Large scale screening of the mitochondrial DNA reveals no pathogenic mutations but a haplotype associated with multiple sclerosis in Caucasians

We report the first large-scale screening of mitochondrial (mt) DNA in 77 Caucasian patients with relapsing-remitting or secondary progressive form of multiple sclerosis (MS) and in 84 Caucasian controls by using the method of restriction site polymorphism and haplotype analysis. No pathogenic mtDNA mutation was found in association with MS. However, mtDNA haplotypes K* and J* defined by the simultaneous presence of Ddel restriction sites at nucleotides 10,394 and 14,798 of the mtDNA in haplogroups K and J showed association with MS at a P-value of 0.001. A relative increase of MS patients compared to controls either with the J* or with the K* haplotype (+10,394Ddel/+14,798Ddel in haplogroup J or K) also was detected (each with a P<0.05). No distinct phenotypic characteristics of MS were observed when clinical data of patients with haplotypes K* or J* were analyzed. In addition to previous complete sequencing in several MS patients, the population screening of mtDNA presented here suggests that mtDNA point mutations are not likely to be involved in the pathogenesis of typical forms of MS. However, the mitochondrial genetic background (haplotype K* and J*) may moderately contribute to MS susceptibility. The reported association between MS and Leber's hereditary optic nerve atrophy, a disease caused by mtDNA point mutations preferentially occurring in haplogroup J, may be at least in part related to the overlapping mitochondrial genetic background of the two diseases.

Water-insoluble camptothecin analogues as potential antiviral drugs

In addition to being causative agents of infectious diseases in animals and humans, DNA viruses have served as models for the study of eukaryotic molecular mechanisms including replication and transcription. Studies of DNA virus functions utilizing cell-free systems and virus-infected cells in culture, in the presence of the anticancer drug camptothecin (CPT), have demonstrated that CPT is a potent inhibitor of replication, transcription and packaging of double-stranded DNA-containing adenoviruses, papovaviruses and herpesviruses, and the single- stranded DNA-containing autonomous parvoviruses. CPT inhibits viral functions by inhibiting topoisomer- ase I, a host cell enzyme required for initiation and completion of the viral functions. These findings indicate that CPT analogues could be developed for use as potent drugs against DNA viruses.

Identification and recombinant expression of a Mycobacterium avium rhamnosyltransferase gene (rtfA) involved in glycopeptidolipid biosynthesis

The Mycobacterium avium complex is a source of disseminated infections in patients with advanced AIDS. This group of mycobacteria is distinguished by the presence of highly antigenic, surface-exposed glycopeptidolipids, and these glycolipids possess variant oligosaccharide structures that are the chemical basis of the 28 distinct serovars of the M. avium complex. We previously described the ser2 gene cluster, encoding the synthesis of the haptenic oligosaccharide (2, 3-dimethylfucose-rhamnose-6-deoxytalose-) of the serovar 2-specific glycopeptidolipid, and revealed a locus (ser2A) encoding a putative rhamnosyltransferase. Sequencing of the ser2A locus demonstrated the presence of three open reading frames, two of which yielded significant homology to several glycosyltransferases, and the deduced amino acid sequences of these two putative glycosyltransferases had 63% identity. These two genes were expressed in Mycobacterium smegmatis, and the resulting recombinant glycopeptidolipids were characterized by thin-layer chromatography and gas chromatography-mass spectrometry. These analyses demonstrated that only one of these genes, termed rtfA, encoded the rhamnosyltransferase responsible for the transfer of rhamnose to 6-deoxytalose. The identification of rtfA will permit further evaluation of glycopeptidolipid biosynthesis and the construction of isogenic mutants of multiple M. avium complex serovars. Moreover, such mutants will help define the role of glycopeptidolipids in the intracellular survival of these bacteria.

