Rac3, a Rho GTPase and regulator of actin-based cytoskeletal dynamics

Ras-related C3 botulinum toxin substrate 3 (Rac3) is a 21 kDa GTPase encoded by 192 amino acids that acts as a molecular switch in a variety of cellular events that include cell motility, development, signaling, transport, cytoskeletal organization, cell cycle, reactive oxygen species production, and vesicle trafficking. Along with the Rho isoforms and Cdc42, it is a member of the Rho sub-family of Ras super-family GTPases and is one of 3 Rac isoforms (Rac1 and Rac2 being the others). At the nucleotide level, human Rac3 has 77% identity with Rac1, 83% identity with Rac2, and 69% identity with RhoG. At the amino acid level, Rac3 and Rac1 are 92% identical and Rac3 and Rac2 are 89% identical. Like all Ras super-family GTPases, Rac3 is bound to GTP in its active form, whereas it is inactive in its GDP-bound form. Rac3 is activated by guanidine activating proteins (GEFs) that exchange bound GDP for GTP and in-activated by GTPase-activating proteins (GAPs) that promote GTP hydrolysis. Because of the hydrophobic isoprenyl moiety at the C-terminus, Rac3 is associated with endo-membranes and cell membranes. Nuclear localization has also been reported. In the cytoplasm it associates with the chaperone Rho GDP-dissociation inhibitor (RhoGDI).

Rac3 mRNA is present in a variety of human cancer cell lines and tumor tissue samples including brain, liver, kidney, pancreas, breast, and prostate. Active Rac3 has been detected in MDA-435, T47D, and MCF7 breast cancer cell lines and treatment of cells with siRNA against Rac3 inhibits SNB19 glioblastoma and BT549 breast cancer cell line invasion in an in vitro assay. Conversely, expression of a constitutively active Rac3 isoform in MDA-MB-435 breast cancer cells resulted in increased invasion and motility in vitro.

Images of Rac3 

Rac activation in Swiss 3T3 cells. F-actin is visualized with fluorescent green phalloidin staining (Cat.# PHDG1) and nuclear blue DNA staining with Dapi. Cells were activated with Cat. # CN04 (right).

Immunofluorescence image of mouse Swiss 3T3 cells stained with Anti-Rac1  monoclonal antibody (Cat. # ARC03). Swiss 3T3 cells were grown to semi-confluency and fixed with methanol. Immunofluorescence staining using 1 µg/ml (1:20 dilution) of ARC03 antibody is shown (red). The primary antibody was detected with a 1:500 dilution of goat anti-mouse rhodamine conjugated antibody. Photograph was taken with a 100X objective lens.

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Basso V. et al. 2011. Absence of Rac1 and Rac3 GTPases in the nervous system hinders thymic, splenic and immune-competence development. Eur. J. Immunol. 41, 1410-1419.

Baugher P.J. et al. 2005. Rac1 and Rac3 isoform activation is involved in the invasive and metastatic phenotype of human breast cancer cells. Breast Cancer Res. 7, R965-R974.

Bolis A. et al. 2003. Differential distribution of Rac1 and Rac3 GTPases in the developing mouse brain: implications for a role of Rac3 in Purkinje cell differentiation. Eur. J. Neurosci. 18, 2417-2424.

Chan A. Y. et al. 2005. Roles of the Rac1 and Rac3 GTPases in human tumor cell invasion. Oncogene. 24, 7821-7829.

Corbetta S. et al. 2009. Essential role of Rac1 and Rac3 GTPases in neuronal development. FASEB J. 23, 1347-1357.

Heisterkamp, N.C. 2007. RAC3 (ras-related C3 botulinum toxin substrate 3 (rho family, small GTP binding protein Rac3)). Atlas Genet. Cytogenet. Oncol. Haematol. 11, 209-212.

Hwang S.L. et al. 2005. Expression of Rac3 in human brain tumors. J. Clin. Neurosci. 12, 571-574.

Keller P.J. et al. 2005. Rac3-mediated transformation requires multiple effector pathways. Cancer Res. 65, 9883-9890.