Epstein-Barr virus (EBV) BBLF1 shares 13 to 15% amino acid sequence identities with the herpes simplex virus 1 UL11 and cytomegalovirus UL99 tegument proteins, which are involved in the final envelopment during viral maturation. This study demonstrates that BBLF1 is a myristoylated and palmitoylated protein, as are UL11 and UL99. Myristoylation of BBLF1 both facilitates its membrane anchoring and stabilizes it. BBLF1 is shown to localize to thetrans-Golgi network (TGN) along with gp350/220, a site where final envelopment of EBV particles takes place. The localization of BBLF1 at the TGN requires myristoylation and two acidic clusters, which interact with PACS-1, a cytosolic protein, to mediate retrograde transport from the endosomes to the TGN. Knockdown of the expression of BBLF1 during EBV lytic replication reduces the production of virus particles, demonstrating the requirement of BBLF1 to achieve optimal production of virus particles. BBLF1 is hypothesized to facilitate the budding of tegumented capsid into glycoprotein-embedded membrane during viral maturation.

Autophagy is an intracellular degradation pathway that provides a host defense mechanism against intracellular pathogens. However, many viruses exploit this mechanism to promote their replication. This study shows that lytic induction of EpsteinBarr virus (EBV) increases the membrane-bound form of LC3 (LC3-II) and LC3-containing punctate structures in EBV-positive cells. Transfecting 293T cells with a plasmid that expresses Rta also induces autophagy, revealing that Rta is responsible for autophagic activation. The activation involves Atg5, a key component of autophagy, but not the mTOR pathway. The expression of Rta also activates the transcription of the genes that participate in the formation of autophagosomes, including LC3A, LC3B, and ATG9B genes, as well as those that are involved in the regulation of autophagy, including the genes TNF, IRGM, and TRAIL. Additionally, treatment with U0126 inhibits the Rta-induced autophagy and the expression of autophagy genes, indicating that the autophagic activation is caused by the activation of extracellular signal-regulated kinase (ERK) signaling by Rta. Finally, the inhibition of autophagic activity by an autophagy inhibitor, 3-methyladenine, or Atg5 small interfering RNA, reduces the expression of EBV lytic proteins and the production of viral particles, revealing that autophagy is critical to EBV lytic progression. This investigation reveals how an EBV-encoded transcription factor promotes autophagy to affect viral lytic development. IMPORTANCEAutophagy is a cellular process that degrades and recycles nutrients under stress conditions to promote cell survival. Although autophagy commonly serves as a defense mechanism against viral infection, many viruses exploit this mechanism to promote their replication. This study finds that a transcription factor that is encoded by Epstein-Barr virus (EBV), Rta, activates autophagy, and the inhibition of autophagy reduces the ability of the virus to express viral lytic proteins and to generate progeny. Unlike other virus-encoded proteins that modulate autophagy by interacting with proteins that are involved in the autophagic pathway, Rta activates the transcription of the autophagy-related genes via the ERK pathway. The results of this study reveal how the virus manipulates autophagy to promote its lytic development.