Molecular interaction of CD1b with lipoglycan antigens

The ability of human CD1b molecules to present nonpeptide antigens is suggested by the T cell recognition of microbial lipids and lipoglycans in the presence of CD1b-expressing antigen-presenting cells. We demonstrate the high-affinity interaction of CD1b molecules with the acyl side chains of known T cell antigens, lipoarabinomannan, phosphatidylinositol mannoside, and glucose monomycolate. Furthermore, CD1b-antigen binding was optimal at acidic pH, consistent with the known requirement for endosomal acidification in CD1b-restricted antigen presentation. The mechanism for CD1b-ligand interaction involves the partial unfolding of the alpha helices of CD1b at acidic pH, revealing a hydrophobic binding site that could accommodate lipid. These data provide direct evidence that the CD1b molecule has evolved unique biochemical properties that enable the binding of lipid-containing antigens from intracellular pathogens.

Mycobacterial lipoarabinomannan: an extraordinary lipoheteroglycan with profound physiological effects

Detailed structural and functional studies over the last decade have led to current recognition of the mycobacterial lipoarabinomannan (LAM) as a phosphatidylinositol anchored lipoglycan with diverse biological activities. Fatty acylation has been demonstrated to be essential for LAM to maintain its functional integrity although the focus has largely been on the arabinan motifs and the terminal capping function. It has recently been shown that the mannose caps may be involved not only in attenuating host immune response, but also in mediating the binding of mycobacteria to and subsequent entry into macrophages. This may further be linked to an intracellular trafficking pathway through which LAM is thought to be presented by CD1 to subsets of T-cells. The implication of LAM as major histocompatibility complex (MHC)-independent T-cell epitope and the ensuing immune response is an area of intensive studies. Another recent focus of research is the biosynthesis of arabinan which has been shown to be inhibitable by the anti-tuberculosis drug, ethambutol. The phenomenon of truncated LAM as synthesized by ethambutol resistant strains provides an invaluable handle for dissecting the array of arabinosyltransferases involved, as well as generating much needed structural variants for further structural and functional studies. It is hoped that with more systematic investigations based on clinical isolates and human cell lines, the true significance of LAM in the immunopathogenesis of tuberculosis and leprosy can eventually be explained.

The mycobacterial cell wall: structure, biosynthesis and sites of drug action

Structural analysis has been successfully implemented recently to obtain valuable information on the mycobacterial cell wall components, many of which have formed the basis for biosynthesis and functional studies towards developing better drugs and possible vaccines. The highly complex and well organized structure unique to mycobacteria, represents the best target for novel antimycobacterial agents. Until recently, our knowledge of the enzymes responsible for the biogenesis of the cell wall components was almost negligible. The pathways are now being elucidated in several laboratories. Highlights of this review include significant advances in the structure and biochemistry of the major cell wall components and potential targets for generation of new drugs.

Galactosamine in walls of slow-growing mycobacteria

Galactosamine was found consistently as a minor component of the envelope of five species of slow-growing mycobacteria, including all the major human pathogens, but not three rapid-growing species. The amino sugar was a component of the arabinogalactan of the cell wall skeleton, and occurred at the level of about one residue per arabinogalactan chain. Its amino group was in the free, un-N-acetylated state. Examination of oligosaccharides released by partial acid hydrolysis of arabinogalactan by fast atom bombardment-MS and gas chromatography-MS identified a series of oligoarabinans, each possessing one GalN unit, linked to position 2 of arabinose. It is proposed that the GalN residues occur as stub branches of 1-->5-linked arabinose chains in the arabinogalactan. Possible functions of GalN are discussed.

Monocytic differentiation of HL-60 promyelocytic leukemia cells correlates with the induction of Bcl-xL

