Musaab Ahmed1, Sabina Honisch1, Lisann Pelzl1, Myriam Fezai1, Zohreh Hosseinzadeh1, C-Thomas Bock2, Reinhard Kandolf2, Florian Lang3. 1. Department of Physiology, University of Tuebingen, Gmelinstr. 5, 72076 Tuebingen, Germany. 2. Department of Molecular Pathology, University of Tuebingen, Liebermeisterstraße 8, 72076 Tuebingen, Germany. 3. Department of Physiology, University of Tuebingen, Gmelinstr. 5, 72076 Tuebingen, Germany. Electronic address: florian.lang@uni-tuebingen.de.
Abstract
BACKGROUND: Clinical disorders caused by parvovirus B19 (B19V) infection include endothelial dysfunction with cardiac ischemia. The virus is effective in part by lysophosphatidylcholine-producing phospholipase A2 (PLA2) activity of B19V capsid protein VP1. Mechanisms compromising endothelial function include up-regulation of amiloride sensitive epithelial Na(+)-channel ENaC leading to endothelial cell stiffness. Regulators of ENaC include ubiquitin-ligase Nedd4-2. The present study explored whether VP1 modifies ENaC-activity. METHODS: cRNA encoding ENaC was injected into Xenopus oocytes without or with cRNA encoding VP1. Experiments were made with or without coexpression of Nedd4-2. ENaC activity was estimated from amiloride (50 μM) sensitive current. RESULTS: Injection of cRNA encoding ENaC into Xenopus oocytes was followed by appearance of amiloride sensitive current, which was significantly enhanced by additional injection of cRNA encoding VP1, but not by additional injection of cRNA encoding PLA2-negative VP1 mutant (H153A). The effect of VP1 on ENaC was mimicked by treatment of ENaC expressing oocytes with lysophosphatidylcholine (1 μg/ml). The effect of VP1 and lysophosphatidylcholine was not additive. ENaC activity was downregulated by Nedd4-2, an effect not reversed by VP1. CONCLUSIONS: The B19V capsid protein VP1 up-regulates ENaC, an effect at least partially due to phospholipase A2 (PLA) dependent formation of lysophosphatidylcholine.
BACKGROUND: Clinical disorders caused by parvovirus B19 (B19V) infection include endothelial dysfunction with cardiac ischemia. The virus is effective in part by lysophosphatidylcholine-producing phospholipase A2 (PLA2) activity of B19V capsid protein VP1. Mechanisms compromising endothelial function include up-regulation of amiloride sensitive epithelial Na(+)-channel ENaC leading to endothelial cell stiffness. Regulators of ENaC include ubiquitin-ligase Nedd4-2. The present study explored whether VP1 modifies ENaC-activity. METHODS: cRNA encoding ENaC was injected into Xenopus oocytes without or with cRNA encoding VP1. Experiments were made with or without coexpression of Nedd4-2. ENaC activity was estimated from amiloride (50 μM) sensitive current. RESULTS: Injection of cRNA encoding ENaC into Xenopus oocytes was followed by appearance of amiloride sensitive current, which was significantly enhanced by additional injection of cRNA encoding VP1, but not by additional injection of cRNA encoding PLA2-negative VP1 mutant (H153A). The effect of VP1 on ENaC was mimicked by treatment of ENaC expressing oocytes with lysophosphatidylcholine (1 μg/ml). The effect of VP1 and lysophosphatidylcholine was not additive. ENaC activity was downregulated by Nedd4-2, an effect not reversed by VP1. CONCLUSIONS: The B19V capsid protein VP1 up-regulates ENaC, an effect at least partially due to phospholipase A2 (PLA) dependent formation of lysophosphatidylcholine.