title: Impairment of HIV-1 cDNA synthesis by DBR1 knockdown.
abstract: Previous studies showed that short hairpin RNA (shRNA) knockdown of the RNA lariat debranching enzyme (DBR1) led to a decrease in the production of HIV-1 cDNA. To further characterize this effect, DBR1 shRNA was introduced into GHOST-R5X4 cells, followed by infection at a multiplicity near unity with HIV-1 or an HIV-1-derived vector. DNA and RNA were isolated from whole cells and from cytoplasmic and nuclear fractions at different times postinfection. Inhibition of DBR1 had little or no effect on the formation of minus-strand strong-stop cDNA but caused a significant reduction in the formation of intermediate and full-length cDNA. Moreover, minus-strand strong-stop DNA rapidly accumulated in the cytoplasm in the first 2 h of infection but shifted to the nuclear fraction by 6 h postinfection. Regardless of DBR1 inhibition, greater than 95% of intermediate-length and full-length HIV-1 cDNA was found in the nuclear fraction at all time points. Thus, under these experimental conditions, HIV-1 cDNA synthesis was initiated in the cytoplasm and completed in the nucleus or perinuclear region of the infected cell. When nuclear import of the HIV-1 reverse transcription complex was blocked by expressing a truncated form of the mRNA cleavage and polyadenylation factor CPSF6, the completion of HIV-1 vector cDNA synthesis was detected in the cytoplasm, where it was not inhibited by DBR1 knockdown. Refinement of the cell fractionation procedure indicated that the completion of reverse transcription occurred both within nuclei and in the perinuclear region. Taken together the results indicate that in infections at a multiplicity near 1, HIV-1 reverse transcription is completed in the nucleus or perinuclear region of the infected cell, where it is dependent on DBR1. When nuclear transport is inhibited, reverse transcription is completed in the cytoplasm in a DBR1-independent manner. Thus, there are at least two mechanisms of HIV-1 reverse transcription that require different factors and occur in different intracellular locations.
  
  
  OBJECTIVE
  This study shows that HIV-1 reverse transcription starts in the cytoplasm but is completed in or on the surface of the nucleus. Moreover, we show that nuclear reverse transcription is dependent on the activity of the human RNA lariat debranchng enzyme (DBR1), while cytoplasmic reverse transcription is not. These findings may provide new avenues for inhibiting HIV-1 replication and therefore may lead to new medicines for treating HIV-1-infected individuals.
authors.affiliation: Department of Molecular Biology & Biochemistry, University of California, Irvine, California, USA Division of Infectious Disease, University of California, Irvine, California, USA Cancer Research Institute, University of California, Irvine, California, USA Center for Virus Research, University of California, Irvine, California, USA Institute for Immunology, University of California, Irvine, California, USA.
authors.forename: Alvaro E
authors.initials: AE
authors.lastname: Galvis
authors.affiliation: Division of Infectious Disease, University of California, Irvine, California, USA Cancer Research Institute, University of California, Irvine, California, USA Center for Virus Research, University of California, Irvine, California, USA Institute for Immunology, University of California, Irvine, California, USA.
authors.forename: Hugh E
authors.initials: HE
authors.lastname: Fisher
authors.affiliation: Department of Molecular Biology & Biochemistry, University of California, Irvine, California, USA Cancer Research Institute, University of California, Irvine, California, USA Center for Virus Research, University of California, Irvine, California, USA.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Nitta
authors.affiliation: Department of Molecular Biology & Biochemistry, University of California, Irvine, California, USA Cancer Research Institute, University of California, Irvine, California, USA Center for Virus Research, University of California, Irvine, California, USA.
authors.forename: Hung
authors.initials: H
authors.lastname: Fan
authors.affiliation: Department of Molecular Biology & Biochemistry, University of California, Irvine, California, USA Division of Infectious Disease, University of California, Irvine, California, USA Cancer Research Institute, University of California, Irvine, California, USA Center for Virus Research, University of California, Irvine, California, USA Institute for Immunology, University of California, Irvine, California, USA david.camerini@uci.edu.
authors.forename: David
authors.initials: D
authors.lastname: Camerini
mesh_terms: D002467:Cell Nucleus / Q000821:virology; D003593:Cytoplasm / Q000821:virology; D018076:DNA, Complementary / Q000235:genetics* / Q000378:metabolism; D055785:Gene Knockdown Techniques; D015658:HIV Infections / Q000201:enzymology* / Q000235:genetics / Q000821:virology*; D015497:HIV-1 / Q000235:genetics* / Q000502:physiology; D006801:Humans; D012316:RNA Nucleotidyltransferases / Q000235:genetics* / Q000378:metabolism; D012367:RNA, Viral / Q000235:genetics / Q000378:metabolism; D014779:Virus Replication
chemical_list: D018076:DNA, Complementary; D012367:RNA, Viral; C000591939:Dbr1 protein, human; D012316:RNA Nucleotidyltransferases