Construction of a human immunodeficiency virus type 1 (HIV-1) library containing random combinations of amino acid substitutions in the HIV-1 protease due to resistance by protease inhibitors

Human immunodeficiency virus type 1 (HIV-1) heterogeneity contributes to the emergence of drug-resistant virus, escape from host defense systems, and/or conversion of the cellular tropism. To establish an in vitro system to address a heterogeneous virus population, we constructed a library of HIV-1 molecular clones containing a set of random combinations of zero to 11 amino acid substitutions associated with resistance to protease inhibitors by the HIV-1 protease. The complexity (2.1 x 10(5)) of the HIV-1 library pNG-PRL was large enough to cover all of the possible combinations of zero to 11 amino acid substitutions (a total of 4,096 substitutions possible). The T-cell line MT-2 was infected with the HIV-1 library, and resistant viruses were selected after treatment by the protease inhibitor ritonavir (0.03 to 0.30 microM). The viruses that contained three to eight amino acid substitutions could be selected within 2 weeks. These results demonstrate that this HIV-1 library could serve as an alternative in vitro system to analyze the emergence of drug resistance and to evaluate the antiviral activity of novel compounds against multidrug-resistant viruses.     

Identification and characterization of the UL56 gene product of herpes simplex virus type 2

The UL56 gene product of herpes simplex virus (HSV) has been shown to play an important role in viral pathogenicity. However, the properties and functions of the UL56 protein are little understood. We raised rabbit polyclonal antisera specific for the UL56 protein of HSV type 2 (HSV-2) and examined its expression and properties. The gene product was identified as three polypeptides with apparent molecular masses ranging from 32 to 35 kDa in HSV-2-infected cells, and at least one species was phosphorylated. Studies of their origins showed that the UL56 protein of HSV-2 is also translated from the upstream in-frame methionine codon that is not present in the HSV-1 genome. Synthesis was first detected at 6 h postinfection and was not abolished by the viral DNA synthesis inhibitor phosphonoacetic acid. Indirect immunofluorescence studies revealed that the UL56 protein localized to both the Golgi apparatus and cytoplasmic vesicles in HSV-2-infected and single UL56-expressing cells. Deletion mutant analysis showed that the C-terminal hydrophobic region of the protein was required for association with the cytoplasmic membrane and that the N-terminal proline-rich region was important for its translocation to the Golgi apparatus and cytoplasmic vesicles. Moreover, the results of protease digestion assays and sucrose gradient fractionation strongly suggested that UL56 is a tail-anchored type II membrane protein associated with lipid rafts. We thus hypothesized that the UL56 protein, as a tail-anchored type II membrane protein, may be involved in vesicular trafficking in HSV-2-infected cells.     

Effects of amino acid alterations on the transglycosylation reaction of endoglucanase I from Trichoderma viride HK-75

Endoglucanase I (EGI) from Trichoderma viride HK-75 catalyzes not only hydrolysis but also transglycosylation reactions of cellooligosaccharides. In order to characterize the important amino acid residues in transglycosylation of EGI, three Tyr, one Leu, and two Glu residues of EGI were replaced by Trp or Asp. The seven resulting EGI, except for L200W, had reduced activities toward carboxymethyl-cellulose compared to that of wild type EGI. The results from the mutations in the catalytic residues of E196 and E201 indicate that the space just around the catalytic residues is not directly related to the transglycosylation reactions of EGI. Analyses of the enzymes with mutations in the substrate-binding residues showed that Y146, Y170, and L200 of EGI are closely involved in the mode of transglycosylation and that several amino acid residues within the active site are involved in the transglycosylation reaction of EGI.     

FGF10 maintains stem cell compartment in developing mouse incisors

Mouse incisors are regenerative tissues that grow continuously throughout life. The renewal of dental epithelium-producing enamel matrix and/or induction of dentin formation by mesenchymal cells is performed by stem cells that reside in cervical loop of the incisor apex. However, little is known about the mechanisms of stem cell compartment formation. Recently, a mouse incisor was used as a model to show that fibroblast growth factor (FGF) 10 regulates mitogenesis and fate decision of adult stem cells. To further illustrate the role of FGF10 in the formation of the stem cell compartment during tooth organogenesis, we have analyzed incisor development in Fgf10-deficient mice and have examined the effects of neutralizing anti-FGF10 antibody on the developing incisors in organ cultures. The incisor germs of FGF10-null mice proceeded to cap stage normally. However, at a later stage, the cervical loop was not formed. We found that the absence of the cervical loop was due to a divergence in Fgf10 and Fgf3 expression patterns at E16. Furthermore, we estimated the growth of dental epithelium from incisor explants of FGF10-null mice by organ culture. The dental epithelium of FGF10-null mice showed limited growth, although the epithelium of wild-type mice appeared to grow normally. In other experiments, a functional disorder of FGF10, caused by a neutralizing anti-FGF10 antibody, induced apoptosis in the cervical loop of developing mouse incisor cultures. However, recombinant human FGF10 protein rescued the cervical loop from apoptosis. Taken together, these results suggest that FGF10 is a survival factor that maintains the stem cell population in developing incisor germs.     

