Cortical tension regulates desmosomal morphogenesis

Abstract

Mechanical stability is a fundamental and essential property of epithelial cell sheets. It is in large part determined by cell-cell adhesion sites that are tightly integrated by the cortical cytoskeleton. An intimate crosstalk between the adherens junction-associated contractile actomyosin system and the desmosome-anchored keratin intermediate filament system is decisive for dynamic regulation of epithelial mechanics. A major question in the field is whether and in which way mechanical stress affects junctional plasticity. This is especially true for the desmosome-keratin scaffold whose role in force-sensing is virtually unknown. To examine this question, we inactivated the actomyosin system in human keratinocytes (HaCaT) and canine kidney cells (MDCK) and monitored changes in desmosomal protein turnover.Partial inhibition of myosin II by para-nitro-blebbistatin led to a decrease of the cells' elastic modulus and to reduced desmosomal protein turnover in regions where nascent desmosomes are formed and, to a lower degree, in regions where larger, more mature desmosomes are present. Interestingly, desmosomal proteins are affected differently: a significant decrease in turnover was observed for the desmosomal plaque protein desmoplakin I (DspI), which links keratin filaments to the desmosomal core, and the transmembrane cadherin desmoglein 2 (Dsg2). On the other hand, the turnover of another type of desmosomal cadherin, desmocollin 2 (Dsc2), was not significantly altered under the tested conditions. Similarly, the turnover of the adherens junction-associated E-cadherin was not affected by the low doses of para-nitro-blebbistatin. Inhibition of actin polymerization by low dose latrunculin B treatment and of ROCK-driven actomyosin contractility by Y-27632 treatment also induced a significant decrease in desmosomal DspI turnover. Taken together, we conclude that changes in the cortical force balance affect desmosome formation and growth. Furthermore, they differentially modulate desmosomal protein turnover resulting in changes of desmosome composition. We take the observations as evidence for a hitherto unknown desmosomal mechanosensing and mechanoresponse pathway responding to an altered force balance.

Desmosome-anchored intermediate filaments facilitate tension-sensitive RhoA signaling for epithelial homeostasis

“…More generally, our findings potentially identify a new way for the passive mechanical properties of IF to modulate AJ signaling. This reinforces our growing awareness of the diverse mechanisms that can link the desmosome-IF and AJ-actomyosin systems systems 14–16,20 . IF and F-actin networks can be structurally linked by proteins, such as spectroplakins, while IF-desmosomal linkages influence cell mechanics driven by actomyosin and interact with actin regulators 8,36,37 .…”

“…Although desmosomes and AJ make complementary contributions to mechanical homeostasis in epithelia 5,7 , there is increasing evidence to suggest that these cytoskeletal-adhesion systems can interact functionally and biochemically 14–16 . To test whether such interactions might affect the mechanical resilience of epithelia, we stimulated contractility in Caco-2 intestinal epithelial monolayers with the phosphatase inhibitor, calyculin A 12,17,18 .…”

“…IF and F-actin networks can be structurally linked by proteins, such as spectroplakins, while IF-desmosomal linkages influence cell mechanics driven by actomyosin and interact with actin regulators 8,36,37 . Conversely, cortical tension can influence desmosomal biogenesis 16 . Tension-activated RhoA signaling contributes to morphogenetic processes that range from apoptotic extrusion 17 to collective epithelial cell migration 38 .…”

Plakophilin-3 Binds the Membrane and Filamentous Actin without Bundling F-Actin

“…The available data also show that desmosome assembly starts with desmosomal cadherins and desmoplakin clustering. The formation of these initial clusters relies on the actin cytoskeleton but not on intermediate filaments, which anchor matured desmosomes [33][34][35][36][37]. Finally, plakophilins, even though they interact with all known desmosomal proteins and intermediate filaments [3,38], can be recruited to the cell cortex without these interactions [7,12,37].…”

ARHGAP32 as a novel RhoGAP interacting with desmoplakin is required for desmosomal organization and assembly

“…The actin cytoskeleton is reported to be involved in the assembly and turnover of desmosomal components (Fuchs et al, 2023; Godsel et al, 2010; Hiermaier et al, 2021; Moch et al, 2022). The relocation of DSP to the desmosome during desmosome assembly can be accelerated by active RhoA, but the maturation of desmosome plaques is hindered by persistent activation of RhoA (Godsel et al, 2010).…”