CD52/FLAG and CD52/HA Fusion Proteins as Novel Magnetic Cell Selection Markers.

At present, the magnetic selection of genetically modified cells is mainly performed with surface markers naturally expressed by cells such as CD4, LNGFR (low affinity nerve growth factor receptor), and MHC class I molecule H-2Kk. The disadvantage of such markers is the possibility of their undesired and poorly predictable expression by unmodified cells before or after cell manipulation, which makes it essential to develop new surface markers that would not have such a drawback. Earlier, modified CD52 surface protein variants with embedded HA and FLAG epitope tags (CD52/FLAG and CD52/HA) were developed by the group of Dr. Mazurov for the fluorescent cell sorting of CRISPR-modified cells. In the current study, we tested whether these markers can be used for the magnetic selection of transduced cells. For this purpose, appropriate constructs were created in MigR1-based bicistronic retroviral vectors containing EGFP and DsRedExpress2 as fluorescent reporters. Cytometric analysis of the transduced NIH 3T3 cell populations after magnetic selection evaluated the efficiency of isolation and purity of the obtained populations, as well as the change in the median fluorescence intensity (MFI). The results of this study demonstrate that the surface markers CD52/FLAG and CD52/HA can be effectively used for magnetic cell selection, and their efficiencies are comparable to that of the commonly used LNGFR marker. At the same time, the significant advantage of these markers is the absence of HA and FLAG epitope sequences in cellular proteins, which rules out the spurious co-isolation of negative cells.

Large Subunit of the Human Herpes Simplex Virus Terminase as a Promising Target in Design of Anti-Herpesvirus Agents.

Herpes simplex virus type 1 (HSV-1) is an extremely widespread pathogen characterized by recurrent infections. HSV-1 most commonly causes painful blisters or sores around the mouth or on the genitals, but it can also cause keratitis or, rarely, encephalitis. First-line and second-line antiviral drugs used to treat HSV infections, acyclovir and related compounds, as well as foscarnet and cidofovir, selectively inhibit herpesvirus DNA polymerase (DNA-pol). It has been previously found that (S)-4-[6-(purin-6-yl)aminohexanoyl]-7,8-difluoro-3,4-dihydro-3-methyl-2H-[1,4]benzoxazine (compound 1) exhibits selective anti-herpesvirus activity against HSV-1 in cell culture, including acyclovir-resistant mutants, so we consider it as a lead compound. In this work, the selection of HSV-1 clones resistant to the lead compound was carried out. High-throughput sequencing of resistant clones and reference HSV-1/L2 parent strain was performed to identify the genetic determinants of the virus's resistance to the lead compound. We identified a candidate mutation presumably associated with resistance to the virus, namely the T321I mutation in the UL15 gene encoding the large terminase subunit. Molecular modeling was used to evaluate the affinity and dynamics of the lead compound binding to the putative terminase binding site. The results obtained suggest that the lead compound, by binding to pUL15, affects the terminase complex. pUL15, which is directly involved in the processing and packaging of viral DNA, is one of the crucial components of the HSV terminase complex. The loss of its functional activity leads to disruption of the formation of mature virions, so it represents a promising drug target. The discovery of anti-herpesvirus agents that affect biotargets other than DNA polymerase will expand our possibilities of targeting HSV infections, including those resistant to baseline drugs.

L-Lysine-modified Fe3O4 nanoparticles for magnetic cell labeling.

The efficiency of magnetic labeling with L-Lys-modified Fe3O4 magnetic nanoparticles (MNPs) and the stability of magnetization of rat adipose-derived mesenchymal stem cells, lineage-negative (Lin(-)) hematopoietic progenitor cells from mouse bone marrow and human leukemia K562 cells were studied. For this purpose, covalent modification of MNPs with 3-aminopropylsilane and N-di-Fmoc-L-lysine followed by removal of N-protecting groups was carried out. Since the degree of hydroxylation of the surface of the starting nanoparticles plays a crucial role in the silanization reaction and the possibility of obtaining stable colloidal solutions. In present work we for the first time performed a comparative qualitative and quantitative evaluation of the number of adsorbed water molecules and hydroxyl groups on the surface of chemically and physically obtained Fe3O4 MNPs using comprehensive FTIR spectroscopy and thermogravimetric analysis. The results obtained can be further used for magnetic labeling of cells in experiments in vitro and in vivo.

