29.9
Respuesta a la tensión en las uniones Adheren
Las uniones adherentes que anclan las células son complejos multiproteicos que se adaptan dinámicamente a estímulos mecánicos como fuerzas de tracción…
Los tejidos, como la piel y el epitelio intestinal, experimentan constantemente fuerzas mecánicas externas, como pellizcos o estiramientos.
Las uniones adherentes que unen estas células epiteliales pueden cambiar dinámicamente en respuesta a dicha tensión mecánica. Esta conversión de estímulos mecánicos en cambios bioquímicos se denomina mecanotransducción.
En estas células, las uniones adherentes forman una zona continua de unión, el cinturón de adhesión, que comprende grandes grupos de cadherinas, cateninas y haces contráctiles de actomiosina.
Las alfa-cateninas en estas uniones actúan como proteínas mecanosensoriales que cambian de conformación en respuesta a la tensión mecánica.
Cuando el aumento de las fuerzas contráctiles tira de los filamentos de actina, la alfa-catenina cambia de la conformación plegada a la desplegada.
Este despliegue abre un sitio de unión críptico a la vinculina, una proteína de unión al citoesqueleto que permanece en su forma cerrada e inactiva en el citoplasma.
Al unirse a la alfa-catenina, la vinculina cambia de conformación a su forma abierta y activa.
La vinculina activa promueve el reclutamiento de filamentos de actina adicionales al sitio, fortaleciendo así la unión y distribuyendo la fuerza a través de las células.
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Q1: What is mechanotransduction at adherens junctions?
Mechanotransduction is the conversion of mechanical stimuli, such as tension or stretching, into biochemical changes at adherens junctions. Epithelial tissues like skin and intestinal epithelium constantly experience external mechanical forces. Mechanosensory proteins at these junctions detect these forces and undergo conformational changes that alter their function, allowing cells to respond dynamically to mechanical stress.
Q2: How does alpha-catenin respond to mechanical tension?
Alpha-catenin is a mechanosensory protein that changes conformation when contractile forces pull on actin filaments. Under normal conditions, alpha-catenin remains folded with its vinculin homology binding domains inaccessible. When tension increases, alpha-catenin unfolds, exposing these cryptic binding sites and enabling interaction with other proteins like vinculin to strengthen the junction.
Q3: What role does vinculin play in junction strengthening?
Vinculin is a cytoskeletal binding protein that exists in an inactive, closed form in the cytoplasm. When exposed alpha-catenin binding sites activate vinculin, it changes to an open conformation. The active vinculin recruits additional actin filaments to the junction, strengthening it and distributing mechanical force across cells more effectively.
Q4: What is the adhesion belt in epithelial cells?
The adhesion belt is a continuous zone of attachment formed by adherens junctions, comprising large clusters of cadherins, catenins, and actomyosin contractile bundles. This structure anchors epithelial cells together and provides the mechanical foundation for cells to respond to external forces like pinching or stretching while maintaining tissue integrity.
Q5: How does vinculin binding affect the actin cytoskeleton?
When vinculin binds to unfolded alpha-catenin, its open neck region becomes accessible to actin-regulating proteins like Arp2/3. This allows vinculin to recruit more actin filaments and dynamically reorganize the actin cytoskeleton in response to mechanical stress, enhancing junction stability and force distribution.
Q6: Why do adherens junctions need to adapt to mechanical forces?
Tissues like skin and intestinal epithelium experience constant external mechanical forces such as pinching and stretching. Adherens junctions must dynamically adapt to these forces to maintain tissue integrity and prevent cell separation. This adaptive response through mechanotransduction allows cells to strengthen junctions under stress and distribute forces efficiently across the tissue.
Q7: What structural changes occur in alpha-catenin during mechanotransduction?
Alpha-catenin undergoes an allosteric shift from a folded to an unfolded conformation when mechanical tension increases. This unfolding exposes three vinculin homology domains that were previously inaccessible. The conformational change allows these domains to bind vinculin and other actin-binding proteins, initiating the cascade that strengthens the junction.