Rhadinovirus Entry
Final Report Abstract
Kaposi’s sarcoma-associated herpesvirus (KSHV) is the only gamma2-herpesvirus (rhadinovirus) in humans. KSHV is usually apathogenic in immunocompetent individuals in the industrialized world. An exception is the so called classic Kaposi’s sarcoma (KS) that mainly occurs in elderly men of Mediterranean origin. In immunocompromised individuals, KSHV is not only the causative agent of KS, but is also associated with two B cell malignancies, primary effusion lymphoma (PEL) and multicentric Castleman’s disease (MCD). This contrasts with the situation in sub-saharan Africa where KSHV is among the leading causes of cancer and so called endemic KS is among the most frequent tumors. Notably, endemic KS has existed before the HIV epidemic and a considerable portion of endemic KS is not AIDS-related. The rhesus monkey rhadinovirus (RRV) is a natural infectious agent of rhesus monkeys. RRV is closely related to KSHV with practically identical genome organization. RRV causes a similar spectrum of malignancies in lymphoid cells, and although it lacks a tight association with solid tumors there are reports of RRV positive sarcomas. Thus, RRV lends itself to comparative studies with KSHV. At the outset of this project, the Ephrin receptor tyrosine kinase A2 (EphA2) was identified as a cellular receptor for the KSHV gH/gL glycoprotein complex that mediates entry into a variety of cells, among them endothelial cells, the cell type that gives rise to the characteristic spindle cell of KS. It was hypothesized that RRV, like KSHV, engages cellular receptors through its gH/gL complex. Both by unbiased mass spectrometry analysis and through direct interaction studies with 14 different Eph receptors, RRV was found to interact with a wide variety of Eph family receptors of both A- and B-type with the strongest interaction occurring with EphB3. KSHV interacted with high affinity only with EphA2 and weakly with some other A-type receptors. Thus, interaction with Eph family receptors is conserved between the two viruses, but the exact specificities differ. Functionally, entry of KSHV was largely or even completely dependent on EphA2 whereas RRV was able to use a variety of A- and B-type receptors. It was found that RRV is dependent on Eph receptors for entry into B cells and endothelial cells and that this exactly parallels KSHV. Importantly, differences do exist between the two viruses: Entry of RRV into fibroblasts was not or only marginally dependent on the engagement of Eph receptors. This indicated the existence of another entry pathway for RVV into fibroblasts that is not available to KSHV. Accordingly, an Eph-binding deficient gL-deletion mutant of RRV exhibited strongly reduced entry into endothelial cells as compared to fibroblasts. Through testing of mutant gH proteins, the exact receptor binding domain of gH was mapped and conserved residues that are crucial for the interaction of RRV and KSHV with Eph receptors were identified. In addition, a known inhibitor of the interaction of EphA2 with natural Ephrin ligands was found to inhibit the interaction of KSHV gH/gL with the EphA2 receptor. Consequently, this compound also inhibits entry of KSHV. In summary, this body of works identifies Eph family receptor tyrosine kinases as evolutionarily conserved entry receptors for at least two rhadinoviruses and demonstrates the significance of this receptor interaction for future therapeutic approaches.
Publications
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The ephrin receptor tyrosine kinase A2 is a cellular receptor for Kaposi's sarcoma-associated herpesvirus. Nature Medicine, 2012 Jun;18(6):961-6
Hahn AS, Kaufmann JK, Wies E, Naschberger E, Panteleev-Ivlev J, Schmidt K, Holzer A, Schmidt M, Chen J, König S, Ensser A, Myoung J, Brockmeyer NH, Stürzl M, Fleckenstein B, Neipel F
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Rhesus monkey rhadinovirus uses Eph family receptors for entry into B cells and endothelial cells but not fibroblasts. PLoS Pathogens, 2013 May 16;9(5):e1003360
Hahn AS, Desrosiers RC
