CYTOKINESIS ARREST AND REDISTRIBUTION OF ACTIN-CYTOSKELETON REGULATORY COMPONENTS IN CELLS EXPRESSING THE RHO-GTPASE CDC42HS

In mammalian cells, Rho GTPases control the reorganisation of the acti n cytoskeleton in response to growth factors. In the cytoplasm, the po lymerisation of actin filaments and their organisation into complex ar chitectures is orchestrated by numerous proteins which act either dire ctly, by interacting with actin, or by producing secondary messengers which serve as mediators between signal transduction pathways and the microfilament organisation. We sought to determine whether the intrace llular distribution of some of these regulatory components may be cont rolled by the Rho GTPase CDC42Hs. With this aim, we have established H eLa-derived human cell lines in which expression of a constitutively a ctivated mutant of CDC42Hs is inducible. Morphological analysis by imm unofluorescence labelling and confocal laser scanning microscopy revea led a massive reorganisation of F-actin in cortical microspikes as wel l as podosome-like structures located at the ventral face of the cells . Concomitantly, the cells became giant and multinucleate indicating t hat cytokinesis was impaired. The actin bundling protein T-plastin, th e vasodilatator-stimulated phosphoprotein (VASP), a profilin ligand, a s well as the 85 kDa regulatory subunit of the phosphoinosite 3-kinase redistributed with F-actin into the CDC42Hs-induced structures.