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

TLDR

Human parvovirus B19 can cause inflammatory cardiomyopathy with endothelial dysfunction, and its capsid protein VP1 contains a phospholipase A2 motif that generates lysophosphatidylcholine, a known inhibitor of Na⁺/K⁺‑ATPase. The study aimed to determine whether VP1 alters Na⁺/K⁺‑ATPase activity. Using Xenopus oocytes injected with cRNA encoding either wild‑type VP1 or a PLA2‑negative mutant, the authors measured pump currents (Ipump and Iouabain) by dual‑electrode voltage clamp. Wild‑type VP1 markedly decreased both currents, an effect blocked by a PLA2 inhibitor and reproduced by lysophosphatidylcholine, and similarly reduced pump activity in human microvascular endothelial cells, demonstrating that VP1 inhibits Na⁺/K⁺‑ATPase via PLA2‑dependent lysophosphatidylcholine production.

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 (Ipump) as well as ouabain-inhibited current (Iouabain) 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, Ipump and Iouabain 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 Ipump 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.