Most nucleoside analogs require stepwise phosphorylation to the respective triphosphate metabolites to exert their pharmacological activity. L-and D-dCyd analogs are phosphorylated by cytoplasmic deoxycytidine kinase, and dThd analogs are phosphorylated by cytoplasmic thymidine kinase to the monophosphate metabolites. L-FMAU can be phosphorylated by both cytoplasmic deoxycytidine kinase and cytoplasmic thymidine kinase. dCyd analog monophosphates are further phosphorylated by cytidine/uridine monophosphate kinase to the respective nucleoside diphosphate metabolites, whereas the dThd analogs are phosphorylated by thymidine monophosphate kinase (1, 2, 15, 16). Conversion of L-deoxynucleoside analog diphosphates to the pharmacologically active L-deoxynucleoside triphosphate metabolites remains largely unexplored; however, NDPK, which could phosphorylate naturally occurring nucleoside diphosphates, has been assumed to play a role (17-21). The last step of phosphorylation is of potential importance, because analogs like L-Fd4C, L-OddC, L-SddC, and ddC accumulate in the cells as diphosphate metabolites indicating inefficiency of the responsible enzyme (6,(22)(23)(24). However, L-FMAU is efficiently metabolized to .Eight isoforms of NDPK have been isolated in humans, of which nm23-H1 and nm23-H2 have been shown to be cytoplasmic, and are capable of phosphorylating nucleoside diphosphates (26,27). DR-nm23 (28), nm23-H4 (29) and nm23-H6 (30) are localized in the mitochondria, and nm23-H5 is testisspecific (31). Activities of nm23-H7 and nm23-H8 in terms of nucleoside diphosphate phosphorylation are not known (NCBI accession numbers Q9Y5B8 and XP_004705, respectively). NDPKs utilize ATP or other nucleoside triphosphates as a phosphate donor and transfer the phosphate residue onto nucleoside diphosphate via a phosphohistidine intermediate (ping-pong mechanism) (32, 33).Other enzymes that are capable of phosphorylating nucleoside diphosphates are creatine kinase, 3-phosphoglycerate kinase, pyruvate kinase, phosphoenolpyruvate carboxykinase, and adenylosuccinate kinase (34 -36). Based on the high rates of hydrolysis of the phosphate bonds of the donor compounds

Lytic cycle reactivation of Kaposi's sarcoma-associated herpesvirus (KSHV) is initiated by expression of the ORF50 gene. Here we show that YY1 protein specifically binds to the ORF50 promoter (ORF50p) region in vitro and in vivo. After treatment with chemical inducers, including sodium butyrate (SB) and TPA, the levels of YY1 protein are inversely correlated with the lytic induction of KSHV in cells. Overexpression of YY1 completely blocks the ORF50p activation in transient reporter assays, while mutation at the YY1 site in the ORF50p or knockdown of YY1 protein confers an enhancement of the ORF50p activation induced by SB and TPA. YY1 overexpression in a stable cell clone HH-B2(Dox-YY1) also inhibits expression of the ORF50 and its downstream lytic genes. On the other hand, a chimeric YY1 construct that links to its coactivator E1A can disrupt viral latency. These results imply that YY1 is involved in the regulation of KSHV reactivation.

Human UMP/CMP kinase (cytidylate kinase; EC 2.7.4.14) is responsible for phosphorylation of CMP, UMP, and deoxycytidine monophosphate (dCMP) and also plays an important role in the activation of pyrimidine analogs, some of which are clinically useful anticancer or antiviral drugs. Previous kinetic data using recombinant or highly purified human UMP/CMP kinase showed that dCMP, as well as pyrimidine analog monophosphates, were much poorer substrates than CMP or UMP for this enzyme. This implies that other unidentified mechanisms must be involved to make phosphorylation of dCMP or pyrimidine analog monophosphates inside cells by this enzyme possible. Here, we reevaluated the optimal reaction conditions for human recombinant human UMP/CMP kinase to phosphorylate dCMP and CMP (referred as dCMPK and CMPK activities). We found that ATP and magnesium were important regulators of the kinase activities of this enzyme. Free magnesium enhanced dCMPK activity but inhibited CMPK activity. Free ATP or excess ATP/magnesium, on the other hand, inhibited dCMPK but not CMPK reactions. The differential regulation of dCMPK versus CMPK activities by ATP or magnesium was also seen in other 2Ј-deoxypyrimidine analog monophosphates (deoxyuridine monophosphate, 5-fluorodeoxyuridine monophosphate, 1-␤-D-arabinofuranosylcytosine monophosphate, and gemcitabine monophosphate) versus their ribose-counterparts (UMP and 5-fluorouridine monophosphate), in a similar manner. The data suggest that the active sites of human UMP/CMP kinase for dCMP and for CMP cannot be identical. Furthermore, enzyme inhibition studies demonstrated that CMP could inhibit dCMP phosphorylation in a noncompetitive manner, with K i values much higher than its own K m values. We thus propose novel models for the phosphorylation action of human UMP/ CMP kinase.