Treatment of human promyelocytic leukemia HL-60 cells with phorbol esters ultimately induces the differentiation of these cells along the monocyte/macrophage lineage, whereas treatment with retinoic acid or DMSO induces granulocytic/neutrophillic differentiation. In this study, we demonstrate the disparate fates of HL-60 cells treated with the phorbol ester 12,13-phorbol dibutyric acid (PDBu) or DMSO. After DMSO treatment, HL-60 cells eventually died via apoptosis, whereas the viability of PDBu-treated cells was not affected during the same interval. The levels of the apoptosis effector proteins Bak and Bad were enhanced, whereas there was a slight down-regulation of the apoptosis suppressor protein Bcl-2 after treatment of the cells with PDBu and DMSO. Treatment with DMSO resulted in the elevation of the apoptosis effector Bax, whereas treatment with PDBu did not significantly alter the levels of this protein. However, treatment of HL-60 cells with PDBu induced the rapid expression of the apoptosis suppressor protein Bcl-xL, whereas the expression of this protein remained unaltered in DMSO-treated cells. The generality of this finding was confirmed by the induction of Bcl-xL in human myeloid U-937 cells, human peripheral blood monocytes exposed to phorbol ester, and mouse thioglycollate-activated and resident peritoneal macrophages. PDBu-treated HL-60 cells remained viable for 7 days and thereafter began to die via apoptosis, with a concomitant down-regulation of Bcl-xL. In conclusion, we propose that Bcl-xL expression is associated with differentiation and survival of hematopoietic cells along the monocyte/macrophage lineage.

Extracellular ATP and adenosine cause apoptosis of pulmonary artery endothelial cells

ATP acts as an intracellular energy source and an extracellular signaling molecule. We report that extracellular ATP causes apoptosis in pulmonary artery endothelial cells, as assessed by morphological changes and internucleosomal DNA degradation. We investigated the mechanism of this effect using release of tritiated soluble DNA as a marker for apoptosis. We conclude that the metabolite adenosine is responsible for the apoptotic effect of ATP, since nucleotides that can be degraded to adenosine, as well as adenosine itself, cause DNA damage, whereas nonmetabolizable ATP analogs and uridine 5'-triphosphate are inactive. Furthermore, the ecto-5'-nucleotidase inhibitor alpha, beta-methylene-ADP blocks ATP-induced DNA fragmentation. The adenosine receptor agonist 5'-N-ethylcarboxamide adenosine does not cause DNA fragmentation, and adenosine receptor antagonists do not block adenosine-induced apoptosis. However, the nucleoside transport inhibitor dipyridamole prevents extracellular ATP-induced DNA cleavage. These findings indicate that ATP- and adenosine-mediated apoptosis are mediated via intracellular events rather than through cell surface receptor(s). The adenosine metabolites inosine, hypoxanthine, and xanthine do not cause apoptosis. The adenosine analogs 3-deazaadenosine and MDL-28842, which are not metabolized and are S-adenosylhomocysteine hydrolase inhibitors, also cause DNA fragmentation. Therefore, we speculate that extracellular ATP and adenosine cause apoptosis of pulmonary artery endothelial cells by altering methylation reactions that require S-adenosylmethionine as the methyl donor. We speculate that ATP released from cells undergoing cytolysis or degranulation may cause endothelial cell death. Endothelial cell apoptosis may be important in acute vascular injury or in limiting angiogenesis.

Structural characterization of glycophingolipids from the eggs of Schistosoma mansoni and Schistosoma japonicum

The granulomatous pathology in human intestinal schistosomiasis is induced primarily by the egg antigens of schistosome, a parasitic trematode. Glycolipids and glycoproteins were extracted from the eggs of the two major species which infect human, Schistosoma mansoni and Schistosoma japonicum, for structural characterization based on highly sensitive mass spectrometric analysis coupled with chemical derivatization. Here, we demonstrate that a series of uniquely multifucosylated glycosphingolipids constitute the major egg glycolipids of S. mansoni but not of S. japonicum. The S. mansoni glycosphingolipids were found to be extended by varying numbers of an unusual repeating unit, -->4(Fuc1-->2Fuc1-->3)GlcNAc1-->, and terminating as +/-Fuc1-->2Fuc1-->3GalNAc1--> at the nonreducing terminus. The similarity of these fucosylated structures, particularly the nonreducing terminal sequence, to the previously identified multifucosylated O-linked oligosaccharides of the cercarial glycocalyx, suggests that they may constitute the cross-reacting epitopes between the egg antigens and cercariae of S. mansoni. On the other hand, the difucosylated GalNAc terminal epitope was not found on the glycosphingolipids of S. japonicum. Thus, it qualifies for a possible role as a species-specific recognition glycan.

