MAPKs (ERK½, p38) and AKT Can Be Phosphorylated by Shear Stress Independently of Platelet Endothelial Cell Adhesion Molecule-1 (CD31) in Vascular Endothelial Cells

Bauer E Sumpio,Sangseob Yun,Alfredo C Cordova,Masae Haga,Jin Zhang,Yongbok Koh,Joseph A Madri

doi:10.1074/jbc.m414631200

Abstract

PECAM-1 (CD31) is a member of the Ig superfamily of cell adhesion molecules and is expressed on endothelial cells (EC) as several circulating blood elements including platelets, polymorphonuclear leukocytes, monocytes, and lymphocytes. PECAM-1 tyrosine phosphorylation has been observed following mechanical stimulation of EC but its role in mechanosensing is still incompletely understood. The aim of this study was to investigate the involvement of PECAM-1 in signaling cascades in response to fluid shear stress (SS) in vascular ECs. PECAM-1-deficient (KO) and PECAM-reconstituted murine microvascular ECs, 50 and 100% confluent bovine aortic EC (BAEC), and human umbilical vein EC (HUVEC) transfected with antisense PECAM-1 oligonucleotides were exposed to oscillatory SS (14 dynes/cm2) for 0, 5, 10, 30 or 60 min. The tyrosine phosphorylation level of PECAM-1 immunoprecipitated from SS-stimulated PECAM-reconstituted, but not PECAM-1-KO, murine ECs increased. Although PECAM-1 was phosphorylated in 100% confluent BAEC and HUVEC, its phosphorylation level in 50% confluent BAECs or HUVEC was not detected by SS. Likewise PECAM-1 phosphorylation was robust in the wild type and scrambled-transfected HUVEC but not in the PECAM-1 antisense-HUVEC. ERK(1/2), p38 MAPK, and AKT were activated by SS in all cell types tested, including the PECAM-1-KO murine ECs, 50% confluent BAECs, and HUVEC transfected with antisense PECAM-1. This suggests that PECAM-1 may not function as a major mechanoreceptor for activation of MAPK and AKT in ECs and that there are likely to be other mechanoreceptors in ECs functioning to detect shear stress and trigger intercellular signals.

Highlights

Vascular endothelial cells (ECs)1 line the luminal surface of blood vessels and are constantly exposed to hemodynamic forces of blood flow such as fluid shear stress, cyclic strain, and blood pressure
Other investigators have recently demonstrated that a glycoprotein, platelet endothelial cell adhesion molecule-1 (PECAM-1) is rapidly tyrosine-phosphorylated in bovine ECs (BAEC) exposed to fluid flow; this is thought to play important roles in transducing chemical stimuli received on the cell surface to the cytoplasmic aspects of the cell (13, 14)
Effect of Cell-Cell Contact of bovine aortic EC (BAEC) or human umbilical vein EC (HUVEC) Exposed to Fluid Shear Stress on PECAM-1 Tyrosine Phosphorylation and ERK1/2, p38 mitogen-activated protein kinase (MAPK), and AKT Activation—PECAM-1 protein is predominantly localized at lateral cell-cell adhesion sites in confluent EC but not in sparsely cultured cells

Summary

Introduction

Vascular endothelial cells (ECs) line the luminal surface of blood vessels and are constantly exposed to hemodynamic forces of blood flow such as fluid shear stress, cyclic strain, and blood pressure. These mechanical forces induce morphological, physiological, and biochemical changes of ECs (1, 2). We and other laboratories have reported that fluid shear stress activates several members of the MAPK family including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK in cultured bovine ECs (1, 25) Another distinct but important cell signaling pathway, phosphatidylinositol 3-kinase-AKT, has been shown to be activated by fluid shear stress and other hemodynamic forces (26, 27). We compare the results from confluent cultured and sparsely cultured BAEC and HUVEC

Objectives

Results

Conclusion