"A crucial step in the adaptation of mammalian cells to oxygen deficiency is the transcriptional activation of hypoxia-inducible genes. Hypoxia-inducible transcription factors (HIFs) are master regulators for the up-regulation of these genes under physiological as well as pathophysiological conditions, such as tumor development and metastasis, cardiovascular diseases and inflammation. HIFs are O2-dependently hydroxylated at conserved prolyl residues by recently discovered prolyl-4-hydroxylase domain proteins (PHDs). Therefore, PHDs function as molecular oxygen sensors by determining the protein stability of HIFα subunits. Importantly, non-HIFα proteins have been reported to represent PHD hydroxylation substrates, indicating that O2-dependent prolyl hydroxylation might be a more common post-translational modification than previously expected. The aim of this grant application is to study the function of the RNA helicase HELZ that was identified to interact with PHD2. HELZ has been shown to be important for the function of SMYD3, a histone lysine methyltransferase which has been implicated in tumorigenesis. Preliminary data demonstrate O2-dependent regulation of HELZ protein abundance and suggest that HELZ might be a novel PHD2 hydroxylation substrate. The goal is to generate a conditional HELZ gene targeting model to characterize the O2-dependent function of HELZ in vivo and to investigate PHD2-dependent HELZ protein hydroxylation by mass spectrometry."