Structural mapping of the glycans from the egg glycoproteins of Schistosoma mansoni and Schistosoma japonicum: identification of novel core structures and terminal sequences

The structural diversity of the glycans from Schistosoma mansoni and Schistosoma japonicum egg glycoproteins was investigated using high sensitivity fast atom bombardment mass spectrometric screening of glycan pools released enzymically or chemically from egg extracts. The egg glycoproteins from the two species carry a comparable range of high mannose and complex type N-glycans with both lacNAc and lacdiNAc constituting the backbones of the antennae in the latter class. Truncated N-glycans similar to those found on nematodes, insects, and plants were also identified. Sequential digestion with peptide N-glycosidase F and peptide N-glycosidase A afforded effective release and separation of N-glycans with nonfucosylated or alpha6-monofucosylated trimannosyl N,N'-diacetyl-chitobiose cores from those carrying core alpha3-, alpha6-difucosylation, all of which were found to be present in both species. Remarkably, a portion of the N-glycans from S. mansoni eggs was shown to be based on a xylosylated, alpha6-fucosylated trimannosyl core, whereas a portion of those from S. japonicum contains a xylosylated alpha3-, alpha6-difucosylated core which has not been previously described in any organism. O-Glycans were chemically released from the de-N-glycosylated glycopeptides and found to carry terminal sequences similar to those in the N-glycans. This study provides further evidence that multi-fucosylated terminal HexNAc units, previously identified on the cercarial glycocalyx O-glycans and egg glycosphingolipids, and now on the egg N- and O-glycans, are unique features of S. mansoni glycans. These multifucosylated terminal structures, which were not detected on the egg glycans of S. japonicum, are likely to constitute the cross-reacting epitopes between the eggs and cercariae of S. mansoni. Interestingly other HexNAc termini, including an unusual stretch of HexNAc3, were found to be common to both species. The mapping studies reported in this article provide an important foundation for further structural work in this challenging and important area of glycobiology.

Induction of apoptosis in malignant and camptothecin-resistant human cells

Flow cytometry studies demonstrate that androgen-independent human prostate carcinoma DU-145 cells are arrested at the G1-phase of the cell cycle in the presence of suramin, but they die by apoptosis in the presence of 9-nitrocamptothecin (9NC). The addition of cytostatic concentrations of suramin increases the apoptotic action of 9NC on DU-145 cells, and induces apoptosis in 9NC-resistant DU-145/RC cells that were derived from the parental DU-145 cells by continuous exposure to progressively increased concentrations of 9NC. In addition, the topoisomerase II-directed drug etoposide exerts more extensive apoptotic action on DU-145/RC than DU-145 cells. Increased resistance of DU-145 cells to 9 NC and collaterally increased sensitivity to etoposide and suramin appear to correlate with alterations in the structure rather than synthesis of topoisomerases and possibly with specific cellular proteins that regulate apoptosis. The results suggest that etoposide and suramin may be successful alternative treatments for 9NC-resistant androgen-independent prostate cancer.

Truncated structural variants of lipoarabinomannan in ethambutol drug-resistant strains of Mycobacterium smegmatis. Inhibition of arabinan biosynthesis by ethambutol

The anti-tuberculosis drug, ethambutol (Emb), was previously shown to inhibit the synthesis of arabinans of both the cell wall arabinogalactan (AG) and lipoarabinomannan (LAM) of Mycobacterium tuberculosis and other mycobacteria. However, an Emb-resistant mutant, isolated by consecutive passage of the Mycobacterium smegmatis parent strain in media containing increasing concentrations of Emb, while synthesizing a normal version of AG, produced truncated forms of LAM when maintained on 10 microg/ml Emb (Mikusová, K., Slayden, R. A., Besra, G. S., and Brennan, P. J. (1995) Antimicrob. Agents Chemother. 39, 2482-2489). We have now isolated and characterized the truncated LAMs made by both the resistant mutant and a recombinant strain transfected with a plasmid containing the emb region from Mycobacterium avium which encodes for Emb resistance. By chemical analysis, endoarabinanase digestion, high pH anion exchange chromatography, and mass spectrometry analyses, truncation was demonstrated as primarily a consequence of selective and partial inhibition of the synthesis of the linear arabinan terminal motif, which constitutes a substantial portion of the arabinan termini in LAM but not of AG. However, at higher concentrations, Emb also affected the general biosynthesis of arabinan destined for both AG and LAM, resulting in severely truncated LAM as well as AG with a reduced Ara:Gal ratio. The results suggested that Emb exerts its antimycobacterial effect by inhibiting an array of arabinosyltransferases involved in the biosynthesis of arabinans unique to the mycobacterial cell wall. It was further concluded that the uniquely branched terminal Ara6 motif common to both AG and LAM is an essential structural entity for a functional cell wall and, consequently, that the biosynthetic machinery responsible for its synthesis is the effective target of Emb in its role as a potent anti-tuberculosis drug.

