30.11
Coordenação Citoesquelética na Migração Celular
Uma célula em migração muda sua forma durante os eventos cíclicos de fixação e desprendimento do substrato e reposiciona as organelas celulares de for…
A migração celular é um processo complexo que requer coordenação precisa entre diferentes componentes celulares, particularmente o citoesqueleto que compreende filamentos de actina, microtúbulos e filamentos intermediários.
Durante a migração, os filamentos de actina são reorganizados dinamicamente na periferia da célula e ajudam a estabelecer as bordas de ataque e fuga da célula.
Essa polaridade direciona o centrossomo, um centro organizador de microtúbulos, para se posicionar na frente do núcleo e orientar os microtúbulos em crescimento em direção à borda de ataque.
Os motores de cinesina transportam várias cargas nessas trilhas de microtúbulos, incluindo vesículas exocíticas contendo integrinas e novos componentes de membrana, proteínas de remodelação de actina e filamentos intermediários.
Os filamentos intermediários estabilizam e promovem a maturação das aderências focais recém-formadas.
Na borda de fuga, as aderências focais são desmontadas e os motores de dineína transportam as integrinas endocitadas ao longo dos microtúbulos em direção à borda de ataque para reciclagem.
Além disso, os componentes do citoesqueleto são reticulados entre si e outras organelas por meio de proteínas ligantes.
Essas pontes cruzadas permitem que os componentes do citoesqueleto sincronizem sua polaridade e formem uma rede coesa para a migração celular.
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Q1: How do actin filaments and microtubules work together during cell migration?
Actin filaments reorganize dynamically at the cell periphery to establish leading and trailing edges, while microtubules extend from the centrosome toward the leading edge. Linker proteins like spectraplakin cross-bridge these components, enabling them to synchronize their polarity. This coordination allows the cytoskeleton to form a cohesive network that directs cell movement and maintains directional migration.
Q2: What role do Rho proteins play in establishing cell polarity?
Rho family proteins, including RhoA, Cdc42, and Rac1, are master regulators that act on all three cytoskeletal components to establish cell polarity. Cdc42 directs actin reorganization at the leading edge and regulates intermediate filament transport on microtubules. These small GTPases coordinate cytoskeletal crosstalk through signaling cascades, maintaining synchronized polarity across the entire network.
Q3: How are integrins recycled during cell migration?
Kinesin motors carry exocytic vesicles containing integrins along microtubule tracks toward the leading edge for new membrane assembly. At the trailing edge, focal adhesions disassemble and dynein motors transport endocytosed integrins back along microtubules toward the leading edge for recycling. This continuous recycling process supports sustained cell migration and adhesion turnover.
Q4: What is the function of intermediate filaments in focal adhesion maturation?
Intermediate filaments stabilize and promote maturation of newly formed focal adhesions at the leading edge during cell migration. These filaments are transported on microtubule tracks and cross-linked to other cytoskeletal components via linker proteins. Their stabilizing role ensures robust adhesion formation necessary for the cell to generate traction and move forward.
Q5: How does cytoskeletal crosstalk maintain coordinated cell migration?
Cytoskeletal crosstalk occurs through direct communication via linker proteins that form cross-bridges between actin filaments, microtubules, and intermediate filaments, and indirect communication through signaling cascades involving Rho proteins. Microtubules transport proteins and vesicles that regulate actin dynamics at the leading edge, creating positive feedback that synchronizes polarity across all three cytoskeletal components.
Q6: What cargo do kinesin motors transport on microtubules during migration?
Kinesin motors carry multiple types of cargo along microtubule tracks, including exocytic vesicles containing integrins and new membrane components, actin remodeling proteins, and intermediate filaments. This coordinated transport delivers essential building blocks and regulatory proteins to the leading edge, supporting dynamic cytoskeletal reorganization and sustained directional migration.
Q7: How does the centrosome position itself during cell migration?
The centrosome, a microtubule organizing center, is directed by actin filament polarity to position itself in front of the nucleus during cell migration. This positioning orients growing microtubules toward the leading edge, enabling efficient transport of cargo and proteins needed for migration. The centrosome's strategic location ensures microtubules can deliver vesicles and regulatory factors to support leading edge dynamics.