The expression of a constitutively active G protein-coupled receptor is expected to trigger diverse cellular changes ranging from normal to adaptive responses. We report that confluent HEK-293 cells stably expressing the constitutively active mutant N111G-AT1 receptor for angiotensin II spontaneously exhibited dramatic morphological changes and cytoskeletal reorganization. Phase-contrast microscopy revealed that these cells formed a dense monolayer, whereas cells expressing the WT-AT1 receptor displayed large intercellular spaces and numerous filopodia. Confocal microscopy revealed an elaborate web of polymerized actin at the apical and basolateral surfaces of cells expressing the N111G-AT1 receptor. Interestingly, these phenotypic changes were prevented by culturing the cells in the presence of the inverse agonist EXP3174. Similar morphologic rearrangements and de novo polymerized actin structures were found in Ang II-stimulated cells expressing the WT-AT1 receptor. We further showed that AT1 receptor-induced cell-cell contact formation did not require an increase in intracellular Ca2+ concentration or the activity of protein kinase C. However, pretreatment with Y-27632 revealed that Rho-kinase activity was required for cell-cell contact formation upon AT1 receptor activation. These observations demonstrate that the expression of the constitutively active mutant N111G-AT1 receptor had a significant impact on the morphology and cytoskeletal organization of HEK-293 cells, possibly via a mechanism involving the activity of Rho-kinase.