title: Hypoxia alters the recruitment of tropomyosins into the actin stress fibres of neuroblastoma cells.
abstract: BACKGROUND
  Neuroblastoma is the most common extracranial solid tumor of childhood. The heterogeneous microenvironment of solid tumors contains hypoxic regions associated with poor prognosis and chemoresistance. Hypoxia implicates the actin cytoskeleton through its essential roles in motility, invasion and proliferation. However, hypoxia-induced changes in the actin cytoskeleton have only recently been observed in human cells. Tropomyosins are key regulators of the actin cytoskeleton and we hypothesized that tropomyosins may mediate hypoxic phenotypes.
  
  
  METHODS
  Neuroblastoma (SH-EP) cells were incubated ± hypoxia (1 % O2, 5 % CO2) for up to 144 h, before examining the cytoskeleton by confocal microscopy and Western blotting.
  
  
  RESULTS
  Hypoxic cells were characterized by a more organized actin cytoskeleton and a reduced ability to degrade gelatin substrates. Hypoxia significantly increased mean actin filament bundle width (72 h) and actin filament length (72-96 h). This correlated with increased hypoxic expression and filamentous organization of stabilizing tropomyosins Tm1 and Tm2. However, isoform specific changes in tropomyosin expression were more evident at 96 h.
  
  
  CONCLUSIONS
  This study demonstrates hypoxia-induced changes in the recruitment of high molecular weight tropomyosins into the actin stress fibres of a human cancer. While hypoxia induced clear changes in actin organization compared with parallel normoxic cultures of neuroblastoma, the precise role of tropomyosins in this hypoxic actin reorganization remains to be determined.
authors.affiliation: Oncology Research Unit, School of Medical Sciences, UNSW Australia, Room 229, Wallace Wurth Building, Sydney, NSW, 2052, Australia. glassj@student.unimelb.edu.au.|Current address: ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, and Department of Microbiology and Immunology, The University of Melbourne, at the Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, 3010, Australia. glassj@student.unimelb.edu.au.
authors.forename: Joshua J
authors.initials: JJ
authors.lastname: Glass
authors.affiliation: Pancreatic Cancer Translational Research Group, Lowy Cancer Research Centre, UNSW Australia, Sydney, NSW, 2052, Australia. p.phillips@unsw.edu.au.
authors.forename: Phoebe A
authors.initials: PA
authors.lastname: Phillips
authors.affiliation: Oncology Research Unit, School of Medical Sciences, UNSW Australia, Room 229, Wallace Wurth Building, Sydney, NSW, 2052, Australia. p.gunning@unsw.edu.au.
authors.forename: Peter W
authors.initials: PW
authors.lastname: Gunning
authors.affiliation: Oncology Research Unit, School of Medical Sciences, UNSW Australia, Room 229, Wallace Wurth Building, Sydney, NSW, 2052, Australia. justine.stehn@novogen.com.
authors.forename: Justine R
authors.initials: JR
authors.lastname: Stehn
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D015687:Cell Hypoxia / Q000235:genetics; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000235:genetics; D049109:Cell Proliferation / Q000235:genetics; D006801:Humans; D009361:Neoplasm Invasiveness / Q000235:genetics; D009447:Neuroblastoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D022502:Stress Fibers / Q000235:genetics / Q000378:metabolism; D014335:Tropomyosin / Q000378:metabolism*
chemical_list: D000199:Actins; D014335:Tropomyosin