AJP - Cell Physiology, Vol 263, Issue 4 C767-C772, Copyright © 1992 by American Physiological Society
Induction of ICAM-1 by TNF-alpha, IL-1 beta, and LPS in human endothelial cells after downregulation of PKC
C. L. Myers, S. J. Wertheimer, J. Schembri-King, T. Parks and R. W. Wallace
Department of Biochemistry, Boehringer Ingelheim Pharmaceuticals, Ridgefield, Connecticut 06877.
The intercellular adhesion molecule 1 (ICAM-1) is induced on endothelial
cells by tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1
beta), and lipopolysaccharide (LPS). We have reported the sensitivity of
cytokine-induced ICAM-1 expression to protein kinase inhibitors, including
inhibitors of protein kinase C (PKC) [C. L. Myers, S. N. Desai, J.
Schembri-King, G. L. Letts, and R. W. Wallace. Am. J. Physiol. 262 (Cell
Physiol. 31): C365-C373, 1992]. To directly investigate the role of PKC in
ICAM-1 induction, we downregulated PKC by pretreatment of human umbilical
vein endothelial cells with phorbol 12-myristate 13-acetate (PMA) and
assessed ICAM-1 protein and mRNA induction elicited by subsequent exposure
to inflammatory stimuli. PMA treatment results in ICAM-1 protein induction
that declines to basal levels by 3 days. Western blots of endothelial cell
lysates reveal a nearly complete loss of immunologically reactive PKC.
Subsequent activation with cytokine or LPS leads to reinduction of ICAM-1
protein and mRNA; however, the cells no longer produced substantial amounts
of ICAM-1 protein or mRNA in response to PMA stimulation. Cross
desensitization is observed with phorbol dibutyrate, while 4 alpha-phorbol
has no desensitizing effect. The data indicate that PKC activation, while
capable of inducing ICAM-1 expression, is not essential for ICAM-1
induction by the inflammatory mediators TNF-alpha, IL-1 beta, or LPS.
