Down-Regulation of Na+/K+ ATPase Activity by Human Parvovirus B19 Capsid Protein VP1

Abstract

Background/Aims: Human parvovirus B19 (B19V) may cause inflammatory cardiomyopathy (iCMP) which is accompanied by endothelial dysfunction. The B19V capsid protein VP1 contains a lysophosphatidylcholine producing phospholipase A2 (PLA) sequence. Lysophosphatidylcholine has in turn been shown to inhibit Na⁺/K⁺ ATPase. The present study explored whether VP1 modifies Na⁺/K⁺ ATPase activity. Methods: Xenopus oocytes were injected with cRNA encoding VP1 isolated from a patient suffering from fatal B19V-iCMP or cRNA encoding PLA2-negative VP1 mutant (H153A) and K⁺ induced pump current (I_pump) as well as ouabain-inhibited current (I_ouabain) both reflecting Na⁺/K⁺-ATPase activity were determined by dual electrode voltage clamp. Results: Injection of cRNA encoding VP1, but not of VP1(H153A) or water, was followed by a significant decrease of both, I_pump and I_ouabain in Xenopus oocytes. The effect was not modified by inhibition of transcription with actinomycin (10 µM for 36 hours) but was abrogated in the presence of PLA2 specific blocker 4-bromophenacylbromide (50 µM) and was mimicked by lysophosphatidylcholine (0.5 - 1 µg/ml). According to whole cell patch clamp, lysophosphatidylcholine (1 µg /ml) similarly decreased I_pump in human microvascular endothelial cells (HMEC). Conclusion: The B19V capsid protein VP1 is a powerful inhibitor of host cell Na⁺/K⁺ ATPase, an effect at least partially due to phospholipase A2 (PLA2) dependent formation of lysophosphatidylcholine.