[Expression of fused luxAB gene of bacterial luciferase in liver carcinoma cells]

OBJECTIVE

This work was done to look into the expression of fused luxAB gene of bacterial luciferase as a reporter gene in liver carcinoma cells.

METHODS

The mammalian expression vector pcDNA3-luxAB gene, constructed by the fusion of luxA and luxB genes, were amplified in the polymerase chain reaction (PCR) directed site mutagenesis from the vibrio harveyi 1600 strain and inserted into the plasmid of pcDNA3. This analysis was to confirm the fused luxAB gene and the positive clones obtained by the G418 resistant stable selection and transfected by lipofectin, when they were confirmed by the PCR. The growth curve of cell population and luminescence of bacterial luciferase was obtained through MTT and bioluminescence, respectively.

RESULTS

The fused luxAB gene, being a monocistron, completely agreed with the design. No significant difference in the growth curves of cell population was observed between the transfected cells and untransfected ones. The recombinant plasmid was likely to be expressed in a stable fashion in the BEL7402 cell. Meanwhile, the maximum cellular level in terms of vitro bioluminescent strength reached the point of (8.71 +/- 1.21) mV/40 micrograms protein.

CONCLUSION

Bacterial luciferase luxAB gene may become the first choice as a new, sensitive and non-invasive reporter gene in the research on liver cancer cells.

Spongistatins as tubulin targeting agents

Recently identified novel agents that disrupt tubulin polymerization include synthetic spiroketal pyrans (SPIKET) targeting the spongistatin binding site of b-tubulin. These agents exhibit anticancer activity by disrupting normal mitotic spindle assembly and cell division as well as inducing apoptosis. At nanomolar concentrations, the SPIKET compound SPIKET-P caused tubulin depolymerization in cell-free turbidity assays and exhibited potent cytotoxic activity against cancer cells as evidenced by destruction of microtubule organization, and prevention of mitotic spindle formation in human breast cancer cells. SPIKET compounds represent a new class of tubulin targeting agents that show promise as anti-cancer drugs.

Experiences from a collaborative project on the prevention of disability in leprosy patients in Shandong Province, the People's Republic of China

Shandong Province (present population 89 million) in the People's Republic of China established a leprosy control programme in 1955. Between that year and the end of 1999, allowing for death and migration, the cumulative number of cases registered was 53,618, including 120 cases on multiple drug therapy (MDT) and 18,248 who had completed satisfactory courses of dapsone monotherapy and/or MDT. Of this latter group, 9500 cases (52%) suffered from visible disabilities (grade 2 of the WHO classification). Prevalence and incidence rates of leprosy have decreased dramatically since 1955 and, on average, only 50-70 new cases are now being detected annually in the entire province. Leprosy is thus no longer a public health problem, but the existence of such a large number of patients with grade 2 disabilities is clearly a matter of serious concern. This paper describes a pilot project to investigate the potential of health personnel in the leprosy programme and the dermatology and sexually transmitted diseases services to (a) prevent deterioration of existing disabilities in ex-patients through self-care and (b) prevent new neuritis in patients on MDT through early detection and the use of steroids.

Transcription factor STAT5A is a substrate of Bruton's tyrosine kinase in B cells

STAT5A is a molecular regulator of proliferation, differentiation, and apoptosis in lymphohematopoietic cells. Here we show that STAT5A can serve as a functional substrate of Bruton's tyrosine kinase (BTK). Purified recombinant BTK was capable of directly binding purified recombinant STAT5A with high affinity (K(d) = 44 nm), as determined by surface plasmon resonance using a BIAcore biosensor system. BTK was also capable of tyrosine-phosphorylating ectopically expressed recombinant STAT5A on Tyr(694) both in vitro and in vivo in a Janus kinase 3-independent fashion. BTK phosphorylated the Y665F, Y668F, and Y682F,Y683F mutants but not the Y694F mutant of STAT5A. STAT5A mutations in the Src homology 2 (SH2) and SH3 domains did not alter the BTK-mediated tyrosine phosphorylation. Recombinant BTK proteins with mutant pleckstrin homology, SH2, or SH3 domains were capable of phosphorylating STAT5A, whereas recombinant BTK proteins with SH1/kinase domain mutations were not. In pull-down experiments, only full-length BTK and its SH1/kinase domain (but not the pleckstrin homology, SH2, or SH3 domains) were capable of binding STAT5A. Ectopically expressed BTK kinase domain was capable of tyrosine-phosphorylating STAT5A both in vitro and in vivo. BTK-mediated tyrosine phosphorylation of ectopically expressed wild type (but not Tyr(694) mutant) STAT5A enhanced its DNA binding activity. In BTK-competent chicken B cells, anti-IgM-stimulated tyrosine phosphorylation of STAT5 protein was prevented by pretreatment with the BTK inhibitor LFM-A13 but not by pretreatment with the JAK3 inhibitor HI-P131. B cell antigen receptor ligation resulted in enhanced tyrosine phosphorylation of STAT5 in BTK-deficient chicken B cells reconstituted with wild type human BTK but not in BTK-deficient chicken B cells reconstituted with kinase-inactive mutant BTK. Similarly, anti-IgM stimulation resulted in enhanced tyrosine phosphorylation of STAT5A in BTK-competent B cells from wild type mice but not in BTK-deficient B cells from XID mice. In contrast to B cells from XID mice, B cells from JAK3 knockout mice showed a normal STAT5A phosphorylation response to anti-IgM stimulation. These findings provide unprecedented experimental evidence that BTK plays a nonredundant and pivotal role in B cell antigen receptor-mediated STAT5A activation in B cells.

