Page 382 - Review of Medical Microbiology and Immunology ( PDFDrive )

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CHAPTER 43 Tumor Viruses
371
viruses cause tumors in humans, and no adenoviral DNA
has been detected in the DNA of any human tumor cells.
carcinoma because countries with a high incidence of chronic
hepatitis B also have a high incidence of hepatocellular
Adenoviruses undergo both a permissive cycle in some
carcinoma.
cells and a nonpermissive, transforming cycle in others.
(D) Human T-cell leukemia virus is a retrovirus that was found
The linear genome DNA circularizes within the infected
associated with leukemia in Japan but is not found in the
cell, but—in contrast to the papovaviruses, whose entire
United States.
genome integrates—only a small region (10%) of the ade-
novirus genome does so; yet transformation still occurs.
following is most accurate?
This region codes for several proteins, one of which is the 2. Regarding the oncogenes of DNA tumor viruses, which one of the
(A) They encode protein kinases that phosphorylate p53 protein.
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T (tumor) antigen. Adenovirus T antigen is required for
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(B) They interact with cellular proto-oncogenes and activate them.
transformation and is antigenically distinct from the poly-
(C) They encode cellular growth factors that activate S-phase DNA
omavirus and SV40 virus T antigens.
synthesis.
(D) They encode proteins that bind to the proteins encoded by
tumor suppressor genes.
Herpesviruses
Several animal herpesviruses are known to cause tumors.
cause malignant transformation, which one of the following is
Four species of herpesviruses cause lymphomas in nonhu-
most accurate?
man primates. Herpesviruses saimiri and ateles induce
(A) They cause point mutations in cellular regulatory genes.
T-cell lymphomas in New World monkeys, and herpesvi-
(B) They carry the genes for proteins that act as cellular growth
factors.
ruses pan and papio transform B lymphocytes in chimpan-
zees and baboons, respectively.
p53 protein.
A herpesvirus of chickens causes Marek’s disease, a con-
(D) They encode a recombinase that causes translocation of certain
tagious, rapidly fatal neurolymphomatosis. Immunization (C) They synthesize a protein that inhibits the action of the cellular
chromosomes.
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of chickens with a live, attenuated vaccine has resulted in a
(E) They encode a DNA polymerase that increases the rate of cel-
considerable decrease in the number of cases. A herpesvi-
lular DNA synthesis.
rus is implicated as the cause of kidney carcinomas in frogs.
Poxviruses
1. (C)
Two poxviruses cause tumors in animals; these are the
2. (D)
fibroma–myxoma virus, which causes fibromas or myxo-
3. (B)
mas in rabbits and other animals, and Yaba monkey tumor
virus, which causes benign histiocytomas in animals and
human volunteers. Little is known about either of these
SUMMARIES OF ORGANISMS
viruses.
Brief summaries of the organisms described in this chapter
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review of the essential material.
SELF-ASSESSMENT QUESTIONS
PRACTICE QUESTIONS: USMLE &
1. Regarding viruses that play a role in human carcinogenesis, which
COURSE EXAMINATIONS
one of the following statements is the most accurate?
(A) Epstein–Barr virus is implicated as the cause of nasopharyngeal
Questions on the topics discussed in this chapter can be found
carcinoma primarily in Asia, where it is transmitted by mos-
in the Clinical Virology section of Part XIII: USMLE (National
quitoes in rural areas.
Board) Practice Questions starting on page 723. Also see Part
(B) Evidence for hepatitis C virus (HCV) as a cause of hepatocel-
XIV: USMLE (National Board) Practice Examination starting
lular carcinoma includes finding a DNA copy of the HCV
on page 751.
genome integrated into the DNA of hepatocytes.
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