Identification and Characterization of Two Novel Spliced Genes Located in the orf47-orf46-orf45 Gene Locus of Kaposi's Sarcoma-Associated Herpesvirus

Abstract

The orf47-orf46-orf45 gene cluster of Kaposi's sarcoma-associated herpesvirus (KSHV) is known to serially encode glycoprotein L (gL), uracil DNA glycosylase, and a viral tegument protein. Here, we identify two novel mRNA variants, orf47/45-A and orf47/ 45-B, alternatively spliced from a tricistronic orf47-orf46-orf45 mRNA that is expressed in the orf47-orf46-orf45 gene locus dur- IMPORTANCEEmerging evidence has shown that several viruses appear to use different strategies to control ER homeostasis for supporting their productive infections. The two parts of this study identify two aspects of the association between the regulation of ER homeostasis and the progression of the KSHV lytic cycle. The first part characterizes the function of two early lytic cycle proteins, ORF47/45-A and ORF47/45-B, on the activation of a major ER chaperone protein, GRP78. In addition to the ability to promote GRP78 upregulation, the ORF47/45 proteins also activate the phosphorylation of RSK and ERK. The second part reveals that upregulation of GRP78 is essential for the progression of the KSHV lytic cycle, especially at late stages. We therefore propose that activation of GRP78 expression by viral proteins at the early lytic stage may aid with the protection of host cells from severe ER stress and may directly involve the assembly or release of virions.

Deregulation of KSHV latency conformation by ER-stress and caspase-dependent RAD21-cleavage

“…Previous studies suggest that the UPR strongly contributes to regulation of KSHV lytic replication [ 31 – 37 ]. It has been proposed that the viral early lytic proteins, including ORF47/45, may control and promote BiP expression to protect host cells from ER stress to facilitate the assembly and release of virions [ 31 ].…”

“…Previous studies suggest that the UPR strongly contributes to regulation of KSHV lytic replication [ 31 – 37 ]. It has been proposed that the viral early lytic proteins, including ORF47/45, may control and promote BiP expression to protect host cells from ER stress to facilitate the assembly and release of virions [ 31 ]. A recent study shows that KSHV-encoded LANA and v-cyclin can suppress the transcription of the ER stress sensors IRE1 and PERK to sensitize PEL cells to ER stress inducers [ 32 , 33 ].…”

Regulation of the Abundance of Kaposi’s Sarcoma-Associated Herpesvirus ORF50 Protein by Oncoprotein MDM2

“…The preparation of shRNA lentiviral particles has been described previously [ 42 ]. All RNAi reagents were obtained from the National RNAi Core Facility Platform at the Institute of Molecular Biology/Genomic Research Center, Academia Sinica.…”

Regulation of gammaherpesvirus lytic replication by endoplasmic reticulum stress–induced transcription factors ATF4 and CHOP

“…ulates tetradecanoylphorbol acetate-induced KSHV lytic cycle progression in primary effusion lymphoma cells (46). The discrepancy might be attributed to the distinct signaling pathways regulated by tetradecanoylphorbol acetate and BCR.…”