Active center cleft residues of pokeweed antiviral protein mediate its high-affinity binding to the ribosomal protein L3

Pokeweed antiviral protein (PAP) is a ribosome-inactivating protein (RIP) which catalytically cleaves a specific adenine base from the highly conserved alpha-sarcin/ricin loop (SRL) of the large ribosomal RNA and thereby inhibits the protein synthesis. The ribosomal protein L3, a highly conserved protein located at the peptidyltransferase center of the ribosomes, is involved in binding of PAP to ribosomes and subsequent depurination of the SRL. We have recently discovered that recombinant PAP mutants with alanine substitution of the active center cleft residues (69)NN(70) (FLP-4) and (90)FND(92) (FLP-7) that are not directly involved in the catalytic depurination at the active site exhibit >150-fold reduced ribosome inhibitory activity [(2000) J. Biol. Chem. 275, 3382--3390]. We hypothesized that the partially exposed half of the active site cleft could be the potential docking site for the L3 molecule. Our modeling studies presented herein indicated that PAP residues 90--96, 69--70, and 118--120 potentially interact with L3. Therefore, mutations of these residues were predicted to result in destabilization of interactions with rRNA and lead to a lower binding affinity with L3. In the present structure-function relationship study, coimmunoprecipitation assays with an in vitro synthesized yeast ribosomal protein L3 suggested that these mutant PAP proteins poorly interact with L3. The binding affinities of the mutant PAP proteins for ribosomes and recombinant L3 protein were calculated from rate constants and analysis of binding using surface plasmon resonance biosensor technology. Here, we show that, compared to wild-type PAP, FLP-4/(69)AA(70) and FLP-7/(90)AAA(92) exhibit significantly impaired affinity for ribosomes and L3 protein, which may account for their inability to efficiently inactivate ribosomes. By comparison, recombinant PAP mutants with alanine substitutions of residues (28)KD(29) and (111)SR(112) that are distant from the active center cleft showed normal binding affinity to ribosomes and L3 protein. The single amino acid mutants of PAP with alanine substitution of the active center cleft residues N69 (FLP-20), F90 (FLP-21), N91 (FLP-22), or D92 (FLP-23) also showed reduced ribosome binding as well as reduced L3 binding, further confirming the importance of the active center cleft for the PAP--ribosome and PAP--L3 interactions. The experimental findings presented in this report provide unprecedented evidence that the active center cleft of PAP is important for its in vitro binding to ribosomes via the L3 protein.

Spleen tyrosine kinase (Syk) deficiency in childhood pro-B cell acute lymphoblastic leukemia

The cytoplasmic spleen tyrosine kinase (SYK) is a key regulator of signal transduction events, apoptosis and orderly cell cycle progression in B-lineage lymphoid cells. Although SYK has not been linked to a human disease, defective expression of the closely related T-cell tyrosine kinase ZAP-70 has been associated with severe combined immunodeficiency. Childhood CD19(+)CD10(-) pro-B cell acute lymphoblastic leukemia (ALL) is thought to originate from B-cell precursors with a maturational arrest at the pro-B cell stage and it is associated with poor prognosis. Since lethally irradiated mice reconstituted with SYK-deficient fetal liver-derived lymphohematopoietic progenitor cells show a block in B-cell ontogeny at the pro-B to pre-B cell transition, we examined the SYK expression profiles of primary leukemic cells from children with pro-B cell ALL. Here we report that leukemic cells from pediatric CD19(+)CD10(-) pro-B cell ALL patients (but not leukemic cells from patients with CD19(+)CD10(+) common pre-pre-B cell ALL) have markedly reduced SYK activity. Sequencing of the reverse transcriptase-polymerase chain reaction (RT-PCR) products of the Syk mRNA in these pro-B leukemia cells revealed profoundly aberrant coding sequences with deletions or insertions. These mRNA species encode abnormal SYK proteins with a missing or truncated catalytic kinase domain. In contrast to pro-B leukemia cells, pre-pre-B leukemia cells from children with CD19(+)CD10(+) common B-lineage ALL and EBV-transformed B-cell lines from healthy volunteers expressed wild-type Syk coding sequences. Examination of the genomic structure of the Syk gene by inter-exonic PCR and genomic cloning demonstrated that the deletions and insertions in the abnormal mRNA species of pro-B leukemia cells are caused by aberrant splicing resulting in either mis-splicing, exon skipping or inclusion of alternative exons, consistent with an abnormal posttranscriptional regulation of alternative splicing of Syk pre-mRNA. Our findings link for the first time specific molecular defects involving the Syk gene to an immunophenotypically distinct category of childhood ALL. To our knowledge, this is the first discovery of a specific tyrosine kinase deficiency in a human hematologic malignancy.

