Micro Test 4: Retroviruses

  1. Every chicken you eat is  contaminated with these viruses
    Avian leukosis virus
  2. Why are retrovirsuses difficult to eliminate?
    They are ubiquitous and they integrate into the host chromosome.
  3. Occupy as much as 7% of the human genome
    Human endogenous retroviruses (HERVs)
  4. HERVs:
    Transmitted horizontally or vertically?

    *But produce few, if any, infectious particles
  5. Family:  Retroviridae
    Subfamily:  Orthoviridae
    • 4 genera of oncogenic retroviruses
    • Alpha (Rous Sarcoma virus)
    • Beta (Mouse Mammary Tumor Virus)
    • Gamma (Feline Leukemia Virus)
    • Delta (HTLV)
  6. Family:  Retroviridae
    Subfamily:  Orthoretrovirinae
    Genus:???? - (encompasses HIV-1, HIV-2, SIV)
  7. Family:  Retroviridae
    Subfamily 1: ???
    Subfamily 2: ???
    • Orthoretrovirinae
    • Spumaretrovirinae
  8. Family:  Retroviridae
    Subfamily:  Spumaretrovirinae
    Spumavirus (Foamy viruses)

    *Spumaretrovirinae do not typically cause human disease
  9. Only human virus derived from animals we've ever successfully linked to a tumor
  10. Retrovirus (HIV-1) Structure:
    Genome:  ssRNA, diploid + tRNA
  11. Retrovirus (HIV-1) Structure:
    • 1)  GAG (Group-specific AntiGen):  MAtrix, CApsid, NucleoCapsid
    • 2POL (RNA-Dependent DNA POLymerase):  PRotease, RevTranscriptase, INTegrase
    • 3)  ENV (ENVelope proteins):  SUrface (gp120) and TransMembrane (gp41)
    • 4)  Regulatory Proteins:  TAT, REV, NEF, VIF, VPU, and VPR
  12. HIV-1 Protein:
    GAG encodes
    Matrix, Capsid, Nucleocapsid

    (aka these are the structural proteins)
  13. HIV-1 Proteins:
    POL encodes
    Protease, Reverse Transcriptase, Integrase

    *POL proteins are the ones that enter the host chromosome
  14. HIV-1 Proteins:
    ENV encodes
    Surface (gp 120), Transmembrane (gp41)

    *Both of these proteins play a part in virus entry
  15. HIV-1 Proteins:
    Name 6 Regulatory Proteins
    TAT, REV, NEF, VIF, VPU, and VPR
  16. HIV-1 protein that encodes the structural proteins
  17. Type of Polymerase encoded for by POL
    RNA-dependent DNA Polymerase
  18. POL is accessed by
  19. ENV mRNA formation involves
  20. Generates final viral protein products
    Proteolytic cleavage
  21. Some oncogenic retroviruses (replication incompetent) have lost replicative genes and replaced these with
    viral oncogenes (vONCs)
  22. Retrocompetent Cell:  MC29
    • Oncogene= myc
    • Replication incompetent virus, must replicate with another virus that has a GAG and POL gene
  23. HIV-1 Attachment and Entry:
    Viral protein that mediates attachment
  24. HIV-1 Attachment and Entry:
    Viral protein that mediates fusion
  25. HIV-1 Attachment and Entry:
    HIV-1 "co-receptors" or "ultimate receptors"
    CCR5, CXCR4
  26. HIV-1 Attachment and Entry:
    Bind virus and facilitate interaction with CD4 and CCRs
    • DC-SIGN (dendritic cells/ macrophages)
    • a4B7 integrin (GALT CD4+ T cells)
  27. Primary cell target of HIV-1 virus
    CD4 TH cells
  28. Cells lacking this receptor cannot be infected with HIV-1

    (Cells lacking CD4 receptors can still be infected, although this is not normal)
  29. HIV-1 CCRs are
    chemokine receptors
  30. Chemokines (RANTES, MIP-1alpha, MIP-1beta) are thought to block HIV replication by
    binding to their receptors (CCRs) and blocking entry

    (In some individuals, high expression of CCL3L1 blocks virus entry)
  31. 10% of caucasians are heterozygous for a deletion within the CCR5 gene, and 1% lack it completely.  Why is this significant?
    The 1% that lack CCR5 completely show resistance to HIV-1 infxn
  32. New anti-HIV drug that is a CCR5 antagonist
    Selzentry, Maraviroc
  33. HIV-virus enters the cells as a:
    Once in the cell, virus turns into:
    • Enters:  ssRNA
    • Turns into:  dsDNA

