Enilza M. Espreafico

Brain myosin-V is a two-headed unconventional myosin with motor activity

Chicken myosin-V is a member of a recently recognized class of myosins distinct from both the myosins-I and the myosins-II. We report here the purification, electron microscopic visualization, and motor properties of a protein of this class. Myosin-V molecules consist of two heads attached to an approximately 30 nm stalk that ends in a globular region of unknown function. Myosin-V binds to and decorates F-actin, has actin-activated magnesium-ATPase activity, and is a barbed-end-directed motor capable of moving actin filaments at rates of up to 400 nm/s. Myosin-V does not form filaments. Each myosin-V heavy chain is associated with approximately four calmodulin light chains as well as two less abundant proteins of 23 and 17 kd.

Griscelli Syndrome: Characterization of a New Mutation and Rescue of T-Cytotoxic Activity by Retroviral Transfer of RAB27A Gene

Griscelli syndrome (GS) is caused by mutations in the MYO5A (GS1), RAB27A (GS2), or MLPH (GS3) genes, all of which lead to a similar pigmentary dilution. In addition, GS1 patients show primary neurological impairment, whereas GS2 patients present immunodeficiency and periods of lymphocyte proliferation and activation, leading to their infiltration in many organs, such as the nervous system, causing secondary neurological damage. We report the diagnosis of GS2 in a 4-year-old child with haemophagocytic syndrome, immunodeficiency, and secondary neurological disorders. Typical melanosome accumulation was found in skin melanocytes and pigment clumps were observed in hair shafts. Two heterozygous mutant alleles of the RAB27A gene were found, a C-T transition (C352T) that leads to Q118stop and a G-C transversion on the exon 5 splicing donor site (G467+1C). Functional assays showed increased cellular activation and decreased cytotoxic activity of NK and CD8+ T cells, associated with defective lytic granules release. Myosin-Va expression and localization in the patient lymphocytes were also analyzed. Most importantly, we show that cytotoxic activity of the patients CD8+ T lymphocytes can be rescued in vitro by RAB27A gene transfer mediated by a recombinant retroviral vector, a first step towards a potential treatment of the acute phase of GS2 by RAB27A transduced lymphocytes.

Chapter 3 Structural and Functional Dissection of a Membrane-Bound Mechanoenzyme: Brush Border Myosin I

Publisher Summary The only vertebrate myosin I that has been thoroughly characterized is termed brush border (BB) myosin I and is expressed within the microvilli of the intestinal epithelial cell. This chapter discusses the structural and functional properties of brush border myosin I— the subunit composition, the protein domain structure, and the primary structure of its heavy chain— with compliment of multiple calmodulin (CM) light chains. The chapter also discusses the acid binding properties— that is, stoichiometry and Ca 2+ dependence and actin filament cross-linking by brush border Myosin I. It describes the adenosine triphosphate (ATP)ase properties of the brush border myosin I, its mechanochemistry, the function of brush border myosin I calmodulin light chains, the role of calmodulin light chains as repressors rather than activators of brush border myosin I Mg 2+ -ATPase. The chapter discusses the interaction of brush border myosin I, with the microvillar membrane, with acidic phospholipids, the evidence for a microvillar membrane “Docking” protein for brush border myosin I and notions regarding brush border myosin I function. A ∼140-kDa glycoprotein (GP-140) binds to the heavy chain of BB myosin I. GP-140 is the linker protein that tethers BB myosin I to the microvillus (MV) membrane. The disk-bound BB myosin I molecules are tethered to the membrane by their tails. The bound BB myosin I retain all the activities, associated with the free molecule, including actin binding and mechanochemical activity. BB myosin I might participate in the biogenesis and recycling of the apical membrane, by transporting vesicles, up through the terminal web. BB myosin I could cause a relative downward or perhaps rotational movement of the core within the MV membrane and could promote bulk movement of the membrane upward along the MV axis, as a part of an active vesicular shedding mechanism.

Myosin Drives Retrograde F-Actin Flow in Neuronal Growth Cones

Actin filaments assembled at the leading edge of neuronal growth cones are centripetally transported via retrograde F-actin flow, a process fundamental to growth cone guidance and other forms of directed cell motility. Here we investigated the role of myosins in retrograde flow, using two distinct modes of myosin inhibition: microinjection of NEM inactivated myosin S1 fragments, or treatment with 2,3-butanedione-2-monoxime, and inhibitor of myosin ATPase. Both treatments resulted in dose-dependent attenuation of retrograde F-actin flow and growth of filopodia. Growth was cytochalasin sensitive and directly proportional to the degree of myosin inhibition, suggesting that retrograde flow results from superimposition of two independent processes: actin assembly and myosin-based filament retraction. These results provide the first direct evidence for myosin involvement in neuronal growth cone function.

Long Noncoding RNAs in HPV-Induced Oncogenesis

Long noncoding RNAs (lncRNAs) play important roles in a wide range of oncogenic processes, including malignant transformation, epigenetic reprogramming, epithelial-to-mesenchymal transition, and metastasis development. LncRNAs induced by oncogenic viral proteins were shown to play critical roles in tumor initiation and progression. Despite this, little is known about Human papillomavirus (HPV)-induced modulation of host’s lncRNAs. In this review, we gathered published information about altered lncRNAs upon HPV status (infection/protein activity), making use of descriptive research works and published gene expression microarray experiments. A diversity of lncRNAs demonstrated to be altered, including metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), H19, and maternally expressed gene 3 (MEG3). Their functions in several cancers were reviewed, indicating that they may represent potential candidates for future research on HPV-induced oncogenesis.