Phospholipase A2 Activity-Dependent Stimulation of Ca ²⁺ Entry by Human Parvovirus B19 Capsid Protein VP1

Abstract

Recent reports demonstrated an association of human parvovirus B19 with inflammatory cardiomyopathy (iCMP), which is accompanied by endothelial dysfunction. As intracellular Ca 2؉ activity is a key regulator of cell function and participates in mechanisms leading to endothelial dysfunction, the present experiments explored the effects of the B19 capsid proteins VP1 and VP2. A secreted phospholipase A2 (PLA2)-like activity has been located in the VP1 unique region of the B19 minor capsid protein. As PLA2 has recently been shown to activate the store-operated or capacitative Ca 2؉ channel I CRAC , we analyzed the impact of the viral PLA2 motif on Ca 2؉ entry. We cloned the VP1 and VP2 genes isolated from a patient suffering from fatal B19 iCMP into eukaryotic expression vectors. We also generated a B19 replication-competent plasmid to demonstrate PLA2 activity under the control of the complete B19 genome. After the transfection of human endothelial cells (HMEC-1), cytosolic Ca Human parvovirus B19, a nonenveloped virus of about 22 to 24 nm in diameter, is a member of the genus Erythrovirus within the family of Parvoviridae (35). B19 infection occurs frequently in humans, and this is documented by the high prevalence of specific immunoglobulin G (IgG) antibodies in young children (5% to 15%), adults (60%), and seniors older than 69 years (85%) (15). B19 is the causative agent of erythema infectiosum (fifth disease), hydrops fetalis, and transient aplastic anemia (1,86). Several studies disclosed an association between B19 and a variety of diseases (43,48,63,80), such as arthritis (56, 77), vasculitic syndromes (19, 24, 31, 80), hepatitis (27,36,38,75,85), and neurological disorders (2, 85). Specifically, B19 infections have been observed to be associated with acute and chronic myocarditis (13,16,30,44,53,(58)(59)(60)71). Moreover, the development of endothelial and isolated left ventricle diastolic dysfunction has been associated with B19 infection (81). During pregnancy, parvovirus B19 infection may cause maternal and fetal myocarditis, congenital abnormalities, stillbirth, and abortion (10, 21, 39, 61). The particularly severe course of the antenatal disease may relate to the preference of B19 for proliferating tissues (79).The cellular receptor for B19 infection has been regarded as a blood group P antigen based on the failure of B19 infection in a patient with a hereditary P antigen defect (12). The P antigen is necessary for B19 binding but not sufficient for virus entry into cells. In this regard, the ␣5␤1 integrin and the recently identified Ku80 autoantigen act as cellular coreceptors for human parvovirus B19 infection (57, 82). Therefore, target cells of B19 are mainly erythroid progenitor cells expressing high levels of P antigen as well as the coreceptors ␣5␤1 integrin and Ku80 autoantigen. However, nonerythroid cell lineages, such as fetal myocytes, follicular dendritic cells, and endothelial cells can be infected by B19 (12,28,29,57,82). We have recently localized B19 genomes in endothelial cells of my...

Molecular Characterization of Infectious Clones of the Minute Virus of Canines Reveals Unique Features of Bocaviruses

“…Further attempts to knock out the (pA)p sites were not tried since this region is in the coding region for the VP1 unique part. In all parvoviruses except Aleutian mink disease virus, the minor structural protein, VP1, possesses motifs that have PLA 2 activity shown to be essential for nuclear entry of the virus during infection (22,27,42,54,67). The HDXXY motif that was found in the catalytic site of sPLA 2 s (21) is also predicted to be present in the VP1u of MVC (58).…”

Surface-Exposed Adeno-Associated Virus Vp1-NLS Capsid Fusion Protein Rescues Infectivity of Noninfectious Wild-Type Vp2/Vp3 and Vp3-Only Capsids but Not That of Fivefold Pore Mutant Virions

“…These studies also suggest that prior to escaping the endosome, the virion must undergo conformational changes, leading to the exposure of the unique N terminus of Vp1 and the N terminus of Vp2 required for endososmal escape and nuclear entry (6, 9, 19, 33,35). The unique N terminus of Vp1 contains a conserved PLA2 domain (8,15,18,28,52) that is essential for infectivity and is thought to be required for endosomal escape. A suggestion that the N termini of Vp1 are located within the virion and become surface exposed naturally within the cell, via an induced conformational change, is consistent with the observation that while intact capsids do not have PLA2 activity, heat or acidic-pH treatment of virions elicits this function (37,52).…”

Molecular phenotypes of human parvovirus B19 in patients with myocarditis

“…It has been shown that active persistent B19V-infection is responsible for triggering inflammatory response in the myocardium [18] . Recently, we demonstrated that B19V and the viral proteins of B19V play an important pathophysiological role in modulating inflammatory signaling, regulation of pro-apoptotic processes and modulation of the intracellular Ca 2+ -activity leading to endothelial dysfunction [26,33,34] . It is important to note that B19V DNA is more frequently found in EMBs of patients with chronic myocarditis (59.6%) compared to control cardiac tissue samples from individuals without heart failure (7.7%), a finding consistent with other reports [2,35] .…”