HIF-1α stabilisation regulates cell area.

<p>(A) Schematic drawing of HIF-1 and its regulation in normoxia and hypoxia. The stability of the HIF-1α subunit is regulated by prolyl-4-hydroxylase domain (PHD) enzymes in an oxygen dependent manner. Following hydroxylation of the critical prolyl residues under normoxic conditions, the ubiquitin ligase von Hippel-Lindau tumor suppressor protein (pVHL) recognises HIF-1α subunits and targets them for rapid ubiquitination and proteasomal degradation under normoxic conditions. Hypoxia impairs the hydroxylation, which results in HIF-1α stabilisation, nuclear accumulation, heterodimerisation with HIF-1β and subsequent hypoxia-inducible gene expression. (B) Inhibition of PHDs by DMOG causes HIF-1α stabilisation under normoxic conditions. L929 cells were treated with 1 mM DMOG for 48 hrs and total extracts were analysed by immunoblot with the respective antibodies. (C) The cell area of DMOG treated cells increased significantly. The cell area of single cells was measured and was calculated as fold change compared to 20% O_2. (D) Two HIF-1α knock down cell clones (c1, c2) and a non-target control shRNA cell clone (shC) were obtained via stable transduction of specific sh-plasmids. The HIF-1α knock down was verified in western blot experiments of cell lysates from cells incubated at 20% O₂ or 1% O₂. β-tubulin was used as a loading control. (E) HIF-1α knock down cell clones (c1, c2) do not respond to hypoxia with an increase in cell area. The cell area of single cells was measured and was calculated as fold change compared to the cell clone cultivated at 20% O₂. (F) Flow cytometry analysis of cell volume after incubation in normoxia and hypoxia. shC, c1 and c2 cells were harvested after 24 hrs of normoxic (20% O₂) or hypoxic (1% O₂) incubation. Single cell suspension was prepared by enzymatic digestion. Note that hypoxia increases the cell volume independently of the HIF-1α knock down.