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The immunosuppressant,rapamycin,inhibits cell growth by interfering with the function of a novel kinase,termed mammalian target of rapamycin (mTOR). The putative catalytic domain of mTOR is similar to those of mammalian and yeast phosphatidylinositol (PI) 3-kinases. This study demonstrates that mTOR is a component of a cytokine-triggered protein kinase cascade leading to the phosphorylation of the eukaryotic initiation factor-4E (eIF-4E) binding protein,PHAS-1,in activated T lymphocytes. This event promotes G1 phase progression by stimulating eIF-4E-dependent translation initiation. A mutant YAC-1 T lymphoma cell line,which was selected for resistance to the growth-inhibitory action of rapamycin,was correspondingly resistant to the suppressive effect of this drug on PHAS-1 phosphorylation. In contrast,the PI 3-kinase inhibitor,wortmannin,reduced the phosphorylation of PHAS-1 in both rapamycin-sensitive and -resistant T cells. At similar drug concentrations (0.1-1 microM),wortmannin irreversibly inhibited the serine-specific autokinase activity of mTOR. The autokinase activity of mTOR was also sensitive to the structurally distinct PI 3-kinase inhibitor,LY294002,at concentrations (1-30 microM) nearly identical to those required for inhibition of the lipid kinase activity of the mammalian p85-p110 heterodimer. These studies indicate that the signaling functions of mTOR,and potentially those of other high molecular weight PI 3-kinase homologs,are directly affected by cellular treatment with wortmannin or LY294002. View Publication

Natural and synthetic retinoids have proved to be effective in the treatment and prevention of various human cancers. In the present study,we investigated the effect of retinoids on Epstein-Barr virus (EBV)-infected lymphoblastoid cell lines (LCLs),since these cells closely resemble those that give rise to EBV-related lymphoproliferative disorders in the immunosuppressed host. All six compounds tested inhibited LCL proliferation with no significant direct cytotoxicity,but 9-cis-retinoic acid (RA),13-cis-RA,and all-trans-RA (ATRA) were markedly more efficacious than Ro40-8757,Ro13-6298,and etretinate. The antiproliferative action of the three most effective compounds was confirmed in a large panel of LCLs,thus appearing as a generalized phenomenon in these cells. LCL growth was irreversibly inhibited even after 2 days of treatment at drug concentrations corresponding to therapeutically achievable plasma levels. Retinoid-treated cells showed a marked downregulation of CD71 and a decreased S-phase compartment with a parallel accumulation in Gzero/ G1 phases. These cell cycle perturbations were associated with the upregulation of p27 Kip1,a nuclear protein that controls entrance and progression through the cell cycle by inhibiting several cyclin/cyclin-dependent kinase complexes. Unlike what is observed in other systems,the antiproliferative effect exerted by retinoids on LCLs was not due to the acquisition of a terminally differentiated status. In fact,retinoid-induced modifications of cell morphology,phenotype (downregulation of CD19,HLA-DR,and s-Ig,and increased expression of CD38 and c-Ig),and IgM production were late events,highly heterogeneous,and often slightly relevant,being therefore only partially indicative of a drug-related differentiative process. Moreover,EBV-encoded EBV nuclear antigen-2 and latent membrane protein-1 proteins were inconstantly downregulated by retinoids,indicating that their growth-inhibitory effect is not mediated by a direct modulation of viral latent antigen expression. The strong antiproliferative activity exerted by retinoids in our experimental model indicates that these compounds may represent a useful tool in the medical management of EBV-related lymphoproliferative disorders of immunosuppressed patients. View Publication

