identified as being after passage through the Golgi compartment. Proteolytic processing of PPHbeta thus provides a means for secretion of alphabeta heterodimers.

Identification and cloning of the membrane-associated serine protease, hepsin, from mouse preimplantation embryos

Previous studies have suggested the existence of a membrane-associated serine protease expressed by mammalian preimplantation embryos. In this study, we have identified hepsin, a type II transmembrane serine protease, in early mouse blastocysts. Mouse hepsin was highly homologous to the previously identified human and rat cDNAs. Two isoforms, differing in their cytoplasmic domains, were detected. The tissue distribution of mouse hepsin was similar to that seen in humans, with prominent expression in liver and kidney. In mouse embryos, hepsin expression was observed in the two-cell stage, reached a maximal level at the early blastocyst stage, and decreased subsequent to blastocyst hatching. Expression of a soluble form of hepsin revealed its ability to autoactivate in a concentration-dependent manner. Catalytically inactive soluble hepsin was unable to autoactivate. These results suggest that hepsin may be the first serine protease expressed during mammalian development, making its ability to autoactivate critical to its function.

Polarised expression of human intestinal N-benzoyl-L-tyrosyl-p-aminobenzoic acid hydrolase (human meprin) alpha and beta subunits in Madin-Darby canine kidney cells

N-Benzoyl-L-tyrosyl-p-aminobenzoic acid hydrolase (PPH, human meprin), is a peptidase found in the microvillus membrane of human small intestinal epithelial cells. PPH belongs to the astacin family of zinc-metalloendopeptidases and is a protein complex composed of two glycosylated subunits, alpha and beta. The present report describes the cloning of the complete beta subunit and the remaining N2-terminal end of the alpha subunit for analysis of their primary structures in addition to the examination of their biogenesis in transfected cell cultures. The complete open reading frame of the PPH beta cDNA translates into 700 amino acid residues compared with 746 residues for the PPH alpha cDNA. The primary structure of beta and alpha subunits are 44% identical and 61% similar. As predicted from their primary structure, the two subunits of PPH have identical modular structures; starting at the N2-terminus both contain a signal peptide, a propeptide, a protease domain containing the astacin signature, a meprin A5 protein tyrosine phospatase mu (MAM) and a meprin and TRAF homology domain (MATH) domain, an epidermal growth factor(EGF)-like domain, a putative transmembrane anchor domain and a short cytosolic tail. Pulse/chase labelling and immuno-Gold electronmicroscopy of recombinant PPH beta and alpha subunits expressed in transfected Madin-Darby canine kidney (MDCK) cells show that post-translational processing and transport of the two subunits are very different. When expressed alone, the beta subunit acquired complex glycan residues, readily formed homodimers and was transported to the plasma membrane. Small amounts of PPH beta were found in the culture medium. In contrast, the cell-bound alpha subunit, when expressed alone, remained primarily in the high-mannose form, was aggregated and not expressed at the cell surface. However, the bulk of mostly endo-beta-N-acetylglucosaminidase H-resistant alpha subunit was found in the filtered culture medium. The proteolytic event that leads to the formation of this soluble transport-competent form occurs in the endoplasmic reticulum (ER). Coexpression of the alpha subunit with the beta subunit allowed the localisation of the alpha subunit to the plasma membrane. These studies indicate that assembly of the two subunits of PPH is required for the localisation of the alpha subunit to the plasma membrane. In contrast to rodent meprin, both PPH subunits are apically secreted from MDCK cells.

Species-dependent migration of fish hatching gland cells that express astacin-like proteases in common [corrected]

Two constituent proteases of the hatching enzyme of the medaka (Oryzias latipes), choriolysin H (HCE) and choriolysin L (LCE), belong to the astacin protease family. Astacin family proteases have a consensus amino acid sequence of HExxHxxGFxHExxRxDR motif in their active site region. In addition, HCE and LCE have a consensus sequence, SIMHYGR, in the downstream of the active site. Oligonucleotide primers were constructed that corresponded to the above-mentioned amino acid sequences and polymerase chain reactions were performed in zebrafish (Brachydanio rerio) and masu salmon (Oncorynchus masou) embryos. Using the amplified fragments as probes, two full-length cDNA were isolated from each cDNA library of the zebrafish and the masu salmon. The predicted amino acid sequences of the cDNA were similar to that of the medaka enzymes, more similar to HCE than to LCE, and it was conjectured that hatching enzymes of zebrafish and masu salmon also belonged to the astacin protease family. The final location of hatching gland cells in the three fish species: medaka, zebrafish and masu salmon, is different. The hatching gland cells of medaka are finally located in the epithelium of the pharyngeal cavity, those of zebrafish are in the epidermis of the yolk sac, and those of masu salmon are both in the epithelium of the pharyngeal cavity and the lateral epidermis of the head. However, in the present study, it was found that the hatching gland cells of zebrafish and masu salmon originated from the anterior end of the hypoblast, the Polster, as did those of medaka by in situ hybridization. It was clarified, therefore, that such difference in the final location of hatching gland cells among these species resulted from the difference in the migratory route of the hatching gland cells after the Polster region.

Structure of the gene encoding the sea urchin blastula protease 10 (BP10), a member of the astacin family of Zn2+-metalloproteases

Blastula protease 10 (BP10), a metalloprotease of the astacin family, is secreted at the blastula stage by the sea urchin embryo. The BP10 gene shows a precise temporal and spatial regulation during embryogenesis. It has been cloned from a sea urchin lambda genomic library and the transcription unit has been entirely sequenced. It spans 6kb and contains seven exons (2.8 kb) and six introns (3.2 kb). Sequence comparison and phylogeny analysis show that BP10 belongs to a sub-family of molecular proteins which all play a role during development. In the two cases where the exon/intron organization of the gene is known (BP10 and tolloid), the modular structure of the protein is not reflected at the gene level, which indicates that this sub-family probably did not evolve by exon shuffling.

Molecular cloning of Ebnerin, a von Ebner's gland protein associated with taste buds

Salivary secretions modulate taste perception. Taste buds in the circumvallate and foliate papillae are bathed in secretions of unique lingual salivary glands, von Ebner's glands (VEG). We have identified a rat cDNA encoding a novel protein of 1290 amino acids, Ebnerin, that is specifically expressed in VEG and released onto the tongue surface along the apical region of taste buds in the clefts of circumvallate papillae. Ebnerin possesses a putative single transmembrane domain at the C terminus with 17 amino acids in the cytoplasmic area. The extracellular region of Ebnerin contains a number of repeated domains with homology to the scavenger receptor cysteine-rich domain and to a repeated domain of bone morphogenetic protein-I and other related proteins. Western blot analysis reveals that Ebnerin exists in particulate and soluble forms in VEG and is present in secretions from VEG. In situ hybridization and immunohistochemistry demonstrate that Ebnerin is located in secretory duct epithelial cells of VEG and is released onto the tongue surface along the apical region of taste buds in the clefts of circumvallate papillae. The unique structure and localization of Ebnerin suggest that it may function as a binding protein in saliva for the regulation of taste sensation.