Molecular mechanisms of cancer.

Cancer is caused by specific DNA damage. Several common mechanisms that cause DNA damage result in specific malignant disorders: First, proto-oncogenes can be activated by translocations. For example, translocation of the c-myc proto-oncogene from chromosome 8 to one of the immunoglobulin loci on chromosomes 2, 14, or 22 results in Burkitt''s lymphomas. Translocation of the c-abl proto-oncogene from chromosome 9 to the BCR gene located on chromosome 22 produces a hybrid BCR/ABL protein resulting in chronic myelogenous leukemia. Second, proto-oncogenes can be activated by point mutations. For example, point mutations of genes coding for guanosine triphosphate-binding proteins, such as H-, K-, or N-ras or G proteins, can be oncogenic as noted in a large variety of malignant neoplasms. Proteins from these mutated genes are constitutively active rather than being faithful second messengers of periodic extracellular signals. Third, mutations that inactivate a gene can result in tumors if the product of the gene normally constrains cellular proliferation. Functional loss of these "tumor suppressor genes" is found in many tumors such as colon and lung cancers. The diagnosis, classification, and treatment of cancers will be greatly enhanced by understanding their abnormalities at the molecular level.     

Notes on the life history of the planktonic alga, Dysmorphococcus globosus (Volvocales)

Several strains of Dysmorphococcus globosus, a planktonic greenflagellate, were examined during this study. Dysmorphococcusglobosus has a generation rime of 48 h, at which time four bi-flagellateddaughter cells were released. In some instances, four to eight,rarely 16, noo-flagellated aplanospores will be formed per cell,germinating when placed in fresh medium with the subsequentrelease of from one to four motile individuals. Sexual reproductionwas recorded in detail for the first time although it had beenpreviously reported that pairs of individual cells had beenobserved attached at their anterior poles. Sexual reproductionwas isogamous to anisogamous with the clones being homothallic.During zygote germination, the zygote undergoes two rapid divisionsto form four products of meiosis which were released followingrupture of the lorica.     

Analysis of the Pseudomonas solanacearum polygalacturonase encoded by pglA and its involvement in phytopathogenicity.

A major endopolygalacturonase excreted by Pseudomonas solanacearum was purified to greater than 95% homogeneity and shown to have an isoelectric point of 9.0 and a subunit molecular mass of 52 kilodaltons (kDa). The gene encoding this enzyme (pglA) was isolated from a genomic library of P. solanacearum DNA based on its expression in Escherichia coli and shown to be contained on a 1.8-kilobase DNA fragment. The identity of the pglA gene product and the 52-kDa polygalacturonase was demonstrated by immunoadsorption and isoelectric focusing experiments. The cloned pglA gene was apparently expressed from its own promoter in E. coli and its product was partially secreted into the periplasm. The pglA gene was insertionally inactivated in vitro and used to mutate the chromosomal pglA gene of P. solanacearum by marker exchange mutagenesis. The resulting mutant strain was deficient in production of the 52-kDa polygalacturonase and took twice as long to wilt and kill tomato plants as the wild-type parent in plant bioassay experiments. Complementation in trans with the wild-type cloned pglA gene restored virulence to near wild-type levels. The data indicate that the pglA gene is important, but not absolutely necessary, for pathogenesis.     

NMR studies of the interaction of the antibiotic nogalamycin with the hexadeoxyribonucleotide duplex d(5'-GCATGC)2

1H resonance assignments in the NMR spectra of the self-complementary hexadeoxyribonucleoside pentaphosphate d(5'-GCATGC)2 and its complex with the antibiotic nogalamycin, together with interproton distance constraints obtained from two-dimensional nuclear Overhauser effect (NOE) spectra, have enabled us to characterize the three-dimensional structure of these species in solution. In the complex described, two drug molecules are bound per duplex, in each of two equivalent binding sites, with full retention of the dyad symmetry. Twenty-eight NOE distance constraints between antibiotic and nucleotide protons define the position and orientation of the bound drug molecule. Nogalamycin intercalates at the 5'-CA and 5'-TG steps with the major axis of the anthracycline chromophore aligned approximately at right angles to the major axes of the base pairs. The nogalose sugar occupies the minor groove of the helix and makes many contacts with the deoxyribose moieties of three nucleotides along one strand of the duplex in the 5'-TGC segment. The charged dimethylamino group and hydroxyl functions of the bicyclic sugar lie in the major groove juxtaposed to the guanine base, the bridging atoms of the bicyclic sugar making contacts with the methyl group of the thymine. Thus the antibiotic is not symmetrically disposed in the intercalation site but is in close contact in both grooves with atoms comprising the 5'-TGC strand. The intercalation cavity is wedge-shaped, the major axes of the base pairs forming the site being tilted with respect to one another. All base-pair hydrogen-bonding interactions are maintained in the complex, and there is no evidence for Hoogsteen pairing. The free duplex adopts a regular right-handed B-type conformation in which all glycosidic bond angles are anti and all sugar puckers lie in the C2'-endo range. In the complex the glycosidic bond angles and the sugar puckers deviate little from those observed for the duplex alone. The presence of two bound nogalamycin molecules substantially slows the "breathing" motions of the base pairs forming the intercalation cavity, and the observation of two downfield-shifted resonances in the 31P NMR spectrum of the complex suggests a pronounced local helix unwinding at the drug binding site. The footprinting data of Fox and Waring [Fox, K.R., & Waring, M.J. (1986) Biochemistry 25, 4349-4356] imply that the highest affinity binding sites of nogalamycin have the sequence 5'-GCA (or 5'-TGC).(ABSTRACT TRUNCATED AT 400 WORDS)     

