Rac1 and Cdc42 GTPases regulate shear stress-driven β-catenin signaling in osteoblasts.

Beta-catenin-dependent TCF/LEF (T-cell factor/lymphocyte enhancing factor) is known to be mechanosensitive and an important regulator for promoting bone formation. However, the functional connection between TCF/LEF activity and Rho family GTPases is not well understood in osteoblasts. Herein we investigated the molecular mechanisms underlying oscillatory shear stress-induced TCF/LEF activity in MC3T3-E1 osteoblast cells using live cell imaging. We employed fluorescence resonance energy transfer (FRET)-based and green fluorescent protein (GFP)-based biosensors, which allowed us to monitor signal transduction in living cells in real time. Oscillatory (1Hz) shear stress (10 dynes/cm2) increased TCF/LEF activity and stimulated translocation of β-catenin to the nucleus with the distinct activity patterns of Rac1 and Cdc42. The shear stress-induced TCF/LEF activity was blocked by the inhibition of Rac1 and Cdc42 with their dominant negative mutants or selective drugs, but not by a dominant negative mutant of RhoA. In contrast, constitutively active Rac1 and Cdc42 mutants caused a significant enhancement of TCF/LEF activity. Moreover, activation of Rac1 and Cdc42 increased the basal level of TCF/LEF activity, while their inhibition decreased the basal level. Interestingly, disruption of cytoskeletal structures or inhibition of myosin activity did not significantly affect shear stress-induced TCF/LEF activity. Although Rac1 is reported to be involved in β-catenin in cancer cells, the involvement of Cdc42 in β-catenin signaling in osteoblasts has not been identified. Our findings in this study demonstrate that both Rac1 and Cdc42 GTPases are critical regulators in shear stress-driven β-catenin signaling in osteoblasts.

Wan Q ，Cho E ，Yokota H ，Na S ... -  《-》

RhoA GTPase interacts with beta-catenin signaling in clinorotated osteoblasts.

Wan Q ，Cho E ，Yokota H ，Na S ... -  《-》

Cross-talk between Rac1 GTPase and dysregulated Wnt signaling pathway leads to cellular redistribution of beta-catenin and TCF/LEF-mediated transcriptional activation.

Esufali S ，Bapat B 《ONCOGENE》

Regulation by afadin of cyclical activation and inactivation of Rap1, Rac1, and RhoA small G proteins at leading edges of moving NIH3T3 cells.

Miyata M ，Rikitake Y ，Takahashi M ，Nagamatsu Y ，Yamauchi Y ，Ogita H ，Hirata K ，Takai Y ... -  《-》

Differentiation-inducing factor-1 alters canonical Wnt signaling and suppresses alkaline phosphatase expression in osteoblast-like cell lines.

Matsuzaki E ，Takahashi-Yanaga F ，Miwa Y ，Hirata M ，Watanabe Y ，Sato N ，Morimoto S ，Hirofuji T ，Maeda K ，Sasaguri T ... -  《JOURNAL OF BONE AND MINERAL RESEARCH》