Persistence of plasmid-mediated expression of transgenes in human mesenchymal stem cells depends primarily on CpG levels of both vector and transgene.

BACKGROUND: Gene therapy and cell modification for clinical applications using plasmid vectors are considered to be a safe and promising strategy. One of the major problems with plasmid vector-based constructs is a rapid decline of transgene expression in cells in vitro and in vivo. An important role of CpG motifs or bacterial vector backbone in expression silencing has been suggested. METHODS: To address the effects of CpG motifs on transgene expression maintenance in stem cells in vitro, we constructed a novel pMBR2 plasmid vector containing 13 CpG motifs only. pMBR2 constructs with CpG-free and CpG-replete firefly luciferase inserts were introduced into cultured human adipose-derived mesenchymal stem (MSCs) by electroporation, and luciferase expression levels were monitored for 3 weeks. RESULTS: The pMBR2 vector with CpG-free luciferase insert demonstrated the highest persistence of expression, whereas the wild-type luciferase insert containing 97 CpG motifs demonstrated lower expression maintenance in the same vector. In comparison, the same inserts in the CpG-replete pCDNA3 vector demonstrated significantly lower expression levels and only a minimal persistence of expression. ß-galactosidase and enhanced green fluorescent protein genes inserted into pMBR2 vector also demonstrated higher expression levels and better maintenance compared to the same genes in pCDNA3 vector. CONCLUSIONS: The persistence of plasmid vector expression in human MSCs is determined primarily by CpG content of both vector and transgene. The data obtained in the present study indicate that the pMBR2 vector with a minimized number of CpG motifs is appropriate for extended plasmid-mediated expression of transgenes in MSCs and possibly other types of stem cells.

Formaldehyde Fixation of Extracellular Matrix Protein Layers for Enhanced Primary Cell Growth.

Coating tissue culture vessels with the components of the extracellular matrix such as fibronectin and collagens provides a more natural environment for primary cells in vitro and stimulates their proliferation. However, the effects of such protein layers are usually rather modest, which might be explained by the loss immobilized proteins due to their weak non-covalent association with the tissue culture plastic. Here we describe a simple protocol for a controlled fixation of fibronectin, vitronectin and collagen IV layers by formaldehyde, which substantially enhances the stimulation of primary cell proliferation by these extracellular proteins.

Isolation and Expansion of Mesenchymal Stem Cells from Murine Adipose Tissue.

Mesenchymal stem cells (MSCs) are currently intensively studied due to significant promise which they represent for successful implementations of future cell therapy clinical protocols. This in turn emphasizes importance of careful preclinical studies of MSC effects in various murine disease models. The appropriate cell preparations with reproducible biological properties are important to minimize variability of results of experimental cell therapies. We describe here a simple protocol for isolation of murine MSCs from adipose tissues and their reproducible multi-log expansion under hypoxia conditions.

Combined treatment, based on lysomustine administration with mesenchymal stem cells expressing cytosine deaminase therapy, leads to pronounced murine Lewis lung carcinoma growth inhibition.