CD1c restricts responses of mycobacteria-specific T cells. Evidence for antigen presentation by a second member of the human CD1 family

Previous studies suggest that CD1 is a family of Ag-presenting molecules distantly related to those encoded by the MHC. However, of the four known human CD1 proteins, only CD1b has been shown to restrict Ag-specific T cell responses. In this study, we have shown that a second member of the human CD1 family, CD1c, could also mediate Ag presentation to T cells. Three T cell lines recognizing mycobacterial Ags in a CD1c-restricted manner were isolated from normal donor blood. These T cells were MHC unrestricted, and their recognition of Ag was independent of the products of the transporter associated with Ag presentation-1/2 and DMA/B genes that are generally required for Ag presentation by MHC-encoded Ag-presenting molecules. Furthermore, unlike MHC-restricted responses to peptides, the CD1c-restricted T cell lines recognized protease-resistant mycobacterial lipid Ags. These T cell lines also showed significant cytotoxicity toward CD1c-expressing target cells even in the absence of mycobacterial Ags, which was shown by clonal analysis to be mediated by a subpopulation of T cells directly reactive to CD1c molecules. Our findings establish the ability of a second member of the CD1 family to restrict responses of Ag-specific T cells, and thus support the general hypothesis that the CD1 family comprises a third lineage of Ag-presenting molecules that presents a novel class of foreign and self Ags to MHC-unrestricted T cells.

CD1c restricts responses of mycobacteria-specific T cells. Evidence for antigen presentation by a second member of the human CD1 family

Previous studies suggest that CD1 is a family of Ag-presenting molecules distantly related to those encoded by the MHC. However, of the four known human CD1 proteins, only CD1b has been shown to restrict Ag-specific T cell responses. In this study, we have shown that a second member of the human CD1 family, CD1c, could also mediate Ag presentation to T cells. Three T cell lines recognizing mycobacterial Ags in a CD1c-restricted manner were isolated from normal donor blood. These T cells were MHC unrestricted, and their recognition of Ag was independent of the products of the transporter associated with Ag presentation-1/2 and DMA/B genes that are generally required for Ag presentation by MHC-encoded Ag-presenting molecules. Furthermore, unlike MHC-restricted responses to peptides, the CD1c-restricted T cell lines recognized protease-resistant mycobacterial lipid Ags. These T cell lines also showed significant cytotoxicity toward CD1c-expressing target cells even in the absence of mycobacterial Ags, which was shown by clonal analysis to be mediated by a subpopulation of T cells directly reactive to CD1c molecules. Our findings establish the ability of a second member of the CD1 family to restrict responses of Ag-specific T cells, and thus support the general hypothesis that the CD1 family comprises a third lineage of Ag-presenting molecules that presents a novel class of foreign and self Ags to MHC-unrestricted T cells.

Establishment of human prostate tumor xenografts in nude mice and response to 9-nitrocamptothecin in vivo and in vitro does not correlate with the expression of various apoptosis-regulating proteins

