title: Overexpression of myosin IB in living Entamoeba histolytica enhances cytoplasm viscosity and reduces phagocytosis.
abstract: The human parasite Entamoeba histolytica is an ancient protozoan that expresses only one unconventional myosin, which has homology with myosin IB from other amoebae. Myosin IB is involved in phagocytosis of human cells by E. histolytica. In this work, we developed a microrheological technique, analysing magnetic phagosomes, which allowed us to probe the density of the F-actin network in living cells. Using this technique, we showed that overexpression of myosin IB led to an increase in cytoplasm viscosity, which correlated with a delay in initiating human cell phagocytosis. To investigate which myosin IB domains sustain cell viscosity changes, we overexpressed truncated forms of the protein. Our results demonstrate that both actin-binding sites that are present in the heavy chain but not the SH3 domain are required to modulate the density of the actin network. These data suggested that, as well as the motor activity, myosin IB in E. histolytica plays a structural role on the actin network owing to its ability to cross-link filaments. The gelation state of cell cytoplasm and the dynamics of cortical F-actin during phagocytosis seem to be modulated by the myosin IB structuring cytoskeleton activity.
authors.affiliation: Unité de Biologie Cellulaire du Parasitisme, INSERM U389, Institut Pasteur, 28 rue du Dr Roux 75724, Paris CEDEX 15, France.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Marion
authors.forename: Claire
authors.initials: C
authors.lastname: Wilhelm
authors.forename: Heike
authors.initials: H
authors.lastname: Voigt
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Bacri
authors.forename: Nancy
authors.initials: N
authors.lastname: Guillén
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D003593:Cytoplasm / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D004748:Entamoeba histolytica / Q000378:metabolism*; D006454:Hemoglobins / Q000737:chemistry; D006801:Humans; D008280:Magnetics; D024461:Myosin Type I / Q000096:biosynthesis* / Q000737:chemistry; D010587:Phagocytosis; D010588:Phagosomes / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013997:Time Factors; D014783:Viscosity; D018909:src Homology Domains
chemical_list: D000199:Actins; D006454:Hemoglobins; D024461:Myosin Type I