Bioactive Compounds from Marine Bacteria and Fungi

Marine bacteria and fungi are of considerable importance as new promising sources of a huge number of biologically active products. Some of these marine species live in a stressful habitat, under cold, lightless and high pressure conditions. Surprisingly, a large number of species with high diversity survive under such conditions and produce fascinating and structurally complex natural products. Up till now, only a small number of microorganisms have been investigated for bioactive metabolites, yet a huge number of active substances with some of them featuring unique structural skeletons have been isolated. This review covers new biologically active natural products published recently (2007–09) and highlights the chemical potential of marine microorganisms, with focus on bioactive products as well as on their mechanisms of action.     

Deposition of eosinophil cationic protein in granulomas in allergic granulomatosis and vasculitis: the Churg-Strauss syndrome.

Biopsy specimens and tissues obtained at necropsy from two women who died after developing the Churg-Strauss syndrome were analysed to see whether granulomas in these patients contained activated eosinophils or secreted eosinophil cationic proteins, or both. Immunocytochemical studies with monoclonal antibody EG2 showed large amounts of eosinophil cationic protein and eosinophil protein-X (which are toxic for heart cells and other tissues) in the granulomas. Many activated and degranulating eosinophils were seen to be migrating from the blood into these areas. Eosinophils may play a central part in the development of lesions in the heart and other tissues in the Churg-Strauss syndrome.     

Differences in sequence selectivity of DNA alkylation by isomeric intercalating aniline mustards

Two DNA-targeted mustard derivatives, N,N-bis(2-chloroethyl)-4-(5-[9-acridinylamino]-pentamido)aniline and 4-(9-[acridinylamino]butyl 4-(N,N-bis[2-chloroethyl]-aminobenzamide, which are isomeric compounds where the mustard is linked to the DNA-binding 9-aminoacridine moiety by either a -CONH- or a -NHCO- group, show significant differences in the sequence selectivity of their alkylation of DNA. The CONH isomer is a more efficient alxylating agent than the NHCO compound by an order of magnitude, consistent with the larger electron release of the CONH group to the aniline ring. However, the pattern of alkylation by the two compounds is also very different, with the CONH isomer preferring alkylation of guanines adjacent to 3'- or 5'-adenines and cytosines (for example those in sequences 5'-CGC, 5'-AGC, 5'-CGG and 5'-AGA) while the isomeric NHCO compound shows preference for guanines in runs of Gs. In addition, both isomers alkylate 3'-adenines in runs of adenines. Both compounds also show completely different patterns of alkylation to their untargeted mustard counterparts, since 4-MeCONH-aniline mustard alkylates all guanines and adenines in runs of adenines, while 4-Me2NCO-aniline mustard fails to alkylate DNA at all. These differences in alkylation patterns between the CONH- and its isomeric NHCO- compounds and their relationships between the alkylation patterns of the isomers and their biological activities are discussed.     

High level expression of human apolipoprotein A-I in transgenic rats raises total serum high density lipoprotein cholesterol and lowers rat apolipoprotein A-I

To examine the consequences of increased apolipoprotein A-I production on cholesterol and lipoprotein metabolism, we have produced two lines of transgenic rats; one expressing moderate and one very high levels of human apolipoprotein A-I. The rats were produced by microinjection of a 13 kbp DNA fragment containing the human apolipoprotein A-I gene plus 10 kbp of its 5′ flanking sequence and 1 kbp of its 3′ flanking sequence. Both lines of transgenic rats express human apolipoprotein A-I mRNA in liver and human apolipoprotein A-I in plasma. Sera from these rats contain significantly higher levels of total apolipoprotein A-I, high density lipoprotein cholesterol and phospholipid than sera from non-transgenic littermates. Transgenic rats expressing high levels of human apolipoprotein A-I have reduced levels of serum rat apolipoprotein A-I suggesting a mechanism exists to down-regulate apolipoprotein A-I production. These transgenic rats provide a unique animal model to examine the effects of increased apolipoprotein A-I production on lipid and lipoprotein metabolism.