Nuclear Relocalization of Polyadenylate Binding Protein during Rift Valley Fever Virus Infection Involves Expression of the NSs Gene

Abstract

Rift Valley fever virus (RVFV), an ambisense member of the family Bunyaviridae, genus Phlebovirus, is the causative agent of Rift Valley fever, an important zoonotic infection in Africa and the Middle East. Phlebovirus proteins are translated from virally transcribed mRNAs that, like host mRNA, are capped but, unlike host mRNAs, are not polyadenylated. Here, we investigated the role of PABP1 during RVFV infection of HeLa cells. Immunofluorescence studies of infected cells demonstrated a gross relocalization of PABP1 to the nucleus late in infection. Immunofluorescence microscopy studies of nuclear proteins revealed costaining between PABP1 and markers of nuclear speckles. PABP1 relocalization was sharply decreased in cells infected with a strain of RVFV lacking the gene encoding the RVFV nonstructural protein S (NSs). To determine whether PABP1 was required for RVFV infection, we measured the production of nucleocapsid protein (N) in cells transfected with small interfering RNAs (siRNAs) targeting PABP1. We found that the overall percentage of RVFV N-positive cells was not changed by siRNA treatment, indicating that PABP1 was not required for RVFV infection. However, when we analyzed populations of cells producing high versus low levels of PABP1, we found that the percentage of RVFV N-positive cells was decreased in cell populations producing physiologic levels of PABP1 and increased in cells with reduced levels of PABP1. Together, these results suggest that production of the NSs protein during RVFV infection leads to sequestration of PABP1 in the nuclear speckles, creating a state within the cell that favors viral protein production.

Poly(A)-binding proteins and mRNA localization: who rules the roost?

“…Nuclear accumulation of PABP occurs during infection with members of several virus families [23] and can in many cases be explained by alterations in the import/export mechanisms described above. For instance, PABP1 nuclear relocalization occurs during infection with bunyaviruses that inhibit cellular transcription [24][25][26][27], but not with those that do not [27]. This is consistent with impeded mRNA-export dependent or TD-NEM-mediated PABP export.…”

Common Dysregulation of Innate Immunity Pathways in Human Primary Astrocytes Infected With Chikungunya, Mayaro, Oropouche, and Zika Viruses

“…The pathway reactome corroborates the overall tendency in OROV infection, up-regulating pathways related to DNA condensation (mainly through the core H2, H3, and H4 histones), cell cycle checkpoints and G2 arrest, and telomere maintenance ( Figure 3C and Table S3 ). Some proteins from related orthobunyaviruses were already demonstrated to have nuclear localization, interfering with cell cycle and hampering global cellular transcription through histone modification ( Copeland et al., 2013 ; Gouzil et al., 2017 ). The genes in the reactome corroborated this hypothesis, as many histones, CENPs , and other G2/M step related proteins were up-regulated.…”

Rift Valley fever virus NSs protein functions and the similarity to other bunyavirus NSs proteins

“…The polyadenylate binding protein 1 (PABP1) binds to the polyA tail and the cap of mRNA via eIF4G, and mRNA forms a circular structure for efficient translation [ 110 ]. RVFV NSs protein did not directly bind to PABP1, however, PABP1 was sequestered to nuclear speckles in cells expressing RVFV NSs protein [ 111 , 112 ]. Nuclear retention of PABP also occurred in BUNV-infected cells at late stage of infection, and it probably due to decreased host mRNA in cytoplasm during NSs-mediated transcriptional shutoff [ 113 ].…”