Abstract
The activation/inactivation of HIF1α is precisely regulated in an oxygen-dependent manner. HIF1α 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 HIF1α 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 HIF1α, because we identified that VHL, a negative regulator of HIF1α, is a novel target of miR-101 and over-expression of miR-101 decreased VHL levels and subsequently stabilized HIF1α and induced its downstream target VEGFA. Furthermore, we demonstrated that siRNA-mediated knockdown of VHL or HIF1α 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 HIF1α, could rescue cells from such inhibition. These results reveal a novel regulatory mechanism of HIF1α induction in normoxia and suggest that miR-101 mediated proliferation inhibition may through HIF1α mediated apoptosis and cell cycle arrest.