A Molecular Clutch between the Actin Flow and N-Cadherin Adhesions Drives Growth Cone Migration

Abstract

The adhesion molecule N-cadherin plays important roles in the development of the nervous system, in particular by stimulating axon outgrowth, but the molecular mechanisms underlying this effect are mostly unknown. One possibility, the so-called "molecular clutch" model, could involve a direct mechanical linkage between N-cadherin adhesion at the membrane and intracellular actin-based motility within neuronal growth cones. Using live imaging of primary rat hippocampal neurons plated on N-cadherin-coated substrates and optical trapping of N-cadherin-coated microspheres, we demonstrate here a strong correlation between growth cone velocity and the mechanical coupling between ligand-bound N-cadherin receptors and the retrograde actin flow. This relationship holds by varying ligand density and expressing mutated N-cadherin receptors or small interfering RNAs to perturb binding to catenins. By restraining microsphere motion using optical tweezers or a microneedle, we further show slippage of cadherin-cytoskeleton bonds at low forces, and, at higher forces, local actin accumulation, which strengthens nascent N-cadherin contacts. Together, these data support a direct transmission of actin-based traction forces to N-cadherin adhesions, through catenin partners, driving growth cone advance and neurite extension.

E-cadherin is under constitutive actomyosin-generated tension that is increased at cell–cell contacts upon externally applied stretch

“…Thus, the cadherin/catenin complex may be a constitutive membrane anchor for the cortical actomyosin cytoskeleton. In this context, it is noteworthy that cadherin lateral mobility in the plasma membrane depends on the catenin-binding region of the cytoplasmic domain even outside of cell-cell contacts and is regulated by the underlying cortical actin cytoskeleton (54,55). That the cadherin/catenin complex functions in membrane-to-cortex attachment may explain why this complex is important for regulating macropinocytosis in contact-free protruding membranes (56), single-cell wound closure in Drosophila (57), and plasma membrane blebbing during early embryogenesis in zebrafish (58).…”

EMT, the cytoskeleton, and cancer cell invasion

“…Interestingly, PDGF induces the translocation of cortactin to podosomes via the GAP BPGAP1 and Rac1, indicating that PDGF receptor is involved in the formation of podosomes [226,227]. As described above, PDGFR colocalizes with N-cadherin in membrane ruffles, and both N-cadherin and cortactin are found in the growth cones of emerging neuronal axons and exert a crucial role in neuron guidance [81,228]. The co-localization of cortactin with the Ncadherin/NCAM/FGFR complex and NCAM-mediated FGFR signaling have been shown to contribute to neurite outgrowth [95].…”

“…Like its epithelial counterpart, N-cadherin is connected via α-catenin and β-catenin to the cytoskeleton and functions as both a mechanical cell adhesion component and a signaling molecule. Recently, it has been reported that during neurite extension the traction forces generated by retrograde actin flow are directly transmitted to N-cadherin adhesions, thereby mechanically linking N-cadherin with the formation of motile structures [81]. Interestingly, the authors show that the mechanical engagement of Ncadherin induces local actin polymerization and thereby ensures the integrity of the adhesion complex.…”

Cadherin-based intercellular adhesions organize epithelial cell–matrix traction forces

“…Our study highlights intercellular adhesions' ability to impact cell-ECM force generation, which allows for bidirectional feedback between cell-cell and cell-matrix forces. Indeed, tension at cadherin junctions (13,54) is known to elicit cell-signaling events and actin dynamics (52, [55][56][57][58] and contribute to collective cell migration (26,59,60). In light of these prior results on integrin-cadherin feedback, it is somewhat surprising that a minimal physical model can capture the observed dependence of cell-matrix forces on the strength of cadherin-mediated cell-cell adhesions.…”