Stereochemistry as a major determinant of the anti-HIV activity of chiral naphthyl thiourea compounds

Eleven chiral naphthyl thiourea (CNT) compounds were synthesized as non-nucleoside inhibitors (NNI) of the reverse transcriptase (RT) enzyme of HIV-1. Molecular modelling studies indicated that, because of the asymmetric geometry of the NNI binding pocket, the 'R' stereoisomers would fit the NNI binding pocket of the HIV-1 RT much better than the corresponding 'S' stereoisomers, as reflected by their 10(4)-fold lower Ki values. The 'R' stereoisomers of all 11 compounds inhibited the recombinant RT in vitro with lower IC50 values than their enantiomers. Of seven CNT compounds whose 'R' stereoisomers exhibited nanomolar IC50 values against recombinant RT, five were further evaluated for their ability to inhibit HIV-1 replication in human peripheral blood mononuclear cells (PBMC). All five 'R' stereoisomers were active anti-HIV agents and inhibited the replication of the HIV-1 strains HTLV-IIIB (NNI-sensitive), A17 (NNI-resistant, Y181C mutant RT) and A17Var (NNI-resistant, Y181C plus K103N mutant RT), as well as primary HIV-1 isolates from AIDS patients in human PBMC at nanomolar concentrations, whereas their enantiomers were inactive. The lead compounds, 1R and 5R, were 3 log more potent than the standard NNI drug nevirapine against the NNI-resistant HIV-1 strains. Our data establish the stereochemistry as a major determinant of the potency of this new class of NNI.

Binding interactions between the active center cleft of recombinant pokeweed antiviral protein and the alpha-sarcin/ricin stem loop of ribosomal RNA

Pokeweed antiviral protein (PAP) is a ribosome-inactivating protein that catalytically cleaves a specific adenine base from the highly conserved alpha-sarcin/ricin loop of the large ribosomal RNA, thereby inhibiting protein synthesis at the elongation step. Recently, we discovered that alanine substitutions of the active center cleft residues significantly impair the depurinating and ribosome inhibitory activity of PAP. Here we employed site-directed mutagenesis combined with standard filter binding assays, equilibrium binding assays with Scatchard analyses, and surface plasmon resonance technology to elucidate the putative role of the PAP active center cleft in the binding of PAP to the alpha-sarcin/ricin stem loop of rRNA. Our findings presented herein provide experimental evidence that besides the catalytic site, the active center cleft also participates in the binding of PAP to the target tetraloop structure of rRNA. These results extend our recent modeling studies, which predicted that the residues of the active center cleft could, via electrostatic interactions, contribute to both the correct orientation and stable binding of the substrate RNA molecules in PAP active site pocket. The insights gained from this study also explain why and how the conserved charged and polar side chains located at the active center cleft of PAP and certain catalytic site residues, that do not directly participate in the catalytic deadenylation of ribosomal RNA, play a critical role in the catalytic removal of the adenine base from target rRNA substrates by affecting the binding interactions between PAP and rRNA.

Cloning and characterization of a novel human alkaline ceramidase. A mammalian enzyme that hydrolyzes phytoceramide

Ceramidases are enzymes involved in regulating cellular levels of ceramides, sphingoid bases, and their phosphates. Based on sequence homology to the yeast alkaline ceramidases YPC1p (Mao, C., Xu, R., Bielawska, A., and Obeid, L. M. (2000) J. Biol. Chem. 275, 6876--6884) and YDC1p (Mao, C., Xu, R., Bielawska, A., Szulc, Z. M., and Obeid, L. M. (2000) J. Biol Chem. 275, 31369--31378), we report the identification and cloning of a cDNA encoding for a novel human alkaline ceramidase (aPHC) that hydrolyzes phytoceramide selectively. Northern blot analysis showed that aPHC was ubiquitously expressed, with the highest expression in placenta. Green fluorescent protein tagging showed that it was localized in both the Golgi apparatus and endoplasmic reticulum. Overexpression of aPHC in mammalian cells elevated in vitro ceramidase activity toward N-4-nitrobenz-2-oxa-1,3-diazole-C(12)-phytoceramide. Its expression in a yeast mutant strain devoid of any ceramidase activity restored the ceramidase activity and caused an increase in the hydrolysis of phytoceramide in yeast cells, thus leading to the decreased biosynthesis of sphingolipids. These data collectively suggest that, similar to the yeast phytoceramidase YPC1p, aPHC has phytoceramidase activity both in vitro and in cells; hence, it is a functional homolog of the yeast phytoceramidase YPC1p. However, in contrast to YPC1p, aPHC exhibited no reverse activity of ceramidase either in vitro or in cells. Biochemical characterization showed that aPHC had a pH optimum of 9.5, was activated by Ca(2+), but was inhibited by Zn(2+) and sphingosine. Substrate specificity showed that aPHC hydrolyzed phytoceramide preferentially. Together, these data demonstrate that aPHC is a novel human alkaline phytoceramidase, the first mammalian alkaline ceramidase to be identified as being specific for the hydrolysis of phytoceramide.

