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Biomedical subjects

J Harford

Publications and source records attributed to J Harford.

At least 19 recordsLinked to original sources
PubMed2003

A comparison of population-based cancer incidence rates in Israel and Jordan.

Reliable information about comparative cancer incidence in the Middle East has been lacking. The Middle East Cancer Consortium (MECC) has formed a network of population-based registries with standardized basic data. Here the age-adjusted cancer incidences are compared for four populations: Israeli Jews, Israeli non-Jews, Jordanians and the US Surveillance Epidemiology and End Results (SEER) population, for the years 1996-1997 (Israel) and 1996-1998 (other populations). The all-sites rate of cancer is approximately twice as high in Israeli Jews and SEER, compared with Israeli non-Jews and Jordanians. Rates of lung cancer are similar among Israeli Jews and non-Jews and about twice as high as in Jordanians. Childhood leukaemia rates in Jordan are higher than in Israeli Jews, but lower than SEER. Hodgkin lymphoma rates in Israeli non-Jews and Jordanians are similar to SEER, but non-Hodgkin lymphoma rates are lower than SEER. The previous suspicion of higher overall leukaemia and lymphoma rates in Jordan is thus not confirmed.

Adolescent↗
PubMed2001

Cancer registration in the Middle East.

This project signals an advance in cancer registration in the Middle East region. While it is too early to declare a major breakthrough, significant strides have been made toward establishing a basis for reliable information on the cancer burden at a population level and future collaborative efforts in cancer epidemiologic research and prevention.

Humans↗
PubMed1998

Life as a dying man.

Explore the source record for details and available documents.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Myosin rod-packing schemes in vertebrate muscle thick filaments.

Muscle myosin filament backbones are known to be aggregates of long coiled-coil alpha-helical myosin rods, but the packing arrangement is not understood in detail. Here we present new data on fish muscle myosin filaments from low-angle X-ray diffraction and from freeze-fracture, deep-etch electron microscopy which put constraints on the kind of models that might explain all of the observations. In particular, it is known in the case of vertebrate striated muscle thick filaments that the myosin head array in resting muscle is not perfectly helical but contains periodic perturbations. We show by analysis of low-angle X-ray diffraction patterns from resting bony fish muscle that any radial, azimuthal, and axial perturbations of the myosin head origins on the filament surface (due to perturbed myosin rod packing) must all be rather small and that the main perturbations are in the myosin head configurations (i.e., tilts, slews, rotations) on those origins. We provide evidence that the likely arrangement of titin molecules on the myosin filament is with them aligned parallel to the filament long axis, rather than following helical tracks. We also show from freeze-fracture studies of fish muscle that the myosin filament backbone (including titin and other extra proteins) has a radius of about 65-75 A and appears to contain a small (approximately 15-20 A radius) hollow core. Together with previously published evidence showing that the myosin rods are nearly parallel to the thick filament long axis, these results are consistent with the curved crystalline layer model of Squire (J. M. Squire, 1973, J. Mol. Biol. 77, 291-323), and they suggest a general structure for the C-zone part of the thick filament

Animals↗
PubMed1998

Myosin crossbridge configurations in equilibrium states of vertebrate skeletal muscle. Heads swing axially or turn upside-down between resting and rigor.

The positions and orientations of the myosin heads in relaxed, active, rigor and S1-labelled fish muscle are being determined by analysis both of electron micrographs and of low-angle X-ray diffraction patterns. The X-ray analysis of resting muscle makes use of the head shape defined from the study of S1 crystals, with variable head configurational parameters being used on each of the three different 3-fold symmetric 14.3 nm-spaced 'crowns' of myosin heads within the 42.9 nm axial repeat of the myosin filaments. Diffraction patterns were stripped using CCP13 fibre diffraction software. Searches and optimisation were carried out using simulated annealing and local refinement procedures to give a 'best fit' relaxed structure with a crystallographic R-factor of about 4%. It had heads oriented all the same way up (i.e. with similar rotations around their own long axes) on the myosin filament, but with a small range of axial tilts. Head configuration in rigor fish muscle is being determined by X-ray diffraction and electron microscopy of normal rigor muscle and of skinned muscle soaked with extrinsic myosin S1. Computed 3-D reconstructions of acto-S1 using X-ray amplitudes and phases from electron microscopy are informative and help to analyse the X-ray diffraction data that extend axially to about 1 nm resolution. An ambiguity is the axial direction of the observed resting myosin head array relative to the known polarity of the actin filaments. One polarity would give little axial displacement (2-3 nm) between opposite ends of the resting and rigor heads, and in this case the heads would need to rotate around their own long axes by about 115 degrees to make a rigor attachment. The other (preferred) filament polarity would provide considerable axial swinging (14-15 nm) between the two states. We are attempting to define the absolute polarity of the resting muscle myosin head array using electron microscopy and image processing either of cryo-sections or of replicas from shadowed, freeze-fractured, rapidly frozen fish muscle fibres.

