Rac1 augments Wnt signaling by stimulating β-catenin–lymphoid enhancer factor-1 complex assembly independent of β-catenin nuclear import

Abstract

ABSTRACTβ-Catenin transduces the Wnt signaling pathway and its nuclear accumulation leads to gene transactivation and cancer. Rac1 GTPase is known to stimulate β-catenin-dependent transcription of Wnt target genes and we confirmed this activity. Here we tested the recent hypothesis that Rac1 augments Wnt signaling by enhancing β-catenin nuclear import; however, we found that silencing/inhibition or up-regulation of Rac1 had no influence on nuclear accumulation of β-catenin. To better define the role of Rac1, we employed proximity ligation assays (PLA) and discovered that a significant pool of Rac1–β-catenin protein complexes redistribute from the plasma membrane to the nucleus upon Wnt or Rac1 activation. More importantly, active Rac1 was shown to stimulate the formation of nuclear β-catenin–lymphoid enhancer factor 1 (LEF-1) complexes. This regulation required Rac1-dependent phosphorylation of β-catenin at specific serines, which when mutated (S191A and S605A) reduced β-catenin binding to LEF-1 by up to 50%, as revealed by PLA and immunoprecipitation experiments. We propose that Rac1-mediated phosphorylation of β-catenin stimulates Wnt-dependent gene transactivation by enhancing β-catenin–LEF-1 complex assembly, providing new insight into the mechanism of cross-talk between Rac1 and canonical Wnt/β-catenin signaling.

Retracted: MicroRNA‑224 promotes the sensitivity of osteosarcoma cells to cisplatin by targeting Rac1

“…Rac1 overexpression has been found in various types of cancer, such as lung cancer, gastric cancer, pancreatic cancer, bladder cancer and breast cancer 43, 44, 45, 46, 47. Moreover, activation of Rac1 can increase cancer cell migration, adhesion, invasion, proliferation and metastasis 40, 44, 48, 49, 50. In our previous study, we found that miR‐124 repressed osteosarcoma cell proliferation, migration and invasion by targeting Rac1 expression 34.…”

“…Rac1 is a member of the Ras superfamily of Rho proteins, and it plays an essential role in many cellular processes, including mitogenesis, kinase cascade activation, transcriptional activation, DNA synthesis and cytoskeleton reorganization [37][38][39][40][41][42]. Rac1 overexpression has been found in various types of cancer, such as lung cancer, gastric cancer, pancreatic cancer, bladder cancer and breast cancer [43][44][45][46][47].…”

Regulating Rho GTPases and their regulators

“…Phosphorylation of RAC1 on Thr108 by extracellular signal-related kinase (ERK) in response to epidermal growth factor (EGF) causes RAC1 to translocate to the nucleus 32 , which is proposed to sequester it away from RhoGEFs and prevent its activation during cell migration. However, RAC1 can also regulate actin polymerization 33 and transcription factors such as β-catenin 34 and nuclear factor-κB 35 in the nucleus and thus has a distinct nuclear function. In addition, enforced localization of RAC1 to the nucleus alters the balance of RAC1 and RhoA in the cytoplasm and promotes RhoA-driven invasion 33 .…”

Inhibition of Rac1 activity by NSC23766 prevents cartilage endplate degeneration via Wnt/β‐catenin pathway

“…Wu et al have demonstrated that Rac1 activation could cause the elevated catenin level and nuclear translocation and contribute to aberrant activation of canonical Wnt signalling in cancer cells, indicating the important roles of Rac1 in β‐catenin nuclear localization and β‐catenin‐dependent transcriptional activation . Moreover, Jamieson et al have proved that Rac1 enhanced the interaction between β‐catenin and LEF‐1, further identifying the role of Rac1 in augmenting transactivation of Wnt target genes . Buongiorno et al have demonstrated that Rac1 and the Rac1‐specific activator Tiam1 were components of transcriptionally active beta‐catenin/TCF complexes at Wnt‐responsive promoters, revealing a novel functional mechanism underlying the cross‐talk between Rac1 and the canonical Wnt signalling pathway in colorectal cancer cells .…”