B10: endogenous RVs Flashcards

1
Q

What distinguishes retroviruses that cause cancer?

A

They carry an extra viral oncogene (v-onc) in addition to the core retroviral genes, which is “pirated” from a cellular gene (c-onc) and drives cell proliferation.

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2
Q

How is a viral oncogene (v-onc) typically different from its cellular counterpart?

A

v-onc is usually constitutively “on” (switched on permanently) with no feedback control, leading to uncontrolled cell growth.

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3
Q

What are the five classes of retroviral oncogenes?

A

They include regulators of cell proliferation such as growth hormones, receptors for extracellular growth signals, G proteins, protein kinases, and transcription factors.

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4
Q

Which virus, recovered by Peyton Rous over 100 years ago, provided the first evidence of viral oncogenesis?

A

Rous sarcoma virus (RSV) recovered from a chicken sarcoma.

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5
Q

What oncogene does Simian Sarcoma Virus encode and what is its function?

A

It encodes v‑sis, a homolog of the PDGF growth factor.

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6
Q

Which oncogene is carried by avian erythroblastosis virus, and what cellular function does it mimic?

A

It carries v‑erb, which is related to the Epidermal Growth Factor Receptor.

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7
Q

What does the v‑ras oncogene from murine sarcoma virus encode?

A

A small G protein (GTPase) that functions in signal transduction.

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8
Q

What is the role of v‑src in Rous sarcoma virus?

A

v‑src encodes a tyrosine kinase that is constitutively active (lacking negative regulatory regions).

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9
Q

What does v‑mos from Moloney murine virus encode?

A

A serine–threonine kinase involved in cell cycle regulation.

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10
Q

What is the function of v‑myc encoded by MC29 avian myelocytoma virus?

A

It encodes a transcription factor that regulates cell proliferation.

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11
Q

Why are many retroviruses carrying oncogenes replication defective?

A

They often have deletions in one or more core genes and express the oncogene as a Gag‑Onc fusion; they require co-infection with a helper virus for replication.

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12
Q

How can retroviruses without oncogenes cause cancer?

A

Through proviral insertional mutagenesis, where integration near a cellular proto-oncogene (c-onc) upregulates its expression, or by producing novel transforming factors, including transforming Env proteins.

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13
Q

How do proviral long terminal repeats (LTRs) contribute to cellular transformation?

A

They can act as promoters/enhancers for nearby c-onc genes, leading to fusion transcripts, stabilized mRNA, and increased oncogene expression.

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14
Q

What is proviral insertional mutagenesis?

A

: It is when integration of the provirus disrupts normal gene function (e.g., in gatekeeper genes like Rb) or alters splicing, leading to deregulated cell division.

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15
Q

What is the function of the HTLV-1 Tax protein?

A

Tax is a multifunctional regulatory protein (≈40 kDa) that drives viral gene expression and can stimulate cellular transformation.

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16
Q

How can retroviral Env proteins induce transformation?

A

For example, Friend spleen focus-forming virus (SFFV) expresses an Env protein (gp55) that binds and activates the erythropoietin receptor, leading to erythroid hyperplasia.

17
Q

What is the role of JSRV Env protein in transformation?

A

It activates cell-signaling pathways that contribute to cellular transformation.

18
Q

What are endogenous retroviruses?

A

ERVs are retroviral sequences that have integrated into the germline and are inherited as part of the host genome.

19
Q

How do HERVs contribute to genetic variability?

A

They provide multiple insertion sites for recombination, leading to duplications, deletions, and chromosomal rearrangements, influencing species evolution.

20
Q

What is Syncytin-1 and why is it important?

A

It is a captive Env protein derived from a HERV that mediates fusion of placental cytotrophoblasts to form the syncytiotrophoblast, essential for placental development.

21
Q

Can HERVs produce virus particles?

A

Most HERVs are defective due to mutations; however, HERV‑K subtypes can produce virus-like particles (VLPs) in certain tissues and tumors.

22
Q

What diseases are HERVs potentially linked to?

A

Oncogenesis, autoimmunity, inflammation, diabetes, and antiviral resistance.

23
Q

: How might HERVs contribute to cancer?

A

HERV RNA and proteins, such as HERV‑K Rec and Np9, may be upregulated in cancers like teratocarcinoma, seminoma, and melanoma, stimulating transformation.

24
Q

Which autoimmune condition has been linked with HERV upregulation?

A

Inflammatory lesions in multiple sclerosis have shown increased HERV RNA and protein expression.

25
Q

What is the proposed link between HERVs and neurological disorders?

A

Elevated levels of specific HERV RNA and proteins have been found in the brain tissue of patients with schizophrenia.

26
Q

Why are porcine endogenous retroviruses (PERVs) a concern in xenotransplantation?

A

PERVs can produce particles that infect human cells, posing a potential risk when pig tissues or organs are transplanted into humans.

27
Q

What are LTR retrotransposons and how are they related to retroviruses?

A

They are transposable elements that replicate via an RNA intermediate, are related to retroviruses but lack the env gene, so they have no extracellular phase.

28
Q

What is the difference between Type I and Type II transposable elements?

A

Type I elements (retrotransposons) use an RNA intermediate, whereas Type II elements (DNA transposons) do not.

29
Q

What components make up a retroviral gene therapy vector?

A

A retroviral DNA vector containing LTRs and a packaging signal (Ψ) with the gene of interest, and a packaging cell line that supplies gag, pol, and env proteins.

30
Q

What are the advantages of lentiviral vectors and how are pseudotypes used for safety?

A

Lentiviral vectors (often based on HIV‑1) efficiently infect non-dividing cells and integrate stably. They are designed without most HIV genes and can be pseudotyped (e.g., with VSV‑G protein) to avoid using the native HIV envelope, enhancing safety.