Structure-based design of novel anticancer agents

Recently identified agents that interact with cytoskeletal elements such as tubulin include synthetic spiroketal pyrans (SPIKET) and monotetrahydrofuran compounds (COBRA compounds). SPIKET compounds target the spongistatin binding site of beta-tubulin and COBRA compounds target a unique binding cavity on alpha-tubulin. At nanomolar concentrations, the SPIKET compound SPIKET-P causes tubulin depolymerization and exhibits potent cytotoxic activity against cancer cells. COBRA-1 inhibits GTP-induced tubulin polymerization. Treatment of human breast cancer and brain tumor cells with COBRA-1 caused destruction of microtubule organization and apoptosis. Other studies have identified some promising protein tyrosine kinase inhibitors as anti-cancer agents. These include EGFR inhibitors such as the quinazoline derivative WHI-P97 and the leflunomide metabolite analog LFM-A12. Both LFM-A12 and WHI-P97 inhibit the in vitro invasiveness of EGFR positive human breast cancer cells at micromolar concentrations and induce apoptotic cell death. Dimethoxyquinazoline compounds WHI-P131 and WHI-P154 inhibit tyrosine kinase JAK3 in leukemia cells. Of particular interest is WHI-P131, which inhibits JAK3 but not JAK1, JAK2, SYK, BTK, LYN, or IRK at concentrations as high as 350 microM. Studies of BTK inhibitors showed that the leflunomide metabolite analog LFM-A13 inhibited BTK in leukemia and lymphoma cells. Consistent with the anti-apoptotic function of BTK, treatment of leukemic cells with LFM-A13 enhanced their sensitivity to chemotherapy-induced apoptosis.

Anti-HIV activity of aromatic and heterocyclic thiazolyl thiourea compounds

Several thiazolyl thiourea derivatives were designed and synthesized as non-nucleoside inhibitors (NNRTI) of HIV-1 reverse transcriptase. Six lead compounds were identified that showed subnanomolar IC50 values for the inhibition of HIV replication, were minimally toxic to human peripheral blood mononuclear cells (PBMC) with CC50 values ranging from 28 to >100 microM, and showed remarkably high selectivity indices ranging from 28,000 to >100,000. The most promising compound was N-[1-(1-furoylmethyl)]-N'-[2-(thiazolyl)]thiourea (compound 6), which showed potency against two NNRTI-resistant HIV-1 isolates (A17 and A17 variant) at nanomolar to low micromolar concentrations, exhibited much greater potency against both wild-type as well as NNRTI-resistant HIV-1 than nevirapine, delavirdine, HI-443, and HI-244, was minimally toxic to PBMC, and had a selectivity index of > 100,000. The potency and minimal cytotoxicity of these aromatic/heterocyclic thiourea compounds suggest that they may be potentially useful as anti-AIDS drugs.

Spectrochemical investigations in molecularly organized solvent media: evaluation of pyridinium chloride as a selective fluorescence quenching agent of polycyclic aromatic hydrocarbons in aqueous carboxylate-terminated poly(amido) amine dendrimers and anionic micelles

The ability of pyridinium chloride (PC) to selectively quench alternant as opposed to nonaltemant polycyclic aromatic hydrocarbons (PAHs) in organized media is examined. PC was previously shown to be a selective quenching agent of alternant PAHs in neat polar solvents. Carboxylate-terminated poly(amido) amine (PAMAM-CT) dendrimers and anionic surfactants--sodium dodecanoate (SD), sodium octanoate (SO), and sodium dodecylsulfate (SDS)--were chosen as the solubilizing media for this study. Selective quenching of alternant PAHs is observed in the presence of the SDS and SO micelles. However, the extent of PAH quenching in SO is significantly reduced compared to PAHs dissolved in either water or SDS micelles. In the case of the smaller generation 4.5 (G4.5) PAMAM-CT dendrimers, PC was prevented from quenching both alternant and nonalternant PAHs to any appreciable extent. The dendrimer is able to "protect" the PAHs from the PC quencher that resides at the dendrimer surface. Both, SD and G5.5 PAMAM-CT precipitated out of solution with the addition of PC. Differences between traditional micelles and "unimolecular micelle" dendrimers were also examined. These studies further confirm that the PAHs did not reside in the "analogous" palisade region of the dendrimers as they do in micelles. The PAHs must reside in the outermost branches of the dendrimer, but sufficiently far enough away from the charged surface groups, where PC associated, to prevent fluorescence quenching. This work further illustrates the differences between "unimolecular micelle" dendrimers and traditional micelles.

