Microrna-101 Targets Von Hippel-Lindau Tumor Suppressor (Vhl) To Induce Hif1 Alpha Mediated Apoptosis And Cell Cycle Arrest In Normoxia Condition

The activation/inactivation of HIF1 alpha is precisely regulated in an oxygen-dependent manner. HIF1 alpha is essential for hypoxia induced apoptosis and cell cycle arrest. Several recent studies indicated that the expression of miRNAs can be modulated by hypoxia. However, the involvement of miRNAs in the regulation of HIF1 alpha induction remains elusive. In present study, we demonstrated that miR-101 was rapidly and transiently induced after hypoxia in breast cancer cells. Over-expression of miR-101 significantly inhibited cell proliferation in breast cancer cells through increased apoptosis and cell cycle arrest in normoxia condition. This inhibitory phenomenon seems due to miR-101-mediated induction of HIF1 alpha, because we identified that VHL, a negative regulator of HIF1 alpha, is a novel target of miR-101 and over-expression of miR-101 decreased VHL levels and subsequently stabilized HIF1 alpha and induced its downstream target VEGFA. Furthermore, we demonstrated that siRNA-mediated knockdown of VHL or HIF1 alpha overexpression could also induce apoptosis and cell cycle arrest whereas enforced expression of VHL, administration of anti-miR-101 oligos or treatment of 2-MeOE2, an inhibitor of HIF1 alpha, could rescue cells from such inhibition. These results reveal a novel regulatory mechanism of HIF1 alpha induction in normoxia and suggest that miR-101 mediated proliferation inhibition may through HIF1 alpha mediated apoptosis and cell cycle arrest.