JVI Accepts, published online ahead of print on 18 March 2009

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J. Virol. doi:10.1128/JVI.00109-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

EVIDENCE THAT PRODUCTIVE HUMAN IMMUNODEFICIENCY VIRUS TYPE 1 ASSEMBLY CAN OCCUR IN AN INTRACELLULAR COMPARTMENT

Anjali Joshi, Sherimay D. Ablan, Ferri Soheilian, Kunio Nagashima, and Eric O. Freed^*

Virus-Cell Interaction Section, HIV Drug Resistance Program, National Cancer Institute, Frederick, MD 21702-1201; Image Analysis Laboratory, Advanced Technology Program, SAIC-Frederick, National Cancer Institute at Frederick, Frederick, MD 21702-1201

^* To whom correspondence should be addressed. Email: efreed{at}mail.nih.gov.

Human immunodeficiency virus type 1 (HIV-1) assembly occurs predominantly at the plasma membrane of infected cells. Targeting of assembly to intracellular compartments such as multivesicular bodies (MVBs) generally leads to a significant reduction in virus release efficiency, suggesting that MVBs are a non-productive site for HIV-1 assembly. In the current study, we make use of an HIV-1 Gag-matrix mutant, 29/31KE, that is MVB-targeted. We previously showed that this mutant is severely defective for virus particle production in HeLa cells but more modestly affected in primary macrophages. To examine more broadly the consequences for virus production of MVB targeting, we investigated 29/31KE particle production in a range of cell types. Surprisingly, this mutant supported highly efficient assembly and release in T cells despite its striking MVB Gag localization. Manipulation of cellular endocytic pathways revealed that unlike Vpu-defective HIV-1, which demonstrated intracellular Gag localization as a result of Gag endocytosis from the plasma membrane, 29/31KE-mutant Gag was targeted directly to an MVB compartment. The 29/31KE mutant was unable to support multiple-round replication; however, this defect could be reversed by truncating the cytoplasmic tail of the transmembrane envelope glycoprotein gp41 and by the acquisition of a 16EK change in matrix. The 16EK/29/31KE matrix mutant replicated efficiently in the MT-4 T-cell line despite maintaining an MVB-targeting phenotype. These results indicate that MVB-targeted Gag can be efficiently released from T cells and primary macrophages, suggesting that under some circumstances late endosomal compartments can serve as productive sites for HIV-1 assembly in these physiologically relevant cell types.