The experiment was done three times. b The RhoA GTP-loading data was corroborated by indirect immunofluorescence-staining of cells on fibronectin-coated cover slips with anti-RhoA antibody (red) and photography at 630 x magnification. Growing cells exhibited membrane localization of RhoA (arrows) which disappeared in dormant cells. Blocking antibody to integrin α5β1 2 μg/ml induced re-localization of RhoA to the membrane, while blocking antibody to integrin α2β1 2 μg/ml had only a minimal effect. Nuclear DAPI staining is shown in blue To determine if the actin reorganization selleck products was dependent on RhoA inactivation, we transfected cells on fibronectin-coated cover slips with wild type,

constitutively active and dominant negative RhoA expression vectors and quantitated the percentage of transfected cells with cortical actin by indirect immunofluorescence. Cells were transiently co-transfected with a GFP vector and ten-fold excesses of the various RhoA expression vectors. Actin localization in green fluorescent cells was determined by rhodamine red phalloidin staining. Figure 4a demonstrates prototypical membrane localization of actin in GFP-only- and dominant negative RhoA 19N-transfected dormant cells and significantly diminished peripheral actin localization in

wild type- or constitutively active Rho 63L-transfected dormant cells. In the latter transfectants, the appearance of stress fibers became evident. The data, graphed in Fig. 4b, confirms once again the increase in the percentage of cells with cortically rearranged actin around more than 50% of the periphery from 9 + 0.7% of the growing cells click here to 80 + 2% of the dormant cells (p < 0.01). No significant differences were noted between mock transfected and GFP only-transfected dormant cells. Transfection of dormant cells with dominant negative RhoA 19N did not decrease the percentage of cells with cortical actin. However, transfection with constitutively active 63L and wild type RhoA decreased the percentage of cells with cortical actin to 24 + 2 (p < 0.001) and 10 + 4%, Plasmin (p < 0.02),

respectively. These data demonstrate that inactivation of RhoA is necessary to permit the acquisition of the dormant phenotype. To determine if inactivation of RhoA was sufficient to induce the state of dormancy, as defined by a spread cellular appearance and cortical actin redistribution, growing cells were transfected with dominant negative RhoA 19N vector. Figure 4c demonstrates that the cells did not acquire the characteristic appearance and did not develop cortically rearranged actin. Figure 4d demonstrates that there was no statistically significant increase in the percentage of cells with cortical actin between GFP only-transfected and RhoA 19N-transfected growing cells, nor did the cells acquire the typically large, spread out appearance of the dormant cells. Transfection with wild type and dominant negative vectors had no effect either, as expected (data not shown).