Glycoprotein K8.1A of Kaposi's Sarcoma-Associated Herpesvirus Is a Critical B Cell Tropism Determinant Independent of Its Heparan Sulfate Binding Activity

Abstract

B lymphocytes are the major cellular reservoir in individuals infected with Kaposi’s sarcoma-associated herpesvirus (KSHV), and the virus is etiologically linked to two B cell lymphoproliferative disorders. We previously described the MC116 human B cell line as a KSHV-susceptible model to overcome the paradoxical refractoriness of B cell lines to experimental KSHV infection. Here, using monoclonal antibody inhibition and a deletion mutant virus, we demonstrate that the KSHV virion glycoprotein K8.1A is critical for infection of MC116, as well as tonsillar B cells; in contrast, we confirm previous reports on the dispensability of the glycoprotein for infection of primary endothelial cells and other commonly studied non-B cell targets. Surprisingly, we found that the role of K8.1A in B cell infection is independent of its only known biochemical activity of binding to surface heparan sulfate, suggesting the possible involvement of an additional molecular interaction(s). Our finding that K8.1A is a critical determinant for KSHV B cell tropism parallels the importance of proteins encoded by positionally homologous genes for the cell tropism of other gammaherpesviruses.IMPORTANCEElucidating the molecular mechanisms by which KSHV infects B lymphocytes is critical for understanding how the virus establishes lifelong persistence in infected people, in whom it can cause life-threatening B cell lymphoproliferative disease. Here, we show that K8.1A, a KSHV-encoded glycoprotein on the surfaces of the virus particles, is critical for infection of B cells. This finding stands in marked contrast to previous studies with non-B lymphoid cell types, for which K8.1A is known to be dispensable. We also show that the required function of K8.1A in B cell infection does not involve its binding to cell surface heparan sulfate, the only known biochemical activity of the glycoprotein. The discovery of this critical role of K8.1A in KSHV B cell tropism opens promising new avenues to unravel the complex mechanisms underlying infection and disease caused by this viral human pathogen.

The Kaposi’s Sarcoma-Associated Herpesvirus (KSHV) gH/gL Complex Is the Predominant Neutralizing Antigenic Determinant in KSHV-Infected Individuals

“…However, since the input plasmids transfected into the cells was based on total DNA amount, rather than equal copy number, there is some variation in expression among different glycoproteins. For most of the KSHV glycoproteins, their corresponding bands, as reported by other groups, were detected by immunoblot in the total cell lysates [17,20,22,35]. However, the molecular weight of the gM protein in our study is higher than its theoretical size of 45 kDa.…”

Kaposi Sarcoma-Associated Herpesvirus Glycoprotein H Is Indispensable for Infection of Epithelial, Endothelial, and Fibroblast Cell Types

“…This infection was characterized by lytic induction, as evidenced by readily detectable K8.1 protein without artificial induction of lytic replication using chemical reagents. Given our preliminary observations that gH-null virus was infectious to B cells, we speculate that KSHV entry into B cells likely occurs through another envelope glycoprotein, K8.1, and its binding to a yet-to-be determined receptor, as was recently reported (53). The importance of K8.1 for B cell infection was recently demonstrated by Dollery et al (52,53); their group showed that blocking K8.1 with MAbs or a K8.1-null mutant, rKSHVΔK8.1 (29,67), significantly reduced KSHV infection of a B cell line (MC116) and tonsillar primary B cells but not epithelial or endothelial cell lines.…”

“…B cells typically exhibit poor permissiveness to KSHV infection in vitro, which is thought to be due to lack of appropriate receptors (53). Remarkably, when we infected a B cell line (MC116) with the purified virions and then used flow cytometry to quantitate infection, we observed that rKSHV WT-eGFP, rKSHVΔgH-eGFP, and rKSHVgH-eGFP Rev infected the cells (Fig.…”

EphA7 Functions as Receptor on BJAB Cells for Cell-to-Cell Transmission of the Kaposi's Sarcoma-Associated Herpesvirus and for Cell-Free Infection by the Related Rhesus Monkey Rhadinovirus

“…KSHV transmission to BJAB cells and other lymphoblastoid cell lines as well as primary B cells is low even in cell-to-cell systems (12) compared to infection of adherent cells by free KSHV, which has been attributed to a heparan sulfate-dependent attachment defect of KSHV on BJAB (9). Additionally, a role for glycoprotein K8.1A, independent of its heparan sulfate binding activity, has been described for the infection of B cells by KSHV (29). Although infection of BJAB cells by cell-to-cell transmission was not analyzed in these studies, the role of glycoprotein K8.1A in the infection of B cells but not in the infection of other cell types (29,30) and the described defect at the attachment step (9) hint at possible mechanistic differences specific for B cell infection.…”