Identification of ISC1 (YER019w) as inositol phosphosphingolipid phospholipase C in Saccharomyces cerevisiae

Sphingolipids have emerged as novel bioactive mediators in eukaryotic cells including yeast. It has been proposed that sphingomyelin (SM) hydrolysis and the concomitant generation of ceramide are involved in various stress responses in mammalian cells. The yeast Saccharomyces cerevisiae has inositol phosphosphingolipids (IPS) instead of SM and glycolipids, and synthesis of IPS is indispensable to its growth. Although the genes responsible for the synthesis of IPS have been identified, the gene(s) for the degradation of IPS has not been reported. Here we show that ISC1 (YER019w), which has homology to bacterial neutral sphingomyelinase (SMase), encodes IPS phospholipase C (IPS-PLC). First, we observed that overexpression of ISC1 greatly increased neutral SMase activity, and this activity was dependent on the presence of phosphatidylserine. Cells deleted in ISC1 demonstrated negligible neutral SMase activity. Because yeast cells have IPS instead of SM, we investigated whether IPS are the physiologic substrates of this enzyme. Lysates of ISC1-overexpressing cells demonstrated very high PLC activities on IPS. Deletion of ISC1 eliminated endogenous IPS-PLC activities. Labeling yeast cells with [(3)H]dihydrosphingosine showed that IPS were increased in the deletion mutant cells. This study identifies the first enzyme involved in catabolism of complex sphingolipids in S. cerevisiae.

Molecular determinants of ligand binding to the human melanocortin-4 receptor

To elucidate the molecular basis for the interaction of ligands with the human melanocortin-4 receptor (hMC4R), agonist structure-activity studies and receptor point mutagenesis were performed. Structure-activity studies of [Nle(4), D-Phe(7)]-alpha-melanocyte stimulating hormone (NDP-MSH) identified D-Phe7-Arg8-Trp9 as the minimal NDP-MSH fragment that possesses full agonist efficacy at the hMC4R. In an effort to identify receptor residues that might interact with amino acids in this tripeptide sequence 24 hMC4R transmembrane (TM) residues were mutated (the rationale for choosing specific receptor residues for mutation is outlined in the Results section). Mutation of TM3 residues D122 and D126 and TM6 residues F261 and H264 decreased the binding affinity of NDP-MSH 5-fold or greater, thereby identifying these receptor residues as sites potentially involved in the sought after ligand-receptor interactions. By examination of the binding affinities and potencies of substituted NDP-MSH peptides at receptor mutants, evidence was found that core melanocortin peptide residue Arg8 interacts at a molecular level with hMC4R TM3 residue D122. TM3 mutations were also observed to decrease the binding of hMC4R antagonists. Notably, mutation of TM3 residue D126 to alanine decreased the binding affinity of AGRP (87-132), a C-terminal derivative of the endogenous melanocortin antagonist, 8-fold, and simultaneous mutations D122A/D126A completely abolished AGRP (87-132) binding. In addition, mutation of TM3 residue D122 or D126 decreased the binding affinity of hMC4R antagonist SHU 9119. These results provide further insight into the molecular determinants of hMC4R ligand binding.

Multimerization-cyclization of DNA fragments as a method of conformational analysis

Ligation of short DNA fragments results in the formation of linear and circular multimers of various lengths. The distribution of products in such a reaction is often used to evaluate fragment bending caused by specific chemical modification, by bound ligands or by the presence of irregular structural elements. We have developed a more rigorous quantitative approach to the analysis of such experimental data based on determination of j-factors for different multimers from the distribution of the reaction products. j-Factors define the effective concentration of one end of a linear chain in the vicinity of the other end. To extract j-factors we assumed that kinetics of the reaction is described by a system of differential equations where j-factors appear as coefficients. The assumption was confirmed by comparison with experimental data obtained here for DNA fragments containing A-tracts. At the second step of the analysis j-factors are used to determine conformational parameters of DNA fragments: the equilibrium bend angle, the bending rigidity of the fragment axis, and the total twist of the fragments. This procedure is based on empirical equations that connect the conformational parameters with the set of j-factors. To obtain the equations, we computed j-factors for a large array of conformational parameters that describe model fragments. The approach was tested on both simulated and actual experimental data for DNA fragments containing A-tracts. A-tract DNA bend angle determined here is in good agreement with previously published data. We have established a set of experimental conditions necessary for the data analysis to be successful.

