African Swine Fever Virus Uses Macropinocytosis to Enter Host Cells

Abstract

African swine fever (ASF) is caused by a large and highly pathogenic DNA virus, African swine fever virus (ASFV), which provokes severe economic losses and expansion threats. Presently, no specific protection or vaccine against ASF is available, despite the high hazard that the continued occurrence of the disease in sub-Saharan Africa, the recent outbreak in the Caucasus in 2007, and the potential dissemination to neighboring countries, represents. Although virus entry is a remarkable target for the development of protection tools, knowledge of the ASFV entry mechanism is still very limited. Whereas early studies have proposed that the virus enters cells through receptor-mediated endocytosis, the specific mechanism used by ASFV remains uncertain. Here we used the ASFV virulent isolate Ba71, adapted to grow in Vero cells (Ba71V), and the virulent strain E70 to demonstrate that entry and internalization of ASFV includes most of the features of macropinocytosis. By a combination of optical and electron microscopy, we show that the virus causes cytoplasm membrane perturbation, blebbing and ruffles. We have also found that internalization of the virions depends on actin reorganization, activity of Na + /H + exchangers, and signaling events typical of the macropinocytic mechanism of endocytosis. The entry of virus into cells appears to directly stimulate dextran uptake, actin polarization and EGFR, PI3K-Akt, Pak1 and Rac1 activation. Inhibition of these key regulators of macropinocytosis, as well as treatment with the drug EIPA, results in a considerable decrease in ASFV entry and infection. In conclusion, this study identifies for the first time the whole pathway for ASFV entry, including the key cellular factors required for the uptake of the virus and the cell signaling involved.

Involvement of a Rac1-Dependent Macropinocytosis Pathway in Plasmid DNA Delivery by Electrotransfection

“…8,83,85,86 Vesicles in clathrin-and caveolin-mediated endocytosis are small in size (<100 nm), which can significantly limit their transport capacities for pDNA with a similar size. In contrast, macropinocytosis, which is known to be responsible for cellular uptake of viruses, 87,88 nanoparticles, 89 and naked pDNA, 90 can generate vesicles with sizes of up to 5 mm that could transport a significantly larger amount of pDNA per vesicle. In previous and current studies, it was observed that pDNA could form aggregates in solution with certain sizes or complexes with the plasma membrane.…”

Transcriptional immunoresponse of tissue-specific macrophages in swine after infection with African swine fever virus

“…This activation has been detected by ultrastructural study and immunohistochemically in the lymphoid organs, lungs, liver, and kidneys (14,28,29). A significant increase in serum TNF-α and IL-1β levels has been observed from 2 d pi in different experiments with pigs infected with highly-virulent strains.…”

“…However, ASFV is a monocytotropic virus, and observations made in non-leukocyte cell lines do not necessarily relate to events involving macrophages during virus infection (2). Moreover, another observation indicates that ASFV can only enter macrophages via receptor-mediated endocytosis to achieve productive infection only (3,29). Analysis of the mechanisms of entry into macrophages, the natural host cells of ASFV, is hindered by the fact that these cells have a heterogeneous surface marker profile and only restricted macrophage subpopulations are susceptible to this virus (11).…”

Molecular Signaling and Cellular Pathways for Virus Entry

“…Under different signaling regulations, the macropinosomes can fused with EE or recycled back to plasma membrane. To date, several viruses have been found to enter their host cells by macropinocytosis, including vaccinia virus, HIV-1, coxsackievirus B (CVB), herpes simplex virus type 1 (HSV-1), african swine fever virus (ASFV), human papillomavirus type 16 (HPV-16), and KSHV [11][12][13]69]. Recently, it was reported that vaccinia virus entry relies on type II membrane glycoprotein CD98 associated integrin 1 triggered PI3 K/Akt signaling and ERK, PKC, and PAK1 that are required for macropinosome closure [70,71].…”

“…e cell endocytic mechanism also provides a route for virus internalization. Recent research has discovered that numerous viruses favor the endocytosis as clathrin-mediated endocytosis (CME) [2][3][4][5][6][7], caveolae/lipid ra-mediated endocytosis [8][9][10], macropinocytosis [11][12][13], and several other unusual pathways [14,15] by eliciting the endocytic signaling pathways. is review focuses on the elements that are involved in regulating the mechanism of virus entry and their traffic systems.…”