Alpha-enolase in viral target cells suppresses the human immunodeficiency virus type 1 integration.

BACKGROUND: A protein exhibiting more than one biochemical function is termed a moonlighting protein. Glycolytic enzymes are typical moonlighting proteins, and these enzymes control the infection of various viruses. Previously, we reported that glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and alpha-enolase (ENO1) are incorporated into human immunodeficiency virus type 1 (HIV-1) particles from viral producer cells and suppress viral reverse transcription independently each other. However, it remains unclear whether these proteins expressed in viral target cells affect the early phase of HIV-1 replication. RESULTS: Here we show that the GAPDH expression level in viral target cells does not affect the early phase of HIV-1 replication, but ENO1 has a capacity to suppress viral integration in viral target cells. In contrast to GAPDH, suppression of ENO1 expression by RNA interference in the target cells increased viral infectivity, but had no effect on the expression levels of the HIV-1 receptors CD4, CCR5 and CXCR4 and on the level of HIV-1 entry. Quantitative analysis of HIV-1 reverse transcription products showed that the number of copies of the late products (R/gag) and two-long-terminal-repeat circular forms of viral cDNAs did not change but that of the integrated (Alu-gag) form increased. In contrast, overexpression of ENO1 in viral target cells decreased viral infectivity owing to the low viral integration efficiency. Results of subcellular fractionation experiments suggest that the HIV integration at the nucleus was negatively regulated by ENO1 localized in the nucleus. In addition, the overexpression of ENO1 in both viral producer cells and target cells most markedly suppressed the viral replication. CONCLUSIONS: These results indicate that ENO1 in the viral target cells prevents HIV-1 integration. Importantly, ENO1, but not GAPDH, has the bifunctional inhibitory activity against HIV-1 replication. The results provide and new insights into the function of ENO1 as a moonlighting protein in HIV-1 infection.

Virion-Packaged Pyruvate Kinase Muscle Type 2 Affects Reverse Transcription Efficiency of Human Immunodeficiency Virus Type 1 by Blocking Virion Recruitment of tRNALys3.

Human immunodeficiency virus type 1 (HIV-1) recruits diverse cellular factors into viral particles during its morphogenesis, which apparently play roles in modulating its infectivity. In our study, proteomic techniques demonstrated that a key glycolytic protein, pyruvate kinase muscle type 2 (PKM2), is incorporated into viral particles. Here, we show that virion-packaged PKM2 significantly reduces viral infectivity by affecting the incorporation level of a cellular tRNALys3 into virions. Enhanced expression of PKM2 in HIV-1-producing cells led to a higher incorporation level of PKM2 into progeny virions without affecting the viral maturation process. Compared with the control virus, the high-level-PKM2-packaging virus showed decreased levels of both reverse transcription products and cellular tRNALys3 packaging, suggesting that the shortage of intravirion tRNALys3 suppresses reverse transcription efficiency in target cells. Interestingly, the enhanced expression of PKM2 also suppressed the virion recruitment of other nonpriming cellular tRNAs such as tRNALys1,2 and tRNAAsn, which are known to be selectively packaged into virions, without affecting the steady level of the cytoplasmic pool of those tRNAs in producer cells, suggesting that PKM2 specifically impedes the selective incorporation of tRNAs into virions. Taken together, our findings indicate that PKM2 is a vital host factor that negatively affects HIV-1 infectivity by targeting the tRNALys3-mediated initiation of reverse transcription in target cells.

Virion-incorporated alpha-enolase suppresses the early stage of HIV-1 reverse transcription.

Human immunodeficiency virus type-1 (HIV-1) particles contain not only viral-encoded but also host-encoded proteins. Interestingly, several studies showed that host proteins play a critical role in viral infectivity, replication and/or immunoreactivity in the next target cells. Here, we show that alpha-enolase (ENO1) is incorporated into HIV-1 virions and the virion-incorporated ENO1 prevents the early stage of HIV-1 reverse transcription. We found that viral particles contain two isoforms of ENO1 with different isoelectric points by two-dimensional electrophoresis. Suppression of ENO1 expression by RNA interference in the HIV-1 producer cells decreased ENO1 incorporation into virions without altering the packaging of viral structural proteins and viral production but increased viral infectivity. Although the low-level-ENO1-packaging virus maintained comparable levels of reverse transcriptase activity, viral genomic RNA and tRNALys3 packaging to the control virus, its levels of early cDNA products of reverse transcription were higher than those of the control virus. In contrast, the high-level-ENO1-packaging virus, which was produced from ENO1-overexpressing cells, showed decreased infectivity and the levels of early cDNA products. Taken together, these findings reveal a novel function of ENO1 as a negative regulation factor targeting HIV-1 reverse transcription.

The C-terminal domain of glyceraldehyde 3-phosphate dehydrogenase plays an important role in suppression of tRNALys3 packaging into human immunodeficiency virus type-1 particles.

Human immunodeficiency virus type-1 (HIV-1) requires the packaging of human tRNALys3 as a primer for effective viral reverse transcription. Previously, we reported that glyceraldehyde 3-phosphate dehydrogenase (GAPDH) suppresses the packaging efficiency of tRNALys3. Although the binding of GAPDH to Pr55 gag is important for the suppression mechanism, it remains unclear which domain of GAPDH is responsible for the interaction with Pr55 gag . In this study, we show that Asp256, Lys260, Lys263 and Glu267 of GAPDH are important for the suppression of tRNALys3 packaging. Yeast two-hybrid analysis demonstrated that the C-terminal domain of GAPDH (151-335) interacts with both the matrix region (MA; 1-132) and capsid N-terminal domain (CA-NTD; 133-282). The D256R, K263E or E267R mutation of GAPDH led to the loss of the ability to bind to wild-type (WT) MA, and the D256R/K260E double mutation of GAPDH resulted in the loss of detectable binding activity to WT CA-NTD. In contrast, R58E, Q59A or Q63A of MA, and E76R or R82E of CA-NTD abrogated the interaction with the C-terminal domain of GAPDH. Multiple-substituted GAPDH mutant (D256R/K260E/K263E/E267R) retained the oligomeric formation with WT GAPDH in HIV-1 producing cells, but the incorporation level of the hetero-oligomer was decreased in viral particles. Furthermore, the viruses produced from cells expressing the D256R/K260E/K263E/E267R mutant restored tRNALys3 packaging efficiency because the mutant exerted a dominant negative effect by preventing WT GAPDH from binding to MA and CA-NTD and improved the reverse transcription. These findings indicate that the amino acids Asp256, Lys260, Lys263 and Glu267 of GAPDH is essential for the mechanism of tRNALys3-packaging suppression and the D256R/K260E/K263E/E267R mutant of GAPDH acts in a dominant negative manner to suppress tRNALys3 packaging.