HIF-2alpha-dependent PAI-1 induction contributes to angiogenesis in hepatocellular carcinoma.
Hypoxia promotes progression of hepatocellular carcinoma (HCC), not only affecting tumor cell proliferation and invasion, but also angiogenesis and thus, increasing the risk of metastasis. Hypoxia inducible factors (HIF)-1α and -2α cause adaptation of tumors to hypoxia, still with uncertainties towards the angiogenic switch. We created a stable knockdown of HIF-1α and HIF-2α in HepG2 cells and generated cocultures of HepG2 spheroids with embryonic bodies as an in vitro tumor model mimicking the cancer microenvironment. The naturally occuring oxygen and nutrient gradients within the cocultures allow us to question the role of distinct HIF isoforms in regulating HCC angiogenesis. In cocultures with a HIF-2α knockdown, angiogenesis was attenuated, while the knockdown of HIF-1α was without effect. Microarray analysis identified plasminogen activator inhibitor 1 (PAI-1) as a HIF-2α target gene in HepG2 cells. The knockdown of PAI-1 in HepG2 cells also lowered angiogenesis. Blocking plasmin, the downstream target of PAI-1, with aprotinin in HIF-2α knockdown (k/d) cells proved a cause-effect relation and restored angiogenesis, with no effect on control cocultures. Suggestively, HIF-2α increases PAI-1 to lower concentrations of active plasmin, thereby supporting angiogenesis. We conclude that the HIF-2α target gene PAI-1 favors the angiogenic switch in HCC.
['Geis|Theresa|T|', 'Döring|Claudia|C|', 'Popp|Rüdiger|R|', 'Grossmann|Nina|N|', 'Fleming|Ingrid|I|', 'Hansmann|Martin-Leo|ML|', 'Dehne|Nathalie|N|', 'Brüne|Bernhard|B|']
D051792:Basic Helix-Loop-Helix Transcription Factors D014408:Biomarkers, Tumor D015153:Blotting, Western D006528:Carcinoma, Hepatocellular D005434:Flow Cytometry D005455:Fluorescent Antibody Technique D020869:Gene Expression Profiling D015972:Gene Expression Regulation, Neoplastic D006801:Humans D007124:Immunoenzyme Techniques D008113:Liver Neoplasms D009389:Neovascularization, Pathologic D020411:Oligonucleotide Array Sequence Analysis D017395:Plasminogen Activator Inhibitor 1 D012333:RNA, Messenger D060888:Real-Time Polymerase Chain Reaction D020133:Reverse Transcriptase Polymerase Chain Reaction D014407:Tumor Cells, Cultured
Plasmin Aprotinin Spheroid-embryonic body-coculture Tumor hypoxia