Migration, mechanisms and regulation principles

Ruch i migracja są jedną z głównych funkcji życiowych komórek. W odpowiedzi na różne bodźce, dynamiczny cytoszkielet aktynowy generuje siłę umożliwiającą komórce przemieszczanie się w trójwymiarowej sieci zewnątrzkomórkowej macierzy czy po płaskim podłożu. Wydłużanie filamentów aktynowych na ich kolczastych końcach wypycha błonę komórkową w kierunku migracji, formując strefę frontalną zwaną lamellipodium. Skurcz włókien naprężeniowych umożliwia oderwanie tylnej części komórki i przesunięcie jej do przodu. W odpowiedzi na bodźce ze środowiska, receptory komórki inicjują wiele szlaków sygnałowych powodujących reorganizację mikrofilamentów aktynowych oraz skurcz układu akto-miozynowego. Głównymi regulatorami tych procesów są białka z rodziny Rho, fosfolipidy PIP2 oraz jony wapnia. Receptory nukleotydowe P2Y2 w połączeniu z białkami G regulują poziom fosfatydyloinozytolu-4,5-bisfosforanu (PIP2), który moduluje funkcje białek wiążących aktynę i aktywuje białka Rac1 oraz RhoA. Szlak sygnałowy RhoA/ROCK odgrywa ważną rolę w generowaniu skurczu włókien naprężeniowych. Z kolei białko Rac1 poprzez swój efektor kinazę PAK1 reguluje procesy formujące lamellipodium oraz wysuwanie strefy wiodącej podczas migracji.Motility is a common feature of numerous cell types. In response to various stimuli, the dynamic actin cytoskeleton and contractility generate forces needed to drive the cell forward. Actin filament elongation on the barbed ends pushes the plasma membrane forward during lamellipodium formation. Stress fibers contraction and/or the contraction of the cortical network are responsible for detaching the rear part of the cell and enable cell body to follow the progressing front. In response to extracellular stimuli, multiple signaling pathways are initiated resulting in the actin filament network reorganization and contractility of acto-myosin system. The key regulators of these processes are Rho family proteins, PIP 2 and calcium ions. Nucleotide receptors P2Y 2 coupled with G-proteins regulate the level of phosphatidylinositol-4,5-bisphosphate (PIP 2 ), which in turn modulates a variety of actin binding proteins, is involved in calcium response, and activates Rac1 and RhoA proteins. The RhoA/ROCK signaling pathway plays an important role in contractile force generation needed for the assembly of stress fibers, focal adhesions and for tail retraction during cell migration. The Rac1 via its effector Pak1 regulates lamellipodium formation and protrusion of the leading edge

Effect of Rho-associated kinase inhibition on actin cytoskeleton structure and calcium response in glioma C6 cells

The role of actin cytoskeleton functional state in glioma C6 cell morphology and calcium signaling was investigated through modification of myosin II activity by blocking Rho-associated kinase with the specific inhibitor Y-27632. Treatment of glioma C6 cells with ROCK inhibitor resulted in actin cytoskeleton reorganization and also in the changed shape and distribution of mitochondria. Changes in the distribution of ER, the main calcium store in glioma C6 cells, were not visible. The inhibition of myosin II activity influences the first phase of calcium signaling evoked by agonist, and both phases of thapsigargin-evoked calcium response. We suggest that the observed increase in Ca2+ release from intracellular stores induced by IP3 formation as well as inhibition of SERCA ATPase is at least in part related to severely affected mitochondria. Enhancement of capacitative calcium entry evoked by thapsigargin is probably associated with the reorganization of the acto-myosin II system. ATP-induced calcium response presents no changes in the second phase. We observed that ATP stimulation of Y-27632 pretreated cells leads to immediate morphological rearrangement of glioma C6 cells. It is a consequence of actin cytoskeleton reorganization: formation of stress fibers and relocation of phosphorylated myosin II to actin filaments. It seems that the agonist-evoked strong calcium signal may be sufficient for myosin II activation and the stress fiber organization. This is the first work showing the dependence between the functional state of the acto-myosin II system and calcium signaling stressing the reversible character of this relationship

Is MLC phosphorylation essential for the recovery from ROCK inhibition in glioma C6 cells?

Inhibition of Rho-associated protein kinase (ROCK) activity in glioma C6 cells induces changes in actin cytoskeleton organization and cell morphology similar to those observed in other types of cells with inhibited RhoA/ROCK signaling pathway. We show that phosphorylation of myosin light chains (MLC) induced by P2Y2 receptor stimulation in cells with blocked ROCK correlates in time with actin cytoskeleton reorganization, F-actin redistribution and stress fibers assembly followed by recovery of normal cell morphology. Presented results indicate that myosin light-chain kinase (MLCK) is responsible for the observed phosphorylation of MLC. We also found that the changes induced by P2Y2 stimulation in actin cytoskeleton dynamics and morphology of cells with inhibited ROCK, but not in the level of phosphorylated MLC, depend on the presence of calcium in the cell environment