Flow cytometry and microscopy analyses have demonstrated that 9-nitrocamptothecin (9NC) induces apoptosis in prostate carcinoma LNCaP, DU-145 and PC-3 cells grown in culture or as xenografts. 9NC induces apoptosis regardless of the ability of the cells to induce tumors following xenografting into nude mice. Detection of apoptosis by flow cytometry was preceded or accompanied by increased cell size, loss of nuclear structure and vacuolization, as the tumor regressed, but no visible chromatin fragmentation. This is the first demonstration that 9NC is curative for human prostate carcinoma xenografts in the nude mouse model in the absence of detectable drug-induced toxicity during and after tumor regression. These findings indicate that 9NC may develop into a chemotherapeutic drug for the effective treatment of prostate cancer patients. Further, there was no apparent correlation of the steady-state level of the apoptosis-regulating proteins, Bcl-2, Bcl-XL, Bax and Ich-1, with tumorigenicity of the prostate cells xenografted in nude mice, aggressiveness of tumors grown in nude mice, and induction of apoptosis by 9NC. However, the TIAR protein was present at markedly high levels in all prostate carcinoma cell lines and this may correlate with their susceptibility to 9NC-induced apoptosis.

Monocytic differentiation and synthesis of proteins associated with apoptosis in human leukemia U-937 cells acquiring resistance to vincristine

Human leukemia U-937/WT cells were exposed to stepwise increased concentrations of Vincristine so that Vincristine-resistant cell sublines (termed U-937/RV) were developed. Established U-937/RV cell sublines have continuously propagated over a year, both in absence and presence of VCR, and have demonstrated similar features. In contrast to U-937/WT cells, U-937/RV cells have longer doubling time, and are more differentiated as determined by appearance of distinct morphological features and synthesis of mRNA that codes for the monocyte colony-stimulating factor-1 receptor (c-fms). Both apoptosis-suppressing Bcl-2 and Bcl-XL proteins were undectable in U-937/WT cells, whereas Bcl-2 was nearly detectable and Bcl-XL readily detectable in U-937/RV cells. The apoptosis-promoting Bax protein was also absent in U-937/WT cells and readily detected in U-937/RV cells. Vincristine-resistant cells with different levels of resistance synthesize similar levels of c-fms mRNA and Bax protein. Finally, unlike U-937/WT cells, U-937/RV cells have no ability to induce tumors when xenografted in immunodeficient mice. The findings collectively suggest that development of resistance to Vincristine in U-937/WT cells may correlate with cell differentiation and synthesis of proteins that regulate apoptosis.

Novel O-methylated terminal glucuronic acid characterizes the polar glycopeptidolipids of Mycobacterium habana strain TMC 5135

Mycobacterium "habana" strain TMC 5135, which has been proposed as a vaccine against both leprosy and tuberculosis, is considered to be a strain of serotype I of the recognized species Mycobacterium simiae. We have now shown that each of these strains possesses characteristic polar glycopeptidolipids (GPL) which are sufficiently different to allow unequivocal strain identification. Thin layer chromatographic analysis demonstrated that M. habana synthesizes a family of apolar GPLs and three distinct polar GPLs (pGPL-I to -III) which exhibited migration patterns different from those of M. simiae serotype I (pGPL-Sim). Using a combination of chemical, mass spectrometric, and proton-NMR analyses, the GPLs from M. habana were determined to be based on the same generic structure as those from the M. avium complex, namely N-fatty acyl-D-Phe-(O-saccharide)-D-allo-Thr-D-Ala-L-alaninyl-O-m onosaccharide. The de-O-acetylated apolar GPLs contain a 3-O-Me-6-deoxy-Tal attached to the allo-Thr and either a 3-O-Me-Rha or a 3,4-di-O-Me-Rha attached to the alaninol. In the pGPLs, oligosaccharides were found to be attached to the allo-Thr. The oligoglycosyl alditol reductively released from the least polar pGPL-I was fully characterized as L-Fucp alpha 1 in --7 with 3-(6-O-Me)-D-Glcp beta 1 in --7 with 3-(4-O-Me)-L-Rhap alpha 1 in --7 with 3-L-Rhap alpha 1 in --7 with 2-(3-O-Me)-6-deoxy-Tal. In pGPl-II and -III, the terminal Fuc residue is further 3-O-methylated and 4-O-substituted with an additional 2,4-di-O-Me-D-GlcA and 4-O-Me-D-GlcA, respectively. The corresponding oligosaccharide from pGPL-Sim was shown to be of identical molecular weight to pGPL-II but terminating with a 3,4-di-O-Me-GlcA. Enzyme-linked immunosorbent assay-based serological studies using anti-M. habana and anti-M. simiae sera against whole cells and purified pGPLs firmly established the polar GPLs as important antigens and indicated that the terminal epitopes L-Fuc-, 2,4-di-O-Me-D-GlcA, and 4-O-Me-D-GlcA uniquely present in pGPL-I, -II, and -III, respectively, confer sufficient specificity for the identification of M. habana as a distinct serotype of M. simiae.

