p42/p44 mitogen-activated protein kinases phosphorylate hypoxia-inducible factor 1 alpha (HIF-1 alpha) and enhance the transcriptional activity of HIF-1
De. Richard et al., p42/p44 mitogen-activated protein kinases phosphorylate hypoxia-inducible factor 1 alpha (HIF-1 alpha) and enhance the transcriptional activity of HIF-1, J BIOL CHEM, 274(46), 1999, pp. 32631-32637
Hypoxia-inducible factor-1 (HIF-1) controls the expression of a number of g
enes such as vascular endothelial growth factor and erythropoietin in low o
xygen conditions. However, the molecular mechanisms that underlie the activ
ation of the limiting subunit, HIF-1 alpha, are still poorly resolved, Resu
lts showing that endogenous HIF-1 alpha migrated 12 kDa higher than in vitr
o translated protein led us to evaluate the possible role of phosphorylatio
n on this phenomenon. We report here that HIF-1 alpha is strongly phosphory
lated in vivo and that phosphorylation is responsible for the marked differ
ences in the migration pattern of HIF-1 alpha, In vitro, HIF-1 alpha: is ph
osphorylated by p42 and p44 mitogen-activated protein kinases (MAPKs) and n
ot by p38 MAPK or c-Jun N-terminal kinase, interestingly p42/p44 MAPK stoic
hiometrically phosphorylate HIF-1 alpha in vitro, as judged by a complete u
pper shift of HIF-1 alpha. More importantly, we demonstrate that activation
of the p42/p44 MAPK pathway in quiescent cells induced the phosphorylation
and shift of HIF-1 alpha, which was abrogated in presence of the MEK inhib
itor, PD 98059, Finally, we found that in a vascular endothelial growth fac
tor promoter mutated at sites previously shown to be MAPK-sensitive (SP1/AP
2-88-66 site), p42/p44 MAPK activation is sufficient to promote the transcr
iptional activity of HIF-1, This interaction between HIF-1 alpha and p42/p4
4 MAPK suggests a cooperation between hypoxic and growth factor signals tha
t ultimately leads to the increase in RIF-l-mediated gene expression.