Abstract
Nucleocytoplasmic transport of signaling modulators is essential for regulating cellular responses to extracellular stimulation and stress, as well as pathogen infection. Exportin 1 (XPO1), also known as chromosomal maintenance 1 (CRM1), mediates nuclear export of proteins, rRNAs, snRNAs, and some mRNAs. In this study, we have identified an essential role of XPO1 in regulating Kaposi’s sarcoma-associated herpesvirus (KSHV) lytic replication during primary infection of primary human umbilical vein endothelial cells. Treatment with an XPO1 inhibitor KPT-8602 and short hairpin RNA (shRNA)-mediated knockdown of XPO1 reduced KSHV lytic replication but had no effect on KSHV entry and trafficking. XPO1 inhibition induced retention of autophagy adaptor protein p62 (SQSTM1) in the nucleus, which enhanced activation of TBK1 and IRF3. As a result, nuclear accumulation of p62 increased expression of innate immune-related genes including IRF7, ISG15, IFIT1, IFIT2, and IFIT3, leading to a reduction of KSHV lytic replication. These results illustrate a novel mechanism by which XPO1 mediates innate immune response and KSHV replication, and identify XPO1 as a potential therapeutic target and KPT-8602 as a promising therapeutic agent for KSHV infection.
Highlights
Kaposi’s sarcoma-associated herpesvirus (KSHV) is a gammaherpesvirus etiologically associated with Kaposi’s sarcoma and several other lymphoproliferative diseases[1,2,3]
We show that XPO1 inhibition with KPT-8602 and by short hairpin RNA (shRNA) knockdown significantly reduces infectious virions by inhibiting viral gene expression
We further examined p62’s role in KSHV primary infection. p62 knockdown had no effect on KSHV infectivity as there was no obvious change in LANA-positive cells with or without KPT-8602 treatment (Fig. 6A–C). p62 knockdown had no effect on LANA staining pattern and intensity (Fig. 6B), and the number of KSHV particles docked at the perinuclear region (Fig. 6D, E)
Summary
Kaposi’s sarcoma-associated herpesvirus (KSHV) is a gammaherpesvirus etiologically associated with Kaposi’s sarcoma and several other lymphoproliferative diseases[1,2,3]. KSHV has both latent and lytic replication cycles regulated by intracellular and extracellular signals[4]. In lytic replication-permissive cells such as primary human umbilical vein endothelial (HUVEC), activation of ERK, p38, and JNK pathways promotes expression of viral lytic genes, and KSHV undergoes robust lytic replication before entering into latency[5,6,7,8]. Activation of NF-κB pathway promotes the expression of latent genes and KSHV enters into latency in nonpermissive cells such. The exchange of signaling molecules between nuclear and cytoplasmic compartments is essential for cellular functions. This process is mediated by a nuclear pore complex (NPC) inserted across the nuclear envelope (NE). Unlike smaller molecules, which diffuse through NPCs, the shuttling of proteins larger than 40 kDa is regulated by karyopherins (Kaps), which interact with NPC components nucleoporins (Nups) to cross NE13
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