    (The dsDNA integrates into the host chromsome allowing the virus to replicate)
  34. When HIV-1 enters the cell, it is bound to a?
    What region is always present?
    • tRNA
    • Always present= LTR (Long Terminal Regions)
  35. Binds to LTR and activates HIV replication
    NFkB (So every infxn you get, increases replication and makes your immune system weaker)
  36. In contrast to other viruses, when HIV is released
    It is still maturing due to proteases in the capsule
  37. HIV Reverse Transcription:
    Virion-associated Reverse Transcriptase synthesizes a copy of?
    Uses what as a template and what as a primer?
    • cDNA
    • Template:  Genome RNA
    • Primer: tRNA
  38. HIV Reverse Transcription:
    Virion RNA is degraded by?
    And a second strand of DNA is synthesized by?
    • RNase H
    • RT
  39. HIV Reverse Transcription:
    dsDNA copy of the viral genome is flanked by
  40. Retrovirus Integration:
    Although integration is random, HIV-1 preferentially integrates into
    active genes

    (If HIV does not replicate at an active gene, you will not see it)
  41. Integrated viral DNA, part of the host chromosome, inactive not making viral proteins, but could be activated  if that portion of DNA is activated.  This complicates HIV therapy.
    Proviral DNA
  42. HIV-1 Transcription and Genome Synthesis:
    Enzyme that synthesizes both genomic (unspliced) and mRNA (both spliced and unspliced) using proviral DNA as the template.
    Host Pol II (DNA-dependent RNA Polymerase)
  43. HIV-1 Transcription and Genome Synthesis:
    2 Ways transcription is upregulated
    • Binding of transcription factors within LTR
    • Action of TAT
  44. HIV Translation:
    Synthesis of capsid and catalytic proteins uses a genome-sized template and involves
    • Synthesis of a polyprotein
    • Frameshifting/ readthrough
    • Proteolytic cleavage
  45. HIV Translation:
    Regulatory and glycoproteins are translated from
    spliced mRNAs
  46. Because both structural and catalytic proteins are generated by cleavage from a larger precursor protein....
    blocking protease activity inhibits viral assembly

    (A number of protease inhibitors are currently in use and have dramatically lowered the mortality associated with HIV-1 infxns)
  47. HIV Assembly:
    Where does virion assembly take place
    In the vicinity of the plasma membrane
  48. HIV Assembly:
    Assembly is determined by?
    Driven by?
    • Concentration of precursors
    • Proteolytic cleavage
  49. Regulatory Proteins of HIV-1
    • TAT- upregulates transcription
    • REV- promotes nuclear export of unspliced and partially spliced mRNAs
    • VIF- suppresses an innate anti-viral activity found in some T cells
    • VPU- Degrades CD4 in ER and promotes virus release
    • NEF-  downregulates CD4 and MHC class I from the cell surface
    • VPR-  promotes nuclear translocation of pre-integration complex
  50. Regulatory Protein of HIV-1: Upregulates transcription
  51. Regulatory Protein of HIV-1:
    Promotes nuclear export of unspliced and partially spliced mRNAs
  52. Regulatory Protein of HIV-1:
    Suppresses innate anti-viral activity foundin some T cells
  53. VIF counteracts the effect of
    APOBEC3G (a cytidine deaminase)

    *APOBEC3G is likely responsible for hypermutation within HIV-1 DNA (Deaminated viral DNA is degraded by the DNA repair apparatus.)  VIF binds APOBE3G and recruits ubiquitin ligase that degrades it.
  54. HIV-1 Regulatory Protein:
    Degrades CD4 in ER and promotes virus release
  55. HIV infxn w/ no clinical tx generally progresses to clinical diseases within
    8-10 years
  56. HIV-1 Regulatory Protein:  Downregulates CD4 and MHC class I from the cell surface; induces infected macrophages to secrete MIP-1alpha and -1beta which attracts and activate CD4+ cells and leads to their infxn.

    (SIV and HIV NEF deletion mutants are attenuated in vivo)
  57. HIV-1 Regulatory Protein:  Promotes nuclear translocationof pre-integration complex
Card Set
Micro Test 4: Retroviruses
Micro Test 4 Retroviruses HIV