1. The effects of the non-selective phosphodiesterase (PDE) inhibitor theophylline and the selective PDE4 inhibitor rolipram on leukotriene C4 (LTC4) synthesis and chemotaxis of complement 5a (C5a)- and platelet-activating factor (PAF)-stimulated human eosinophils obtained from normal and atopic donors were investigated. 2. Eosinophils were purified from peripheral venous blood of normal and atopic subjects by an immunomagnetic procedure to a purity textgreater 99%. Eosinophils were stimulated with PAF (0.1 microM) or C5a 0.1 microM for 15 min and LTC4 was measured by radioimmunoassay (RIA). Eosinophil chemotaxis in response to PAF and C5a was assessed with 48-well microchambers (Boyden). 3. Under these conditions substantial amounts of LTC4 (about 300-1000 pg per 10(6) cells) were only detectable in the presence of indomethacin (0.1-10 microM). To explain this finding it was hypothesized that indomethacin reversed the inhibition of LTC4 synthesis by endogenously synthesized prostaglandins,in particular prostaglandin E2 (PGE2). In fact,eosinophils release 23 pg PGE2 per 10(6) cells following PAF stimulation; this PGE2 synthesis was completely inhibited by indomethacin and readdition of PGE2 inhibited eosinophil LTC4 synthesis (IC50 = 3 nM). The following experiments were performed in the presence of 10 microM indomethacin. 4. Theophylline (IC50 approximately 50 microM) and rolipram (IC50 approximately 0.03-0.2 microM) suppressed PAF- and C5a-stimulated LTC4 synthesis. This PDE inhibitor-induced suppression of LTC4 generation is mediated by activation of protein kinase A,since it was reversed by the protein kinase A inhibitor Rp-8-Br-cyclic AMPS. In addition,exogenous arachidonic acid concentration-dependently (0.3 microM-3 microM) reversed the inhibition of LTC4 synthesis by the PDE inhibitors,indicating that theophylline and rolipram suppress the mobilization of arachidonic acid. The beta 2-adrenoceptor agonist salbutamol inhibited eosinophil LTC4 synthesis (IC50 = 0.08 microM). The combination of salbutamol with theophylline (10 microM) or rolipram (3 nM) appeared to be additive. 5. Theophylline (IC50 approximately 40 microM),rolipram (IC50 approximately 0.02 microM [C5a],approximately 0.6 microM [PAF]) and PGE2 (IC50 approximately 3 nM) inhibited C5a- and PAF-stimulated eosinophil chemotaxis. The combination of PGE2 with theophylline resulted in an additive effect. 6. Both C5a- and PAF-stimulated eosinophil chemotaxis and LTC4 generation were significantly elevated in eosinophils from atopic individuals compared to normal subjects. However,eosinophils from normal and atopic individuals were not different with respect to their total cyclic AMP-PDE and PDE4 isoenzyme activities as well as the potencies of theophylline and rolipram to suppress LTC4 generation and chemotaxis. View Publication

Reaction with peroxynitrite at pH 7.4 and 37 degrees C was found to increase the 8-oxodeoxyguanosine levels in calf thymus DNA 35- 38-fold. This oxidation of deoxyguanosine,as well as the peroxynitrite-mediated nitration of tyrosine to 3-nitrotyrosine,was significantly inhibited by ascorbic acid,glutathione and (-)-epigallocatechin gallate,a polyphenolic antioxidant present in tea. For 50% inhibition of the oxidation of deoxyguanosine to 8-oxodeoxyguanosine,1.1,7.6 or 0.25 mM ascorbate,glutathione or (-)-epigallocatechin gallate,respectively,was required. For 50% inhibition of tyrosine nitration,the respective concentrations were 1.4,4.6 or 0.11 mM. Thus,(-)-epigallocatechin gallate is a significantly better inhibitor of both reactions than either ascorbate or glutathione. Reaction of (-)-epigallocatechin gallate with peroxynitrite alone resulted in the formation of a number of products. Ultraviolet spectra of two of these suggest that the tea polyphenol and/or its oxidation products are nitrated by peroxynitrite. View Publication

