The Guanine Nucleotide Exchange Factor GBF1 Participates in Rotavirus Replication

Abstract

Cellular and viral factors participate in the replication cycle of rotavirus. We report that the guanine nucleotide exchange factor GBF1, which activates the small GTPase Arf1 to induce COPI transport processes, is required for rotavirus replication since knocking down GBF1 expression by RNA interference or inhibiting its activity by treatment with brefeldin A (BFA) or Golgicide A (GCA) significantly reduces the yield of infectious viral progeny. This reduction in virus yield was related to a block in virus assembly, since in the presence of either BFA or GCA, the assembly of infectious mature triple-layered virions was significantly prevented and only double-layered particles were detected. We report that the catalytic activity of GBF1, but not the activation of Arf1, is essential for the assembly of the outer capsid of rotavirus. We show that both BFA and GCA, as well as interfering with the synthesis of GBF1, alter the electrophoretic mobility of glycoproteins VP7 and NSP4 and block the trimerization of the virus surface protein VP7, a step required for its incorporation into virus particles. Although a posttranslational modification of VP7 (other than glycosylation) could be related to the lack of trimerization, we found that NSP4 might also be involved in this process, since knocking down its expression reduces VP7 trimerization. In support, recombinant VP7 protein overexpressed in transfected cells formed trimers only when cotransfected with NSP4. IMPORTANCE Rotavirus, a member of the family Reoviridae, is the major cause of severe diarrhea in children and young animals worldwide. Despite significant advances in the characterization of the biology of this virus, the mechanisms involved in morphogenesis of the virus particle are still poorly understood. In this work, we show that the guanine nucleotide exchange factor GBF1, relevant for COPI/Arf1mediated cellular vesicular transport, participates in the replication cycle of the virus, influencing the correct processing of viral glycoproteins VP7 and NSP4 and the assembly of the virus surface proteins VP7 and VP4. KEYWORDS GBF1 nucleotide exchange factor, morphogenesis, rotavirus R otaviruses, members of the family Reoviridae, are nonenveloped particles formed by three concentric layers of proteins that surround the 11 genome segments of double-stranded RNA (dsRNA). The innermost layer is composed of the core shell protein VP2, which encloses the replication intermediates, composed of the RNAdependent RNA polymerase VP1 and the guanylyl-methyl transferase VP3. The intermediate layer is formed by VP6, which surrounds the VP2 layer to form double-layered particles (DLPs). Finally, the addition of the glycoprotein VP7 and the spike protein VP4 onto the DLPs forms the infectious triple-layered particles (TLPs) (1, 2). Downloaded fromFIG 2 BFA and GCA inhibit rotavirus replication at a postentry step. (A) MA104 cells were infected with RRV (MOI ϭ 5) at 37°C for 1 h. Unbound virus was removed, and 0.5 g/ml of BFA or 10 M GCA was added at the indicated times postinf...

Exosomal transmission of viruses, a two-edged biological sword

“…The existence of VP4 and VP8 is suitable evidence for exosomal delivery of rotavirus [ 150 ]. Within the cells, the physical interaction of viral factor NSP4 with endoplasmic reticulum DLP provides a platform to increase the interaction of viral VP4 with lipid raft domains, resulting in the penetration of viral particles into the Exo and microvesicles [ 175 ]. In some circumstances, the completion of viral assembly is associated with the activity of Exo.…”

“…As mentioned before, rotaviruses can exploit the Trans-Golgi apparatus for propagation and dissemination. On this basis, the close interaction of GBF1 with NSP4 induces trimerization of VP7, and the association of assembly protein VP7 and spike protein VP4 [ 175 ]. In the next steps, VP4 is localized to lipid raft microdomains Trans-Golgi apparatus, leading to rotavirus capsid assembly.…”

Treading a HOSTile path: Mapping the dynamic landscape of host cell–rotavirus interactions to explore novel host-directed curative dimensions

“…A recent report demonstrated how the host cellular guanine nucleotide exchange factor GBF1 (Golgi-specific brefeldin A-resistance guanine nucleotide exchange factor 1), canonically involved in the Coat protein I/ADP ribosylation factor 1 (COPI/Arf1)-mediated vesicular transport, can be usurped by RVs to promote outer capsid assembly as a part of the viral progeny morphogenesis [ 286 ]. Mechanistic profiling revealed that loss-of-function of GBF1 [through RNAi or by brefeldin A (BFA)/Golgicide A (GCA) treatment], but surprisingly not of Arf1, resulted in significant attenuation of RV progeny yield by impairing VP7 trimerization and assembly onto nascent DLPs.…”

“…Moreover, an altered posttranslational modification pattern of NSP4 in response to GBF1 silencing/inactivation was implicated behind such failure of VP7 trimerization. Whether the GBF1/COPI-mediated vesicular transport (possibly involving GBF1 substrates other than Arf1 such as Arf4/5) at the ER-Golgi interface has direct involvement in regulating RV outer capsid assembly within ER lumen or has some secondary implications in promoting non-canonical transport between ER and LDs or involving ER Golgi intermediate compartment (ERGIC) has remained unanswered [ 286 , 287 ]. Indeed, participation of ERGIC in late stages of TLP assembly has been implicated when VP4 and virion-assembled VP7 were found to co-localize with ERGIC resident protein ERGIC-53 [ 36 ].…”

ARF1 with Sec7 Domain-Dependent GBF1 Activates Coatomer Protein I To Support Classical Swine Fever Virus Entry

“…Additionally, in several viruses, entry into the host cell has been found to involve COP I, which is dependent on the role of COP I-coated vesicles in endosome assembly ( 14 ). However, certain viruses also utilize GBF1 in an ARF1-independent manner or utilize ARF1 in a GBF1-independent manner to promote replication ( 15 , 16 ).…”