The ATF6 branch of unfolded protein response and apoptosis are activated to promote African swine fever virus infection

Galindo, I; Hernáez, B; Muñoz-Moreno, R; Cuesta-Geijo, M A; Dalmau-Mena, I; Alonso, C

ASFV infection does not induce XBP1 splicing in Vero cells. In response to the accumulation of unfolded proteins in the ER, IRE1 is activated by its oligomerization in the membrane, which causes the splicing of the mRNA encoding XBP1 transcription factor. The XBP1 protein encoded by the spliced mRNA is more stable than the unspliced form and is a potent transcription factor of the basic-leucine zipper (bZIP) family and caspase 12 inhibition flow cytometry (FACS ERAD) PDI eIF2a basic-leucine zipper (bZIP) one of the key regulators of ER-folding capacity. 31 Using RT-PCR and specific primers to distinguish between the unspliced (inactive) and spliced (active) forms of the XBP1 transcript, we detected XBP1 splicing in Vero cells treated with the UPR inducer tunicamycin but not in ASFV-infected cells at a range of post-infection times (Figure 5c ). Therefore, it appears that the infection did not increase levels of active XBP1 mRNA. XBP1 mRNA is spliced by IRE1 but is induced by ATF6 activation. 6 The level of endogenous XBP1 mRNA was measured in infected cells using qRT-PCR analysis of RNAs from ASFV-infected samples. We found an increase in the level of XBP1 transcript in cells treated with tunicamycin or dithiothreitol (DTT) compared with the level of mRNA obtained in mock-infected cells. In contrasts, ASFV results in a gradual decrease in the level of XBP1 mRNA over the course of infection (Figure 5d ) indicating the downregulation of this mRNA in ASFV-infected cells.