How does the cell control the level of HIF1 alpha activation? The phosphorylation status of HIF1 alpha is the main mechanism to regulate HIF1 alpha activity. A ligand binds to HIF1 alpha inducing its translocation into the nucleus. The cell controls the level of ARNT A prolyl hydroxylase controls the level of HIF1 alpha proline hydroxylation that can in turn regulate HIF1 alpha proteolysis..