Crimean–Congo hemorrhagic fever virus utilizes a clathrin- and early endosome-dependent entry pathway

Abstract

The early events in Crimean-Congo hemorrhagic fever virus (CCHFV) have not been completely characterized. Earlier work indicated that CCHFV likely enters cells by clathrin-mediated endocytosis (CME). Here we provide confirmatory evidence for CME entry by showing that CCHFV infection is inhibited in cells treated with Pitstop 2, a drug that specifically and reversibly interferes with the dynamics of clathrin-coated pits. Additionally, we show that CCHFV infection is inhibited by siRNA depletion of the clathrin pit associated protein AP-2. Following CME entry, we show that CCHFV has a pH-dependent entry step, with virus inactivation occurring at pH 6.0 and below. To more precisely define the endosomal trafficking of CCHFV, we show for the first time that overexpression of the dominant negative forms of Rab5 protein but not Rab7 protein inhibits CCHFV infection. These results indicate that CCHFV likely enters cells through the early endosomal compartment.

Clathrin Terminal Domain-Ligand Interactions Regulate Sorting of Mannose 6-Phosphate Receptors Mediated by AP-1 and GGA Adaptors

“…2; in contrast to Ref. 39) and by recent studies on the entry of various animal viruses that either use CME or clathrin-independent routes (53). Collectively, these results highlight the importance of using multiple approaches, including compounds and their inactive analogs to increase probability that on target actions are being observed.…”

Hijacking of RIG-I Signaling Proteins into Virus-Induced Cytoplasmic Structures Correlates with the Inhibition of Type I Interferon Responses

“…In addition, the endosomal pathway has been shown to promote internalization and/or virus replication (60)(61)(62)(63). Indeed, entry into Rab5 ϩ early endosomes has been previously described for Uukuniemi virus, another member of the genus Phlebovirus (64).…”

The Envelope Proteins of the Bunyavirales

“…Once in the appropriate endosomal compartment, the virus particle is activated by the acidic environment to fuse with the endosomal membrane. Depending on the virus, this activation can occur in the slightly acidic environment of the early endosomes, for instance for the nairovirus CCHFV or for Lacrosse virus (LACV, an orthobunyavirus), which are activated at pH 6.0 (Garrison et al, 2013;Plassmeyer et al, 2007) or in the more acidic late endosomes, like the UUKV phlebovirus, which is activated at pH 5.4 (Lozach et al, 2010), or the RVFV phlebovirus, which is activated at pH 5.7 (de Boer et al, 2012). In addition to pH, other factors are important to trigger the membrane fusion reaction: proteolytic cleavage of the glycoproteins for nairoviruses (Sanchez et al, 2002) or the presence of specific lipids in the cellular membrane, like cholesterol in hantaviruses (Kleinfelter et al, 2015) or anionic lipids as bis(monoacylglycero)phosphate or phosphatidylglycerol (PG) in the tick-borne UUKV phlebovirus (Bitto et al, 2016).…”