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C Luxford

Publications and source records attributed to C Luxford.

9 recordsLinked to original sources
PubMed2004

Ionic wave propagation along actin filaments.

We investigate the conditions enabling actin filaments to act as electrical transmission lines for ion flows along their lengths. We propose a model in which each actin monomer is an electric element with a capacitive, inductive, and resistive property due to the molecular structure of the actin filament and viscosity of the solution. Based on Kirchhoff's laws taken in the continuum limit, a nonlinear partial differential equation is derived for the propagation of ionic waves. We solve this equation in two different regimes. In the first, the maximum propagation velocity wave is found in terms of Jacobi elliptic functions. In the general case, we analyze the equation in terms of Fisher-Kolmogoroff modes with both localized and extended wave characteristics. We propose a new signaling mechanism in the cell, especially in neurons.

Actin Cytoskeleton↗
PubMed2000

Radicals derived from histone hydroperoxides damage nucleobases in RNA and DNA.

Exposure of individual histone proteins (H1, H2A, H2B, H3, or H4) and histone octamers (consisting of two molecules each of H2A, H2B, H3, and H4) to hydroxyl radicals, generated by gamma-irradiation, in the presence of O(2) generates protein-bound hydroperoxides in a dose-dependent fashion; this is in accord with previous studies with other proteins. These histone hydroperoxides are stable in the absence of exogenous catalysts (e.g., heat, light, and transition metal ions), but in the presence of these agents decompose rapidly to give a variety of radicals which have been identified by EPR spin trapping. Histone hydroperoxide-derived radicals generated on decomposition of the hydroperoxides with Cu(+) react with both pyrimidine and purine nucleobases. Thus, with uridine the histone hydroperoxide-derived radicals undergo addition across the C(5)-C(6) double bond of the pyrimidine ring to give cross-linked adduct species which have been identified by EPR spectroscopy. HPLC analysis of the products generated on reaction of histone hydroperoxide-derived radicals with 2'-deoxyguanosine, or intact calf thymus DNA, has shown that significant levels of the mutagenic oxidized DNA base 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) are formed, with the yield dependent on the individual histone protein, the presence of hydroperoxide functions, and the concentration of metal ion. These studies demonstrate that initial oxidative damage to individual histone proteins or histone octamers can result in the transfer of oxidative damage to associated DNA via the formation and subsequent decomposition of protein hydroperoxides to reactive radicals, and provide a novel route for the formation of mutagenic lesions in DNA.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1999

Histone H1- and other protein- and amino acid-hydroperoxides can give rise to free radicals which oxidize DNA.

Exposure of amino acids, peptides and proteins to radicals, in the presence of oxygen, gives high yields of hydroperoxides. These materials are readily decomposed by transition metal ions to give further radicals. We hypothesized that hydroperoxide formation on nuclear proteins, and subsequent decomposition of these hydroperoxides to radicals, might result in oxidative damage to associated DNA. We demonstrate here that exposure of histone H1 and model compounds to gamma-radiation in the presence of oxygen gives hydroperoxides in a dose-dependent manner. These hydroperoxides decompose to oxygen- and carbon-centred radicals (detected by electron paramagnetic resonance spectroscopy) on exposure to Cu(+) and other transition metal ions. These hydroperoxide-derived radicals react readily with pyrimidine DNA bases and nucleosides to give adduct species (i.e. protein-DNA base cross-links). Product analysis has demonstrated that radicals from histone H1-hydroperoxides, and other protein and amino acid hydroperoxides, can also oxidize both free 2'-deoxyguanosine and intact calf thymus DNA to give the mutagenic oxidized base 7, 8-dihydro-8-oxo-2'-deoxyguanosine (8-hydroxy-2'-deoxyguanosine, 8-oxodG). The yield of 7,8-dihydro-8-oxo-2'-deoxyguanosine is proportional to the initial protein-hydroperoxide concentration, and corresponds (for histone H1-hydroperoxide, 280 microM) to approx. 1. 4% conversion for free 2'-deoxyguanosine (200 microM), and 0.14% for 2'-deoxyguanosine in DNA (70 microgram/ml). Evidence has also been obtained with DNA for reaction at cytosine and thymine, but not adenine; the lack of damage to the latter may result from damage transfer to 2'-deoxyguanosine residues. These studies demonstrate that initial radical-induced damage to nuclear proteins can give rise to subsequent DNA damage; the latter includes both DNA-protein cross-links and formation of oxidized DNA bases.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1999

Normal repair of ultraviolet radiation-induced DNA damage in familial melanoma without CDKN2A or CDK4 gene mutation.

Excessive sun exposure and family history are strong risk factors for the development of cutaneous melanoma. Inherited susceptibility to this type of skin cancer could therefore result from constitutively impaired capacity to repair ultraviolet (UV)-induced DNA lesions. While a proportion of familial melanoma kindreds exhibit germline mutations in the cell cycle regulatory gene CDKN2A (p16INK4a) or its protein target, cyclin-dependent kinase 4 (CDK4), the biochemical basis of most familial melanoma is unknown. We have examined lymphoblastoid cell lines from melanoma-affected and unaffected individuals from large hereditary melanoma kindreds which are not attributable to CDKN2A or CDK4 gene mutation. These lines were tested for sensitivity of clonogenic growth to UV radiation and for their ability to repair transfected UV-damaged plasmid templates (host cell reactivation). Two of seven affected-unaffected pairs differed in colony survival after exposure to UVB radiation; however, no significant differences were observed in the host-cell reactivation assays. These results indicate that melanoma susceptibility genes other than CDKN2A and CDK4 do not impair net capacity to repair UV-induced DNA damage.

