ELL is an HIF-1 alpha Partner That Regulates and Responds to Hypoxia Response in PC3 Cells

BACKGROUND. Eleven nineteen lysine-rich leukemia (ELL) plays an important role in tumorigenesis and animal development. HIF-1 is a transcriptional factor that functions as a master regulator of O-2 homeostasis. Our previous studies showed that a binding partner of ELL, U19/Eaf2, can modulate HIF-1 alpha activity and hypoxia response, suggesting that ELL may also influence HIF-1 alpha pathway and hypoxia response. METHODS. Co-localization and co-immunoprecipitation were performed to test the interaction between ELL and HIF-1 alpha. PC3 cells with stable ELL knockdown and PC3 cells with stable ELL overexpression, along with their controls, were established using lentiviral expression system. Western blot and real-time PCR were performed to test the effect of ELL on HIF-1 alpha protein and its down-stream gene transcription. To elucidate potential effect of hypoxia on ELL, cell growth and colony formation assays were performed using PC3 subline with stable ELL overexpression. RESULTS. ELL is associated with HIF-1 alpha in transfected cells. In PC3 prostate cancer cells, ELL inhibited HIF-1 alpha protein level and down-stream gene expression. As expected, ELL inhibited cell growth and colony formation under normoxia. Interestingly, the inhibition was alleviated under hypoxia. CONCLUSIONS. Our findings suggest that ELL and HIF-1 alpha are binding partners and can modulate the functions of each other in hypoxia. Prostate 70: 797-805, 2010. (C) 2010 Wiley-Liss, Inc