Structure-based drug design of non-nucleoside inhibitors for wild-type and drug-resistant HIV reverse transcriptase

The generation of anti-HIV agents using structure-based drug design methods has yielded a number of promising non-nucleoside inhibitors (NNIs) of HIV reverse transcriptase (RT). Recent successes in identifying potent NNIs are reviewed with an emphasis on the recent trend of utilizing a computer model of HIV RT to identify space in the NNI binding pocket that can be exploited by carefully chosen functional groups predicted to interact favorably with binding pocket residues. The NNI binding pocket model was used to design potent NNIs against both wild-type RT and drug-resistant RT mutants. Molecular modeling and score functions were used to analyze how drug-resistant mutations would change the RT binding pocket shape, volume, and chemical make-up, and how these changes could affect inhibitor binding. Modeling studies revealed that for an NNI of HIV RT to be active against RT mutants such as the especially problematic Y181C RT mutant, the following features are required: (a) the inhibitor should be highly potent against wild-type RT and therefore capable of tolerating a considerable activity loss against RT mutants (i.e. a picomolar-level inhibitor against wild-type RT may still be effective against RT mutants at nanomolar concentrations), (b) the inhibitor should maximize the occupancy in the Wing 2 region of the NNI binding site of RT, and (c) the inhibitor should contain functional groups that provide favorable chemical interactions with Wing 2 residues of wild-type as well as mutant RT. Our rationally designed NNI compounds HI-236, HI-240, HI-244, HI-253, HI-443, and HI-445 combine these three features and outperform other anti-HIV agents examined.

Cloning and characterization of a Saccharomyces cerevisiae alkaline ceramidase with specificity for dihydroceramide

In a previous study, we reported that the Saccharomyces cerevisiae gene YPC1 encodes an alkaline ceramidase with a dual activity, catalyzing both hydrolysis and synthesis of yeast ceramide (Mao, C., Xu, R., Bielawska, A., and Obeid, L. M. (2000) J. Biol. Chem. 275, 6876-6884). In this study, we have identified a YPC1 homologue in S. cerevisiae that also encodes an alkaline ceramidase. We show that these two ceramidases have different substrate specificity, such that YPC1p preferentially hydrolyzes phytoceramide, whereas the new ceramidase YDC1p hydrolyzes dihydroceramide preferentially and phytoceramide only slightly. Neither enzyme hydrolyzes unsaturated mammalian-type ceramide. In contrast to YPC1p, YDC1p had only minor in vitro reverse activity of catalyzing dihydroceramide formation from a free fatty acid and dihydrosphingosine and no activity with phytosphingosine. Overexpression of YDC1p had no reverse activity in non-stressed yeast cells, but like YPC1p suppressed the inhibition of growth by fumonisin B1 albeit more modestly. Deletion of YDC1 and YPC1 or both did not apparently affect growth, suggesting neither gene is essential. However, the Deltaydc1 deletion mutant but not the Deltaypc1 deletion mutant was sensitive to heat stress, indicating a role for dihydroceramide but not phytoceramide in heat stress responses, and suggesting that the two enzymes have distinct physiological functions.

[Simultaneous primary palate repair and alveolar bone grafting in unoperated cleft palate patients over 8 years old]

OBJECTIVE

To analyze the applicability and results of simultaneous primary palate repair and alveolar bone grafting in unoperated cleft lip and palate patients over 8 years old.

METHODS

A retrospective study was performed in a group of unoperated cleft palate patients who received simultaneous primary palate repair and alveolar bone grafting. Between December 1990 and March 1998, a consecutive of 38 complete unilateral cleft lip and palate patients were treated by the procedures of simultaneous primary cleft palate repair and alveolar bone grafting at the Peking University of Cleft Lip and Palate Treatment Center. All the patients had their lip repaired before they were admitted. The age range was 8 to 24 years, with the average of 14.7 years old. The duration of operation as well as the blood loss during the operation was recorded, and compared with those patients who only received alveolar bone grafting. All the patients have been followed up for at least twelve months, and the results of bone grafting were evaluated according to radiographs.

RESULTS

All the operations were successful, and the wound healed well. Compared with simple alveolar bone grafting, simultaneous primary palate repair and alveolar bone grafting prolonged the operation time to an average of 37 minutes. The procedure of simultaneous primary palate repair and alveolar bone grafting did not prolong the operating time compared with simple alveolar bone grafting and no blood transfusion due to bone grafting was needed. All the wounds both in the grafted area and donor site healed uneventfully. No major complications occurred during or shortly after the operation. The overall clinical successful rate of alveolar bone grafting in this group of patients was 89.5%.

CONCLUSION

Simultaneous primary palate repair and alveolar bone grafting are safe and applicable procedure for unoperated cleft palate patients, and this procedure should be performed in those unoperated cleft palate patients above 8 years old.