Chemotactic activity of mycobacterial lipoarabinomannans for human blood T lymphocytes in vitro

A crucial early event in tuberculosis is the ingestion of Mycobacterium tuberculosis (Mtb) by alveolar macrophages. Chemotactic factors released by infected macrophages are likely to initiate a granulomatous response, a key feature of host resistance to tuberculosis. To date, the role of mycobacterial products in regulating the granulomatous response has not been clearly defined. Here we report that the mycobacterial cell wall glycophospholipid lipoarabinomannan (LAM) could specifically induce human peripheral blood T cell chemotaxis in vitro. Both terminally mannosylated LAM isolated from Mtb and LAM lacking the terminal mannosyl units isolated from an avirulent mycobacterium could induce T cell migration in the absence of serum. In contrast, terminally mannosylated LAM isolated from Mycobacterium bovis BCG failed to induce T cell chemotaxis. These observations represent the first report that LAM is capable of directly inducing biologic responses in human T cells. Flow cytometry analysis revealed that CD4+, CD8+, and CD45RO+ lymphocytes were present in the migrating cell populations at ratios similar to those found in nonmigrating cells. The chemotactic response was found to require new protein synthesis, and could be blocked by inhibitors of protein tyrosine kinases at concentrations that did not affect random migration. Acyl groups at the reducing terminus of LAM appear to be required for the chemotactic activity of this mycobacterial glycolipid. Lastly, culture supernatants from human alveolar macrophages infected in vitro with a virulent strain of Mtb could induce T cell migration. Much of the migratory activity present in these supernatants could be blocked using a mAb against LAM, suggesting that LAM is one of the chemotactic factors released by Mtb-infected alveolar macrophages.

Chemotactic activity of mycobacterial lipoarabinomannans for human blood T lymphocytes in vitro

A crucial early event in tuberculosis is the ingestion of Mycobacterium tuberculosis (Mtb) by alveolar macrophages. Chemotactic factors released by infected macrophages are likely to initiate a granulomatous response, a key feature of host resistance to tuberculosis. To date, the role of mycobacterial products in regulating the granulomatous response has not been clearly defined. Here we report that the mycobacterial cell wall glycophospholipid lipoarabinomannan (LAM) could specifically induce human peripheral blood T cell chemotaxis in vitro. Both terminally mannosylated LAM isolated from Mtb and LAM lacking the terminal mannosyl units isolated from an avirulent mycobacterium could induce T cell migration in the absence of serum. In contrast, terminally mannosylated LAM isolated from Mycobacterium bovis BCG failed to induce T cell chemotaxis. These observations represent the first report that LAM is capable of directly inducing biologic responses in human T cells. Flow cytometry analysis revealed that CD4+, CD8+, and CD45RO+ lymphocytes were present in the migrating cell populations at ratios similar to those found in nonmigrating cells. The chemotactic response was found to require new protein synthesis, and could be blocked by inhibitors of protein tyrosine kinases at concentrations that did not affect random migration. Acyl groups at the reducing terminus of LAM appear to be required for the chemotactic activity of this mycobacterial glycolipid. Lastly, culture supernatants from human alveolar macrophages infected in vitro with a virulent strain of Mtb could induce T cell migration. Much of the migratory activity present in these supernatants could be blocked using a mAb against LAM, suggesting that LAM is one of the chemotactic factors released by Mtb-infected alveolar macrophages.

