Myo1c binding to submembrane actin mediates insulin-induced tethering of GLUT4 vesicles

GLUT4-containing vesicles cycle between the plasma membrane and intracellular compartments. Insulin promotes GLUT4 exocytosis by regulating GLUT4 vesicle arrival at the cell periphery and its subsequent tethering, docking, and fusion with the plasma membrane. The molecular machinery involved in GLUT4 vesicle tethering is unknown. We show here that Myo1c, an actin-based motor protein that associates with membranes and actin filaments, is required for insulin-induced vesicle tethering in muscle cells. Myo1c was found to associate with both mobile and tethered GLUT4 vesicles and to be required for vesicle capture in the total internal reflection fluorescence (TIRF) zone beneath the plasma membrane. Myo1c knockdown or overexpression of an actin binding–deficient Myo1c mutant abolished insulin-induced vesicle immobilization, increased GLUT4 vesicle velocity in the TIRF zone, and prevented their externalization. Conversely, Myo1c overexpression immobilized GLUT4 vesicles in the TIRF zone and promoted insulin-induced GLUT4 exposure to the extracellular milieu. Myo1c also contributed to insulin-dependent actin filament remodeling. Thus we propose that interaction of vesicular Myo1c with cortical actin filaments is required for insulin-mediated tethering of GLUT4 vesicles and for efficient GLUT4 surface delivery in muscle cells.     

Human leukemic cells: Cytochemical studies on nuclear proteins

The DNA:histone ratios have been determined by quantitative cytochemical analyses of individual cells in populations of human lymphocytic cells derived in continuous culture from the peripheral blood buffy coats of patients with acute leukemia or infectious mononucleosis. These populations of lymphocytic cells were quite similar with respect to the Feulgen-DNA and protein content per cell. The close association between DNA and histone was reflected in their similar patterns of distribution in fixed and stained cells; and further evidenced by similarities in the DNA: histone ratios characteristic of these different populations of lymphocytic cells. — Chemical acetylation and methylation of nuclear proteins of these cell populations exhibited some quantitative differences. The chemically acetylated histone content was less, and chemically methylated histone content was greater in cells derived from acute leukemia or infectious mononucleosis than in normal human lymphocytes. These quantitative differences in chemical acetylation and methylation may contribute to specific structural alterations in these histones which modify their functional capacity with respect to interactions with DNA. Such alterations may relate to differences in gene expression as reflected, for example, by the biological and biochemical differences among these human lymphocytic cells.These studies were supported in part by research grants C-6516 from the National Cancer Institute and FR-05526 from the Division of Research Facilities and Resources, National Institutes of Health.Holds Research Career Award K6-CA-22,150 from the National Cancer Institute, National Institutes of Health.     

Complete Sequence of Plasmid pLH1 from Lactobacillus helveticus ATCC15009: Analysis Reveals the Presence of Regions Homologous to Other Native Plasmids from the Host Strain

The complete sequence for plasmid pLH1 from Lactobacillus helveticus ATCC15009 has been determined. Analysis of the 19,360-bp primary sequence revealed a putative replication origin and initiation protein, information that could provide the basis for the construction of cloning vectors for L. helveticus. Evidence that pLH1 is theta-replicating could be deduced from the plasmid size, from the homology to the replication protein of the Bacillus natto theta-replicating plasmid pLS32, and from the identification of a putative resolvase gene (orf-195). Although 14 open reading frames capable of encoding polypeptides longer than 100 amino acids were identified, none, on the basis of homology with known sequences, appeared to encode a well-characterized trait relevant to milk fermentation. Plasmid pLH1 revealed regions of identity with the smaller cryptic plasmids (pLH2 and pLH3) from the same strain and with other tracts of DNA, including insertion sequence elements, from a variety of other lactic acid bacteria. The presence of such regions provides a basis for developing an explanation of the phenotypic variability observed in these bacteria. The plasmid also appears to possess a number of genetic elements present in other lactic acid bacterial plasmids, conservation of which would be consistent with an important functional or evolutionary role. It could be argued that the plasmid complement of L. helveticus ATCC15009 consists of parasitic entities concerned only with their own replication and survival.     

Human leukemic cells : Effect of human growth hormone

Human (pituitary) growth hormone of known primary structure exerts a stimulatory effect(s) on experimentally growing human leukemic lumphoblasts in culture, as reflected by temporary increases in DNA, RNA, and protein synthesis. This observation may provide for development of an in vitro bioassay for human growth hormone.