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2005
|
vol. 52
|
issue 4
927-930
EN
In this study the contribution of the ERK1/2 pathway to sphingosine-induced death and morphological changes of the actin cytoskeleton in glioma C6 cells was investigated. Surprisingly, the level of ERK1/2 phosphorylation does not change after incubation of cells with sphingosine. Despite this, sphingosine induces rounding and detachment of cells without formation of apoptotic bodies. To shed light on this process, a specific inhibitor of ERK1/2 phosphorylation, U0126, was used. Cells incubated simultaneously with sphingosine and U0126 not only detached, but also exhibited formation of apoptotic-like blebs. These data suggest that during sphingosine-induced glioma C6 cell death apoptotic blebbing is dependent on ERK1/2 signalling and occurs only when ERK1/2 activity is decreased or abolished.
EN
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.
EN
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.
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