SPIKET and COBRA compounds as novel tubulin modulators with potent anticancer activity

Agents that either promote or inhibit tubulin polymerization exhibit anticancer activity by disrupting normal mitotic spindle assembly and cell division as well as inducing apoptosis. Recently identified novel agents that target tubulin include synthetic spiroketal pyrans (SPIKET), targeting the spongistatin binding site of beta-tubulin, and COBRA compounds, targeting a unique binding cavity on alpha-tubulin. At nanomolar concentrations, the SPIKET compound SPIKET-P caused tubulin depolymerization in cell-free turbidity assays and exhibited potent cytotoxic activity against cancer cells as evidenced by destruction of microtubule organization, and prevention of mitotic spindle formation in human breast cancer cells. Molecular modeling studies predicted a high-affinity interaction of the first COBRA compounds, COBRA-0 and COBRA-1, with a unique hydrophobic binding site on alpha-tubulin located between the GTP/GDP binding site and the M-loop. Further studies showed that COBRA-1 inhibited GTP-induced tubulin polymerization in cell-free tubulin turbidity assays. Treatment of human breast cancer and brain tumor (glioblastoma) cells with COBRA-1 caused destruction of microtubule organization and apoptosis. COBRA-1 activated the pro-apoptotic c-Jun N-terminal kinase (JNK) signal transduction pathway. COBRA and SPIKET compounds represent two new classes of tubulin targeting agents that show promise as anticancer drugs.

Logical computation using algorithmic self-assembly of DNA triple-crossover molecules

Recent work has demonstrated the self-assembly of designed periodic two-dimensional arrays composed of DNA tiles, in which the intermolecular contacts are directed by 'sticky' ends. In a mathematical context, aperiodic mosaics may be formed by the self-assembly of 'Wang' tiles, a process that emulates the operation of a Turing machine. Macroscopic self-assembly has been used to perform computations; there is also a logical equivalence between DNA sticky ends and Wang tile edges. This suggests that the self-assembly of DNA-based tiles could be used to perform DNA-based computation. Algorithmic aperiodic self-assembly requires greater fidelity than periodic self-assembly, because correct tiles must compete with partially correct tiles. Here we report a one-dimensional algorithmic self-assembly of DNA triple-crossover molecules that can be used to execute four steps of a logical (cumulative XOR) operation on a string of binary bits.

Stereochemistry of halopyridyl and thiazolyl thiourea compounds is a major determinant of their potency as nonnucleoside inhibitors of HIV-1 reverse transcriptase

Chiral derivatives of two cyclohexylethyl halopyridyl thiourea compounds (HI-509 and HI-510), two alpha-methyl benzyl halopyridyl compounds (HI-511 and HI-512), and a cyclohexyl ethyl thiazolyl thiourea compound (HI-513) were synthesized as nonnucleoside inhibitors (NNI) of human immunodeficiency virus (HIV) reverse transcriptase (RT). The R stereoisomers of all five compounds inhibited the recombinant RT in vitro with 100-fold lower IC50 values. HI-509R, HI-510R, HI-511R, HI-512R and HI-513R were active anti-HIV agents and inhibited HIV-1 replication in human peripheral blood mononuclear cells at nanomolar concentrations, whereas their enantiomers were inactive. Each of these five compounds was also active against NNI-resistant HIV-1 strains, with HI-511R being the most active agent. When tested against the NNI-resistant HIV-1 strain A17 with a Y181C mutation in RT, HI-511R was found to be 10,000-times more active than nevirapine, 5000-times more active than delavirdine, and 50-times more active than trovirdine. HI-511 R inhibited the HIV-strain A17 variant, containing RT mutations Y181C plus K103N, with an IC50 value of 2.7 microM, whereas the IC50 values of nevirapine, delavirdine, and trovirdine against this highly NNI-resistant HIV-1 strain were >100 microM.

Piperidinylethyl, phenoxyethyl and fluoroethyl bromopyridyl thiourea compounds with potent anti-HIV activity

