The desmosome/intermediate filament linkage regulates cell mechanics

Mechanotransduction, the process by which mechanical forces are translated into biochemical signals, is critical for regulating normal physiological processes during tissue development and homeostasis and also contributes to pathological conditions, including cardiovascular disease and cancer progression. While actin-plasma membrane connections are well known to contribute to this process, the role of intermediate filament (IF) connections is not understood. The major IF connections to the plasma membrane in tissues such as skin and heart that undergo large amounts of mechanical strain are desmosomes. In addition to their essential role in ensuring tissue integrity, desmosomes act as signaling scaffolds regulating physiological processes including epidermal differentiation. We addressed the importance of desmosome-IF interactions in regulating cell mechanics by uncoupling or enhancing the interaction between desmosomes and the IF cytoskeleton using mutant forms of the IF anchoring molecule desmoplakin (DP). DPNTP, an IF-binding domain mutant that uncouples IF from desmosomes, or DP.S2849G, a point mutant that enhances DP’s association with IF by interfering with GSK3Beta-dependent processive phosphorylation, were expressed in doxycycline-inducible keratinocyte cell lines. Micropillar arrays and atomic force microscopy were used to measure the effects of wild type and mutant DP on cell-substrate and cell-cell forces as well as cell stiffness. Uncoupling IF from desmosomes or siRNA-mediated knockdown of DP led to a significant decrease in the average traction and intercellular forces in cell pairs and a significant decrease in cell stiffness of cell pairs and semiconfluent sheets of cells. Enhancing the desmosome-IF interaction led to a significant increase in the average traction and intercellular forces in cell pairs as well as a significant increase in average cell stiffness in cell pairs and cell sheets. The cell stiffness increase was most notable in 6-day confluent cell sheets, by which time desmosomes develop a strong form of calcium-independent adhesion. DP-mediated effects on cell mechanics were abrogated by the actin depolymerizing drug cytochalasin D. These data suggest that strengthening the desmosome-IF network could increase the resistive capacity of the system, allowing for more robust actomyosin-generated tension and increased cell forces/stiffness. The known tissue and differentiation-specific diversity in desmosome/IF composition provides an opportunity to differentially regulate tissue mechanics by balancing and tuning forces among cytoskeletal systems.