Molecular mechanisms of retroviral integration site selection.

Mamuka Kvaratskhelia,Erik Serrao,Ross C Larue,Amit Sharma,Alan Engelman

doi:10.1093/nar/gku769

Abstract

Retroviral replication proceeds through an obligate integrated DNA provirus, making retroviral vectors attractive vehicles for human gene-therapy. Though most of the host cell genome is available for integration, the process of integration site selection is not random. Retroviruses differ in their choice of chromatin-associated features and also prefer particular nucleotide sequences at the point of insertion. Lentiviruses including HIV-1 preferentially integrate within the bodies of active genes, whereas the prototypical gammaretrovirus Moloney murine leukemia virus (MoMLV) favors strong enhancers and active gene promoter regions. Integration is catalyzed by the viral integrase protein, and recent research has demonstrated that HIV-1 and MoMLV targeting preferences are in large part guided by integrase-interacting host factors (LEDGF/p75 for HIV-1 and BET proteins for MoMLV) that tether viral intasomes to chromatin. In each case, the selectivity of epigenetic marks on histones recognized by the protein tether helps to determine the integration distribution. In contrast, nucleotide preferences at integration sites seem to be governed by the ability for the integrase protein to locally bend the DNA duplex for pairwise insertion of the viral DNA ends. We discuss approaches to alter integration site selection that could potentially improve the safety of retroviral vectors in the clinic.

Highlights

Retroviral replication requires the covalent integration of the reverse transcribed viral genome into the host cell chromatin
In vitro and cell culture experiments indicate that the bromo- and extra-terminal domain (BET) proteins function for Moloney murine leukemia virus (MoMLV) like lens epitheliumderived growth factor (LEDGF)/p75 does for HIV-1: specific chromatin tethers that interact with preintegration complex (PIC) by binding their cognate IN and potentially stimulating its enzymatic function
The analysis of HIV-1 and MoMLV PICs derived from cells over expressing the LEDGF/p75 or BET protein IN binding domain (IBD) should reveal if different levels of IN catalytic function determine the differences observed in viral titer under these infection conditions

Summary

Introduction

Retroviral replication requires the covalent integration of the reverse transcribed viral genome into the host cell chromatin. The present review compares the mechanisms of action of LEDGF/p75 and BET proteins in their ability to navigate HIV-1 and MoMLV integration to select chromatin sites and the implications for human gene-therapy.

Results

Conclusion