Actins↗
PubMed1994

Equatorial A-band and I-band X-ray diffraction from relaxed and active fish muscle. Further details of myosin crossbridge behaviour.

It has been known for many years that the vertebrate striated muscle A-bands and I-bands both contribute to the observed equatorial X-ray diffraction patterns. Despite this, the observed equatorial patterns, with the exception of the clearly distinct Z-reflection, have often been analysed as coming solely from the A-band, since it has not been possible to separate the observed intensity distribution into individual A-band and I-band contributions. Here we show, for the case of diffraction from the highly ordered muscles in bony fish, that it is possible to separate these contributions to the diffraction patterns from intact muscles and to compute separate electron density maps for the A and I-bands. Difference A-band density maps between resting and active muscles are distinctly altered when the I-band contribution is removed from the observed equatorial intensity. Results from resting and fully active fish muscle A-bands are compared and interpreted in terms of myosin crossbridge movement; the observations are consistent with specific crossbridge labelling of actin filaments, with a strong azimuthal component of crossbridge movement towards actin. From electron microscopy of freeze-substituted fish muscle, it is shown that the I-band X-ray diffraction pattern probably arises mainly from the thin filament arrangement immediately adjacent to the Z-band.

Actin Cytoskeleton↗
PubMed1993

Time-resolved studies of crossbridge movement: why use X-rays? Why use fish muscle?

The advantages of using time-resolved X-ray diffraction as a means of probing myosin cross-bridge behaviour in active muscle are outlined, together with the reasons that bony fish muscle has advantages in such studies. We show that the observed X-ray diffraction patterns from fish muscle can be analysed in a way that is rigorous enough to allow reliable information about crossbridge activity to be defined. Among the advantages of this muscle are that diffraction patterns from resting, active and rigor muscles are all well-sampled at least out to the 30 row-line, that the resting myosin layer-line pattern can be 'solved' crystallographically to define the starting position of the crossbridges in resting muscle, and that the equatorial intensity distribution, which in all patterns from vertebrate skeletal muscles comprises overlapping peaks from the A-band and the Z-band, can be analysed sufficiently rigorously to allow separation of the two patterns, both of which change when the muscle is active. Finally, we present results both on a new set of myosin-based layer-lines in patterns from active muscle (consistent with the presence of low-force bridges as also indicated by the time-courses of the intensity changes on the equator and the changing mass distribution in the A-band unit cell) and also on changes of the actin-based layer-lines (consistent with stereospecific labelling of the actin filaments by force-producing crossbridges). Our results to date, which demonstrate the enormous power of time-resolved X-ray diffraction studies, strongly support the swinging of myosin heads on actin as part of the contractile cycle.

Animals↗
PubMed1986

"Crystalline" myosin cross-bridge array in relaxed bony fish muscle. Low-angle x-ray diffraction from plaice fin muscle and its interpretation.

Detailed structural analysis of muscles normally used to study myosin cross-bridge behavior (e.g., frog sartorius muscle, insect flight muscle) is extremely difficult due to the statistical disorder inherent in their myosin filament arrays. Bony fish muscle is different from all other muscle types in having a myosin filament (A-Band) array with good three-dimensional (crystalline) regularity that is coherent right across each myofibril. Rigorous structure analysis is feasible with fish muscle. We show that low-angle x-ray diffraction patterns from plaice fin muscle contain characteristic vertebrate layer lines at orders of 429 (+/- 0.2) A, that these layer lines are well sampled by row-lines from a simple hexagonal lattice of a-spacing 470 (+/- 2.0) A at rest length and that there are meridional reflections, due to axial perturbations of the basic helix of myosin heads, similar in position to those from frog muscle but differing in relative intensities. Clear trends based on modeling to a resolution of 130 A of the observed intensities in the low angle x-ray diffraction pattern from relaxed plaice fin muscle suggest that: (a) the pattern out to 130 A is more sensitive to the distribution of the two heads than it is to details of the head shape, (b) both heads in one myosin molecule probably tilt axially in the same direction by approximately 20-40 degrees relative to a normal to the thick filament backbone, (c) the center of mass of the heads is at 145 to 160 A radius, and (d) the two heads form a compact structure by lying closely adjacent to each other and almost parallel. Little rotational disorder of the heads can occur. Because of its crystallinity, bony fish muscle provides a uniquely useful structural probe of myosin cross-bridge behavior in other muscle states such as rigor and active contraction.

