Rac1 Activation Controls Nuclear Localization of β-catenin during Canonical Wnt Signaling

Abstract

Canonical Wnt signaling critically regulates cell fate and proliferation in development and disease. Nuclear localization of beta-catenin is indispensable for canonical Wnt signaling; however, the mechanisms governing beta-catenin nuclear localization are not well understood. Here we demonstrate that nuclear accumulation of beta-catenin in response to Wnt requires Rac1 activation. The role of Rac1 depends on phosphorylation of beta-catenin at Ser191 and Ser605, which is mediated by JNK2 kinase. Mutations of these residues significantly affect Wnt-induced beta-catenin nuclear accumulation. Genetic ablation of Rac1 in the mouse embryonic limb bud ectoderm disrupts canonical Wnt signaling and phenocopies deletion of beta-catenin in causing severe truncations of the limb. Finally, Rac1 interacts genetically with beta-catenin and Dkk1 in controlling limb outgrowth. Together these results uncover Rac1 activation and subsequent beta-catenin phosphorylation as a hitherto uncharacterized mechanism controlling canonical Wnt signaling and may provide additional targets for therapeutic intervention of this important pathway.

Uterine RAC1 via Pak1-ERM signaling directs normal luminal epithelial integrity conducive to on-time embryo implantation in mice

“…Similar observations could be achieved when the Ishikawa cells were transfected with a dominant negative Rac1 (N17Rac1) 26 (Figure 5f). Because Rac1 is a known target of Wnt5a signaling 35,36 that has been shown to be essential for cell polarity induction and epithelial function in various organs including the uterus, 9,11,37 we also analyzed the consequence of Rac1 deficiency on uterine Wnt5a expression.…”

“…Because the systemic Rac1 null mice are embryonic lethal owing to gastrulation defects, 24 to analyze the pathophysiological significance of Rac1 in early pregnancy events, we next used a progesterone receptor (Pgr)-driven Cre (Pgr cre/+ ) mouse model crossed with Rac1 floxed (Rac1 f/f ) mice to achieve uterine-selective deletion of Rac1. [25][26][27] As shown in To ascertain the stage-specific causes accounting for this obvious infertility, we subsequently analyzed the implantation status in mice missing uterine Rac1. Although all Rac1 f/f mice tested showed normal embryo implantation on day 5 morning (Figure 2j).…”

“…Rac1 f/f mice were generated as previously described. 26,27 Uterine-specific mutant mice were generated by crossing Rac1 f/f mice with Pgr Cre/+ mice. 25 All mice were housed in the animal care facility of the Institute of Zoology, Chinese Academy of Sciences, according to the institutional guidelines for the care and use of laboratory animals.…”

A Rac1/PAK1 cascade controls β-catenin activation in colon cancer cells

“…The results indicated that total b-catenin level was clearly reduced (Figures 5a and b). In comparison with the PAK1-knockdown cells, nuclear b-catenin staining was further reduced in Rac1-knockdown cells (compare Figures 5a and 2c) and this is consistent with the previous report that Rac1/JNK2 controls b-catenin nuclear localization (Wu et al, 2008;Phelps et al, 2009). In addition, NSC23766, a Rac1 inhibitor, was also able to reduce total b-catenin in SW480 cells (Figures 5c and d).…”

“…However, it was argued recently that APC mutation alone probably is not sufficient to promote full b-catenin signaling (Anderson et al, 2002;Phelps et al, 2009). Mutation of K-Ras was often observed in more advanced colon cancer samples and it was suggested that a K-Ras/Rac1/ JNK2 cascade may further enhance b-catenin nuclear accumulation by JNK2-mediated phosphorylation of b-catenin at Ser191 and Ser605 (Wu et al, 2008;Phelps et al, 2009). However, Rac1 was also found being able to elevate cytosolic, as well as nuclear levels of b-catenin (Esufali and Bapat, 2004).…”