Brefeldin A (BFA) is a natural product that affects the structure and function of the Golgi apparatus and is in development for cancer chemotherapy. We observed that a wide range of cancer cells could undergo DNA fragmentation associated with apoptosis after BFA treatment. This DNA fragmentation was induced within 15 h in HL60 leukemia cells and after 48 h in K562 leukemia and HT-29 colon carcinoma cells with BFA concentrations as low as 0.1 microM. The DNA fragmentation had the typical internucleosomal pattern in HL60 and HT-29 cells. Apoptotic cells were also detected by microscopy. BFA-induced apoptosis is p53-independent as HL60 and K562 cells are p53 null and HT-29 are p53 mutant cells. BFA could potentiate UCN-01 and staurosporine-induced DNA fragmentation in HL60 cells. Cyclin B1/Cdc2 kinase activity decreased after BFA treatment in HL60 cells,indicating that BFA-induced DNA fragmentation was independent of a cyclin B1/Cdc2 kinase upregulation pathway. Cycloheximide could not prevent BFA-induced DNA fragmentation in HL60 cells,suggesting that protein synthesis is not needed for HL60 cells to undergo apoptosis. On the contrary,cycloheximide blocked BFA-induced DNA fragmentation in HT-29 cells,indicating that apoptosis in HT-29 cells requires macromolecular synthesis. Cell-free system experiments suggested that cytosolic proteins play an important role in triggering DNA fragmentation during apoptosis induced by BFA. Our results show that transduction signaling pathways play central roles in apoptotic regulation. View Publication

To explore membrane-permeable synthetic inhibitors that discriminate between endogenous calpain and proteasome in cells,we examined the inhibition of profiles against calpain and proteasome in vitro and in vivo of peptidyl aldehydes possessing di-leucine and tri-leucine. The tripeptide aldehyde benzyloxycarbonyl-leucyl-leucinal (ZLLLal) strongly inhibited calpain and proteasome activities in vitro. The concentration required for 50% inhibition (IC50) of the casein-degrading activity of calpain was 1.25 microM,and the IC50s for the succinyl-leucyl-leucyl-valyl-tyrosine-4-methylcoumaryl-7-amide (Suc-LLVY-MCA)- and benzyloxycarbonyl-leucyl-leucyl-leucine-4-methylcoumaryl -7-amide (ZLLL-MCA)-degrading activities of proteasome were 850 and 100 nM,respectively. On the other hand,the synthetic dipeptide aldehyde benzyloxycarbonyl-leucyl-leucinal (ZLLal) strongly inhibited the casein degrading activity of calpain (IC50 1.20 microM),but the inhibition of proteasome was weak (IC50S for SucLLVY-MCA- and ZLLL-MCA-degrading activities were 120 and 110 microM,respectively). Thus,while calpain was inhibited by similar concentrations of ZLLal and ZLLLal,the inhibitory potencies of ZLLLal against the ZLLL-MCA- and Suc-LLVY-MCA-degrading activities in proteasome were 1,100 and 140 times stronger than those of ZLLal,respectively. To evaluate the effectiveness of these inhibitors on intracellular proteasome,the induction of neurite outgrowth in PC12 cells caused by proteasome inhibition was examined. ZLLLal and ZLLal initiated neurite outgrowth with optimal concentrations of 20 nM and 10 microM,respectively,again showing a big difference in the effective concentrations for the proteasome inhibition as in vitro. As for the effect on intracellular calpain,the concentration of ZLLLal and ZLLal required for the inhibition of the autolytic activation of calpain in rabbit erythrocytes were 100 and 100 microM or more,respectively. The almost equal inhibitory potencies of ZLLLal and ZLLal were in agreement with the inhibition of calpain in vitro. These differential effects of inhibitors against calpain and proteasome are potentially useful for identifying the functions of calpain and proteasome in cell physiology and pathology. View Publication