Animals↗
PubMed1985

Hemin, chelatable iron, and the regulation of transferrin receptor biosynthesis.

We have examined the mechanism by which hemin regulates the expression of the human transferrin receptor. Previous work led to the suggestion that the regulatory signal is provided by heme (Ward J. H., Jordan, I., Kushner, J. P., and Kaplan, J. (1984) J. Biol. Chem. 259, 13235-13240). We demonstrated that hemin regulates the expression of the receptor via alterations in the rate of receptor biosynthesis. However, this effect can be completely abolished by addition of desferrioxamine, an intracellular iron chelator. Competition curves demonstrate that desferrioxamine and hemin affect the same intracellular iron pool. Since the chelator cannot remove iron from heme, we propose that hemin acts simply by delivering iron to a chelatable iron pool and that levels of chelatable iron provide the regulatory signal for expression of the transferrin receptor gene.

Cell Line↗
PubMed1985

A 20-kDa protein associated with the murine T-cell antigen receptor is phosphorylated in response to activation by antigen or concanavalin A.

Antigen or concanavalin A activation of a murine T-cell hybrid specific for pigeon cytochrome c and restricted to the Ek alpha:Ek beta immune response-associated (Ia) molecule resulted in phosphorylation of a 20-kDa protein that was specifically coprecipitated by a monoclonal antibody binding the T-cell antigen receptor. There was no evidence for phosphorylation of the antigen receptor itself. The phosphorylation of the 20-kDa polypeptide was dependent on the concentration of antigen or lectin used to activate the T-cell hybrid and reached a maximum 40 min after the addition of antigen. Moreover, the phosphorylation induced by antigen in the presence of Ia molecule-bearing B cells was specifically blocked by the addition of appropriate anti-Ia molecule monoclonal antibodies. The 20-kDa protein was also radioiodinated with a hydrophobic photoactivatable labeling reagent. The amount of iodinated 20-kDa protein immunoprecipitable with the anti-receptor antibody did not increase with T-cell activation, indicating that the phosphorylation occurred on a molecule that was constitutively associated with the antigen receptor. Concanavalin A also induced phosphorylation of a 20-kDa polypeptide in a second antigen-specific major histocompatibility complex-restricted T-cell hybrid. Again, the phosphorylated polypeptide was precipitated only by a monoclonal antibody specific for the antigen receptor on this hybrid. Thus, the antigen or concanavalin A-induced activation of T-cell hybrids results in the rapid phosphorylation of a 20-kDa protein that is associated with the T-cell antigen receptor.

Animals↗
PubMed1985

A comparative study of adsorbed tetanus vaccine.

A study is reported in which 197 volunteers were given adsorbed tetanus vaccine from two different sources. Using an ELISA system all pre-vaccination sera were screened. Both pre- and post-vaccination sera from volunteers with an initial antibody level of less than 1 iu/ml were then titrated and the antibody response analyzed. The results confirm that both vaccines produced an excellent antibody response with little difference in reactogenicity.

Adsorption↗
PubMed1984

Muscle crossbridge positions from equatorial diffraction data: an approach towards solving the phase problem.

Following a discussion of the problems involved in the analysis of X-ray diffraction data from muscle, a description is given of a possible procedure for solving the phase problem in the case of equatorial diffraction data. The approach involves the use of the Patterson Function which can be determined unambiguously from the observed diffracted intensities. The method is tested using five different muscle-like model density distributions for which the correct phases can be calculated directly. It is then applied to the equatorial X-ray diffraction data from relaxed frog sartorius muscle where it selects a phase set which is also the most likely to be correct on the basis of other available data on frog muscle. This phase set gives rise to a Fourier synthesis map in which the crossbridges form a uniform shelf of density around the myosin filament backbones. Possible lateral movements of the crossbridges from this relaxed configuration in active and rigor muscle are discussed. The approach to solving the phase problem is now being applied to data from fish muscle, insect flight muscle and crab muscle. It should also have its application to other fibrous materials apart from muscle.

Animals↗
PubMed1984

Rapid internalization of the transferrin receptor in K562 cells is triggered by ligand binding or treatment with a phorbol ester.

