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Journal of Virology, November 1999, p. 9178-9186, Vol. 73, No. 11
University of Pittsburgh Cancer Institute and
Department of Pathology, University of Pittsburgh, Pittsburgh,
Pennsylvania 15213
Received 27 July 1999/Accepted 16 August 1999
We previously showed that B16 melanoma cells produce
ecotropic melanoma-associated retrovirus (MelARV) which
encodes a melanoma-associated antigen recognized by MM2-9B6 monoclonal
antibody. The biological significance of MelARV in melanoma formation
remains unknown. We found that infection of normal melanocytes with
MelARV resulted in malignant transformation. It is likely that MelARV
emerged from the defective Emv-2 provirus, a single copy of ecotropic provirus existing in the genome of C57BL/6 mice. In the present study,
we cloned and sequenced the full-length MelARV genome and its insertion
sites and we completed sequencing of the Emv-2 provirus. Our data show
that MelARV has a typical full-length retroviral genome with high
homology (98.54%) to Emv-2, indicating a close relationship between
both viruses. MelARV probably emerged as a result of recombination
between Emv-2 and an endogenous nonecotropic provirus. Some
observed differences in the gag and pol
regions of MelARV might account for the restoration of productivity and infectivity of a novel retrovirus that somatically emerged during melanoma formation. MelARV does not contain any oncogene and therefore might induce transformation by insertional mutagenesis. We sequenced two insertion sites of MelARV. The first insertion site
represents the 3' coding region of the c-maf proto-oncogene
at 67.0 centimorgans (cM) on chromosome 8. The c-maf
proto-oncogene encodes a basic leucine zipper protein homologous to
c-fos and c-jun. Insertion of MelARV in BL6
melanoma cells resulted in the up-regulation of c-maf. It
is noteworthy that the Emv-2 provirus is also inserted into a noncoding
region at 61.0 cM on the same chromosome 8. The second insertion site
is the 3' noncoding region of the DNA polymerase gamma (PolG) gene on
chromosome 7. The expression of PolG was not affected by the
MelARV insertion. Further investigation of the biological significance
of MelARV in melanoma formation is being undertaken.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Sequence and Insertion Sites of Murine
Melanoma-Associated Retrovirus
*
Corresponding author. Mailing address: 200 Lothrop St.,
Biomedical Science Tower/Room W1053, University of Pittsburgh Cancer Institute and Department of Pathology, University of
Pittsburgh, Pittsburgh, PA 15213. Phone: (412) 624-1490. Fax:
(412) 624-7736. E-mail: mengfeng{at}pitt.edu.
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