Hypoxia-induced pecam-1 phosphorylation and transendothelial
migration of monocytes is due to autocrine effect of paf.
Kalra, Vijay K., Yamin Shen, Chand Sultana, and Vinod Rattan.
Department of Biochemistry and Molecular Biology, University of
Southern California, School of Medicine, Los Angeles, California
90033
APStracts 3:0201H, 1996.
Polymorphonuclear neutrophils (PMN) adhere to the vascular endothelium
under hypoxic conditions, causing microvascular injury. The molecular
mechanism of hypoxia-induced adhesion of PMN to and diapedesis
through the vascular endothelium is poorly understood, although it is
known that platelet-activating factor (PAF) promotes adhesion of PMN.
We examined the effects of hypoxia on the transendothelial migration
of monocytes. Exposure of human umbilical vein endothelial cells
(HUVEC) cultured in Transwell chambers under low oxygen tension (3%
O2, as compared with ambient oxygen tension of 21%) resulted in an
increased rate of migration of both monocyte-like HL-60 cells and
human peripheral blood monocytes. Migration was inhibited by addition
of an antibody to PECAM-1, a protein kinase C (PKC) inhibitor (GF
109203X), or a PAF-receptor antagonist (CV 6209). In HUVEC, hypoxic
conditions (1%, 3%, 5% and 14% O2) increased the phosphorylation of
PECAM-1. The extent of phosphorylation of PECAM-1 was inversely
related to the concentration of oxygen to which HUVEC were exposed:
the phosphorylation of PECAM-1 increased by 26-, 16- and 3-fold when
HUVEC were exposed to 1%, 3% and 5% oxygen tension, respectively.
Hypoxia-induced phosphorylation of PECAM-1 was inhibited by either a
PKC inhibitor or a PAF-receptor antagonist, indicating the
involvement of hypoxia-induced release of PAF in both PKC activation
and the concomitant phosphorylation of PECAM-1. These results were
substantiated by the finding that treatment of HUVEC with 100 nM PAF
under normoxic conditions augmented 11.8-fold the phosphorylation of
PECAM-1 and 2-fold increase in the transendothelial migration of
monocyte-like HL-60 cells. PECAM-1 phosphorylation, as well as
hypoxia- and PAF-induced migration of monocyte-like HL-60 cells, is
increased by the addition of a phosphatase inhibitor, indicating that
PECAM-1 phosphorylation is directly involved in the transendothelial
migration of monocyte-like HL-60 cells. We conclude that PAF,
produced by cultured endothelial cells in response to hypoxia, acts
in an autocrine fashion to activate PKC, causing PECAM-1
phosphorylation and thus the transendothelial migration of monocytes.
Received 4 December 1995; accepted in final form 15 April 1996.
APS Manuscript Number H1125-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 May 96