Treatment of human K562 cells with 4 beta-phorbol 12-myristate 13-acetate (PMA) resulted in an approximately 50% reduction in cell surface transferrin receptors within 30-45 min as judged by binding of both ligand and anti-receptor antibody. The affinity of the remaining surface receptors for diferric transferrin appeared to be unaltered. The time-dependent loss in transferrin receptors was also dependent upon PMA concentration, with a half-maximal effect observed at approximately 1 nM. The kinetic parameters for the binding, internalization, intracellular residency, and recycling of 125I-labeled transferrin were unchanged by PMA treatment, as were the rate and extent of internalization of anti-receptor antibody. Moreover, despite the decrease in surface receptors, uptake of 59Fe from transferrin proceeded at a rate comparable to that seen in untreated cells. Accounting for this observation was the fact that ligand induced a reduction in surface receptors in untreated but not PMA-treated cells. Quantitative immunoprecipitation of transferrin receptors from surface-iodinated K562 cells revealed that little receptor internalization occurred in untreated cells in the absence of ligand, but internalization of ligand-occupied receptors in these cells was readily detected. In contrast, PMA treatment resulted in the rapid internalization of surface receptors irrespective of occupancy. Thus, binding of ligand appeared to trigger the internalization of receptors that were relatively static in their unoccupied state, and a signal for receptor internalization was also provided by PMA treatment. The possibility that this signal involves phosphorylation of the transferrin receptor is discussed.

Biological Transport↗
PubMed1984

Intracellular segregation of asialoglycoproteins and their receptor: a prelysosomal event subsequent to dissociation of the ligand-receptor complex.

Rat hepatocytes in monolayer culture rapidly internalized asialoglycoproteins and the receptors to which they are bound. Subsequent to endocytosis, the receptor-ligand complex is dissociated within an acidic endosome (Harford, J., K. Bridges, G. Ashwell, and R. D. Klausner, 1983, J. Biol. Chem. 258:3191-3197; Harford, J., A. W. Wolkoff, G. Ashwell, and R. D. Klausner, 1983, J. Cell Biol. 96:1824-1828). Here we show that addition of the proton ionophore monensin to the cells after dissociation has occurred results in intracellular rebinding of ligand molecules. With increasing time inside the cell, the ability of ligand to reassociate with receptor progressively decreases consistent with a segregation of receptor and ligand. The combination of colchicine and cytochalasin B appears to retard the process of segregation. In contrast, removal of sodium from the medium, while inhibiting degradation of ligand, does not affect the decrease in monensin-mediated rebinding. Nonetheless, both sodium deprivation and treatment with colchicine plus cytochalasin B result in the ligand remaining in a low density, nonlysosomal subcellular fraction. Thus, segregation, like dissociation, appears to occur in a pre-lysosomal endocytic compartment. Perturbation of the endocytic pathway by reduced temperature (18 degrees C) was also explored. Our data are consistent with two temperature-sensitive steps: receptor-ligand dissociation is inhibited and there is an independent temperature-sensitive step involved in delivery of ligand to lysosomes. This second effect was localized as being beyond the point in the pathway sensitive to sodium deprivation.

Animals↗
PubMed1984

Inhibition of the endocytic pathway for asialoglycoprotein catabolism.

Rat hepatocytes in primary culture bind, internalize and eventually degrade asialoglycoproteins. This process is mediated by a specific receptor in the hepatocyte plasma membrane. The endocytic pathway by which ligand molecules are translocated to lysosomes has been examined by the development of biological assays capable of distinguishing ligand populations at various points in the process. Inhibitors have been identified that perturb particular transitions that define the endocytic pathway. In the present paper, inhibition by the bacterial tripeptide leupeptin is compared to the effect of colchine plus cytochalasin B. The latter combination impedes intracellular segregation of ligand and receptor while leupeptin inhibits intralysosomal proteolysis. However, evidence is presented to indicate that the inhibitory effects colchine plus cytochaasin B consists of at least two components. One component is independent of the presence of ligand whereas the other is observed only when ligand is present together with the drugs.

Animals↗
PubMed1983

Intracellular dissociation of receptor-bound asialoglycoproteins in cultured hepatocytes. A pH-mediated nonlysosomal event.

The binding, internalization, and degradation of 125I-asialo-orosomucoid were studied in primary monolayer cultures of rat hepatocytes. Ligand entered the cell bound to the asialoglycoprotein receptor and subsequently dissociated from the receptor intracellularly. Rate coefficients for each of the transitions that constitute the endocytic pathway were computed. Subcellular fractionation on Percoll gradients revealed that prior to localization in lysosomes, 125I-asialo-orosomucoid resided in a fraction of slightly lower buoyant density than plasma membranes. Neither ammonium chloride (20 mM) nor leupeptin (0.1 mg/ml) affected ligand binding or internalization of prebound ligand. However, both reagents inhibited degradation of ligand by greater than 95%. Of the two, only ammonium chloride inhibited receptor-ligand dissociation. Ammonium chloride treatment resulted in the accumulation of ligand in the prelysosomal fraction. In contrast, exposure of cells to leupeptin led to accumulation of ligand within lysosomes. The results are interpreted in terms of pH-mediated dissociation of ligand-receptor complex within a nonlysosomal endocytic vesicle.

Animals↗