Copyright © 2006, European Society of Cardiology
Down-regulation of ERK but not MEK phosphorylation in cultured endothelial cells by repeated changes in cyclic stretch
aCardiovascular Research Institute, University of Rochester, 601 Elmwood Avenue, Box 679, Rochester, NY 14642, USA
bDepartment of Physiology, Nagoya University Graduate School of Medicine and ICORP/SORST, Cell Mechanosensing, Japan Science and Technology Corporation, Nagoya, Aichi 466-8550, Japan
cDepartment of Molecular Physiology, National Institute for Physiological Sciences, NINS, Okazaki, Aichi 444-8585, Japan
* Corresponding author. Tel.: +1 585 273 5714; fax: +1 585 273 1497. Email address: Keigi_Fujiwara{at}urmc.rochester.edu
Objective: Effects of cyclic stretch on endothelial cells are studied usually by exposing cells cultured under stretch-free conditions to some levels of cyclic stretch, but in vivo these cells experience both increase and decrease in stretch. Experiments were designed to study how endothelial cells maintained under certain levels of cyclic stretch responded to shifts in stretch frequencies and amplitudes.
Methods: Confluent endothelial cells cultured on flexible silicone membranes with or without pre-stretching for 2–12 h were exposed to various levels of stretch amplitude or frequency and assayed for extracellular signal-regulated kinase 1/2 (ERK) phosphorylation.
Results: When endothelial cells without pre-stretching were cyclically stretched, ERK phosphorylation increased, peaking 
15 min and slowly decreased. In contrast, when pre-stretched cells were exposed to either higher or lower stretch condition, ERK phosphorylation transiently decreased within 5 min, indicating that some mechanism which down-regulated ERK phosphorylation was activated. Because phosphorylation of ERK kinase (MEK) was not inhibited in these cells, this mechanism targeted ERK directly, not the upstream kinases of the Ras–Raf–MEK–ERK cascade. Furthermore, this ERK down-regulation in pre-stretched cells was not induced by agonists, was inhibited by Na3VO4 but not okadaic acid, and was detected in the cytosolic fraction. Repeated shifts in stretch conditions induced continuous down-regulation of ERK but not MEK phosphorylation.
Conclusions: Endothelial cells are capable of down-regulating ERK phosphorylation in a cyclic stretch- and tyrosine phosphatase-dependent manner. Frequent changes in stretch conditions constitutively activated this ability, which could play some role in regulating ERK activity in endothelial cells in vivo.
KEYWORDS Endothelial function; MAP kinase; Mechanotransduction; Pre-conditioning; Protein phosphatases
Time for primary review 23 days
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