Aiming straight for the heart: prolyl hydroxylases set the BAR

Therapeutic targeting of 3',5'-cyclic nucleotide phosphodiesterases: inhibition and beyond

Phosphodiesterases (PDEs), enzymes that degrade 3',5'-cyclic nucleotides, are being pursued as therapeutic targets for several diseases, including those affecting the nervous system, the cardiovascular system, fertility, immunity, cancer and metabolism. Clinical development programmes have focused exclusively on catalytic inhibition, which continues to be a strong focus of ongoing drug discovery efforts. However, emerging evidence supports novel strategies to therapeutically target PDE function, including enhancing catalytic activity, normalizing altered compartmentalization and modulating post-translational modifications, as well as the potential use of PDEs as disease biomarkers. Importantly, a more refined appreciation of the intramolecular mechanisms regulating PDE function and trafficking is emerging, making these pioneering drug discovery efforts tractable.

Centrosomes tune in to metabolic state and turn on to oxygen

Events required for cell-cycle progression, including centriole duplication and mitotic spindle formation, are obligatorily linked to the metabolic state of a cell. In this issue of Developmental Cell, Moser et al. (2013) show that PHD1 can act as such a sensor through proline hydroxylation of the centrosomal protein Cep192.

Prolyl hydroxylase domain protein 2 regulates the intracellular cyclic AMP level in cardiomyocytes through its interaction with phosphodiesterase 4D

Cyclic adenosine 3',5'-monophosphate (cAMP), which is synthesized by adenylyl cyclase (AC) and degraded by phosphodiesterase (PDE), plays crucial roles in the regulation of multiple cellular functions and physiological processes. Prolyl hydroxylase domain (PHD) proteins, which belong to a family of dioxygenases that function as oxygen sensors through their hydroxylation activity, have been implicated in multiple signaling pathways. Here, we aimed to determine whether PHD played a role in regulating intracellular cAMP level in cardiomyocytes. Through the overexpression/knockdown of the PHD gene and the measurement of the cAMP content, we found that PHD2, but not PHD1 or PHD3, acts as a regulator of intracellular cAMP. In neonatal rat cardiomyocytes and H9c2 cells, the overexpression of PHD2 increased the intracellular cAMP level, whereas the PHD2 knockdown reduced it. There was no alteration in the AC expression or activity in cells that overexpressed or downregulated PHD2. The overexpression of PHD2 decreased both the protein expression and the activity of phosphodiesterase 4D (PDE4D), whereas the PHD2 knockdown increased the PDE4D expression and activity. Co-immunoprecipitation experiments revealed a direct binding between PHD2 and PDE4D and liquid chromatography-tandem mass spectrometry analyses identified the specific hydroxylation sites on PDE4D. In conclusion, PHD2 may directly interact with PDE4D to function as a novel regulator of the intracellular cAMP levels in cardiomyocytes.

Suppression of glioma progression by Egln3

Grade IV astrocytoma or glioblastoma has a poor clinical outcome that can be linked to hypoxia, invasiveness and active vascular remodeling. It has recently been suggested that hypoxia-inducible factors, Hifs, increase glioma growth and aggressiveness [1], [2], [3]. Here, we tested the hypothesis that Egl 9 homolog 3 (Egln3), a prolyl-hydroxylase that promotes Hif degradation, suppresses tumor progression of human and rodent glioma models. Through intracranial tumorigenesis and in vitro assays, we demonstrate for the first time that Egln3 was sufficient to decrease the kinetics of tumor progression and increase survival. We also find that Klf5, a transcription factor important to vascular remodeling, was regulated by hypoxia in glioma. An analysis of the tumor vasculature revealed that elevated Egln3 normalized glioma capillary architecture, consistent with a role for Egln3 in eliciting decreases in the production of Hif-regulated, angiogenic factors. We also find that the hydroxylase-deficient mutant, Egln3^H196A partially maintained tumor suppressive activity. These results highlight a bifurcation of Egln3 signaling and suggest that Egln3 has a non-hydroxylase-dependent function in glioma. We conclude that Egln3 is a critical determinant of glioma formation and tumor vascular functionality.