Integration is not necessary for expression of human immunodeficiency virus type 1 protein products

Abstract

A common feature in the life cycle of cytocidal retroviruses, including human immunodeficiency virus type 1 (HIV-1), is the accumulation of large amounts of unintegrated viral DNA. As yet, the role of unintegrated viral DNA in the cytopathogenesis of cytocidal retrovirus infections remains unresolved. HIV-1 mutants which were deleted in the integrase/endonuclease gene and which were unable to establish an integrated form of the virus were constructed. Despite an inability to integrate, these mutants were fully competent templates for HIV-1 core and envelope antigen production. HIV-1 antigen could be detected in the supernatants of lymphocyte cultures infected with HIV-1 integrase mutants. However, an inability to rescue infectious virus from these cultures indicated that HIV-1 integration was required for the production of infectious HIV-1. On the basis of the ability of unintegrated HIV-1 DNA to serve as a template for HIV-1 antigen production, it is plausible that unintegrated viral DNA can contribute to the HIV-1 antigen pool during HIV-1 replication.

Detection of intracellular HIV in lymphocytes by flow cytometry

“…Our flow assay was theoretically not as sensitive as PCR or culture techniques since the flow assay detected core protein, present at a later stage of replication, whereas the PCR and culture assays detected viral nucleic acid, although viral protein (p24 antigen) has been detected in mutant HIV-1 cell clones containing only unintegrated viral DNA (48). In our retrospective study of frozen SFMHS PBMC, HIV-1 DNA was detected by PCR in nine seroconversion pbxsamples, HIV-1 DNA and p24 antigen were detected by culture techniques in six of these nine samples, and p24 antigen positive cells were detected by flow cytometry in only three of these nine samples (Table 1).…”

Human immunodeficiency virus type 1 integrase: effects of mutations on viral ability to integrate, direct viral gene expression from unintegrated viral DNA templates, and sustain viral propagation in primary cells

“…These viral DNAs are generally believed to be transcriptionally silent remnants of a failed attempt at retroviral integration. There is a report in the literature, however, suggesting that certain mutants defective in integrase function are capable of limited viral gene expression (48). The replication-defective mutants described here fall into two distinct classes based on their ability to direct the expression of the tat gene from an unintegrated viral circular template DNA.…”

“…It is a relatively protease-resistant domain (18) and contains the active site for all polynucleotidyl transfer activities (16,18,30,49,53). Essential to the active site is the highly conserved D,D-35-E region [D-X (39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58) -D-X (35) -E] with invariant residues at D-64, D-116, and E-152 (18,28,30). The region of integrase necessary for homodimer formation has been mapped to this core domain by both genetic and biochemical analyses (17,25,50).…”

Neuropathology of Human Immunodeficiency Virus Infection

“…These immunocytochemical data in the human (34) correlate extremely well with those obtained in the SIV encephalitis model (25). Moreover, a recent study using the polymerase chain reaction (PCR) technique showed a considerably higher proportion of unintegrated HIV DNA in HIVE than in non-HIVE brains (60); DNA integration is not necessary for expression of HIV protein products (61). HIV gp41-producing microglia/macrophages were recently described as distributed mainly in basal ganglia, midbrain, and dentate nucleus in a pattern resembling a multisystem degeneration (44).…”