Constitutive active GTPases Rac and Cdc42 are associated with endoreplication in PAE cells.

The Rho-like guanine triphosphate (GTP)ases become activated by extracellular ligands and regulate a wide variety of biological processes, including cell motility, spreading of cells, cytoskeletal organisation and transcriptional activity. We studied the effect of expression of WtRac and Cdc42 and of their constitutive active V12 variants on cell cycle transition using the isopropylthiogalactoside (IPTG) inducible Rac and Cdc42 transfectants of porcine aortic endothelial (PAE) cells. Expression of V12Rac or V12Cdc42 resulted initially in an enrichment of cells in G2/M, followed by the appearance of multinucleated cells with some of the nuclei still being able to incorporate bromodeoxyuridine (BrdU). By fluorescent activated cell sorter (FACS) analysis, these cells appeared as polyploid cells. Prolonged activation of V12Rac or V12Cdc42 resulted in genomic instability and these cells finally detached from the culture plate. These findings indicate that induction of the constitutive active V12 forms of Rac and Cdc42 results in 'mitotic slippage', where endoreplication takes place irrespective of the exit from cytokinesis.