Actin-rich protrusions and nonlocalized GTPase activation in Merlin-deficient schwannomas.
Schwannomas lack both alleles for the tumor suppressor Merlin, a cytoskeleton-membrane linker. Previous results showed increased cell spreading of schwannoma cells, but little is known about the underlying mechanisms. Electron microscopy reveals that schwannoma cells not only show more lamellipodia/ruffles but also multiple filopodia. We show that Cdc42, important in filopodia formation, is activated. Both Rac1 and Cdc42 are found all around the cell periphery and in colocalization with their effector phospho-p21 activated kinase in human schwannoma cells. We therefore claim that Rac1 and Cdc42 are activated in a nonlocalized manner, which explains the disperse distribution of lamellipodia/ruffles and filopodia. Using live cell imaging, we further demonstrate continuous remodeling of the many actin-rich protrusions in schwannoma cells. The underlying cytoskeleton of these structures is thin and extensively branched. The actin-related protein 2/3 complex, a major regulator of actin branching, is enriched in the many lamellipodia and ruffles of human primary schwannoma cells. We suggest that the Merlin deficiency in human primary schwannoma cells leads to a random, nonlocalized activation of Rac1 and Cdc42, inducing many actin-rich protrusion zones, not only at the leading edge but also all around the cell periphery. Their nondirectional occurrence together with the continuous and highly dynamic actin remodeling results in the dedifferentiation of these tumor cells.
Flaiz
Christine
C
Department of Clinical Neurobiology, Institute of Biomedical and Clinical Science, Peninsula Medical School, Tamar Science Park, Research Way, Plymouth, United Kingdom.
Kaempchen
Katherine
K
Matthies
Cordula
C
Hanemann
Clemens Oliver
CO
D000199:Actins / Q000378:metabolism*; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000502:physiology; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D008855:Microscopy, Electron, Scanning / Q000379:methods; D009442:Neurilemmoma / Q000378:metabolism* / Q000473:pathology*; D025581:Neurofibromin 2 / Q000172:deficiency*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011554:Pseudopodia / Q000473:pathology* / Q000648:ultrastructure; D012583:Schwann Cells / Q000502:physiology; D014162:Transfection / Q000379:methods; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D054462:p21-Activated Kinases; D020830:rac1 GTP-Binding Protein / Q000378:metabolism
D000199:Actins; D025581:Neurofibromin 2; D049452:Green Fluorescent Proteins; C515903:PAK1 protein, human; C515907:PAK2 protein, human; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D020558:GTP Phosphohydrolases; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein