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released from activated macrophages stabilize
HIF-1
in resting tubular LLC-PK1 cells
1 Department of Cell Biology, Faculty of Biology, University of Kaiserslautern, 67663 Kaiserslautern; 2 Institute of Physiology, Faculty of Medicine, University of Essen, 45122 Essen; and 3 Institute of Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, University of Erlangen, 91054 Erlangen, Germany
Hypoxic/ischemic conditions
provoke activation of the transcription factor hypoxia-inducible
factor-1 (HIF-1). HIF-1 is composed of HIF-1
(subjected to protein
stability regulation) and constitutively expressed HIF-1
. Besides
hypoxia, diverse agonists are identified that stabilize HIF-1
during
normoxia. Here we used a coculture system of RAW 264.7 macrophage cells
and tubular LLC-PK1 cells to establish that
lipopolysaccharide- and interferon-
-stimulated but not resting
macrophages elicited HIF-1
accumulation in LLC-PK1 cells. Via pharmacological interventions such as blockade of nitric oxide (NO) production in macrophages, scavenging of NO with the use of
2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, or application
of tumor necrosis factor-
(TNF-
)-neutralizing antibodies, we
identified NO and TNF-
as signaling molecules. Working in concert,
NO and TNF-
have a stronger response when allowed direct
cell-to-cell contact instead of contact with only the cell supernatant
of activated macrophages. We show that signal transmission by NO with
TNF-
in LLC-PK1 cells is mediated via the
phosphatidylinositol 3-kinase (PI3-K)/Akt pathway, because it is
blocked by wortmannin or dominant-negative forms of PI3-K as well as
protein kinase B. We conclude that NO and TNF-
, derived from
activated macrophages, provoke HIF-1
stabilization in
LLC-PK1 cells under normoxic conditions, which underscores
HIF-1
stabilization due to intercellular regulation.
nitric oxide; tumor necrosis factor-
; hypoxia-inducible
factor-1; intercellular signaling; phosphatidylinositol 3-kinase; cytokine; Akt
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