Derivatives of piperidinylethyl, phenoxyethyl and fluoroethyl bromopyridyl thioureas were designed and synthesized as non-nucleoside reverse transcriptase inhibitors (NNRTIs) of HIV-1 reverse transcriptase (RT). The anti-HIV activity of these compounds was examined by determining their ability to inhibit the replication of the HIV-1 strain HTLV(IIIB) in human peripheral blood mononuclear cells. The unsubstituted parent pyridyl thiourea compound N-[2-(1-piperidine)ethyl]-N'-[2-(pyridyl)] thiourea (1) exhibited no anti-HIV activity, even at 100 microM. However, the thiourea derivatives that contain a bromo- or chloro-substituted pyridyl group, compounds 2 and 5, inhibited HIV-1 replication at nanomolar concentrations. The addition of a methyl group onto the piperidine ring significantly altered the potency of these compounds; while methyl substitution at the 3-position of the piperidine ring reduced the activity, methyl substitution at the 2-position enhanced the anti-HIV activity. The IC50 value of the lead piperidinyl compound, N-[2-(2-methylpiperidinylethyl)]-N'-[2-(5-bromopyridyl)] thiourea (4) was <0.001 microM. All three phenoxyethyl derivatives, including the unsubstituted parent phenoxyethyl pyridyl thiourea compound N-[2-(phenoxy)ethyl]-N'-[2-(pyridyl)]thiourea (8) and the bromo-/chloro-substituted phenoxyethyl halopyridyl thiourea compounds N-[2-(phenoxy)ethyl]-N'-[2-(5-chloropyridyl)]thiourea (9) and N-[2-(phenoxy)ethyl]-N'-[2-(5-bromopyridyl)]thiourea (10) exhibited potent anti-HIV activity with nanomolar IC values. The corresponding fluoroethyl halopyridyl thiourea compounds beta-fluoro[2-phenethyl]-N'[2-(5-chloropyridyl)]thiourea (11) and beta-fluoro[2-phenethyl]-N'[2-(5-bromopyridyl)]thiourea (12) inhibited HIV-1 replication in PBMC with subnanomolar IC50 values and selectivity indices >30000. Compared to the corresponding phenoxyethyl thiourea compounds 9 and 10, these compounds were >4-5-fold more active as anti-HIV agents. Notably, the lead fluorothiourea compounds 11 and 12 were both substantially more active against the NNRTI-resistant HIV strains RT-MDR (V106A) and A17 (Y181C) than nevirapine or delavirdine. Taken together, our results provide additional experimental evidence that the structural features of the 'linker unit' between the pyridyl and phenyl moieties and changes in the phenyl group of PETT-related thiourea compounds significantly affects their biological activity as NNRTIs of HIV-1 RT.

X-ray crystallographic analysis of pokeweed antiviral protein-II after reductive methylation of lysine residues

Pokeweed antiviral protein II (PAP-II) is a naturally occurring protein isolated from early summer leaves of the pokeweed plant (Phytolacca americana). PAP-II belongs to a family of ribosome-inactivating proteins which catalytically deadenylate ribosomal and viral RNA. The chemical modification of PAP-II by reductive methylation of its lysine residues significantly improved the crystal quality for X-ray diffraction studies. Hexagonal crystals of the modified PAP-II, with unit cell parameters a = b = 92.51 A, c = 79.05 A, were obtained using 1.8 M Na/K phosphate as the precipitant. These crystals contained one enzyme molecule per asymmetric unit and diffracted up to 2.4 A, when exposed to a synchroton source.

A histone deacetylase inhibitor potentiates estrogen receptor activation of a stably integrated vitellogenin promoter in HepG2 cells

To compare the role of histone deactylation in estrogen activation of a transiently transfected vitellogenin (VIT) promoter and an integrated VIT promoter in the same cells, we produced three HepG2, human hepatoma, cell lines (HepG2ERV cells) stably expressing human estrogen receptor alpha (hERalpha) and containing an integrated VIT promoter-chloramphenicol acetyltransferase (VIT-CAT) reporter gene. The three ER-positive HepG2ERV cell lines and wild-type, ER-negative, HepG2 cells cotransfected with cytomegalovirus-hERalpha exhibited similar MOX-dependent inductions of 20- to 50-fold with a transiently transfected VIT-luciferase reporter and 15- to 50-fold with a transfected 4-estrogen response element-TATA-luciferase reporter gene. The histone deacetylase inhibitor, trichostatin A, did not enhance MOX induction of the transiently transfected VIT promoter in the HepG2ERV cells. In contrast, trichostatin A dramatically potentiated MOX induction of the stably integrated VIT-CAT reporter gene, resulting in MOX-ER-dependent increases in CAT activity of up to 600-fold. These data demonstrate that although liganded ER exhibits the capacity to fully activate a transiently transfected VIT promoter, under some circumstances the ability to reorganize a repressive chromatin structure may be limiting for steroid receptor action.

COBRA-1, a rationally-designed epoxy-THF containing compound with potent tubulin depolymerizing activity as a novel anticancer agent

A novel mono-THF containing synthetic anticancer drug, COBRA-1, was designed for targeting a previously unrecognized unique narrow binding cavity on the surface of alpha-tubulin. COBRA-1 inhibited GTP-induced tubulin polymerization in cell-free tubulin turbidity assays. Treatment of human breast cancer and brain tumor (glioblastoma) cells with COBRA-1 caused destruction of microtubule organization and apoptosis. Like other microtubule-interfering agents, COBRA-1 activated the proapoptotic c-Jun N-terminal kinase (JNK) signal transduction pathway, as evidenced by rapid induction of c-jun expression.