Abstract
Human phospholipid scramblase 1 (PLSCR1) is strongly expressed in response to interferon (IFN) treatment and viral infection, and PLSCR1 has been suggested to play an important role in IFN-dependent antiviral responses. In this study, we showed that the basal expression of PLSCR1 was significantly elevated in Epstein-Barr virus (EBV)-infected nasopharyngeal carcinoma (NPC). PLSCR1 was observed to directly interact with the EBV immediate-early transactivator BZLF1 in vitro and in vivo, and this interaction repressed the BZLF1-mediated transactivation of an EBV lytic BMRF1 promoter construct. In addition, PLSCR1 expression decreased the BZLF1-mediated up-regulation of lytic BMRF1 mRNA and protein expression in WT and PLSCR1-knockout EBV-infected NPC cells. Furthermore, we showed that PLSCR1 represses the interaction between BZLF1 and CREB-binding protein (CBP), which enhances the BZLF1-mediated transactivation of EBV lytic promoters. These results reveal for the first time that PLSCR1 specifically interacts with BZLF1 and negatively regulates its transcriptional regulatory activity by preventing the formation of the BZLF1-CBP complex. This interaction may contribute to the establishment of latent EBV infection in EBV-infected NPC cells.
Highlights
Human phospholipid scramblase 1 (PLSCR1) is strongly expressed in response to interferon (IFN) treatment and viral infection, and PLSCR1 has been suggested to play an important role in IFN-dependent antiviral responses
Subsequent immunoblot analysis of the immunoprecipitated full-length or truncated BZLF1 complexes revealed that BZLF1(3–169) did not co-precipitate with PLSCR1 (Fig. 3B, lane 14), whereas BZLF1, BZLF1(86 –245), BZLF1(3–227), and BZLF1(3–196) efficiently co-precipitated with PLSCR1 (Fig. 3B, lanes 9 –13). These findings indicated that amino acids 170 –196 of BZLF1, which are included within the DNA-binding domain of the basic leucine zipper (bZIP) motif [27], are required for the interaction of BZLF1 with PLSCR1
This work reveals for the first time that PLSCR1 directly interacts with Epstein-Barr virus (EBV) BZLF1 in vitro and in vivo (Figs. 2 and 3) and that amino acids 1–163 and 160 –250 of PLSCR1 (Fig. 2) and the C-terminal bZIP region of BZLF1 (Fig. 3) are involved in this interaction
Summary
Human PLSCR1 expression has been shown to be induced in response to IFN treatment and viral infection [17, 18]. The levels of BMRF1 mRNA were significantly decreased in the presence of PLSCR1 to ϳ50% of that observed in the empty vector–transfected cells (Fig. 6A, lanes 3 and 4, third panel from the top) These results indicated that PLSCR1 negatively regulates the BZLF1-dependent transactivation of the lytic gene in EBV-infected NPC cells. We were unable to detect endogenous BMRF1 protein expression, the levels of BZLF1-induced BMRF1 protein were significantly increased in the PLSCR1specific shRNA-transfected cells (Fig. 6C, lanes 3 and 4, third panel from the top) Taken together, these observations revealed that PLSCR1 represses BZLF1-dependent lytic gene expression in EBV-infected NPC cells. These results revealed that PLSCR1 represses the interaction between BZLF1 and CBP in vivo
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