Cyclophilin A promotes HIV-1 reverse transcription but its effect on transduction correlates best with its effect on nuclear entry of viral cDNA.
BACKGROUND
The human peptidyl-prolyl isomerase Cyclophilin A (CypA) binds HIV-1 capsid (CA) and influences early steps in the HIV-1 replication cycle. The mechanism by which CypA regulates HIV-1 transduction efficiency is unknown. Disruption of CypA binding to CA, either by genetic means or by the competitive inhibitor cyclosporine A (CsA), reduces the efficiency of HIV-1 transduction in some cells but not in others. Transduction of certain cell types increases significantly when CypA binding to particular HIV-1 CA mutants, i.e., A92E, is prevented. Previous studies have suggested that this cell type-specific effect is due to a dominant-acting, CypA-dependent restriction factor.


RESULTS
Here we investigated the mechanism by which CypA regulates HIV-1 transduction efficiency using 27 different human cell lines, 32 HeLa subclones, and several previously characterized HIV-1 CA mutants. Disruption of CypA binding to wild-type CA, or to any of the mutant CAs, caused a decrease in HIV-1 reverse transcription in all the cell lines analyzed here. This block to reverse transcription, though, did not correlate with cell type-specific effects on transduction efficiency. The level of 2-LTR circles, a marker for nuclear transport of the viral cDNA that results from reverse transcription, correlated closely with effects on infectivity. No correlation was observed between the cell type-specific effects on infectivity and the steady-state CypA protein levels in these cells. Instead, as indicated by a fate-of-capsid assay, CsA released the HIV-1 CA core from an apparent state of hyperstabilization, in a cell type-specific manner.


CONCLUSIONS
These data demonstrate that, while CypA promotes reverse transcription under all conditions tested here, its effect on HIV-1 infectivity correlates more closely with effects on nuclear entry of the viral cDNA. The data also support the hypothesis that a cell-type specific CypA-dependent restriction factor blocks HIV-1 replication by delaying CA core uncoating and hindering nuclear entry.
Alberto
A
De Iaco
Department of Microbiology and Molecular Medicine, University of Geneva, Geneva 1211, Switzerland. jeremy.luban@umassmed.edu.
Jeremy
J
Luban
D021984:Cyclophilin A / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism*; D016655:HIV Core Protein p24 / Q000378:metabolism; D015497:HIV-1 / Q000502:physiology*; D006367:HeLa Cells; D054884:Host-Pathogen Interactions; D006801:Humans; D011485:Protein Binding; D048348:Reverse Transcription; D014161:Transduction, Genetic; D016662:Virus Integration
D018076:DNA, Complementary; D016655:HIV Core Protein p24; D021984:Cyclophilin A