Tipping the balance of PHD-2 leads to tumor growth retardation

Ben Wielockx, Anne Klotzsche-von Ameln, Antje Muschter, Joanna Kalucka, Ina Prade, Soulafa Mamlouk, Maryam Rezaei, Kristin Franke and Georg Breier

Institute of Pathology - University of Technology Dresden – Germany

Aims: The right amount of nutrients and oxygen are crucial for a tumor to develop. Therefore, angiogenesis can be induced by HIF as a response to deprivation of oxygen in the tumor. The HIF-prolyl hydroxylases strictly regulate these processes, but for the moment not many in vivo experiments have been conducted demonstrating the role of PHDs in the tumor cell and highlighting their cross-talk with the endothelium. Therefore, our research group is studying in detail the modulation of PHD-2 in different tumor cell lines in mice.

Results: We demonstrate here that knocking down PHD-2 expression in a mouse osteosarcoma cell line, using independent shRNA constructs, resulted in a significant induction of vessel density in vivo, as could be expected. Surprisingly however was the observation that these tumors hardly grew and in some cases even completely disappeared in time; a feature that was accompanied by a reduced proliferation rate of the tumor cells rather then necrosis. On the other hand, over-expression of hPHD-2 in the same cell line significantly reduced vessel density, again accompanied by retardation of tumor growth and reduced cell death in comparison to their wild type counterparts. In search for the molecular background of these findings we found that the TGF-beta pathway was activated in all PHD-2 modulated cells during all stages of tumor development. On the other hand, we could only significantly reverse tumor growth retardation and proliferation, induced by TGF-beta  in sh-PHD2 tumors. In addition, we were able to identify the proteins that are involved in the activation of TGF-beta.

Conclusions: In conclusion, modulating PHD-2 in this mouse osteosarcoma cell line (and others) always results in reduced tumor growth and is, at least in cells where PHD-2 is knocked down, independent of angiogenesis.