Visualization of the three-dimensional organization of hypoxia-inducible factor-1α and interacting cofactors in subnuclear structures

Cells need oxygen (O-2) to meet their metabolic demands. Highly efficient systems of O-2-sensing have evolved to initiate responses enabling cells to adapt their metabolism to reduced O-2 availability. Of central importance is the activation of hypoxiainducible factor-1 (HIF-1), a transcription factor complex that controls the expression of genes the products of which regulate glucose uptake and metabolism, vasotonus and angiogenesis, oxygen capacity of the blood as well as cell growth and death. Activation of HIF-1 requires the accumulation and nuclear translocation of the HIF-1alpha subunit, its dimerization with HIF-1beta and the binding of coactivator proteins such as p300. In this study we investigated the threedimensional (3D) distribution of HIF-1alpha within the nucleus and assigned its localization to known nuclear compartments. Using twophoton microscopy we determined the colocalization of HIF-1alpha and beta subunits within nuclear domains as well as overlaps between HIF-1alpha and p300. Our data provide information on the nuclear distribution of HIF-1alpha with respect to subnuclear domains that could serve as specific locations for hypoxiainduced gene expression.