DIFFERENTIAL PROPERTIES OF D4 LYGDI VERSUS RHOGDI - PHOSPHORYLATION AND RHO GTPASE SELECTIVITY/

RhoA/B/C and CDC42/Rac, which form two subgroups of the rho guanosine triphosphatase (GTPase) family, regulate various aspects of actin cyto skeleton organisation. In cytosol, guanosine diphosphate (GDP) dissoci ation inhibitor (GDI) interacts with and maintains rho GTPases in thei r inactive GDP-bound form. RhoGDI is a ubiquitously expressed GDI, whe reas D4/LyGDI is hematopoietic cell-specific and 10-fold less potent t han RhoGDI in binding to and regulating rho GTPases. We have combined microanalytical liquid chromatography with the use of specific antibod ies in order to separate D4/ LyGDI and RhoDGI-complexes from the cytos ol of U937 cells and to demonstrate that the two GDIs associate with d ifferent rho protein partners. RhoGDI can form a complex with CDC42Hs, RhoA, Rad and Rac2, while none of these GTPases was found to interact with D4/LyGDI. In addition, me found that stimulation of U937 cells w ith phorbol ester leads to phosphorylation of D4/LyGDI. Our results su ggest that LyGDI forms complexes with specific rho GTPases expressed i n hematopoietic cells where it mag regulate specific pathways. (C) 199 8 Federation of European Biochemical Societies.