Chronic
inflammation leads to the formation of a pro-tumorigenic microenvironment that can promote
tumor development, growth and differentiation through augmentation of
tumor angiogenesis.
Prostate cancer (CaP) risk and prognosis are adversely correlated with a number of inflammatory and angiogenic mediators, including
Toll-like receptors (TLRs), NF-κB and
vascular endothelial growth factor (
VEGF).
Peroxiredoxin 1 (Prx1) was recently identified as an endogenous
ligand for TLR4 that is secreted from CaP cells and promotes
inflammation. Inhibition of Prx1 by CaP cells resulted in reduced expression of
VEGF, diminished
tumor vasculature and retarded
tumor growth. The mechanism by which Prx1 regulates
VEGF expression in normoxic conditions was investigated in the current study. Our results show that incubation of mouse vascular endothelial cells with recombinant Prx1 caused increases in
VEGF expression that was dependent upon TLR4 and required
hypoxia inducible factor-1 (HIF-1) interaction with the
VEGF promoter. The induction of
VEGF was also dependent upon NF-κB; however, NF-κB interaction with the
VEGF promoter was not required for Prx1 induction of
VEGF suggesting that NF-κB was acting indirectly to induce
VEGF expression. The results presented here show that Prx1 stimulation increased NF-κB interaction with the HIF-1α promoter, leading to enhanced promoter activity and increases in HIF-1α
mRNA levels, as well as augmented HIF-1 activity that resulted in
VEGF expression. Prx1 induced HIF-1 also promoted NF-κB activity, suggesting the presence of a positive feedback loop that has the potential to perpetuate Prx1 induction of angiogenesis. Strikingly, inhibition of Prx1 expression in CaP was accompanied with reduced expression of HIF-1α. The combined findings of the current study and our previous study suggest that Prx1 interaction with TLR4 promotes CaP growth potentially through chronic activation of
tumor angiogenesis.