The human severe acute respiratory syndrome coronavirus (SARS-CoV) 8b protein is distinct from its counterpart in animal SARS-CoV and down-regulates the expression of the envelope protein in infected cells

Abstract

The severe acute respiratory syndrome coronavirus (SARS-CoV), isolated from humans infected during the peak of epidemic, encodes two accessory proteins termed as 8a and 8b. Interestingly, the SARS-CoV isolated from animals contains an extra 29-nucleotide in this region such that these proteins are fused to become a single protein, 8ab. Here, we compared the cellular properties of the 8a, 8b and 8ab proteins by examining their cellular localizations and their abilities to interact with other SARS-CoV proteins. These results may suggest that the conformations of 8a and 8b are different from 8ab although nearly all the amino acids in 8a and 8b are found in 8ab. In addition, the expression of the structural protein, envelope (E), was down-regulated by 8b but not 8a or 8ab. Consequently, E was not detectable in SARS-CoV-infected cells that were expressing high levels of 8b. These findings suggest that 8b may modulate viral replication and/or pathogenesis.

Translational control of the subgenomic RNAs of severe acute respiratory syndrome coronavirus

“…Although SARS-CoV 8b gene product could be expressed in vivo when cloned directly behind a promoter [11][12][13]; the expression of 8a and 8b in SARS-CoVinfected cells is still controversial [9,10,13]. As shown above, we were unable to detect the protein expression of sgRNA 8 with the 5 0 viral leader sequence, which corroborated with a recent report on ORF8 expression [13].…”

“…Ten sgRNAs have been identified [5] and the SARS-CoV accessory proteins 3a, 3b, 6,7a, and 7b can be detected in infected cells or SARS patients besides structural proteins [7,8], while the expression of 8a and 8b is controversial [9][10][11][12][13]. Elucidation of the regulatory mechanism in the translation is important for understanding the pathogenesis of SARS-CoV; however, it is hard to compare the differential translation of sgRNAs because the steady-state level of viral proteins in infected cells reflects the sum of transcription, translation, and the relative stabilities of these transcriptional and translational products.…”

Accessory proteins of SARS-CoV and other coronaviruses

“…ORF8b encodes an 84-aa polypeptide and residues 9-84 are identical to the C-terminal of 8ab (Oostra et al, 2007). Whereas Keng et al have demonstrated by indirect immunofluorescence that 8a and 8b are expressed in SARS-CoVinfected Vero E6 cells, Oostra et al were unable to detect 8b in SARS-CoV-infected Vero E6 cells (Oostra et al, 2007;Keng et al, 2006). Although there is no data regarding the expression of 8a or 8b in vivo, Chen et al have identified anti-p8a antibodies in two out of 37 patients with SARS (Chen et al, 2007).…”

The Role of Severe Acute Respiratory Syndrome (SARS)-Coronavirus Accessory Proteins in Virus Pathogenesis

“…Not only do in vitro and in vivo studies show that ORF8ab is ubiquitinated, but both ORF8a and ORF8b also binds to monoubiquitin and polyubiquitin, suggesting the potential involvement of these proteins in the pathogenesis of SARS-CoV [116]. ORF8ab interacts with SARS-CoV proteins S, M, ORF3a and ORF7a [118], all of which have been shown to be structural proteins. …”

“…ORF8b down-regulates the expression of SARS-CoV E, a process that could be inhibited by the addition of proteasome inhibitors [116]. For this reason, E is not detectable in SARS-CoV-infected cells that are expressing high levels of ORF8b [118]. Similarly to ORF6, overexpression of ORF8b in mammalian cells also induces DNA synthesis.…”