Expression of ubiquitin, actin, and actin-like genes in African swine fever virus infected cells

African swine fever virus encodes for an E2-ubiquitin conjugating enzyme that is mono- and di-ubiquitinated and required for viral replication cycle

African swine fever virus is the etiological agent of a contagious and fatal acute haemorrhagic viral disease for which there are no vaccines or therapeutic options. The ASFV encodes for a putative E2 ubiquitin conjugating enzyme (ORF I215L) that shows sequence homology with eukaryotic counterparts. In the present study, we showed that pI215L acts as an E2-ubiquitin like enzyme in a large range of pH values and temperatures, after short incubation times. Further experiments revealed that pI215L is polyubiquitinated instead of multi-mono-ubiquitinated and Cys85 residue plays an essential role in the transthioesterification reaction. In infected cells, I215L gene is transcribed from 2 hours post infection and immunoblot analysis confirmed that pI215L is expressed from 4 hpi. Immunofluorescence studies revealed that pI215L is recruited to viral factories from 8 hpi and a diffuse distribution pattern throughout the nucleus and cytoplasm. siRNA studies suggested that pI215L plays a critical role in the transcription of late viral genes and viral DNA replication. Altogether, our results emphasize the potential use of this enzyme as target for drug and vaccine development against ASF.

Subversion of the actin cytoskeleton during viral infection

Viral infection converts the normal functions of a cell to optimize viral replication and virion production. One striking observation of this conversion is the reconfiguration and reorganization of cellular actin, affecting every stage of the viral life cycle, from entry through assembly to egress. The extent and degree of cytoskeletal reorganization varies among different viral infections, suggesting the evolution of myriad viral strategies. In this Review, we describe how the interaction of viral proteins with the cell modulates the structure and function of the actin cytoskeleton to initiate, sustain and spread infections. The molecular biology of such interactions continues to engage virologists in their quest to understand viral replication and informs cell biologists about the role of the cytoskeleton in the uninfected cell.

The CD2v protein of African swine fever virus interacts with the actin-binding adaptor protein SH3P7

The predicted extracellular domain of the CD2v protein of African swine fever virus (ASFV) shares significant similarity to that of the CD2 protein in T cells but has a unique cytoplasmic domain of unknown function. Here we have shown that CD2v is expressed as a glycoprotein of approximately 105 kDa in ASFV-infected cells. In the absence of an extracellular ligand, the majority of CD2v appears to localize to perinuclear membrane compartments. Furthermore, we have shown using the yeast two-hybrid system and by direct binding studies that the cytoplasmic tail of CD2v binds to the cytoplasmic adaptor protein SH3P7 (mAbp1, HIP55), which has been reported to be involved in diverse cellular functions such as vesicle transport and signal transduction. A cDNA clone encoding a variant form of SH3P7 could also be identified and was found to be expressed in a wide range of porcine tissues. Deletion mutagenesis identified proline-rich repeats of sequence PPPKPC in the ASFV CD2v protein to be necessary and sufficient for binding to the SH3 domain of SH3P7. In ASFV-infected cells, CD2v and SH3P7 co-localized in areas surrounding the perinuclear virus factories. These areas also stained with an antibody that recognizes a Golgi network protein, indicating that they contained membranes derived from the Golgi network. Our data provide a first molecular basis for the understanding of the immunomodulatory functions of CD2v in ASFV-infected animals.