11 research outputs found
Efficient Epstein-Barr Virus Progeny Production Mediated by Cancer-Derived LMP1 and Virally-Encoded microRNAs
Epstein-Barr virus (EBV) genomes, particularly their latent genes, are heterogeneous among strains. The heterogeneity of EBV-encoded latent membrane protein 1 (LMP1) raises the question of whether there are functional differences between LMP1 expressed by cancer-associated EBV and that by non-cancerous strains. Here, we used bacterial artificial chromosome (BAC)-cloned EBV genomes retaining all virally encoded microRNA (miRNA) genes to investigate the functions of cancer-derived LMP1 in the context of the EBV genome. HEK293 cells were stably transfected with EBV-BAC clone DNAs encoding either nasopharyngeal carcinoma (NPC)-derived CAO-LMP1 (LMP1CAO) or LMP1 from a prototype B95-8 strain of EBV (LMP1B95-8). When an EBV-BAC clone DNA encoding LMP1CAO was stably transfected into HEK293 cells, it generated many more stable transformants than the control clone encoding LMP1B95-8. Furthermore, stably transfected HEK293 cells exhibited highly efficient production of progeny virus. Importantly, deletion of the clustered viral miRNA genes compromised the ability to produce progeny viruses. These results indicate that cancer-derived LMP1 and viral miRNAs together are necessary for efficient production of progeny virus, and that the resulting increase in efficiency contributes to EBV-mediated epithelial carcinogenesis
The Endoplasmic Reticulum-associated Degradation of Transthyretin Variants Is Negatively Regulated by BiP in Mammalian Cells*S⃞
Amyloid fibril formation of mutant transthyretin (TTR) that causes familial
amyloid polyneuropathy occurs in the extracellular space. Thus, secretion of
TTR variants contributes to the pathogenesis of amyloidosis. However, the
molecular mechanisms underlying the endoplasmic reticulum (ER) exit or
retention and subsequent degradation of TTR variants remain unclear. Here, we
demonstrated that the nonsecreted TTR variants, such as D18G TTR and
amyloidogenic TTRs with introduced monomeric mutation (M-TTRs), stably
interact with the ER chaperone BiP in mammalian cells. These proteins were
co-secreted with the secreted form of BiP in which the KDEL signal was
removed, indicating that BiP partially contributes to the ER retention of
nonsecreted TTR variants. More interestingly, the degradation efficiency of
nonsecreted TTRs was increased when BiP was down-regulated by small
interfering RNA. Thus, BiP protects the TTR variants from immediate
degradation. Additionally, we showed that the stability of nonsecreted TTR
variants is not disturbed in the coat complex II-deficient conditions, which
are enough to inhibit the ER export of secreted TTR variants, including
wild-type TTR. Therefore, the post-ER retrieval mechanism might not contribute
to the ER-associated degradation of nonsecreted TTR variants. These findings
suggest that the affinity to the ER-resident protein BiP regulates the fate of
TTR variants in the ER
The Endoplasmic Reticulum-associated Degradation of Transthyretin Variants Is Negatively Regulated by BiP in Mammalian Cells*S⃞
Amyloid fibril formation of mutant transthyretin (TTR) that causes familial
amyloid polyneuropathy occurs in the extracellular space. Thus, secretion of
TTR variants contributes to the pathogenesis of amyloidosis. However, the
molecular mechanisms underlying the endoplasmic reticulum (ER) exit or
retention and subsequent degradation of TTR variants remain unclear. Here, we
demonstrated that the nonsecreted TTR variants, such as D18G TTR and
amyloidogenic TTRs with introduced monomeric mutation (M-TTRs), stably
interact with the ER chaperone BiP in mammalian cells. These proteins were
co-secreted with the secreted form of BiP in which the KDEL signal was
removed, indicating that BiP partially contributes to the ER retention of
nonsecreted TTR variants. More interestingly, the degradation efficiency of
nonsecreted TTRs was increased when BiP was down-regulated by small
interfering RNA. Thus, BiP protects the TTR variants from immediate
degradation. Additionally, we showed that the stability of nonsecreted TTR
variants is not disturbed in the coat complex II-deficient conditions, which
are enough to inhibit the ER export of secreted TTR variants, including
wild-type TTR. Therefore, the post-ER retrieval mechanism might not contribute
to the ER-associated degradation of nonsecreted TTR variants. These findings
suggest that the affinity to the ER-resident protein BiP regulates the fate of
TTR variants in the ER