Inhibition of Early Steps of HIV-1 Replication by SNF5/Ini1

Abstract

The replication cycle of human immunodeficiency virus, type 1 (HIV-1) 4 involves the insertion of a DNA copy of its RNA genome into a chromosome of the host cell. Following retrovirus entry, a large nucleoprotein complex called preintegration complex (PIC) is formed in the cytoplasm with components of the virion core and cellular factors. In addition to viral cDNA, PICs contain several viral proteins: matrix, nucleocapsid, reverse transcriptase, VPR protein, and integrase (IN), which carries out DNA-cutting and -joining reactions (1, 2). HIV-1 IN consists of three functional domains: the N-terminal domain (residues 1-49), the catalytic core domain (residues 50 -212), and the C-terminal domain (residues 213-288) (3, 4). The N-terminal domain contains an HHCC motif that binds one Zn 2ϩ atom and is involved in the multimerization of the protein (4). The C-terminal domain binds DNA non-specifically and plays a role in the formation of an active multimer of IN (3). The catalytic core domain contains the canonical 3-amino acid motif, D, D(35)E, that is essential for the catalytic activity of the protein (4). These residues coordinate a divalent metal ion (Mg 2ϩ ) and are highly conserved among all integrases and retrotransposases. Integration proceeds in three steps, 3Ј-processing, strand transfer, and gap repair. Purified IN exhibits both 3Ј-processing and strand transfer in vitro. Double-stranded blunt-ended viral DNA produced by reverse transcription is first cleaved immediately 3Ј of a conserved CA dinucleotide motif. This reaction generates CA-3Ј-hydroxyl DNA ends that are the active intermediates of the strand transfer reaction. Both viral DNA ends are then inserted into a host cell chromosome. Finally, gap filling of the unrepaired 5Ј-ends of the viral DNA is under the control of cellular enzymes. In addition to the integration reaction, non-homologous end-joining and homologous recombination cellular pathways are involved in the formation of 1 and 2-LTR circles that are detected in the nuclei of infected cells (5-7).Cellular factors, such as SNF5/Ini1 (8), LEDGF/p75 (9 -14), EED (15), Rad18 (16), and HSP60 (17), were characterized to interact directly with IN. Other cellular proteins, such as HMG1a and Barrier of Autointegration Factor (BAF) interact with viral cDNA and participate in the integration reaction (18,19). While in vivo HIV-1 integration is not sequence specific, transcriptionally inactive regions of the genome, such as centromeres and telomeres, are disfavored targets (20 -22). Integration of proviral HIV-1 DNA occurs preferentially into transcriptional units of active genes, whereas the oncoretrovirus * This work was supported in part by grants from the Agence Nationale de Recherche sur le SIDA (ANRS), Sidaction, Association Pour la Recherche sur le Cancer, and by EC project "Hidden HIV Challenge" (FP6-2003-LIFESCI-HEALTH-3/012182) (to S. E.). The Benarous and Mouscadet laboratories are supported by EC project TRIoH (LSHB-CT-2003-503480). The costs of publication of this article were defrayed in ...

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