Increasing β-catenin/Wnt3A activity levels drive mechanical strain-induced cell cycle progression through mitosis.

Blair W Benham-Pyle,Beth L Pruitt,Kevin C Hart,Joo Yong Sim,William James Nelson

doi:10.7554/elife.19799

Abstract

Mechanical force and Wnt signaling activate β-catenin-mediated transcription to promote proliferation and tissue expansion. However, it is unknown whether mechanical force and Wnt signaling act independently or synergize to activate β-catenin signaling and cell division. We show that mechanical strain induced Src-dependent phosphorylation of Y654 β-catenin and increased β-catenin-mediated transcription in mammalian MDCK epithelial cells. Under these conditions, cells accumulated in S/G2 (independent of DNA damage) but did not divide. Activating β-catenin through Casein Kinase I inhibition or Wnt3A addition increased β-catenin-mediated transcription and strain-induced accumulation of cells in S/G2. Significantly, only the combination of mechanical strain and Wnt/β-catenin activation triggered cells in S/G2 to divide. These results indicate that strain-induced Src phosphorylation of β-catenin and Wnt-dependent β-catenin stabilization synergize to increase β-catenin-mediated transcription to levels required for mitosis. Thus, local Wnt signaling may fine-tune the effects of global mechanical strain to restrict cell divisions during tissue development and homeostasis.

Highlights

Mechanical cues are critical for regulating cellular growth, morphology, and behavior in developing and adult tissues
The activities of several tyrosine kinases have been reported to affect b-catenin binding to the cadherin adhesion complex (Lilien and Balsamo, 2005), we focused on Src phosphorylation of Y654 b-catenin which has been correlated directly with increased Wnt/b-catenin activity and activation by tissue compression in vivo (Whitehead et al, 2008; Fernandez-Sanchez et al, 2015; Brunet et al, 2013); to block b-catenin degradation in the cytoplasm, we focused on b-catenin phosphorylation by CKI/GSK3b by inhibiting the priming phosphorylation by CKI (Aberle et al, 1997; Amit et al, 2002; Liu et al, 2002)
Inhibition of Epidermal Growth Factor Receptor (EGFR) by PD153035 reduced the increase in pY654 b-catenin following mechanical strain by ~40% (Figure 3—figure supplement 4E,F), unlike the complete inhibition of strain-induced pY654 b-catenin accumulation by the Src inhibitor SU6656 (Figure 3E,F). These results indicate that EGFR activation may contribute to the increase in pY654 b-catenin following mechanical strain (Muhamed et al, 2016) but it is not required for strain-induced pY654 b-catenin-mediated activation of cell cycle progression

Summary

Introduction

Mechanical cues are critical for regulating cellular growth, morphology, and behavior in developing and adult tissues. The cadherin-associated transcriptional co-activator b-catenin accumulates in the nucleus following mechanical strain (Farge, 2003; Benham-Pyle et al, 2015). The E-cadherin-bound pool of b-catenin is regulated by a balance of tyrosine kinase and tyrosine phosphatase activities (Farge, 2003; Benham-Pyle et al, 2015; Muller et al, 1999; Piedra et al, 2001; Lilien and Balsamo, 2005; Tan et al, 2016). The affinity between E-cadherin and b-catenin at junctions is decreased by the activity of cytoplasmic and receptor tyrosine kinases (EGFR, Src, Abl, Fyn/Fer)

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