Plasma Membrane Cholesterol Is a Key Molecule in Shear Stress-dependent Activation of Extracellular Signal-regulated Kinase

Abstract

272, 1395-1401).Here, we examine whether cholesterol-enriched compartments in the plasma membrane are responsible for such differential regulation. Pretreatment of BAEC with a cholesterol-binding antibiotic, filipin, did not inhibit shear-dependent activation of JNK. In contrast, filipin and other membrane-permeable cholesterol-binding agents (digitonin and nystatin), but not the lipid-binding agent xylazine, inhibited shear-dependent activation of ERK. The effect of cholesterol-binding drugs did not appear to be due to membrane permeabilization, since treatment of BAEC with a detergent, Triton X-100 which also permeabilizes membranes, did not inhibit shear-dependent activation of ERK. Furthermore, shear-dependent activation of ERK, but not JNK, was inhibited by cyclodextrin, a membrane-impermeable cholesterol-binding agent, which removes cell-surface cholesterol. Moreover, the effects of cyclodextrin were prevented by adding cholesterol during the incubation. These results indicate that cholesterol or cholesterol-sensitive compartments in the plasma membrane play a selective and essential role in activation of ERK, but not JNK, by shear stress. Although exposure to shear stress (1 h) increased the number of caveolae by 3-fold, treatment with filipin had no effect in either control or shear-exposed cells suggesting that caveolae density per se is not a crucial determinant in shear-dependent ERK activation. In summary, the current study suggests that cholesterol-sensitive microdomains in the plasma membrane, such as caveolae-like domains, play a critical role in differential activation of ERK and JNK by shear stress.Vascular endothelial cells recognize shear stress by unknown mechanosensing system(s) that respond both acutely and chronically to flow by producing autocrine and paracrine factors (1). Through these endothelial responses, shear stress controls vascular tone, vessel wall remodeling, binding of blood cells to endothelium, and hemostasis (1). Shear stress selectively and differentially regulates expression of many genes that are important in the pathophysiology of vessel wall function (2-10). Furthermore, a conserved cis-acting shear stress response element has been identified in many shear-sensitive genes including platelet-derived growth factor-B, intercellular adhesion molecule-1, tissue plasminogen activator, and transforming growth factor ␤-1, suggesting its broad implication in shear-dependent regulation of gene expressions (6,8). Shear stress also transiently activates nuclear factor-B, immediate early response genes, and transcription factors that are likely to be involved in the regulation of shear-dependent gene expression (8,11).How does shear stress selectively and differentially regulate such a diverse range of nuclear responses? At least some of these responses appeared to be mediated through regulation of MAP 1 kinases (12-16). Members of the MAP kinase family, ERK, JNK (also known as stress-activated protein kinase), and p38 kinase, have been proposed as important signaling components li...

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Essential Role of Caveolae in Interleukin-6- and Insulin-like Growth Factor I-triggered Akt-1-mediated Survival of Multiple Myeloma Cells

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