Elevated numbers of primitive Philadelphia chromosome-positive (Ph+) progenitors,including long-term culture-initiating cells (LTC-IC) as well as colony-forming cells (CFC),have been previously described in the blood of patients with chronic myeloid leukemia (CML) in chronic phase with high white blood cell counts. In the present study,which focused primarily on an analysis of circulating progenitors present in such patients at diagnosis,we discovered the frequent and occasionally exclusive presence of circulating normal (Ph-) LTC-IC,often at levels above those seen for LTC-IC in the blood of normal individuals. The presence of detectable numbers of circulating Ph- LTC-IC was independent of the fact that the same peripheral blood samples also contained elevated numbers of predominantly or exclusively Ph+ CFC. Interestingly,both the Ph+ and Ph- LTC-IC in these samples were CD34+CD71- and variably CD38- and Thy-1+,as previously documented for LTC-IC in normal marrow. Thus,neither CD38 nor Thy-1 expression was useful for discriminating between Ph+ and Ph- LTC-IC in mixed populations. Nevertheless,an association of these phenotypes with LTC-IC function did allow highly enriched (textgreater 5% pure) suspensions of either Ph+ or Ph- LTC-IC to be obtained from selected samples of CML blood in which the initial LTC-IC population was either predominantly Ph+ or Ph-,respectively. These findings suggest that the mechanisms causing mobilization of leukemic stem cells in untreated CML patients may affect their normal counterparts. They also indicate a possible new source of autologous cells for the support of intensive therapy of CML patients. Finally,they provide a method for obtaining the most highly purified populations of Ph+ LTC-IC described to date. This method should be useful for further analyses of the molecular activities of these very primitive neoplastic cells. View Publication

We examined the stem cell compartment of patients with acquired aplastic anemia (AA) using the long-term culture-initiating cell assay (LTC-IC),in parallel with measurements of CD34+ cells and mature hematopoietic progenitors. Secondary colonies from cells surviving 5 weeks of long-term bone marrow culture (LTBMC) were determined for the peripheral blood (PB) of 68 AA patients and 13 normal controls and for BM of 49 AA patients and 14 controls; because of low cell numbers,formal limiting dilution analysis could only be performed in 10 patients. The relationship of cell input in LTBMC and the output of secondary colonies was linear,allowing quantification of LTC-IC number from bulk cultures. Secondary colony formation was markedly abnormal in severe AA. In contrast to 7.8 colony-forming cells (CFC)/10(5) mononuclear cells in normal BM and 0.14 CFC/10(5) normal PB mononuclear cells,patients with severe disease showed 0.024 CFC/10(5) in BM and 0.0068 CFC/10(5) in PB. Under limiting dilution conditions,patients' cells also showed markedly lower colony-forming ability. In contrast to 4.3 +/- 1 colonies/normal LTC-IC,we obtained only 1.27 +/- 0.09 and 2.0 +/- 0.35 colonies from BM of acute and recovered cases,respectively. These values were used to extrapolate LTC-IC numbers from secondary colony formation in suspension cultures. In PB,calculated LTC-IC were decreased 7.4-fold in new and relapsed severe AA and 2.8-fold in recovered AA. In BM,LTC-IC were decreased 10-fold in new and relapsed AA and sixfold in recovered cases. Compared with measurements obtained on presentation,LTC-IC were lower in post-treatment samples from patients who had failed to recover after intensive immunosuppression and relatively higher in cases at relapse. In recovered patients,LTC-IC number increased but remained below the normal range in 20 of 25. In patients studied serially for 3 to 12 months after treatment,LTC-IC numbers remained stable but low. LTC-IC number correlated with concurrently determined CD34+ cell number and primary hematopoietic colony formation. These results indicate that stem cell numbers,as quantitated by the LTC-IC assay,are markedly diminished in number in all severe AA. Additionally,the function of the stem cell or the stem cell compartment in AA is also abnormal,as inferred from the low clonogenic potential in secondary colony assays. Early hematologic improvement in some patients occurs without increasing numbers of LTC-IC,and a minority of recovered cases show apparent repopulation of the LTC-IC compartment years after treatment. View Publication