BACKGROUND: The combination of stem cell-based gene therapy with chemotherapy comprises an advantageous strategy that results in a reduction of system toxicity effects and an improvement in the general efficacy of treatment. In the present study, we estimated the efficacy of adipose tissue-derived mesenchymal stem cells (AT-MSCs) expressing cytosine deaminase (CDA) combined with lysomustine chemotherapy in mice bearing late stage Lewis lung carcinoma (LLC). METHODS: Adipose tissue-derived mesenchymal stem cells were transfected with non-insert plasmid construct transiently expressing fused cytosine deaminase-uracil phosphoribosyltransferase protein (CDA/UPRT) or the same construct fused with Herpes Simplex Virus Type1 tegument protein VP22 (CDA/UPRT/VP22). Systemic administration of 5-fluorocytosine (5FC) and lysomustine was implemented after a single intratumoral injection of transfected AT-MSCs. RESULTS: We demonstrated that direct intratumoral transplantation of AT-MSCs expressing CDA/UPRT or CDA/UPRT/VP22 followed by systemic administration of 5FC resulted in a significant tumor growth inhibition. There was a 56% reduction in tumor volume in mice treated by AT-MSCs-CDA/UPRT + 5FC or with AT-MSCs-CDA/UPRT/VP22 + 5FC compared to control animals grafted with lung carcinoma alone. Transplantation of AT-MSCs-CDA/UPRT + 5FC and AT-MSCs-CDA/UPRT/VP22 + 5FC prolonged the life span of mice bearing LLC by 27% and 31%, respectively. Co-administration of lysomustine and AT-MSCs-CDA/UPRT + 5FC led to tumor growth inhibition (by 86%) and life span extension (by 60%) compared to the control group. CONCLUSIONS: Our data indicate that a combination CDA/UPRT-expressing AT-MSCs with lysomustine has a superior antitumor effect in the murine lung carcinoma model compared to monotherapies with transfected AT-MSCs or lysomustine alone, possibly because of a synergistic effect of the combination therapy. Copyright © 2016 John Wiley & Sons, Ltd.

Magnetic stromal layers for enhanced and unbiased recovery of co-cultured hematopoietic cells.

Cell co-culture systems have a long history of application in hematology and hold promise for successful hematopoietic stem and progenitor cell expansion. Here we report that various types of stromal cells used in such co-cultures can be rapidly and efficiently labeled with l-lysine-modified Fe3O4 magnetic nanoparticles. Hematopoiesis-supporting activity does not seem to be compromised after magnetic labeling of stromal cells, and the loss of the label by stromal layers during extended culturing is negligible. Magnetic labeling allows for simple and efficient removal of stromal component, yielding unbiased hematopoietic cell populations. When Lin(-) bone mouse marrow fraction was co-cultured with magnetic stromal layers and resulting cell populations were harvested by trypsinization, the yields of total nucleated cells, colony forming cells, and phenotypically primitive Lin(-)Sca-1(+)c-kit(+) subset were substantially higher as compared with nonadherent cell fractions harvested after conventional stromal co-culture. The advantage offered by the magnetic stroma approach over the traditional one was even more significant after a second round of co-culture and was more dramatic for more primitive hematopoietic cells. We conclude that magnetic stromal layers represent a simple, efficient, and convenient tool for co-culturing and subsequent recovery of sufficiently pure unbiased populations of hematopoietic cells.

TSC-22 contributes to hematopoietic precursor cell proliferation and repopulation and is epigenetically silenced in large granular lymphocyte leukemia.

Aberrant methylation of tumor suppressor genes can lead to their silencing in many cancers. TSC-22 is a gene silenced in several solid tumors, but its function and the mechanism(s) responsible for its silencing are largely unknown. Here we demonstrate that the TSC-22 promoter is methylated in primary mouse T or natural killer (NK) large granular lymphocyte (LGL) leukemia and this is associated with down-regulation or silencing of TSC-22 expression. The TSC-22 deregulation was reversed in vivo by a 5-aza-2'-deoxycytidine therapy of T or NK LGL leukemia, which significantly increased survival of the mice bearing this disease. Ectopic expression of TSC-22 in mouse leukemia or lymphoma cell lines resulted in delayed in vivo tumor formation. Targeted disruption of TSC-22 in wild-type mice enhanced proliferation and in vivo repopulation efficiency of hematopoietic precursor cells (HPCs). Collectively, our data suggest that TSC-22 normally contributes to the regulation of HPC function and is a putative tumor suppressor gene that is hypermethylated and silenced in T or NK LGL leukemia.

The protein encoded by the germ plasm RNA Germes associates with dynein light chains and functions in Xenopus germline development.

