A Unique Herpesviral Transcriptional Program in KSHV-Infected Lymphatic Endothelial Cells Leads to mTORC1 Activation and Rapamycin Sensitivity

SummaryImmunosuppression therapy following organ transplantation is a significant factor in the development and progression of Kaposi’s sarcoma-associated herpesvirus (KSHV)-induced posttransplant Kaposi’s sarcoma (KS). Switching from cyclosporine to the mTOR inhibitor rapamycin is reported to promote KS regression without allograft rejection. Examining the underlying molecular basis for this clinical observation, we find that KSHV infection selectively upregulates mTOR signaling in primary human lymphatic endothelial cells (LECs), but not blood endothelial cells (BECs), and sensitizes LECs to rapamycin-induced apoptosis. Viral transcriptome analysis revealed that while infected BECs display conventional latency, KSHV-infected LECs support a radically different program involving widespread deregulation of both latent and lytic genes. ORF45, a lytic gene selectively expressed in infected LECs, is required for mTOR activation and critical for rapamycin sensitivity. These studies reveal the existence of a unique herpesviral gene expression program corresponding to neither canonical latency nor lytic replication, with important pathogenetic and therapeutic consequences.

► rKSHV.219 infection sensitizes LECs, but not BECs, to rapamycin-induced apoptosis
► mTORC1 is activated in LEC.219 but not in BEC.219
► LEC.219 exhibits dysregulated viral gene expression while BEC.219 is latent
► mTORC1 activation and rapamycin sensitivity in LEC.219 requires KSHV lytic gene ORF45