Retinoids play an important role in development,differentiation,and homeostasis. The discovery of retinoid receptors belonging to the superfamily of nuclear ligand-activated transcriptional regulators has revolutionized our molecular understanding as to how these structurally simple molecules exert their pleiotropic effects. Diversity in the control of gene expression by retinoid signals is generated through complexity at different levels of the signaling pathway. A major source of diversity originates from the existence of two families of retinoid acid (RA) receptors (R),the RAR isotypes (alpha,beta,and gamma) and the three RXR isotypes (alpha,beta,and gamma),and their numerous isoforms,which bind as RXR/RAR heterodimers to the polymorphic cis-acting response elements of RA target genes. The possibility of cross-modulation (cross-talk) with cell-surface receptors signaling pathways,as well as the finding that RARs and RXRs interact with multiple putative coactivators and/or corepressors,generates additional levels of complexity for the array of combinatorial effects that underlie the pleiotropic effects of retinoids. This review focuses on recent developments,particularly in the area of structure-function relationships. View Publication

Human bone marrow (BM) cells contain low levels of the DNA repair protein,O6-alkylguanine-DNA alkyltransferase,which may explain their susceptibility to nitrosourea-induced cytotoxicity and the development of secondary leukemia after nitrosourea treatment. Isolated CD34+ myeloid progenitors were also found to have low levels of alkyltransferase activity. The level of alkyltransferase in CD34+ cells or in mononuclear BM cells did not increase after incubation with granulocyte-macrophage colony-stimulating factor,interleukin-3,stem cell factor,the combination,or 5637 conditioned medium. BCNU sensitivity remained unchanged as well. In addition,O6-benzylguanine depleted alkyltransferase activity in BM cells at concentrations as low as 1.5 mumol/L after a 1-hour exposure. O6-benzylguanine pretreatment markedly sensitized hematopoietic progenitor colony-forming cells to BCNU,resulting in a reduction in the dose of drug (termed the dose-modification factor) required to inhibit 50% of the colony formation (IC50) of threefold to fivefold. Since,unlike many other cell types,proliferating early (CD34+) hematopoietic precursors do not induce alkyltransferase,myelosuppression may be the dose-limiting toxicity of the combination of O6-benzylguanine plus BCNU in clinical trials. View Publication

1. The effect of suramin and pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) on the stimulation of phospholipase C in 1321N1 cells transfected with the human P2U-purinoceptor (h-P2U-1321N1 cells) or with the turkey P2Y-purinoceptor (t-P2Y-1321N1 cells) was investigated. 2-Methylthioadenosine triphosphate (2MeSATP) was used as the agonist at t-P2Y-1321N1 cells and uridine triphosphate (UTP) at h-P2U-1321N1 cells. 2. Suramin caused a parallel shift to the right of the concentration-response curves for 2MeSATP in the t-P2Y-1321N1 cells,yielding a Schild plot with a slope of 1.16 +/- 0.08 and a pA2 value of 5.77 +/- 0.11. 3. Suramin also caused a shift to the right of concentration-response curves for UTP in the h-P2U-1321N1 cells,and on Schild plots gave a slope different from unity (1.57 +/- 0.19) and an apparent pA2 value of 4.32 +/- 0.13. Suramin was therefore a less potent antagonist at the P2U-purinoceptor than the P2Y-purinoceptor. 4. In the presence of the ectonucleotidase inhibitor,ARL 67156 (6-N,N-diethyl-beta,gamma-dibromomethylene-D-ATP) there was no significant difference in the EC50 or shapes of curves with either cell type,and no difference in pA2 values for suramin. 5. PPADS caused an increase in the EC50 for 2MeSATP in the t-P2Y-1321N1 cells. The Schild plot had a slope different from unity (0.55 +/- 0.15) and an X-intercept corresponding to an apparent pA2 of 5.98 +/- 0.65. 6. PPADS up to 30 microM had no effect on the concentration-response curve for UTP with the h-P2U-1321N1 cells. 7. In conclusion,suramin and PPADS show clear differences in their action at the 2 receptor types,in each case being substantially more effective as an antagonist at the P2Y-purinoceptor than at the P2U-purinoceptor. Ectonucleotidase breakdown had little influence on the nature of the responses at the two receptor types,or in their differential sensitivity to suramin. View Publication

