Interferon-induced HERC5 is evolving under positive selection and inhibits HIV-1 particle production by a novel mechanism targeting Rev/RRE-dependent RNA nuclear export.
BACKGROUND
Type I interferon (IFN) inhibits virus replication by activating multiple antiviral mechanisms and pathways. It has long been recognized that type I IFNs can potently block HIV-1 replication in vitro; as such, HIV-1 has been used as a system to identify and characterize IFN-induced antiviral proteins responsible for this block. IFN-induced HERC5 contains an amino-terminal Regulator of Chromosome Condensation 1 (RCC1)-like domain and a carboxyl-terminal Homologous to the E6-AP Carboxyl Terminus (HECT) domain. HERC5 is the main cellular E3 ligase that conjugates the IFN-induced protein ISG15 to proteins. This E3 ligase activity was previously shown to inhibit the replication of evolutionarily diverse viruses, including HIV-1. The contribution of the RCC1-like domain to the antiviral activity of HERC5 was previously unknown.


RESULTS
In this study, we showed that HERC5 inhibits HIV-1 particle production by a second distinct mechanism that targets the nuclear export of Rev/RRE-dependent RNA. Unexpectedly, the E3 ligase activity of HERC5 was not required for this inhibition. Instead, this activity required the amino-terminal RCC1-like domain of HERC5. Inhibition correlated with a reduction in intracellular RanGTP protein levels and/or the ability of RanGTP to interact with RanBP1. Inhibition also correlated with altered subcellular localization of HIV-1 Rev. In addition, we demonstrated that positive evolutionary selection is operating on HERC5. We identified a region in the RCC1-like domain that exhibits an exceptionally high probability of having evolved under positive selection and showed that this region is required for HERC5-mediated inhibition of nuclear export.


CONCLUSIONS
We have identified a second distinct mechanism by which HERC5 inhibits HIV-1 replication and demonstrate that HERC5 is evolving under strong positive selection. Together, our findings contribute to a growing body of evidence suggesting that HERC5 is a novel host restriction factor.
Matthew William
MW
Woods
Jessica Gayle
JG
Tong
Sean Kevin
SK
Tom
Peter Anthony
PA
Szabo
Peter Craig
PC
Cavanagh
Jimmy Dimitrios
JD
Dikeakos
S M Mansour
SM
Haeryfar
Department of Microbiology and Immunology, Dental Sciences Building Room 3006b, The University of Western Ontario, Schulich School of Medicine and Dentistry, Center for Human Immunology, London, Ontario, Canada. stephen.barr@uwo.ca.
Stephen Dominic
SD
Barr
D021581:Active Transport, Cell Nucleus; D019143:Evolution, Molecular; D015497:HIV-1 / Q000276:immunology*; D006801:Humans; D007372:Interferons / Q000276:immunology; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics*; D012367:RNA, Viral / Q000378:metabolism; D012641:Selection, Genetic; D054321:rev Gene Products, Human Immunodeficiency Virus / Q000378:metabolism
C402395:HERC5 protein, human; D047908:Intracellular Signaling Peptides and Proteins; D012367:RNA, Viral; D054321:rev Gene Products, Human Immunodeficiency Virus; C514860:rev protein, Human Immunodeficiency Virus-1; D007372:Interferons