Chloramphenicol O-Acetyltransferase↗
PubMed1993

Functional and phenotypic assessment of neonatal human leucocytes expressing natural killer cell-associated antigens.

A subpopulation of mononuclear leucocytes was prepared from umbilical cord venous blood by immunomagnetic depletion of lymphocytes and monocytes using monoclonal antibodies to CD2, CD3, CD14 and CD19 antigens, and examined for NK cell-associated phenotypic and functional properties. The depleted population was enriched for the NK markers CD16 (mean 53.6% positive) and CD56 (mean 42.7% positive). While there was considerable overlap of these two markers, approximately one-third of CD16+ cells were CD56-; in contrast, few CD56+ CD16- cells were found. CD16+/CD56+ cells also co-expressed CD7 and CD45RA antigens, while a minority weakly expressed CD8. Another marker of adult NK cells, CD57, was virtually absent from CD16+/CD56+ cells, as was MHC Class 2. Freshly depleted cord cells had virtually absent natural cytotoxicity to K562 targets in a chromium release assay, but NK activity could be induced after 18 h exposure to recombinant human IL-2, without significant change in phenotype. These findings confirm the phenotypic differences and functional defects of NK cells in cord blood as compared to adult blood, and identify a subset of cells with unique phenotype (CD2- CD3- CD7+ CD16+ CD56- CD57-). The precise relationship of this subset of cells to NK lineage remains to be defined.

Adult↗
PubMed1993

Confirmation of chromosome 9p linkage in familial melanoma.

Malignant melanoma occurs as a familial cancer in 5%-10% of cases where it segregates in a manner consistent with autosomal dominant inheritance. Evidence from cytogenetics, fine-mapping studies of deletions in melanomas, and recent linkage studies supports the location of a human melanoma predisposition gene on the short arm of chromosome 9. We have carried out linkage analysis using the 9p markers IFNA and D9S126 in 26 Australian melanoma kindreds. Multipoint analysis gave a peak lod score of 4.43, 15 cM centromeric to D9S126, although a lod score of 4.13 was also found 15 cM telomeric of IFNA. These data confirm the existence of a melanoma susceptibility gene on 9p and indicate that this locus most probably lies outside of the IFNA-D9S126 interval. No significant heterogeneity was found between families, when either pairwise or multipoint data were analyzed using HOMOG.

Adult↗
PubMedDate not supplied

Phenotypic characterization of immature lymphoid cells in human umbilical cord blood.

The antigenic phenotype of neonatal lymphoid cells isolated from umbilical cord blood was investigated using monoclonal antibodies and flow cytometry. Although the majority of cells expressed mature T or B cell differentiation antigens, small subpopulations of phenotypically immature lymphocytes were detected. A small proportion (mean 2.8%) of cells expressed the common acute lymphoblastic leukaemia antigen (CD-10), a significantly higher figure than that detected on adult peripheral blood lymphocytes. The cortical thymocyte antigen (CD-1) was detected on a very small subset of cord lymphoid cells, but was also present on adult lymphocytes at approximately the same frequency. The nuclear enzyme terminal deoxynucleotidyl transferase (TdT), a marker of early lymphoid differentiation, was detected by immunofluorescence on 0.031% of mononuclear cells in cytocentrifuge preparations, representing an approximate 10-fold increase in frequency over expression in childhood or adult blood. These circulating TdT+ cells were shown in double labelling experiments to predominantly express markers of B cell differentiation (CD-24, CD-10, MHC Class 2), although occasional cells co-expressing the T lineage marker CD-2 were also seen. These findings are consistent with the circulation of B cell precursors in neonatal blood. The nature of the CD-1+ cells is unclear, although the absence of CD-1+ TdT+ double labelled cells mitigates against the possible presence of immature thymus-processed lymphocytes in these samples.

Adult↗
PubMedDate not supplied

Ribozyme-mediated suppression of v-myc expression abrogates apoptosis in transformed monocytes.

The product of the c-myc oncogene is an important regulator of both cell proliferation and programmed cell death (apoptosis). We have previously shown that a myelomonocytic cell line termed tEMmyc4, with enforced v-myc expression, underwent apoptosis under growth inhibitory conditions. To further investigate the linkage of v-myc expression to apoptosis in these cells, two hammerhead ribozymes were designed and shown to specifically cleave the v-myc though not c-myc transcript in vitro. These ribozymes were then engineered into the pMAMneo vector under the control of MMTV promoter, transfected into tEMmyc4 cells and clonally selected in G418. Molecular analysis revealed reduction of v-myc expression in ribozyme-expressing cells. This reduction was shown to be associated with abrogation of hormone-induced apoptosis (monitored by gel electrophoresis, flow cytometry and TUNEL assay). These results confirm a direct involvement of v-myc in the induction of apoptosis and indicate a potential means to molecularly control apoptosis using a ribozyme-targeting approach.

Animals↗