1. We have investigated the inhibitory effects of RP 73401 (piclamilast) and rolipram against human monocyte cyclic AMP-specific phosphodiesterase (PDE4) in relation to their effects on prostaglandin (PG)E2-induced cyclic AMP accumulation and lipopolysaccharide (LPS)-induced TNF alpha production and TNF alpha mRNA expression. 2. PDE4 was found to be the predominant PDE isoenzyme in the cytosolic fraction of human monocytes. Cyclic GMP-inhibited PDE (PDE3) was also detected in the cytosolic and particulate fractions. Reverse transcription polymerase chain reaction (RT-PCR) of human monocyte poly (A+) mRNA revealed amplified products corresponding to PDE4 subtypes A and B of which the former was most highly expressed. A faint band corresponding in size to PDE4D was also observed. 3. RP 73401 was a potent inhibitor of cytosolic PDE4 (IC50: 1.5 +/- 0.6 nM,n = 3). (+/-)-Rolipram (IC50: 313 +/- 6.7 nM,n = 3) was at least 200 fold less potent than RP 73401. R-(-)-rolipram was approximately 3 fold more potent than S-(+)-rolipram against cytosolic PDE4. 4. RP 73401 (IC50: 9.2 +/- 2.1 nM,n = 6) was over 50 fold more potent than (+/-)-rolipram (IC50: 503 +/- 134 nM,n = 6) ) in potentiating PGE2-induced cyclic AMP accumulation. R-(-)-rolipram (IC50: 289 +/- 121 nM,n = 5) was 4.7 fold more potent than its S-(+)-enantiomer (IC50: 1356 +/- 314 nM,n = 5). A strong and highly-significant,linear correlation (r = 0.95,P textless 0.01,n = 13) was observed between the inhibitory potencies of a range of structurally distinct PDE4 inhibitors against monocyte PDE4 and their ED50 values in enhancing monocyte cyclic AMP accumulation. A poorer,though still significant,linear correlation (r = 0.67,P textless 0.01,n = 13) was observed between the potencies of the same compounds in potentiating PGE2-induced monocyte cyclic AMP accumulation and their abilities to displace [3H]-rolipram binding to brain membranes. 5. RP 73401 (IC50: 6.9 +/- 3.3 nM,n = 5) was 71 fold more potent than (+/-)-rolipram (IC50: 490 +/- 260 nM,n = 4) in inhibiting LPS-induced TNF alpha release from monocytes. R-(-)-rolipram (IC50: 397 +/- 178 nM,n = 3) was 5.2-fold more potent than its S-(+)- enantiomer (IC50: 2067 +/- 659 nM,n = 3). As with cyclic AMP,accumulation a closer,linear correlation existed between the potency of structurally distinct compounds in suppressing TNF alpha with PDE4 inhibition (r = 0.93,P textless 0.01,n = 13) than with displacement of [3H]-rolipram binding (r = 0.65,P textless 0.01,n = 13). 6. RP 73401 (IC50: 2 nM) was 180 fold more potent than rolipram (IC50: 360 nM) in suppressing LPS (10 ng ml-1)-induced TNF alpha mRNA. 7. The results demonstrate that RP 73401 is a very potent inhibitor of TNF alpha release from human monocytes suggesting that it may have therapeutic potential in the many pathological conditions associated with over-production of this pro-inflammatory cytokine. Furthermore,PDE inhibitor actions on functional responses are better correlated with inhibition of PDE4 catalytic activity than displacement of [3H]-rolipram from its high-affinity binding site,suggesting that the native PDE4 in human monocytes exists predominantly in a 'low-affinity' state. View Publication