Existence of cerebroside in Saccharomyces kluyveri and its related species

Sphingolipids are ubiquitous compounds derived from ceramide that consist of a sphingoid long-chain base with a 2-amino group amide linked to fatty acid and are present in the membranes of many organisms. As a principal sphingolipid, Saccharomyces cerevisiae contains a free ceramide and its inositol-phosphorylated derivatives (acidic types) but not a neutral glycosylated ceramide, glucosylceramide (cerebroside), which usually appears in eukaryotic cells. When 31 strains accepted in the genera Saccharomyces, Torulaspora, Zygosaccharomyces, and Kluyveromyces were analyzed for sphingolipids, cerebrosides were found in S. kluyveri, Z. cidri, Z. fermentati, K. lactis, K. thermotolerans, and K. waltii. The cerebrosides of S. kluyveri and K. lactis included 9-methyl 4-trans, 8-trans-sphingadienine and its putative metabolic intermediates. A unique characteristic of S. kluyveri was the presence of a trihydroxy sphingoid base, which rarely occurs in fungal cerebrosides. A polymerase chain reaction with primers targeted to the glucosylceramide synthase gene of other microorganisms amplified the fragments of the expected size from S. kluyveri and K. lactis and further extended to the adjacent regions. The presumed protein of S. kluyveri had 54.4% similarity to that of K. lactis, higher than the glucosylceramide synthases from Candida albicans, Pichia pastoris, and other organisms. From these observations, the divergence of S. kluyveri from the lineage of K. lactis in their evolution is discussed.     

Possible involvement of Fas system in the induction of apoptosis in human astrocytic brain tumors

1. For a better understanding of the biological features of astrocytic tumors, we investigated apoptosis and its pathway, especially in the interaction between Fas and Fas ligand (FasL).2. We examined the presence of apoptosis in human astrocytic brain tumors by terminal deoxynucleotidyl transferase (TdT)-mediated d-UTP-biotin nick end labeling (TUNEL) and then apoptotic index (AI) was calculated. We also examined the distribution of Fas and FasL-positive tumor cells immunohistochemically. Labeling index (LI) for Fas and FasL was calculated as Fas-LI and FasL-LI, respectively, and compared to AI.3. Tumor cells expressing both Fas and FasL were TUNEL positive. Such cells were distributed sparsely in low-grade astrocytomas, but focally in glioblastomas. There was a close correlation among AI, Fas-LI, and FasL-LI, and astrocytic tumors with higher AI were associated with a longer survival time than that with lower AI.4. It was concluded that the Fas system may be involved in the apoptosis of astrocytic tumors, and AI can be a useful parameter for assessing prognosis of astrocytic tumors.     

Human recombinant stem cell factor promotes spermatogonial proliferation,but not meiosis initiation in organ culture of newt testis fragments

We previously showed that mammalian FSH stimulates the proliferation of newt spermatogonia and induces their differentiation into primary spermatocytes in vitro. In the current study, to examine a possibility that stem cell factor (SCF) is involved in the proliferation of newt spermatogonia and/or their differentiation into primary spermatocytes, human recombinant SCF (rhSCF) was added to organ culture of testicular fragments. rhSCF was found to stimulate the spermatogonial proliferation and the spermatogonia progressed to the seventh generation that is the penultimate stage before primary spermatocyte stage. However, the spermatogonia did not differentiate into primary spermatocytes, but instead died of apoptosis. These results indicate that rhSCF promotes the proliferation of newt spermatogonia, but not the initiation of meiosis.     

Dual abnormal effects of mutant MITF encoded by Mi(wh) allele on mouse mast cells: decreased but recognizable transactivation and inhibition of transactivation

Structural localization of a peptide region, KRQPRNPKTDKLVNE, in the catalytic subunit of (Na(+) + K(+))-ATPase was investigated using a specific antibody directed against this peptide in cultured African green monkey kidney CV-1 cells. Immunofluorescence staining of frozen cell sections shows that an anti-KRQPRNPKTDKLVNE antibody (SSA95) interacts with its antigenic site and binds to the extracellular side of the cell membrane. Indirect immunofluorescence and flow cytometric analyses confirmed the presence of this epitope on intact cell surfaces. These results suggest that the KRQPRNPKTDKLVNE region of the (Na(+) + K(+))-ATPase is expressed on the cellular membrane surface.