Regulation of the hypoxia-inducible factor 1 alpha by the inflammatory mediators nitric oxide and tumor necrosis factor-alpha in contrast to desferroxamine and phenylarsine oxide
Kb. Sandau et al., Regulation of the hypoxia-inducible factor 1 alpha by the inflammatory mediators nitric oxide and tumor necrosis factor-alpha in contrast to desferroxamine and phenylarsine oxide, J BIOL CHEM, 276(43), 2001, pp. 39805-39811
Hypoxic/ischemic conditions provoke activation of the hypoxia-inducible fac
tor-1 (HIF-1), which functions as a transcription factor. HIF-1 is composed
of the HIF-1 alpha and -beta subunits, and stability regulation occurs via
accumulation/degradation of HIF-1 a with the notion that a prolyl hydroxyl
ase accounts for changes in protein level. In addition, there is evidence t
hat HIF-1 is up-regulated by diverse agonists during normoxia. We investiga
ted the impact of inflammatory mediators nitric oxide (NO) and tumor necros
is factor-alpha (TNF-alpha) on HIF-1 alpha regulation. For comparison, LLC-
PK1 cells were exposed to hypoxia, stimulated with desferroxamine (DFX, kno
wn to mimic hypoxia), and the thiol-crosslinking agent phenylarsine oxide (
PAO). Although all stimuli elicited HIF-1 alpha stabilization with differen
ces in the time-dependent accumulation pattern, significant variations appe
ared with regard to signaling. With the use of a superoxide anion (O-2(-))
generator, we established an O-2(-)-sensitive pathway that blocked HIF-1 al
pha stabilization in response to NO and TNF-alpha while DFX- and PAO-evoked
HIF-1 alpha stabilization appeared O-2(-)-insensitive. NO and TNF-alpha si
gnaling required phosphorylation events, especially activation of the phosp
hatidylinositol 3-kinase/Akt, which is in contrast to DFX and PAO. Based on
HIF-1-dependent luciferase reporter gene analysis, it was found that, in c
ontrast to NO and TNF-alpha, PAO resembled a stimulus that induced a dysfun
ctional HIF-1 complex. These data indicate that diverse agonists activate H
IF-1 a under normoxic conditions by employing different signaling pathways.