Prolyl-hydroxylase 4 over-expression inhibits tumor growth by stimulating non functional angiogenesis

Anne Klotzsche – von Ameln, Ina Prade, Ben Wielockx and

Georg Breier

Institut für Pathologie, Universitätsklinikum Dresden

Aims: Hypoxia plays a major role in tumor vascularization and progression. The cellular hypoxia response is mediated by hypoxia-inducible factors (HIFs) which in turn are regulated by HIF prolyl-hydroxylases (PHDs). The goal of our project is to elucidate the function of PHD-4 in tumor progression.

Methods: Generation of stable PHD-4 over-expressing LM8 osteosarcomas and embryonic endothelial progenitor cells (eEPCs). In vitro: analysis of the HIF stability by Western blot; microarray analysis and angiogenesis/sprouting assay. In vivo: PHD-4 over-expressing LM8 tumor cells were subcutaneously injected in the back of C3H mice. Tumor growth was monitored and isolated tumors were histologically analyzed. 

Results: PHD-4 over-expressing LM8 tumor cells and eEPCs reduced the HIF2α protein level under hypoxia, whereas there was no effect on HIF1α stability. In a syngeneic mouse tumor model, PHD-4 over-expression in LM8 osteosarcomas reduced tumor growth, due to an increased, but non-functional neoangiogenesis. This can be explained by an increased TGFα expression in LM8 cells over-expressing PHD-4, which increases endothelial cell side-sprout branching.

Conclusions: PHD-4 over-expression in tumor cells reduces tumor growth by the up-regulation of TGFα, which leads to an excessive, but non-functional angiogenesis. These data indicate that PHD-4 plays an important role in tumor progression.