The evolutionary relationship among Caucasian MS patients and controls

Previous observations suggest that the mitochondrial (mt)DNA may confer susceptibility to multiple sclerosis (MS). However, the proportion of affected individuals and the range of contributing mtDNA abnormalities are unknown. To help clarify this question, we analyzed the first hypervariable D-loop sequences of the mtDNA in a group of randomly selected Caucasian MS patients, in MS patients with prominent optic neuritis (PON) and in controls. Phylogenetic analysis of these D-loop sequences revealed that individuals in both groups of patients are generally scattered in the Caucasian phylogeny. However, a small cluster of unrelated MS patients identified by this analysis suggests that a maternal lineage with MS relevant mtDNA sequences may exist, and merits a more comprehensive study.

Isolation and characterization of an apoptosis-resistant variant of human leukemia HL-60 cells that has switched expression from Bcl-2 to Bcl-xL

Human promyelocytic leukemia HL-60 cells treated with 8-chloroadenosine-3',5'-cyclic monophosphate (8-Cl-cAMP) undergo growth arrest and subsequently die by apoptosis. We describe here the isolation of a variant of HL-60 cells, HCW-2, which was resistant to the cytotoxic effects of 8-Cl-cAMP, but still underwent growth arrest. Thus, HCW-2 cells appeared to be altered in their ability to undergo apoptosis. HCW-2 cells were also completely refractory to the apoptotic action of cycloheximide and staurosporine, two compounds which were very potent inducers of apoptosis in the parental HL-60 cells, suggesting that the resistance to apoptosis was not unique to 8-Cl-cAMP. Western blot analysis demonstrated that the parental HL-60 cells expressed both Bcl-2 and Bax, two factors known to be intimately involved in the control of apoptosis. Surprisingly, HCW-2 cells no longer expressed Bcl-2 protein and paradoxically contained Bax protein at a level that was approximately 50-fold higher than in HL-60 cells. However, Northern and Western analyses indicated that the apoptotic suppressor gene, bcl-xL, which is not expressed in the parental HL-60 cells, was expressed in HCW-2 cells. Thus, the Bcl-2-independent resistance of HCW-2 cells to apoptotic induction is discussed in terms of the expression of bcl-xL.

Identification of a novel Bcl-2 related gene, BRAG-1, in human glioma

Programmed cell death (apoptosis) plays a major role in embryogenesis, in mature organ homeostasis and in many disease states including cancer. Apoptosis occurs as an orderly cell-intrinsic suicide program regulated by a family of genes related to Bcl-2. Here, we describe the cloning and molecular characterization of a gene homologous to Bcl-2 from a human glioma. This gene named BRAG-1 (for brain-related apoptosis gene) has an open reading frame that encodes for a protein of 31 kDa sharing significant sequence homology with the Bcl-2 family of genes in the BH1 and BH2 regions. Northern blot analyses revealed that BRAG-1 is expressed in human gliomas as a 1.8 kb message. This gene, interestingly, was found to be expressed predominantly in normal human brain as a 4.5 kb transcript which is different in size from the message found in tumor tissues. These results suggest that BRAG-1 may be rearranged in human gliomas leading to its over-expression as a truncated transcript. Utilizing a bacterial expression vector, we produced BRAG-1 protein which was found to cross-react with a Bcl-2 monoclonal antibody, further suggesting structural and immunological similarity to Bcl-2.

Analysis of six protein structures predicted by comparative modeling techniques

The protein structures of six comparative modeling targets were predicted in a procedure that relied on improved energy minimization, without empirical rules, to position all new atoms. The structures of human nucleoside diphosphate kinase NM23-H2, HPr from Mycoplasma capricolum, 2Fe-2S ferredoxin from Haloarcula marismortui, eosinophil-derived neurotoxin (EDN), mouse cellular retinoic acid protein I (CRABP1), and P450eryf were predicted with root mean square deviations on C alpha atoms of 0.69, 0.73, 1.11, 1.48, 1.69, and 1.73 A, respectively, compared to the target crystal structures. These differences increased as the sequence similarity between the target and parent proteins decreased from about 60 to 20% identity. More residues were predicted than form the common region shared by the two crystal structures. In most cases insertions or deletions between the target and the related protein of known structure were not correctly positioned. One two residue insertion in CRABP1 was predicted in the correct conformation, while a nine residue insertion in EDN was predicted in the correct spatial region, although not in the correct conformation. The positions of common cofactors and their binding sites were predicted correctly, even when overall sequence similarity was low.