Germ plasm plays a prominent role in germline formation in a large number of animal taxons. We previously identified a novel maternal RNA named Germes associated with Xenopus germ plasm. In the present work, we addressed possible involvement of Germes protein in germ plasm function. Expression in oocytes followed by confocal microscopy revealed that the EGFP fused to Germes, in contrast to the free EGFP, co-localized with the germ plasm. Overexpression of intact Germes and Germes lacking both leucine zipper motifs (GermesDeltaLZs) resulted in a statistically significant reduction of the number of primordial germ cells (PGCs). Furthermore, the GermesDeltaLZs mutant inhibited PGC migration and produced abnormalities in germ plasm intra-cellular distribution at tailbud stages. To begin unraveling biochemical interactions of Germes during embryogenesis, we searched for Germes partners using yeast two-hybrid (YTH) system. Two closely related sequences were identified, encoding Xenopus dynein light chains dlc8a and dlc8b. Tagged versions of Germes and dlc8s co-localize in VERO cells upon transient expression and can be co-immunoprecipitated after injection of the corresponding RNAs in Xenopus embryos, indicating that their interactions occur in vivo. We conclude that Germes is involved in organization and functioning of germ plasm in Xenopus, probably through interaction with motor complexes.

Jedi--a novel transmembrane protein expressed in early hematopoietic cells.

Self-renewal and differentiation of hematopoietic stem and progenitor cells are defined by the ensembles of genes expressed by these cells. Here we report identification of a novel gene named Jedi, which is expressed predominantly in short- and long-term repopulating stem cells when compared to more mature bone marrow progenitors. Jedi mRNA encodes a transmembrane protein that contains multiple EGF-like repeats. Jedi and two earlier reported proteins, MEGF10 and MEGF11, share a substantial homology and are likely to represent a novel protein family. Studies of the potential role of Jedi in hematopoietic regulation demonstrated that the retrovirally mediated expression of Jedi in bone marrow cells decreased the number of myeloid progenitors in in vitro clonogenic assays. In addition, expression of Jedi in NIH 3T3 fibroblasts resulted in a decreased number of late and early myeloid progenitors in the non-adherent co-cultured bone marrow cells. Jedi shares a number of structural features with the Jagged/Serrate/Delta family of Notch ligands, and our experiments indicate that the extracellular domain of Jedi, similar to the corresponding domain of Jagged1, inhibits Notch signaling. On the basis of obtained results, we suggest that Jedi is involved in the fine regulation of the early stages of hematopoietic differentiation, presumably through the Notch signaling pathway.

Xenopus Germes encodes a novel germ plasm-associated transcript.

A cDNA tag specific for the vegetal pole of early Xenopus embryo was used to isolate a novel cDNA using RACE technique. The corresponding mRNA demonstrated a localization pattern typical for the germ plasm-associated messages, and was, therefore, named Germes. The open reading frame of Germes encodes a predicted 68 kDa protein with two leucine zipper motifs and a putative EF-hand domain, but otherwise no substantial homology to known proteins. In situ hybridization analysis shows that Germes transcript localizes to the vegetal cortex via the mitochondrial cloud early in oogenesis and segregates with the germ plasm during early embryogenesis. Our data indicate that Germes is a novel germ plasm-specific RNA.

Identification of differentially expressed genes in sorted cell populations by two-dimensional gene-expression fingerprinting.

Differential activity of genes is one of the major mechanisms underlying a vast array of biological phenomena. Classical genetic approaches (from phenotypes to genes) have proven their exquisite potential for dissection of complex signaling pathways regulating the development of organisms and the functioning of individual cells. In recent years, with the advent of a number of techniques for studying gene function, the reverse genetics approach (from genes to phenotypes) has received broad acceptance. One of the advantages of this strategy is that it makes genes, whose dysfunction either does not produce an evident phenotype or is lethal, amenable to analysis. Reverse genetics has spearheaded the development of procedures for identification of candidate genes for this type of analysis by detecting spatial or temporal changes in geneexpression patterns. A significant range of methods have been proposed (1-7); in particular, the advent of microarray hybridization techniques promises to increase gene-expression analysis throughput by two or more orders of magnitude (8,9). Some of these procedures have been used to identify genes expressed differentially during hematopoiesis (10,11).